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February 6

Beautiful sunsets

The sunsets in the San Francisco Bay Area over the last few months have been beautiful. Too beautiful. I don't think they were this nice in past years. Is there more particulate matter in the air right now for some reason? It's not listed as one of the consequences of the April 2010 Eyjafjallajökull eruption... -- BenRG (talk) 02:06, 6 February 2011 (UTC)

This article, from Apr 23, 2010, explains that Eyjafjallajökull had not (by that date, anyway) put enough particulate matter into the stratosphere to have much of a lasting effect on sunsets. WikiDao ☯ 02:18, 6 February 2011 (UTC)

This summary of emissions in California ranks them by source and county using data for 2005. Cuddlyable3 (talk) 03:14, 6 February 2011 (UTC)

The small volcanic ash particles in the stratosphere do not have a lot of "mass". There are some eruptions on the Pacific ring of fire. --Chris.urs-o (talk) 15:01, 6 February 2011 (UTC)

Many eruptions have occurred worldwide since the Icelandic eruption. See list of currently erupting volcanoes. ~AH1^(TCU) 18:28, 6 February 2011 (UTC)

I think this is a result of the fact that we are currently experiencing the strongest La Niña in over ten years, and since around Jan 5 it has been very dry. Dry air tends to give better sunsets than moist air. I don't think the sunsets were so nice back in November and December, when it was rainy as hell. Looie496 (talk) 18:47, 6 February 2011 (UTC)

Well, yes, rain would rinse particulate matter out of the air. PЄTЄRS J V ►TALK 19:00, 6 February 2011 (UTC)

Oh, that makes sense. I don't know why I didn't think of that. -- BenRG (talk) 00:32, 7 February 2011 (UTC)

Reducing noise pollution

Hi, I want to know Is it possible to make a device which will generate sound waves which will counter the sound waves generated in real enviornment. My Idea about this device is that ..... It will detect the frequency of all sound waves around it and simultaniously it will generate counter sound waves which will destroy the real sound wave ..... and our enviorment will be free of noise pollution.. —Preceding unsigned comment added by 220.225.96.217 (talk) 05:03, 6 February 2011 (UTC)

I don't think it's quite that easy. See our article Active noise control. Mitch Ames (talk) 05:08, 6 February 2011 (UTC)

(edit conflict)See Active noise control. If the region in which you are trying to cancel the noise is small (like the space between headphones and your ears) OR if the noise you are trying to cancel is relatively predictable and easily modeled, like a car engine, then technology is already on the market and in consumer products right now. Active noise control is availible in Noise-cancelling headphones you can wear. And some high-end luxury autos use active noise control to minimize the sound of the engine noise and road noise inside the cab of the car. The problem is that you can't design a noise control system for a big space where the sources of the noise and the people are all moving around. The thing about the inside of cars, and the inside of headphones, is that its a small environment to model and its very predictable. People sit in the same place, roughly, inside a car, and the space inside the headphones is really easy to design for. If your thinking of creating a giant noise-cancellation system which would, say, cover your entire house and yard, so that anywhere you were standing in your house would be noise free, its just too complicated to design such a system. The noise cancellation system needs to know where you are, so it can design the correct countrer-noise to broadcast. If you move in the soundspace, the exact anti-noise needed is going to change drasticly. You need a system that follows you around and hears what you hear, hence the headphones. --Jayron32 05:13, 6 February 2011 (UTC)

Another problem with large-scale noise cancellation is that because energy is conserved, canceling the noise in one area necessarily means having MORE noise somewhere else. If you make your house and yard noise-free, the neighbor might object to having an interference maximum inside his house. --99.237.234.245 (talk) 05:58, 6 February 2011 (UTC)

No, that's not necessarily so. The energy needed to create noise cancelation is provided the same way that your lightbulbs light. It doesn't necessarily hold that you have to create more noise somewhere else in order to cancel noise. Total energy is conserved, not total noise! --Jayron32 06:03, 6 February 2011 (UTC)

It doesn't matter how the sound is created in the first place. Once the noise-cancellation sound is created, it has sound energy; the noise that it's meant to cancel also has sound energy. That energy can't simply disappear after the two waves interfere, so if the sound has 0 amplitude in one area, it must have a non-zero amplitude elsewhere. For the same reason, it's not possible to have minima without maxima in a double-slit experiment, or to make the water come to a standstill by throwing pebbles to cancel an existing water wave. --99.237.234.245 (talk) 06:58, 6 February 2011 (UTC)

I agree 99.237.234.245. However as a practical solution you can baffle the anti-sound, and absorb the energy without bothering the neighbors. Ariel. (talk) 09:45, 6 February 2011 (UTC)

Yeah, but then you should also be baffling the original noise at the same barrier, no? Wnt (talk) 15:50, 6 February 2011 (UTC)

Nah, I don't think think Ariel means to insert a baffle barrier between the noise source and the hearer to be protected. Ariel is talking about reducing the added sound contribution outside the protected zone. Another improvement is to radiate the anti-sound at low level from a phased array of speakers that focus maximum power only at the protected hearer.Cuddlyable3 (talk) 18:10, 6 February 2011 (UTC)

Are you talking about white noise? ~AH1^(TCU) 18:27, 6 February 2011 (UTC)

He's still talking about noise cancellation, whic is distinct from white noise. Someguy1221 (talk) 19:39, 6 February 2011 (UTC)

I would still agree with Wnt. If you are adding a baffle to outskirts of the protected zone, it seems likely this be between the hearer and the noise your'e trying to cancel. This would therefore also help stop incoming noise anyway. It's probably not perfect, but that would likely apply to the anti-noise as well in other words you're still making more noise for others even if you're partially baffling it. To put it a different the baffle either works or it doesn't. If it does then why the noise cancellation? If it doesn't then you're still arguably being a nuisance to others. I guess if the source of your anti-noise is from the baffles pointed towards the hearer and the protected zone is quite large your contribution may be minimal compared to the effectiveness of the baffle itself in stopping incoming noise (in other words the baffle may be better at stopping your anti-noise getting out then in stopping other noise coming in) but I'm not that sure, perhaps someone who better understands the physics of baffles and noise can explain? The exception would be if you're trying to cancel noise within the protected zone but as I understood the original premise, the idea was to create a protected zone from external noises like cars, lawn mowers, leaf blowers whatever. If the noise is within the protected zone, tell your partner/flatmate/child/parent/whatever to tone down the noise may work. Nil Einne (talk) 20:40, 6 February 2011 (UTC)

 noise ---> (protection) <--- anti-noise ---> (baffle) [otherwise extra noise would go here]

Ariel. (talk) 21:52, 6 February 2011 (UTC)

Yes that's what I mentioned in the late part of my discussion. My understanding is it wasn't really what the OP was thinking about, but perhaps I'm mistaken. Nil Einne (talk) 08:17, 7 February 2011 (UTC)

That diagram might look plausible, but move "(protection)" half a wavelength and the "noise" and "anti-noise" now add to one another. That's why I was assuming the layout was noise - anti-noise - (protection). Also of course the reality is three dimensional, and spheres don't meet up as nicely as line segments. Wnt (talk) 17:09, 7 February 2011 (UTC)

Gases

A mono atomic gas and a diatomic gas are initially at same temperature and pressure, which are later compressed adiabatically to half their initial volumes. Then which gas has higher temperature? According to thermodynamics TV^(gamma-1) is constant, so that temperature of mono atomic gas is higher. But if we consider like, as attractive forces in diatomic gas are more due to more vander-waal forces of attraction so that, more energy is released and then Potential energy increases and due to which Kinetic energy increase, thus increasing temperature. So, what is the mistake in the latter reasoning? — Preceding unsigned comment added by Krishnashyam1994 (talk • contribs) 09:19, 6 February 2011 (UTC)

In a gas, the molecules spend most of the time so far from each other that there's no forces acting. Exactly which forces act during collisions is not thermodynamically important -- only what comes out of the collision is. The diatomic gas is different because its molecules can store energy in rotational and vibrational modes that do not show up in the kinetic energy of the entire molecule, and this internal energy mixes with the kinetic when collisions happen. There are no such hidden energies in the atoms of a monatomic gass. Therefore, when you add some energy to the gas (by doing mechanical work to compress it), the monatomic gas has to use all of the extra energy to make the molecules move faster (= increased temperature), whereas a diatomic gas can store some of it internally and only uses some of it for kinetic energy (= less increased temperature). –Henning Makholm (talk) 09:43, 6 February 2011 (UTC)

Specific heats

What will be the Cv(Specific heat at const. volume) for triatomic linear and non-linear molecules? i.e., what will be the contribution of rotational and translational freedoms? but for both, translational freedoms are 3R/2 — Preceding unsigned comment added by Krishnashyam1994 (talk • contribs) 09:24, 6 February 2011 (UTC)

You first need to compute the number of degrees of freedom for the vibrational modes. You can do this as follows. A particle considered as a point mass has 3 translational degrees of freedom. A bound state of 3 particles will have 3 degrees of freedom for each particle, so there will be 9 degrees of freedom in total. You can then decompose these 9 degrees of freedom for the bound state in terms of the center of mass motion, rotational and vibrational modes of the bound state. Clearly, there are 3 degrees of freedom for the translational center of mass motion, and you have either 2 or 3 rotational degrees of freedom depending on whether or not you have a linear moelcule or not. In case of a non-linear molecule, you can chose 3 independent axes of roitation, so you have 3 degrees of freedom for rotation. In case of a linear molecule the axis parallel to the molecule is not allowed. The reason for that is that this correponds to a spin degree of freedom of the atoms, which we didn't consider in the total of 9 degrees of freedom. So, we have:

total number of degrees of freedom = 9 = N vibrational modes + 3 translational center degrees of freedom for center of mass + 2 or 3 rotational modes.

So, you can solve for the N vibrational degrees of freedom for the cases of linear and non-linear molecules. Then, the heat capacity per molecule is obtained from the equipartition formula. Since each vibrational modes contributes to two quadratic terms in the Hamiltonian, you get:

C_v = N k_B + 3/2 k_B + (2 or 3)/2 k_B

Count Iblis (talk) 01:31, 7 February 2011 (UTC)

Will it be the same for both ideal and real gases? — Preceding unsigned comment added by Krishnashyam1994 (talk • contribs) 09:07, 7 February 2011 (UTC)

For real gases the total heat capacity will be different due to the potential energy between the molecules. However, the contribution due to the translational, rotational and vibrational degrees of freedom will be the same. Of course, you can still question the exactness of these contributions to the heat capacity. The contribution 3/2 k_B to the translational modes to the heat capacity is almost exact, the corrrections coming from quantum corrections that are only important at extremely low temperatures (usually less than 10^(-10) K). For the vibrational modes, the opposite is true. In most cases, quantum effects leads to these being frozen well above room temperature. Then a few hundred K above room temperature where you would expect the formula to hold, you will see deviations, because describing the molecule as being bound by a harmonic potential isn't that accurate. Then the rotational modes are typically frozen below 100 K or so. There are obvioulsly corrections to the classical formula due to quantum effects. Also, there is a coupling between the rotational modes and the vibrational modes. E.g. if the molecule rotates faster, it stretches a bit which causes the moment of inertia to be larger. So, there is an inherent contradiction in treating the molecule as a rigid rotator and a harmonic oscillator at the same time. Count Iblis (talk) 14:16, 7 February 2011 (UTC)

Tank filling on a cold day

Is it better to your pocket? Gasoline will have less volume, but does it matter? — Preceding unsigned comment added by Quest09 (talk • contribs) 12:10, 6 February 2011 (UTC)

I seem to recall a discussion on this before but can't remember where. In any case, [1] suggest the change in density is only about 0.5% change for 5 degree C change in temperature. In other words even if there's a 30 degree C change between day and night thats only 3% difference. More to the point [2] which is the ref used in the earlier source and [3] mention 2 key things. Number 1 many petrol stations have their tanks underground where the temperature change over the course of a day is minimal. Even if they don't, a large volume of petrol probably doesn't change temperature over the course of the day that much anyway. So this may be an issue in summer vs winter, but day vs night not so much. And even then as both refs mention, most modern pumps are probably sophisticated enough that they do take temperature in to account (and in any case would I expect be periodicly recalibrated probably more then once a year). Nil Einne (talk) 12:36, 6 February 2011 (UTC)

Not to mention that prices fluctuate much more over the year than the density possibly could anyway. –Henning Makholm (talk) 13:18, 6 February 2011 (UTC)

This explains it nicely: Consumer Watchdog--Aspro (talk) 19:05, 6 February 2011 (UTC)

This Fuel dispenser#The metrology of gasoline talks about it a bit. Basically in Canada where the cold temperatures hurt the gas sellers they compensate for the difference. Same for the wholesale level. But in the warm US they don't (the warm south more than compensates for the cold north). People think that's unfair but it's not unfair enough for anyone to get worked up enough to do something about it. Ariel. (talk) 19:10, 6 February 2011 (UTC)

The petrol is stored underground, which means there will be very little temperature variation during the day due to the insulating properties of the ground. There will be a variation from season to season, possibly, but you can't really wait until winter to fill up! --Tango (talk) 22:35, 6 February 2011 (UTC)

