Wikipedia:Reference desk/Science

Welcome to the science section
of the Wikipedia reference desk.

skip to bottom

Select a section:

• Computing
• Entertainment
• Humanities
• Language
• Mathematics
• Science
• Miscellaneous
• Archives

Want a faster answer?

Main page: Help searching Wikipedia

   

How can I get my question answered?

• Select the section of the desk that best fits the general topic of your question (see the navigation column to the right).
• Post your question to only one section, providing a short header that gives the topic of your question.
• Type '~~~~' (that is, four tilde characters) at the end – this signs and dates your contribution so we know who wrote what and when.
• Don't post personal contact information – it will be removed. Any answers will be provided here.
• Please be as specific as possible, and include all relevant context – the usefulness of answers may depend on the context.
• Note:
  • We don't answer (and may remove) questions that require medical diagnosis or legal advice.
  • We don't answer requests for opinions, predictions or debate.
  • We don't do your homework for you, though we'll help you past the stuck point.
  • We don't conduct original research or provide a free source of ideas, but we'll help you find information you need.

Ready? Ask a new question!

How do I answer a question?

Main page: Wikipedia:Reference desk/Guidelines

• The best answers address the question directly, and back up facts with wikilinks and links to sources. Do not edit others' comments and do not give any medical or legal advice.

See also:

• Teahouse
• Help desk
• Village pump
• Help manual

January 28

Can one guess the mass of a dice?

Suppose we have a cube with labeled faces (e.g., one of those objects called dice), with (possibly) inhomogeneous mass. Given the probabilities of the outcomes 1,..,6, (say that we have thrown it so many times that we agree on them), can we at least locate the baricenter? Or conversely: besides the symmetric case, is there a distribution of mass in a cube for which we can guess the frequencies of the outcomes? (Disclaimer: I am not planning to cheat people) --pma (talk) 00:43, 28 January 2009 (UTC) hopefully fixed

Discussion of whether it matters that the OP called it "a dice" instead of "a die" hidden here

There is no such thing as "a dice". --Trovatore (talk) 00:58, 28 January 2009 (UTC)

You can make a guess, but only within certain statistical parameters. Note that casino dice have the pips filled so as to maintain symmetry of mass. — Lomn 01:02, 28 January 2009 (UTC)

He never did say "a dice", he quite correctly and grammatically said "one of those objects called dice" (objects dice plural). Don't be pedantic and wrong. Rotational (talk) 13:40, 29 January 2009 (UTC)

He did say (correctly) "a dice", but has since edited the original question to avoid confusing Americans. DuncanHill (talk) 14:57, 29 January 2009 (UTC)

My mistake......sorry Rotational (talk) 17:19, 29 January 2009 (UTC)

What Trovatore is saying is that "dice" is the plural form of "die". Saying "a dice" is like saying "a cars" or "a books", it doesn't really make sense. -- Mad031683 (talk) 01:21, 28 January 2009 (UTC)

Surely the OP means a die. Surprised no one linked this--GreenSpigot (talk) 01:51, 28 January 2009 (UTC)

Well, the relevant article is at dice, which is far and away the most common form of the word. I'm more surprised that three of four responses ignored the question. — Lomn 01:54, 28 January 2009 (UTC)

OK die redirects to dice. But die is the singular.--GreenSpigot (talk) 01:57, 28 January 2009 (UTC)

We're not really supposed to correct the OP's grammar/vocabulary. If you can't answer the question...don't. SteveBaker (talk) 02:19, 28 January 2009 (UTC)

Correction in this case gives the OP more of a chance of finding what (s)he was looking for: therefore it is legitimate.--GreenSpigot (talk) 02:27, 28 January 2009 (UTC)

Dice is perfectly acceptable as a singular. DuncanHill (talk) 02:32, 28 January 2009 (UTC)

No, it isn't. It sounds seriously uneducated. --Trovatore (talk) 02:34, 28 January 2009 (UTC)

Dice is the normal singular, and the old singular die is confined to a few fixed phrases and certain mathematical contexts. DuncanHill (talk) 02:43, 28 January 2009 (UTC)

No, it isn't. A dice is substandard English, like a bacteria or a criteria. Absolutely unacceptable in formal writing. --Trovatore (talk) 02:45, 28 January 2009 (UTC)

Will you write and tell the OUP that or shall I? DuncanHill (talk) 02:47, 28 January 2009 (UTC)

The Brits do seem to see these things differently. They're wrong, of course. But I'd be surprised about Oxford; I'd need to see evidence there. --Trovatore (talk) 02:51, 28 January 2009 (UTC)

Edmund Weiner, Andrew Delahunty, Oxford Guide to English Usage, 2nd edition 1993, page 130. That do you? DuncanHill (talk) 02:55, 28 January 2009 (UTC)

What does it say, exactly? --Trovatore (talk) 02:56, 28 January 2009 (UTC)

"dice is the normal singular as well as the plural (one dice, two dice); the old singular, die, is found only in the die is cast, straight (or true) as a die, and in mathematical discussions, e.g. Rolling a die will generate a string of random numbers." Further down the same page it has "die (noun); see dice." DuncanHill (talk) 03:00, 28 January 2009 (UTC)

Boy, good thing we Americans are around to save the language. Y'all aren't taking care of it at all.

Anyway, you should be aware that a dice is seriously grating on American ears. In shared situations, if you can't bring yourself to say a die, it would be better to rephrase. --Trovatore (talk) 03:04, 28 January 2009 (UTC)

(ec)God forbid Americans should have to put up with English as She is Spoke in England :) David Crystal in The Cambridge Encyclopedia of the English Language, CUP, 1995, makes a similar point to the Oxford, at page 201. DuncanHill (talk) 03:08, 28 January 2009 (UTC)

Both 'die' and 'dice' are unacceptably vague here, and 'cubic die' sounds unnatural to my ears. The object in question is a d6. Algebraist 03:07, 28 January 2009 (UTC)

I second d6. All Dungeons and Dragons players know that the only acceptable way to reference dice is to day 'd' followed by the number of sides on the dice (die) in question, most commonly d20. -04:00, 28 January 2009 (UTC) —Preceding unsigned comment added by Pete5x5 (talk • contribs)

English is defined solely by how it is used (we don't have an equivalent of the Academie Francaise, for example), dictionaries just report what is used. If enough people make the same mistake, as in this case (or the case of "begging the question", for example), it becomes correct. --Tango (talk) 15:10, 28 January 2009 (UTC)

An easier way than relying on random movements and outcome while rolling the die/dice would be to build yourself a contraption where you could stand/clamp the thingy in question in by 2 diagonally opposed corners [1] and give it a controlled push with a known and repeatable force and speed. Dice with centered mass should spin at the same rate and slow down to a stop within the same time no matter which corners you used. Dice instead of die is common because most of us encounter them before we get to school. (Even in the US.) I learned about a die for casting before I found out it was also (officially) the singular for dice.76.97.245.5 (talk) 03:54, 28 January 2009 (UTC)

Yes, well, that's sort of why it sounds uneducated. --Trovatore (talk) 05:27, 28 January 2009 (UTC)

Thank you everybody! So, I understand that the singular of dice is not so used, like in latin. Maybe I tried the Language desk for the mechanical side of the question...--pma (talk) 09:36, 28 January 2009 (UTC)

Some interesting discussions on two subjects!! The grammar bits were especially entertaining, but neither the title nor the question referred to "a dice". Bazza (talk) 13:41, 28 January 2009 (UTC)

Yes it did. It's been changed. Algebraist 13:44, 28 January 2009 (UTC)

And now I'have re-corrected at least the title so as to keep memory of the lucky occasion that gave origin to this debate. Note that, as a non-native english speaker, I am really glad to be corrected. In fact, I started writing here also to improve my english. And, of course, because I believe in sharing the knowledge with people from different countries. pma (talk) 14:39, 28 January 2009 (UTC)

Determining the centre of mass for the die by how it rolls is probably impossible in practice. The actual way to do it is to attach a string to the die to a bunch of points, one point at a time. The centre of mass will lie along the line that extends downward from the string (to maintain no torques on the die). Do this twice and the intersection of the two lines reveals the location of the centre of mass, but in practice, you're best to do several measurements to beat down the experimental error. WilyD 14:45, 28 January 2009 (UTC)

If we could all just use impeccable grammar, it would be a pair o' dice. Edison (talk) 16:20, 28 January 2009 (UTC)

Thanks Wily. Yes, we can determine geometrically the baricenter, but what I had in mind is another issue: is there a relation between the frequencies and the position of the baricenter? Roughly, the dice will stop more often with their baricenters in the lower position; I just wonder how this can be made quantitative. I had in mind a kind of approach via statistical mechanics and... no matter. I found interesting the linguistic aspect, and even more the anthropological one ;) --pma (talk) 17:42, 28 January 2009 (UTC)

Err, realistically, you'd never work out the relationship theoretically. Depends on the details on the friction in the die roll, the non-cubicity of the die, many unpleasant bits. You could make a simplified model, but the devilish details would cause me, a theorectical physcists to say "This problem is impossibe" - the easiest way to do it would be a bunch of dies with known baricentres, an undergraduate and some money from NSERC (or the NSF or whatnot). WilyD 18:13, 28 January 2009 (UTC)

Ok, that's what I also suspect; too many details are to be fixed. Now, trying to answer by myself, a simple model is: an cubic die with sharp edges, rolling under the effect of impulses randomly distributed. The six positions are local minima for the energy, and a 90 degrees rotation from one face (i) to another (j) needs a small amount of energy, δ_ij -it's how much the baricenter has to be raised. This should give a transition probability p_ij for any pairs of adjacent faces; p_ij is related to δ_ij according to the distribution of the random impulses. Now we have a Markov chain and I may think that the corresponding stationary distribution is the probability distribution for the stopping positions. The idea is that at a certain moment the die just decides to stop for reason of his own (otherwise, in alternative one may think of a slowly decaying energy, acting till the die can't move any longer). Anyway, my interest about it is just linked to dinner conversations; I'm not a physicist nor a probabilist and can't say how fool is this picture. pma (talk) 19:59, 28 January 2009 (UTC)

(Thanks for hiding the off topic!) The problem is there are even more details than just the dice itself. Even consider the initial position as random, the initial hight and spin have an impact. If it drops from a large hight with little spin, it is much more likely to make it into some equilibrium position before hitting the ground. It also depends on how much the die bounces on the surface it is being dropped. A lot of bouncing would again lead to more randomness and less predictability which would mean you'd have to use a die with a weight even more from the center. If you wanted to make a situation where the dice would land more predictably I may suggest dropping into a large tank of undisturbed water with sand at the bottom. The large decent would give it enough time to reach its equilibrium state and its landing would be slow because of the water so it'd probably just stick into the sand the same direction that it was falling. Even for a dice that was just off a little, you may find that you get the same number almost every time in this situation. Anythingapplied (talk) 21:40, 28 January 2009 (UTC)

Yes, the way it's thrown is clearly relevant. For the slow die in water that you are describing, the probability to land on a face should be proportional to the solid angle subtended by that face at the baricenter, I think. Anyway, I would expect just a rough correspondence between a true die and a mathematical model. Thanks again pma (talk) 22:10, 28 January 2009 (UTC)

I think you're model is solid. If you use some sort of machine to throw dice consistantly and fit variables to the model, I think it'd work quite well for a controlled situation. If you could use a high speed camera to record the initial side that hit the ground, the number of bounces, and all the intermediary sides to be face up when making contact with the ground you'd be able to fit your variables with much higher relaibilty and far fewer experimental throws. Determining what probability distrabution to use for the amount of initial energy would be the most difficult part in my opinion. Anythingapplied (talk) 22:23, 28 January 2009 (UTC)

Actually, I think one could get an approximate answer that while far from complete might none the less be interesting. If you watch a die, then at any given instant there is nearly always one side that is more approximately "up" than the others, and the die will either settle on that side or rotate to another. The question of whether it rotates to another side is dependent on whether it has enough angular momentum to carry its center of mass against gravity across a pivot point. A higher center of mass is easier to flip than a lower one. If one chooses to consider only the "last flip", when the angular momentum of the die is sufficient to rotate over once more but no further, one should be able to state roughly how much easier it is to flip the die in one configuration versus another based on the position of that center of mass. If one assumes that the last part of the roll, when the die is about to settle, is the most important, then this would give a rough way of estimating. Obviously there are a lot of other details that could modify that conclusion, but I think there is nonetheless a tractable (though still complicated) starting point for making such estimates. Dragons flight (talk) 22:35, 28 January 2009 (UTC)

Hey! Someone deleted my answer!! (restoring it) I've been thinking about this for the past day or so while all of the babble about die/dice was going on. I think we don't have enough information. Think about the mechanisms by which a 'weighted' dice ends up being 'unfair':

• If it were being tossed in a vacuum, then while it was in the air, it would rotate about it's center of gravity (which would be off-center) but that would only affect it's rate of rotation because of the changed moment of inertia of an off-center center of gravity compared to a dice with the CofG in the middle. So the initial force imparted to roll the dice would have a different resulting spin rate - but once launched, it would still land (essentially) randomly depending on the precise speed and height it was thrown from...and (of course) what orientation it was in at the start of the toss. But a dice with a heavy weight just under the '1' face wouldn't preferentially come up '6' for this reason.
• In the presence of air resistance, there would be a tendency for it to slowly stop rotating and to fall 'heavy-side-down'. But the degree to which that happens would have to depend on the lightness of the body of the dice. Imagine something like a shuttle-cock - those lightweight feathers result in it's flight rapidly stabilising to a 'heavy-end-first' approach. But if you imagine a 4 ton solid steel dice with a similarly off-center weight, you'd imagine that air resistance would be negligable. So this tells us that the weight, size, aerodynamics of the dice will affect the degree to which the thing will or will not tend to stabilise.
• Then, when the dice hits the ground and starts rolling there will be the question of whether the corner of the dice has enough friction to allow it to flip over onto the next face instead of merely sliding along the table without rolling. Offsetting the weight further from the point where the friction is applied gives it a greater turning moment when the weight is high up - and reduces the turning moment when the weight is at the bottom - so that's going to increase the probability of it ending up heavy-side down rather than managing to rotate another 90 degrees. The degree to which this effect works depends on how steeply the dice is dropped (if it's vertical - then this has little effect - if it's rolled horizontally - such as as a casino 'craps' table - then it's very significant).

So here's the problem. The degree to which weighting the dice affects the outcome depends on (at least) the air resistance, the moment of inertia of the unweighted version of the dice, the frictional forces between dice and table and the angle from which the dice is thrown. All of those things will alter the probability of the dice to be 'unfair'. If the degree of unfairness (statistical irregularity) depends on something OTHER than the placement of the weight in the volume of the dice - then you can't use statistical methods to determine how far the weight is from the center. You almost certainly can determine the direction in which it's displaced because that's just the degree of asymmetry in the statistics. But the AMOUNT of displacement would require knowing an awful lot about the detailed physics.

SteveBaker (talk) 00:38, 29 January 2009 (UTC)

Very clear. By the way, now I understand why casino dice have sharp edges: one good reason is that rounded corners would make it easier to stop on the lower position of the baricenter, if it's not perfectly centered - as extreme case, a ball would do it certainly. --pma (talk) 07:36, 29 January 2009 (UTC)

PS: It seems it was me the vandal... sorry Steve.pma (talk) 11:58, 29 January 2009 (UTC)

Yes - I wondered the same thing. It does make sense that square-cornered dice would be somewhat less prone to weighting - but on the other hand, they might be more prone to not being so random by virtue of not rolling so well. If you imagine some kind of dice that would somehow not roll at all (maybe it has spikes on the corner that dig into the table!) - it would be pretty easy to cheat by tipping it out of your hand - or perhaps the dice cup - in some kind of carefully controlled manner. An almost spherical dice seems less problematic in this regard. Going back to the 'dungeons & dragons' dice - a 20 sided icosahedral dice rolls forever - but a d4 (which is a tetrahedron) really doesn't roll at all. I have a set of d4 dice that are cylindrical 8-sided things with each number printed on them twice. They are much nicer to play with. I often suspect people of kinda gently tipping the tetrahedral ones onto the table to get the number they want. However, that may not be an issue for casino's where they make you roll the dice the entire length of that L-O-N-G table. SteveBaker (talk) 19:12, 29 January 2009 (UTC)

Backwards FET operation

Can I use a FET backwards to generate the square root of the drain current by looking at the Vgs?--GreenSpigot (talk) 02:05, 28 January 2009 (UTC)

It won't work if you just use the FET on its own, which is what I think you mean. The FET won't 'know' that you want the Vgs to vary with the drain current. You can, however, put the FET in the feedback loop of an amplifier and reverse its operation that way. There's an example here. --Heron (talk) 09:55, 28 January 2009 (UTC)

Yes but the opamp in that cct is only used to generate a drain (actually source current in that config) current proportional to the signal voltage. Id rather not use an op amp as Im considering very high frequencies. So if I was to force a drain current and use the developed Vds to act on the gate as feedback, do you think it may work?--GreenSpigot (talk) 13:33, 28 January 2009 (UTC)

In essence, you can't "reverse" the FET but you can ask the question "What voltage, when squared, would equal this voltage?" - and that is the answer you want. Hence User:Heron's idea of using a feedback approach. So (effectively) you compare the output of the FET to the voltage you are trying to take the square root of - and adjust the input of the FET up or down until they match. (Or if you don't need to do it too quickly you could use a $5 microprocessor that has A/D and D/A and do it in software!) SteveBaker (talk) 14:01, 28 January 2009 (UTC)

Its ok I modelled it on spice and it works.--79.75.56.52 (talk) 17:14, 28 January 2009 (UTC)

BTW thats SPICE--GreenSpigot (talk) 01:13, 29 January 2009 (UTC)

intensity light

SteveBaker, You said if I'm on Mars I won't notice the vermilion color becasue my eyes is in vermilion color, and the color I'll see is just tranparent light. Then why on Earth, on foggy day the I still notcie white, I see sky everyday, they always look azure (light blue). The yellow (signal light), I think way inside, humans can notice the yellow colour. But on Saturn/Titan, the problem is the light we get is 1/100 that of Earth, that is only light of a thunder hit our house at night. If I orbit around looking down, would Saturn look almost black? When I descend in Titan's atmosphere, you said I won't see the orange color because orange colour is in my eyes. I thought the color won't burn my eyes blind, just turn my color vision off? is strong color not rich just burn off vision?--69.226.46.118 (talk) 02:00, 28 January 2009 (UTC)

You seem to be referring to this thread. Be aware that if you show up here continuing a discussion from a week ago, and speaking directly to an unspecified person (who are you talking to, anyway?), most people here will wonder what on earth you're talking about. Algebraist 03:12, 28 January 2009 (UTC)

I think it's a steganographic message of some sort. Taking 1=color and 0=colour, it comes out 111010111. Not very good steganography — low information density; easily broken. Reminds me of this. --Trovatore (talk) 03:21, 28 January 2009 (UTC)

To avoid confusion the OP modified the post, original was here [2]. To the OP, it is usually considered poor form to modify your post in such a way that you make proceeding discussion meaningless. You should at least mention it was modified or better still, if modifying your post will confuse the situation, just reply to your post with the additional information Nil Einne (talk) 11:16, 28 January 2009 (UTC)

• Trova, What??--69.226.46.118 (talk) 04:26, 28 January 2009 (UTC)

He's referring to the fact your original message was fairly cryptic. Nil Einne (talk) 11:16, 28 January 2009 (UTC)

Unfortunately, he feels very bad when he finds mis-spells and typos, and goes crazy. Usually these are results of a severe education... --pma (talk) 11:55, 28 January 2009 (UTC)

(Background: The OP had been asking a lot of questions - with a lot of follow-ups about the general topic of the color that planets would seem to be if you were really there. (S)he started asking more of these questions over on my UserTalk: page - and I requested that they not be posted there - but here, where they belong. IMHO, between several L-O-N-G answers here - and more on my UserTalk: the question has already been fully answered and there is little (if anything) more to be said on the subject. IMHO, the OP should carefully read the previous replies and desist from further posting on the subject until all of that material has been properly absorbed. At any rate - I've had enough.) SteveBaker (talk) 13:54, 28 January 2009 (UTC)

What matters isn't what colour the things you're seeing are, but rather what colour the ambient light is. On Earth, the ambient light is almost always white (that's why our eyes see the frequencies they do) - while the sky is blue, the sun is yellow, and they add together to make white (in fact, the light from the sun started out as white and was split into blue and yellow by the atmosphere). On Mars, the ambient light is going to be more red because the dust in the atmosphere absorbs other colours (this is different from the scattering that makes our sky blue - that just makes different colours seem to come from different places, it doesn't absorb anything so the result is still white), and your eyes would very quickly get used to that and you wouldn't notice (if it was too red you would notice because certain colours (eg. blue) would appear extremely dark, even black, but on Mars it wouldn't be that severe). --Tango (talk) 15:05, 28 January 2009 (UTC)

This reminds me of the Goethe vs. Newton dispute on the theory of colours... even Newton had enough of it, at a certain point ;) pma (talk) 18:18, 28 January 2009 (UTC)

Newton avoided the worst of that dispute by dying two decades before Goethe was born. Algebraist 15:13, 29 January 2009 (UTC)

...as everybody knows, as I assume... as a joke was a disaster :( pma (talk) 18:55, 29 January 2009 (UTC) I'm talking of my post, the silly one with ";)"

Feed the sailors with carrots so they'll have better eyesight.

The Japanese battleship Yamato was the last serious and also the largest navy battleship ever built. It was sunken by U.S. navy pilots in 1945. In 1941, it had a very traditional battleship vs. battleship configuration. In 1944, they removed two 155 mm turrets and installed 138 25 mm AA guns.

Armament	1941	1944
46 cm (18.1 in)	9	9
155 mm (6.1 in)	12	6
127 mm (5 in)	12	24
25 mm anti-aircraft	24	162
13.2 mm anti-aircraft	4	4

Nevertheless, Yamato was still sunken. They had too few AA guns. The first wave of attack consists of 280 planes and the second one over 100. It had taken 386 airplanes to bring down Yamato which only had 162 25 mm AA guns and a very small fleet of 9 escort ships. The special AA ammunitions for the 18.1" guns were found useless. Yes, they used the 18.1" guns as if they were shotguns.

The 25 mm AA guns, clustered around the bridge, were mostly destroyed by the bombs before Yamato's demise. Then the battleship had taken 10 torpedo hits (1 starboard, 9 port, the U.S. navy was very clever) and went off-balanced.

Since the Japanese Empire did not have the resources to build additional aircraft carriers and more airplanes in 1944, air support was out of the question. From a 20-20 hindsight point of view, how many 25 mm AA guns were required to defend against 386 U.S. airplanes? How many anti-torpedo weapons did it take? How many 18.1" turrets needed to go to make room for all these self-defense weapons? Did Yamato still have a chance if it cleans up the whole deck and give each of its sailor a 25 mm AA gun? -- Toytoy (talk) 09:58, 28 January 2009 (UTC)

Japan did not have the proximity fuse at that time, using time fuses or barometric fuses as always, and nobody had radar-guided anti-aircraft guns on their ships. It's surprisingly hard to hit a moving airplane from a moving ship with a projectile by eye, and it's almost impossible to set a fuse so it goes off near an approaching plane. If the entire deck of the Yamato had been covered in AA guns, it would still have taken only one well-placed bomb to sink her. The battleship was a doomed dinosaur even before the Yamato was commissioned. (It was a beautiful ship, though, wasn't it?) --Milkbreath (talk) 12:37, 28 January 2009 (UTC)

Also, if it was sufficiently well defended from air attack, it would have been attacked in other ways, such as a submarine torpedo attack or even a traditional battleship-to-battleship "crossing the T" engagement. High altitude bombers, which are out of range of anti-aircraft guns, would be another option, although their low accuracy means that many more bombs would need to be dropped. They also might not destroy the battleship directly, but could disable most of the anti-aircraft guns, allowing for low-altitude torpedo plane attacks. Mines could also be laid in it's path. If, by some miracle, the Yamato managed to survive all such attacks, the US might have even used an atomic bomb on it, when they became available, but, having only 2, they were in short supply. Still, if an "unsinkable" ship could be sunk instantly, especially if close enough to Japan to provide a sufficient demonstration, it might be a good use, perhaps sparing the 2nd city bombed, Nagasaki, of it's fate. Some of these approaches would have required a "strategic withdrawal" of the US fleet, to give time to prepare an adequate "reception". StuRat (talk) 14:51, 28 January 2009 (UTC)

I don't know that nuking a battleship would have done much. The US didn't know at the time (and so it can't really be used to justify the theoretical decision), but Crossroads Able wasn't much of a ship-killer, and that sort of airburst is a good approximation of how an attack would have gone. — Lomn 18:25, 28 January 2009 (UTC)

It sank 5 ships, despite having missed the target, and disabled many more. Also, I'm not sure if an air-burst is the best way to sink a single ship; a surface burst might be more effective, by swamping the ship. StuRat (talk) 15:07, 29 January 2009 (UTC)

Incidentally, in reference to your topic heading, the idea that carrots significantly boost eyesight is a myth [3]. The myth was created intentionally by the British during WWII as a cover story to explain why the British were able to locate approaching German bombers so easily at night. The real answer is that the British had a top secret new invention: radar! Dragons flight (talk) 16:08, 28 January 2009 (UTC)

Indeed. As I understand it carrots are only going to improve your night vision (day vision is completely unaffected) if you actually have a vitamin A deficiency (which cases nightblindness). If you have reasonable night vision already, it's not going to get any better. --Tango (talk) 18:11, 28 January 2009 (UTC)

To take a different tack, I'll address the US Army Air Corps' approach to this problem. Faced with bombers that were outranging their fighter cover (and being mauled by the Luftwaffe for it), the AAC decided that the Flying Fortress, with its 10 or so antiaircraft guns, was insufficient to hold fighters at bay. They rebuilt B-17s into YB-40s, flying gunships that eschewed bomb loads in favor of additional powered turrets, ammunition, and armor. The effort, in short, flopped. YB-40s could not keep fighters at bay, could not keep up with the standard bomber formations, and could not drop bombs to salvage any cause for their inclusion in the flight line. It seems likely that the same sort of result would have come of a full conversion of a battleship to an antiaircraft platform -- as far as I know, no modern air assault has ever been substantially ablated by fixed-position fire (and yes, I'm lumping aerial and naval gunships into "fixed" -- relative to the attacking aircraft, they're effectively immobile), and a potentially effective battleship would have been lost in the process to boot. — Lomn 18:25, 28 January 2009 (UTC)

The combination of radar gunlaying and radar proximity fuses permitted an 82% kill rate for antiaircraft guns defending against the V-1 cruise missile during World War II. --Carnildo (talk) 02:19, 29 January 2009 (UTC)

Without a radar-controlled AA system, you can hardly hit any airplane with no matter how many guns. And without a radar system capable of tracking and engaging dozens of targets at once (good computers + phase-array antennas), your defense can be saturated in a matter of seconds. But just how good were these WWII planes and their ammunitions? The steel hull of Yamato was very thick. It was designed to take serious punishments. Its sister ship Shinano was sunken by torpedos because of some poor design mistakes. If the design and manufacturing were perfect, could these outdated heavy weight battleships survive non-nuclear air attacks? Could a thick-shelled turtle return home? -- Toytoy (talk) 18:31, 28 January 2009 (UTC)

Given that the Yamato and the Musashi were both sunk via aerial attacks, the answer is quite obviously "no". By 1944, US Naval bombers were lugging around one-ton bombs or torpedoes -- about the same throw weight as battleship shells. Since this wasn't an era where armor reigned supreme (contrast with the Battle of Hampton Roads for such a case]]), it's not controversial to say that any conventional ship* of the era could be sunk by any conventional aerial attack.

*See Project Habakkuk for what could have been an interesting exception. — Lomn 21:18, 28 January 2009 (UTC)

Organ donor records

Who is the youngest organ donor? And who holds the record for being the oldest at the time of organ donation? In multiple organ donors, what is the maximum number of organs that have been donated by a person? Or is there any article similar to World records in medical science? Jay (talk) 10:03, 28 January 2009 (UTC)

Youngest? Stillborn babies can become organ donors [4]. If you want to get technical, I guess you should count from conception. I'm somewhat doubtful anyone has records of that sort of thing Nil Einne (talk) 11:11, 28 January 2009 (UTC)

Does destroying a few day old embryo in order to harvest embryonic stem cells count as "organ donation"? Technically, I suppose there weren't any "organs" yet. But in general, I believe finding the youngest organ donor is mostly a question of how one chooses to define "organ" and "donor". Dragons flight (talk) 16:01, 28 January 2009 (UTC)

If you accept it, younger than this seems difficult! pma (talk) 22:30, 28 January 2009 (UTC)

Making the queries more specific, I would like age to mean post live childbirth, and organ donation in the context of organ transplantation. Rather than the exact answers, what I'm looking for, in the absence of an available article, is ideas on which articles these details can be inserted into, or suggestions on title of a new article. Jay (talk) 08:36, 29 January 2009 (UTC)

That sounds like a miscellaneous fact; in light of the objections raised above regarding ambiguous definitions, you might want to reconsider adding such information to any article. We have a trivia guideline information page; that page may help you decide the applicability of this policy. Nimur (talk) 18:40, 29 January 2009 (UTC)

Osmole Confusion Part II

I asked a previous question (here) here, that was partially answered, but I find myself still confused.

The question was (edited a little): If I took 500 sodium ions and put them in 1 L in one container. In another contained, I put 500 glucose molecules. which has the greater osmolarity?

The answer that I found most helpful was this one, by Jayron32: So a 1 molar solution of NaCl will have double the osmolarity of a 1 molar solution of glucose, because dissolving 1 mole of NaCl in a liter of solution will produce double the number of particles that dissolving 1 mole of glucose will.

What I`m really confused about is the plasma osmolality equation. Posm=2xNA+GLUC/18+BUN/2.8 or something like that. Why does the concentration of sodium atoms contribute 36 times more to the osmolality than glucose?

Thanks! --Cacofonie (talk) 16:16, 28 January 2009 (UTC)

The sodium does not contribute 36x more than the glucose -- you have to pay attention to the units. The short-hand calculation for plasma osmolality corrects for the different units that are given for the measurement of sodium (mEq/L), glucose (mg/dL), and BUN (mg/dL).

1. The mass of glucose is ~180g/mol. Let's say you measure a typical plasma glucose of 90 mg/dL. First, let's convert to g/L for a plasma glucose of 0.9 g/L. Divide by 180g/mol and you get 0.005 mol/L or 5 mM. This is the same thing as dividing the plasma glucose by 18. A similar calculation is made for BUN. (corrected numbers... oops... stupid math... --- Medical geneticist (talk) 19:37, 28 January 2009 (UTC))
2. Jayron already stated this, but again, in a biological context, sodium is never present on it's own but as a sodium salt, predominantly sodium chloride (but also, importantly, sodium bicarbonate). When in aqueous solution (as in blood), one mole of sodium chloride dissociates into a mole of sodium and a mole of chloride. Thus, in the calculation, you just double the amount of measured plasma sodium milliequivalents to account for the fact that the other (unmeasured) components (chloride and bicarbonate) of the sodium salts are present in solution.
3. Adding together the molarity of sodium+chloride, glucose, and BUN gives a decent approximation of plasma osmolality.

--- Medical geneticist (talk) 18:31, 28 January 2009 (UTC)

It should also be noted that bicarbonate, being a weak electrolyte, introduces some serious complications should you want to be scrupulously correct in your calculations. Because bicarbonate, in a water solution, produces small amounts of SEVERAL different kinds of particles, it has a non-integer Van't Hoff factor, and as such, makes the calculations quite messy. However, as a first approximation, assuming sodium bicarbonate has a Van't Hoff factor of "approximately 2" usually gets things close enough for government work... Thus, as noted, you can assume "sodium" in this context to mean "sodium, and whatever negative ions it is draging along". So, we have some assumed NaX compound, which produces 2 moles of ions (Na+ and X-) and we just take it to mean that the identity of X (be it chloride, bicarbonate, or melange of several different kinds of ions) to be moot for colligative purposes. --Jayron32.talk.contribs 04:56, 29 January 2009 (UTC)

Wearing a coat inside making the cold outside feel colder.

I wear my winter jacket inside a lot of the time. I'm told that doing this will make the outside "colder" (it's winter) when I go outside. People recommend that I take off my coat when inside so that I don't get as cold outside.

Is this true? If so, how/why is this?

141.117.29.242 (talk) 16:40, 28 January 2009 (UTC)

Perhaps it is because sweat glands, our natural cooling system, adjust to current conditions. When a coat is worn indoors, the glands open to produce more cooling. If the coat wearer then goes outdoors, it takes a little time for the sweat glands to adjust to the new condition. – GlowWorm. —Preceding unsigned comment added by 98.17.34.148 (talk) 16:58, 28 January 2009 (UTC)

I agree with the above, in that if you're so hot you're sweating indoors, you should definitely take the coat off indoors. However, if you are cold enough to feel you need it indoors, then wear it. StuRat (talk) 17:04, 28 January 2009 (UTC)

See Thermoregulation in humans. 76.97.245.5 (talk) 17:07, 28 January 2009 (UTC)

That sounds about right, thanks a lot. 141.117.29.242 (talk) 17:17, 28 January 2009 (UTC)

The article on thermoregulation says, "Horses and humans are two of the few animals capable of sweating." I wonder whether monkeys and apes sweat. It is also surprising that two creatures as unlike as horses and humans both sweat. Where did it start in the evolutionary chain? Did the same thing crop up twice in evolution? Also, sweating is one of those things that are a stumbling block to the theory of evolution - an organ cannot perform its function unless it is already perfected, or nearly perfected. – GlowWorm. —Preceding unsigned comment added by 98.17.34.148 (talk) 18:21, 28 January 2009 (UTC)

Dogs have things that are essentially sweat glands in the their paws. This appears to be so that they can leave a scent trail for their pack-mates to follow rather than to cool themselves. That suggests an evolutionary means to adapt that kind of capability into something for cooling through relatively simple genetic changes. These "stumbling blocks to the theory of evolution" almost always turn out to be something like that. Some piece of biological machinery that was originally intended for one purpose gets re-purposed in some unexpected manner. The business about it only being in horses and humans sounds unlikely - but bear in mind that it's possible for the common ancestor of humans and horses to have had functioning sweat glands and that all of the other species descended from that point didn't need them anymore and lost the capability. Evolution is just as capable of deleting a feature as adding one. SteveBaker (talk) 18:48, 28 January 2009 (UTC)

Or, it could be convergent evolution, although that seems even more unlikely. Interesting, sweat gland says that mammary glands are often considered modified sweat glands, which would suggest sweating pre-dates the evolution of mammals. --Tango (talk) 20:26, 28 January 2009 (UTC) --Tango (talk) 20:26, 28 January 2009 (UTC)

The use of sweating for thermoregulation is rare, but many organisms, including mammals, reptiles and insects, all excrete pheromones for various purposes, and it would not surprise me if scent glands developed for that purpose were modified to produce sweat glands. Dragons flight (talk) 20:42, 28 January 2009 (UTC)

Sweat glands in dog's feet still had to be nearly perfected if they were to work at all. Sweat glands have to perform the complex function of converting bodily fluids, probably blood, into sweat. A duct to the surface also had to be developed. The same requrements apply to mammary glands. - GlowWorm —Preceding unsigned comment added by 98.17.34.148 (talk) 19:31, 28 January 2009 (UTC)

Sweat could have started off as just blood plasma or interstitial fluid and still served a purpose, so there it doesn't have to be one big leap. --Tango (talk) 20:26, 28 January 2009 (UTC)

I still think the organ-specialism problem presents a serious difficulty to the theory of evolution. Those who wish to deny this difficulty say, in any particular case, that there was adaptation of something else. But they cannot show a partially-adapted organ (midway between two functions) in living things or in fossils. Their denial of the difficulty seems to me to be in the same category as the original denial of evolution itself. There was immense opposition to the theory - in England especially - when Darwin's work was first published. However, by now a great mass of supporting evidence for the theory of evolution has been adduced. There is so much supporting evidence that the main thrust of the theory cannot be denied except by religious fundamentalists, who take a nonscientific approach. But I think there is more to be said - in a scientific manner - about evolution. And it is something important. – GlowWorm

One major part of the problem may just be that soft tissue doesn't fossilise particularly well so it is very difficult to tell when organs an extinct creature had. Even if these missing links exist, we would probably struggle to find them. --Tango (talk) 22:47, 28 January 2009 (UTC)

Organs are never "partially adapted". To suggest such a thing implies a teleology to evolution — as if an organ starts out performing function A, but then somehow decides that it should instead be performing function B and starts moving that way. The only way organs can be repurposed is if, at every single step along the way, the changes provide a larger advantage (in performing function B better) than they do disadvantage (in performing function A worse). Every organism in the evolutionary chain that leads to us was a successful reproducer in its own right, there are no inferior halfway points between well-adapted creatures. Maelin (Talk | Contribs) 00:50, 29 January 2009 (UTC)

That's not entirely true - as long as there isn't a significant disadvantage to the change it may spread just by random chance, especially in a small population. Advantageous mutations are more likely to spread, but that doesn't mean that all neutral mutations die out. --Tango (talk) 14:00, 29 January 2009 (UTC)

Another simpler explination is that if you wear your jacket indoors you will sweat in it (not necessarially because you are hot but because you normally sweat a little in most of your normal daily activities). When you go back outside this slight dampness will make you significantly colder. It is the same effect if you've ever worn the same socks two days in a row and notice that on the second day your feet are colder. This is also why they advice changing cloths before bed when doing winter camping, to make sure the cloths are dry and clean to keep you as warm as possible. Anythingapplied (talk) 20:36, 28 January 2009 (UTC)

Not just sweat; we have a variety of ways to regulate our temperature, such as dilating blood vessels. Someone who has adapted to live in Scotland is likely to feel rather hot in Miami, and someone adapted to Miami is probably going to feel chilly in Scotland. Even if the two people wear the same clothes in the same places. We adapt to regulate our temperatures so our internal body temperature stays constant. On a smaller scale, if you wear more clothes than strictly necessary inside in the winter you'll get used to being snuggly and warm while regulating your temperature for warmer conditions. When you go outside, you need to shift to working harder at keeping warm. In particular, if you wear your coat inside you're likely to have more warm blood flowing near the surface of your skin. When you go outside you're suddenly in a situation where your skin is much warmer than the outside air (far more so than if you hadn't kept your coat on), so you quickly lose a lot of heat. Losing heat feels cold. 79.66.105.133 (talk) 20:35, 29 January 2009 (UTC)

Synthesis of Benzene

Resolved

Hi, I was told you cannot "make" benzene from cyclohexane as Benzene cannot be treated as a molecule with 3 isolated double bonds- as bond lengths indicate equal bond lengths. So is the following not possible then? Because you can Birch reduce Benzene to cyclohexane.
Notify me of a response by copying and pasting the following on my talk page, Thanks --DFS454 (talk) 17:12, 28 January 2009 (UTC)
{{newmessages|Wikipedia:Reference desk/Science#Synthesis of Benzene}}

Birch reduction of benzene gives cyclohexadiene, not cyclohexane, and dissolving-metal reductions don't usually touch simple alkenes at all. That's two bits of evidence that benzene is something other than "cyclohexatriene". DMacks (talk) 18:36, 28 January 2009 (UTC)

The alternating-double-bond model that makes benzene appear to be "cyclohexatriene" is largely an artifact of the diagrams used to draw benzene, or reliance upon models of molecular bonding which fall short of fully explaining the situation. There are several good models of bonding which actually reliably predict that benzene will NOT behave as "cyclohexatriene" would be expected to. For example, hybridization theory shows that every carbon atom is "sp2" hybridized, and its just not possible to justify having 6 identical atoms bonded to each other with alternatingly different length and strength bonds. It just doesn't make sense. Likewise, Molecular Orbital Theory, sort of a "hybridization theory on steroids", makes a perfect prediction of the "correct" structure of benzene. The problem is that the standard "stick and ball" model, or the condensed structural formula model shown above, do not allow themselves to easily represent the reality of the delocalized pi-bonding system present in benzene. Its a case of inadequate models more than anything. Once you realize what benzene really is, as explained by hybridization theory and MOT, then its properties and reactions make MUCH more sense. --Jayron32.talk.contribs 04:48, 29 January 2009 (UTC)

Such excellent answers have rarely benzene at the Ref Desk. StuRat (talk) 14:56, 29 January 2009 (UTC)

ha! DMacks (talk) 18:22, 29 January 2009 (UTC)

Yeah, without MO theory, it's hard to explain why benzene is like this, but cyclooctatetraene is really just cyclooctatetraene alternating single and double bonds. DMacks (talk) 18:22, 29 January 2009 (UTC)

• One of the issues would be the comformation of the cyclohexane. It has a chair or boat conformation while the benzene ring is flat. - Mgm|^(talk) 08:52, 30 January 2009 (UTC)
  • Thanks for the explanations everyone! DFS454 (talk) 13:32, 2 February 2009 (UTC)

Letter to the BMJ

While reading, with some amusement, about the cello scrotum hoax, I noticed the original letter to the editor finishes, "... — I am, etc. <signed>" It appears, from the other letters on that page and Ghits, [5] that this is a standard sign off for letters published in this journal. What does the etc replace and why is it used by all correspondents? Rockpocket 18:10, 28 January 2009 (UTC)

I'm guessing - but I get the impression that somewhen in (roughly) Victorian times, there was a large amount of flowery crap you had to put on the end of a letter ("I am yours faithfully") with the complexity of the protocol required to say 'faithfully' on business letters unless it's to a loved one ('eternally') or to a lawyer ('respectfully') or a government official or some minor royalty ('loyally'). Keeping all of that straight - especially when writing (in effect) to a large number of unknown people in a journal - got so bothersome that people would just stick an 'etc' in there an let people figure it out for themselves! It's come a long way from there to ~~~~ or '-- Steve' which is what I use on email! SteveBaker (talk) 18:36, 28 January 2009 (UTC)

Yes, you are correct. I just looked at some of the letters from the first issues in the 1840s and, back then the standard sign-off was "... — I am, gentlemen, your very obedient servant,<signed>." The "gentlemen" are the editors of the journal to whom the letters are addressed. Rockpocket 19:11, 28 January 2009 (UTC)

Note, "yours" in "yours faithfully",etc., is short for "your servant" (as in "I'm at your service", not necessary actually employed to scrub floors!). We do, of course, have an article: Valediction. --Tango (talk) 19:35, 28 January 2009 (UTC)

Which somehow fails to mention the Italian form sono vostro schiavo, "I am your slave"; a flowery formula of the highborn that somehow morphed into today's extremely informal ciao. --Trovatore (talk) 23:26, 28 January 2009 (UTC)

Wikipedia - the free encyclopedia that anyone can edit. SteveBaker (talk) 00:29, 29 January 2009 (UTC)

Well, true. I can't be bothered at the moment to look up sources and so on. I wasn't really criticizing the article, just remarking on the fact itself, which seemed germane to the discussion. --Trovatore (talk) 01:44, 29 January 2009 (UTC)

Isn't the "etc." put in by the editors? the original letter would still have a valediction.124.176.236.32 (talk) 07:41, 29 January 2009 (UTC)

Such letters to the editor are always published in exactly the same format, so I would expect people to just write them in that format to start with. If they don't, it might well be edited to fit the standard format (there is usually a disclaimer somewhere saying they might edit your letters). --Tango (talk) 13:49, 29 January 2009 (UTC)

Hmmm - that might make sense. If the author wrote TO the editor using a valediction appropriate to the editor - then the editor might wish to redact it when printing the letter to be read by others to whom that valediction was not appropriate. This stuff mattered a lot more 35 years ago than it does today. I'm fairly sure we'd have been taught the correct way to address a letter to a person of importance when I was in high school around about then...sadly, that's exactly the kind of thing I forgot about a nanosecond later! SteveBaker (talk) 18:59, 29 January 2009 (UTC)

I don't think it's a matter of appropriateness, they're just abbreviating it because it's very long. These days "Yours faithfully" would be standard (since letters to the editor are usually addressed "Dear Sir"), but publications like the BMJ have been around so long they probably like to stick to old fashioned versions just for the hell of it. --Tango (talk) 20:08, 29 January 2009 (UTC)

Autodidact: how to prove that you learned something

How can an autodidact prove that he learned something about this or that science? Is there any independent examination out there?--80.58.205.37 (talk) 18:16, 28 January 2009 (UTC)

Well, you could try answering 10 questions a day on the WP RefDesk and if you get through a month without getting ripped to shreds by the other editors then you've probably made it! But seriously: I don't know at what level you are working - but you could take a look at the resources available to parents of home-schooled children...somehow they must be able to do it. SteveBaker (talk) 18:39, 28 January 2009 (UTC)

Actually, if you answer enough Q's here you will get ripped to shreds, even if the answers are correct, if they lack references to expert sources (even though they agree with the experts). If, on the other hand, your answers are correct, but disagree with the current experts, then God help you. StuRat (talk) 14:51, 29 January 2009 (UTC)

Well the reason you get ripped to shreds is because without references no one has a way of knowing if they really agree with the experts. That is after all the wikipedia way. Trust no one. (Okay maybe I'm mixing up my metaphors but it works) Nil Einne (talk) 19:45, 1 February 2009 (UTC)

In the same line: General Educational Development certifies that the taker has American or Canadian high school-level academic skills. For more advanced skills you could try the GRE. It is done before graduate school, however, I don't think you have to have a Bachelor degree to apply for it. There are also several IT certificates that don't require that you follow an specific path. Mr.K. (talk) 18:58, 28 January 2009 (UTC)

You could make and publish ground-breaking discoveries. --NorwegianBlue ^talk 19:36, 28 January 2009 (UTC)

For jobs at my organization, experience can be substituted for formal education. The idea being that if you have done a type of work sucessfully for a long time, that is as good as or better that a degree saying that you know how to do the job. ike9898 (talk) 19:48, 28 January 2009 (UTC)

I think we would be better able to address your question if we know: (1) the (equivalent) education level; (2) area of study; and, (3) country you are interested in, since there is a huge difference between being a "certified" autodidact in, say, web-design vs surgery. Abecedare (talk) 20:08, 28 January 2009 (UTC)

No, I don't have any interest in becoming a certified surgeon or certifying my knowledge in another highly regulated profession. I only have an interest in certifying my knowledge in some natural sciences above undergraduate level without putting a huge amount of money and time into a degree program. So far I found Graduate_Record_Examination#GRE_Subject_Tests. --88.0.97.125 (talk) 10:43, 29 January 2009 (UTC)

edit conflict

The GRE Physics subject test is a good start, but even some physicists consider it "irrelevant" because it emphasizes certain areas of research over others. (If only I had known ahead of time!) This is a general problem of any testing methodology.

Whether you are an autodidact or a formally trained scientist, you are fundamentally trying to establish credibility, if not expertise, in a specific subject area. The best way to do this is to participate in mainstream discussions with your specific community of interest. In modern science contexts, such conversations take the more structured format of journal publications, conference presentations, and grant requests. In the (slightly less formal) Wikipedia community, you can follow SteveBaker's advice - the Reference Desk is a cut-throat community of hardened misanthropic science-enthusiasts who will gladly correct your errors until you learn the ways of its in-crowd. It's not so very different from regular academia. Nimur (talk) 18:45, 29 January 2009 (UTC)

January 29

Parallel Universes' Laws of Physics

Hello,

According to String Theory ("M" theory in particular), there is the possibility of many other parallel universes just out of our "dimensional reach". Interestingly, The Elegant Universe by Brian Greene, gives rise to the possibility that these universes (if they exist) could reasonably have different laws regarding physics as we know it. My question is how is this possible?

Why would other universes have completely different laws? I can understand that there may be different parameters than ours (temperature, structure, makeup, etc...) but I don't understand that there can be a universe with laws that wouldn't make any sense! For example, if our universe had different laws, such as "F=m/a" or "E=mc", it would fall apart quite quickly, correct? Can universes really exist if they, say, violate the Laws of Thermodynamics? Or am I reading too much into the hypothetical implications to a hypothetical theory?

On a side note, could anyone please provide links or reading from a respectable (read "scientifically accepted") journal, website, book etc... for either the acceptance or denial of the Laws of Physics changing over time? Multiple sources or conflicting viewpoints are fine as well!

Thank you for your time, additional reading or information would be greatly appreciated!

Cheers! ❦ECH3LON❦ 00:28, 29 January 2009 (UTC)

Scroll up and read Cosmic gods Rotational (talk) 13:52, 29 January 2009 (UTC)

I suspect a lot of assumptions are hidden here under the term "laws of physics". Are we talking about "laws" like E=mc^2 or "F=m/a" or are we talking about, say, the number of quarks in existence, the relative strength of gravity, the same bestiary of particle physics? It's easy to imagine a universe where gravity is more powerful than it currently is; it's hard to imagine a universe in which simple relationships were not the same. --98.217.14.211 (talk) 00:43, 29 January 2009 (UTC)

The problem is that any parallel universe which is 'inaccessible' to us is inaccessible to our theories too. So we have no way (even in principle) to probe the other universe to figure out what its' laws are. Do we have any reason to assume the laws ARE the same? Npt really. Heck, we don't even know for 100% sure whether the laws we've worked out apply everywhere in OUR universe. We don't know - we can't know - so the safe assumption is that they could be different. SteveBaker (talk) 00:48, 29 January 2009 (UTC)

Well, I don't know if it's a "safe assumption." I hate invoking anything resembling the anthropic principle, because I find it less than explanatory, but from an issue of pure incidences, we certainly know that our particular configuration seems to work and appear fairly steady. We have no evidence that anything else could be. We have no evidence (and no reason to assume) our particular universe is anything special, that our particular place in it is particularly privileged. So it seems to me like we'd have more reason to assume that things elsewhere are similar to the way they are here. That's no rigorous proof, obviously. But I'm not sure there's any reason to assume they are different elsewhere. I don't see why, in the absence of evidence, it makes sense to assume that something is different than the case we know, even though the sample size is blindingly small (n=1). --98.217.14.211 (talk) 01:41, 29 January 2009 (UTC)

(Edit Conflict) By "laws of physics" (sorry for the vague term), I meant the relationships (mathematically) that we understand. For example, F=ma,

E=mc^2, Laws of thermodynamics, Maxwell's equations, etc... Does this help? Cheers! ❦ECH3LON❦ 00:51, 29 January 2009 (UTC)

If I recall that book correctly, he was talking about different values for physical constants such as c, μ₀, and particle masses, though I might be wrong. They say that if the strong nuclear force were only a few percent stronger than it is, then tetraneutrons could exist, which would make for an interesting universe (and would also throw our notions of radioactivity to hell). There are actually theories that some physical constants might change over time. It's a fun thought experiment to imagine a universe where the speed of light is only a few hundred miles an hour. But I digress.

Any notion of different laws of physics would be completely incomprehensible; asking how other physical laws are possible in other universes is like saying "how is it possible that God exists"? We only say it's "possible" because its outside of the realm of physics to say it's impossible. It's all a thought experiment anyway, like working with four-dimensional geometry. It doesn't exist in any way that we could ever observe it, so it isn't worth worrying about.-RunningOnBrains 01:31, 29 January 2009 (UTC)

Heh, I'm reading that book at the moment too. I wonder if I know you ;) —Cyclonenim (talk · contribs · email) 07:45, 29 January 2009 (UTC)

Unfortunately, I lost my copy of that book years ago (I should buy another one...), so I'm not sure quite what he was talking about. However, things like the inverse square law are easy to change - in a universe with 4 spacial dimensions, you get an inverse cube law (which messes with things like orbits to the point where everything either flies apart or crashes together). --Tango (talk) 13:55, 29 January 2009 (UTC)

Centripetal vs. Centrifugal

Could someone please explain to me the difference between centripetal acceleration and centrifugal acceleration? Also, what is the dostinction between centripetal acceleration and centripetal force? Yakeyglee (talk) 01:58, 29 January 2009 (UTC)

If you swing a mass round in a circle, there must be a force acting on the mass to stop it flying off in a straight line (as per Newton). This force is directed toward the center of rotation and is called the centripetal force. Every action has an equal and opposite reaction (some one called Newton again) so the centripetal force is balanced by the centrifugal force (which is what you feel when in a centrifuge. Force = mass*acceleration (that Newton chap again)--GreenSpigot (talk) 02:17, 29 January 2009 (UTC)

That last part isn't entirely correct. Every action has an equal and opposite reaction, yes, but you're confusing where the reaction is. The string is pulling the mass inwards, and the equal and opposite reaction is the string pulling your hand outwards. (When you're wondering about equal and opposite reactions, it's always best to consider that the forces are almost always applied to different objects, because if they were applied to the same object the equal forces would mean that nothing would ever move). For a better explanation of centrifugal force, see the article linked. It's a tricky one, because many over-zealous physics teachers will tell you that centrifugal forces "do not exist." This isn't quite true, it's just that they only exist in the frame of reference of the object being spun. — Sam 146.115.120.108 (talk) 03:40, 29 January 2009 (UTC)

Our article on inertial frames of reference has a nice explanation too. Basically, if you have to invoke forces that have no obvious physical origin and that act on all particles within a body (like centrifugal force and Coriolis force) then this shows that you are working in a non-inertial reference frame. A hypothetical Foucault pendulum at the North pole illustrates the difference nicely - what causes its plane of oscillation to rotate through 360 degrees every 24 hours ? Non-inertial frame answer - Coriolis force. Inertial frame answer - the plane of oscillation doesn't rotate, the Earth rotates around it. Gandalf61 (talk) 12:20, 29 January 2009 (UTC)

Obligatory xkcd reference. — DanielLC 16:48, 29 January 2009 (UTC)

According to Newton's first law, in the absence of an external force, a body will continue to move with uniform velocity in a straight line. The force that causes a body to deviate from a straight line and move along a circular path is called a centripetal force. However when you make measurements in a frame of reference that is intself rotating (such a frame of reference is called a non-intertial frame of reference), you get a "fictitious force" which is experienced in that non-intertial frame. This fictitious force is called the centrifugal force. So, if you you use an inertial frame of reference you experience a body getting deviated into a circular path due to a centripetal force. If on the other hand you are using a non inertial force which is rotating (revolving?) along with the body, you experience a centrifugal force on everything in that frame of reference. Gosh I always think I will be the first to answer some easy question I can answer but get beaten to it everytime :-( ReluctantPhilosopher (talk) 09:25, 30 January 2009 (UTC)

Actually - it's not a matter of being first - or even being the first to be correct - it's a matter of being the first to be both correct AND sufficiently lucid for the OP to understand what you're saying. I think you nailed that this time. There were other explanations ahead of yours - but I think you was the first that was really clearly explained. Sadly, there are no prizes being handed out (I need to make a T-shirt: "I made 15,000 useful posts and all I got was this lousy barnstar.")!! SteveBaker (talk) 12:28, 30 January 2009 (UTC)

Yes seems a very good answer to me. Perhaps some of the text of this answer could actually be incorporated in the relevant articles as a non technical explanation of this misunderstood topic?--GreenSpigot (talk) 18:42, 30 January 2009 (UTC)

Seeing bubbles on a leaf in water

If I put a leaf in water for a while, I see lots of bubbles. "Weeee!!! The plant is photosynthesizing!" I think, "I'll demo this for my students!" But... then I put a pen in water for a while, and I see just as many bubbles. Hmmm....

1) Why do bubbles build on the pen? Yes, I know there are dissolved gasses in the water, but why to they build on the pen?

2) Does anyone know a good lab that makes it clear that the bubbles on the leaf are being produced by photosynthesis?

Thanks! — Sam 146.115.120.108 (talk) 03:17, 29 January 2009 (UTC)

1) Nucleation

2) Not right off, since leaves are not exempt from nucreation you'd have to separate that out. The article hints that pure water might work, but then how do you prove to your students that they are seeing two different effects. Someone probably has a nicer set up up their sleeve. 76.97.245.5 (talk) 04:01, 29 January 2009 (UTC)

It might work if you degas the water immediately before. I can't comment on if you'd actually see the bubbles from photosynthesis - I'm not much of a biologist. --Bennybp (talk) 04:07, 29 January 2009 (UTC)

I think the water can be degasified by boiling it. Then, of course, let it cool before putting the leaf in. — GlowWorm. —Preceding unsigned comment added by 98.17.34.148 (talk) 04:24, 29 January 2009 (UTC)

The leaf will need CO2 to be in the water, so you can't de-gas it. --Milkbreath (talk) 11:50, 29 January 2009 (UTC)

You're right, Milk. Boiling the water will remove the CO2. But that could be the basis of another classroom demonstration. Put a leaf in an inverted test tube full of unboiled water in a beaker of unboiled water. Put another leaf in the same situation with boiled water. Put both beakers under a strong light. I think oxygen bubbles will appear only on the leaf in the unboiled water. This will demonstrate that the leaf takes in CO2, extracts the carbon and keeps it, and exhales the oxygen. Perhaps it could be demonstrated that the gas which collect at the top of the unboiled water test tube is actually oxygen, though I don't know of an easy way to do that. The leaf being under water is not its natural conditiion, but still... - GlowWorm. —Preceding unsigned comment added by 98.17.34.148 (talk) 18:34, 29 January 2009 (UTC)

You could show that the gas in the test tube is probably oxygen by putting a heat-glowing stick or cotton swab in the test tube. The glowing item will burst into flame. - GlowWorm. —Preceding unsigned comment added by 98.17.34.148 (talk) 18:51, 29 January 2009 (UTC)

(ec)I like it, but how do you convince the kids that boiling removes gasses? (I once lost an eyebrow demonstrating fractional distillation for my step-daughter with a saucepan, some vodka, and a match.) Maybe you could boil some seltzer water and show that it's flat. Also, you'd need to seal the boiled water against the air to keep CO2 from getting into the water, and the plain water, too, for equivalency, which would put a time limit on the effect. I've seen a simple test for oxygen done by introducing a glowing splint of wood, which flares up in the presence of it. If you use a small enough test tube and let it go long enough to get a good amount of oxygen, you could evacuate the water by bubbling air into it through some tubing, leaving the air-oxygen mixture in the tube, hopefully concentrated enough to test positive for O2. --Milkbreath (talk) 18:59, 29 January 2009 (UTC)

(ec)1) Dunno. Maybe the air is coming out of the plastic as the water cools it; maybe the rough surface of the pen is providing nucleation sites for dissolved gases that are coming out of solution as the water comes up to room temperature.

2) Fill a test tube with water and place a sprig of elodea inside. Invert the tube in a pan of water. You might have to set up a clamp or something to keep it from falling over. Do the same with a fake plastic sprig of elodea as a control. Keep the rig well lit and the live elodea should outpace the plastic one in bubble production by quite a lot. --Milkbreath (talk) 04:12, 29 January 2009 (UTC)

I think that nailed it pretty neatly. Does anyone know if the Lotus effect would also work in reverse, i.e. would gas bubbles in water on a lotus leaf behave like water in air? 76.97.245.5 (talk) 04:25, 29 January 2009 (UTC)

Thanks! That sounds like a great setup. — Sam 146.115.120.108 (talk) 12:08, 29 January 2009 (UTC)

The plant doesn't just generate oxygen from nowhere - it converts CO2 to O2 in the presence of light - and reverses the direction of the reaction (O2 to CO2) in the dark. So there needs to be dissolved oxygen in the water in order for you to see CO2 bubbles. De-gassing your water seems like it's going to prevent photosynthesis. SteveBaker (talk) 18:39, 29 January 2009 (UTC)

The process doesn't "reverse" in the dark; cellular respiration occurs at all times, it's just that photosynthesis overwhelms that process during sunlit hours to obscure that fact. </pedant> Matt Deres (talk) 14:20, 2 February 2009 (UTC)

Atomic Bombs and Radiation Burns

On the recent episode of Lost, they make reference to the fact that several people suffered radiation burns/radiation poisoning from an unexploded nuclear weapon (a hydrogen bomb). I was under the impression that the uranium/plutonium used in nuclear weapons is comparatively inert and relatively not that radioactive, at least up to the point it goes supercritical. Given the amount and type of radioactive material in an unexploded nuclear bomb, how close would you have to be to the bomb, and how long would you have to stay there to get enough radiation for acute effects to occur? (The bomb was depicted as leaking, so figures for both with and without typical shielding are appreciated.) -- 76.204.94.153 (talk) 04:46, 29 January 2009 (UTC)

You won't get radiation burns from the core of a nuclear weapon unless it is having some sort of criticality accident (i.e. if a gun-type weapon was submerged in water it could basically become a light-water reactor). But that doesn't sound like the case here—just Hollywood B.S. (no h-bomb would use a gun-type design). (Something similar happens in the film version of Sum of All Fears, if I recall.) To be sure, a hydrogen bomb contains a lot of unpleasant and exotic material, but until it goes critical its hazards are not radioactive (they are toxic, but that's a different issue). If just being near a nuclear weapon would burn you up, you can be sure that a lot of photos would probably indicate that. --98.217.14.211 (talk) 05:02, 29 January 2009 (UTC)

When the last poster writes "its hazards are not radioactive", I'm sure the intended meaning is that there is not enough radioactivity to be an immediate hazard. I mention this because it might be taken as saying that there is no radioactive material in the bomb; and since it contains a fission bomb, that would of course be wrong. --Anonymous, 07:25 UTC, January 29, 2009.

Well, right. What I meant is, "radioactivity is really not your biggest problem in a situation like that." There are far more dangerous materials in an unexploded bomb (high explosives, beryllium, etc.). The radioactivity of an unexploded bomb will only be a problem if, say, the high explosives go off and litter the surrounding area with a nice mist of plutonium, but even that won't give you radiation burns, per se, which is characteristic of highly radioactive material. (Materials of low radioactivity are still dangerous, mind you, but not because they will burn you or give you radiation sickness—they'll get in your lungs and bones and just radiate for ages, and eventually you'll get cancer and die. hooray.) --98.217.14.211 (talk) 12:37, 29 January 2009 (UTC)

But given the timetravel and other such events on the show, I think its safe to say the laws of physics as we know them do not apply to the island and therefore anything is possible. I try to turn the scientific portion of my brain off when watching, since its more of a fantasy setting than sci-fi. I'm not quite sure why bad science doesn't bother me on "Lost" but it does on "Fringe". Maybe its because Fringe acts like it is based on real science while Lost is so far out there they don't even try. -- Mad031683 (talk) 18:21, 29 January 2009 (UTC)

We don't have to even assume different laws of physics, though. We can just assume that it's a really poorly made hydrogen bomb, one that they happened to shove a bunch of raw fission products into. --140.247.243.29 (talk) 18:56, 29 January 2009 (UTC)

Oh lord fringe is so bad. They look at the guy's browsing history or something and get the street address of someone downloading the same thing right now? The platters of the hard drive are fused together but it's ok they have a special program that can recover data? °_o .froth. (talk) 18:44, 29 January 2009 (UTC)

Loss of memory cells

If you lose a lot of blood, will you also lose the immunological memory contained in those memory B cells you lost? Will you be once again susceptible to some diseases you've suffered in the past? Thanks for your answers. --Leptictidium (mt) 10:56, 29 January 2009 (UTC)

Typically you will retain more than one memory B cell per pathogen, so the odds of all of one of a particular type being flushed out – even with extended bleeding and multiple transfusions – is low. Further, at least some cells will likely remain in areas that won't drain readily, including the spleen and lymphatic system. TenOfAllTrades(talk) 14:20, 29 January 2009 (UTC)

Another thing to consider is the distribution of B lymphocytes in your body: Only roughly 2% of your total B cells are at any timepoint in your blood, 98% are in your tissues and lymphatic system. So the chance of completely eradicating a specific memory clone is rather low. In addition, even a heavy blood loss normally leaves several liters of blood even in a smaller human body (otherwise you will die rather quickly). So even the 2% that actually swim in your blood will not be drained completely. TheMaster17 (talk) 14:45, 29 January 2009 (UTC)

The new blood will contain Immune memory of diseases the donor has had. Will the recipient of the blood acquire those immunities? - GlowWorm. —Preceding unsigned comment added by 98.17.34.148 (talk) 18:55, 29 January 2009 (UTC)

The "new blood" as you call it is not typically whole blood, but only plasma and/or red blood cells. But even in cases where whole blood is given, the few remaining living cells in the "new blood" are quickly eradicated by the recipient's immune system, because they are recognized as foreign antigen. So no "transfer of immunological memory" is possible simply by blood tranfusion. :-) PS: It is considered polite on wikipedia to sign your posts by adding four tildes [~] at the end. TheMaster17 (talk) 19:52, 29 January 2009 (UTC)

(edit conflict)

Donated blood is usually split into two or three components in the blood bank - the red cells, the plasma and often, but not always, the platelets. The plasma may be used either for producing plasma-derived proteins for treatment of specific diseases, or as whole plasma, which is used for stopping bleeding. When asking about the "immune memory" in the blood , you could refer to the T and B lymphocytes, and possibly also to the antibodies in the plasma.

First, the T and B cells: When these are transfused, they do not under normal circumstances transfer any useful immunity to the recipient - on the contrary, they act as antigens in the recipient, and are destroyed. This will lead to the recipient producing antibodies against the Human Leukocyte Antigens of the donor. Such antibodies can cause problems in subsequent transfusions, both febrile transfusion reactions and poor response to platelet transfusions. Very rarely, the transfused lymphocytes survive, and attack the cells of the recipient, causing graft versus host disease. Because of the problems the lymphocytes cause, it is mandatory in many countries to remove the white blood cells by filtering the red cell and platelet concentrates. In addition, for patients that are especially vulnerable (immunosuppressed), the blood bank will irradiate the blood to ensure that white cells that have managed to get past the filter cannot multiply in the recipient.

Second, the antibodies in the plasma: As said above, whole plasma (as well as platelets) is used for stopping bleeding. The amount of antibodies in whole plasma is too small to have any significant beneficial effect in the recipient, and again, it may cause problems. Plasma from a donor of blood group A has antibodies against blood group B, and would cause a transfusion reaction if transfused to a recipient of blood group B. However, as mentioned above, plasma is also used as raw material for industrial production of specific proteins, such as concentrated amtibodies. Such antibody concentrates are used to treat patients with immune deficiencies, and transfer immunity in a passive way.

The procedure of intentionally transferring functional immune cells is called stem cell transplantation, and the stem cells are either harvested from the bone marrow (bone marrow transplantation), or from the blood. However, to get stem cells in any significant amounts to enter the blood stream requires that the donor is treated beforehand, and it also requires that the donor is carefully selected to match the tissue types of the patient. --NorwegianBlue ^talk 20:27, 29 January 2009 (UTC)

Doctors in Médecins Sans Frontières

When Médecins Sans Frontières sends a doctor to say Rwanda, Sierra Leone or whatever, what is the status of this doctor? Does he have a degree to be a doctor in these countries? Is he illegally working as a doctor but since nobody cares, he can get away with it?--Mr.K. (talk) 11:06, 29 January 2009 (UTC)

From the article Médecins Sans Frontières:

Medical volunteers include physicians, surgeons, nurses, and various other specialists, all of whom usually have training in tropical medicine and epidemiology. In addition to operating the medical and nutrition components of the field mission, these volunteers are sometimes in charge of a group of local medical staff and provide training for them.

So the doctors definitely have degrees at least in the own countries. I would assume that they don't have degrees in the countries they are flying to, but I'm not sure why you would call this "illegal." They are not prescribing drugs, and I don't think there are laws that prevent anyone at all from giving medical care, or even performing surgery. If you wanted to reset my broken arm, and I was ok with you doing it, there is no legal reason that you couldn't. — Sam 146.115.120.108 (talk) 12:18, 29 January 2009 (UTC)

This string is a bit off topic but I think the word "volunteers" is a bit misleading since although hats off to them for volunteering to go, AFAICT they are still paid a salary comparable to an expat doctor for a multi-national? However since they are paid by MSF in whatever offshore location they may not have to be qualified to practice (meaning doing paid work) locally. I know plenty of people who were medically qualified in the UK who couldn't work for pay as a doctor in whatever non-Commonwealth country Africa but were welcomed to work as unpaid volunteers there. Paid by an offshore NGO is probably similar--BozMo talk 12:31, 29 January 2009 (UTC)

It should also be noted that MSF tends to operate in areas which are often described as "Failed states" or "failing states". In many of these areas, there are may be so few qualified doctors that there does not exist any real regulatory apparatus; or the government has so little control that any regulation on paper, especially one as esoteric as the regulation of doctors (which the country may not have many of to begin with), is essentially unenforcable. Even if the doctors are not technically "certified" in the states in which they are working, its hard to imagine that, if someone showed up and said "Hey, we want to cure your 3-year old kids of Diphtheria" that anyone would turn them away. It happens (in Rwanda, for example) that sometimes the doctors are unwelcome, and are murdered as such; however in general many places recognize the charity they provide for what it is and raise no objections.--Jayron32.talk.contribs 14:48, 29 January 2009 (UTC)

@Sam 146.115.120.108: I do believe there are laws in many countries regulating medicine in general and not just people prescribing drugs.

There is still a third possibility: there may be a special UN regulation for the case of catastrophic events, and doctors working for a specific international institution only have to be certified at home. MSF - and other international institutions like Red Cross- often works in failed stated, but also in war-torn regions, earthquakes...80.58.205.37 (talk) 15:20, 29 January 2009 (UTC)

AFAIK if there is an de facto government then that gets to decide what foreign help to accept and what not. There have been cases in the past where the local government has turned away help despite their people suffering. (e.g. Myanmar, [6]) Most countries regulate entry of people wishing to work in their country via visas. A government that accepts help from an international aid organization and issues visas to their employees will probably also accept their qualification. 76.97.245.5 (talk) 04:47, 30 January 2009 (UTC)

About Ocean Tides

Moon has less gravitational pull when compared to Earth's gravity.But how it is possible for moon to pull the water body(ocean) of the earth? —Preceding unsigned comment added by 117.200.112.103 (talk) 13:09, 29 January 2009 (UTC)

It's not the gravitational "pull" itself that causes the tides, it is the difference between the pulling forces at that side of the Earth that faces the moon, the centre of the Earth, and the side that faces away from the moon. Those differences are large enough to cause the tides as we see them (locally the effect can be enhanced by resonant and even interferometric effects due to the shape and size of ocean and sea basins). --Wrongfilter (talk) 13:32, 29 January 2009 (UTC)

But, if the Moon had comparable oceans, it would indeed have tides. StuRat (talk) 14:39, 29 January 2009 (UTC)

Even without oceans, the moon can have "solid" tides in the crust or mantle. That's how the moon's rotational energy dissipated to the point that now the moon always shows the same side to earth. Dauto (talk) 15:19, 29 January 2009 (UTC)

Perhaps the easiest way to think about it is that the ocean water that's closest to (vertically below) the moon feels the earth's gravity MINUS the gravity of the moon. That makes the effective gravity (and therefore the weight of the water) be a bit less there. That reduces the pressure of the water - and the higher pressure water off to the sides and further away that aren't feeling the moon's gravity quite so much are able to push inwards towards the point of least "gravity". That causes a bulge in the ocean vertically beneath the moon. It's actually more complicated than that because there are actually TWO high tides per day - one when the moon is overhead and ANOTHER when it's vertically beneath your feet.

That second tide is harder to explain:

Because the earth and the moon are rotating about a common point that's at the center of gravity of the two bodies, the earth doesn't spin perfectly about it's center - it orbits about a point that's a bit closer to the moon than the true center of the globe. So the part of the ocean that's furthest from the moon experiences centrifugal force that's a little higher than for the rest of the ocean. This results in an outward centrifugal force that ALSO causes the water to bulge outwards - but opposite from where the moon is.

To add to the complication, the sun also causes tides - but much smaller ones than the moon. So depending on the time of year and the time of the month and day - the sun's tidal force may add to or reduce the height of the tides. It ends up being rather complicated!

SteveBaker (talk) 18:32, 29 January 2009 (UTC)

Are you sure about that? I don't think it has anything to do with centrifugal force, it's just tidal forces (ie. the difference between the strength of gravity on different parts of the object due to different distances). The bit of Earth closest to the Moon feels the most gravity, the centre of the Earth feels a little less and the bit on the far side of the Earth feels even less, that causes the Earth to be stretched along the line joining the Earth and Moon. Both tides are caused by exactly the same thing. (Low tides are caused by each side of the Earth being pulled towards the centre of the Moon, so they are pulled at slightly different angles, the net result is that they get pulled towards each other.)--Tango (talk) 18:45, 29 January 2009 (UTC)

The viscosity of water has to be taken into consideration. As the moon pulls the ocean toward it, water flows from all parts of the earth to be closer to the moon. But viscosity slows down the flow. This will not produce a high tide on the far side, but it will lessen the high-tide effect. - GlowWorm.