From the consumer watchdog PDF linked above 513.8 million gallons of gasoline sold in the summer 2007 will be attributable to the thermal expansion of gasoline. can I just say I had to nudge my eyes back into their sockets. It still doesn't fail to stagger me every time I hear statistics about how much gas we churn through, I think this should really be something kids are taught in schools. We've reached peak oil already, if you argue we haven't, then you can't argue will very very soon, and most people are still completely oblivious to the staggering amount of resource we pull out of the ground and burn every year.. Vespine (talk) 01:27, 7 February 2011 (UTC)

Volume statistics get impressive very quickly; still, consider that this is only 800 times larger than one gallon of gas on a side. At a cost (rather optimistically) of $3 a gallon, that is $1.5 billion worth - the price of four or five Boeing 747s. Wnt (talk) 18:28, 10 February 2011 (UTC)

Magma

A while ago I recall a wiki user stating that the Earth's structure is solid throughout. Meaning that if you drill down to the core, you won't encounter magma (he said magma was formed through other means). I'm sure the outer core is liquid, but is it magma? The article on mantle states part of it is melting. Would that be magma? If we were to drill down to the core of the planet, would we eventually encounter magma? ScienceApe (talk) 15:02, 6 February 2011 (UTC)

Magma is formed when part of the earth (mantle or crust) melts because conditions locally (e.g. relatively high levels of water i.e. above a subduction zone or areas where the temperature is relatively high considering the pressure i.e. decompression melting) mean that the melting temperature is reached. Only part of the rock actually melts (partial melting) and a magma forms when the melt rises and starts to form distinct bodies of molten rock. This is different from the outer core, which is all liquid. You would only encounter magma on drilling if you did it at one of the locations where partial melting is happening. Mikenorton (talk) 15:26, 6 February 2011 (UTC)

Do you mean the "outer core is all liquid"? All of the links in this vicinity describe the inner core as solid. SemanticMantis (talk) 15:37, 6 February 2011 (UTC)

I am getting mixed up in my old age - corrected. Mikenorton (talk) 16:03, 6 February 2011 (UTC)

Our article on Structure of the Earth tells us "The liquid outer core surrounds the inner core and is believed to be composed of iron mixed with nickel and trace amounts of lighter elements." So no, the outer core is not magma. SemanticMantis (talk) 15:30, 6 February 2011 (UTC)

(ECx2) Well Structure of the Earth says "The liquid outer core surrounds the inner core and is believed to be composed of iron mixed with nickel and trace amounts of lighter elements." This doesn't sound much like what people commonly think of as magma which is of course discussed in our article. I'm suspect the temperature and pressure differences with places were magma is formed are enough that even if it were rock you wouldn't get something people would think of as magma either. Nil Einne (talk) 15:34, 6 February 2011 (UTC)

So would it look like liquid metal? ScienceApe (talk) 17:28, 6 February 2011 (UTC)

The asthenosphere of the mantle is generally semi-solid, but the lower mesosphere is solid. ~AH1^(TCU) 18:24, 6 February 2011 (UTC)

The asthenosphere is fully solid (apart from a suggested 1% melt), but at the slow rates of deformation that occur in the uppermost mantle it acts like a highly viscous fluid, a form of rheid. As to the appearance of the outer core, we have no way of knowing - the conditions can be recreated using a diamond anvil cell in the laboratory but we can't look at it as the sample is so small. Mikenorton (talk) 19:23, 6 February 2011 (UTC)

The liquid outer core is composed primarily of metals. But it may or may not look like molten metal at atmospheric pressure. SemanticMantis (talk) 19:58, 6 February 2011 (UTC)

The inner core would look like molten metal at atmospheric pressure (assumin the temp stayed the same). The only reason the inner core is solid is the massive pressure that it is under. For example, Ice VII is a form of water ice that doesn't melt until over 400 degC because it is at 10 GPa. Googlemeister (talk) 15:05, 7 February 2011 (UTC)

Refilling the Ogallala aquifer

One of the leading regional creeping-doom scenarios in the U.S. concerns the rapid draining of the Ogallala aquifer, leading to reduced potential for agriculture throughout much of the Great Plains. What I don't understand is that the barrier to refilling is apparently mostly a matter of permeability, and there are four major rivers crossing the aquifer region. Why don't people just drive wells down from the river to the aquifer every hundred yards for its length to refill it? (To avoid confusion, I mean wells with some degree of filtering, close to the surface of the water) Wnt (talk) 21:29, 6 February 2011 (UTC)

Well, there are also major disputes about the usage of water from the rivers. For example, Nebraska and Kansas have been involved in lawsuits about Republican River water rights, and Nebraska and Colorado have struggled with rights to the South Platte River. In recent years it has been common for the middle Platte River (upstream of Columbus, Nebraska, where it is joined by the Loup River) to dry up completely in the summer. I'm sure similar issues occur in states other than Nebraska; I only know of these examples because Nebraska is my home state. For more information, you might try http://water.unl.edu/. —Bkell (talk) 21:40, 6 February 2011 (UTC)

Obviously rivers are not infinite supplies of water. If you were to drain hydrologically significant quantities of water from the river, in order to "re-fill" the aquifer, you'd be extracting enormous quantities of water; and you can't just assume that "more river water will just keep flowing." Extraction of such volumes of water would have as much ecological impact as the depletion of the reservoir in the first place! The water cycle is a closed system - if the aquifer is being depleted, the water is ending up somewhere else. The real issue is, though, that where it ends up is not economically useful. The water that has been extracted from the aquifer be distributed globally in the form of increased precipitation somewhere else in the world. If the water is pumped out for crops and agriculture, and significant amounts undergo evapotranspiration and end up as rain over the Atlantic Ocean, then that freshwater is "lost" as a useful reservoir. However, that means that there's more water in the ocean, and less in the atmosphere; so there will be increased oceanic evaporation, and new clouds will form, and rain will precipitate somewhere else (maybe in Africa or Asia or the Pacific). If we're lucky, and if all things were "equitable and fair," this would also mean more rain in the Mississippi River basin - so the rivers would have higher throughput, so we could sustainably "drain off" a few billion gallons per year to "pump back into the ground." The point is, though, that the implications of hydrology on the scales of continent-sized aquifers are part of the entire global climate system. For every place that undergoes desertification or aquifer depletion, somewhere else on the planet is receiving more fresh-water. Unfortunately, this redistribution often occurs in a way that is neither useful for human economic activity or agriculture, nor for ecosystems. If you could make a convincing scientific case that depleting the river water flow, and pumping or "sequestering" water in an aquifer would actually result in increased economic activity, you'd have an easy time finding major industrial sponsors to start the pumping. Nimur (talk) 22:17, 6 February 2011 (UTC)

I really doubt that "For every place that undergoes desertification or aquifer depletion, somewhere else on the planet is receiving more fresh-water." There's no reason why the oceans couldn't give up a few inches of water and all the land would become wetter, if local conditions permitted it. That said, if the river is being sucked dry, obviously that's a problem. I still think of the area as a place for "500-year floods"^[4] but of course that's not every year. I'd call it a missed opportunity, but then again, I don't know how well the system would work in muddied raging floodwaters anyway. Wnt (talk) 01:41, 7 February 2011 (UTC)

You're right; I should clarify that if the "conserved quantity" of fresh water ends up raining in the ocean, it's no longer really "fresh water." If climate-sized quantities of rainfall over the ocean change, the salinity will decrease by some microscopic amount, but that's not really helpful (it's still not going to be "freshwater"). My earlier comments were not meant to imply that there's a fixed amount of fresh water that we're guaranteed to always have distributed throughout Earth. Nimur (talk) 02:50, 7 February 2011 (UTC)

You would also have to worry about contamination of the aquifer. I do not have pollution data handy, but I would expect that a deep aquifer would have less pollutants then a surface river which gets fertilizer runoff. Googlemeister (talk) 14:59, 7 February 2011 (UTC)

My feeling is that runoff that makes its way down through natural rock from the fields themselves would be worse, but I don't really know. It is an interesting idea for a whole new kind of ecological disaster: bacterial overgrowth and contamination in aquifers due to excessive nutrients. New idea, new environmental disaster - that's about the pace of things, isn't it. But I wonder if those farmers' fields could invent the problem on their own. Wnt (talk) 18:12, 11 February 2011 (UTC)

What's really needed is a way to get flood water down into the aquifer, properly filtered, rather than have it flood people's homes. However, the engineering challenge of processing such huge volumes of water would make this impractical. StuRat (talk) 06:41, 10 February 2011 (UTC)

Since the Laurentide ice sheet was likely a major source of the aquifer, the lack of any similar source today limits the degree to which the aquifer can refill. ~AH1^(TCU) 22:58, 11 February 2011 (UTC)

How deep is the deepest parking garage? Could one ever be built deep enough to reach Hell, like in this commercial?

This 2003 Honda Pilot Commercial depicts a full parking garage for the first many levels. Soon, they reach some humid utility area 96 levels down, and eventually a Hell-like cavern 720 levels below.

The head sticking out appears to be the last sentry of Upper Hell before the realm's exit, and what a surprise - there are still lower levels.

For those of you who don't believe in Hell, could one ever be made deep enough to reach a Hell-like place?

Anyway, what has been the deepest parking garage ever made and what feats of engineering and financing would it take to reach a Hell-like area below the surface? At what depth/floor level would it get unrealistic and why? --70.179.181.251 (talk) 22:00, 6 February 2011 (UTC)

You mean down into the mantle? I suppose it would be possible, but possible and practical are two very different things. The mantle is 75 km below the surface in places. Building a car garage even close to that depth would need an elevator, and fan system to remove carbon dioxide, and a humidity regulator. Sure, it can be done, but that's an idea like a floating city - possible, but completely pointless. One thing that should be noted is that it's not like a surface that you break through and then magma; the rock gets more and more plasticy as one goes down. You also only need to go down a few miles before it starts to get noticeably hotter. --T H F S W (Contact) 22:08, 6 February 2011 (UTC)

Just in terms of feasibility, it's of note that the lowest point ever drilled by humans — the Kola Superdeep Borehole — was only about 12.3 km below the surface, and that was not very easy. --Mr.98 (talk) 01:40, 7 February 2011 (UTC)

That also links to Extreme points of Earth#Lowest point (artificial) which notes the 'lowest human-sized point underground' is the TauTona Mine which is 3.9 kilometers deep. Our article notes 'The journey to the rock face can take 1 hour from surface level. The lift cage that transports the workers from the surface to the bottom travels at 16 metres per second (58 km/h).' I don't know if there's any shaft large enough for a car, perhaps not. As for 'hell like' well 'The mine is a dangerous place to work and an average of five miners die in accidents each year' ('employs some 5,600 miners') and 'Air conditioning equipment is used to cool the mine from 55 °C (131 °F) down to a more tolerable 28 °C (82 °F). The rock face temperature currently reaches 60 °C (140 °F)' Nil Einne (talk) 06:10, 7 February 2011 (UTC)

I see a couple of places that were planning to have seven underground parking levels, one in Vancouver and another in Chicago. Don't know if either got built. Clarityfiend (talk) 22:29, 6 February 2011 (UTC)

The Torre del Caballito in Mexico City reportedly has 15 (fifteen!) underground parking levels. I don't know if that's a world record, but I couldn't readily locate anything deeper. TenOfAllTrades(talk) 03:04, 7 February 2011 (UTC)

I love the "For those of you who don't believe in Hell"! Even if I believed in Hell, could I seriously believe that it is inside the Earth? If so, I would start a campain for the governements get drilling and free those souls! --Lgriot (talk) 10:55, 7 February 2011 (UTC)

Do you also want to campaign to go around all the maximum security prisons opening doors? If you believe in Hell, you probably would believe that they are there for a reason. Googlemeister (talk) 14:53, 7 February 2011 (UTC)

I am sorry my irony in this post didn't get through. The underlying assumption is that God, being all-knowing, including our future, knew that these people would have a bad life, yet, he let them be born, and after their death let them then be condemned to hell. So my view is that God is a very bad being to let people be born, have a bad life and then punish them for something he knew would happen and let it happen anyway. To punish him, we should free all the bad and let them loose in heaven where they can think of ways to annoy God. that would be fun to watch, wouldn't it? It isn't the same as human justice where the judges are genuinely not responsible for the prisonners actions (well, most of the time). --Lgriot (talk) 15:43, 7 February 2011 (UTC)

But logically, God would know what you were going to do, and having infinite power, could stop you if he felt it would actually be irritating, so it really wouldn't work. Googlemeister (talk) 16:07, 7 February 2011 (UTC)

Again, failed, sorry. I seem to have a problem making Googlemeister understand that I am joking. Maybe because I am the only one to see how funnily ridiculous the idea of an all powerful god is? --Lgriot (talk) 08:59, 8 February 2011 (UTC)

I think we could make a fair scientific argument for opening the prisons - or rather, can anyone show evidence that having them is useful? At least in the U.S., which invented them and seems to think that they can cure virtually any problem whatsoever (and when they don't, that's irrelevant). As for Hell, well, if God is an author, and he throws rough drafts that aren't going anywhere into the fire, then the fire burns always, the drafts burn but a moment, and the characters in those drafts do not suffer, but neither are they saved. Wnt (talk) 17:22, 7 February 2011 (UTC)

The US invented prisons ? No, they've been around as long as civilization, probably longer. While they seem to be fairly useless at reform, they do prevent many crimes, since criminals spend years removed from potential victims. StuRat (talk) 18:56, 7 February 2011 (UTC)

While I agree the idea the US invented prisons is bizzare, you appear to have a fairly naïve view of the interaction between crimes, prisons and criminals. In particular, you appear to be assuming prisons make no difference as to how likely a criminal is to commit a crime. Yet there is some evidence prisons may in some instances increase the likelihood someone will commit further crimes in the future, for example by these related issues of teaching someone to be a better criminal, by disconnecting someone from society, by for lack of better description 'reducing their humanity', making it more difficult for someone to interact acceptably in society (e.g get a legitimate job), and simply by familiarising someone with criminals and crime as a way of life. If you lock someone up for 20 years of their life in total and they commit 10 crimes during that life regardless vs if you don't lock someone up at all and they only commit 5 crimes during their live then clearly you have not prevented many crimes but increase the number. And many would agree some crimes are worse then others so going solely by the number doesn't work very well anyway. And without getting in to rehabilitation at all, all that money you spend on prisons as well as associated costs like courts and police is money you can't spend elsewhere, whether you believe that should be improving the lot of those in a very bad situation or reducing taxes. (If you believe prisons do reduce the number of crimes then the cost of running prisons can partially be offset against what you save from the reduction in crimes but as I've said that hasn't been established.) Note that I'm not arguing completely removing punishment or justice would result in less crime personally I don't believe it will although I do agree with Wnt that the current system in the US isn't working very well but that's somewhat beside my point which is you can't simply say 'people in prison can't commit crimes so you have less crimes/victims' since there is clearly a complex interaction, the fact people in prisons can't commit crimes doesn't help you if people are more likely to commite crimes when they aren't. Nil Einne (talk) 05:42, 8 February 2011 (UTC)

I think by the time most people end up with prison sentences, they are already career criminals. First time offenders typically don't get caught, or, if caught, aren't charged or get a suspended sentence or community service. However, another factor supporting your contention, is that some crimes seem as though they are likely to occur regardless of the criminal. If you arrest a drug dealer, another will work the same location to supply the customers there. If you arrest a hit man, those who would have hired him just hire somebody else. StuRat (talk) 06:02, 8 February 2011 (UTC)

I'm pretty sure that depends where you live. In any case, even in the US there have been notable cases with the Three strikes laws where someone has been sentence to very long prison terms for what seem like minor offences long after their previous convictions (which were usually more serious convictions). I'm not sure if you consider these people 'career criminals' and these may have been an exception and while given how long these sentences are I'm guessing most of these are still in prison it's unclear to me that they would have necessarily commited any further crimes had they not been locked up and in particular it seems hardly surprising if these people will have a major slide back downwards so that when they are released they will be more likely to commit crimes...

I'd call the grammar police on you for that 84 word run-on sentence, but you'd probably just get off with a warning, if this is your first offense. :-) StuRat (talk) 06:29, 10 February 2011 (UTC)

You might want to take a look at When the World Screamed first. --Stephan Schulz (talk) 11:08, 7 February 2011 (UTC)

I have to admit, I didn't think anyone still believed that hell was literally, physically inside the Earth. APL (talk) 17:31, 7 February 2011 (UTC)

I don't believe in any sort of literal hell. But hell is certainly a fun theological and philosophical tool for analyzing meaning and reality and destiny. Modern views vary widely, ranging from purely secular interpretations of the writings in the various holy-books, to mainstream theological interpretations in major world religions. Here's our article on Hell in Christian theology - I bring this up because Pope John Paul II reversed some major Catholic doctrine in the 1970s by stating that hell wasn't actually inside the Earth; in this 1999 speech, he said it's not a place at all. That should give you some perspective on just how modern that viewpoint is. More recently, in 2007, Pope Benedict has emphatically denied John Paul II's statements, claiming that Hell is actually a real place inside the Earth. Unfortunately, Popes tend to speak a cryptic and poetic dialect of heavily-Latin-influenced Italian, and rarely go to great lengths to unambiguously clarify their dictums; much meaning is lost through translation and interpretation. (It is my opinion that if any religious doctrine were to be laid out in unambiguous and clear language, the silly ideas could be easily refuted, leaving only a modernized, secular philosophy). I'm neither a Catholic nor very religious at all, but I have read many of John Paul II's speeches and writings, and I can say that he was a much more rational and intelligent pope than most - a suitable religious leader in the era of space travel and scientific reason. Nimur (talk) 21:01, 7 February 2011 (UTC)

Neither of those external links actually say what you say they say. Is that intentional? Some sort of test to check people are actually following links? John Paul II was referring to what was already in the Catechism (he refers to it by name) in saying that Hell is a state of being: he makes no mention of it being 'inside the Earth' because that hasn't been Catholic teaching since I don't know when. Benedict XVI says that Hell is very real, even though people don't talk about it much anymore, and it is a state of separation from God: he makes no mention of location or of it being 'inside the Earth' because that hasn't been Catholic teaching since I don't know when. He is particularly talking to support the new version of the Catechism, which explains (again) that Hell is a state of separation from God with no particular worldly location. Seriously, your links say nothing even close to what you say they do. Benedict XVI is a smart cookie steeped in rational study (of Catholic and related theology), although he sometimes forgets his audience and ends up too esoteric. 86.162.68.36 (talk) 22:36, 8 February 2011 (UTC)

In fact, this must be a test to see if people are actually following your links, because the very internal link you provided explains that neither Pope was saying what you said they were saying, and that this is a piece of misinformation spread by misreporting. Either that, or you don't read the links you provide yourself... 86.162.68.36 (talk) 22:46, 8 February 2011 (UTC)

I respectfully disagree with your assertions, but I'll concede that I may have read my own interpretation into the speeches in the links I provided. If anything, that only solidifies my earlier assertion that the Pope(s) used ambiguous language. Nimur (talk) 07:44, 9 February 2011 (UTC)

I came here to apologise for harshness of my phrasing, because there was no need to be unpleasant. Sorry. But I am genuinely baffled by how you can have thought that was what they were saying. I mean, it's right there in your links that both agree with each other and are saying things that were already Catholic teaching. All I can think is that you saw the word place and automatically thought that meant "place within the Earth", but that makes no more sense than assuming that any reference to Heaven as a place means "a place in the sky we could find with a rocketship". This very misunderstanding of the word place is why many (particularly in the 20th century) have preferred to use the word state, although in either case they are referring to a situation that souls experience, which is not in this world. Taking it as someone is very versed in Catholic theology, there was no ambiguity at all for me in their words, except in the usual "this is the limit of what we feel we know, so I'm phrasing it to make it clear I'm not insisting on something being true which is a matter of individual faith" sort of thing. The alternative is that a Pope or priest lays out some alternatives and explains who has argued them and how, but that tends to get misreported too, and can get long and uninteresting for much of the laity. 86.162.68.36 (talk) 09:25, 9 February 2011 (UTC)

This does bring a scientific question to mind after all: is there anywhere that you can actually encounter lava magma (??) in an underground cave? I know of course about lava tubes, but they seem too close to the surface and too transient to count. I mean, is there anywhere in the world that you find lava/magma bubbling away in a rock formation that hasn't been fresh-frozen from it, which is deep under the ground? Or is every volcano found on the surface, simply because the time for the magma to rise all the way up is so short in a geologic sense, and the area where caves are found is so small? Wnt (talk) 09:47, 10 February 2011 (UTC)

February 7

What happens when black holes collide?

I thought that there would be an almighty bang, with cosmic rays galore, and local solar systems devestated. Because I was thinking of a sun being sucked into a black hole. As it spiraled in, it would be spaghettified, ripped apart, and there would be an extremely powerful radiation that would be seen for galaxies around. But then I thought, with black holes, NOTHING can escape, not light, matter, nothing. So even the most powerful collision between two of them would hardly matter. Consider a technology superior to ours which, instead of sending two atomic particles on collision courses in something like the Large Hadron Collider, they sent two massive black holes, both at nearly the speed of light directly at each other. What would happen? No explosion. Maybe one would bounce of the other, or they would just integrate, like two blobs of paint. Much less dramatic than the collision of two suns. And no one around would notice, let alone be obliterated. Is that right? Myles325a (talk) 06:43, 7 February 2011 (UTC)

Although a collision of black holes doesn't give off matter or light, it does give off energy in the form of gravitational waves. In the most realistic case of a collision that isn't exactly head on, the two black holes will inspiral for a short time before they coalesce into a single black hole, and the gravitational waves produced will carry away angular momentum. The gravitational waves produced by the merger of two black holes also carries away linear momentum, producing a recoil on the merged black hole. In the case of the merger of two supermassive black holes, the recoil can be huge enough to wind up kicking the merged black hole out of its host galaxy. The ejected black hole can rip some stars away from the galaxy when it leaves, producing a hypercompact stellar system. See Gravitational wave#Energy, momentum, and angular momentum carried by gravitational waves. Red Act (talk) 07:58, 7 February 2011 (UTC)

The aftermath of two black holes colliding is formidable. During the inspiral, you'll have a moderate set of waves coming out, which increase somewhat exponentially with time. They reach their peak during coalescence, which is a short period of time where the two black holes become one. Then, there will be a dumbbell shaped black hole, which will 'ring down' into a sphere, emitting more waves. This pattern of waves (inspiral, coalescence, ringdown) is quite distinctive, and is one of the ways we can detect (colliding) black holes. The nature of the coalescence waves can give us an insight to black hole physics. In fact, there's a very large experiment called LIGO going on, which attempts to detect these waves as they reach Earth. ManishEarth^{Talk • Stalk} 16:06, 7 February 2011 (UTC)

How does the black hole decide which way to move, relative to the center of mass of the two colliding precursors? Wnt (talk) 16:46, 7 February 2011 (UTC)

If the collision is a head on collision between two non-rotating black holes than there is no recoil. A more realistic collision wouldn't be so symmetric and there might be "some" recoil. Dauto (talk) 19:13, 7 February 2011 (UTC)

The recoil encountered during the merger of two black holes can be huge. In the paper I reference below, describing calculations of the mergers of two black holes with spins of magnitude S/m²=0.8 under various initial conditions, the recoil came to more than 1000 km/s in all but one case. That's about 1/300 of the speed of light, and about 33 times faster than the orbital speed of the Earth around the sun. The merger of even non-spinning black holes of unequal mass can have a recoil of up to 175 km/s, which is still more than 5 times faster than the orbital speed of the Earth. When black holes merge, the resulting black hole goes flying off at a very high speed relative to the initial center of mass, in a hard-to-predict direction. Gravitational waves carry away a huge amount of linear momentum when black holes merge. Red Act (talk) 22:08, 7 February 2011 (UTC)

I know. That's why I put the word some within quotation marks. Dauto (talk) 03:24, 8 February 2011 (UTC)

Oh, OK, I understand now. I mistook the quotes as connoting downplaying, instead of connoting ironic understatement. Sorry. Red Act (talk) 04:42, 8 February 2011 (UTC)

In realistic cases, a precise head-on collision isn't going to occur, and the black holes are going to be a binary system for a while before they merge. The merger of non-spinning black holes of equal sizes produces no kick (a.k.a. recoil). For the merger of two non-spinning black holes of different sizes, the kick direction (which of course must be in the orbital plane, due to mirror-image symmetry) is mainly determined by the relative positions of the two black holes before their very last orbit and merger. The net radiated linear momentum before then is small, because it's fairly close to being equal in all directions over time when the orbits of the two black holes are nearly circular. However, much larger kicks occur when the merger is between two spinning black holes, in which case the initial spin orientations play a crucial role in the kick direction, and the kick direction is no longer even confined to the orbital plane. As in the case of non-spinning black holes, almost the entire kick is accumulated during the final merger phase, so the kick direction is highly sensitive to initial conditions, and there isn't some simple formula for it. For more information, see this paper. Red Act (talk) 19:58, 7 February 2011 (UTC)

Scientific name etymology

Hi. Several sources (including Wikipedia) state that the scientific name Leptictidium means "graceful weasel". However, this etymology seems to correspond to Leptictis (lepti+ictis) rather than to Leptictidium. So what does Leptictidium actually mean? What's the difference in meaning between Leptictidium and Leptictis? Thanks. --79.89.248.158 (talk) 07:17, 7 February 2011 (UTC)

The suffix '-idium' is from the greek suffix '-idion' meaning smaller or lesser. Mikenorton (talk) 07:55, 7 February 2011 (UTC)

Why don't we have pneumatic tubes?