That's not true, the moon doesn't pull the ocean towards it. The Earth and Moon orbit each other, that means they are in free-fall so are weightless. It's tidal forces (the difference in gravity between different points), not gravity itself, that cause the tides. It does take time for the water to move, though, which means the tidal bulges are offset slightly from the line joining the Earth and Moon - this is what causes tidal locking (gravity pulling on the bulge pulls against rotation, slowing it down). --Tango (talk) 19:32, 29 January 2009 (UTC)

It's just a matter of terminology. "Pull" in this context signifies the difference between the earth's gravitation and the moon's gravitation. - GlowWorm. —Preceding unsigned comment added by 98.17.34.148 (talk) 21:44, 29 January 2009 (UTC)

It's not the difference between the Earth's gravity and the Moon's, it's the difference between the Moon's at one point on Earth and the Moon's at another point on Earth (because they are different distances away from the Moon, or the Moon is in different directions). It isn't pulled towards the Moon, it's pulled away from the centre of the Earth in the direction towards the Moon and towards the centre of the Earth in the perpendicular direction. There is absolutely no difference between "directly towards the Moon" and "directly away from the Moon" - the ocean is pulled the same amount in each direction. Our article, Spaghettification, has some good explanation (with diagrams) - the tides caused by the Moon are far less extreme than those described in the article (which is about black holes), but the principles are the same. --Tango (talk) 22:46, 29 January 2009 (UTC)

Crystal violet staining for cell-counting

In a lab where I'm an intern, we perform crystal violet staining of cells for subsequent assessment of cell-growth inhibition of certain compounds. My problem is thus: the current protocol requires the removal of the medium (DMEM, 10% FBS, 1% P/S antibiotics) before addition of the crystal violet/ethanol solution. The methods for currently employed for medium removal are a) shake the (96-well) plate in a large beaker or b) pipette the medium off the bottom. Option a) results in the cell culture leaving the bottom of the plate in a more or less random pattern, leading to large irregular patches of cells disappearing. Option b) results in small marks in almost every well where abrasion by the pipette tip has resulted in removal of cells from the bottom of the plate. My solution is to add 100% formaldehyde directly to the medium without removing first (intended end concentration 10% = 20 ul formaldehyde + 200 ul medium), fixing the cells and preventing them from leaving the plate during the exercise of medium-removal-option a) (shaking the plate). Thus, my question is: will formaldehyde be able to fix cells to the bottom of the plate in the presence of the DMEM? ----Seans Potato Business 14:17, 29 January 2009 (UTC)

Not an answer to your Q, but have you considered using a needle and syringe instead of a pipette ? An even better option may be to put a sterile paper towel at the lower corner of the plate, to absorb the solution. StuRat (talk) 14:37, 29 January 2009 (UTC)

You haven't stated what kind of cells you're working with, but from your description of the experiment and medium removal techniques, it sounds like they are adherent cells. I don't know about formaldehyde, but paraformaldehyde is often use for fixation of cells in suspension before doing flow cytometry. In that setting, the paraformaldehyde does not make the cells stick to the plastic walls of the 96-well plates (or the tubes) that you're working with, at least not to an extent that causes problems. Why don't you try it out experimentally? Take three plates, seed out equal cell numbers in a couple of concentrations with several replicates for each concentration, and then try the three techniques for medium removal, and compare the variances between the methods? It doesn't sound like a difficult or expensive experiment, and you're the one who is in the position to perform it. If the reproducibility is poor, I would consider a redesign of the technique you use for getting a readout, using a staining method that doesn't require that the medium be removed. --NorwegianBlue ^talk 21:41, 29 January 2009 (UTC)

The DMEM probably isn't going to be a problem; the FBS might be. (Typical DMEM composition is here: [7].) Protein in the serum - mostly bovine serum albumin (BSA) - is going to be crosslinked and fixed by the formalin/formaldehyde. This may affect the degree of fixation of your cells, and may also result in a noisy result in your assay (as large amounts of precipitated, crosslinked protein is left behind). You may have to try it and see.

In lieu of violent shaking over a beaker, can you get an equally effective result - that doesn't detach cells - by gently inverting the plate over a stack of paper towels or other absorbent material? Gently refilling with PBS and dumping a second time may be required to clear most of the media before fixation. One last thought - perhaps you could look for 'stickier' plates. Different manufacturers offer tissue culture plates with different coatings; some will hold cells better than others. TenOfAllTrades(talk) 23:32, 29 January 2009 (UTC)

Swollen abdomen in Kwashiorkor

From the article "One important factor in the development of kwashiorkor is aflatoxin poisoning. Aflatoxins are produced by molds and ingested with moldy foods. They are toxified by the cytochrome P450 system in the liver, the resulting epoxides damage liver DNA. Since many serum proteins, in particular albumin, are produced in the liver, the symptoms of kwashiorkor are easily explained. "

Does this albumin deficiency causes the abdomen to swell? Why does it happen? 80.58.205.37 (talk) 16:32, 29 January 2009 (UTC)

According to the german language WP, albumin is mainly responsible for the colloid-osmotic pressure of blood, i.e., its content of solved substances. If that goes down, tissues near the blood will draw water, and this water can't be reuptaken by the veins---which are the most numerous in the belly. --Ayacop (talk) 17:08, 29 January 2009 (UTC)

Hypoalbuminemia (low albumin in the blood) causes transudative ascites. Axl ¤ [Talk] 18:40, 4 February 2009 (UTC)

Cause of death in the ocean

I’m curious as to what the frailest part of a person is while in the ocean. In particular say a person is in the ocean, perhaps a few miles off the coast of Florida, I’m wondering what factor would kill them if they don’t or can’t get help/swim to shore. Presumably the person would be able to float sufficiently well to not drown. And they probably don’t look enough like food to be eaten by something. So I would guess that either hypothermia, dehydration or salt overdose would be the actual killer. Any ideas as to which would come first, or how I would figure this out? Thanks 130.127.186.172 (talk) 17:41, 29 January 2009 (UTC)

In cold water, hypothermia is probably your primary concern. In extremely hot conditions, dehydration would be a problem. In more temperate conditions, exhaustion, leading to drowning, would probably be what gets you (while people float pretty well in salt water, it does take a certain amount of effort to keep your head above water, particularly in rough seas). This is just off the top of my head, though, we don't seem to have a relevant article (at least, not one I can find)... --Tango (talk) 18:00, 29 January 2009 (UTC)

Without flotation aids, I'd expect that both hypothermia and salt ingestion lead to drowning as the immediate cause of death, since those conditions would cause on to lose the ability to keep one's head above water before they actually become fatal. With a life jacket, I'd guess hypothermia is the killer for large portions of the ocean. Dragons flight (talk) 18:16, 29 January 2009 (UTC)

I've often heard "exposure" as a cause of death in those cases, which I would guess is by a combination of severe sunburn, dehydration, and exhaustion (since it would be tough to sleep while keeping your head above water). A lot of times desperately dehydrated people with no survival skills will drink seawater, which leads to confusion, hallucinations, and a fairly quick death.-RunningOnBrains 20:23, 29 January 2009 (UTC)

Guidance required.

Hello all, most initially, sorry for putting such an odd question here. But I want to create a new Project about Development of Science in Ancient India. Can anyone please tell me how should I proceed since I am new to this site? Anirban16chatterjee (talk) 17:50, 29 January 2009 (UTC)

Try the Wikipedia:Help desk for advice on how to contribute to Wikipedia (the Ref Desk is more about helping people get the most out of what is already written). It sounds like an interesting topic to write about - good luck with it! --Tango (talk) 17:54, 29 January 2009 (UTC)

Thank you very much, for rendering your kind hand of cooperation. And, thank you for your best wish! Best Regards. Anirban16chatterjee (talk) 18:09, 29 January 2009 (UTC)

Do you really mean "Project" (as in WikiProject) or do you just want to write an article? Writing an article is very easy and there are lots of tutorials out there. However, if you really do want to start a project (as in a collaboration between a number of editors to write, grade, produce standards and maintain a body of articles relating to a common topic) then I STRONGLY recommend that you write some articles in the areas of your interest, gradually find out who the active editors in those areas are - get to know them and gradually form a consensus to start a 'Project'. If a relative newcomer just dives in and starts trying to do such ambitious things - well, let's just say that it won't end well!

If you do actually just want to write an article then I recommend starting with Wikipedia:Introduction, then Wikipedia:Introduction_2, then go to the full Wikipedia:Tutorial. There are lots of quick guides out there - I'm going to recommend the one on my own off-site Wiki: http://www.sjbaker.org/wiki/index.php?title=The_simplest_possible_guide_to_writing_MediaWiki

There are already a couple of dozen WikiProjects relating to India Wikipedia:WikiProject_Council/Directory/Geographical/Asia#India and also a fairly large and active project that handles issues relating to the history of science in general: Wikipedia:WikiProject_History_of_Science. You might want to talk to the people on those projects about your ideas...I'm sure you'll find them a helpful and useful resource.

SteveBaker (talk) 18:18, 29 January 2009 (UTC)

Tons to kN conversion

I've found a source relating to the collapse of a bridge saying that the wind "applied an estimated lateral force of 90 tons (40 kN)" I pretty sure "kN" is kilonewtons, but which type of ton (short ton-force, long ton-force ect) is given? I have tried converting them myself, but I couldn't get the numbers to match up. --​​​​D.B.^{talk•contribs} 17:58, 29 January 2009 (UTC)

I can't get the numbers to match either... If I'm doing the conversion right (well, typing the right things into google!), 90 short tons-force is 816 kN, 90 long tons-force is 914 kN and 90 metric tons-force (tonnes) is 900 kN. Perhaps tons-force isn't related to tons-mass in the way I would think (1 tons-force being the weight of 1 ton at the Earth's surface). Our article, Ton#Units of force has the necessary numbers, and they give roughly the same answers as I got (the difference is probably because I used g=10m/s², not 9.81), and certainly not anything close to 40kN. I think your source is wrong. --Tango (talk) 18:08, 29 January 2009 (UTC)

It probably was a mistake in their calculations. I went and checked another source and it gives the 90 tons measurement but doesn't provide any conversion. I'm assuming that because it's a U.S. source, it means short tons-force. Thanks for checking. --​​​​D.B.^{talk•contribs} 18:44, 29 January 2009 (UTC)

No problem. --Tango (talk) 19:13, 29 January 2009 (UTC)

Just a thought, might the 40 kN be 40 kn = knots and the wind speed [8]?76.97.245.5 (talk) 05:09, 30 January 2009 (UTC)

NPN transistor as a switch

Would this work? If not, why? Normally the transistor is wired up differently (emitter connected to ground).

File:NPN transistor switch inverse.png —Preceding unsigned comment added by Jcmaco (talk • contribs) 18:36, 29 January 2009 (UTC)

Sure. See "Common collector". --Milkbreath (talk) 18:45, 29 January 2009 (UTC)

If you define "work" and define the "load" more specifically, it will be possible to evaluate your question more rigorously. Nimur (talk) 18:51, 29 January 2009 (UTC)

IMO this is not really a good switch circuit (unless the base voltage is slightly greater than the positive supply voltage) because the voltage applied to the load can only be about 0.6 v below the base voltage and the transistor cannot saturate. Much better to put the load in the collector then you can saturate the transistor and get minimum power loss in the transistor itself.--GreenSpigot (talk) 02:38, 30 January 2009 (UTC)

Space

So far how many countries have succesfully landed on a space using space rockets? who are these countries? —Preceding unsigned comment added by 196.200.102.42 (talk) 18:53, 29 January 2009 (UTC)

If you mean landing (or purposely crashing) on somewhere other than Earth:

• the Moon - U.S., Soviet Union, European Union, Japan, and India
• the International Space Station - U.S., Russia, and the European Union
• everywhere else - see Robotic spacecraft#List of space probes. Clarityfiend (talk) 19:15, 29 January 2009 (UTC)

If you mean landed people, then only the US have landed people on any other world (namely, the Moon). If you count putting people into Earth orbit, then the US, Russia and China have done that. Other countries have sent people into space, but only in someone else's spacecraft. --Tango (talk) 19:28, 29 January 2009 (UTC)

Doesn't it depend what you meanby 'world'? The moon is a natural satellite of earth and is sufficiently large to gravity that you can feel it but it's not a planet by any definition. The space stations are/were artificial satellites and aren't large enough for gravity you can feel. Both artificial and natural satellites could be counted as other worlds or neither. Nil Einne (talk) 17:29, 1 February 2009 (UTC)

Yes, it does depend on your definitions, but it isn't uncommon to call the Moon a "world". --Tango (talk) 19:12, 3 February 2009 (UTC)

It is worth noting that this questioner's IP address maps to Eritrea, and it is probable that she/he is a non-native English speaker. Judging from Languages of Eritrea, it is likely that the questioner will understand at least one of the following articles:

• Veicolo spaziale (italiano)
• مركبة فضائية (Arabic/ عرابي )
• صاروخ

Our English articles, Spacecraft and Spaceflight, are available in many other languages as well. Hopefully this will help... Nimur (talk) 15:52, 4 February 2009 (UTC)

Determing the thermoelectric cooler's current output when using a fan as a load

Through amateur experimentation, I have found that a thermoelectric cooler has a varying current whenever it has a fan attached to it as a load.

These coolers are old technology that are being implemented recently into computer CPUs to recover some of the waste heat emitted as exhaust. While attempting to measure the total power output (I know the Current input, voltage input, and therefore the Power input) the current constantly fluctuates.

I am using a resistor to emulate the CPU and it can produce up to 130degrees C. (Any temperature above 130degrees C. can cause damage to both the thermal probe and my TEC plate.)

When I used a ~5 Ohm resistor as a load, it gave me a constant current allowing me to find my efficiency at 2.25% with a maximum voltage of 2.5V and a maximum current of .5A yielding a power output of 1.25 watts. When entered into the equation: Power Output/ Power input (the input is 56.25W) I obtained my efficiency of 2.25%.

My problem lies in the fact that whenever I change my load from a constant resistor to a fan, I cannot determine the current, yet my voltage has increased to 3.7V and 5.9V (using a small fan on top of the heatsink [3.7V] and a larger fan [5.9V]).

I cannot determine the efficiency because I can't find the current of the output.

It should be noted that the current has very frequent oscillations instead of reading a blank value.

Can you help me?

Thank you. —Preceding unsigned comment added by 24.3.140.186 (talk) 19:46, 29 January 2009 (UTC)

Fans, like other electric motors, have a current roughly approximated by Current_To_Overcome_Friction (small) + Current_For_Acceleration (large and dynamic). It's possible that your fan is not operating at constant speed; a common cause is due to dust or dynamic mechanical behaviors. Nimur (talk) 20:14, 29 January 2009 (UTC)

small computer fans switch the current on and off rapidly. I dont know but I speculate that using current smoothing devices could help give a steady reading. If the speed of the fan is the same as when it is in the open, and the voltage is the rated voltage printed on the fan then the current should also be very close to the rated current.Polypipe Wrangler (talk) 01:39, 30 January 2009 (UTC)

humans ≠ able to tell time

Clocks are very, very simple mechanisms. Small enough to be put inside a very, very small box and be strapped to your wrist, and still be able to tell time. Humans have a very big, very functional brain that is infinitely more complex and infinitely smarter than a standard wristwatch, yet humans cannot accurately keep time. I tried this thing at a museum to see if you could press a button when exactly a minute had passed. I couldn't, and the tour guide said that he couldn't remember a single case where someone could do it more than one time without getting completely off the second time. Why can't humans do this simple task? flaminglawyer 00:20, 30 January 2009 (UTC)

Sure we could, it would just take practice. Here's a guy who memorized the first 67,000 digits of pi. You don't think he could learn to count to 60 reliably? --Sean 23:01, 29 January 2009 (UTC)

What does memory have to do with precision timing? --Tango (talk) 23:05, 29 January 2009 (UTC)

My point is that humans can do all kinds of things with practice. The only thing we can do without practicing is clamber up to a nipple and suck on it. --Sean 13:11, 30 January 2009 (UTC)

Because it isn't a skill that makes you more likely to pass on your genes to the next generation (or, at least, wasn't until the industrial revolution when precise timings became useful), so there is no evolutionary pressure towards developing such a skill. There are other animals that have very precise measures of time, as I recall (fireflies perhaps - do they flash at a very precise rate?) - the skill is useful for them, it isn't useful for us (or, at least, hasn't been for long enough for evolution to have a chance at giving it to us - and given that we've replaced the need for such a skill with technology, it will probably never happen). --Tango (talk) 23:05, 29 January 2009 (UTC)

Any drummer worth their salt should be able to keep to 60bpm for a while.91.109.221.91 (talk) 23:24, 29 January 2009 (UTC)

You don't hang out with many drummers do you:) "How do you know if there's a drummer at your door?" "The knocking keeps speeding up." DMacks (talk) 21:05, 30 January 2009 (UTC)

You can teach yourself - definitely. There is a long section in one of Richard Feynmann's books about how he taught himself to count seconds very accurately. He didn't find that terribly difficult. He then tried to learn to do other things at the same time as keeping track of seconds and was interested to discover that there were some classes of task that he could do while keeping track of seconds accurately - and others where his timing went wildly off whenever he did it. Sadly, I'm not near my books right now so I can't get you the exact title of the book or a more precise description of what transpired. As to why humans can't "just do it" - we had no need to do so throughout the evolutionary process that developed out brains. We probably have a need to look at the sun and the horizon and guess whether we have time to hunt down another mastodon before bedtime - but nothing precise. Even nowadays when it would be exceedingly handy to be able to do it, that ability would be unlikely to get you laid any more often - hence not much evolutionary pressure there. But the brain is amazingly adaptable - and with practice and determination - I bet you could prove the tour guide wrong. SteveBaker (talk) 23:33, 29 January 2009 (UTC)

(sorry, forgot to sign my post up there, I guess Sinebot missed it? <oh no!>) Then why hasn't anyone done it? Surely people have tried (they've tried just about everything else, like that Lu Chao guy, remembering pi), but no one can, so that means that they must've failed. But humans should be able to do it. Think: Computers, like the one you're sitting in front of right now, are displaying Firefox, running an anti-virus scan, maintaining an operating system, etc., yet they still can give you an exact time. (technically, it's beamed in from timeservers, but how do you think timeservers do it?) The human brain is so much more efficient and capable of much greater things (bigger, built with proteins instead of metal, etc.) but it can't even do tell time. So, since no one can do it, I guess it's impossible. Why? My confidence in mankind used to be a bit bigger :( . (sorry for not posting this earlier, but I got e/c'd a couple times and gave up) flaminglawyer 00:20, 30 January 2009 (UTC)

Who says no-one can do it? Steve says Feynmann could do it, and the anon points out that drummers can probably do it. As for why we can't do things computers can - that's because computers are specially built for those kind of things, we're not. My wrist watch is a tiny fraction the size of me and is far far better at telling the time, but it is rubbish at reproducing itself. We're each made for different purposes, so each have different abilities. --Tango (talk) 00:29, 30 January 2009 (UTC)

Feyman could only do it if that was the only thing he was doing. And I'll bet that any drummer would lose his beat if he had to do anything else. Even the simplest of tasks, like drinking coffee. But I get it, so

Resolved

. flaminglawyer 00:36, 30 January 2009 (UTC)

Unresolved

It seems a little arrogant to stick a 'resolved' sticker on an answer when you've just disagreed with a Nobel-winning scientist. You didn't even check the book - or search the web or anything! As you'll see below - you are quite utterly WRONG. A little humility please! SteveBaker (talk) 01:33, 30 January 2009 (UTC)

No - categorically not. Feynmann found that there WERE some tasks he could perform while maintaining his count...but others not. Argh - I wish I could look it up - but I don't have my book collection with my right now. As I recall, he hypothesised that there was some particular brain function of which we only had one that was enabling him to keep good time...so long as the other activity doesn't require that brain function, one may multitask. SteveBaker (talk) 01:16, 30 January 2009 (UTC)

Aha! Google books to the rescue! "The Pleasure of Finding Things Out" - in the chapter called "It's as Simple as One, Two, Three". [9] - He found WITHOUT ANY PRACTICE that he could 'time' 48 seconds plus or minus one second by counting to 60. He found that he could fill out a form and use a typewriter while keeping good time - but he couldn't count things 'normally' - but he could mentally group things into three and tick off three per second and keep good time. He could read a newspaper and keep good time - he could run up and down stairs and keep good time. He could NOT talk and count. Then another guy tries it - and he finds that he CAN talk and keep good time...but he keeps time by visualising a tape with numbers on it scrolling past his mind's eye - so he's not counting. Try as he might, he could not find a way to read out loud and keep good 'mental' time. As usual, Feynmann (who is my personal hero) likes to experiment with the simplest of problems and invariably discovers something fascinating. SteveBaker (talk) 01:29, 30 January 2009 (UTC)

I've been looking for the following anecdote since this question was asked, and I finally googled it loose: Maestro Eugene Ormandy was asked by a radio producer how long a certain piece of music he was to conduct on the radio later would run. He replied that he didn't know, having never timed it, but he spotted someone nearby with a stopwatch and told him to start it. Two phone calls and a couple of conversations later he said stop, right on the money. (One for Ripley, or not?) --Milkbreath (talk) 02:05, 30 January 2009 (UTC)

Yeah - that's exactly the kind of thing Feynmann was saying. Presumably, the Maestro set the music playing 'in his head' and because he's good at it - the imaginary music plays at precisely the right tempo. Evidently he is able to talk and 'play music in his head' at the same time - so it all turned out OK. Feynmann too claimed that he could read and perform various other tasks while counting - but he couldn't speak. Then his colleague reports that he visualises an image of a band of numbers scrolling past in his mind's eye - so he can talk while "watching" the band scroll by - but he can't read. So this anecdote further shows that you CAN produce reasonably precise timings AND do something else at the same time...providing it doesn't use the same part of your brain. Now, if you were REALLY smart - you could count like Feynmann and read a book - then, if the phone rings, stop counting and start scrolling a 'tape' with numbers on it past your mind's eye or start listening to Bach harpsichord music in your head while you talk to the person on the phone - then revert to counting when you sit back down to read. With a big enough range of alternative timing tricks and enough practice that this became automatic - I think you could probably teach yourself to measure time automatically all day long...which would be a neat party trick! I feel an experiment is needed. I'm going to practice listening to Queen's "Bohemian Rhapsody" (which I know well) in my head - and I know it's 5'55" long (I used to be a radio DJ when I was in college - I used to tell my listeners that I put it on so I had time to go outside and wash my car during the show...which wasn't true - but it's a great line!). Anyway - I'm going to listen to it 'in my head' and try to write C++ code at the same time. I'll report back later. SteveBaker (talk) 12:21, 30 January 2009 (UTC)

Anectodally, the music thing works pretty well. When I was a kid, I had insomnia, and to pass the time, I would sing "99 Bottles of Beer" to myself, in my head, and found that it took almost exactly 22 minutes for me to run through the entire song. I then did some math and found meant that meant it took roughly 13 seconds to do one iteration of the song, or that 4-5 iterations was about a minute. Its a skill I lost, but for many years it was how I would keep time while doing stuff where I didn't have a clock to look at, and I found I could keep time to within about 5 minutes in an hour. I would just play the song in my head, and however many bottles of beer were left on my wall, I could quickly estimate how long it took me to do a task. It got to be almost automatic. Came in handy on things like the SAT, where I only had a certain amount of time to complete a task, and I could fairly reliably estimate my mile time when running on my High School cross country team. So, with some training, humans can fairly accurately measure time while completing other tasks, even those (like taking a test) that require some other intense mental work as well. --Jayron32.talk.contribs 17:02, 30 January 2009 (UTC)

More WP:OR: I have found that -- with statistically improbable frequency -- I will wake up exactly one minute before my alarm clock rings if I have set it to some unusually early time the next morning. --Sean 17:59, 30 January 2009 (UTC)

OR results are in. Evidently my head replays Bohemian Rhapsody quite a bit faster than Queen - my five tries to keep it playing in my head while working were very successful - I didn't "lose my place" or pause or anything at any point in my testing. But each time the times were well short of the 5'55" that the tune is supposed to take: 5'22", 5'25", 5'23", 5'27" and 5'20". However - as Feynmann pointed out in his book, that doesn't really matter. So long as you know the factor that you are 'off' by, you can correct for it. That's a variation of +/- 4 seconds - which is about +/- 1% accuracy. That's comparable to Feynmann's figures for counting and reading at the same time. Having a fairly accurate five minute timer in your head is pretty useful - so I'm actually going to figure out whether there is a convenient 24 second-ish chunk I can cut out of the song to make it fit in 5 minutes. Anyway - as the Mythbusters say, this one is "Confirmed". SteveBaker (talk) 20:36, 30 January 2009 (UTC)

That's what I would have expected. The important thing is not that you can reproduce Queen's version of Bohemian Rhapsody, it's that your version is consistant. Which it would appear to be... --Jayron32.talk.contribs 20:44, 30 January 2009 (UTC)

Yep - exactly. SteveBaker (talk) 01:30, 31 January 2009 (UTC)

We're still missing the point. I know that you can measure an amount of time if you know the offset factor, etc., etc. My intention was for the question to say something like, "Why can't humans tell time in their head while doing completely different things?" I realize that this is completely redundant to a wristwatch, but it seems so simple, and so doable... I also realize that this has already been answered (kind of) so I feel that I could correctly stick a {{resolved}} on it. But I won't. I still disagree with a Nobel-winning scientist. flaminglawyer 00:42, 31 January 2009 (UTC)

You aren't just disagreeing with Feynmann. We've shown that (a) Professor Richard Feynmann (Nobel Prize winner)...AND... (b) Feynmann's colleague (c) Maestro Eugene Ormandy (d) Jayron32 (Grand Tutnum, esteemed member of The Bathrobe Cabal and winner of twenty-three and a half barnstars) and (e) Me (someone who now has the bloody 'Bohemian Rhapsody' stuck in his head) - could ALL count time fairly accurately by more than one method whilst simultaneously doing something else. The evidence is IN. This is the science desk - not the ignoring-all-of-the-evidence-because-it-doesn't-fit-our-world-view desk. Are you calling ALL of us liars? If you thought you knew the answer before we started and are going to disagree with all of the evidence then why the heck did you ask the question in the first place?! To say this as clearly as possible: I was EASILY able to keep track of time to about +/-1% precision while simultaneously writing a particularly tricky C++ class for managing shader uniform state efficiently in both OpenGL and Direct3D. We have evidence that at least four others are capable of this feat. So there is really zero doubt that one CAN both keep reasonably accurate time AND perform at least some other tasks at the same time. Dude - I did it...just this morning! SteveBaker (talk) 01:24, 31 January 2009 (UTC)

Now I'll stick a resolved sticker on it so I can quit while I'm only a little bit behind. flaminglawyer 05:45, 1 February 2009 (UTC)

Resolved

Earth without a moon.

Theoretically, what would be the effect if our moon just magically disappered. Would the tides stop and how would this affect sea-life. Would it change the weather drastically? Would our orbit around the sun change?91.109.221.91 (talk) 23:29, 29 January 2009 (UTC)

There was a question about this a while back. The synopsis is: Yes, our orbit would change because we're currently going around the sun in a wobbly orbit - and it would straighten out - but I doubt we'd notice. The majority of the tides would go away - but there are tides due to the sun that would continue (albeit at a much smaller scale). Doubtless that change would have some effect on the weather and to marine-life that depends on tides (eg the kind that live in rock-pools) - but it's hard to predict what that effect would be. If the moon vanished 'abruptly' - much larger and more drastic consequences are possible due to the sudden 'jolt' due to vanishing gravitational fields...but we'll assume you aren't really talking about that kind of thing. The lack of moonlight at night would help some hunters with really good night vision (maybe owls) and worsen the outcome for their victims - other nighttime predators might do worse...again, it's hard to predict because the world is such a complicated place. SteveBaker (talk) 23:40, 29 January 2009 (UTC)

Why would owls hunt better when it's darker? Just because they can hunt in the dark doesn't mean it isn't easier when it's light. Unless they're competing for the same pray with hunters with worse eyesight, I guess... --Tango (talk) 00:15, 30 January 2009 (UTC)

I'm assuming that the owl's reduction in acuity as it gets darker is more than counter-balanced by the lack of acuity on behalf of it's prey. So in moonlight, the owl can see the mouse very well indeed - but the mouse can also see the owl. When it's pitch-black, the owl can still see reasonably well - but the mouse is effectively blind. That may or may not actually be true - but it's certainly a cause to suspect that the lack of moonlight might affect certain aspects of the ecosystem. SteveBaker (talk) 01:12, 30 January 2009 (UTC)

An owl doesn't need to see the mouse in order to catch it. Experiments show that owls can hear the tiny rustlings of a mouse, even under thick leaves or snow. ~AH1^(TCU) 19:44, 30 January 2009 (UTC)

The Moon is presently the largest torque acting on the tilt of the Earth's axis (its obliquity). Because it is so large and so close, the Moon dominates over other perturbations and effectively stabilizes the Earth's tilt with only small variations over time. If you take away the Moon, the tilt of our planet would be expected to slowly random walk over millions of years due to perturbations from the Sun and other planets. (This same process is believed to be ongoing with Mars, which lacks a large moon.) As this occurred it would have the potential to create radical changes in the intensity of the seasons experienced on Earth. Dragons flight (talk) 01:50, 30 January 2009 (UTC)

As noted above, if the moon magically disappeared, there would still be tides but they would be smaller -- less than half of their present size. They would also differ from the present tides in two other ways. First, they would be the same size all the time, instead of varying every 15 days between stronger "spring" tides and weaker "neap" tides. And second, high tide at a particular place would be at the same two times every day, instead of changing every day -- on open coastline it'd be around noon and midnight.

Another thing is that we would have to change the calendar, and there might be detectable changes in the climate too.

As noted above, the Moon causes the Earth to wobble slightly in its orbit: when the Moon goes away, the wobble ends. But this doesn't mean the Earth resumes its average course; rather, it just keeps going in whatever direction it was wobbling in at the time. Now this wobble is small: the Earth's center orbits the Earth-Moon center of gravity at about 25 to 30 mph (depending on where in its orbit the Moon is), which isn't much in comparison with the Earth's orbital speed of about 66,500 mph around the Sun. But still, it's enough of an effect to be detectable.

For example, say that the Moon disappears at full moon. Then its orbital velocity is in the same direction as the Earth's orbital velocity around the Sun, so the Earth itself is wobbling the other way -- moving in its orbit about 25 to 30 mph slower than usual. When the Moon disappears, the Earth will no longer resume its normal speed. Say it's at aphelion when this happens: then the aphelion remains the same but the perihelion becomes lower. I have calculated (when this question was asked in another forum in the past) that the mean Earth-Sun distance will reduce by about 0.1%. Since the amount of sunlight varies as the inverse square of the distance, it would increase by somewhat about 0.2% on the average, with the greatest increase (about 0.4%) in January when the Earth is nearest the Sun. Very likely that is enough to create detectable climate changes.

And this orbital change would shorten the year from about 365.24 days to something more like 365.03 days. We would only need leap years about 3 times per century.

Conversely, if it happened in the opposite set of circumstances, the Earth-Sun distance would increase, the amount of sunlight would decrease, and we would need leap years more often. And in in-between circumstances, there would be other results of similar or lesser magnitude. You get the idea. --Anonymous, 11:57 UTC, January 30, 2009.

Also, there's the problem that it's not the Earth in isolation now that is orbiting the sun, it's the "Earth-Moon system". If the Moon just disappeared, the Earth-Moon system would still need to conserve its momentum, but it would have just lost 1/6th of its mass. The result would be that Earth would speed up in its orbit. This increase in speed would cause the Earth to change its orbit around the sun; possibly outside of the narrow band of "livable distance" we occupy now. --Jayron32.talk.contribs 16:50, 30 January 2009 (UTC)

First, we were told that the Moon was destroyed magically; there was nothing about its momentum being transferred to the Earth or to any other specific body. Obviously the momentum magically disappears.

Second, let's suppose that's wrong and its momentum actually was transferred to the Earth. The Earth now varies between 91,500,000 miles from the Sun at perihelion to 94,500,000 miles at aphelion and therefore, by Kepler's third law, its orbital speed varies by the same ratio, from about 65,520 mph at aphelion to 67,760 mph at perihelion. The Moon has 1/81 of the Earth's mass, so transferring its momentum to the Earth would -- in addition to canceling the effect I described above with regard to the wobble -- increase the Earth's orbital speed by 1/81 or say 820 mph.

If this happened at aphelion, the 65,520 mph speed would become 66,340 mph. This is only about 250 mph above the speed for a circular orbit at that distance. Therefore the Earth's perihelion would rise to give a perihelion speed about 500 mph faster (yes, I know, this is an approximate method, but it's good enough for this purpose) or 66,840 mph; the perihelion would therefore be at 94,500,000*66,340/66,840 = 93,800,000 miles, and the mean distance would be 94,150,000 miles. The length of the year would increase by a factor of sqrt(94.15/93) to about 367.5 days, and the mean intensity of sunlight would drop by a factor of (94.15/93)², or by about 2.5%. That might produce an ice age but I doubt it would leave the planet uninhabitable. But at least February could become a month of 30 or 31 days like all the rest.

If it happened at perihelion, we'd be worse off. Now the perihelion would remain the same but now it would be the aphelion that'd rise, making the orbit significantly more eccentric. The aphelion increase would be by roughly the same amount, so aphelion would be somewhere around 96,800,000 miles. The reduction in sunlight would be the same on average, but now its intensity would increase from July to January by a factor of (96.8/91.5)² or almost 12% instead of (94.5/91.5)² or about 6.7% as it does now, and that might be enough to have additional climatic effects. If it happened in between aphelion and perihelion, of course, the results would be in between.

--Anonymous, 06:23 UTC, January 31, 2009.