It seems people in the past (like end of nineteenth century) thought that by now -- in the 21st century -- we would have pneumatic tubes everywhere, for fast delivery. Why don't we? Is there something wrong with the idea after all, that makes it impractical, etc? I can't get a homecooked meal in my house any faster than either making it, going to go get it myself, or having someone deliver it. Whereas with tubes, I could just get one as from a buffet... Is there some reason the idea doesn't actually work? (even though more than a hundred years ago, people were convinced it would). 109.128.127.87 (talk) 12:01, 7 February 2011 (UTC)

Such pneumatic tube systems were quite widely used in the 20th century in industrial and commercial settings, such as factories, banks and department stores, and even across cities, to transport packages of documents, cash, postal items, etc. They remain in use in a variety of specialist settings - my local Tesco supermarket, for example, uses such a system to send containers of cash from tills to a central cashier's office. Although our article is not explicit, my guess (as someone professionaly experienced in Facilities management) is that the necessary servicing and maintenance required to keep them working is relatively impractical in a domestic setting, making rival technologies or methods more economical. 87.81.230.195 (talk) 12:39, 7 February 2011 (UTC)

Document distribution has become overwhelmingly electronic, information is no longer the prisoner of sheets of processed dead tree. The need to transport a specific piece of paper within a single physical facility has become relatively rare.

I know some large hospitals use pneumatic systems to transport laboratory specimens and urgent medications.

City-wide "public utility" systems ran into scalability problems. What works well in a single building gets hopelessly snarled up in a city-wide system - the information and communication technology of the late 19th - early 20th century simply could not do the job economically. Roger (talk) 13:16, 7 February 2011 (UTC)

Rival technologies - there is none. If I want piping hot food in my house, I have to make it, or someone has to walk it to my doorstep (probably me). There is nothing that replaces it. Dodger67, I understand about late 19th - early 20th century limitations. My question is: what about today? 109.128.127.87 (talk) 13:18, 7 February 2011 (UTC)

Using magnetic levitation and propulsion would get over some of the difficulties of long distance operation -if it can be made to work economically.A visionary idea for modernising the goods-distribution network --Aspro (talk) 13:57, 7 February 2011 (UTC)

The infrastructure needed would mean that there would be high start up costs, which would make it a risky investment, and probably high running costs. The Royal Mail had a narrow gauge railway under London which they closed in 2003 due to running costs. -- Q Chris (talk) 14:14, 7 February 2011 (UTC)

I'm not sure that pneumatic tubes are ideally suited to food delivery. The acceleration and deceleration, not to mention the sudden twists and turns would thoroughly scramble most food items.

A pizza would be disastrous, and the wrong shape anyway. Some Chinese-food items would be OK, but some would not survive. Grinders would be the ideal shape of course, but I think that even tightly wrapped in wax paper they'd be pretty badly damaged. I'll bet all the meat would wind up bunched up at one end and the bread would be soaked from the obliterated tomato. I'll bet a burger would be just as bad, but with more grease.

Maybe some systems go a lot slower than I'm imaginingAPL (talk) 16:20, 7 February 2011 (UTC)

"I'll bet all the meat would wind up bunched up at one end and the bread would be soaked from the obliterated tomato." It's a sacrifice I'm willing to make. 109.128.127.87 (talk) 16:32, 7 February 2011 (UTC)

Well if it was spag bol, it wouldn't matter. But in other cases, the food could be vaccuum sealed in a heavy plastic wrapper, which would prevent it from moving around. Myles325a (talk) 00:44, 8 February 2011 (UTC)

Actually I would think unmanned aerial vehicles would offer a rival technology, when appropriately optimized for the task. "All hail the Pizza Bomber!" But unless you teach a parachutist pizza how to ring a doorbell, you'll need some specialized slot in your hose for the planes to dock, deliver their cargo and take off again. Conceptually, the friction of moving air in a sufficiently long pneumatic tube should eventually exceed the necessary lift and drag of a tiny airplane. Wnt (talk) 16:55, 7 February 2011 (UTC)

NOW you're talking. Smart Quadrocopters could flit all over town carrying precious fast-food take out. They could use cel-phones to alert buyers when they're about to land. I wonder how much you have to tip a delivery robot. APL (talk) 17:26, 7 February 2011 (UTC)

OK, now for a list of shortcomings of pneumatic tubes:

1) As Wnt mentioned, friction is more of a problem the longer the tubes are (and the more bends). You would need to put more and more pressure in the tubes, the longer they are, to get them to work. This would require that the tubes be thicker and better sealed, and the container would also need to seal more closely with the tube, to prevent air leakage, which in turn would also increase friction. Perhaps powdered graphite or some other lubricant would be needed along the inside of the tubes, which would, unfortunately, tend to blow out black dust at the ends. Also, at such pressures you could no longer have the tubes be open at the end. While this results in a harmless puff of air for short lengths, for the lengths you are talking about, the air pressure blast would blow your ear drums out. Instead, you'd need to have the pipe open up to a chimney on the roof, and would need special baffles or maybe use active electronic noise reduction methods, to prevent it from making loud sounds.

2) As APL mentioned, food might get messed up by the forces involved. Soda, even if well sealed, would likely explode when you opened it.

3) Switching systems would be needed, as a single tube from every fast food restaurant to every home wouldn't work. This is another opportunity for air to leak out. I suppose an automated system using bar codes could be used.

4) There could be a security concern, as somebody could send bombs this way, or stop your food and poison it. StuRat (talk) 18:31, 7 February 2011 (UTC)

Now for some places where it could work:

A) Hotels. Rooms service would no longer require that you put your robe on. As for scrambling the food, the relatively short distances would mean that they could move it rather slowly. Another way to do the same thing would be with dumb waiters. The latter wouldn't allow going around corners, but you would need a vertical shaft between every pair of rooms (or maybe every 4 rooms, if the halls are on the outside, as in a motel). The dumb waiter system might be quieter and allow a full tray of food, but either system would need to control the door at the room end, so people couldn't just steal food sent to another room.

B) Skyscraper apartment buildings.

C) Hospitals.

D) Retirement homes. StuRat (talk) 18:44, 7 February 2011 (UTC)

Bellamy in 1887 wrote "Looking Backward", a sort of time travel or futurism forecast of what the world of 2000 would be like. He forecast an underground delivery system, whereby you could order and get automatically delivered food, clothing, or whatever. Picture the Denver Airport luggage handling fiasco. Such a system would likely cost more to set up and maintain than just getting stuff delivered by car from the pizza place, or by FedEx from internet merchants for books or clothes. Edison (talk) 19:59, 7 February 2011 (UTC)

It might also be useful to list some of the alternatives:

- For horizontal transport (or slight angles): Conveyor belts.

- For downward transport: Chutes. No power required.

- For upward transport: Elevators.

The additional flexibility of pneumatic tubes to transport in any direction apparently doesn't make up for the other short-comings of such a system.

Incidentally, it might interest you to know that the first New York Subway and an early London Underground were both pneumatic. StuRat (talk) 23:32, 7 February 2011 (UTC)

We currently use a pneumatic tube system at the hospital where I'm employed. It's primarily for sending samples to the lab, and medicines to various floors. We used to use a dumb waiter for moving large charts up to Medical Records, but most charting is electronic now, so that's obsolete. Suffice to say, I don't see much use for pneumatic tubes outside our current implementation. — The Hand That Feeds You:^Bite 23:45, 8 February 2011 (UTC)

In fairness to the tubes, you shouldn't really need to have the entire tube powered by an end-to-end difference in air pressure - you could e.g. have pistons at regular intervals which pull out as the package approaches and push in after it passes; this creates a gradient of air pressure only over a shorter interval. That said, pneumatic propulsion is (as with the railway) simply an alternative to an engine power, and eventually it still makes sense to have one engine that goes with your package rather than dozens or hundreds along the way. (Unless you have a whole lot of packages?) Wnt (talk) 00:53, 9 February 2011 (UTC)

How do the birds "print" spots on their eggs?

Guillemot eggs

Do they have "printers" in the cloaca? -- Toytoy (talk) 14:40, 7 February 2011 (UTC)

I found this in the article eggshell:

In an average laying hen, the process of shell formation takes around 20 hours. Pigmentation is added to the shell by papillae lining the oviduct, coloring it any of a variety of colors and patterns depending on species. -- Toytoy (talk) 15:04, 7 February 2011 (UTC)

You seem to have answered your own question in part, but in case you're also interested in why you might like to read this. This book also has more details on the how. SmartSE (talk) 16:30, 7 February 2011 (UTC)

capillary

what is capillary action? —Preceding unsigned comment added by 59.92.106.164 (talk) 14:52, 7 February 2011 (UTC)

See Capillary action. Red Act (talk) 15:11, 7 February 2011 (UTC)

the environment.

Does nuclear energy destroy the environment? — Preceding unsigned comment added by Drloic (talk • contribs) 15:10, 7 February 2011 (UTC)

See Environmental effects of nuclear power. Red Act (talk) 15:14, 7 February 2011 (UTC)

If it is released all at once, it has a very negative impact on the local environment. Googlemeister (talk) 16:05, 7 February 2011 (UTC)

There are some rather spectacular products of nuclear energy that could adversely affect the environment, however we'd all die without it. -- JSBillings 16:16, 7 February 2011 (UTC)

Short version: if there are no accidents, the net pollution is probably a couple of orders of magnitude less than coal. The "long version" explanation would include the probability of accidents (never non-zero, but lower than most people think; but the consequences of them are high), and the question of whether coal is the appropriate alternative to compare it to (whether that comparison creates a false dichotomy or not). You have to compare it to something, because all forms of energy generation have some environmental effects. --Mr.98 (talk) 16:36, 7 February 2011 (UTC)

I agree - coal power actually releases more radiation into the environment than nuclear: [5] [6] and the waste from coal can lead a very nasty mess [7] which is worse than anything proven about nuclear waste AFAIK. SmartSE (talk) 16:41, 7 February 2011 (UTC)

Note that nuclear decommissioning hasn't really been done that often, and until it is done we don't know whether the radioactive components inside will really be disposed of neatly in some small underground place we agree never to go to again, or dispersed all over the countryside during war or civil unrest as accidental discharges or dirty bombs. Wnt (talk) 17:05, 7 February 2011 (UTC)

I think the most important detail is that nuclear fission power stations produce a small, solid waste-product (which I can admit is fairly hazardous). But unlike any fossil-fuel power plant, the waste is not tons of gas that is just vented to the atmosphere. Nuclear waste can be safely carried to a secure location for disposal, while carbon dioxide, other noxious gases, and the soot and particulate pollutants of fossil fuel plants (especially coal) are just haphazardly thrown to the wind. Nimur (talk) 17:06, 7 February 2011 (UTC)

Yes, this is a very important thing to keep in mind. Containment is much easier for solids than gasses. SemanticMantis (talk) 21:21, 7 February 2011 (UTC)

An appropriate syllogism is "Nuclear power is to coal power as air travel is to car travel". As in, air travel is orders of magnitude safer than car travel, and yet when we have plane crashes they are Major Events, whereas someone dies of a car crash so often, no one notices (someone, right now in fact, is probably dying in a horrific car crash). In the same way, nuclear is far and away safer and more environmentally friendly than coal, but coals effects are more insidious, while nuclears is more disasterous. Thus, we overemphasis the danger of nuclear and underemphasize that of coal, much as plane crashes are big news, and car crashes are ignored. --Jayron32 22:07, 7 February 2011 (UTC)

There are several problems with nuclear energy. Apart from the fact that we have not yet found a proven solution for long-term treatment and/or storage of nuclear waste, the overall CO2 footprint is not that small. The power plant itself does not emit much CO2, but mining, transporting, and refining uranium is, at the moment, fairly CO2 intensive. A study a few years back found that nuclear power plants are better than coal (big challenge...), but slightly worse than natural gas in total CO2 production. The major snag for nuclear is, however, that it does not scale. Even now, people are not happy with Iran and North Korea expanding their nuclear capabilities. And I really don't want to see 10 reactors each in Nigeria, Eritrea, Colombia, Burma, Syria and Yemen. It enormously increases the risk of proliferation, and it's very uncertain if politically unstable countries can operate nuclear plants safely and securely. If we do not develop an energy solution with global reach, fossil fuel burning will simply shift to other countries. --Stephan Schulz (talk) 23:53, 7 February 2011 (UTC)

I would just like to note that theoretically the reactor problem does not have to be a big proliferation problem. There are types of reactors that are relatively proliferation resistant and would require really a lot of obvious effort to make a weapon out of. Extracting plutonium from spent fuel is not something that can be done in your basement.

The real proliferation problem is the fuel cycle. If you permit enrichment, then the proliferation problem is huge. If you permit recycling, it is not only monumentally huge, but you also raise the very real possibility that material can be stolen. (The "material unaccounted for" at a recycling plant the size of Rokkasho Reprocessing Plant, for example, is around 50 kg a year or so. That means that there is really no way for them to know whether a missing bomb's worth of plutonium is just lost in the pipes somewhere, or has been smuggled out by an employee.) --Mr.98 (talk) 01:04, 8 February 2011 (UTC)

Don't forget that in assessing the carbon footprint of a power station you need to do a life-cycle analysis from construction to decommissioning, not just a snapshot of consumption in normal use. Nuclear power stations are made of many tons of concrete, and manufacture of cement requires a very high energy input. Itsmejudith (talk) 12:29, 8 February 2011 (UTC)

Somehow that logic doesn't seem to add up. If a nuclear power plant really needs that much fossil fuel input than the energy prices from those plants wouldn't be competitive in the market place. We know that nuclear power is fairly competitive. Dauto (talk) 16:11, 8 February 2011 (UTC)

"We know that nuclear power is fairly competitive" - um, yes, once the government provides heavily subsidised risk insurance and waste disposal, not to mention the fact that governments underwrote most of the R&D to begin with. I don't think nuclear has ever competed fairly in a open market. --Stephan Schulz (talk) 21:28, 8 February 2011 (UTC)

Neither has coal, really. And I'm speaking as a Kentuckian. — The Hand That Feeds You:^Bite

It's hard to get raw economic numbers that are unbiased by politics on any infrastructure project, especially if the order-of-magnitude investment is going to be a few billion dollars. Thorough study of the reported costs will require parsing through thousands of analyses of construction, operation, labor, and technology costs; and it's naive to assume that a straight answer is available from every single contractor, who will act in good faith, provide correct numbers, and act selflessly to make sure the best technology wins (irrespective of individual profit potential). That's why the issue is so murky. For example, I hear the "concrete carbon footprint argument" a lot. I don't think nuclear plants require that much concrete, proportional to the energy they deliver. Remember: we're talking about an energy production system that can power an entire city for a thirty to fifty year lifespan. How much electricity and gasoline does one concrete factory use up, even accounting for all the embedded energy inputs in the mining and transportation? I'm astonished at the assertion that the amount of fossil fuel required to construct one building is even relevant. How can that amount of energy possibly compare to the amount of coal that is not burned as a result - literally an entire city's worth of fossil fuel, over a time-span of decades? A nuclear plant, at full capacity, produces about a gigawatt - that's one billion joules every second. Nimur (talk) 00:06, 9 February 2011 (UTC)

Isn't the comparison between nuclear and natural gas not nuclear and coal? Nil Einne (talk) 06:52, 9 February 2011 (UTC)

(EC)n the history of nuclear power plant operation, the radioactivity released to the environment has been at trace levels, except for Chernobyl type accidents. Coal contains Uranium and Thorium, which are released up the smokestack when the coal burns. See a paper from Oak Ridge National Laboratory, a nuclear think tank, which has a graph indicating about 12000 metric tons of Uranium and 3000 metric tons of Thorium released into the atmosphere from coal combustion in 2000. It says people living downwind from a coal plant are exposed to more radioactivity from the combustion of coal than if they lived downwind from a nuclear plant operated per regulations (again, excepting major accidents). It says the radioactive elements released from coal combustion far exceed the radioactive fuel used in nuclear reactors. Edison (talk) 16:16, 8 February 2011 (UTC)

"In the history of nuclear power plant operation, the radioactivity released to the environment has been at trace levels, except for Chernobyl type accidents." Didn't Marion Barry once say Washington, DC was safe except for murders? -- Mwalcoff (talk) 03:39, 10 February 2011 (UTC)

The nuclear pellets and other nuclear waste represent a storage and disposal problem as the involved radioisotopes often have a long half-life, as is the case for Uranium-238 which eventually decays to toxic lead. ~AH1^(TCU) 22:54, 11 February 2011 (UTC)

density

A NEEDLE IS IMMERSEDIN WATER BUT A HEAVY SHIP IS NOT. WHY —Preceding unsigned comment added by 122.179.85.65 (talk) 15:29, 7 February 2011 (UTC)

From Buoyancy: "A ship will float even though it may be made of steel (which is much denser than water), because it encloses a volume of air (which is much less dense than water), and the resulting shape has an average density less than that of the water". -- Q Chris (talk) 15:36, 7 February 2011 (UTC)

(EC) See Archimedes' principle, which should help. Mikenorton (talk) 15:37, 7 February 2011 (UTC)

Actually, a needle can also float, even though it's denser than water, due to a different reason than why a ship can float, namely surface tension. Red Act (talk)

Motor oil LD50

What is the LD50 of 10W40 motor oil? I saw the Quantum Solice James Bond where a guy was thinking about drinking it and wondered how toxic the stuff actually was. Googlemeister (talk) 16:23, 7 February 2011 (UTC)

You need to improve your google skills! This says the LD50 varies on the route of ingestion. Inhalation = 2.18 to >4 mg/l (Rat) Dermal = 2 gm/kg (Rabbit) and orally = 5 ml/kg (Rat). SmartSE (talk) 16:34, 7 February 2011 (UTC)

As an indication of how toxic it is compared to other oils though, it looks similar as they all seem to have similar LD50s. SmartSE (talk) 16:37, 7 February 2011 (UTC)

But does an LD50 of 5 ml/kg on a rat mean it is the same 5ml/kg on a human? I mean the metabolism is very different between a human and a rat and the digestive systems aren't quite the same etc... Googlemeister (talk) 17:34, 7 February 2011 (UTC)

Well I doubt anyone is going to feed engine oil to people and see how much it takes to kill them... Rat and human metabolism is very similar and tbh I doubt that engine oil is going to be metabolised anyway. SmartSE (talk) 17:54, 7 February 2011 (UTC)

Fair enough, but what specifically in the motor oil is toxic to people and how does it cause the harm? Does it paralyze muscles, or does it block neural signals or does it cause ruptures in the digestive tract or what? Googlemeister (talk) 20:01, 7 February 2011 (UTC)

"Symptoms of motor oil ingestion are depression, lethargy, paralysis of hind legs, staggering, vomiting and coma, in very severe cases." They're talking about dogs by the way. SpinningSpark 20:29, 7 February 2011 (UTC)

Sounds like a muscle relaxant then. Googlemeister (talk) 21:54, 7 February 2011 (UTC)

I do not believe that 5ml/kg is a sensible LD50. I would imagine anyone could drink 250ml. Meanwhile, fatty mc fatterson at 150kg could never finish 750ml. Just doesn't sound right to me. No source! Egg Centric (talk) 21:43, 11 February 2011 (UTC)

Veinal sins

The site where blood is removed and replaced in the veins and arteries, for dialysis, seems to deteriorate over time, such that they need to periodically change the location. What's the name and cause of this problem ? StuRat (talk) 18:04, 7 February 2011 (UTC)

Scar formation. Roger (talk) 18:23, 7 February 2011 (UTC)

Right, but what about dialysis causes the veins and arteries to scar ? Is it due to pressure, infections, some type of chemical imbalance, or something else ? StuRat (talk) 18:48, 7 February 2011 (UTC)

I presume it's just due to the repeated breaking of the vein wall by the insertion of the needle (or whatever the proper word is) and the resultant healing. I have a similar problem as a result of having donated blood many times: the staff sometimes have trouble finding a suitable spot to stab. AndrewWTaylor (talk) 18:54, 7 February 2011 (UTC)

In patients that are undergoing hemodialysis, there is usually a surgically created arteriovenous fistula or shunt. The various alternatives and some of the complications of this process are discussed at Hemodialysis#Access. --- Medical geneticist (talk) 19:16, 7 February 2011 (UTC)

Thanks. That said "The catheter is a foreign body in the vein and often provokes an inflammatory reaction in the vein wall". Doesn't medical science have any catheter material which doesn't provoke an inflammatory reaction ? StuRat (talk) 23:18, 7 February 2011 (UTC)

Dicrocoelium dendriticum or Dicrocoelium dentriticum?

Is it: Dicrocoelium dendriticum or Dicrocoelium dentriticum? I see sources for both. Is one simply a typo, or are both valid? Ariel. (talk) 21:59, 7 February 2011 (UTC)

Google scholar shows sources using both, but over ten times as many using the d, and many that use the t appear to be from non-native-English speakers. In short, the t form appears to be a relatively common error, but an error nonetheless. Looie496 (talk) 22:08, 7 February 2011 (UTC)

Chromatid is to sister chromatid as chromosome is to what?

What's the associated chromosome that every chromosome typically has in humans, among others? Not sister chromosome? --90.213.111.224 (talk) 22:21, 7 February 2011 (UTC)

Homologous chromosome? Not sure I understand what particular "association" you have in mind. DMacks (talk) 22:39, 7 February 2011 (UTC)

Life span of cut dogwood

I have some dogwood branches from a florist that I bought about a week ago. They've been sitting in my car (I live in Canada, it's pretty much been below freezing thus far). If I put them in a bucket of water now will they be okay? Or has it been too long and the branches are likely dead? Thanks. --生け花 23:23, 7 February 2011 (UTC)

There doesn't seem to be much cost to trying. One suggestion, cut the last bit of the branches off, under water. This will hopefully remove the dead, dried out portion, without introducing air bubbles into the circulation system of the branches, which would tend to prevent the uptake of water. StuRat (talk) 23:36, 7 February 2011 (UTC)

My grandmother could grow pants from cuttings such as a rose bush from cut flowers. Perhaps one has to be something of a "plant witch" to achieve such success. Edison (talk) 03:23, 8 February 2011 (UTC)

Were they in leaf, in bloom, or dormant? If they were already dormant, they still may well take root and sprout. As StuRat point out, it's a low-risk experiment. Good luck! SemanticMantis (talk) 04:17, 8 February 2011 (UTC)

They're..."dormant", I guess, since they are no leaves or flowers on them. I've placed them in water...hard to tell if it's having any effect though. :P --生け花 22:27, 8 February 2011 (UTC)

February 8

Pinhole

A single pinhole lens provides a single, dim image with an infinite field of focus. So:

1) Can multiple pinhole images be combined to create a single, bright image of infinite focus, using either mirrors to combine the images or electronic image capture from each pinhole to combine them ?

2) Or, if combining all those slightly different images leads to a fuzzy image, could adaptive optics be used to restore the composite image to a perfect focus ? StuRat (talk) 04:05, 8 February 2011 (UTC)

Pinhole lenses are pretty much poor-man's optics. If you're already going to use mirrors/lenses/digital processing to resolve an image, it seems that the pinhole becomes pragmaticly worthless. I suppose you could technically do all of the above, but it strikes me as rather pointless to use a lens or mirror to focus multiple pinhole images into a brighter image where the lens or mirror itself would do the job better by itself... --Jayron32 04:11, 8 February 2011 (UTC)

I think this was a physics question, not an engineering question. Ariel. (talk) 05:34, 8 February 2011 (UTC)

Also, there are ideas to image distant planets using an enormous pinhole camera. http://www.universetoday.com/9934/biggest-pinhole-camera-ever/ Ariel. (talk) 05:38, 8 February 2011 (UTC)

Actually, despite the article's name, I don't think that's really a pinhole camera. It's basically an artificial eclipse, which screens out the parent star so that the planet can be seen with a telescope. It looks to me like it is not a device meant to create an image somewhere based on the physical separation of rays with different angles as they pass through the pinhole. Wnt (talk) 01:01, 9 February 2011 (UTC)

The multiple pinholes would have different points of view, so their combined image via mirrors would inevitably be blurred, if there is anything in the foreground and if the pinholes are any distance apart. And a pinhole image is inherently blurry, not at all of "infinite focus." It is more of "no focus." It's just that nearby and distant objects are equally blurry, with the blur circles related to the size of the pinhole. A large pinhole lets in more light but has more blur. A very small pinhole has more diffraction. There is an optimum, as discussed in books by Ansel Adams. I have made pinhole images on photographic paper, then scanned the (negative) image, reversed it via Photoshop, and sharpened it via Photoshop, resulting in a very pleasing image. Photographic paper or film does a nice job of integrating photons over an extended exposure. Edison (talk) 04:49, 8 February 2011 (UTC)

I think there may be some miscommunication here. In the limit of a hole of width zero, StuRat is quite correct that a pinhole image has perfect focus regardless of the location of the target (but also zero brightness). And it is indeed possible to reconstruct a scene from an image formed using multiple pinholes -- there is a substantial literature on "multiple-pinhole image reconstruction". The technique is particularly useful for images formed using types of radiation for which no good lenses or mirrors exist. Looie496 (talk) 05:17, 8 February 2011 (UTC)

If the goal here is to create an image with infinite depth of field, I think a simpler solution would be to use a traditional camera and focus stacking. --Daniel 05:21, 8 February 2011 (UTC)

Edison is correct. In the limit of zero width the image becomes blurry. Dauto (talk) 05:28, 8 February 2011 (UTC)

Anti-Histamines + Zantac

Is there a reason why no drug company has marketed a anti-histamine such as Allegra (H1 blocker) + Zantac (H2 blocker) in one pill? I have patients with serious hives taking it and I hear it works much better than an anti-histamine alone. Would Zantac alone help also? —Preceding unsigned comment added by 76.169.33.234 (talk) 08:05, 8 February 2011 (UTC)

We do not give medical advice. And, yeah, that's it. --Ouro (blah blah) 12:30, 8 February 2011 (UTC)

Perhaps drug companies think that such pills will become cheaper than the price of the two separate pills. Count Iblis 14:11, 8 February 2011 (UTC)

I think we can answer parts of this question without violating the med advice restriction.