Many animals depend on the moon for some activities. Some Religious holidays worldwide are also defined by the phases of the moon. Near-Earth asteroids might also behave differently around an Earth without a moon. ~AH1^(TCU) 19:39, 30 January 2009 (UTC)

Isaac Asimov had some interesting thoughts about what would have been different if the Earth had no moon. 152.16.59.190 (talk) 11:31, 31 January 2009 (UTC)

The tides would drop, as mentioned, to a third of their current level, precession of the equinoxes would stop, there would be no more eclipses, and werewolves would get more sleep. B00P (talk) 13:08, 31 January 2009 (UTC)

Hmmm...according to this documentary [10] the moon actually stabilizes the tilt of the Earth's axis and without it, the Earth would wobble violently. It also states that the Earth would spin much faster resulting in 4 hour days. Our Rare Earth Hypothesis article states the moon "act[s] as a gyroscope, stabilising the planet's tilt; without this effect the tilt will be chaotic, presumably also causing difficulties for developing life forms." A Quest For Knowledge (talk) 17:07, 31 January 2009 (UTC)

A Quest For Knowledge has misunderstood both the question and what must have been presented on the show. The questioner wanted to know what would happen if the Moon suddenly (and magically) disappeared now. That business of a four-hour day refers to the situation if the Moon had never existed. As for wobbling, Venus doesn't have a moon, and it doesn't "wobble violently" nor is its axial tilt "chaotic." Why should Earth behave differently? B00P (talk) 00:53, 1 February 2009 (UTC)

Sure, there'a difference between what would happen if the moon disappeared and if it had never existed, but that doesn't mean that that none of the information in the documentary or Wikipedia article applies. I'm not an astrophysist or a even a scientist for that matter but both say that the moon stabalises the Earth's tilt. Whether they're right or wrong, I can't say; I'm just repeating what they're saying. When I get a chance, I'll watch that documentary again (although by that time, this thread will be long gone out of the main page). A Quest For Knowledge (talk) 15:05, 2 February 2009 (UTC)

January 30

Rice and Play-doh

Having visited my baby brother recently, and having decided to make rice for dinner, I'm struck by the similarity in scents given off by the cooking rice and the new Play-doh my brother got for Christmas. Why do they smell nearly the same? It's kind of putting me off my dinner plans... Kuronue | Talk 01:04, 30 January 2009 (UTC)

Was your brother's Play-Doh home-made? It's possible to make your own with rice flour. Apparently the real stuff uses wheat flour though. — Matt Eason ^{(Talk &#149; Contribs)} 02:07, 30 January 2009 (UTC)

Nope, brand new, little yellow containers. He got a set designed to make hamburgers and hotdogs as well as a set of four neon colors. Someone on IRC suggested maybe the surfactant is a rice protein? Kuronue | Talk 02:11, 30 January 2009 (UTC)

I'm not sure about the smell, but rice and play-doh may have a few similar properties. They are both sticky and easy to mold into shapes. It's easy to smudge cooked rice and use it as a type of glue, which dries after a while. ~AH1^(TCU) 19:32, 30 January 2009 (UTC)

I'm extremely glad you noticed that too. I've used the-point-at-which-rice-doesn't-taste-like-play-doh as my cooking indicator for years, and people never seem to know what I mean. School rice always tasted like play-doh, presumably because it was undercooked. While unable to answer your question, I just wanted to thank you for reassuring me :) 79.66.71.197 (talk) 23:14, 30 January 2009 (UTC)

Digestive grinding stones

Dinosaurs and birds eat stones and this is supposedly good for the digestive system. I do not drink 2 litres of water any more because I know that if I do not pump the whole thing around, it's not very good for your stomach and your kidneys. If I started swallowing big stones, would I eat less and digest more or would it constipate me until I got surgery? What shape and size of a stone and how often to swallow one or what stones are the best mineral? ~ R.T.G 02:24, 30 January 2009 (UTC)

You are not a bird or dinosaur. Eating stones will not help your digestion, and may well do you harm. Don't do it. Algebraist 02:28, 30 January 2009 (UTC)

interesting idea. Here's a question ... what's the easiest but most dangerous weight loss techniques? a) intestinal parasites - tapeworms Giardia, b) amphetamines, c) fasting (I hear you aren't hungry after a week or so)? TungstenCarbide (talk) 02:57, 30 January 2009 (UTC)

Drinking more (water not softdrinks or coffee/tea) is actually good for you. See Dehydration and Fluid balance. While one can get into trouble drinking excessive amounts of water in one sitting (Water intoxication), drinking 2 liters throughout the day may just about cover what you need. Not drinking water when you are thirsty doesn't sound like a great idea. Your body tells you when it needs water. No clue where you found the information this might be bad for you, but I'd check whether you might not have misunderstood something or whether maybe the writer might have not thoroughly researched the topic. For certain medical conditions doctors may advise you on restricting your water consumption, but that should always be done as instructed by a qualified medical professional. Dietary minerals are only the same as minerals on a chemical element level. The body requires certain forms of these minerals and in combination with certain other chemicals. Even dietary supplements which are a far cry from eating rocks [11] aren't metabolized as efficiently/in the same way as minerals from food sources. [12]76.97.245.5 (talk) 04:05, 30 January 2009 (UTC)

DIY surgery is an easy but very dangerous weight loss technique.-gadfium 04:21, 30 January 2009 (UTC)

FYI, under Crocodiles it says this: "Many large crocodilians swallow stones (called gastroliths or stomach stones) and they are believed to be of use in acting as ballast to balance their body. Other suggestions have been made that they may have a function similar to that of grit in birds, which is in crushing food." In other words, to help them dive deeper, and birds chip away at grit, not stones. And opera diva Maria Callas was rumoured to have lost 80 lb thanks to a tape worm. She put it down to chicken salad. Julia Rossi (talk) 07:59, 30 January 2009 (UTC)

I was looking at Speckled Mousebird which appears well written and says they swallow "pebbles" and I just know that some dinosaurs and lizards eat rocks. The truth may be that drinking only water does more good for you. I am 6 feet and between 11.5-12.5 stone, I eat a medium to large cornflakes in the morning and around five medium to large teas every day, fairly average but if I add two full litres of water to that without exercising to exhaustion (at least) I get runs to the toilet or sore kidneys/sore larger stomach/thirst for loads of water (like diabetes). I always intended to drink 2 liters as per doctors recommend but I just can't do it. I do know water is good for me but took me a while to see the over-excessive part. I think what is meant to be said is that "The most healthy people drink 2 liters of water a day" rather than "Drink to liters of water a day to make yourself healthy". I may have small kidneys or something but that is unlikely (lol, say nothing) and I can eat a lot so my stomach couldnt be too small. I would have thought that swallowing stones big enough for grinding stuff would be difficult for people. It's funny, when my family were all on Slim Fast, the rumour went around that there was worms in it and that it was recalled but I don't see that on snopes or the search engines, lol, 90s paranioa! I beleived that whole-heartedly. Crocodiles only eat once or twice a year (true carivores do not eat all the time, I !can't! find a reference to that if anyone knows of one for the crocodile article, I think they eat between 3 and 18 or 3 and 6 months or something the [wikiversity] page is good but can't find that on animal planet or anything). ~ R.T.G 13:01, 30 January 2009 (UTC)

Birds and reptiles swallow stones because they can't chew. Humans have molars for that, swallowing rocks won't help your digestion because your food is already mashed enough by the time it gets to your stomach. Rocks would either get stuck in your digestive system requiring surgery to remove them, or cause a very unpleasant bathroom experience when they passed through. -- Mad031683 (talk) 17:26, 30 January 2009 (UTC)

Some snakes can eat without even biting... they don't swallow rocks do they? (I think it's right you would need a surgeon) ~ R.T.G 20:54, 30 January 2009 (UTC)

Eosinophil

The normal range of eosinophil counts is 0 to 4 %. What does 7% mean? Thank You! AJ —Preceding unsigned comment added by Adrianajensen (talk • contribs) 03:49, 30 January 2009 (UTC)

Eosinophil granulocyte? Whith questions like yours it always helps to let us know what you need the answer for. We can't give medical advice and won't do homework. 76.97.245.5 (talk) 04:12, 30 January 2009 (UTC)

Don't get me wrong, but isn't a 7% eosinophil count simply termed 'increased eosinophil count'? —Cyclonenim (talk · contribs · email) 07:46, 30 January 2009 (UTC)

It's called Eosinophilia. Meaning um.... "increased eosinophil count". Medical jargon eh? Fribbler (talk) 10:42, 30 January 2009 (UTC)

More to the point, eosinophilia can mean either "a larger proportion of eosinophils among the white blood cells" (which is all that 7% tells you), or "a higher than normal absolute number of eosinophils in the body" which is what an absolute eosinophil count would tell you. In either case, there's virtually no significance to a single reading that's marginally high (like 7%), unless there's a clinical setting that would make it so. So as in all these cases, the doctor who ordered the test is the one who has to tell you if this (mildly elevated) value means [1] nothing or [2] something. Persistent elevated values, or isolated significantly elevated values, would make one think of allergies and parasites first, and other things in the differential in the eosinophilia article second. - Nunh-huh 11:35, 30 January 2009 (UTC)

What makes heating a house using geothermal inefficient in the US

When I was in Germany I encountered many people who had installed geothermal heating in their houses. (Geothermal heat pump) When geothermal is mentioned in the media in the US there is usually a comment that it's inefficient here. Comparing the climate information for Germany and Georgia temperature can't be the factor that makes the difference.[13] Climate of Georgia (U.S. state) Since I find it hard to believe that the Germans would install inefficient heating systems, does anyone know what makes things that different here? 76.97.245.5 (talk) 05:46, 30 January 2009 (UTC)

I'm surprised that you'd say "inefficient". The reasons I've heard (and they aren't unique to the USA) are that geothermal is expensive to set up - and that it's not necessarily "renewable". The way it works is that you pump cold water down into some hot rocks and then pump it back out again - and when it comes back, it's hot water that you can use to heat your house and make hot water via heat exchangers. There are two problems with that:

1. It's great when your primary energy cost is heating - but it would be useless in large parts of the USA where you need air conditioning to cool the house over a large fraction of the year. To convert the hot water into electricity and then use the electricity to run your A/C is a much bigger problem.
2. The capital cost of all of that drilling and pumping is not a one-time problem. The rocks at the depth you can afford to drill down to aren't really all that hot - and after years of use, you can actually drop their temperature significantly - causing the geothermal plant to run less and less efficiently. So the geology of the area matters.

What is really needed is a larger scale plant - where you drill much deeper so that instead of getting water back out, you get steam - then you can run a turbine and easily generate electricity from that.

However, I'm a little surprised that there isn't more emphasis on that approach here. But honestly - I think a combination of large wind farms and nuclear power will ultimately be the US solution...possibly augmented by rooftop solar panels.

For homes - our best bang-for-buck would be to sink some serious money into better insulation. My house (which has four times better insulation of a typical American home consumes about a third of the amount of electricity that my neighbours use. This added about 5% to the construction cost of the house - and pays for itself in about 5 years. Why aren't all houses built like that? Well, it's because of 'sticker shock'. People buy what's cheapest without looking at the future running costs. What is needed is government grants that pay that extra 5% directly to the home builder - and recoup the money from the electricity companies who are required to charge (say) twice as much for domestic electricity to houses that were built under this scheme - giving half of that back to the government as a tax. That way, everyone wins. The consumer gets slightly reduced electricity bills - and without having to pay a cent more for their houses. The electricity companies get to build less power plants yet still make more profit in the long run once they don't have to pay the "new house" tax on their electricity. The government gets reduced dependence on non-renewable fuels and could (with care) make a profit on the grant scheme. Everyone wins through greenhouse gas emissions reductions. You could also give people the option to pay the extra 5% on their house cost - and NOT have doubled electricity prices from then on. This is easy to do - all it takes is someone in government to sign the right bit of paper to make it happen.

That's a much better bang-for-buck than any other form of new power generation system - and it works in hot climates as well as cold ones.

SteveBaker (talk) 12:03, 30 January 2009 (UTC)

Also, geothermal energy is far more efficient when there are "hot rocks" near the surface. In the US, such places tend to be public land, like Yellowstone National Park, and thus unavailable for this kind of development. I'm not aware of Germany having much of this geology, but Iceland does, so geothermal is far more practical there than in the US.

Finally, when comparing whether geothermal energy makes sense in a nation, we should consider the cost of alternatives. The US has vast, cheap supplies of natural gas, which is used for heating in much of the US. If Germany lacks this, and must instead import natural gas from unreliable sources like Russia, then investigating home-grown alternatives like geothermal energy makes more sense. StuRat (talk) 13:06, 30 January 2009 (UTC)

Thanks Steve and Stu. The "only works with hot rocks and large plants" arguments was what didn't work for me in comparison since in Northern Germany there aren't hot rocks where I saw it done (it's mostly leftover ice-age rubble and marshland) and they do it in small units, too. So the difference is that they don't do AC and don't have local fuel resources (if you don't count canola oil which is used in some diesel engines there.) That makes more sense. 76.97.245.5 (talk) 15:28, 30 January 2009 (UTC)

I believe Steve and Stu are confusing Geothermal heat pumps with Geothermal power. It is the latter where you pump water over very hot rocks and use the steam for heating and for electrical generation. Most geothermal heat pumps don't need hot rocks, and in fact work best when the ground source is a moderate temperature, usually slightly below room temperature (50-75 F, 10-25 C). Unlike geothermal energy, you're not trying to extract energy from the ground, you're simply using it as a stable, very large capacity heat bath, to which you attach a heat pump (a conventional air conditioner is a heat pump). As the efficiency of heat pumps is related to the temperature differential between the two sides, having the "outside" being very close to the inside temperature greatly increases efficiency. So instead of running an air conditioner where you dump excess heat from your 72 F (22 C) into the 100 F (38 C) outside, you dump it into the 60 F (15 C) ground, which is much more efficient, electrically speaking. Also in winter, you can "reverse" the heat pump, pulling heat from the ground and dumping it into your house, which takes much less electricity than creating the heat directly from the electricity. As to why they aren't common in the US, I'm not sure. One reason may be that most people, even otherwise well read and knowledgeable ones, haven't heard of them. Part of that may be due to installation costs. There's a big up-front cost to put the radiator in the ground and to buy the size/quality heat pump needed. Although it'll probably save you money in the long term, when building the house it's much cheaper to put in a simple furnace/air conditioner combo. Adding the system after the house is build means tearing up the lawn. Another big reason may be that natural gas, propane, fuel oil, and other petroleum based products are massively less expensive than electricity in the US. I think it's cheaper to burn gas/oil for heat in winter versus pay for the electricity to run the heat pump, even though the heat pump is more energy efficient. Without the winter savings, the payback period gets much longer, especially in the north where air conditioning is only lightly used. Increases to petroleum prices in the future, however, may see more systems installed in the US. -- 76.204.94.153 (talk) 18:33, 31 January 2009 (UTC)

Geothermal heat pumps use an electric compressor to increase the temperature of a fluid. This fluid is used to collect heat from outside the buiilding at a low temperature and transfer it to an internal space at a higher temperature. Rather than measuring 'efficiency' of these systems, it is better to use the measure 'coefficient of performance'. This is a measure of how much heat is transfered to the building as a proportion of the electricity used by the system to transfer this heat. For many systems, this coefficient is around 3 - ie 3 times as much energy is transfered into the building as is consumed by the compressor. However - the electricity that is being used has probably come from burning coal or gas (depending on where you live). These power plants generally have an efficiency of around 30% - ie 30% of the energy in thc coal or gas ends up in your home as electricty. From an environmental viewpoint then, you are using the same amount of raw energy if you intall a gas heater in your home as a ground source heat pump (assuming coefficient of performance of 3 and power system efficiency of 30%). Before purchasing systems, it is worth carrying out a study to calculate the net energy gain and how much this will cost you. Im afraid I dont know what other reasons would alter the 'efficiency' of such a system between nations. TomStroud 16:50, 5 February 2009

Just to update my figures - modern gas power stations can be about 50% efficient and good ground source/air source heat pumps can have a cop of 4 - therefore providing an overall system efficincy of 200%!! TomStroud 22:08, 9 April 2009 (UTC)

UFOs

So if I understand correctly, accroding to currently established thinking in the scientific world, it is mathematically highly probable that extraterrestrial life exists, but it is too unlikely that such an alien life has the means or intelligence or technology to conduct intersteller travel - so UFOs being real is ruled out. That is, alien civilisations probably exist, but we can never contact them. Is that correct? ReluctantPhilosopher (talk) 09:35, 30 January 2009 (UTC)

See Fermi paradox and Drake equation. It's all a giant guess where those little green buggers are. Someguy1221 (talk) 09:48, 30 January 2009 (UTC)

Wow, I never knew there was a named paradox for that. Thank you, Someguy1221 :-) ReluctantPhilosopher (talk) 10:21, 30 January 2009 (UTC)

We know that the speed of light is the cosmic speed limit. We know that the closer you get to that speed - you need exponentially more energy to accelerate and decelerate. This makes interstellar travel exceedingly difficult and costly no matter what technology you use. Also, aliens that do have the capability will have to dedicate a large fraction of their resources to each craft they launch - so they are unlikely to simply go out visiting stars randomly looking for life. No - they are going to do what we do. Search the skies for radio signals - and look closely at exo-planets with spectrographic signatures that indicate life. Then they'll probably beam a high power, tightly focussed beam of radio waves containing the usual stuff like sequences of prime numbers and digital pictures with prime-number dimensions.

Consider that we've only been putting out radio broadcasts at any reasonable power for about 50 years. Even with close-to-the-speed-of-light spacecraft, an alien civilisation would have to be within 25 light years to even know we're here and then come visiting. Worse still - it is interesting to note that with the most powerful radio telescopes we have - we would be unable to detect the most powerful radio transmitter we have at the distance of the nearest star (4 light years). So the aliens would not only have to be close enough to have heard us and have had time to get here - they ALSO need to have some pretty amazing radio-telescopes. So the fundamental limits of the laws of physics (the speed of light, relativity, the inverse square law of electromagnetic radiation) make it unlikely in the extreme that an alien civilisation could possibly show up on our doorstep anytime in our lifetimes. Unless these aliens are VERY close to us already they have literally NO WAY to even know we're here. There really aren't many stars that close to us - so unless intelligent alien life is VASTLY more common than even the most optimistic Drake-equation predictions, it isn't coming visiting anytime soon.

IMHO, unless our alien species has extraordinary long lifespans and/or a biochemistry that allows them to shut down cognitive facilities and preserve their bodies without consuming resources over a long trip (eg cryogenics) - we aren't ever going to see them in person. What we MIGHT get would be their computers...some kind of robotic emmisary. We know that if we had to send something to (say) Alpha Centauri (4 light years away), we'd probably send a robot because it could take a few hundred years to get there - and four years to report back - but since it could be shut down for most of the ride, we could probably do it.

But think about that for a moment. If that's all they are going to send, they might as well just transmit the plans to build that computer - plus all of it's software and data over a radio link and have us build it for them - rather than spending all of that effort to physically transport the computer to us. So IMHO, the SETI effort has vastly more chance of success than the UFO spotters do!

The only time I could imagine an alien species coming to visit us in person would be in some vast colony ship. If aliens see the imminent demise of their star - then they might consider packing everyone into some vast 'generational' ship - maybe a hollowed out asteroid or comet - maybe spin-stabilised for gravity with huge nuclear/fusion power plants providing energy with a complete 'biosphere' on board to provide their people some kind of a bearable lifestyle. This craft might take thousands of years and hundreds of generations to slowly plod from one star system to the next. If something like that shows up - we're in real trouble because they'll have started out on their journey thousands of years ago - having looked carefully at our planet by astronomical means. But thousands of years ago was back before we dominated the place. And seen from 50 light years away, there would have been no indication of a pre-industrial society living here. So they'd have seen a highly suitable environment for their people and set off. Then, (presumably to their extreme horror) as they start to approach their new home, they see a budding intelligent civilisation start to appear on it! As time goes by they see us develop nuclear weapons and space craft - and then (worse still) we start screwing with the atmosphere and heating the place up! They have millennia to plan what to do about that - but when they get here, they won't be happy - and that'll be a big surprise to us! Think "Independence Day (movie)" - but without the possibility to use a computer virus to take them down (which was one of the worst "and then the aliens all die" endings since the cop-out at the end of War of the Worlds!).

SteveBaker (talk) 11:37, 30 January 2009 (UTC)

"Space is big. You just won't believe how vastly, hugely, mind- bogglingly big it is. I mean, you may think it's a long way down the road to the chemist's, but that's just peanuts to space." Douglas Adams Gandalf61 (talk) 12:40, 30 January 2009 (UTC)

I think someone else pointed this out before. If an alien civilization did send a probe to our solar system (assuming their probes are similar to ours) it would be so small that it could pass through our system without ever being noticed. A Quest For Knowledge (talk) 14:53, 30 January 2009 (UTC)

There's also the problem that if life DOES exist, that it somehow must exist at only a slightly (say a thousand years or two) more advanced state than we are in. It is entirely statisticly more likely that alien life does exist, but is millions of years, evolutionarily speaking, behind us, or millions of years ahead of us. Either way, there is a good chance that the evidence of that life has either not reached us yet, or that civilization is long past, and the evidence of it has already blown past us. The idea that there is an alien civilization at all in history is pretty good; the idea that there is an alien civilization close enough to us to detect and within that relatively narrow window of emiting the sorts of radiation that are detectable is mindbogglingly small. Also, consider that we generally confine out understanding of alien civilization to this Galaxy. Make a few tweaks to the Drake equation, and you may well find that you can come up with an average of one technological civilization per galaxy. In that case, we may not be alone, but there may very well be no conceivable way for us to ever contact or have knowledge of these other civilizations. --Jayron32.talk.contribs 16:38, 30 January 2009 (UTC)

I little aside here: can people PLEASE stop using "UFO" as a synonym for "Spacecraft from a sentient alien race". I can't tell you how much that pisses me off, even these renowned so-called "Ufologists" do it. There is no doubt in the entire world that UFOs exist. What is in doubt is whether some of these UFOs were alien spaceships.</rant>-RunningOnBrains 17:26, 30 January 2009 (UTC)

It has definitely not been ruled out that UFOs that are alien spaceships exist. Tens of thousands of sightings have been reported worldwide, from an unusual light in the sky, to multiple witnesses reporting a spaceship over a mile wide, to reported abductions by aliens. Most of these reports can be explained by more rational possibilities, and most scientists reject the notion that alien spaceships have visited Earth, citing lack of evidence. The always remains, however, a handful of sightings with very good credibility and which still cannot be explained. I personally don't believe the Fermi paradox is so hard to solve, and this is just one reason why. There is also a list of UFO sightings. ~AH1^(TCU) 19:23, 30 January 2009 (UTC)

I'm not sure if that was directed at me, but I certainly wasn't implying that all UFOs have logical explanations. You can't prove a negative, so obviously its possible that some unsolved UFO incidents are in fact extraterrestrial craft of some kind. I'm just saying saying that sometimes people get caught up in the hype of a supposedly-paranormal event and don't look for obvious solutions. I cite Occam's razor: is it more likely that that mysterious craft in the sky is an alien spacecraft, or some secret government project? Since we know that governments perform classified experiments with aircraft, and we don't know if extraterrestrial life exists, it makes sense to believe the latter unless there is serious evidence to the contrary. Similarly, is it more likely that the person telling the story about the spacecraft that landed in his yard had a hallucination, is crazy, or is lying? We know those kind of people exist in the world, but we don't know if aliens exist. It's certainly not a foolproof argument, but it helps me sleep better at night.-RunningOnBrains 19:42, 30 January 2009 (UTC)

"The always remains, however, a handful of sightings with very good credibility and which still cannot be explained. I personally don't believe the Fermi paradox is so hard to solve, and this is just one reason why" - so there are credible non-explained UFO sightings? That's what I wanted to know. Thanks ReluctantPhilosopher (talk) 17:35, 3 February 2009 (UTC)

Mitochondrial DNA from sperm to zygote

I recently saw a cautious quotation in a book saying that in most organisms the mitochondrial DNA is derived only from the egg. So what exceptions are known ? Shyamal (talk) 11:39, 30 January 2009 (UTC)

Never mind, found it here http://mbe.oxfordjournals.org/cgi/content/full/18/7/1168 Shyamal (talk) 11:44, 30 January 2009 (UTC)

Scientific question

number of stars which appear from earth incerase? —Preceding unsigned comment added by Sovit mundhra (talk • contribs) 13:15, 30 January 2009 (UTC)

You need to clarify your question, especially the use of the word "increase". Are you asking if the number of stars visible from Earth is increasing ? If so, I'd say not with the naked eye, no. It's possible that better telescopes could increase the number of stars we can see, but such new telescopes tend to be located in space, like the Hubble Space Telescope, to avoid interference from Earth's light sources and atmosphere. StuRat (talk) 14:06, 30 January 2009 (UTC)

If you're asking whether the number of stars visible from any one location on Earth to the naked eye is usually increasing, then no. Most locations are suffering from more and more light pollution. ~AH1^(TCU) 19:13, 30 January 2009 (UTC)

To add insult to injury the universe is expanding, looks like a solid no on all fronts.Bastard Soap (talk) 08:09, 5 February 2009 (UTC)

Firing a pistol sideways

Is there any real advantage in turning a pistol 90 degrees to the right when shooting? Gangsta style, in other words. If not, why do people do that? --84.66.59.206 (talk) 14:08, 30 January 2009 (UTC)

We seem to have two articles on pistol shooting technique: "Modern Technique of the Pistol" and "Point shooting". I skimmed them both, and neither seems to mention specifically the style you're asking about. "Point shooting" does, however, suggest there is value in this style, especially at close quarters, speaking of methods that "do not rely on the sights, and ... strive to increase the shooter's ability to hit targets at short range under the less than ideal conditions expected in self defense and combat situations." The stereotypical Hollywood "gangsta" style of firing—with one hand, held above the level of the head, and with the gun held sideways—would lend itself to certain combat situations, such as firing blind over a wall or in through a high window. Also, the one-handed style leaves the off hand free for other uses, such as balance, reloading prep, or parry. The high hold makes it more difficult for your opponent to seize the gun or disarm you at close quarters, and the downward angle keeps the muzzle on your foe if he ducks, an instinctive reaction. Offhand pistol shooting can be made fairly accurate through practice, and whatever style one uses, practice will probably bring sufficient accuracy for short-range work. Also, being accustomed to firing from awkward positions and around obstacles, and combining hand-to-hand fighting with pistol must surely increase a combatant's chances of survival. So, "gangsta" style would be a valuable addition to a pistol fighter's repertoire, I think. On the other hand, if you don't practice and are more than ten feet away, it would be pure luck if you hit anything that way. You might as well shut your eyes, too. The prescribed methods were arrived at by discovering what works; the guy who lived through the gunfight wrote the book.

As for "why", I can't even say that the style is ever used in the real world. I don't live in an area where people do any such thing ever, and I don't go where they are likely to. But, if it is a common practice, my guess would be it's done for intimidation—to express the earnestness of one's intention to shoot—and to keep a downward trajectory with an eye to minimizing collateral damage in an urban setting. --Milkbreath (talk) 14:56, 30 January 2009 (UTC)

Anyone who was really serious about hitting someone, gangster or not, would fire in a way to maximize that—which doesn't look as "cool" so nobody does that in music videos. --98.217.14.211 (talk) 15:08, 30 January 2009 (UTC)

Mightn't be relevant, but standing side-on presents less of a shooter's body to his opponent - so perhaps it's defensive. Bazza (talk) 16:03, 30 January 2009 (UTC)

NY Times: It's to look cool, but makes it harder to control the gun. WikiAnswers suggests it may be used in movies to show more of an actor's face, to look unusual, or as the result of a misunderstanding about some legitimate shooting tactics. --Maltelauridsbrigge (talk) 16:11, 30 January 2009 (UTC)

Yeah, pretty much all gun use in Hollywood shows a lack of basic understanding. Also, the downward angle to reduce collateral damage sounds reasonable, except that I doubt people having gunfights in cities (and not aiming) care much about that. Friday (talk) 16:23, 30 January 2009 (UTC)

As I understand it (IANAG), when 'someone other than the intended target' gets shot by mistake, the attitude is very much "well, if (s)he didn't want to risk getting shot, (s)he shouldn't have been hanging around those assholes" or "some folks are born lucky, some ain't". Back on topic though - as the NYT link suggests, I think that it's often a case of the gangstas (many of whom are little more than kids) seeing the sideways-shooting thing in gangsta movies (or the dual wield thing) and simply believing that it's an effective way. Thinking about it though, if you're firing a pistol from a car window, there may be a (perceived?) benefit in being able to rest the flat of the wrist against the window frame in order to steady your shot. --Kurt Shaped Box (talk) 17:30, 30 January 2009 (UTC)

Whatever rational they may use in their heads to try and justify collateral damage, I'm somewhat doubtful that they really don't care at all about collateral damage. For staters, they would know the cops are far more likely to be concerned it they kill an innocent bystander then another 'gangsta'. Also as Sean suggested below it's likely many don't want to kill anyone and I suspect even less an innocent. I think most people, even criminals do still have some moral compass even if it warped and may not stop them doing incredibly bad stuff. As with most matter, oversimpfying the people involved is a mistake. Of course this doesn't mean avoid collateral damage is a consideration in sideways shooting actually I agree there's a good chance it isn't. Nil Einne (talk) 17:19, 1 February 2009 (UTC)

Perhaps its intent is to *reduce* accuracy. Why would a gangsta want to do that, you ask? I can think of two reasons: 1) as a form of stotting, which is something gazelle will sometimes do to slow themselves down when being chased by a predator, as a way of saying "I'm such a badass I'll even give you a better shot at me", and 2) because even gangstas would probably prefer not to kill anyone; On Killing documented that many soldiers would deliberately miss their targets, and they -- in contrast to our gangsta -- were in a situation where they would be rewarded rather than punished for a successful shot. --Sean 18:16, 30 January 2009 (UTC)

According to one cop, it's done because it looks cool. DMacks (talk) 20:10, 30 January 2009 (UTC)

Engineering Book for Children

Please advise if there is a book which explains the basic priniciples of engineering that is geared toward children between the ages of 5 and 8 years old. Any type of engineering is fine. Thanks! --Emyn ned (talk) 14:09, 30 January 2009 (UTC)

The Way Things Work by David Macaulay. Gandalf61 (talk) 14:37, 30 January 2009 (UTC)

Actually, just about anything by Macaulay would work. He's got LOTS of great books for kids on all sorts of architecture and engineering, including Pyramid and Castle and Cathedral and most of these had filmed versions as well, IIRC. --Jayron32.talk.contribs 16:31, 30 January 2009 (UTC)

Quantam Mechanics, de Broglie wavelength, baseball

We know that the debroglie wavelength, which applies to all matter is given by h/p = h=mv. Suppose there was a baseball or pingpong ball traveling at a slow enough speed, or with a small enough mass such that the de broglie wavelength was visible (a) or the debroglie wavelength was large enough to measure, (b) on the magnitude of meters. What physical phenomenon would result? —Preceding unsigned comment added by 128.8.177.117 (talk) 14:10, 30 January 2009 (UTC)

What you're basically asking is "how would a very macroscopic object look if we regarded it as a quantum-sized object" which isn't terribly sensible. But let's just say, well, if a baseball could exhibit quantum wave effects, then you could do things like diffract it. It would, in certain ways, act like a wave. How would that "look"? Heck if I know. That's the problem in trying to apply quantum effects to macroscopic objects—it just doesn't make sense to our clunky macroscopic brains. --98.217.14.211 (talk) 14:26, 30 January 2009 (UTC)

Hm, my physics teacher tried to explain this to us at school. I really should have a deeper understanding of these matters now (and also this was back in 1988), but I don't and as far as I remember it goes like this: If you keep hitting ping pong balls through a slit (or two slits, whatever) at a wall (slit large enough for it to pass through, obviously), most of them would go through unimpeded (and hit the opposite wall directly behind the slit(s)). A few however would change direction (it'll probably look as though they bounced off the edge of the slit), *but* the funny thing is if you mark at the wall where the balls hit, over time you'd get a diffraction pattern. Wave of the ping-pong ball interfering with itself. 195.128.250.163 (talk) 22:34, 2 February 2009 (UTC)

My UFO Story or What did I see?

When I was a little kid, maybe about 5 - 7 years old, I saw what I thought to be a UFO an alien space craft. It looked like a half-moon, with red lights on each tip. That is to say that it was sort of a white-ish half circle with red lights at the tips. It flew across our backyard. I wasn't the type of kid to simply make up stuff or not be able to tell the difference between imagination and reality, so I think I really did see something. This probably would have been the mid to late 1970s. I lived in a major metropolitan area (Chicago) so if it really was an alien space craft, I would think that it would have been reported by lots of people, and I don't recall anyone else reporting this. Of course, I'm not sure I was old enough to be able to read a newspaper, so maybe it was reported, but I don't recall any of the neighbors talking about it. Anyway, I'm not one of those UFO nuts so I assume that there's a rationale explanation that doesn't involve aliens from outer space. But I don't believe it was my imagination either. Is there any type of aircraft that matches this description or comes in any way close to it? I lived a few miles from Midway Airport so there would have been a high volume of air traffic in my neighborhood. A Quest For Knowledge (talk) 14:46, 30 January 2009 (UTC)

You note that the UFO had red lights on each tip. Typically aircraft have a red light on one of the wing tips (presumably this is port side) and a green light on the other side (I presume this is the starboard side) as in ships. They also have a red beacon on the top and bottom of the fuselage. See: http://www.aerospaceweb.org/question/electronics/q0263.shtml You don;t mention whether it was day or night but since you could tell the colour of the fuselage was white then it must have been daytime or close to night. I can't tell you much about aircraft types but I would suggest if a plane was banking heavily, to line up with the runway of Midway for example, and orientated wierdly then just a typical jumbo could look a bit like a UFO to a 5 - 7 year old. Jdrewitt (talk) 15:28, 30 January 2009 (UTC)

I'm pretty sure it was night, or at least evening. A Quest For Knowledge (talk) 15:33, 30 January 2009 (UTC)

One point: You said "I saw what I thought to be a UFO". Since UFO stands for "Unidentified Flying Object", that's precisely what you saw. Unfortunately, many people use UFO to mean "alien spacecraft", which is a horrid misuse of the term. StuRat (talk) 15:56, 30 January 2009 (UTC)

How large did it appear in the sky? Did it appear larger or smaller than a half-moon in the sky? Did you notice any detail other than the red lights? Did it move towards the curved part of the half-circle, or the straight-edge part? Did it appear more yellowish or more bluish? How fast did it move? Did it move in a straight line or a more erratic pattern? Did the brightness of the object change at all during its flight? How long did you see it for? These questions may be useful in assisting the possible identification of the object. ~AH1^(TCU) 19:27, 30 January 2009 (UTC)

It sounds from the description like an airliner with the top and bottom beacons and some section of the fuselage between being lit up for some reason....perhaps some of the light from a landing light glinting off of the fuselage. The circular cross-section of the fuselage would certainly produce a semi-circular or 'moon-shaped' white area - and some part of the wing could cut it off to make a semi-circle...and it's no stretch to imagine the red beacons above and below. So there are without doubt ways to explain this UFO without resorting to little-green men. Even if that's not a perfect explanation - even if it requires a really extended set of coincidences (eg two planes flying parallel to each other to make two red lights with a third aircraft closer to you providing the white shape...or something) then it's still vastly more likely than that it was a flying saucer. This is the thing that UFO nuts don't appreciate. Even if there is only a one in a million probability of some particular chance formation of lights happening on any given observation means that perhaps 300 people will see such a phenomenon every single night...in the USA alone! In fact, when you stop to think about it - it's quite amazing that you don't hear more reports than we actually do! 20:15, 30 January 2009 (UTC)

If there was an airport nearby you might have seen a mirage. Good ones are so rare that one just doesn't expect it could have been that. I once spotted a perfect one of a bicycle on a neighbor's roof. All I could think was "What the...". Thank goodness aliens aren't reported to ride bicycles. (Except maybe in baskets.) 76.97.245.5 (talk) 20:57, 30 January 2009 (UTC)

AstroHurricane001 - I think it looked bigger than the moon. Probably at least twice as big. It was white-ish. I don't think there was a yellow or blue tint. It didn't streak across the sky like a lightning bolt and nor did it hover. I guess I would say it appeared to fly at a speed consistant with an airplane. It flew in a straight line, no crazy 90 degree turns that defy the laws of physics or anything like that. I passed overhead in maybe 2-3 seconds. A Quest For Knowledge (talk) 21:29, 30 January 2009 (UTC)

I and a friend of mine, an ex–Navy Seal, sat in a pickup truck and watched Venus for half an hour around sunset one time because it looked for all the world as if it was something in our atmosphere. Of course, we thought it was Venus, but neither of us had been keeping abreast of our planet positions, so we tested our theory by observation. I'm saying that two unsuperstitious, rather intelligent men were momentarily fooled by appearances. I have no doubt whatsoever that a similar phenomenon is responsible for 100% of the unexplained sightings of UFOs. As a kid I watched The Day the Earth Stood Still a hundred times, so I'd like nothing better than to take our new friends to our leader, but it ain't gonna happen. --Milkbreath (talk) 16:15, 31 January 2009 (UTC)

Skywarn Spotter Training

Does someone need to register with SKYWARN to take part in one of their classes. I can't seem to find the answer.Nick (talk) 19:01, 30 January 2009 (UTC)nicholassayshi

NEVER MIND!!! —Preceding unsigned comment added by Nicholassayshi (talk • contribs) 19:11, 30 January 2009 (UTC)

Atlantic hurricane tracks

Hi. In the image of the Atlantic hurricane tracks from 1851 to 2005 (see right), could anyone identify the following hurricanes shown in the map:

• The storm which tracked over southern Lake Simcoe as an extratropical storm at TS strength (wait, is it the Galveston hurricane of 1900?);
• The storm that made it across Mexico as a TD and tracked into the Gulf of California;
• The hurricane that tracked through the center of the Cape Verdes as a cat. 1, then quickly strengthened into a cat. 2;
• The hurricane that made it through the channel between Ireland and Iceland as a fully tropical cat. 2, then weakened to a cat. 1 as it passed north of Scotland;
• The hurricane that crossed northwestern Ireland as a fully tropical cat. 1;
• The extratropical storm which tracked across Ireland, Wales, and England at cat. 1 strength; and
• The extratropical storm that hit Lisbon, Portugal while weakening to TD strength.

Anyone able to identify these? Thanks. ~AH1^(TCU) 19:02, 30 January 2009 (UTC)

One quick answer:

• The hurricane that made it through the channel between Ireland and Iceland as a fully tropical cat. 2, then weakened to a cat. 1 as it passed north of Scotland;: Hurricane Faith (1966)

You could try contacting one of the regular members of Wikipedia:WikiProject Tropical cyclones. Someone there might be best able to answer your question. --Jayron32.talk.contribs 20:37, 30 January 2009 (UTC)

The storm that crossed Mexico and entered the Gulf of California is Hurricane Debby (1988). –Juliancolton ^{Tropical Cyclone} 20:40, 30 January 2009 (UTC)

Robert Burns and gold conductor

Robert Burns wrote a poem on wedding rings

She asked why wedding rings are made of gold;
I ventured this to instruct her;
Why, madam, love and lightning are the same,
On earth they glance, from Heaven they came.
Love is the soul's electric flame,
And gold its best conductor."

Where would he have got the idea that gold was the best conductor? I know silver and copper are better but Volta only invented the electric cell in 1800 and Burns died in 1796. Dmcq (talk) 19:17, 30 January 2009 (UTC)

I believe he meant that gold was love's best conductor, not gold. flaminglawyer 19:35, 30 January 2009 (UTC)

See history of electromagnetism. People knew about electricity (long) before batteries were invented. --Sean 20:00, 30 January 2009 (UTC)

Ben Franklin had experimented with electricity during Burn's lifetime, for example. bibliomaniac15 21:25, 30 January 2009 (UTC)

Thanks very much. I hadn't realized about them testing conduction using electrostatic machines. Following up that Franklin I came upon something by Joseph Priestly where he thought gold was a better conductor than silver. Burns kept up with things like that so that's probably where he go it from. See The Conducting Power of Gold which describes Priestly's experiments on the conductance of wires. I'm really quite surprised that his method gave the wrong result. He connected wires together of the same diameter and the one that didn't melt was the one he said was the better conductor. I would have thought the gold wire would have melted before the silver one as it has a higher resistance and has only a slightly higher melting point. So seemingly Burns was right according to the best science of the day. Dmcq (talk) 23:42, 30 January 2009 (UTC)

Resolved

Dmcq (talk) 00:45, 31 January 2009 (UTC)

Islam...

we all hear that Islam is the most expanding religion now ... why is that ... and whats the proof that its the right religion ... i heard they have scientific proofs that their book(Quraan) did talked about recentlly dicovered scientific facts before more than 1000 years ... thank you ...? —Preceding unsigned comment added by 212.38.147.41 (talk) 20:59, 30 January 2009 (UTC)

Extraordinary claims require extraordinary evidence. It's no good basing your whole philosophy of life on what's most popular, or what you heard; look it up! I doubt there's anything there, but who knows, maybe while riding on his magical horse Muhammad spied a coelacanth. --Sean 23:29, 30 January 2009 (UTC)

I would be interested in some evidence of these prophecies. I have not heard of them, do you have some reference that can be followed up? Dmcq (talk) 23:53, 30 January 2009 (UTC)

will i heared about how there shuttels couldnt leave the earth atmosphere but through acertain places in the atmosphere and such things ... i will look for it , but this will take time . —Preceding unsigned comment added by 94.249.99.222 (talk) 05:36, 31 January 2009 (UTC)

The number of Muslims is growing because, like poor people worldwide, they have a high birthrate.

Claims for amazing scientific insights in the Qur'an (like the old assertion that baseball is a Russian invention, and the ludicrous claims for the Kim dynasty in North Korea) derive from a deep societal inferiority complex. If the Qur'an, which among other things posits a flat Earth, were really a repository of advanced scientific knowledge, the Muslim world would not have to wait for Western scientific advances, and then claim that they were predicted 1400 years ago. Orthodox Muslims would be at the forefront of science and picking up Nobel Prizes in bunches. That they are not highlights the emptiness of such claims.

B00P (talk) 13:32, 31 January 2009 (UTC)

However, Islamic scholars were at one time far ahead of their counterparts in the West. Arabic Islamic scholars gave us algebra, algorithm, and alkali. Arabic Islamic mathematicians also gave us the cipher for zero. The BBC has a programme which is being shown at the moment called "Science and Islam", and the OP may wish to investigate the re-runs on the iPlayer. This link gives you Jim Al-Khalili's article. [14] —Preceding unsigned comment added by TammyMoet (talk • contribs) 15:12, 31 January 2009 (UTC)

There is no doubt that at one time, arabic mathematicians and other scientists were streets ahead of the the europeans. Quite how they lost that advantage is hard to say - but I've gotta guess that adherence to overly strict religion has a lot to do with it. When clear, open-minded thinking is discouraged in favor of mindless obeyance of some thousand-year-old tradition - science is guaranteed not to flourish. One only has to see the rise of christian fundamentalism in America doing precisely that. The pressure to tell our kids that evolution isn't one of the most solid scientific theories that we have - and the efforts to suppress stem cell research - signs of denial of the Big Bang - denial of global warming - these are classic examples of the same nonsense happening here. Newton was the closest thing modern science had to a priest at the turn of the last century. When Einstein said he was wrong - people were sceptical - when it was PROVEN that Newton was wrong (well - in realms beyond where he could test at least), the scientific world changed. Well, now we know conclusively that the garden of eden didn't happen - it's time to drop that dusty old book and go with something a little more real. 72.183.123.248 (talk) 23:55, 31 January 2009 (UTC)

...But what does the OP mean by "right religion"? The one referring to the real God? I hope he's not such a naive thinking, come on. A religion is an anthropologic and cultural phenomenon, and as such you shall explain its degree of success. And, of course, there is the individual contribution of some genial persons. Take for instance Paul of Tarsus, the inventor of Christianism: a true genial mind thinking big, like was John D. Rockefeller for capitalism. Had it been for the first Christians, they would have disappeared in few decades, like dozens of other messianic religions continuously appearing in that area. Paul was initially planning to make a career, as a Jew, fighting these Christians, but it was really not a worth job; then had the great idea (the anecdote says he drop from the horse at the illumination): "but what the holy fuck am I doing wasting my time in fighting these guys": he entered the bunch and in few weeks became their chief. He called himself "Apostolus", to make it clear. Then, he made special offers to everybody for joining the Christians: you don't need to be free man; you don't need to be circumcise; you don't need to be a man either, and many other facilities. He managed to become Roman citizen and to have the support of Rome. Nothing similar had been seen before. Recall that the oldest and more important religion of the area, Judaism, was extremely strict and very proud about its tradition. This way in few times he took over all small religions around and became the first Religious Group of the area, just like Rockfeller's Standard Oil at Cleveland when he swallowed every single refiner around. He too was thinking big, and started proselitism travelling and sending letters all around the Mediterranean sea, and finally got to Rome. To have an idea of his accuracy in all detalis, think of how he just planned the clothing. "I wanna last at least a couple of millenniums or so: who is here around that was able to do so? Egyptians, of course". Consequently, the clothings for the new religion were inspired to the Faraons fashion (look at the Pope, how dressed he goes around). Just to communicate: "We will stay here around forever". Of course you are free to think that there is the God's hand in the expansion of Christianism, or of Islam, or that Rockfeller was a philanthropist, &c... pma (talk) 00:22, 1 February 2009 (UTC)

A God that monitors which religion s growing fastest or is biggest or some combination of the two. A God that jumps on the latest bandwagon. That's a good one. Sounds like a politician, I am your leader, tell me what you want. Dmcq (talk) 12:07, 1 February 2009 (UTC)

will.. assuming there is agod ... and god want to give you a life way ... a path to walk on , some kind of ascale so you can know right from wrong ... now , how did you think that god should make you belive that he do exist , what kind of proof would you accept , will its easier to think that mother nature did this ... our creation not but acoincidence ... but if your ascientist then god will convince you by science

fact 1 ... in quraan ... sura(The believers) from(12-14) ([23:12] We created the human being from a certain kind of mud. [23:13] Subsequently, we reproduced him from a tiny drop, that is placed into a well protected repository.

[23:14] Then we developed the drop into a hanging (embryo), then developed the hanging (embryo) into a bite-size (fetus), then created the bite-size (fetus) into bones, then covered the bones with flesh. We thus produce a new creature. Most blessed is GOD, the best Creator.) this fact wasnt known before 1400 years ago ... i dont find any source said that this fact was known before the 1900 . so the question is did muhammed knew that ... or this is some kind of evidance from god .

fact 2 ... in quraan ... sura(women) (56) ([4:56] Surely, those who disbelieve in our revelations, we will condemn them to the hellfire. Whenever their skins are burnt, we will give them new skins. Thus, they will suffer continuously. GOD is Almighty, Most Wise)

will ... this one talk about that humans couldnt feel but by there skin ... so if your skin gets burned you will feel nothing and this is aproven fact in the modern science ...

so did you still think that muhammed knew that before 1400 years ago ... if not so who did ...??? —Preceding unsigned comment added by 94.249.85.66 (talk) 17:51, 2 February 2009 (UTC)

It is obvious that you have not checked any of what you say. Where people pick up the slightest thing in favour of their point of view are are blinkered to conflicting evidence is called confirmation bias. The reference desk will I'm sure be happy to help you check up on each particular item in your list. Dmcq (talk) 14:51, 3 February 2009 (UTC)

Hey 94, have you ever read the Iliad? To make only one example, the author perfectly knows about the flies laying eggs in the dead bodies, and the generated larvae eating the corpses (Iliad T ,25-28); read it, I'm not talking of allegories to be interpreted, but of precise statements even more clear that the ones in your quotation: and they are 1000 years older than yours. And the spontaneous generation has been confuted only in 1668 by Francesco Redi. But nobody claims that the Iliad's author was inspired by God (though, concerning how to write epic poems, he is a god). Now, the point is that if you say: "what is written in this book is God's word, therefore is right because God is omnisicent", it is not correct, because the complete statement should be: "In my opinion what is written in this book is God's word, therefore is right because etc.."; and since you are not God, the appeal to God does not give any authority to that book, nor to your opinion. Without offense, I cannot understand why so many religous people are so dumb that they don't see this small yet important logic detail. I do not even understand why so many people are so concerned about claiming that God exists/ God does not exist: but why to care about it? Suppose one proves one statement or the other: will this solve one of the thousands problems of the earth? Will this stop men to kill each other? You are free to believe or not, and I will respect your feelings, but keep it for you, and remember that it's just your opinion (and if you positively happen to find a real and true proof in one sense or the other, not just bullshit, no need to tell me: I don't think I would be so interested). --pma (talk) 02:07, 4 February 2009 (UTC)

Gravity escaping black holes.

How can gravity escape from a black hole? Taemyr (talk) 21:16, 30 January 2009 (UTC)

Complicated question, especially considering no one is entirely sure what gravity is represented as in our universe other than a feature of space-time curvature. Although it's believed to be conducted by a particle called the graviton, there is, as yet, no proof of this particle existing. The following website goes into a lot of detail in one of it's answers. It was a good read. Clicky. —Cyclonenim (talk · contribs · email) 21:25, 30 January 2009 (UTC)

Thinking more, another point of view is that black holes only attract particles into them due to gravity. If gravitons mediate this force, then they are doing the attracting, and are therefore unlikely to be affected by the field itself (since they must be massless). —Cyclonenim (talk · contribs · email) 21:29, 30 January 2009 (UTC)

Your speculation in general would be wrong. Massless particles, such as photons, are affected by gravity. We would however assume that massless gravitons are not themselves a significant source of gravity, which is an important distinction. (By contrast, gluons are themselves a source of the strong force and this ultimately leads to quark confinement.) However, as you say, gravitons are unobserved, so this is theoretical at the moment. Dragons flight (talk) 06:16, 31 January 2009 (UTC)

I was under the impression that gravity can't escape the black hole, and the gravitons pulling everything in are hawking radiation. The idea that gravity isn't effected by gravity wouldn't explain why black holes can have an electric charge. — DanielLC 22:19, 30 January 2009 (UTC)

I've never heard anyone propose gravitons are hawking radiation. I think you have a few things mixed up. And I'm no physicist but I really don't follow your logic about gravity being affected by gravity having anything to do with the electric charge. Gravitons shouldn't be affected by gravity—they are gravity. You can't electrocute electrons, it just doesn't make sense. --98.217.14.211 (talk) 01:11, 31 January 2009 (UTC)

Gravity being effected by gravity has nothing to do with electric charge. Gravity escaping a black hole does. Photons, which are effected by gravity, can mediate the electromagnetic force between the black hole and another object. There's no reason why gravity couldn't do the same. Also, I find it hard to believe that any particle could not be effected by gravity. What's keeping you from sending gravitons up, changing them to photons, sending them back down, changing them back to gravitons, etc. to create a perpetual motion machine? — DanielLC 16:45, 31 January 2009 (UTC)

And how exactly does one turn a graviton into a photon, now? Again, I don't see the logic in "gravity escaping a black hole"—gravity escaping gravity. Doesn't make a wit of sense to me—the gravity is not attracted by gravity, it is gravity. I think you're taking the particle model a little too literally here, or at least negating that the graviton must be massless. My understanding of this is not deep, to say the least, but I really don't follow your logic at all here; it seems totally implausible, sorry. --98.217.14.211 (talk) 17:07, 31 January 2009 (UTC)

Gravitational waves are a form of energy, just like electromagnetic waves. If you just want an example of how to convert between the two, you could use a charged pendulum. The gravitational waves would cause the pendulum to swing, and the moving charge would emit electromagnetic waves. Why would gravitons being the mediator of gravity prevent them from being effected by it? Photons are massless too. — DanielLC 00:57, 1 February 2009 (UTC)

You're confusing your own logic. Gravitons wouldn't be affected by gravity, just as photons aren't affected by light—because they are light! We're not saying gravitons won't be affected by gravity because they're massless, but rather because it is gravity. —Cyclonenim (talk · contribs · email) 20:34, 1 February 2009 (UTC)

We were overdue for a black hole question! Gravity does not escape from the object causing it, instead it is an effect on the space time by the mass. It may help you if you consider the formation of a black hole. To start with the mass is not behind an event horizon, and casues gravity in the normal way. As the mass approaches being a black hole, the mass or total energy does not change and the field remains the same. From your point of view outside the black hole, you never see the mass enter the black hole, so you would never see a vanishing of the gravity causing material. Graeme Bartlett (talk) 23:16, 30 January 2009 (UTC)

Books on string theory

After reading the thread above, and finishing the book, The Elegant Universe], I was wondering if someone could propose a book to follow on with string theory which is perhaps a tad more mathematical but still not a full-on dive into the realms of complicated mathematics. By this, I mean I'm an A2 student so I'm not sure I'd understand much more than A level maths. —Cyclonenim (talk · contribs · email) 21:22, 30 January 2009 (UTC)

I haven't read any so sorry can't recommend anything but String theory#Further reading gives some popular books, maybe google some of the titles and look for reviews. Jdrewitt (talk) 23:03, 31 January 2009 (UTC)

January 31

momentum object

If a point object is rotating at radius r, and the radius of rotation is suddenly halved, by the consevation of angular momentum the velocity will double. But how then is linear momentum conserved? Is there a force acting tagentially to the radius? —Preceding unsigned comment added by 70.52.46.213 (talk) 00:00, 31 January 2009 (UTC)

It's hard to imagine any mechanism that would abruptly reduce the radius without exerting some force - and right there, you've blown all hopes of appealing to conservation laws. SteveBaker (talk) 00:51, 31 January 2009 (UTC)

Right, there would have to be a radial force to reduce the radius, but this force would be perpendicular to the motion and so would not affect the speed of the object. —Preceding unsigned comment added by 70.52.46.213 (talk) 01:25, 31 January 2009 (UTC)

For every action, there is an equal and opposite reaction. Linear momentum will be conserved for the entire system, meaning that the barycenter of the two rotating objects will not exhibit a change in momentum. You can't have it both ways with the "instantaneous" change of velocity... any real force, such as a rocket propulsion system, would operate on a conservation of momentum principle. If the linear momentum of the space craft changes, then so must the linear momentum of the earth, or of the rocket exhaust gases, or some other entity. Nimur (talk) 01:52, 31 January 2009 (UTC)

I agree, but there still isn't a force acting in the plane of the object's motion. How can the tangential speed change is there isn't any force acting in the same direction? —Preceding unsigned comment added by 70.52.46.213 (talk) 02:41, 31 January 2009 (UTC)

In that case, (say an orbiting spacecraft fires a rocket towards the planet, with no component of the impulse along the current tangential motion), then the tangential speed does NOT change. The object moves to a lower orbit, and the orbit becomes elliptical, because it now has a tangential velocity that is too fast for circular orbit at the new radius. See orbital transfer for a good overview, and Hohmann transfer orbit for a specific example with diagrams of this situation. Nimur (talk) 16:48, 31 January 2009 (UTC)

Wouldn't that violate convservation of angular momentum and Kepler's Third Law?

No. If you're worried that something is violating conservation, make sure you consider all the components of the system. Don't forget the rocket exhaust gases! Those have mass and momentum, and they go somewhere! Let me emphasize - the rocket exhaust gases are not a "small effect" - they are the entire means of momentum transfer. Nimur (talk) 19:14, 31 January 2009 (UTC)

For concreteness, let's suppose the point mass is moving in a circle on a table and tethered to a string. Further suppose that string isn't simply anchored but instead feeds through a hole in the table so that someone underneath can shorten the string by pulling on it. As someone pulls on the string, the point mass will have a component of its velocity that it radial (i.e. carrying it towards the hole). Since the tension in the string is no longer perpendicular to the motion, that tension will act to increase the velocity. Incidentally, since the total velocity is increasing the centripetal acceleration must be increasing as well, which implies the puller will have to exert increasing amounts of force to continue. Dragons flight (talk) 05:53, 31 January 2009 (UTC)

Sorry, why would the tension force not be perpendicular to the motion?

Because the "pulling-in" motion needed to reduce the length of the string involves moving the object in the same direction as the tension. Dragons flight (talk) 19:11, 31 January 2009 (UTC)

Wouldn't that mean that there's a torque being applied, and that the angular momentum would increase? —Preceding unsigned comment added by 70.52.46.213 (talk) 23:22, 31 January 2009 (UTC)

No, if you calculate everything from the axis of rotation about the hole in the table, then the radial vector ${\vec {r}}$ (which is always measured from the axis of rotation) stays parallel to the force at all times and consequently the torque is always 0. In the case described above the velocity ${\vec {v}}$ ceases to be perpendicular to ${\vec {r}}$ during the transition but that is simply the same as saying that the object is not moving in a perfect circle. Dragons flight (talk) 00:09, 1 February 2009 (UTC)

Really - the bottom line here is that if you don't account for absolutely ALL of the forces, precisely, mathematically (not "Um - it seems like this...") then anytime you find anything weird going on, you are missing something. Probably something simple. Dragon flight's observation about the changing angle of that shortening string is a classic case in point. You think about the mass moving tangentially to the circle and the string acting at right angles to it - but the moment you pull on the string, the mass is moving in a SPIRAL - not a CIRCLE - and the string is not quite at right angles anymore because a line at right angles to a spiral doesn't go through the center of the spiral. Simply discounting this effect because it seems negligable is OK...right up to the point where you proclaim that you've managed to violate some fundamental law! Then you must carefully backtrack over your assumptions and find out where you screwed up. In this case, a spiral isn't a circle - so different math applies and I'm 100% certain that if you crunch the numbers, it'll come out right. It's not necessary for us here on the RD to actually do that - it's sufficient to point out "you've missed this effect" and move on. 72.183.123.248 (talk) 23:40, 31 January 2009 (UTC)

Ah thank you very much, I think I understand. Now for a loosely related question: Consider the table with hole and rope running through it apparatus mentioned above. If the spinning object had mass m, and was fired at a tangential velocity v at a radius r from the hole, and the other end of the rope was attached to a brick of mass mv^2/(rg), would the brick fall? —Preceding unsigned comment added by 70.52.46.213 (talk) 00:59, 1 February 2009 (UTC)

general theory of relativity

please explain this formula for a tenth grade student in detail$R_{\mu \nu }-{1 \over 2}g_{\mu \nu }\,R+g_{\mu \nu }\Lambda ={8\pi G \over c^{4}}T_{\mu \nu }$ thanks —Preceding unsigned comment added by 117.193.228.220 (talk) 01:44, 31 January 2009 (UTC)

I'll direct you to the key terms (i.e. metric tensor, stress-energy tensor, Ricci tensor, Ricci scalar and cosmological constant), but I believe it is impossible to explain this in detail to someone with a tenth-grade level of understanding. I won't rule out that some tenth graders may be able to understand it, but if they did so it would indicate a mastery of significant college level topics. In general, we also have an articles on Einstein's field equations and introduction to mathematics of general relativity as well as general relativity and introduction to general relativity. That last one in particular might be where you want to start. Dragons flight (talk) 06:06, 31 January 2009 (UTC)

I think it can be explained in a fairly simple qualitative way. The first part of the equation, $R_{\mu \nu }-{1 \over 2}g_{\mu \nu }\,R$, is called the Einstein tensor. It describes the extent to which space and time are curved or bent away from flat or Euclidean space-time. The term on the right hand side, $T_{\mu \nu }$, is the stress-energy tensor. It describes the amount of matter, gravitational energy and electromagnetic energy at or near a given point in space-time. Ignoring the cosmological constant, $\Lambda$, for a moment, we have

$R_{\mu \nu }-{1 \over 2}g_{\mu \nu }\,R={8\pi G \over c^{4}}T_{\mu \nu }$

which says that the curvature of space-time at each point in space-time is proportional to the amount of matter and energy near that point. The constant of proportionality, ${8\pi G \over c^{4}}$ is numerically very small when we measure it in everyday units of metres, kilograms and seconds - so this means that it takes a very large concentration of matter or energy to bend space-time by any measurable amount. But if you get enough matter close enough together - say something the size of a planet - then it will bend the surrounding space-time so that nearby objects tend to move towards it. This bending of space-time is what we call "gravity".

The cosmological constant term, $g_{\mu \nu }\Lambda$, means that even where there is no matter or energy density, and the stress-energy tensor is zero, space-time still has a built-in tendency to be curved. From observations of distant stars and galaxies, cosmologists now think that Λ has a small positive value, which means that space-time has a built-in tendency to expand. What we aren't yet certain about is the actual physical source of this built-in expansion - what exactly causes Λ to be greater than zero, and what gives it one value rather than another.

(Yes, yes, I know this is incomplete. If anyone feels I have over-simplified or missed out an important point, feel free to add your own simple explanations). Gandalf61 (talk) 11:09, 31 January 2009 (UTC)

The equation is expressed in terms of tensors and you really need to understand these before you can understand the equation. Our article on tensors is quite confusing for beginners. Instead, I recommend that you read the opening chapter of of this book which you can read online. It explains the concept in a very accessible way. SpinningSpark 11:47, 31 January 2009 (UTC)

electrodepostion of copper, efficiency of cathode?

In an experiment when measuring the percentage copper in copper ore by electrodeposition, i have read that cathode efficiency (which is the ratio of weight of metal deposited and the weight that would be if all the current had been used for deposition) is not always 100%, why is this? —Preceding unsigned comment added by 146.179.199.116 (talk) 15:48, 31 January 2009 (UTC)

Not every electron coming off that cathode reduces a copper ion to make copper metal. Some may reduce hydrogen, some may make a negative ion, some may reduce something that is immediately oxidised. Graeme Bartlett (talk) 21:09, 31 January 2009 (UTC)

Make our brain store memory.

Well we're all obviously familiar with how the brain functions in relation to storing memory and all. But just last week i was just sitting down and doing some random thinking when it struck me.....how is it that when we experience something really good or really nasty or anything for that matter the brain stores it in the memory.....something like your first girlfriend or your first day at your first job or your children's wedding day ,it automatically gets stored in the brain.....but at other times when you experience something and you know it ain't that great a memory but you want it to last forever and no matter how much you tell your brain "STORE IT" -- it never will. So my question is WHY?..WHY can't we tell our brain to store memory for us? Wouldn't that be such an amazing thing?You know like a normal hard drive....where you write something in a notepad file and save it and VOILA! its stored on your hard drive forever unless something tragic happens to it.On the same lines WHY can't ALL HUMANS DO THE SAME?ANd i mean like you just tell your brain - integral of cos(x) is sin(x) and it just saves it the first time you tell your brain to do it such that it never gets deleted from your memory I know the neurons get destroyed and all and the memories might get lost but even then in the short term .....example a year!Imagine a student whose a science student and hates history but has to pass it.If he just read through the textbook in one full day and told his brain to remember it ,he would not have to study it ever again and at the end of the year when the exams get over he could easily ask his brain to remove that memory.Wouldn't it be terribly advantageous?Why haven't we as humans tried this on a large scale?Or as a matter of fact why is it not possible? STEVE,if your reading this do answer! i know you might have something to say on this!Vineeth h (talk) 15:52, 31 January 2009 (UTC)

You can force yourself to memorize things, by repeatedly thinking of them many times, over many days. For example, flash cards can be useful to memorize things for a test. If, however, you don't care about it after the test, and never think about it again, it will slowly fade from memory after that. Only thinking about it from time to time will cause the memory to be retained. StuRat (talk) 16:01, 31 January 2009 (UTC)

Have also a search to the archive of this RD, because I remember this is a recurrent topic, although I do not remember exactly everything that has been said --you know, it's human memory pma (talk) 18:34, 31 January 2009 (UTC)

Unfortunately we don't know how the brain functions in relation to storing memory. We have clues and models based on those clues, but we don't have a a precise mechanism worked out yet. Further, memory is is probably encoded by many different mechanisms, depending on what type. For example, most people can "tell themselves" to remember something trivial and recall it a short time later. Some people are extremely good at this and others poor, probably for genetic reasons, but most people can get reasonable good at it with the right training. But long term memories (such as events in your life that made an emotional impact) are likely to be encoded in a very different way. They way these sort of memories are stored and retrieved do not lend themselves to that sort of training, and thus are outwith conscious control. This is probably a evolutionary relic of the origin of the two types and what parts of the brains they are encoded in. How and why is not known for sure, but I'm sure there are lots of models out there. Rockpocket 18:56, 31 January 2009 (UTC)

I imagine noradrenaline has something to do with long-term storage of memories, and other catecholamines which are released whilst experiencing something highly emotional. Where as revising is not at all emotional. --Mark PEA (talk) 23:25, 31 January 2009 (UTC)

See amygdala, part of the limbic system of the brain. The amygdala is involved in learning under particularly emotional conditions (fear, reward, etc.). It's hooked up to the hippocampus which is known to be involved in memory formation. You might be able to harness the amygdala for learning, say calculus, but you'd have to make the accompanying stimulus either really good or really nasty...--- Medical geneticist (talk) 04:25, 1 February 2009 (UTC)

Well thats all good...but you guys still haven't understood my question.....We've all seen "the matrix" right?Or atleast i'm hoping most of you have.Well you know how NEO finds out that they're all infact controlled by machines and stuff......like someone else is controlling them.....well in the same way.....well StuRat you said if we keep saying it over and over again we'll remember it.....but its going to fade away really really soon....and definitely wouldn't last a little over a month!....Its almost as if we aren't in control of our brain!...we can't make it do anything we wan't it to do.....its the brain making us to what IT wants us to do!.....so the real question was that we aren't in total control because like the others mentioned.....various chemicals are responsible and stuff and these aren't released because we tell them to be.....its our brain making all this happen!.....so it may sound pretty dumb but really if you think about it you really can't make your brain to much.....its like your a slave to your brain most of the time....It's like a symbiotic relationship.....we have the brain to make decisions and the brain has our skull for protection! but its just that its got a more parasitic character cause its in control almost all the time.......So really will be ever be able to be in total control over our brain? Yohttp://en.wikipedia.org/w/index.php?title=Wikipedia:Reference_desk/Science&action=edit&section=41u know literaly make it do even the SMALLEST of things that we want it to! You know i was just thinking of some more advantages.....think of a person with a tumour somewhere on their body and suppose that there's a cancerous growth of cells there...well instead of the doctor having to do something to break down the cancerous cells we could just take in the medicine orally and tell our brain to transfer the medicine via the blood stream and control it to move in such a manner that it directly reaches the tumour and starts working on it.....Well i don't know about you guys but it'd be pretty interesting if we could do this......and i do have some more crazy ideas but it'd be quite long.....so in short WHY CAN"T WE DO THIS!Vineeth h (talk) 06:00, 1 February 2009 (UTC)

On a practical level, we can't do it because we don't have the molecular mechanisms in place to do so. How exactly would your brain transfer medicine via the blood stream directly to one cell? Our bodies don't work by magic, they use electrical signals, chemicals and proteins to communicate between cells. Even if you can come up with some feasible mechanism for how this could work, it would require millions of years to evolve. For 99.999999999999% of human evolution there was no anti-cancer medicines, so there was no advantage to evolving a mechanism for delivering it!

On a more fundamental level, you are making the mistake of thinking of your consciousness as a little person sitting in in your skull, pushing buttons and telling your body what to do. It doesn't work like that. What you think of as "you" - really your consciousness - is created by your brain. So ultimately it controls you, because "you" don't exist outside the electrical connections of a few million neurons. If it makes it easier to understand, consider that your genes encode a brain that has made a "Matrix" that your consciousness exists in. Your genes have reserved a part of the brain, the cerebral cortex, for your consciousness to use for its own ends. Its this part that your consciousness has some control over. But your genes keep the rest of the brain for itself, particularly the limbic system, which is involved in emotion, instinct, and long term memory. These things are really important in ensuring your survival (and hence the survival and reproduction of your genes, which is the ultimate goal). Hence your genes are going to make sure it is reserved for these important functions, and not "stolen" by your consciousness to store some history homework for a week! Rockpocket 08:28, 1 February 2009 (UTC)

With all due respect, Rockpocket, aren't you unquestionably implying materialism in that reply? --ReluctantPhilosopher (talk) 16:12, 1 February 2009 (UTC)

Yes, I am. I purposely expressed a rather simplistic eliminativist explanation for maximum contrast with the OP's position. Rockpocket 19:25, 1 February 2009 (UTC)

But should we be peddling our prejudices on the refdesk? ReluctantPhilosopher (talk) 15:13, 2 February 2009 (UTC)

If forgoing a spiritualist explanation in favor of a purely scientific answer is prejudicial in your opinion, then yes. This is a science refdesk and science deals with matter, molecules, cells and their interactions. Neuroscientists, in general reject dualism. Reflecting that in an answer is hardly peddling prejudice in my opinion. That said, the OP may also be interested in reading our rather good philosophy of mind article, and make up his own mind. Rockpocket 20:31, 2 February 2009 (UTC)

The degree of conscious control that out OP considers would be rapidly lethal to us! If we could consciously control all of that super-delicate machinery - without the slightest understanding of how it works - then you could easily make a mistake and kill yourself. Protecting your body from your conscious mind is a vital part of what makes our bodies work. Suppose you got distracted and forgot to make your heart beat - or if you turned off blood supply to your left leg and forgot to turn it back on again! No - this would be nothing short of a death sentence! SteveBaker (talk) 15:00, 1 February 2009 (UTC)

The OP should read up on determinism and Free will#In science. "You" cannot control your brain's actions because "you" are the result of your brain's actions. Of course this sparks many debates with almost all religions and the whole topic of spirituality. Ethical issues are discussed in the determinism article also (i.e. is someone with a psychological illness guilty of their actions, when they commit a crime). You can then ask the question if other mammals have free will, if anything with a CNS has free will, or maybe even a bacterium. Or you can just believe that neurons process it all and there is no "spirit" --Mark PEA (talk) 20:19, 2 February 2009 (UTC)

Grrr... if only I had the references... I will eventually get them and fix the biased articles written by materialists and determinists. I already fixed the free will article some time ago which, in all it's magnificence, had no section on libertarian (non-compatiblist) free will at all before. _lol ReluctantPhilosopher (talk) 16:45, 3 February 2009 (UTC)

If anyone can help me out here... two of the references I am looking for are the ones that say that 1) Physicists today reject out of hand any theory that denies free will (I heard this in a program on Discovery channel about the current theories of the universe and its origin), and 2)Most physicists try to keep free will out of their theories because it confuses matters (I read this on some webpage). Or may be I'll have to ask at the humanities web page. I know some wonderful philosophers who are much clearer on the issue involved in the discussion of free will than most of the physicists. Read this for starters. It's a must read for those who think the issue of free will can be settled through physics --ReluctantPhilosopher (talk) 17:03, 3 February 2009 (UTC)

Best way to pour liquid out of a cup without it dribbling down the side?

Does physics have something to say about this? Thank you Louis Waweru  Talk  16:05, 31 January 2009 (UTC)

Surface tension is a general idea of liquid sticking together as a blob (cohesion among itself) rather than just going with gravity as a perfect liquid would, and adhesion to the vessel could then pull that blob away from "straight down". More technically, consider the contact angle between the liquid and the edge vs the angle at which the edge is while pouring. DMacks (talk) 17:42, 31 January 2009 (UTC)

In fact, for this operation chemists usually have a glass stick into the lower vessel, so that the liquid adhere to it instead of adhering to the cup's side, especially when the liquid has to be poured very slowly. This also works for everyday needs, of course. Another way to prevent adhesion to the cup (only for kitchen use) is, pouring the water or milk with a certain velocity; I follow this method with reasonably good results, say I made only few disasters, very seldom. It's important to remember that the lower cup has to be stable enough, otherwise the flow just take it away on the floor. pma (talk) 18:25, 31 January 2009 (UTC)

So, putting a chopstick or something in the lower glass, and pouring onto the chopstick? Is that the idea? (Just tried it, works much better!) Louis Waweru  Talk  19:21, 31 January 2009 (UTC)

Yeah, just hold the chopstick over the top of the container you need to pour liquid out of and let the liquid run down the chopstick into the other cup. 96.242.34.226 (talk) 19:42, 31 January 2009 (UTC)

And if you need to use it frequently, you may want to get the apposite tool, which is named stirring rod (here [15] is a quick view). There are of various sizes, both for lab and kitchen, usually by glass. If you google it you'll find a lot of info about where to find it, and how to use it properly (like this [16] for lab's use). pma (talk) 20:05, 31 January 2009 (UTC)

I've noticed this problem is worst when pouring a small amount out of a large container, especially when the liquid is quite thick. This comes up often with liquid laundry detergent. One solution I've seen is a double circular rim. The detergent pours out of the inner rim. The outer rim catches any spills, and they slowly dribble back down a drainage hole (DH) back into the container. The top screws on outside the outer rim. Here's a cross-section:

         INNER
          RIM 
         |    |
   <-  | |    | | OUTER           HANDLE
 POUR  | |      | RIM      +-------------------+
  DIR  +-+  DH /           | +---------------+ |
         |    /            | |               | |
     +---+    +------------+ +---------------+ +--+
     |            CONTAINER                       |

StuRat (talk) 01:56, 1 February 2009 (UTC)

Electric shock

Is there a danger of getting an electric shock when a person(standing on the ground) touches one of the wires of two phase generator of electricity that is not grounded? —Preceding unsigned comment added by 202.70.74.181 (talk) 17:46, 31 January 2009 (UTC)

Definitely. It sounds like that arrangement is a guaranteed way to create a life-threatening electrocution hazard. Worse yet: the most dangerous hazard is the possibility that the wiring is not correct, or does not match the schematic, or otherwise has high voltage and high current in places you might not expect. Even a wire which "should be" safe may actually be live. You should always assume a wire is live and dangerous unless you are trained to make a more thorough assessment. Nimur (talk) 19:18, 31 January 2009 (UTC)

Well its definitely not a safe thing to do but I think the question was more theoretical. If the generator is genuinely isolated from earth then you should not get a shock if you were to touch only one conductor. However, it is too difficult in practice to prevent accidental grounding in a real electrical distribution system. The only places this is done to my knowledge is on oil rigs were sparks to ground are a bigger safety hazard than electric shock and even then there are additional safeguards. SpinningSpark 01:25, 1 February 2009 (UTC)

Urban legend regarding pitbulls

Is there any truth to the claim that if a pitbull is allowed to taste human blood, it will become uncontrollable and keep attacking humans to experience that delicious taste again(and likely have to be euthanized)? Is this true of any dogs, or any animals? 69.224.37.48 (talk) 19:51, 31 January 2009 (UTC)

No. — Lomn 22:38, 31 January 2009 (UTC)

No. They don't do that for (for example) cow blood. A dog that once tastes a steak doesn't subsequently lose all control of itself whenever there is another steak around. Why would human blood be any different? Nope - this is nonsense...please tell whoever told it to you. The world needs fewer of these stupid urban legends. 72.183.123.248 (talk) 23:24, 31 January 2009 (UTC)

Okay, no, dogs that taste human blood don't inherently go crazy and become uncontrollable. However, there is still some legitimate cause for concern. An animal that bites people may be sick or dangerously vicious (not because blood makes it crazy, but because it was already violent to begin with). The former may be treatable, while the latter might be controllable with reasonable precautions. There is also a risk that some animals that bite people might come to think it is okay to do so again in the future, i.e. a form of learned behavior, so one needs to be careful about not encouraging such behavior. In general, a dog that has bitten people is probably one that it is best to keep away from unfamiliar people and take greater care around. I will also note that it is common in many jurisdictions to euthanize animals that have attacked people. Dragons flight (talk) 00:28, 1 February 2009 (UTC)

There is cause for concern - sure. If a dog gets the idea that it is the alpha-dog in the 'pack' of humans with which it lives then the humans who live with it had better plan on taking back the alpha slot - or being continually hassled by the dog. If the dog tries this on - you need to wrestle it to the ground - roll it onto it's back - place your hand around it's throat and squeeze gently. This says "I am the dominant animal in this pack and don't you ever forget it!". You also need to ensure that when you and the dog approach a doorway - you go first. Don't feed the dog until AFTER the family has eaten. Make a point of taking away the dog's food while it's eating (you can give it back later). Basically, it's got to know that it's place in the pack is somewhere below the lowest human. This seems a little sad - but a dog is happy to be what it is. What they don't like is uncertainty. 72.183.123.248 (talk) 02:14, 1 February 2009 (UTC)

That's good advice ....248. There are no bad dogs just bad owners. Richard Avery (talk) 08:40, 1 February 2009 (UTC)

Its good advice except for the rolling the dog on its back part. This actually says to the dog "I am going to kill you." Would you feel comfortable living with someone who was threatening your life everytime you walked in to the room? Especially bad if the dog is violent. Don't do this. Livewireo (talk) 20:34, 2 February 2009 (UTC)

i dont want JOWLS

how do i keep from getting JOWLS when im old. i'm 25. this is not a request for medical advice. —Preceding unsigned comment added by 82.120.227.157 (talk) 21:07, 31 January 2009 (UTC)

There are exercises you can do. One is to bring your bottom lip over your top one and hold it there for 5 seconds, then relax. Then do the same thing while smiling. Also keeping all your teeth helps! --TammyMoet (talk) 21:39, 31 January 2009 (UTC)

Unfortunately, a lot of this stuff is genetic; if you dad and/or mom had jowls, you are more likely to have them as well. --Jayron32.talk.contribs 22:25, 31 January 2009 (UTC)

February 1

How delicate is the universe?

If the universe was one millidegree cooler would it be nonexistent? Would it regret not having created me to gaze at it's wonders? One little atom out of place and the whole thing collapses? Is it that sensitive? Has a mini universe ever been created in the labratory under slightly different conditions? If so, I wonder if any scientist ever snapped and became "God" of his newly created universe?--Dr. Carefree (talk) 00:47, 1 February 2009 (UTC)

$(no)^{6}\,$

SpinningSpark 01:28, 1 February 2009 (UTC)

If you don't have an answer - please don't answer. K'thnks. 72.183.123.248 (talk) 01:48, 1 February 2009 (UTC)

Well, on the bulk scale - the universe is the exact temperature it is for some reason or other (I don't know why) - if it were even a millionth of a degree different than it actually is then there would have to be something different about it at the start. The subtle difference in temperature might not be enough to make a very large difference - but the fact that things were different at the outset might be exceedingly significant. The cosmic background temperature is around 3 degrees kelvin - so a 'millidegree' would represent an 0.3% change - that implies a pretty large change in one or more fundamental constants or one or more laws of physics. That would cause who-knows-what consequences...maybe stars don't form or planets don't orbit. It's really tough to speculate on (a) what might cause a one millidegree difference and (b) what the consequences of that difference might be.