• The first question "Is there a reason why no drug company has marketed..." is probably simply because the combination of H1 and H2 blockers hasn't been proven to be efficacious and the FDA (presuming this is referring to the US) has not approved the use of H2 antagonists for this purpose. If a well designed randomized controlled trial demonstrated that a combination drug was superior to the single drug standard of care, it would probably be marketed quickly to replace the old stand-bys. And I doubt that it would be cheaper -- they would come up with a fancy name like Zanyryx XR (lots of x's, y's, and z's means its a really good drug), package it up in a nice box, spend gazillions on marketing to convince the general public to "ask your doctor how Zanyryx can help you" and quadruple the price of the two individual components. Who wants to take two separate pills when you can take just one!
• With regard to the last question "Would Zantac alone help also?" we can't really say for any given patient whether ranitidine would be helpful, but for general information about this topic we can point the OP towards references ([8] and [9]) the latter of which says: "An H2-antihistamine administered concurrently with an H1-antihistamine may modestly enhance relief of itching and wheal formation in some patients with urticaria refractory to treatment with an H1-antihistamine alone. The available evidence does not justify the routine addition of H2-antihistamine treatment to H1-antihistamine treatment."

Does that help? --- Medical geneticist (talk) 14:45, 8 February 2011 (UTC)

My guess is that the biggest reason you don't see an Allegra/Zantac combo pill (at least in the US) is that Allegra was approved for treatment of allergies, and Zantac was approved for treatment of stomach issues. Although doctors are free to prescribe drugs for off-label use once they are approved, the FDA has some pretty stringent rules on marketing drugs for off-label use. Who would you "officially" sell the combo pill to? People with both allergies and acid reflux? Combo pills like Ezetimibe/simvastatin (Vytorin) and amoxicillin/clavulanic acid (Augmentin) are sold because both drugs treat the same condition. A pill for treatment of two different conditions doesn't have as large a market (and you can't sell it to treat a single condition, because the drugs aren't approved to treat a single condition). Even if the combo does better than one drug alone, the FDA (or insert-country-specific-regulatory-agency) wouldn't approve it until you did a clinical trial to show that it did. That's a massive expenditure of cash for drugs which are off patent, even if prior approval means you can skip most of the safety stages. -- 174.24.195.38 (talk) 16:22, 8 February 2011 (UTC)

Thanks for the answers. I don't really see how this is medical advice and it kind of irritates me how a lot of times when people ask questions that aren't really medical advice, its considered that. I work in a pharmacy and have seen the combination recommended more than once. I know it wouldn't be cheaper, but drug companies are always looking to make more money. For example, they combined Imitrex which is now available in generic with aleve to make a new migraine drug just to make a new brand name drug. Aleve isn't used to treat migraines, if anything, it can treat minor headaches at the most. —Preceding unsigned comment added by 76.169.33.234 (talk) 05:57, 9 February 2011 (UTC)

What you are seeing is called "off-label use" as implied by user 174.24.195.38, when doctors prescribe a drug that is FDA approved for one use but is found by the medical community to be useful for something else. This practice is part of the discretion that a physician has in treating patients, but it is a little risky to prescribe a drug for something that has not been rigorously proven beneficial. p.s. the reason your question got flagged as possible med advice is that you mentioned a very specific patient scenario, about which we cannot give information --- Medical geneticist (talk) 12:09, 9 February 2011 (UTC)

What causes you to want to stretch in the morning?

What causes you to want to stretch in the morning? It seems as though it is almost an involuntary action, or at least that you would be very silly to resist the urge when it comes. I am looking for a reason on some molecular or cellular level if possible.

I asked some friends about this and we came to the educated guess that it had something to do with your muscles/other tissues wanting more oxygen, so they output some chemical that sends a signal to your brain to stretch, making more blood flow to your muscles....

Is this even remotely accurate? what are the processes involved and why does your body force you to stretch?

137.81.116.186 14:29, 8 February 2011 (UTC) —Preceding unsigned comment added by 137.81.116.186 (talk)

I can't comment at the molecular level, but think the reason for it is to prevent muscle injuries. Just like you should stretch before running, you should also do that before using muscles for the first time each day. One thought is that it may be simply to increase the temperature, as muscles, tendons, etc., become more flexible and less likely to tear at higher temps. Locations far from the body core, like say the Achilles tendon, are perhaps most likely to be cold in the morning (especially if your feet stick out from under the blankets), and thus in most need of a few warm-up exercises. StuRat 16:58, 8 February 2011 (UTC)

As discussed in Stretching#Research and controversy, the research is unclear about whether a few minutes of static stretching (the typical kind) before activities like running actually does prevent any injuries, and pre-event stretching may even have a negative impact on performance. Stretching matters more in sports where you need a very large range of motion, but running isn't one of those. Others suggest that dynamic stretching may have more of a benefit, but there isn't much research on that either way. It is however good to stretch or participate in other cool-down activities after exercise (including running), because it helps the muscles relax gradually and that is clearly found to help prevent injury. What any of this means for the early morning stretch, I don't really know. Dragons flight (talk) 21:00, 8 February 2011 (UTC)

There is a stretching "controversy", lol. I don't know why but I find that really funny.. Forgive me I haven't had my coffee yet. Vespine (talk) 21:37, 8 February 2011 (UTC)

It's a combination of two things, first the fact that joints and muscles tend to stiffen when they are not in use due to the formation of adhesions between muscle fibers, second the properties of circadian rhythms. During the nighttime hours, body temperature drops and a variety of injury-repair mechanisms are activated -- both of these tend to promote formation of muscle and joint adhesions that are broken by stretching. Looie496 (talk) 22:54, 8 February 2011 (UTC)

A rifle with a barrel made of heat resistant ceramic

Is it possible to make something like this? ScienceApe (talk) 15:01, 8 February 2011 (UTC)

Yes. It is possible. However, it is not as good as a regular barrel. Instead, it is common to have a regular barrel with a ceramic lining or coating. -- kainaw™ 15:04, 8 February 2011 (UTC)

Ceramics are generally too brittle to absorb shock loads without damage. The elasticity of the types of steel used for rifle barrels is what allows them to contain the shock (abrupt change in pressure) of firing. I would like to see some evidence of User:Kainaw's claim that ceramic coatings or linings are common. I've seen and handled many different rifles in my life and I have yet to lay eyes on one with such a lining or coating. The overwhelming majority of rifle barrels are just steel with various finishes ranging from blueing, Parkerizing, nitriding, case hardening to plain and simple enamel paint. Roger (talk) 16:15, 8 February 2011 (UTC)

Something I know next to nothing about but I wonder about that too from my searches. These 2 refs from 2003-2004 suggest it's an area of active research for the US army but not currently very successful [10] [11]. Things may have changed a lot since then but if not I wonder how common it can be if even the army isn't doing it. It seems some companies to offer to coat existing guns, e.g. [12] [13] but this doesn't sound like something which would be common. Incidentally from some of those refs I think chrome line barrels may be somewhat common. Nil Einne (talk) 16:23, 8 February 2011 (UTC)

(ECx3)Ceramics can be resistant to high temperature, and can have great compression strength. Do ceramics have the tensile strength to prevent the barrel splitting open from the outward directed pressure, without having a ridiculous wall thickness making the weapon non-portable? Aren't they generally brittle? Edison (talk) 16:25, 8 February 2011 (UTC)

As a general rule, ceramics are not good at tensile strength. Some composite materials like carbon fiber might be able to give greater tensile strength then ceramics, but they might still be brittle enough to shatter in that application.

Hot body in vacuum

Suppose a solid sphere of metal of 1 sq.m (choose a convenient substance) of 100 deg.C perfectly isolated by any incoming energy in perfect vacuum. How much time it will take to get to the lowest temperature it can reach? --M121121121 (talk) 20:53, 8 February 2011 (UTC)

This sounds suspiciously like a homework question. No one here at Wikipedia is going to answer the question for you, but if you want some background on the concepts you need to solve it, see black body and thermal radiation. --Jayron32 21:03, 8 February 2011 (UTC)

Forever. Assuming it were perfectly isolated (which is impossible, but we can assume it anyway), it would radiate energy away in ever decreasing amounts as it's temperature decays towards but never actually reaches 0 K. For details, see Stefan-Boltzmann equation. Dragons flight (talk) 21:06, 8 February 2011 (UTC)

It's not homework, but you're right. Who/where should I ask for this calculus? Please advice. --M121121121 (talk) 21:24, 8 February 2011 (UTC)

The appropriate equation to apply is the Stefan–Boltzmann law, which defines the rate of heat loss from a body. It's worth noting that if the object is in the "empty vacuum of space", the relevant "cold sink" is the cosmic microwave background, at around 3 kelvins. Nimur (talk) 21:30, 8 February 2011 (UTC)

You said it is "perfectly isolated by any incoming energy":

A) Assuming "by" means "from", that would mean it would also be perfectly isolated as far as radiating out energy. If there was such a perfect thermos, it would stay the initial temperature forever.

B) If, however, we assume that it's the only source of energy in the universe, then it would radiate energy but not receive any back. In that case the temperature would decrease at a decreasing rate, but would still never quite reach absolute zero.

C) If we assume it's in the real universe, but far from any source of energy, as in a galactic void, then the temperature would again decline at a decreasing rate, gradually approaching the average temperature in that void. StuRat (talk) 22:50, 8 February 2011 (UTC)

Far out, when you were at school did you try to lecture your teacher about how there's no such thing as a perfectly frictionless surface? Don't take it personally but I completely don't see the problem with the way the question was asked. For the majority of hypothetical physics questions I've ever seen you are expected to leave the assumptions at the door. If it doesn't mention air resistance, ignore it, if it doesn't mention MBR: ignore it. If it says "perfect vacuum" don't think it actually means "real vacuum of space'… Given this premise, what is the result? Full stop. As far as I can tell, Dragon flight and StuRat answer B give the answer forever, which I think is correct, but if you had the "method" which I admit I don't, you could at least come up with some more meaningful replies, like maybe how long would it take to get to 50%, 1% and 0.1% of the absolute temperature. . Vespine (talk)

I have no problem with questions which have assumptions that don't exist in the real world, but we do need to be very specific about what those assumptions are, as they can change the answer dramatically. StuRat (talk) 06:18, 10 February 2011 (UTC)

Reformulating the initial question: how much time needs an isolated object to loose all (as much as possible) its energy only by radiation? A naked human in outer space will freeze? (leave the zero pressure problem at this time)M121121121 (talk) 07:39, 9 February 2011 (UTC)

The colder it gets the slower it radiates (temperature to the power 4), so there is no answer to your first question. To your second question, if the human is in sunlight they won't freeze (but will get a horrible sunburn). If in the shade they will freeze eventually, see Stefan–Boltzmann law for the numbers. Ariel. (talk) 08:41, 9 February 2011 (UTC)

Assuming that the sphere is hollow, painted black (special black to be a black body), and has a high conductivity, then the temperature will fall very quickly to a few (tens of) degrees Kelvin (because rate of fall in temperature is roughly proportional to the fourth power of absolute temperature if background microwave absorption is ignored). (The human body would lose heat much more slowly because of low conductivity.) I'm struggling with the constants to be able to find the solution to the differential equation. Perhaps someone more knowledgeable could make an estimate for a typical sphere. Dbfirs 08:44, 9 February 2011 (UTC)

Homemade cavendish experiment .

I do enjoy this facinating webpage. I like seeing the videos of the "mass attracting mass" but I am still a little skeptical.

http://www.fourmilab.ch/gravitation/foobar/

It still seems a little strange to me to actually see gravity interacting with such homemade apparatus. Are the masses too small? Is there some kind of experimental error going on? Perhaps an electric force is causing this?

What do you think? —Preceding unsigned comment added by 92.17.89.69 (talk) 21:09, 8 February 2011 (UTC)

Well, the Cavendish experiment is well known; and you can, using simple Newtonian physics equations, estimate what the force should be and decide if the magnitude of errors introduced by, say, turbulent air currents or electric forces are relevant. You can also eliminate (or at least, reduce) electrostatic effects by grounding all involved objects with electrically conductive wire. I have to say, the experiment seems pretty fantastic! But, as a firm believer in Gravity, I am at a loss to come up with a more plausible reason why the balance would torque in this way. (Though I admit, gravity is a bit implausible, but I observe it daily nonetheless). Nimur (talk) 21:39, 8 February 2011 (UTC)

Do objects tend to drift like this on say the ISS? Say they left a bowling ball hovering, would it accelerate towards the center of gravity on the space station? —Preceding unsigned comment added by 92.17.89.69 (talk) 21:59, 8 February 2011 (UTC)

Assume a spherical hollow metal spaceship in orbit and a bowling ball released at a random spot inside, with no air currents. If I remember my physics course correctly, unless the spaceship accelerates, there is no reason for the bowling ball to move from its random release point, since the gravitation attraction of the spacecraft for its contents is effectively zero. The attraction from one part of the craft is cancelled by the attraction of the rest of the craft.