We haven't created any other universes - we have no idea (even in principle) how to do that - and the amount of energy that might take sounds like it would be impossible for us to obtain...but who knows? Was our universe created by some little green man with a white lab coat and a petri-dish? We don't know - we can't ever know - so it's pointless to speculate.

The 'anthropic principle' really does apply here. If the universe were different than how it is - then we could be different too - and we'd still be asking the exact same question of the different universe. If the universe were different in some other ways, then perhaps sentient beings would be impossible - or perhaps stars would not form - perhaps even atoms might not exist. In those cases, there would be nobody there to speculate. If we buy into the idea that there are an infinite number of universes out there - then (by definition) we MUST live in one that allows us to have to evolved - so the precise conditions (however far-fetched) that are required to make a creature exactly like us MUST be the conditions in any universe in which we are present to observe it. The anthropic principle is a less comfortable explanation than "The charge on the electron absolutely has to be such-and-such because <some really good reason>" - but in the absence of such a reason, it is a good explanation.

72.183.123.248 (talk) 01:48, 1 February 2009 (UTC)

Temperature isn't constant, either in time or space, so it can change without any significant consequences (depending on what caused the change, there may be other consequences in the details, but the basic structure of the universe and physics would be the same). It's more interesting to consider what would happen if various physical constants were changed. I've heard that changes to some constants of less than 1% would make it impossible for stars to form, or other consequences that preclude life as we know it. So, in that sense the universe it pretty sensitive. We do, of course, have an article: Fine-tuned Universe. --Tango (talk) 14:00, 1 February 2009 (UTC)

The current temperature of the Universe (which I take to be the temperature of the cosmic microwave background) is 2.725 Kelvin. As the Universe expands its temperature drops, and it will be cooler by 1 millikelvin in about 5 million years (computed with Ned Wright's cosmology calculator [17]). If there are astronomers around at that time, they will measure a lower temperature than we do today and there will be nothing weird about that. The actual temperature is largely a contingent feature of the Universe, it is not prescribed by any physical principles; it is more a question of when it is measured. There is presumably a time window of some sort in the history of the Universe in which intelligent life can form and exist, and that time window can be translated into a "temperature window". That window is, however, certainly much larger than the 1 Millidegree (or 5 million years) you quote. Incidentally, 1 millidegree corresponds roughly to the accuracy of our measurements of the mean temperature of the CMB. --Wrongfilter (talk) 14:25, 1 February 2009 (UTC)

How much would an outside observer (an alien scientist, if you like) be able to determine about life on Earth as a whole...

...from the study of one living earth creature? Supposing the one creature was (just an example chosen at random from the bird articles on my watchlist) a Green Cheeked Conure of the female sex. By examining just this one bird as a representative of all life, what (correct) conclusions could be drawn? --Kurt Shaped Box (talk) 02:07, 1 February 2009 (UTC)

Quite a lot, I would imagine. If the scientist could keep the poor creature alive (which would be very hard) he'd know something about atmosphere, temperature range, gravity, etc. But the odds are good that the creature would be dead in short order...but even so, you'd find a lot about biochemistry. With technology like ours, it might take a long time to figure out things like DNA - but that depends on how similar we are to them. If (for example) they are very similar to us - then the relative differences would tell them a great deal in detail. If they are very different from us (I dunno - silicon-based lifeforms from a high gravity, high air pressure planet where temperatures hover around 100degC all the time) - then they'd see that the spindly legs and the light build implies less gravity - and the nature of the lungs and flimsyness of the musculature for operating the lungs would suggest that there is a less dense atmosphere than they are used to. Liquid water everywhere in the body tells them that the temperatures must be lower...there's a lot they could figure out. But I doubt those silicon beings would be able to fathom out the function of DNA (for example) with a dead parrot. 72.183.123.248 (talk) 02:25, 1 February 2009 (UTC)

Nothing about life as a whole. Any generalized conclusion would be invalidated by nonprobability sampling. The only think one could infer would be that there is at least one species that can fly, has feathers, has DNA, etc. They could infer things about the earth's environment, though Rockpocket 02:32, 1 February 2009 (UTC)

Thanks. When I posted my Q, I was actually thinking about how human astronauts would go about studying the life in the hypothetical oceans of Europa from a single specimen, or a small number of specimens that they managed to fish out by pure luck during a manned mission. --Kurt Shaped Box (talk) 02:50, 1 February 2009 (UTC)

First off the scientist would have more than one species in their hands. The bird is essential a viral and bacterial colony. Furthermore by looking at the organelles of the cells they could infer a great deal out evolutionary history. They would be sure that there was "at least one" but it would be foolish not to infer such a complex creature is at least representative of a portion of the unknown planets life. Just from the design of GI track the scientists would know some constraints concerning its diet even if the bird had its stomach pumped before abduction. If they could read the birds genetic structure they could probably start making extrapolations about its genetic heritage and evolution. If I found an alien critter that couldn't live in our environment I would promptly freeze it and start looking for the things I've described above. Of course the first thing to do would be to get a handle on its fundamental chemical make up which I didn't discuss but we haven't provided time constraints. It would take years, huge amount of resources by our standards, and a host of researchers but it would be ultimately informative.

I know modern science insists on postulating that there are endless possible forms life, ie alternative biochemistry. I believe this more was developed to avoid developing a anthrocentric perspective which makes sense. At the same time I've never heard of any molecular system that could accomplish the task that our proteins and DNA accomplish. No one has been able to suggest anything reasonable for silicone biochemistry. This lack of an alternative wouldn't be a big deal if there was more elements to discover but there aren't. So it seems reasonable to expect a fair amount of convergent evolution; which we see all over the place in nature, my favorite example is social insects. The alien very well may have the opposite chirality on a molecular level, run some metabolic process the opposite way, and have a drastically different appearance. But odds seem high to me that they evolved to manipulate metal in a very similar way we did. Hell even their bodies temperatures upper limits are probably governed by the temperature at which most proteins denature around 40C. I say that with full respect for extremophiles while noting that they are all unicellular or close to it. Multicellulars don't do real well above 40C unless its at high pressures. Thus the qualification begins. So I'll end there, comment please.--OMCV (talk) 03:05, 1 February 2009 (UTC)

I wrote my answer before the last entree you might want to check out [18] it talks about life sense devices with the potential to be on future space missions.--OMCV (talk) 03:09, 1 February 2009 (UTC)

Interesting, thanks. I wonder if NASA has yet devised a 'standard procedure' for the handling and storage of extraterrestrial biological specimens, what with the manned Mars and deep-sea Europa missions possibly happening in the not-too-distant future? I can't help but wonder what they'd actually do if they chanced across something macroscopic. --Kurt Shaped Box (talk) 17:27, 1 February 2009 (UTC)

OMCV makes a good point, we shouldn't under-estimate how much scientific value one can obtain from a single sample. I know I said the "only thing" one could infer, but even proving that there is at least one alien species that respires, has carbon based DNA etc would without a doubt a scientific discovery of the century. Moreover, comparative studies of our vast knowledge of life on our own planet would enable many general conclusions to be drawn, many of which would probably prove to be correct. But taking these beyond the level of hypothesis would require greater sampling, though. Rockpocket 03:11, 1 February 2009 (UTC)

If they fail to understand anything, they can safely say that Creationism has control over Earth too :) manya (talk) 04:24, 2 February 2009 (UTC)

explanation on tensors

please help me, a tenth grade student in detail abt tensors. please. i have understood the special theory of relativity but i want to do the same on general theory of relativity. --Harnithish (talk) 02:40, 1 February 2009 (UTC)

There is some information in the tensor article regarding applications to physics, and links from there to more detail. If you have a specific question, people here may be able to help if you state it clearly. For some aspects of tensors, the math RefDesk may be a helpful alternative. Best wishes for your studies - sounds like you are off to a great start! --Scray (talk) 17:17, 1 February 2009 (UTC)

The simple answer is that tensors are complicated beasts, and as a 10th grade student you would almost certainly have trouble understanding them. However, that doesn't mean you shouldn't try, and as such it would probably be good for you to first get a grasp of vectors and matrices, and of calculus - particularly solving differential equations. Tensors are then an extension of vectors and matrices, and then in differential geometry and GR calculus is added into the mix. You might also want to track down the book "Gravity: An Introduction to Einstein's General Relativity", by James Hartle, which takes an approach that avoids a lot of the tensor calculus and looks more at things in terms of undergraduate physics. Confusing Manifestation(Say hi!) 23:30, 1 February 2009 (UTC)

books on physics theories

is there some book which can be e-downloaded freely on quantum theory, string theory, general theory of relativity and something exciting for the students in the age group of 14-16--Harnithish (talk) 02:58, 1 February 2009 (UTC)

I don't know about the age range - but here are the freely downloaded "books" that I could find:

Wikibooks (a Wikipedia sister project) has two books on Special relativity [19] - one at undergraduate level and another at an 'intermediate' reading level that only requires basic algebra as a prerequisite. There is a general relativity book - that appears to be about half-finished - but it looks too complex for 14-16 year olds because it goes into tensor algebra and such. This is alse a book on String Theory that's in the process of being written - but it's very sketchy right now. We also have This Quantum World - which also seems a little high level - although 16 year old's might manage it if they have been doing calculus at a level similar to British 16 year-olds rather than the rather pathetic level that it's taught at in US high schools.

Project Gutenberg has a vast repository of free eBooks - including Einsteins' own book on Special and General relativity:[20] (you can read it in the original German too!) - It's actually surprisingly readable. They have Lorentz's book on the same topic [21]

Wikisource (yet another Wikipedia sister project) has [22] which is Einsteins rebuffing of people who disbelieved in relativity. It's somewhat entertaining. Wikisource also has [23] Einstein's book that I mentioned earlier.

Wikiversity (yeah - guess) has a couple of 'courses' on Quantum theory: [24], [25] on Special relativity and [26] on General relativity.

Sadly, most of those things descend into a sea of equations pretty quickly. Surprisingly, perhaps, Einsteins' works are the pretty approachable if you take it slowly and work to understand each part before skipping on to the next. Well, I'm not sure I helped very much...but that's what I found. SteveBaker (talk) 00:18, 2 February 2009 (UTC)

Hey, how do they know they've discovered methane (tm?) gas on Mars?

That's like,-way over there. And we're we're like,-down here. Were at the center of the universe (comparatively speaking). With no machinery or people on Mars, how can they tell? Sometimes I wonder if scientists are just desperate for headlines and figure we'll believe anything. Sorry.--Hey, I'm Just Curious (talk) 03:28, 1 February 2009 (UTC)

By using NASA's Infrared Telescope Facility and W. M. Keck Observatory both in Hawaii. The scientists attached spectrometers to the telescopes to spread light into its component colors. They looked for dark areas in light spectrum where methane was absorbing sunlight reflected from the Martian surface. They found three - so-called absorption lines - which together form a definitive signature of methane. They were able to distinguish the Martian methane from that in Earth's atmosphere because the lines were disturbed in sync with the planets motion. Rockpocket 03:37, 1 February 2009 (UTC)

There is an example of of methane's IR absorption fingerprint on Methane (data page) near the bottom of the page.--OMCV (talk) 03:42, 1 February 2009 (UTC)

Well, we do have quite a bit of machinery on Mars - Spirit rover and Opportunity rover for example. We also have Mars Reconnaissance Orbiter and something like four other spacecraft in orbit around Mars. But in this case the information was obtained spectrographically from an earth-based telescope. We routinely collect spectrographic data from stars that are millions of lightyears away - so this isn't that tough to do! Each chemical absorbs and reflects light differently - which is why some things look different colors to others. By splitting the light coming from Mars' atmosphere into a spectrum (a 'rainbow' if you like) there are lots of dark lines corresponding to colors that should be there in the sunlight - but aren't there in light reflected back from Mars because something is absorbing it. Some of those missing lines evidently correspond exactly with the precise colors that methane gas absorbs. The exciting thing is that methane cannot exist long in the atmosphere of a planet - so whatever put it up there is still making the stuff!! Since the most common source of methane on Earth is animals - one possible reason for the methane to still be there in the Martian atmosphere is because there are still living creatures there...which would be a very exciting conclusion! Sadly - as with the other signs of life on Mars that we've seen, this is not 100% conclusive because there are complicated non-biological processes that could possibly produce methane too. SteveBaker (talk) 04:50, 1 February 2009 (UTC)

I don't know, but we can smell the methane gas around Uranus from here. —Preceding unsigned comment added by 82.120.227.157 (talk) 14:28, 1 February 2009 (UTC)

Methane is an odorless gas....oh...wait...you were trying to be funny right? Oh, OK - well...um...ha,ha then. SteveBaker (talk) 14:48, 1 February 2009 (UTC)

Now, the next step for the scientists is to determine whether the methane was produced by biogenic or abiogenic sources. This is why the news became so exciting. ~AH1^(TCU) 17:54, 1 February 2009 (UTC)

Are you saying that there's something living on the surface of Uranus?

Sorry. --Kurt Shaped Box (talk) 17:59, 1 February 2009 (UTC)

Clearing Brush

I was wondering about the activity that former President Bush enjoyed at his Crawford Ranch. What does "brush" consist of? What is the purpose of clearing brush? Is it to use the soil for agriculture? Once the brush is cleared, what is usually done with it? What kinds of tools are used to clear brush? Is the process mechanized, or still done by hand? Are there people who do this as a profession? 211.109.12.170 (talk) 04:31, 1 February 2009 (UTC)

The brush normally consists of fallen tree branches (or entire trees), dead bushes, fallen leaves, etc., and sometimes also live trees or bushes. The primary purpose of clearing brush is to prevent fires from spreading. A secondary purpose is to allow easy access to the property, which might otherwise become overgrown. Some of the smaller items could be raked up, larger branches would need to be carried off individually, and the largest branches (or entire trees) would need to be cut up and then carried away. The leaves are likely composted, while branches could possibly be burnt in a fireplace. (Leaf-burning is usually prohibited, since it puts out a lot of smoke.) StuRat (talk) 04:43, 1 February 2009 (UTC)

(Hmmm - we don't really have any kind of an article on brush wood and brush (disambiguation) doesn't mention it.) Wiktionary says that 'brush' is plant growth that's larger than grasses and smaller than trees. Once you've collected it, you can burn it - but you can also toss the stuff into a wood chipper which chops it up into teeny-tiny chunks that can be used as a mulch to help keep weeds from growing around desirable plants. Other machinery could be anything from an axe or a Machete to a chainsaw. There are also Brush hogs and brush mowers that chop the stuff up and leave it on the land. These exist as large lawn-mower-like contraptions that you walk behind - or bigger ones that you tow behind a tractor. The purpose of clearing brush on a working ranch is to allow the cattle to gain access to the grass beneath - and to reduce the risk of wildfire. While you can use machinery out in open areas - in tight corners where there are trees, it's a mostly manual process. There are people you can pay to clear your brush - but it's essentially an unskilled and fairly mindless task...the perfect thing to occupy the time of a US president.

President Bush's ranch out in Crawford (not far from where I lived until recently) probably contains a bunch of bushy texas cedar trees (they aren't true cedars) that have the annoying property of having branches that grow out parallel to the ground as the tree gets bigger - these die off - but don't fall off. So a group of these trees forms an impenetrably woven mass of thin, dead, spikey branches that even a cow won't walk through. Getting in there with a machete (and occasionally, a chainsaw) allows you to remove all of these dead lower branches and produce a nice tree with a clean trunk and a bushy green top. Clearing the lower branches of cedars improves an otherwise useless piece of land by allowing both humans and animals to get into it. Since the branches are dead anyway - this does no harm to the trees and the resulting mulch is useful. With my wife and I, a chainsaw, a couple of machetes and a gasoline powered wood-chipper, we were able to clear the lower branches from an acre and a half of cedars around our house over a couple of weekends. Removing the dead trees also let in more light and gave us a large stock of logs to burn in our open fireplace. 10 years later, the lower branches of the cedars have not grown back and the resulting improvement of the land is well worth the effort. SteveBaker (talk) 05:18, 1 February 2009 (UTC)

I think President Reagan also talked of doing brush clearing. But I think both presidents spoke of it in a double sense. Clearing away brush meant not only eliminating unwanted undergrowth, it also meant clearing away liberal ideas and negating progressive legislation. – GlowWorm. —Preceding unsigned comment added by 98.17.34.148 (talk) 06:07, 1 February 2009 (UTC)

Very interesting, thanks all! I also looked at that disambiguation page without finding anything. I previously had the misconception that clearing brush involved pulling out live undergrowth. I wonder if removing all the dead wood hurts the ecosystem? Does one generally remove all the brush or just paths to give accessibility and act as fire breaks? I wasn't aware of the double meaning and history of the expression - also interesting! 211.109.12.170 (talk) 06:42, 1 February 2009 (UTC)

Whether you'd only remove brush that's obstructing access or remove it all depends on your local fire department. In some counties fire prevention requires that you basically strip everything between the height of grass and grown trees. The county in California we used to live in traded increased fire safety for erosion of hillsides and mudslides this way. Controlled burning of underbrush is not practiced in residential areas, but has proven successful in some managed forests. It's not for the layman, though, and can't be done during a drought. 76.97.245.5 (talk) 10:57, 1 February 2009 (UTC)

I think that brush clearing might well involve removing live vegetation. If the Wiktionary definition is correct then live as well as dead material can be considered "brush". In the context of the Crawford ranch - it's possible that there was some 'undeveloped' acreage that had a lot of live brush in it that would need to be cleared for the purposes of increasing the amount of land available for cattle. Removing dead material certainly does hurt the ecosystem - the nutrients that were absorbed from the soil in growing that material is not being returned through the normal processes of decay - so if you did this repeatedly, the nutrient levels in the soil would indeed decline. Also, the rotting wood acts as food and habitat for insects and such like. In the case of the ranch, this may ultimately be a problem. In the case of my back yard, the chipped brushwood was spread back onto the land - so there was no loss. SteveBaker (talk) 14:42, 1 February 2009 (UTC)

Well to my Rocky Mountain brain, brush is Sagebrush (disambiguation). He's clearing tough woody shrubs to enable edible grasses to grow. He's making food for cattle. --Mdwyer (talk) 18:43, 1 February 2009 (UTC)

Kaiser Bill spent a lot of time chopping wood for the silent movie newsreel cameras. Any coincidence? It is mediagenic busywork. Edison (talk) 03:00, 2 February 2009 (UTC)

ina pasture, "brush" is basically anything except the grass, clover, and alfalfa. If a pasture is left fallow for more than about two years, brush (small woody bushes) starts to grow and crowd out the grass. The farmer must then cut down the brush before using the pasture. You typically use a bush hog for this. -Arch dude (talk) 00:14, 3 February 2009 (UTC)

About the cooling and heating of the air as an affect of clouds

Note:this question was moved from Portal:Weather by User:Runningonbrains.

About the cooling and heating of the air as an affect of clouds. It was hard for me to understand why the air is cooler when there is a clear sky and warmer when clouds are present. It has the same principals as a vacuum or a fridge. A vacuum, for example. The point is to have a space with no air in it, so that it will suck up all of the dirt you have on your floor. But if you are going to take all of the air out of an area, the excess wind has to have somewhere to go. If you feel a slight breeze on your legs while vacuuming, this is where the excess air is exiting. Perhaps a better example is a fridge, as it contains the same components, heat and cold. In order to make a refridgerator, the heat in that space must be removed. As with a vacuum, (and the air) the heat must go somewhere, so it it expelled out the back. Like both of these examples, the heat is dispelled out of the clouds. Clouds are made up of tiny ice/water droplets. These obviously are very cold. When the heat exits, it must go somewhere else, so it goes to the surrounding air. When there are no clouds in the sky, the heat that exits the clouds normally does not exit, and the cold that is captured in the clouds is not inhibited by the boundaries of the cloud, therefore spreading in the surrounding air. This is why it is generally colder when there are clouds in the sky, and generally warmer when there are no clouds in the sky.-— Preceding unsigned comment added by Smartcookie1596 (talk • contribs)

Even though, as you say, the clouds are made of tiny, cold ice and water droplets. Then think of them as a sort of igloo. Despite being cold themselves, they have an insulating effect on the Earth. Its not that clouds cause the Earth to be heated, they more effectly trap the heat that is already here than do cloudless days. The effect is that the clouds act as a blanket of sorts. It should also be noted that its not that simple, since the ambient temperature can affect cloud formation as well; warm air rises and warm air carries more humidity than does cold air, so rising warm air has the effect of creating more clouds. On colder days, there is just less moisture in the air, and less "lift" bringing that moisture to altitude where it can create clouds. --Jayron32.talk.contribs 12:14, 1 February 2009 (UTC)

Yes, clouds work based on the greenhouse effect. That is, like the glass in a greenhouse, they let light from the Sun in but don't let heat back out. (Well, they let most light in and block most heat from escaping.) So, the effect is that it warms up more quickly below the clouds during the day, and cools off more slowly during the night. The "extra heat" is actually in the form of less heat radiated into space. So, in other words, space (and the air above the clouds) is cooler when the Earth is covered with clouds. Of course, there's such a small amount of heat added to the many widely spaced objects in space that it doesn't increase the temp there by a measurable amount. StuRat (talk) 14:23, 1 February 2009 (UTC)

This is a very complicated effect that is giving the climate change modellers headaches. On nights and winter days, low clouds trap in warm air, while when there are no clouds, the heat escapes to space. On a summer's day, clouds cool the air because they block the heat of the sun. When it's clear, however, humidity can still build up, which makes it feel even hotter than it is. High clouds during daytime can also cool temperatures: when the entire American air fleet was grounded for three days following 9/11, the average temperature of the entire continental United States rose by 1 C (1.8 F), because the cooling effects of the high clouds produced by the contrails were removed. In the same manner, some man-made pollutants are not only contributing to global warming, but they're hiding its effects as well. Soot, found in brown clouds of pollution travelling across the Indian and Pacific oceans, cause warming by absorbing heat and decreasing albedo when they land on ice in the Arctic, but they also hide the warming effect by blocking sunlight during the day. This also produces global dimming. Clouds play an important, but confusing, role in determining the effects of climate change. When factoring the possible effects of clouds and water vapour in global warming simulations by computer models, the upper limit for possible temperature rise in the next 100 years rises from 6C (11F) to 11C (20F). PS. What's your question? ~AH1^(TCU) 17:46, 1 February 2009 (UTC)

what is the detail standard of MS20995AB32 or NASM20995AB32

Hi, I need to know the detailed standard of these MS20995AB32 or NASM20995AB32. I cannot get free information online. Is anyone can help? —Preceding unsigned comment added by Decowire (talk • contribs) 07:37, 1 February 2009 (UTC)

If you have a university or engineering college nearby they usually have a reading room with all/most of the standards. Otherwise you might get lucky if you contact local manufacturers or associations. OK it's an military aircraft part, a wire to be exact. That can get tricky, doubt a reading room would have that. 76.97.245.5 (talk) 10:47, 1 February 2009 (UTC)

IMHO this is a very vague question, surely you could have provided some context to this question, you might know exactly why you want/need this information and what the numbers relate to but I suspect that to everyone else it is just some number. What specifications are you actually after? Googling finds: http://www.casa.gov.au/rules/1998casr/021/021c99s2c09.pdf Which states:

Wire type	Material	Colour	Size	ID
Shear or Seal Wire for Magnesium Parts	Aluminium Alloy (Anodized)	Blue	0.032 inch	MS20995AB32 9525-01-031-1086

but I don't know if that has answered your question, probably not. Jdrewitt (talk) 14:25, 1 February 2009 (UTC)

Clones and lung problems

I was reading this article about the newly cloned extinct ibex (first time they've cloned a extinct animal, woot!). There is this line:

Sadly, the newborn ibex kid died shortly after birth due to physical defects in its lungs. Other cloned animals, including sheep, have been born with similar lung defects.

Why is this the case? (Assuming we know). Unless they somehow keep screwing up the DNA is some specific way, I would guess it has to do with the insemination process rather than the cloning process? Looks like that is what took Dolly_(sheep) down for the count too. Anythingapplied (talk) 08:44, 1 February 2009 (UTC)

I remember reading at the time this was first noticed that the best guess of those involved was the ageing process: in other words, the cells that had been cloned were the same age as the parent and therefore had degraded through the ageing process. --TammyMoet (talk) 09:54, 1 February 2009 (UTC)

Yes, in reproductive cloning, the cell nucleus from one individual is placed into an embryo which has had it's nucleus removed. The problem is that the cell nucleus has an "age", as defined by the length of it's telomeres, and thus any organism cloned from the cell will continue to age, starting from the age of the organism which contributed the nucleus. Using a younger donor for the nucleus will help to reduce this problem. StuRat (talk) 14:05, 1 February 2009 (UTC)

In the future, it's quite likely that this can be fixed by increasing the length of the telomeres in the DNA before implantation. An additional problem for cloning extinct animals is finding a suitable animal to provide the womb for the developing animal. In the case of an ibex, there are plenty of similar species around that will work - but if you were thinking in terms of 'bringing back' (say) Giant Sloths - then there would be considerable difficulties even with suitable DNA. The problems with cloning for extinct species can also be fixed without telomere lengthening by cloning both a male and female of the species and breeding them (possibly artificially) before their short lives expire. The lambs born to Dolly seem perfectly normal - so this appears to be a viable approach. SteveBaker (talk) 14:26, 1 February 2009 (UTC)

Despite the speculation, the answer is no-one really knows. Some clones appear perfectly fine, others die early. We don't really have enough of them to do the controlled experiments to determine if there is any pattern. In Dolly's case, she was probably the most abnormal sheep in history in terms of her environment, therefore we have no real way of knowing whether her lung disease was due to being a clone, due to being kept indoors, or just dumb bad luck. If and when cloning becomes commonplace, we will be able to control for these factors and answer your question. Its worth noting, though, that when IVF was first being developed there was all sorts of concerns that it was unnatural and would lead to defects and premature death. There is still debate over that subject, but the worst cases scenario never panned out and IVF is extremely well tolerated. Rockpocket 19:47, 1 February 2009 (UTC)

In addition to the telomere length problem mentioned earlier, there is also the possibility that epigenetic plays an important role in cloning. Every cell has a pattern of silenced and activated genes in its DNA, called "epigenetic programming". In short, this means that the DNA is chemically modified to change its structure. To become a fully potent stem cell (to then develop into an embryo), these "activation marks" have to be erased to enable a "start from scratch" for the new organism (and in most cases, this works perfectly, which is still not really understood). Some studies suggest that a "faulty start up" of the genetic machinery is sometimes involved when stem cells don't really become totipotent after nuclear transfer. And one could speculate that this could also lead to minor defects, let's say in lung development, when only a fraction of genes is not properly "reset". TheMaster17 (talk) 09:16, 2 February 2009 (UTC)

It seems odd though that this kind of genetic problem would affect the lungs in preference to other organs in so many cases. SteveBaker (talk) 16:24, 3 February 2009 (UTC)

Nothin' for nothin', but it could be that they have many other defects that don't have time to kill the clones before the bum lungs do. --Milkbreath (talk) 16:31, 3 February 2009 (UTC)

Day with the most number of deaths

In recorded history, on which day did the most people die? Thanks LotsOfJam (talk) 10:19, 1 February 2009 (UTC)

List of causes of death by rate quotes the World Health Organization as estimating that 58 million people died in 2005, and slightly less in 2002. That's 158,904 per day. We can assume that there will be some seasonal variation, especially since the world population is concentrated in the Northern Hemisphere, but I don't know how to allow for that.

The largest death toll in recent years caused by a disaster was the result of the 2004 Indian Ocean earthquake, with 229,866 deaths, according to our article. Almost all of these are likely to have died on the day of the earthquake, 26 December 2004. Together with the average death rate per day calculated above, that makes 388,770 deaths on that day.

While I don't have figures for the average daily death rate in much earlier years, the 1556 Shaanxi earthquake killed about 830,000 people. I don't know how many of these were killed in a single day; probably most of them. This places 23 January 1556 as the answer to your question. Some unknown number of people will have also died unrelated to the earthquake around the world on that day. The article World population doesn't give a population for around that date, but we can assume it was between 300 and 800 million. Someone else can provide a refinement of that range, I'm sure. You could look at Life expectancy and try to calculate an average number of deaths per day to add to the earthquake figure if you want a total number of deaths for all reasons on that day.

The article List of natural disasters by death toll gives a number of disasters with much higher death tolls, but these were spread out over a month or two, and probably didn't result in such a high number of deaths in any single day as the 1556 earthquake.-gadfium 11:24, 1 February 2009 (UTC)

For comparison, the firebombing of Tokyo on the night of March 9-10, 1945 is probably the biggest man-made catastrophe in a single 24-hour period, with an estimated 100,000 dead. That total is somewhat more than died from the immediate effects of the nuclear bombing of Hiroshima and Nagasaki (which of course occurred on separate days). Dragons flight (talk) 11:39, 1 February 2009 (UTC)

Concerning daily death rate, Mortality rate gives a crude death rate (annual) of 9.6 per thousand. That would be 2.63 per day per 100,000. The caveat here is that 9.6 per thousand is the *current* crude death rate, which was probably different hundreds of years ago. 152.16.59.190 (talk) 11:45, 1 February 2009 (UTC)

information in Dutch about Cryptosporidium parvum

Hello,

I would like to now more about Cryptosporidium parvum because we have ill animals with this illness.

Can you send us informaion in Dutch??

Thank you very mutch.

J en M Steeghs Holland.

Sorry, no. We're not supposed to give out medical (or even vetinary) advice. Also, we're only able to provide advice in English. You need to see a veterinarian. We have an article on Cryptosporidium parvum - but it's only available in English, German, Spanish, Polish and Indonesian. SteveBaker (talk) 14:12, 1 February 2009 (UTC)

You could try the informatiebalie on the Dutch language wikipedia, although that seems to be a surprisingly quiet place. --Wrongfilter (talk) 14:26, 1 February 2009 (UTC)

Should my adam's apple be perfectly symmetrical?

←Sorry, but this most certain should not be answered by anyone here, Wikipedia does not provide medical advice. You stated that you were concerned about it being cancer in your original question. That's most certainly a request medical advice, and I must insist that you seek help from a medical professional rather than asking a question here. My apologies for removing the answers from other users, but I do feel this is in the OP's best interest. —Cyclonenim (talk · contribs · email) 19:10, 1 February 2009 (UTC)

Correct. You are right, Cyclonenim. --VanBurenen (talk) 19:24, 1 February 2009 (UTC)

Sound in Water

I have just been informed (on Mythbusters) that sound travels 5 times faster underwater than in air, due to the closer proximity of the molecules. Why, then, does it not sound at a higher pitch?--KageTora (talk) 15:44, 1 February 2009 (UTC)

It's easy is see why. That sound travels faster in water only means that the time it takes for sound to travel from a source to an observer is short than in air. However, peaks of successive cycles still experience the same delay traveling from the source to the observer. If they are separately by time $\Delta t$ at the source, after the same delay, their arrivals at the observer will still be separated by $\Delta t$. --98.114.146.178 (talk) 17:14, 1 February 2009 (UTC)

To put it succinctly,

$\lambda *f=v_{sound}$

wavelength times frequency = wave speed

In water, the wave speed has changed, and the wave length has changed, but the frequency is still the same frequency due to the source of the noise. Nimur (talk) 17:35, 1 February 2009 (UTC)

Air waves vibrate the ear drum. That stimulates auditory nerves to convey nerve impulses to the brain. If the air waves are at an audio frequency, the brain then experiences "sound". The actual nature of what the brain experiences is as much a mystery as the brain's experience of "color" in response to impulses on the optic nerves. With audio air waves, does the brain respond to the wavelength or frequency of the received audio signal? Is the wavelength of the nerve impulses the same as the wavelength in air? What if the ear channel was filled with water; as Nimur has pointed out,the frequency would be the same but the wavelength would be different; would the sound experienced by the brain be different? – GlowWorm.

Does the brain respond to the wavelength or the frequency of light? – GlowWorm —Preceding unsigned comment added by 98.17.34.148 (talk) 16:11, 2 February 2009 (UTC)

The brain does not respond to light directly; light is first converted by the rod cells and cone cells in the retina, and the messages are passed over the optic nerve. The cone cells, responsible for color vision, probably respond to frequency, rather than wavelength, because the detection of light is a photochemical reaction. In any case, the eye is a fairly controlled, non-dispersive medium with a fixed index of refraction so the frequency and wavelength should be directly related. See visual perception for a high-level overview. Nimur (talk) 17:10, 3 February 2009 (UTC)

Setting up a temporary "cleanroom" at home

What can you do to set up a low-dust environment at home (a makeshift cleanroom of sorts) for cleaning/servicing dust-sensitive equipment (say a scanner)? --98.114.146.178 (talk) 16:53, 1 February 2009 (UTC)

Avoid rooms with carpet. You may be able to buy a HEPA filter but it has been my experience that these are useless. Nimur (talk) 17:35, 1 February 2009 (UTC)

I would say the emptier a room the better. If you have a completely empty room, vacuum the floors, walls and ceiling and then wash them with a wet cloth. It goes without saying that you should keep the door/s (and any windows) closed at all times and turn off any fans. I would expect you'd get a reasonably dust free room although obviously not even close to enough to make microchips Nil Einne (talk) 17:39, 1 February 2009 (UTC)

I suppose take a look at cleanroom for a start. An air filter is a good idea. This might be excessive for your purposes, but a mycology lab used a HEPA quality airfilter to keep contaminating spores and bacteria from mucking up growth media plates. A wood turner I know uses a standard shop vac to cut down on the dust. Before you start, wash down all the surfaces of wherever you set up, including the walls, floor, and ceiling if you can get to it. Maintaining a positive air pressure in your work environment is a good idea. A lot of cleanrooms I have seen have those cleanroom sticky mats which pull dirt and dust from your shoes when you walk over them. Google cleanroom sticky mat for suppliers. As far as ersatz goes, someone from slashdot had this method for making an improv cleanroom:[27]. Hope this gives you some ideas. 152.16.15.23 (talk) 17:48, 1 February 2009 (UTC)

It might be easier to make a chamber with gloves and a window rather than a room you go into yourself. Make sure theres no gap around the HEPA filter. Dmcq (talk) 18:04, 1 February 2009 (UTC)

If you're just trying to keep particulates off a work surface (and you're not worried about nasty fumes or biohazardous materials), the solution may be a laminar flow cabinet. The simplest models are enclosed at top, bottom, and sides. Room air is HEPA-filtered and blown in along the back wall, over the work surface, and exhausted into the room at the front. (The picture in our article shows a Class 2 device that is designed for biohazardous materials; it is equipped with germicidal UV lamps, and the second set of vents at the front of the cabinet collects the exhaust air to refilter it. What you would need is a much cheaper version which exhausts direct to the room — more like this, this, or this.) TenOfAllTrades (talk) 18:36, 1 February 2009 (UTC)

For one off or infrequent use, things like an Atmos bag can act as a portable glove box provided you have a way to fill them with a filtered supply of air. Dragons flight (talk) 23:18, 1 February 2009 (UTC)

TenOfAllTrades beat me to it. Just make an enclosed workbeanch. Improvise a sealed passthrough with gloves. Air enters the top and is drawn through the bottom. Calculate the required flowrate to maintain laminar conditions.

Not sure if you want a medical cleanroom or a fabrication cleanroom, but the following is what I've seen in fab plants. You want smooth surfaces inside, use stainless and Polypropylene. PP is an inexpensive high purity plastic. Exposed stainless steel should be passivated (there is a certain type used in the semiconductor industry that electrochemically blows off surface impurities). In fab pants, new equipment gets a 'superclean' cycle; swab every inch with isopropyl alcohol and special towelettes (made for clean rooms). No paper or pencils allowed inside! (you can order special cleanroom paper). Also, look into a positive pressure feed and looping the air through the filter (polishing). --TungstenCarbide (talk) 00:32, 2 February 2009 (UTC)

PS, not sure what you want a clean room at home for but if it's to screw with your disk drive be careful, that usually requires a class 100, which takes a lot of effort to achieve. --TungstenCarbide (talk) 00:46, 2 February 2009 (UTC)

Back when window-modding of computer hard drives was in vogue, the recommended method for creating an ad-hoc cleanroom was to steam up the bathroom and let the steam (and hopefully any airborne dust) settle out on the walls, then work quickly while it was still humid. This would result in a working hard drive about one time in three. --Carnildo (talk) 01:05, 3 February 2009 (UTC)

The OP said he wanted one for cleaning a scanner. 99.50.50.41 (talk) 17:11, 3 February 2009 (UTC)

Identify plant?

Does anyone recognize the plant at [28] (other pictures of same plant at [29] and [30])? The photos were taken in July in Connecticut. RJFJR (talk) 17:40, 1 February 2009 (UTC)

Is it Echium vulgare or Viper's bugloss? Julia Rossi (talk) 22:18, 1 February 2009 (UTC)

I read the article and it could be. Thank you. (I'm disappointed it doesn't flower perennially, those flowers were pretty and I was wondering if I could plant some). RJFJR (talk) 01:38, 2 February 2009 (UTC)

I guess it depends how you want to feature it. All by itself is too much for it as a monocarpic type of perennial, but mixed with others varieties, it would just keep coming along, if that helps. It looks quite tough, self-seeding in the roadside turf like that. I'd try taking it home to grow roots and all, or leave it on the surface of prepared soil, to shed some seeds on the spot. Julia Rossi (talk) 03:46, 2 February 2009 (UTC)

what are the best arguments for there being no objective truth?

what are the best arguments for there being no objective truth?

See Relativism, also it is a good idea to study objectivism. It used to be a good way to be a bright young pain in the neck and get some groupies to make out with but I think it's a bit passé now. Dmcq (talk) 21:56, 1 February 2009 (UTC)

What are the arguments for there being an objective truth? As far as I know its a reasonable assumption.--OMCV (talk) 21:58, 1 February 2009 (UTC)

It's an unfalsifiable proposition. I can never prove that there IS objective truth because you can always say that whatever evidence I offer is a figment of my imagination. The best we could hope to offer is some kind of Occam's razor kind of thing - but even that is a bit flakey. I don't think there can be any evidence the other way either. If you have proof that there is no objective truth - then that, in itself would be an objective truth - so we can show by reductio ad absurdum that no such proof can exist. Hence we might as well operate under the assumption that universe exists and we along with it because the world would be a mighty boring place otherwise. SteveBaker (talk) 23:23, 1 February 2009 (UTC)

(At some point in this discussion - I'm going to need to say that "Philosophers are a waste of quarks" - I thought I'd get it over with early.) SteveBaker (talk) 23:33, 1 February 2009 (UTC)

A lot of it comes down to defining what one means by "objective" and "truth", as well. Both of those are often presented as if they are straightforward concepts, when both can be quite difficult to nail down in a precise way. --98.217.14.211 (talk) 00:59, 2 February 2009 (UTC)

Electron configurations

For my homework (let me finish, I'm attempting it) there's the following question:

"If the oxidation state of Vanadium is +3 in VCl₃, what is the electron configuration vanadium in VCl₃ and explain why it is considered a transition metal"

I've worked out that I think the configuration is 1s²2s²2p⁶3s²3p⁶4s², but this would mean that it's not a transition metal since it has an empty 3d orbital. I'm guessing I've made a mistake with filling 4s before 3d in this case, should it be 4s¹3d¹, or 4s⁰3d²? Cheers. —Cyclonenim (talk · contribs · email) 21:57, 1 February 2009 (UTC)

Yes, your last configuration is correct (4s⁰3d²). The common rule is that transition metal cations (but not neutral atoms) will lose their s electrons before their d electrons. (Don't worry, I made this mistake until I was well into college :) ) --Bennybp (talk) 22:25, 1 February 2009 (UTC)

Ah I see, thanks. So they empty first just like they fill first? —Cyclonenim (talk · contribs · email) 22:27, 1 February 2009 (UTC)

The statement The common rule is that transition metal cations (but not neutral atoms) will lose their s electrons before their d electrons. needs more qualification. The idea that s electrons empty first just like they fill first is "fudge" general chemistry teachers teach to avoid going into details. Logically and experimentally it doesn't make sense. The electron configuration model your using is accurate when the neutral transition metal is not bound to anything and in its ground state. Finding a unbound transition in a ground state is more the exception than the rule. Most metal centers have something that is described as a coordination sphere or they have metal metal bonds. In solid VCl₃ for example every Vanadium bound to six chlorides (which is shares with neighbors) forming a common octahedral coordination sphere. Once there is a coordination sphere even if the metals not oxidized such as [M(O)L_n] its best to discuss them in terms of ligand field theory or if you are old fashioned crystal field theory. Either way the electron configuration is then described by the d electron count which fits experimental results for metals in complexes (in most situations). With that all said most general chemistry classes are looking for the answer in the form Bennybp provided. Good luck with your chemistry studies.--OMCV (talk) 23:10, 1 February 2009 (UTC)

(ec) Thanks for your expansion, but I do believe that is probably a stage ahead of what I need to know currently. I'm currently studying A level Chemistry, which is a step below an undergraduate degree in terms of scale. The 'general chemistry teacher explanation' is probably good enough for now, but it was an interesting read nonetheless :) —Cyclonenim (talk · contribs · email) 23:16, 1 February 2009 (UTC)

(post ec)What Bennybp said is often true for the transition metals, although you usually fill the 4s before the 3d orbitals according to the Aufbau principle. Some transition metals even in their "neutral" state will "push" electrons from the Ns to the (N-1)d if it means they will have 5 or 10 electrons in their d orbital. Common oxidation states of first series transition metals have 3, 5, or 6 electrons in their d orbital. (I speculate the reason for the 3 and 6 have to do with 3 of the d orbitals being lower energy than the other 2 in certain situations) I go by the principle the more electrons an atom has the more likely it will violate the filling order you would expect. See Atomic electron configuration table

In the first row transition metals the violaters in neutral are:

Chromium with [Ar] 3d⁵ 4s¹. Chromium (III) ([Ar] 3d³) is the most stable, Chromium (II) and (VI) come up often, while (I) is rare although it would seem to make sense.

Copper with [Ar] 3d¹⁰ 4s¹ but note that its most common oxidation state is (II) (3d⁹) rather than (I) (3d¹⁰) which you think would make sense

First row transition metals lose their 4s² electrons before the 3ds with the following common exception: Cobalt (III) (4s¹ 3d⁵). Manganese III and Manganese VI may also have an unexpected electron configuration but I can't find a source to verify it. See [31] for more. 152.16.15.23 (talk) 00:28, 2 February 2009 (UTC)

That last post just isn't up to speed; the author clearly doesn't understand transition metal electron configurations. The "push" idea is still based on metal center not bound to anything and in its ground state situation. As for "common oxidation states" it goes beyond speculation into imagination on the authors part. a quote from his reference.

Some oxidation states, however, are more common than others. The most common oxidation states of the first series of transition metals are given in the table below. Efforts to explain the apparent pattern in this table ultimately fail for a combination of reasons. Some of these oxidation states are common because they are relatively stable. Others describe compounds that are not necessarily stable but which react slowly. Still others are common only from a historic perspective.

This citation is mostly accurate but I would also say most of the M(0) oxidation state are common as well as and few other neglected configuration suchg as Co(I). Its enough to say first row transition metal centers vary from d⁰ to d¹⁰ and depend on many features directly tied to the specific metal center. I can personally verify that Co(III) is usually low spin diamagnetic d⁶. If you don't know what you are talking about don't write anything.--OMCV (talk) 01:00, 2 February 2009 (UTC)

Please don't criticize other editors for attempting to help, especially when they've cited a reliable source. There's always someone that knows more than you do, and the great thing about open discussion is that we all can learn if we listen (or read...). --Scray (talk) 02:21, 2 February 2009 (UTC)

Ok, your right I should have just said that they were wrong and didn't read the source they cited. The personal aspect was a mistake.--OMCV (talk) 03:12, 2 February 2009 (UTC)

There seems to be a disconnect here. There are two ways of answering the question; the easier method is "here's a heuristic (aka rule to follow) which will produce the right answer" and the other is to explain what is really happening. Its possible to apply the heuristic and get the right answer almost all the time, and never understand the physics behind what is going on; at the A-level a student is probably on the "heuristic" level; it is not until one gets to about 3rd year of an undergraduate chemistry degree that one begins to understand the actual bonding symmetry and nature of the metal-ligand bond to the degree that OMCV is describing. So yes, OMCV is scrupulously correct here in his explanation, however no high school chemistry student is going to have the background to parse his explanation. Hence, the heuristic trick of "add 4s before 3d" and "remove 4th level before 3rd level" to get the answer here. --Jayron32.talk.contribs 04:24, 3 February 2009 (UTC)

Frankly I wonder why anyone teaches that form of electron configuration since its utterly meaningless and just makes things confusing latter on. I guess all the other elemental electron configurations are comparably meaningless formalisms used solely to familiarize student with quantum numbers of atomic orbitals and little more. So what Jayron32 said is true and the configurations mentioned above are gospel truth right through the chemistry GREs (at least in the states).--OMCV (talk) 04:37, 3 February 2009 (UTC)

Actually, what I said was that the use of electron configurations is a "heuristic" (aka a teaching tool) as a means of preparing students who otherwise lack the background to learn such concepts. All students in the United States who go on to major in chemistry and chemical engineering degrees learn The Truth(tm) during their studies, usually in physical chemistry and advanced inorganic chemistry classes; though freshman level college chemistry almost always introduces the basics of Hybridization theory and Molecular orbital theory, which begins to deconstruct the standard "high school model" of the atom. Rather than being confusing, it allows a student to get a cursory understanding of the quantum model of the atom, without necessily having to work with Schrodinger's equations and eigenstate functions and all that fun stuff. For a high school student who has no interest in pursuing a career in chemistry, its probably good enough. There's not enough time in the 4 years of high school to teach every student every fact ever learned in every discipline ever. --Jayron32.talk.contribs 05:36, 3 February 2009 (UTC)

As it turns out the ACS accreditation and most universities in the US don't require a regular inorganic chemistry class let alone and "advanced" one for a chemistry degree; And d electron counts aren't covered in every pchem class either. I think pchem could easily be expanded to a year and half and still be a superficial survey of material. My point was that I question the value of the way the atomic "electron configuration" is presented even as a "heuristic" teaching tool and wonder if it is more "historic" (like our appendix). I think this sort of "historic" concepts is an issue in chemistry for example why is crystal field theory still taught and the language of oxidation and reduction is cumbersome? Although I could never unlearn it, I see the value of developing more logical language? The origin of the term "reduction" is from the mass lost when taking a metal oxide to it metallic form, "oxidation" is adding the oxygen back to the metal form to make the metal oxide. Each term boarders on many related meanings which makes the concepts very hard for student to learn.

I understand people taking a survey of the field won't get all the details but it would be nice if chemists didn't waste their time with busy work. All the quantum number are good information but it seems as if the electron configurations are designed to act only as test questions. You note that Hybridization theory and Molecular orbital theory deconstruct the "high school model", as a side note hybridization is taught in most high schools these days since its hard to talk about sigma or pi bonds with out it; Back to my point which is that I think that your ability to see a deconstruction is mostly insight on your own part and no thanks to standard teaching methods. My experience with undergraduates is that they have a hard time connecting what their learning with the real world. They treat science as ritual or game that needs to be played for a year or two in college. They don't feel the need to make chemistry self consistent. I think it might be easier for them if they weren't taught so many contradictory models or at least identified them as contradictory models. If you look classic general chemistry texts like Chang or Silberberg at no point does it say heads up kids now that you are using the hybridization model or MO model, carbon doesn't have the 2s² 2p² configuration anymore. On most general chemistry final you will find questions on each of the three subjects but never have a question asking the students to compare and contrast the hybrization model with the MO model let alone and how our understanding of atomic orbitals work into each model. Then there is the big secret even most chemistry majors never internalize which is the Schrodinger's equations and eigenstate functions only work for a one electron system, the hydrogen like atom; Every other application is an approximation, the value of which is often questionable. I know it might sound like I'm missing your point but I actually appreciate you writing so that I can vent on the subject. Have a good one.--OMCV (talk) 13:21, 3 February 2009 (UTC)

Gaur image

I've been searching tirelessly to no effect for an image that shows an average human next to a gaur. I'd like to see how big it looks, thanks. --Taraborn (talk) 22:06, 1 February 2009 (UTC)

Here's one next to a 4x4 http://flickr.com/photos/pixbykris/2307472690/in/photostream/ Jdrewitt (talk) 22:29, 1 February 2009 (UTC)

I think the gaur facing off the pickup truck is a young one or a female. Wikipedia says a gaur is larger than a bison - that's pretty big. Wiki gives weight and shoulder-height of the gaur. A full grown male can weigh more than a ton and a half. If it was me driving that pickup, I'd put it in reverse and tromp on the accelerator - fast! :) GlowWorm. —Preceding unsigned comment added by 98.17.34.148 (talk) 23:23, 1 February 2009 (UTC)

Well maybe its not fully grown, but it still looks pretty heavy to me though, can easily see that one being a ton, and is the same height as the truck. Jdrewitt (talk) 10:16, 2 February 2009 (UTC)

Here's a couple, [32][33] both dead. I don't think it's very safe to stand next to a live one. SpinningSpark 01:31, 2 February 2009 (UTC)

Testing for air tightness

Is it true that one can test a container for airtightness just by using a lamp in a darkened room to see if any light leaks out? Is so, then you are not airtight?--GreenSpigot (talk) 23:51, 1 February 2009 (UTC)

That method is useful for showing you gaps at edges and joints especially when the material is dark. There are problems of course if the material you used isn't opaque, or you seal edges with a transparent material like epoxy. Then the light can leak out through the epoxy, but the container may really be sealed. On the flipside, you can imagine a case where a series of switchbacks occurs which blocks the light although the material isn't airtight. I suppose it you really wanted to check for airtightness, you could pump said container to a higher pressure, seal it and see if the pressure decreases over time or stays constant. You could also fill the container with colored smoke, water, or some other gas or liquid and look for leakage that way. 152.16.15.23 (talk) 00:47, 2 February 2009 (UTC)

While that method may give you an indication, it is obviously not going to be definitive. Consider the inside of a camera, it is lightproof, but not usually airtight, or even watertight. If you are just checking the hoses of a compressor, for instance, it might not be important that there is a small amount of leakage. If you are dealing with something dangerous like silane on the other hand, you need to use a more professional method. Leaks will usually occur at joints in pipeworks, inspection covers, access plates etc. One way to test is to slightly pressurise with air and use bubble leak detector solution on all the joints prior to letting in the working gas. SpinningSpark 02:24, 2 February 2009 (UTC)

When building rockets, we are very concerned with quality of seals. Rather than a binary "airtight"/"not airtight", we rate a particular vessel as pressure-tested to a certain pressure. Usually this is accomplished by hydro testing, in which the sealed vessel is filled with pressurized water and held at pressure for a specified quantity of time (e.g., "holds 1500 psi water for 10 minutes with no leak" would indicate a pretty darn good seal). I would never trust this "lightbulb test" - light does not "leak", and is a terrible analogy for finding a gas or fluid path. Nimur (talk) 03:52, 2 February 2009 (UTC)

One disadvantage to this method is that an object with a small leak that could have been fixed, or no leak initially, could be destroyed. StuRat (talk) 10:04, 2 February 2009 (UTC)

Sure, but you can start at lower pressure and work up to the rated pressure test. A catastrophic failure at 1500 psi may be manifested as a slow trickle leak at 800 psi. Also, because water doesn't expand or contract volumetrically by any significant amount when depressurized, there's not a lot of danger from a hydro test (pressurizing with gas could lead to explosive decompression). Nimur (talk) 13:26, 2 February 2009 (UTC)

The light test may also fail to detect materials which are gas-permeable, such as certain plastics. StuRat (talk) 10:07, 2 February 2009 (UTC)

Some critical structures (and one that I happen to know about is rollercoaster tracks) are pressurized with nitrogen and have continual monitoring of the gas leakage rates. Any sudden decrease in the rate of leakage can be attributed to a crack or failed weld somewhere in the system leading to it being shut down and tested. These systems are pretty amazingly sensitive - they have to be calibrated to cope with things like the expansion of the metal as the sun shines on it - which increases the volume and temporarily decreases the pressure. SteveBaker (talk) 14:56, 2 February 2009 (UTC)

the optimal test for you is going to depend on the kind of container you are using and how you will be using it. Anyway, here's a leakage test that's used for gas lines: pressurize the container, then spray it's surface with a soapy solution. Bubbles will form at leak locations. --Shaggorama (talk) 19:47, 2 February 2009 (UTC)

To avoid further unnecessary speculation, I should say at this point that the container is a loudspeaker reflex cabinetGreenSpigot (talk) 19:46, 2 February 2009 (UTC)

Just be thorough. Some good tips on sealing your project can be found here. -Shaggorama (talk) 19:59, 2 February 2009 (UTC)

With a speaker enclosure, being perfectly gastight isn't really necessary because the high pressure impulses are of very short duration. All you need is to ensure that the 'impedance' of the leaks is sufficiently high. Although...are you perhaps the OP who was talking to us a month or so ago about making pressurized speaker enclosures to effectively reduce the size of cabinet needed or something? SteveBaker (talk) 16:21, 3 February 2009 (UTC)

February 2

Blood tests

Over a lifetime annual physical exams and diagnostic lab work will have taken blood from the elbow veins many, many times. Is that ever a concern in non-immunodeficient individuals? Thanks. Imagine Reason (talk) 01:32, 2 February 2009 (UTC)

Do you mean, could someone be harmed by removal of blood from the same location? The venipuncture article has information about this procedure. The risks are quite minimal, and relate to the puncture of skin, the vein, and any inadvertently-punctured structures nearby. Removed blood must be replaced through hematopoeisis and other processes, but this is a systemic, not local effect. In other words, if you have blood removed always from the left antecubital fossa, this has no special effect on the blood present in the left arm 10 minutes later - circulation takes care of that. By the same token, the blood tests taken from one arm are expected (within certain levels of approximation) to represent the rest of venous blood. Perhaps I misunderstand your question, though. --Scray (talk) 02:10, 2 February 2009 (UTC)

I guess there might be a question about scarring or weakening of the vein itself...but I have no idea. SteveBaker (talk) 02:40, 2 February 2009 (UTC)

Even under ideal conditions, there is always a small risk of infection associated with venipuncture. If proper precautions are taken and the individual has a reasonably healthy immune system, this risk is quite small. (I don't have statistics handy, but bear in mind that otherwise healthy individuals are permitted to donate blood, platelets, or plasma hundreds of times, generally without incident.)

Repeated insertion of intravenous lines can lead to local scarring of the vein, making it more difficult to insert a needle in the future. This is sometimes a problem for repeat blood donors, and more often a problem for intravenous drug abusers or for individuals who have chronic illnesses requiring frequent, recurring blood draws.

Problems may also arise in individuals whose blood clotting is severely compromised. TenOfAllTrades(talk) 04:33, 2 February 2009 (UTC)

Repeated access to the blood stream is a big problem for hemodialysis patients. That's why they get AV grafts to help with any scarring of a natural vein. --Ayacop (talk) 11:14, 2 February 2009 (UTC)

Snow fleas

Why do snow fleas cluster on the surface of snow? There can be little of nutrient value there. They particularly seem to cluster on the sides of indentations in the show surface, such as footprints. Is there any explanation for this? Thanks. Marco polo (talk) 02:05, 2 February 2009 (UTC)

There can well be all kinds of algae (see Snow algae and Chlamydomonas nivalis) thriving in the thawing snow. There can also be a lot of microscopic detritus adhering to the surface of the snow, especially in the depressions of the surface. I would guess snow-fleas gather to feed on that. --Dr Dima (talk) 03:05, 2 February 2009 (UTC)

Dwarfism due to gas attack?

Are any of the chemical weapons used in the First World War known to cause reproductive genetic damage? Could such damage cause dwarfism? I recently met a man, approximately five feet tall andwith a prepubescent-sounding voice, who said that because his grandfather sustained a gas attack while serving in the war, his mother and all her siblings have dwarfism. A mutual friend describes him as a "storyteller" but confirms he is 25 years old. NeonMerlin 02:48, 2 February 2009 (UTC)

To establish it as a credible fact, there would need to be more than a single incident. I found this book, Veterans at Risk, by the Institute of Medicine (U.S.). Committee to Survey the Health Effects of Mustard Gas and Lewisite, Constance M. Pechura, David P. Rall. "Sulfur mustard causes chromosome breakage and induces sister chromatid exchanges in a wide variety of cells. Epidemiologic studies have also led the International Agency for Research on Cancer to classify sulfur mustard as a human carcinogen. These observations underscore the potential of this compound to induce genetic damage. They also suggest that sulfur mustards could be a reproductive toxin." Dwarfism does not appear specifically mentioned. Nimur (talk) 03:37, 2 February 2009 (UTC)

Wouldn't it have been quite cruel by the grandfather to father more dwarfs after he saw what his first offspring became? That's why I don't believe this. --Ayacop (talk) 11:08, 2 February 2009 (UTC)

Try not to be too judgmental of other peoples' reproductive decisions. Families affected by genetic conditions are often in an excruciatingly difficult situation trying to decide whether or not to have additional children. To say that it was "cruel" for the grandfather to try to have more children after the birth of an affected child is not warranted. We don't know the circumstances of his situation. --- Medical geneticist (talk) 14:49, 2 February 2009 (UTC)

An alternative explanation could be that the grandfather sought some sort of external rationalisation for the fathering of dwarf offspring as he may have been unable to accept that it was a genetic anomaly within himself. Richard Avery (talk) 11:36, 2 February 2009 (UTC)

Achondroplasia, the most commonly recognized form of dwarfism is caused (in the vast majority of cases) by a de novo mutation of a particular nucleotide of the FGFR3 gene. It is plausible that chemical agents that are known mutagens such as mustard gas could increase the rate of spontaneous mutations at mutable sites such as this. However, I couldn't find any references citing such an event. I doubt that the OP's 5' tall friend could have achondroplasia, which is usually associated with much shorter stature (around 4'4" for males) and a very recognizable appearance (disproportionately short limbs vs. trunk). Probably something else leading to proportionate growth restriction, which may or may not be true dwarfism. --- Medical geneticist (talk) 15:17, 2 February 2009 (UTC)

Wind powered

Can you build a machine that moves downwind faster than the wind, without using anything but the wind as a source of energy? Nadando (talk) 05:10, 2 February 2009 (UTC)

I can imagine a machine that operates in two alternating modes. First, it affixes itself to the ground and deploys a windmill to collect and store energy. It would then retract the windmill and use that stored energy to propel itself. Given a sufficiently efficient design (large, lightweight, and reasonably streamlined), the average velocity could exceed the original wind velocity. It might even be possible to take that design a step further and design a machine for continuous operation by having multiple parts that cycle between wind-collection and streamlined advancement. -- Tcncv (talk) 06:29, 2 February 2009 (UTC)

From the article, sailing - "When moving, the motion of the boat creates its own apparent wind. Apparent wind is what is experienced onboard and is the wind that the boat is actually sailing by. Sailing into the wind causes the apparent wind to be greater than the true wind and the direction of the apparent wind will be forward of the true wind. Some extreme design boats are capable of traveling faster than the true windspeed." Nimur (talk) 06:38, 2 February 2009 (UTC)

Here's a fun video which I found while searching... Under the ruler faster than the ruler. Nimur (talk) 06:49, 2 February 2009 (UTC)\

That's not what he asked. Many sail boats are capable of traveling faster than the true windspeed. The question is whether you can go downwind faster than true windspeed. The traditional answer to this problem is no. When the boat matches the windspeed the relative airspeed drops to zero and the boat can not accelerate. APL (talk) 15:55, 2 February 2009 (UTC)

You could split the energy 'generation' by using windmills that transfer generated energy by microwave laser to the ship. In effect, the amount and with it the speed is thus only limited by that of light. --Ayacop (talk) 11:02, 2 February 2009 (UTC)

Given a straightforward interpretation of the question (can a sailboat or the like move downwind faster than the wind?), the answer is no. Once your machine reached windspeed, it would have no further thrust. However, it may be worth noting that sailboats move fastest when the wind is abeam (that is, at right angles to the direction of motion). It might be possible under those circumstances to exceed wind speed in a non-downwind direction. — Lomn 14:12, 2 February 2009 (UTC)

removing duplicated posts... Nimur (talk) 14:29, 2 February 2009 (UTC)

Yes but it wouldn't go faster all the time. A windmill gathers the electric for a while, then it takes off faster than the wind. Wind is a force of gravity and convection. If you can beat gravity downwind or turn it sideways, you may do it. ~ R.T.G 14:17, 2 February 2009 (UTC)

Actually wind has much more to do with pressure gradient force than any of those things </nitpicking> -RunningOnBrains 00:34, 3 February 2009 (UTC)

Certainly it's possible to sail a yacht faster than the prevailing wind. If you have a decent keel - you can aim the boat at (say) 45 degrees to the wind - so the wind is coming from behind - but at an angle. Suppose the wind is blowing from the South - and you are sailing towards the North-East. If your sail was 100% perfect and your boat was infinitely slippery - then for every kilometer the wind moved northwards, you'd move a kilometer northwards AND (because the keel is preventing you from being blown sideways) a kilometer to the east. Your net speed is therefore about 1.4 times the wind speed. Sailing ever closer to 90 degrees to the wind would theoretically make you go yet faster. The practical limit of how close you can get to that ideal depends on the design of the yacht. Land-yachts (which have wheels instead of a keel and have a MUCH lower coefficient of drag than a water-bound yacht can get up to 100mph in a mere 30mph wind! SteveBaker (talk) 14:47, 2 February 2009 (UTC)

OK, but he asked specifically about sailing downwind. Ever since I first heard this problem years ago, I've wondered if a solution like Tcncv's solution above could work, alternating between energy storage and energy use. I can't see any reason it wouldn't in theory, if you could get good enough parts. (If continuous down-wind motion is required, you could imagine all sorts of crazy schemes, imagine two pontoons alternating between stored energy and energy use and leap-frogging each other. Between them is the passenger compartment being dragged along by ropes at the average speed.) APL (talk) 16:06, 2 February 2009 (UTC)

Perhaps this isn't the paradox that physics professors would have us believe. Discussions here, and here. Personally, I fully don't understand how these devices are claimed to work. I'm not sure that they do, or if they do that they work for the reasons provided. APL (talk) 16:36, 2 February 2009 (UTC)

There seems to be very few videos of these devices actually going against the wind 'in the wild' as opposed to a treadmill. Even then they don't seem to make any attempt to measure the speed of the craft or the wind. I suspect wishful thinking of the same sort that plagues perpetual motion inventors. APL (talk) 16:43, 2 February 2009 (UTC)

Rule #1: Anything at all that you find on peswiki.com is crap...anything...no exceptions!

Rule #2: All videos on Youtube that purport to break the laws of physics are faked.

The video of the craft moving rapidly along the road with the little white flag flapping out of the back was probably running downhill. In the shots of the treadmill tests, how do you know there isn't a big fan just off-camera? Scepticism is required here. We KNOW these machines can't possibly work (see Rule #1 above) - it's just a matter of why. Since we know for 100% sure that people WILL fake videos on YouTube (see Rule #2 above) - it's just down to the tedious business of figuring out why. Because you don't know what's happening off-camera, it's a trivial matter to do this stuff. SteveBaker (talk) 03:03, 3 February 2009 (UTC)

OK - so here's another idea. Let's suppose you have a yacht with a big sail and a very slippery hull. We imagine it being pushed through the water VERY close to the wind speed with the wind right behind it. We imagine that if we were able to go any faster than the wind then the sail would collapse and turn into a parachute - slowing the yacht down again - so there would be no way to collect more energy. But we forget that the boat is now moving very fast compared to the water. So could we not deploy a turbine to collect energy from the water that's rushing past at high speed - and use that to produce a little more power to overcome the drag of the 'parachute' sail? I rather doubt it because in order to move at the same speed as the wind (and parallel to it's motion) you need a zero-drag hull - and as soon as you increase the drag by extracting energy from the water - you're going slower than the wind.

OK - so if we are talking about the speed of the yacht in a direction parallel to the wind velocity - then what I said before doesn't work. So can a yacht (or anything else for that matter) move faster than the wind IN THE DIRECTION THE WIND IS BLOWING. I think the answer is a definite "NO" - but it takes some jiggling around with frames of reference to prove it.

It's easier if you forget the wind and think in terms of the frame of reference of the yacht. From the point of view of a yacht with a really HUGE sail and a super-slippery hull that's moving at almost exactly the speed of the wind - and parallel to it - then from the perspective of a guy sitting on the deck, you have (let's say) negligable forward wind speed - but lots and LOTS of water coming towards you. Your hull is so slippery that despite the huge speed of the water - it produces negligable drag - so you can just sit there - despite the negligable wind-speed relative to you. So to move forwards (ie to move faster than the wind - as a "stationary" observer would say)...you have to turn that backwards water motion into forward motion of the boat...but you have to do it in such a way that the drag-force of the water on the front of the boat doesn't increase by as much as the thrust you're generating from it.

I don't see how that's possible - it seems like it would be a violation of conservation of momentum. You can't have the yacht move forwards without the water moving backwards even faster than it is now.

We can go one step forward from there. Since the wind speed is negligable when viewed from the yacht's perspective - we could pretend the yacht was sitting there in a vacuum - with just the water flowing past it's hypothetical zero-drag, zero-friction hull. If it could somehow move forwards against the flow - then we could transfer our mental coordinate system to the frame of reference of the water itself. It would appear that our boat is moving at uniform speed relative to the water (which it can do - per Newton's laws - providing it has a zero-drag hull) - but then suddenly it accelerates without any source of motive power! Where did the energy come from? SteveBaker (talk) 19:57, 2 February 2009 (UTC)

If you use the difference between wind speed and water speed to produce energy, the boat will have a limitless source of energy, and the boat can have arbitrarily low friction, so there's no limit to how fast it can go. Interestingly, even if you only use the wind and the boat (or airplane, which would work better for this case), you can still go faster than it. Imagine the air is stopped and you are moving, which is equivalent. Turn around. Of course, that limits your top speed. — DanielLC 22:59, 2 February 2009 (UTC)

You didn't read a single word of what I just wrote - did you? It's a matter of conservation laws. The boat has to (at some point) travel at the same speed as the wind. At this point the air is stationary relative to the boat. So you have a boat travelling through water - and according to Newton's laws - it'll continue at a constant speed until acted on by an external force. Where is that force coming from? It can only be from the water (since the air is effectively stationary relative to the boat). In order to extract energy from the water, you need to change it's momentum. But conservation of momentum says that you have to push the water YET FASTER behind the boat in order to allow it to move forwards. So what concievable thing could SPEED UP the water and use that to make the boat go faster? Nothing - because to do so is to violate all three laws of thermodynamics. So this CAN'T work...it just can't. SteveBaker (talk) 03:03, 3 February 2009 (UTC)

The question was about traveling downwind. I don't think there is any known or theoretical craft that can do that. APL (talk) 00:09, 3 February 2009 (UTC)

I'm pretty certain it should be possible to make a land vehicle that goes downwind faster than the wind. I'm not certain if that video where they claimed it was happening really had a machine that would do it as it would be quite difficult to achieve. The under the ruler faster than the ruler video shows the principle. You just have to use the wind instead of the ruler. An interesting aspect is that using a turbine it should go in the opposite direction to which one would expect when the wind blows on it, I couldn't see in the video if that was happening. Dmcq (talk) 00:08, 3 February 2009 (UTC)

These are two VERY different scenarios. By going faster than the wind, you actually introduce forces in opposition to your movement, as opposed to the ruler, which is still providing a forward thrust to the cart.-RunningOnBrains 00:34, 3 February 2009 (UTC)

They are not different scenarios. You might see it easier if you attach little paddles round the big wheel in the video and only blow over the top wher the ruler went. The paddles at the top would still go slower than the wind even though the vehicle goes faster. The same would happen with a turbine suitably geared. This is why the turbine would appear to be going round the wrong way. Dmcq (talk) 01:12, 3 February 2009 (UTC)

Several people have pointed out scenarios where one can reach speeds faster than the wind by traveling at an angle to the wind. If you can do that, then all you need is a way to efficiently turn. Carry that extra momentum with you as you turn to the same direction as the wind, and you will for a while be able to coast at a speed faster than the wind. Once you lose momentum, turn back to an angle to pick up speed again. Lather. Rinse. Repeat. Assuming the vehicle can turn efficiently enough and coast at very low drag, it should be possible for one to travel with an average velocity greater than the wind. Dragons flight (talk) 00:49, 3 February 2009 (UTC)

There is no denying that you can attain a SPEED greater than that of the wind. Yachts do it all the time. The question is whether you can move fast IN THE DIRECTION THE WIND IS BLOWING (ie: If the wind is blowing from the south, can you move northwards faster than the wind. Zigzagging does indeed let your speed be much higher than the wind - but your net progress IN THE DIRECTION OF THE WIND won't be any faster at all. SteveBaker (talk) 03:03, 3 February 2009 (UTC)

Steve, if you are moving faster than the wind speed at a angle and you turn to the direction of the wind, then conservation of momentum will now have you moving temporarily faster that the wind in the direction of the wind, at least until friction and air resistance slow you down to match the wind speed. This may not be practical in a boat, but I am fairly sure one could achieve useful results with a sail car. The turning allows one to achieve temporary bursts of speed in the direction of the wind that exceed the speed that the wind blowing behind you could support. In other words, by zig-zagging under the right conditions, one can achieve an average speed in the direction of the wind that is faster than the wind. Dragons flight (talk) 06:36, 3 February 2009 (UTC)

Momentum is a VECTOR quantity - not a SCALAR. SPEED is not the same thing as VELOCITY - and momentum is MASS x VELOCITY - not MASS x SPEED. Hence when your boat turns a corner - momentum isn't being conserved so some energy input is required. Bottom line is that to turn a yacht you need either a winch or some big muscular sailors hauling on ropes. That's an energy input - and once you have that, it's not a closed system anymore - so all bets are off. SteveBaker (talk) 16:14, 3 February 2009 (UTC)

Actually, I think the key factor is the water. By turning the boat (which requires a small amount of energy input, admittedly) you change the hydrodynamics and the water pressing against you is what changes your velocity. Consider a glider - the energy required to move the flaps (or whatever part of the glider it is that makes it turn) is minuscule compared the the energy required to turn the glider around, that extra energy comes from the air (well, I'm not sure there's an actual transfer of energy, but in any case it's interaction with the air that changes the momentum). --Tango (talk) 16:22, 3 February 2009 (UTC)

Are sailboats and yachts limited to wind speed when heading directly downwind? Yes. However, the original question involved a "machine that moves downwind", and is not limited to a sailboat (with relatively few moving parts). We are free to design a much more complicated machine, one such design I put forth below.

• The machine would consist of multiple Wind Energy Collection Assemblies (WECAs) that would take turns collecting, converting, and supplying energy to the base assembly that would use that energy to drive its propulsion system.
• Each WECA would contain a wind collection device, such as a turbine, plus a ground support structure (legs) that would brace the WECA against the ground.
• Two or more WECAs would be mounted on a tank-track-like system that would rotate such that the top of the track remains stationary relative to the ground, while the bottom advances at 2x vehicle ground speed.
• Each WECA would have a deployed and retracted configuration. While a WECA is on the top of the track, it would deploy its support structure and wind energy collection device. As the back end of the machine reaches a WECA. that WECA would disengage its ground supports, retract its wind collection device, and configure itself in a compact arrangement for transport to the front of the machine, where it will redeploy for another cycle.
• Energy collected by the WECAs would be used by the base assembly to power the machine's propulsion system, such as power driven wheels, and to replenish any energy lost by the other moving parts due to mechanical friction.

Would it work? The ground supports will transfer the reactive force from the wind energy collection to the ground, so there is no force acting against the WECA track. With an even number of WECAs on the track, conservation of momentum will allow the WECAs to rotate through the system with no sustained energy requirements. The mechanism for deploying and retracting the WECA could be designed using energy recovery techniques. A streamlined enclosure would be designed around the propulsion system and the lower part of the WECA track (including the advancing WECAs) to minimize air resistance. Note that the energy gathered is dependent on the gradient between the wind and the ground, and does not depend on vehicle speed.

Energy collection would be limited by the size of the deployed wind collection devices, which could be arbitrarily large. Some energy collection opportunity would be lost during the time its takes for each WECA to reconfigure itself between deployed and retracted. Energy losses would include vehicle aerodynamic drag, the aerodynamic drag of the retracted WECAs being transported internally, ground friction, and the mechanical friction from the sum of all moving parts. With good engineering, this loss could be kept to a minimum (theoretically approaching zero). The difference collected and lost energy is available for propulsion, and could accelerate the machine up to a speed at which the energy losses match the energy collected. Theoretically, with a machine of sufficient scale and engineering perfection, there is no upper limit.