Center of Gravity? An object floating free in a orbiting vessel would be affected by the sum of the masses around it, relative speed and the air currents of the air conditioning system. Also, it may be deflected on route, by any skittles it meets on the way. The article on Micro-g environment may be of interest too.--Aspro (talk) 22:15, 8 February 2011 (UTC)

(ec) The ISS, and other manned spacecraft, are in "microgravity" - which is to say, not quite freefall. There's a small but measurable net force on the spacecraft at almost all times, caused by the acceleration due to non-ideal effects like gas drag and orbit correction maneuvering (stationkeeping). Stanford's Gravity Probe B might be interesting, though - an entire spacecraft was launched just to measure the gravitational nonlinearity under ideal conditions. Preliminary results were announced a couple of years ago (see this press release from April 2007's APS Plenary; unfortunately, the mission wasn't well-received when the data turned out to be noisier than expected. Nimur (talk) 22:18, 8 February 2011 (UTC)

Speaking of spacecraft that are solely to measure gravity, check out the Gravity Recovery and Climate Experiment. Here, two spacecraft make fine measurements of the Earth's (slightly non-uniform) gravitational field. It's pretty amazing being able to watch the mass of the amazon change depending on which season it is. Buddy431 (talk) 02:33, 9 February 2011 (UTC)

The experimenter apparently did nothing to rule out electrostatic attraction as an explanation for the effects. The plastic foam arm is an excellent insulator, as is the monofilament line, and it would be amazing if there were no electric charge on the arm or the weights. A metal support wire, a wooden arm, and a wooden frame holding the other weights and all connected together like the Cavendish apparatus would be an improvement, since wood is a poor insulator in static electric terms. I have seen demos of charging a piece of PVC pipe by friction from a piece of fur, then using it to make a can of pop roll rapidly toward it, a stronger force by orders of magnitude than the gravitational attraction of the small weights. Edison (talk) 00:04, 10 February 2011 (UTC)

The straw that stirs the drink

Whenever I pour a carbonated beverage into a glass and stick a straw in it, CO2 bubbles invariably attach to the straw, then lift it to the point where it seems like the straw should fall out of the glass. However, I have never had a straw actually fall out. What provides the force keeping the straw in place? Is there a length beyond which the straw will tumble? Hemoroid Agastordoff (talk) 22:03, 8 February 2011 (UTC)

I have often had a straw fall out. Perhaps I fill my glass fuller? 86.162.68.36 (talk) 22:17, 8 February 2011 (UTC)

Surface tension will sometimes prevent the straw from falling out, even when the centre of mass is outside the rim of the glass, but it will often be insufficient to prevent a long straw from falling out of a full glass. Dbfirs 08:12, 9 February 2011 (UTC)

clouds

why are clouds white? 71.2.42.116 (talk) 22:11, 8 February 2011 (UTC)

Have you discovered our search box? It just so happens, we have a article section on the colour of clouds.--Aspro (talk) 22:23, 8 February 2011 (UTC)

Sanitary drain(industrial sewer) sizing and design discharge flow rate estimate

how do I estimate discharge flow rate (L/s) based on the number of fixture units?--165.228.109.94 (talk) 22:21, 8 February 2011 (UTC)

Kilos instead of larger units

Why planet and star masses are commonly indicated in kilograms instead of more handy larger units, such as gigatonnes or teratonnes (where no exponentiation would be necessary)? —Preceding unsigned comment added by 89.76.224.253 (talk) 22:28, 8 February 2011 (UTC)

Actually, most astrophysicists use cgs units - that is, grams, to measure the mass of planets. Why? Because they're dealing with many orders of magnitude during different calculations, so they must use scientific notation anyway. In other words, exponentiation will be required, no matter what, so we might as well use it consistently. (Though, Griffiths and others attribute the cgs preference to electrodynamics, where the gauss and the convention of unitary permittivity- and permeability- of free space, require "less writing." Other physicists, cosmologists in particular, prefer dimensionless physical constants, so they prefer the ("horribly inconvenient") SI units normalized by the values fundamental constants, called "planck units." As physicists, when we study planets and space science, we try to isolate any "biases" we might have in our system of units that are historical artifacts of measuring the size of the Earth. SI and cgs is not entirely guilt-free in that respect, as the meter is historically defined as a ratio to the earth's circumference. But in any case, if you're going to measure a planet's mass, it's still going to be "huge", whether you measure it in grams, tons, or solar mass units; and if you measure two planets, chances are you'll need scientific notation in any unit system. Nimur (talk) 22:45, 8 February 2011 (UTC)

Careful there Nimur. If one uses solar masses than the mass of a planet will not be a huge number and in fact that is the most common choice among astrophysicists (That is the choice of most of my books). Also, the Planck units are not horribly inconvenient. If they were, nobody would use them. Finally, the Plank system of units is not based on the SI as you stated. Dauto (talk) 02:47, 9 February 2011 (UTC)

I think you misread Nimur's phrasing. To be fair to you, it was not as hard to misread as it could have been. The "horribly inconvenient" refers, I think, to SI rather than to Planck units, and I don't see anything that suggests Nimur claimed the latter were based on the former. --Trovatore (talk) 03:18, 9 February 2011 (UTC)

"Horribly inconvenient" was meant to be tongue-in-cheek; obviously, any reasonable unit system has a purpose. And regarding "huge": I consider 1x10^-6 solar masses to be "huge", even if the number is represented as a minuscule fraction; my point was to illustrate that representational units don't actually change the size of the object. Nimur (talk) 07:56, 9 February 2011 (UTC)

Help understanding Parsec illustration

Can someone chime in at Talk:Parsec#Dots in image? I didn't understand the image used in the article and would appreciate some help in that regard. Thanks, Waldir ^talk 22:54, 8 February 2011 (UTC)

I think has been resolved. --Mr.98 (talk) 13:50, 9 February 2011 (UTC)

Trampolining gives you muscles?

An acquantance of mine has an amazing body. He has big legs, a six pack, good arms, and generally good upper body and back. When I asked him how many times a week he worked out he replied that hedidn't work out at all. He said he uses his mini trampoline every day. Can this be true? Google shows many health benefits of trampolining but it doesnt go into detail about muscle growth. I can understand how it might get you big legs but a six pack!?! Surely that would be reason enough for every guy anywhere to get one? Surely such a thing would widely known and not such a well kept secret? And asked him another day whether he really meant a mini trampoline and he replied affirmatively. I mean you cant ever do sommersaults on those! So how do you explain the good arms and upper body? Edit: oh and by 'big' I may be exaggerating slightly. He doesnt loook like a body builder but he does have a very impressive slim athletic physique. —Preceding unsigned comment added by 91.49.33.244 (talk) 23:32, 8 February 2011 (UTC)

What he didn't tell you is about all the steroids he takes. Looie496 (talk) 01:32, 9 February 2011 (UTC)

I think as much as a lot of people argue to the contrary, not everyone is created equal. Genetics plays a not insignificant part in how your body will look as well as a countless number of other factors which might not even be considered "exercise". Things like diet and eating habits, sleep habits, lifestyle in general, things like how much you walk and even seemingly inconsequential things like do you "fidget", all these play a part in your physique. One very interesting comparison you can easily make is look at the competitors of fighting sports like UFC, they are all without a doubt extremely fit individuals who train very hard but they still have widely varying body types. No doubt some of the extremes are due to drugs like the above suggests, but I believe even if you excluded that, you would still see a big difference between body shapes, like shoulder width, muscle definition even amongst people who have similar exercise routines.. There was a time before my brother and I had ever gone to the gym but he's always been much bigger then me, we grew up eating the same foods and doing similar activities, even though he was only 18 months older then me, in our teens I weiged between 60 and 70 and he weighed between 80 and 90 and wasn't slim but not exactly what you'd call "fat". Vespine (talk) 02:49, 9 February 2011 (UTC)

February 9

What's a good nonpolar organic solvent?

Preferably not carcinogenic. --75.15.161.185 (talk) 00:26, 9 February 2011 (UTC)

Can you be a bit more specific about your needs? How about cyclohexane? TenOfAllTrades(talk) 00:53, 9 February 2011 (UTC)

It should be able to dissolve lipids but not other compounds in food. --75.15.161.185 (talk) 02:32, 9 February 2011 (UTC)

Lipids are basically the entire class of all hydrophobic biological compounds, so by definition if it dissolves substantially in cyclohexane, it is a lipid. I am pretty sure that's how lipids were classified in the earliest days when such things were classified. See Lipid for more. --Jayron32 03:57, 9 February 2011 (UTC)

Vegetable_oil#Extraction notes that hexane and supercritical carbon dioxide are used commercially to extract oils from the vegetable matter. (I assume that there's probably a food-grade hexane for that purpose.)-- 174.24.195.38 (talk) 04:10, 9 February 2011 (UTC)

Flight control surfaces on modern airliners

In modern airliners, how do the flight control surfaces work? I know that they are usually powered by hydraulics, but how is the power applied from the hydraulic system to the control surfaces? Is it a cable system, levers and hydraulic cylinders, etc.? Also, what does the mechanism inside the flap canoes/fairings look like and how do they work?67.169.5.125 (talk) 05:25, 9 February 2011 (UTC)

The engines drive hydraulic pumps through their accessory gearboxes. The control inputs by the pilots are interpreted by the flight control computers which in turn actuate various valves to move the relevant hydraulic rams attached to the control surfaces. Feedback from the surfaces is returned to the flight control computers which in turn move the controls to provide tactile feedback to the pilots. This is the short answer - for a more comprehensive answer, read Fly-by-wire. Roger (talk) 08:44, 9 February 2011 (UTC)

Homework question on momentum + pendulum

Hi all,

I have a physics homework that I am completely stuck on. I have no clue how to approach this question at all. Any help would be appreciated!

In a ballistic pendulum an object of mass m is fired with an initial speed v_0 at a pendulum bob. The bob has a mass M, which is suspended by a rod of length L and negligible mass. After the collision, the pendulum and object stick together and swing to a maximum angular displacement theta as shown . http://session.masteringphysics.com/problemAsset/1010989/28/1010989A.jpg

Find an expression for v_0, the initial speed of the fired object.

Again, any help would be appreciated!! —Preceding unsigned comment added by 169.232.78.43 (talk) 05:45, 9 February 2011 (UTC)

The calculations actually have two parts. When the bullet impacts the bob, kinetic energy is lost to friction, but momentum is concerved. When angle theta is reached and the bob is at rest, the remaining kinetic energy (which you can calculate from knowing what the momentum will be) has become gravitational potential energy. If you can write out the formulae for all of that, you can solve for V_o in terms of theta, L, m and M. Someguy1221 (talk) 05:56, 9 February 2011 (UTC)

Initially, I would tackle this problem using the principle of conservation of linear momentum. Momentum of object prior to impact equals momentum of object plus bob after impact.

Mechanical energy is not conserved during the collision because some of the initial energy of the object is converted to heat, and some is used in deformation of itself and the bob as it enters. Kinetic energy and potential energy can be calculated for the period after the collision. Mechanical energy is then conserved for the period from the end of the collision until the bob comes to rest, and that should yield your answer. Dolphin (t) 07:16, 10 February 2011 (UTC)

are

are concrete warehouses like bestbuy insulated i see none — Preceding unsigned comment added by Tomjohnson357 (talk • contribs) 06:44, 9 February 2011 (UTC)

Punctuation would help us to understand your question. --Lgriot (talk) 08:34, 9 February 2011 (UTC)

There's lots of ways they could do it. Probably the simplest is a double wall with insulation in between like this: Insulated concrete form. Or you install metal studs inside the building and insulation between them, then drywall. Ariel. (talk) 08:46, 9 February 2011 (UTC)

If the universe is not spherical...

When something expands at the same rate from a single point, the result is a sphere. If something expands at different rates in different places, the final result is a non-spherical shape.

So, if the universe is flat, saddle-shaped or anything but a sphere, what mechanism explains this uneven distribution of expansion? Thanks. Leptictidium (mt) 07:35, 9 February 2011 (UTC)

If I'm reading you right, your question assumes that the universe expanded from a point into the nothingness around it. That's not the case. The universe would have always had its current overall topology, and has simply been getting bigger. Someguy1221 (talk) 08:29, 9 February 2011 (UTC)

So, assuming the universe is flat: the Universe wouldn't have expanded from a single point, as proposed by the Big Bang theory, but rather from a single, infinitely small, "sheet of paper"? Leptictidium (mt) 09:18, 9 February 2011 (UTC)

No, but I'm going to wait for someone with a better grasp of generaly relativity to really answer that, but in the meantime please treat yourself to metric expansion of space. Someguy1221 (talk) 09:25, 9 February 2011 (UTC)

If you insist on imagining that the universe expanded from a single point then you have to remember that this point is not embedded in some empty space. The point is the entire space, it is not embedded in anything. However, it is better to remember that the "Big Bang" is actually nothing but the result of an extrapolation of the observed expansion backwards in time, and in fact beyond the limits where our understanding of physics holds (which gets close to the BB but does not reach it). We do not know what the Big Bang looked like. --Wrongfilter (talk) 09:41, 9 February 2011 (UTC)

Indeed. The Big Bang theory does not assume that the Universe "expanded from a single point". It proposes that the Universe was originally in a very hot, dense state; it makes no assumptions about the topology of spacetime in this state. Also, Leptictidium, I think you have misunderstood the meaning of "flat" when applied to a four-dimensional manifold such as spacetime. You may learn more by reading our articles on the shape of the Universe and the flatness problem. Gandalf61 (talk) 09:57, 9 February 2011 (UTC)

Why would faster than light travel mean going back in time?