Could it be be built? I believe it would be quite an engineering challenge, but I think the concept is sound. Have I missed anything? -- Tcncv (talk) 03:56, 3 February 2009 (UTC)

Yeah - you've missed EVERYTHING! As the vehicle accelerates to a speed equal to that of the wind - there is a point when there is zero relative wind-speed. To someone standing on top of the vehicle, it would be exactly like the wind just stopped blowing. At that moment, where do you collect the energy from to accellerate the vehicle to higher speed? It's exactly like saying that I could make my car go faster by collecting the air that's pushing against the front of the car at 50mph and use that to make the car go faster. You simply can't do that - it's a perpetual motion machine and the laws of physics won't let you do that. This whole thread is just a matter of people wildly speculating without looking at the very basic underlying physics. There is simply no such thing as perpetual motion. I don't care how clever you get with WECA's and other bullshit - I don't even have to read your long explanation. You can't beat the laws of thermodynamics no matter how hard you try - period. Just give it up. 16:06, 3 February 2009 (UTC)

Right. From the reference frame of the vehicle, the wind has stopped moving. But now the ground is moving BACKWARDS. THAT is what you harness. Get out of the mindset of thinking that your energy comes from air moving relative to the vehicle. It doesn't. It comes from the GROUND and the AIR moving RELATIVE TO EACH OTHER. Maelin (Talk | Contribs) 16:44, 3 February 2009 (UTC)

It certainly is possible. Here is a video of some fellows testing such a device under fairly careful conditions. They first show the video of someone performing the experiment on a road, and then produce a replica of the device on a treadmill. Maelin (Talk | Contribs) 15:52, 3 February 2009 (UTC)

You can't tell anything from those videos. Remember: a YouTube video does not constitute scientific evidence - people make fake YouTube videos all the time - and we get asked about them here all the time. The device running down the road is probably going downhill - the road looks level - but if the camera is mounted horizontally in the car and the car is going down the same hill - then that's exactly how it WOULD look. In the case of the treadmill, there is probably a fan blowing on it off-camera. Please don't fall for that kind of crap. This is a classic "free energy" nutjob thing - it's been around for years - along with all of the other crazy perpetual motion machines. SteveBaker (talk) 16:06, 3 February 2009 (UTC)

I've just had a good look at that video and it all seems to be in accord with how I would expect such a machine to work and the fan is turning the way I thought it would rather than how a hoaxer would do it and th proportions seem about correct. I believe it is all kosher. I'm surprised it worked quite so well, perhaps there is hope for one that would actually work in 5 knot winds on water. Dmcq (talk) 16:22, 3 February 2009 (UTC)

How do you account for Steve's point that when travelling at wind speed, there is no wind? Where does the energy come from to get you past that point? Are you trying to collect energy from the wind going backwards once you are faster than wind speed (having used stored energy to get there)? Doesn't the added drag from such a system at least balance the energy gain? --Tango (talk) 16:27, 3 February 2009 (UTC)

When travelling at wind speed the propellor is driven by the wheels to cut into the wind and pull the cart forward into the wind. Drag will eventually limit the speed but is not enough at that point to overcome the energy generated using the difference between the air speed and the ground speed. Dmcq (talk) 16:36, 3 February 2009 (UTC)

The energy comes from the fact that the air and the ground are moving relative to each other and that for all intents and purposes they are immutable things. The fact that it's air just confuses matters - you'd be better to look at those charming "Under the ruler faster than the ruler" videos (first one here) to see how such a system is perfectly plausible. Maelin (Talk | Contribs) 16:42, 3 February 2009 (UTC)

do insects have kidneys?

… and if it has a different name, which is it? I'm sure they have, as they also have blood which must be cleaned somehow. The insect article anatomy picture doesn't show anything, nor does the kidney article have an evolutionary section. --Ayacop (talk) 10:55, 2 February 2009 (UTC)

Do they have blood? they dont have a circulatroy system. And the insect article says that they have no closed veins or arteries. So I dont see how there could be a fluid analogous to blood from larger organisms. —Preceding unsigned comment added by 129.67.37.225 (talk) 11:43, 2 February 2009 (UTC)

The equivalent of blood in insects is hemolymph. I believe it does carry waste away from cells, so I guess there must be some way of filtering it. I've found a paper ([34]) talking about it. I haven't researched it in detail, but there is clearly something that serves an equivalent purpose to kidneys in insects. --Tango (talk) 11:51, 2 February 2009 (UTC)

See Malpighian tubule system. Gandalf61 (talk) 12:04, 2 February 2009 (UTC)

Do not expose to direct sunlight

Does that mean "while switched on"? ~ R.T.G 13:49, 2 February 2009 (UTC)

No. APL (talk) 13:51, 2 February 2009 (UTC)

Well its short but i sort of believe it :) ~ R.T.G 14:18, 2 February 2009 (UTC)

It depends, though. If it's a camera with a sensitive image sensor, it might not do to point it at the sun: but if the shutter is closed because it's off, nevermind.

It would help to know what the heck you're talking about...but unless it's a bomb with a solar-powered detonator...it's hard to imagine anything that would be damaged by sunlight exposure ONLY when it's switched on. SteveBaker (talk) 14:37, 2 February 2009 (UTC)

Many plastics break down in the presence of UV light from direct sunshine and many types of paper yellow and weaken; such products should always be kept out of direct sunlight. StuRat (talk) 17:47, 2 February 2009 (UTC)

Yes, indeed - but why only "while switched on" - as the OP asks? SteveBaker (talk) 18:57, 2 February 2009 (UTC)

I just made a general comment about why to avoid direct sunlight, which applies when on or off. My comment wasn't an answer to you, it only appeared to be because you hadn't indented your answer to the Original Poster. StuRat (talk) 21:59, 2 February 2009 (UTC)

In my student days, I turned on a sensitive detector while the lights were on in the observatory, thereby annoying my astronomy professor. Clarityfiend (talk) 19:32, 2 February 2009 (UTC)

Turning it on and off shouldn't have made any difference. Un-capping it in sunlight would be the problem. SteveBaker (talk) 20:22, 2 February 2009 (UTC)

Maybe they are trying to avoid the equipment becoming toast or starting a fire.76.97.245.5 (talk) 20:56, 2 February 2009 (UTC)

LCD screens can be damaged by prolonged sun exposure. I can only find forum postings as sources [35], but I'm pretty sure it's true.-RunningOnBrains 00:41, 3 February 2009 (UTC)

Well, my lcd monitor can get some direct sunlight from behind it and I just was switching it off or closing the blinds and it is only temporary but I had to worry if it was still getting damaged (and my computer is in the same situation). Sometimes the sun is hot around here, even when its been snowing, so hopefully I don't wreck my little monitor or my nice computer. Although not using as much energy as CRT, LCDs do cope with more localised heat but that doesnt mean that UV doesn't degrade it. ~ R.T.G 12:10, 3 February 2009 (UTC)

The degradation due to sunlight is the same no matter whether it's turned on or off...it's a pretty tiny effect though. I wouldn't worry about it personally. SteveBaker (talk) 15:14, 3 February 2009 (UTC)

OK thanks Steve ~ R.T.G 16:36, 3 February 2009 (UTC)

wind power

Is there any wind power or wind mills to generate current for a individual home(220v) in a city?Prince sha (talk) 14:32, 2 February 2009 (UTC)

If you google for "domestic wind power" you'll find a ton of small windmills suitable for powering an individual home. Their effectiveness in a city may be a little tricky though - adjacent buildings could do some very strange things to your wind-flow. Also, in a confined space you may find that your local planning laws prevent you from putting one up. SteveBaker (talk) 14:40, 2 February 2009 (UTC)

Plus small single domestic installations rotate fast and make a lot of noise. However tiny top up wind turbines to provide a small amount of electric power are possible although uneconomic. [36] discusses one put up by the leader of the opposition in the UK. --BozMo talk 14:47, 2 February 2009 (UTC)

Wow! In the study, one of the domestic wind turbines didn't generate enough electricity to power it's own electronics! Ouch! The average turbine produced 214 watt/hours per day...so three or four lightbulbs. They say that on average people are saving 33 UKpounds per year from their 1500 UKpound investment. Since I very much doubt they'd survive 45 years of continual service - they'll never pay for themselves. However, the study also showed that one of these turbines that they studied DID produce enough electricity to run the house because it was situated on top of a 10 storey building. So it all CRUCIALLY depends on where the thing is situated...because anything from using more electricity than it makes(!) to running your entire house is a pretty huge range - and if the average is a 45 year payback time - then you'd better be installing it somewhere very much better than the average household is managing to do! SteveBaker (talk) 20:21, 2 February 2009 (UTC)

Hand over your geek card, Steve... It's "watt hours", not "watt/hours" - it's power times time, not power divided by time. And three or four lightbulbs might use around 214 watts, not 214 watt hours (unless they were on for an hour). You're a disgrace... --Tango (talk) 16:09, 3 February 2009 (UTC)

Old-fashioned windmills have wide, slow-turning, blades. Modern wind-powered generators have narrow blades. Would wide, slow-turning blades be best for low wind velocities? It seems that the wide blades would generate more torque, which would partly compensate for their slower speed of rotation. A wide-blade windmill might also make less noise. —Preceding unsigned comment added by 98.17.34.148 (talk) 17:35, 2 February 2009 (UTC)

It's probably safe to assume that the manufacturers already tried that. It's certainly notable that airplane and helicopter propellers (which are really just backwards windmills) are all very skinny - but boat and submarine propellers are always very fat and short...and so are desk fans and airconditoner fans. SteveBaker (talk) 20:21, 2 February 2009 (UTC)

For mounting on the roof of a city building, such as a 3 story apartment building, consider a vertical axis wind turbine. They are more attractive than the horizontal axis ones, and can be mounted much like a TV antenna, resting on a plate on the roof and guyed to the wall of the staircase projection. Installation cost/payback is the question. Edison (talk) 20:25, 2 February 2009 (UTC)

Savonius wind turbines are easiest to DIY. Although they are less efficient the low installation cost makes them one of the more economical choices for a home installation. AFAIK they are also less fragile in case of occasional high winds, which can break DIY horizontal axis designs. Studying wind patterns throughout the year to find the best location for installation is definitely indicated. Just putting it on the roof of a shed because it looks good there isn't the thing to do. 76.97.245.5 (talk) 21:13, 2 February 2009 (UTC)

Many are available for that and as I live in a windy area myself I was enquiring about it and a very good expert swore to me black and blue that they need to be way up in the air, that rooftop ones are more or less crap. Now I looked into it a lot and if you have a lot of wind I reckon you could get you lighting and stuff but to be fair to the guy (the guy involved in Scoraigwind as it happens), to power your cooker and fridge etc. you need wind strong enough to force the blades against strong magnets. You need something like 20 metres clearance for the best wind and in a city, the houses slow the wind down, nevermind tall commercial buildings and apartment blocks. ~ R.T.G 16:42, 3 February 2009 (UTC)

In saying that, if you can put one up in the air (citys wont let you do that) you can make them out of car alternators with a basic mechanical, carpenting skill. Look at http://www.scoraigwind.co.uk it gives stacks of info and links ~ R.T.G 16:45, 3 February 2009 (UTC)

People who "Don't like music"

I have a friend who has claimed over the years that he "doesn't like music" and I believe him. Oddly enough however if you spend time with him you'd think he's hyperactive and he will ALWAYS be humming or singing a song - usually with the lyrics corrupted to something else - or just repeating a tune to a popular song. This might seem contradictory, but I gather he doesn't intentionally listen to music, but if he hears any it will get stuck in his head.
Notably, he has a form of dyslexia, an above-average IQ and above-average level of general knowledge. He strictly only listens to talk radio.
Based upon his remarks I assume he has no "appreciation" of music, and has no favourite songs".
Do you have any references or explanations for this type of thing?
From my unhelpful googling for other cases, someone suggested checking if he's tone deaf or has other audio-perceptual problems - but the other day in the car he managed to hit the requested note when repeating a song -- and all his other songs tend to be in tune.
Rfwoolf (talk) 17:06, 2 February 2009 (UTC)

If it comes to that, a lot of people don't like classical music.

Maybe he doesn't like music precisely because it gets stuck in his head, which can be annoying. StuRat (talk) 17:43, 2 February 2009 (UTC)

I have no explanations, but I can do anecdotes, if that helps: I have nothing against music, but I rarely make an active choice to listen to it. It just doesn't interest me. I have great difficulty making out the lyrics in songs, but I don't know if that is cause or effect. I hum and sing to myself about as much as anyone else, I think. I am a mathematician and am quite interested in music from a technical perspective, and I do appreciate music when I do listen to it. I have, at various times, played the recorder, piano and trumpet, although never had the dedication to get anywhere with them. I'm not dyslexic, but I do have an above-average IQ and level of general knowledge (like most Ref Deskers, I guess!). I don't know if any of that helps. --Tango (talk) 18:40, 2 February 2009 (UTC)

One explanation may be rooted in human communication. Research found that when people are talking they are trying to reach a common "hum". Individuals higher up in the hierarchy literally "set the tune" with lower level people "chiming in", (Our language developed phrases for this before science found what was going on.) So people who are attuned to communications are more prone to being influenced by ambient muzak. (I bet you can find the study wigh some googling. I'm afraid I'm a bit too busy to dig it up.) There's even an association that has been trying to limit the use of muzak. My sympathies to your friend. It must be somewhat like hearing the phone ring running to pick it up and finding it was on TV. 76.97.245.5 (talk) 20:36, 2 February 2009 (UTC)

Thanks for the interesting comments. The idea about communication is interesting and I will continue to monitor his communication skills and communication behaviour. I'm still trying to fathom through what you're trying to say though - are you saying people that tend to "set the tune" would be put off by music, while those of us that "chime in" would like to 'chime in' to a song? Or are you saying conversely that those of us that are better at communication in terms of oration, diction, tone, emphasis, expression etc would appreciate music more than those who lack the aforementioned? (I tend to think that a person's taste in music could be linked to that -- people that favour rap music for example, compared with those that favour classic music, or those that favour jazz, or heavy rock - surely it is about expression, and therefore no matter how tone-deaf, monotone, tone-deaf, or communicationally unadept an individual is they will always find something in the musical spectrum that they like??). I will keep thinking. Thanks again Rfwoolf (talk) 22:08, 2 February 2009 (UTC)

For myself I can't see why people would want to listen to a piece of music more than once or a couple of times. There may be a few films or books one wants to read more than once but going around listening to the same bit of music 50 times just seems weird to me. Dmcq (talk) 09:42, 3 February 2009 (UTC)

Earthing

What is the reason behind earthing a electric neutral wire.If earth is used for conducting electricity then why does a wire needed for it? —Preceding unsigned comment added by 120.89.115.198 (talk) 18:22, 2 February 2009 (UTC)

The earth is only there for safety purposes, it makes sure any electricity that gets to the wrong place (eg. the metal casing of the device) goes safely the earth rather than shocking anyone that touches it. The neutral is there is complete the circuit in ordinary circumstances. --Tango (talk) 18:33, 2 February 2009 (UTC)

In some countries the "neutral" isn't earthed, but is "negaitve live". It is a perfectly valid way of doing things, but isn't the UK way. -- SGBailey (talk) 18:46, 2 February 2009 (UTC)

Which particular countries are you thinking of? I would be interested in how they do it.--GreenSpigot (talk) 19:40, 2 February 2009 (UTC)

Also in those countries, is the negative live always negative or does it have alternating voltage on it?--GreenSpigot (talk) 20:13, 2 February 2009 (UTC)

May be one of those urban legends. Or I may have been thinking of US 240V supply. In any case I haven't found a reference, so forget it. -- SGBailey (talk) 21:49, 2 February 2009 (UTC)

(edit typos)In the early days of telegraphs and telephones, it was discovered that substantial money could be saved by running only 1 wire per circuit from terminus to terminus, and using a buried metal plate or ground rod to connect to the earth at each terminus. When 2 wires were used per circuit, it was called a "metallic" circuit. There was less noise and crosstalk with a 2 conductor metallic circuit. Some high voltage DC transmission lines have a + and - conductor, but in an outage of one conductor, they can operate with the other conductor and a ground conductor. In your home, the grounding of the neutral is a safety measure. Without it, a transformer failure or a broken high voltage line falling on the wires to the house could result in the full high voltage being on all the wires in the house, electrocuting anyone who came near anything electrical. What is a "negative live? Maybe they refer to providing 2 wires with 240 volts between them. In countries I am familiar with, there would still have to be a ground conductor from the utility to the building to ground the switch/breaker/fuse enclosure, so that an insulation failure does not energize it at 240 volts to ground. This would be true even if it is 3 phase service or 240 volt service without a neutral. Edison (talk) 20:21, 2 February 2009 (UTC)

AFAIK, Neutral is earthed by the the electricity company at the substation. Earthing neutral in your home sounds a bad idea that would unbalance the system. Earthing earth should be done locally (and at the sub-station). -- SGBailey (talk) 21:49, 2 February 2009 (UTC)

That's my understanding as well (at least for the UK). --Tango (talk) 22:48, 2 February 2009 (UTC)

In a typical U.S. home, we get a single "240VAC" phase delivered on two wires plus a ground wire to the Electrical distribution panel in the home. At the distribution panel, ground wire is tied to anther ground wire that in turn runs to a long copper rod that is driven into the earth outside the home. In the panel, the house neutral and the safety ground are both connected to the panel ground. approximately half of the home's "120VAC" circuits use one of the two hot wires and neutral. The other half of the "120VAC" circuits use the other hot wire and neutral. the "240VAC" circuits in the house are connected to both hot wires. -Arch dude (talk) 00:08, 3 February 2009 (UTC)

From our article on ground and neutral, it seems that both European and North American installations generally link earth and neutral wires at some point between the final distribution transformer and the end user's fuse or breaker panel. Separate earth and neutral wires are only maintained inside the residence. TenOfAllTrades(talk) 00:02, 3 February 2009 (UTC)

So ArchDude, in the US home you get 2 phases: each of 120V balanced about ground. Is that what you are saying?--GreenSpigot (talk) 01:04, 3 February 2009 (UTC)

Nope, it's single phase, or split-phase. You could say one line is ∠0° and the other ∠180°, but that's just a matter of how you are measuring, there is still only one waveform. It's "balanced" if there are equal loads on each line and there is no current through the neutral. The neutral wire between the breaker box and the pole transformer carries a current equal to the difference in the currents of the other two lines (see Kirchhoff's Current Law). Typical distribution systems in the U.S. are "wye circuits" and are grounded at the breaker box, the pole transformer, each pole, and the step-down transformer at the substation. Most transmission lines, and i think some distribution systems are "delta circuits"—no neutral wire so no connection to ground.—eric 02:57, 3 February 2009 (UTC)

Also, SGB seems to be contradicting him/herself by at once saying that earthing the neutral in the home is a bad idea and then proposing that it should be done locally (in addition to the substation)--GreenSpigot (talk) 01:10, 3 February 2009 (UTC)

see Earthing system.—eric 03:03, 3 February 2009 (UTC)

As noted in previous Q&A, in U.S. residential wiring the power company provides one phase with 120 to ground from each hot wire and 240 between the hot wires. The neutral and ground conductors are bonded together at the transformer and then at the house main breaker panel. In the house, the neutral carries the imbalance between the 2 hot conductors back to the main panel, if 2 hot wires and a neutral are used as a set. More modern wiring provides a neutral for each hot wire, since with electronic loads the neutral currents do not cancel like they tended to with resistive or reactive passive loads. There are some customers in downtown areas who get 120/208 volt service, since they actually are provided with 2 phases 120 electrical degrees apart. Each hot wire is 120 volts from ground/neutral, and the voltage between them is 208 volts. This system is for the benefit of busnisses who need three phase service, and who just have the third phase brought in. Edison (talk) 16:11, 3 February 2009 (UTC)

Would lens flares ever have motion blur?

I was just curious if real world lens flares would ever have motion blur? --70.167.58.6 (talk) 19:32, 2 February 2009 (UTC)

Motion blur is a consequence of the recording technique you are using - film, digital photosensors, etc. If the light source is moving - then the lens flare must also move - and the recording media can't tell whether the light that's hitting it is a lens flare or light from an actual object - so, Yes - lens flares do exhibit motion blur in things like cameras, etc. Human eyes don't exhibit lens flare per-se - although you do get effects like starbursts from bright light due to the behavior of our eyelashes. Our brains visual cortex "hides" motion blur from our consciousness - so we don't really "see" it as such - although if you could monitor the output of a rod or cone cell, it would have to be there because no image sensor can ever be infinitely fast. SteveBaker (talk) 20:06, 2 February 2009 (UTC)

[medical Q] identify a tool

What is this tool called? It's, I think, informally called a "stripper" and is used, if I understand it correctly, to clamp an IV (infusion) tube and roll the tube through the tool in order to push the tube's contents down along the tube and out.—msh210℠ 22:00, 2 February 2009 (UTC)

Yes, "stripper" is correct. The same tool is pictured in online catalogs here and here. --Scray (talk) 04:00, 3 February 2009 (UTC)

Black dwarf sun and planets drfiting

The time the sun becoems a black dwarf, is it trillion of years. Since sun will have lost about 90% of gravity by the time it becomes a white dwarf, is this possible Uranus and beyond would have flown off it's orbit? Why will planets eventually drift away and left with black sun with no planets around it?--69.226.46.118 (talk) 23:22, 2 February 2009 (UTC)

According to Stellar evolution#White dwarfs, the Sun should only lose about 40% of its mass. The planets will move into higher orbits, but they won't escape completely without some kind of external interaction (another star passing close by, perhaps). Baring such interactions, the radiation of gravity waves will cause a loss or energy and the planets will very slowly spiral in (over the course of trillions of years, if not longer). --Tango (talk) 00:11, 3 February 2009 (UTC)

• They said on Formation and evolution of the Solar System eventually sun will just be left with no planets orbiting around it. And what does and the planets will very slowly spiral in (over the course of trillions of years, if not longer). mean?--69.229.108.39 (talk) 00:53, 3 February 2009 (UTC)

  General relativity predicts that orbiting objects will emit gravity waves. This means there is a loss of energy so the planet will fall towards the sun (just friction causes a ball rolling round inside a funnel to fall towards the middle). On the scales of planets orbit the sun (rather than, for example, neutron stars orbiting each other), this effect is tiny, so it would take trillions of years for the planets orbits to decay noticeably. --Tango (talk) 15:12, 3 February 2009 (UTC)

Talking about 90% of gravity is awkward since the force of gravity changes over distance. It would be better to talk in terms of mass. Assuming a circular orbit for Uranus, the mass of the sun required to keep it in place at a certain distance r and orbital velocity v is

$m_{sun}={\frac {r{v}^{2}}{G}}$

where mass is in kilograms, r is the distance from Uranus to the earth in meters, and v is the velocity of Uranus orbiting the sun in meters per second and G is the gravitational constant. If Uranus hasn't slowed down or changed its radius from the sun appreciably by the time the sun loses a significant portion of its mass, you can see that rv² will stay the same but because the mass of the sun has dropped

$m_{sun}<{\frac {r{v}^{2}}{G}}$

This means that Uranus's orbit must change. Either it will settle out in an orbit more distant from the sun or it will escape entirely. For it to escape the gravitational effect of the sun it must have a high enough velocity. The escape velocity is given by:

$v_{e}={\sqrt {\frac {2Gm_{sun}}{r}}}$

which expressed in terms of v_e is

$m_{sun}={\frac {{v_{e}}^{2}}{2Gr}}$

If $m_{sun}<{\frac {{v_{uranus}}^{2}}{2Gr}}$ then Uranus will escape. I leave it as an exercise to the reader to determine if Uranus will escape given the questioner's parameters. (Translation: I feel too lazy to track down the speed of Uranus, the average orbital radius and plug it in myself) 152.16.15.23 (talk) 00:54, 3 February 2009 (UTC)

February 3

Front and back

There is a form of Antipredator adaptation where the front end of an animal looks the same as it's back. What is this called? (... and do we have a page?) 76.97.245.5 (talk) 00:18, 3 February 2009 (UTC)

The Rubber Boa when threatened hides its real head under the rest of its body and uses its fat stumpy tail as a decoy to lure predators into attacking its back end rather than the front. Its apparently convincing judging by individuals observed with quite a number of scars on the tail. I don't know if this type of mimicry has a particular name. 152.16.15.23 (talk) 01:03, 3 February 2009 (UTC)

Then there's the creepy earwig. StuRat (talk) 15:04, 3 February 2009 (UTC)

Just found the name for it: Automimicry 152.16.15.23 (talk) 01:33, 3 February 2009 (UTC)

Thanks a million.--76.97.245.5 (talk) 01:46, 3 February 2009 (UTC)

Breeding budgies and cockatiels

Is it possible to work out what the baby birds will look like, just by looking at the colour and markings of the parents and not knowing anything about their genetics or pedigree? The Budgerigar colour genetics and Cockatiel colour genetics articles don't really answer my question and use wording that I don't really understand. --84.68.231.212 (talk) 00:44, 3 February 2009 (UTC)

To help with understanding the wording, I would start by looking at Dominance (genetics) and dominance relation. If you can look at your birds and determine their phenotype you can hazard a guess at their genotype and do a Punnett square to determine what patterns of genes the offspring will receive. Once you know the genes the offspring have, you can hazard a guess at what phenotype they will have. You probably will not be able to determine appearence absolutely as there are many genetic factors which interact with one another (see Variable Expressivity and Penetrance) and some aspects of appearence are determined randomly. It may help if you can describe what varieties of birds you have: i.e are they an albino variety? Have a look at the list of common names for Budgerigar varieties and that mess of description in Cockatiel colour genetics. 152.16.15.23 (talk) 01:29, 3 February 2009 (UTC)

btw (sorry, don't have an answer - I never breed my birds for colour), those '...colour genetics' articles (which I've been minimally involved with) could probably do with a good cleanup and some rewriting from a more general perspective. Hint, hint... ;) --Kurt Shaped Box (talk) 02:51, 3 February 2009 (UTC)

Antidepressent

Medical question removed SteveBaker (talk) 02:26, 3 February 2009 (UTC)

I'm not sure that this question:

"This section says that semen has antidepressant properties. What would be the effects of injecting semen intravenously? Would shooting up semen (that's a horrible pun :) ) give you a better mood? flaminglawyer 01:10, 3 February 2009 (UTC) "

-constitutes a request for medical advice. The Flaming Lawyer is simply posing a hypothetical question (as lawyers do).

The answer, by the way, is that you'd most likely die suddenly from the semen embolism lodging in your cerebral arteries (causing a stroke) or coronary arteries (causing a myocardial infarction). So don't do it!

The Semen article does mention the putative antidepressant qualities of semen, based largely on an article published in New Scientist, in which the authors claim that women engaging in unprotected penile-vaginal intercourse scored better on depression scales than women who used condoms. It doesn't seem terribly responsible to promote unprotected sex, when at best their results indicate only an association, and not causation. The article speculates about the antdepressent effect of orally and anally administered semen, but has no supportive data. That's why the WP article uses the phrase "may have antidepressent qualities".

Stay safe! Mattopaedia (talk) 06:33, 3 February 2009 (UTC)

On further thought, it could also be very much like an amniotic fluid embolism. Still another reason to heed my previous advice - don't do it! Mattopaedia (talk) 13:05, 3 February 2009 (UTC)

Brain wave crosstalk

Is it theoretically possible for one person's brain waves to spill over into another nearby person's brain and affect its functioning? NeonMerlin 02:15, 3 February 2009 (UTC)

No. The signal strength is VASTLY too small - and there is nothing in our heads that is even remotely like an antenna. SteveBaker (talk) 02:25, 3 February 2009 (UTC)

(after ec): Given the frequency range of the brain waves is roughly 1 - 100 Hz, most people think it is not possible. Many household and industrial appliances of the last 100+ years produce or used to produce much stronger electromagnetic emissions in that range than your neighbor's brain ever will. Still, there are no reports I am aware of that link any of these appliances to any systematic disruption or alteration of the thought process. --Dr Dima (talk) 02:32, 3 February 2009 (UTC)

Theoretically, could brain waves be transferred over a wired connection between two brains, as a matter of interest? --Kurt Shaped Box (talk) 02:36, 3 February 2009 (UTC)

Yes. You can use electrodes of appropriate types to inject any current(s) into any area(s) of the brain, provided your experiment conforms with the ethics requirements. You can therefore record a signal from one brain, amplify it, filter it, and inject it into another brain. That process will, most likely, not transfer any thoughts or qualia, though. For example, simply injecting current into a primary visual cortex location may produce a percept of a phosphene (small flash of light) at the corresponding retinotopic location; but not much more. Injecting a more complicated waveform is likely to have the same result, as the brain activity of the "donor" and "recipient" is neither coherent nor even necessarily similar. So a USB port on someone's forehead is still quite a few years away :) . On a somewhat related subject, you can also look at the deep brain stimulation article. --Dr Dima (talk) 03:08, 3 February 2009 (UTC)

Look there are (literally) a trillion neurons in your head. Maybe 10% of them are firing at the same time. That makes about a hundred billion teeny-tiny electrical signals...the total 'transmission' would be like all of the cellphone calls from the whole of planet earth all mixed up together...times about a thousand! If you don't have a trillion wires - you can't carry all of the information. But worse still (MUCH WORSE STILL) the arrangements of the memories and neural connections in my brain are TOTALLY different from yours. It's not a matter of connecting neuron A in my brain to Neuron A in yours, then B to B, C to C. My thoughts relate to my memories in ways that totally don't translate to those in your brain. So this isn't gonna work...and it's technically ridiculous. SteveBaker (talk) 03:23, 3 February 2009 (UTC)

Heidi (my wife) often knows what I'm thinking :) -hydnjo talk 04:03, 3 February 2009 (UTC)

'::::::Please explain "qualia." Edison (talk) 05:37, 3 February 2009 (UTC)

Women's Intuition, man's terra incognita.--Lenticel ^(talk) 05:39, 3 February 2009 (UTC)

Qualia. Richard Avery (talk) 08:34, 3 February 2009 (UTC)

Islam ... previous article

Removed Welcome to the Wikipedia Reference Desk. This is a place for people to ask questions that they are having trouble finding the answers for themselves. It is not a chat board or discussion site. There are many forums you can visit if you would like to expound your views on religion; this is not one of them. Thank you. 79.66.57.25 (talk) 08:20, 3 February 2009 (UTC)

Well, it's certainly great to see such an unbiased search for knowledge! Can we have the soap box back when you're done?

Anyway, I'll play along: if you think that people 1400 years ago didn't know that an embryo turned into a fetus, and so forth, you're wrong. (Furthermore, a fetus doesn't first grow bones and then cover them with flesh, so if that's what Mohammed thought, he was wrong.)

Likewise, the idea that you can only feel if you have your skin is wrong. (In fact, that's so obviously wrong that it boggles the mind. Haven't you ever heard of a toothache, for example?) If you mean that you can only experience a touch through skin, that's also wrong -- although it's certainly true that there may be no sensation in burned skin, the human somatosensory system also works in muscles and even bones. It's just that we aren't usually aware of such sensations. (What, you think they didn't have third degree burns 1400 years ago?)

As for what it would take to convince me that God exists, hey, I'm easy. A miracle will do just fine. It doesn't have to be a big miracle, either, it just needs to be unambiguous. He could use his awesome power to levitate me for a moment. Or he could appear to me and tell me to get with the program. Or he could turn someone I know and love into a pillar of salt, give me a dose of that Old Testament tough love. Trust me, I'll convert in a flash. I'd probably end up being a real zealous bastard, too. -- Captain Disdain (talk) 08:43, 3 February 2009 (UTC)

If God's going to turn people into pillars of salt, make sure he turns a few into pillars of pepper, for those of us who need to avoid salt in our diets. :-) StuRat (talk) 14:57, 3 February 2009 (UTC)

Trolling... —Preceding unsigned comment added by 129.67.37.225 (talk) 14:00, 3 February 2009 (UTC)

The OP sounded to me like someone who is genuinely ignorant of basic anatomy rather than a troll, though yes this is a reference desk for asking questions rather than just pushing ones opinion. Dmcq (talk) 15:31, 3 February 2009 (UTC)

Anyone who tries to push such opinions on this Reference Desk typically gets their arguments ripped to tiny little shreds under the withering force of actual science...I don't know what they think they might achieve by doing that - but for sure it ain't gonna make any converts. Quite the opposite in fact! SteveBaker (talk) 16:34, 3 February 2009 (UTC)

Map projection where area is proportional to a statistic

I've read somewhere that it is possible to generate a map where the areas of the countries are proportional to some statistic (such as population), however, the countries are still recognizable. Any info on that? —Preceding unsigned comment added by Lev (talk • contribs) 07:58, 3 February 2009 (UTC)

There's a little bit at cartogram. Both this and the main map article are disappointingly short, though. --Anonymous, 08:54 UTC, February 3, 2009.

While the article isn't great, you can find some maps from a search. E.g. Population 1 Population 2 GDP per capita (2000) Nil Einne (talk) 09:33, 3 February 2009 (UTC)

You may want to read our article on Geographical information system which is much longer, and may be what the OP is talking about. --Jayron32.talk.contribs 12:32, 3 February 2009 (UTC)

What the weather feels like

Resolved

On the news they say the temperature is 3 deg C, but it feels like 0 deg C. The latter is attributed to the wind chill factor. Then how do they measure these two temperatures? Why aren't they the same?--DFS454 (talk) 12:13, 3 February 2009 (UTC)

The two articles you should read are Wind chill and Heat index, the former tends to make us feel colder, and the latter warmer. With both of these, the relevent measurement is how fast your body dissipates heat. How warm or cold you feel is a factor of how fast your body is losing energy. This will be dependent on ambient temperature, but it is ALSO dependent on other factors as well. With wind chill, the wind (moving air) will tend to pull heat from your body faster, making you feel colder. With heat index, high humidity will make you sweat less, thus decrease your rate of cooling, thus make it feel warmer. Your perception of the temperature is largely based on how fast your body cools off, not on any direct measurement of the temperature outside of your body. Thus, "wind chill" and "heat index" corrected temperatures tend to be more useful to people, who, after all, are mostly concerned with how to correctly dress for the outdoors based on what they will feel like... --Jayron32.talk.contribs 12:30, 3 February 2009 (UTC)

As for how to measure wind-chill, use a wet bulb thermometer (a normal thermometer with a wet rag tied around it). A dry bulb thermometer (just a normal thermometer which is kept dry) is used to measure the regular temperature. StuRat (talk) 14:49, 3 February 2009 (UTC)

What's going on is that a layer of air is trapped close to your skin (eg by hair or clothing) which is close to body temperature. This insulates us from feeling the 'true' temperature of the air. When the wind blows harder - that layer of air is moved out of the way and we feel more accurately what the TRUE air temperature is. So when there is no wind, 3degC feels a certain way - but when the wind blows, it feels colder. Someone in the dim and distant past figured that 3degC with a 10mph wind feels like 0degC with no wind (or whatever it is) so we have this concept of 'wind chill'. Similarly at temperatures above body heat - when it's 40degC here in Texas - you feel cooler when there is NO WIND than when there is wind...same deal, the air near our skin has been cooled by sweating - but when the wind blows you feel hotter. Sadly, this is far from being exact science - if you have more or less clothes on then your experience of the wind chill will be different than the forecasters have stated. Humidity can also affect our feelings of high temperatures (hence "Heat Index") because when the air is very humid, sweat cannot evaporate anymore and we can't cool ourselves off naturally. When the air is very dry, sweat evaporates more easily and we feel cooler - even though the temperature is the same. So, again, we have this somewhat ad-hoc concept of 'heat index' that takes that into account and says that even though the air temperature is (say) 35 degrees C, it "feels like" 38 degrees because it's so humid. Of course if you've covered every inch of your body with antiperspirant...your mileage may vary! SteveBaker (talk) 15:01, 3 February 2009 (UTC)

(It has been pointed out to me that I shouldn't be encouraging people to cover every inch of their bodies with antiperspirant...I kinda thought that was inherent in what I just said - but just to be REALLY, REALLY CLEAR: If you cover yourself with to much antiperspirant, your body will be unable to shed heat - if you get into any kind of warm situation - you could easily get a life-threatening dose of hyperthermia. That's hypERthermia - not hypOthermia.) SteveBaker (talk) 16:29, 3 February 2009 (UTC)

Excellent thorough answers, thanks everyone--DFS454 (talk) 17:06, 3 February 2009 (UTC)

Which is more prestigious as an honour;FBA or FRS

Both there are regarded as apex academic honours in Britain.Which is more prestigious? —Preceding unsigned comment added by 212.247.70.129 (talk) 13:53, 3 February 2009 (UTC)

FRS. There is also the business that people outside science need an honour like that so they know whether the person is distinguished or not whereas for the FBA they would be known for what they did anyway without it. Dmcq (talk) 15:20, 3 February 2009 (UTC)

Is that really true? My uncle (an economist) was made an FBA, but I doubt many people outside his field (or his sideline as a chess problemist) would have heard of him. In any case, the two awards apply to different areas, so they aren't directly comparable (is there anyone who has both?). I would guess that more people are familiar with FRS than with FBA. AndrewWTaylor (talk) 15:30, 3 February 2009 (UTC)

Answering my own question, it seems there are plenty of people with both awards]. AndrewWTaylor (talk) 15:31, 3 February 2009 (UTC)

Protein Supplements in diet

If you are doing significant amounts of anaerobic workouts, with an eye to maximum power gain in the relevant muscles and muscle mass gain, every 2 - 3 days; when is the best time in relation to working out to supplement your diet with extra protein? Would it be before working out, so that it is in your system as soon as your body starts repair the damage; or would it be after so that the protein comes in when the body is doing most of the growth over the next few days? Are there any other specifics or dietry supplements other than protein that can aid muscle growth without causing you to build up fat? —Preceding unsigned comment added by 129.67.37.225 (talk) 14:07, 3 February 2009 (UTC)

There was a question on the reference desk quite recently about this, see: Wikipedia:Reference_desk/Archives/Science/2009_January_18#Muscle_Tone_and_Protein_Intake. The general consensus is to eat protein as soon as possible after the workout. Read the studies for further information. --Mark PEA (talk) 16:47, 3 February 2009 (UTC)