It's a point that I don't really understand. Yeah, sure, perhaps nothing can go faster than light, but I don't get the "going back in time" bit. If when I look at the Moon, I see it as it was about 1.5 seconds ago, then if I flash myself there instanteously, I would be there as it is right now, 1.5 seconds into the future of what I was seeing. What is paradoxical about that? When I am far away from a man chopping wood, I hear the axe hit the wood well after I see it strike. If I move next to him, then I see and hear the chop at the same time. If everyone was blind, and had to depend to sound only, would someone argue that if sound could travel instantaneosly, you could go back into time?

Also, while it has been observed and now measured very thoroughly, we know that everyone sees light travelling at the same speed regardless of their own local motion, or that of the object which is transmitting the light. But I don't think it has ever been shown why this is true, or has to be true. Is that right? Myles325a (talk) 11:07, 9 February 2011 (UTC)

To answer your first question - strictly speaking, the special theory of relativity does not forbid an object from travelling faster than the speed of light - it forbids an object from accelerating from a slower-than-light speed to a faster-than-light speed (or vice versa). This is because an object with a non-zero rest mass would have an infinite relativistic mass and hence infinite energy if it ever travalled at the speed of light. Photons side step this problem by having zero rest mass - but as a result they can only ever travel at the speed of light, and cannot speed up or slow down. Physicists have postulated hypothetical particles called tachyons that always travel faster than the speed of light. Although tachyons do not violate special relativity, they have some strange properties such as "imaginary" mass, and they also appear to violate the principle of causality, so most physicists do not believe they can exist in our universe. Gandalf61 (talk) 11:46, 9 February 2011 (UTC)

I've drawn some ASCII space-time diagrams in the early history of the internet, but can't seem to find them anymore. The problem is that if you go faster than the speed of light in one inertial system, you go back in time in another (relatively moving) inertial system. Take a look at Minkowski diagram, and in particular at Minkowski diagram#Constancy_of_the_speed_of_light and the following two sections. --Stephan Schulz (talk) 12:28, 9 February 2011 (UTC)

See also this article: Tachyonic antitelephone. So, if you can violate the speed of light limit by merely being able to send information faster than light (regardless of how you do it), then you can exploit this to build a device that is able to send information back into your own past. You can then build a "telephone" with which you can talk to yourself in the past. This then leads to a causal paradox because if you receice a phonecall now from your future self living tomorrow, you can then decide not to call past self tomorrow while, if you don't receive a phonecall, you can decide to call yourself. So, a clear paradox is obtained. Count Iblis (talk) 13:50, 9 February 2011 (UTC)

You say "you can decide", but this seems open to dispute. One assumes that a four-dimensional spacetime that in some region curves back on itself admits a mathematical solution, just as one which does not. Wnt (talk) 21:13, 9 February 2011 (UTC)

Light cone in 2D space plus a time dimension.

Let me explain using the light cone picture I've added. For any given point in space-time, the remainder of space-time can be divided into four zones called the absolute future (points that can be reached by traveling slower than light), the absolute past (points from which the current point can be reached by traveling slower than the speed of light), the absolute present (points lying directly on the light cone), and the absolute elsewhere (points lying outside both the future and past light cones). These zones are the same regardless of the velocity of the observer. If it is possible to send signals faster than the speed of light, then it is possible to send signals to points in the absolute elsewhere. In fact, by altering the velocity of the signal source, it is possible to send signals to any point in the absolute elsewhere. But if you pick a point in the absolute elsewhere and draws its light cone, you will see that the absolute elsewhere for that second point overlaps with the absolute past of the first point -- meaning that a return signal from the second point can end up in the past of the first point. The crucial point is that the only velocity-independent distinction between past and future is that given by the light cone. Within the absolute elsewhere, the distinction between past and future is a function of the velocity of the observer -- any particular point can lie either in the past or the future, depending on how the observer is moving. Looie496 (talk) 17:46, 9 February 2011 (UTC)

This assumes that the person can travel infinitely fast in any frame. However, it is possible that an ansible may allow infinitely fast transport in only one privileged frame at any given point in space, such as the frame of the cosmic microwave background or the aggregate mass of the universe. This frame presumably varies according to Hubble expansion, gravity and so on. In this way, an observer with some velocity relative to this absolute frame may see the ansible capable of transmitting into the past in one direction, but only into the future at a finite faster than light velocity in the opposite direction. But he never sees anything capable of transmitting into its own past. (this is akin to the one-way speed of light mind game) Wnt (talk) 22:22, 9 February 2011 (UTC)

Orbits and angular momentum

I love science but i'm not a scientist, so apologies if some of the terminology in this question is incorrect. Why do the planets orbit the sun on a single plane? Similar examples are planetary discs, or the stars within a galaxy - they all orbit on a plane as opposed to on a shell (think of the simplistic model of an electron 'shell' orbiting a nucleus). Is it something to do with angular momentum? —Preceding unsigned comment added by 80.168.88.74 (talk) 12:17, 9 February 2011 (UTC)

The article Formation and evolution of the Solar System and related Protoplanetary disk and nebular hypothesis explain quite a bit. In simplest terms (and I may get this a bit wrong, so actual physics people can correct me) is that as a cloud of debris rotates around a star, it forms a disk around the equator of the sun, the forces involved in the spinning encourge that shape. Since the planets all form out of the material of that disk, they retain that roughly planar orientation with each other. This is different from electrons "orbiting" a nucleus, because the electron cloud itself doesn't revolve around the nucleus. Also, so-called "spins" in electrons and in the nucleus of an atom is not actual physical "spinning", rather it is a property which obeys the mathematical rules of spinning; but it does not seem that electrons and nuclei actually rotate like a star or planet does. --Jayron32 13:06, 9 February 2011 (UTC)

Thank you Jayron. From the Formation article you linked to - "the competing forces of gravity, gas pressure, magnetic fields, and rotation caused the contracting nebula to flatten into a spinning protoplanetary disc". Could you explain how these forces cause the flattening? The spinning/flattening pizza dough in the article is a good analagy, it's just understanding how all these forces result in the net effect of flattening that I struggle to understand. —Preceding unsigned comment added by 80.168.88.74 (talk) 14:03, 9 February 2011 (UTC)

Very simple explanation: gravity wants $x=y=z=0$, but conservation of angular momentum prevents x and y from being 0 (except momentarily in the course of an orbit). Gravity gets its way in the third dimension, so the result is flat.

More detail: The angular momentum effect is quantified in the effective potential that prohibits having all the mass at the center (consider what happens in the last equation in that article when r is very small). Nothing prevents most of the mass from piling up at the center: that's the Sun. Moreover, the restriction only applies in the one plane perpendicular to the momentum; anything outside that plane returns to it at some point during its orbit, and it then has the opportunity to collide with other objects in the plane. Eventually almost all motion perpendicular to the plane is arrested and you get a disk. (I don't know the particular role that magnetism plays here.) --Tardis (talk) 16:45, 9 February 2011 (UTC)

The mathematics of the principal axes might be useful here. Without diving too deeply in to complicated mechanics treatment, it is a fact of physics that angular momentum must be conserved; and it is also a fact that in a lossy system (e.g., an n-body system with non-negligible gravitation between particles, and with collisions), even if rotational kinetic energy is initially distributed uniformly in the macroscopic system, inter-particle interactions will "leak" energy into the principle axes of the system. (You can accept this on faith, or you can work out the long-term evolution of the statistics of the equipartition theorem for an n-body gravitational system with collisions). It's not all that different from these nifty toys: tops that "only spin in one direction". The thing is, the system has conditions that allow energy to transfer from one mode of rotation (say, "aplanar" orbits with random alignments), towards a preferred, principle mode of rotation (planar orbits, aligned in the plane of the system's initial net angular momentum vector). Because of lossy system-instabilities, rotational energy concentrates into one mode. Nimur (talk) 22:55, 9 February 2011 (UTC)

Accretion disc is an interesting article about the subject. - manya (talk) 04:06, 10 February 2011 (UTC)

Aha! I've just had a eureka moment! I've been reading the articles you've all kindly linked to and they all helped. My understanding is that gravity and angular momentum are the two main forces. Gravity reduces the z axis to 0, whilst angular momentum prevents the x and y axis from being 0, the shape of which is a flat disc. This looks similar to Tardis' description, but it's taken all your responses to get me there, so thanks. —Preceding unsigned comment added by 80.168.88.74 (talk) 10:44, 10 February 2011 (UTC)

Straight line contrails

Why is it that nearly all vapour trails from aircraft show as a straight line? I have seen them expand as they get further from the plane but I would expect them to curve as the effects of cross winds move the vapour accross the sky.82.69.87.152 (talk) 12:56, 9 February 2011 (UTC)

The contrails do move with the wind. But that's no reason for them to curve. If the wind and the plane's course are both steady, you get straight contrails that extend from the current position of the plane in a direction that differs slightly from the plane's (ground-based) course. –Henning Makholm (talk) 13:23, 9 February 2011 (UTC)

Here's an illustration of Henning's point. The photo at the link shows the contrails left by an aircraft in a holding pattern, flying a 'racetrack' circuit over and over. While the plane always passes over the same track on the ground, the wind moves the contrails so that each loop of the pattern is offset slightly from the one before. TenOfAllTrades(talk) 14:19, 9 February 2011 (UTC)

is it a scientific fact that there is never a miscommunication between the tides and the moon that causes them?

Is it a scientific fact that there is never a miscommunication between the tides and the moon that causes them? 217.136.92.148 (talk) 13:07, 9 February 2011 (UTC)

First, you must define what you mean by "miscommunication". Otherwise, your question is nonsense. It is not possible to provide a reference for nonsense questions. Because this is not a chat room, we do not chat about nonsense. -- kainaw™ 13:16, 9 February 2011 (UTC)

The only possible way I can think of for the tides to not sync properly with the moon would be if there was a celestial body that had a gravitational influence on earth that was a significant percentage of the gravitational influence the moon had which was on the opposite side of the earth. In normal circumstances, the sun has the second greatest impact on the tides though it is too small to cancel out the lunar tidal impact in even the most extreme circumstances. This would mean that you would need something extremely large to pass by the earth at close range to cancel out the tidal force generated by the moon, and in that case, I would be far more worried about impacts to earth's orbit around the sun then a short term hiccough in the tidal cycle. Googlemeister (talk) 14:13, 9 February 2011 (UTC)

I suggest you read our article on tides and then come back here if there is something you don't understand.--Shantavira|^{feed me} 14:08, 9 February 2011 (UTC)

The original post is just trolling about the scientific illiteracy of Bill O'Reilly: [14]. TenOfAllTrades(talk) 14:12, 9 February 2011 (UTC)

You guys are not reading my question. I want to know if there's ever been a case of MISCOMMUNICATION - where the moon's gravity was not properly communicated, and the tides did not come in in response. I can put it to you this way: if gravitons are what transfer gravity, and gravitons are particles, has there ever been a case of a service interruption between the moon and Earth, so that these particles were dropped. Or, have they ALWAYS, come through, never a miscommunication? 217.136.92.148 (talk) 14:52, 9 February 2011 (UTC)

Only if you didn't pay your bill for gravitation service. You did remember to pay, didn't you? Acroterion _(talk) 15:00, 9 February 2011 (UTC)

Ha,ha, very funny. I've only been around since 1985, whereas there have been references to the moon and tides since at least the nineteenth century. 217.136.92.148 (talk) 15:02, 9 February 2011 (UTC)

There have been references to tides for as long as people have lived next to the sea and written about it. In seriousness, tides can be interrupted locally or otherwise affected by abnormal meteorological conditions, or, as we saw a few years ago, by earthquakes, neither of which have anything to do with the earth vs. Moon. Note that the sun makes tides too, accounting for spring tide and neap tide. Interruptions in gravity would be apparent by astronomical observation; so far as anybody knows, gravity has worked continuously since shortly after the Big Bang. Acroterion _(talk) 15:10, 9 February 2011 (UTC)

yeah I'm not asking about other disruptions in the tide, but about a miscommunication with the moon. I'm not interested in gravity everywhere, but the communication of gravity between the mean and the tides it causes. Scientifically, has there ever been a miscommunication? 217.136.92.148 (talk) 15:15, 9 February 2011 (UTC)

No there has not; neither can I think of a mechanism which would cause any such "miscommunication". Can we close the matter now? --Tagishsimon (talk) 15:18, 9 February 2011 (UTC)

You say "now" as though this answer has been given above: in fact, you are the first to reply to my question. (And then only at my repeated insistence). Now, this being the reference desk, would you have any way to tell me why you answer "no there has not"... How would we know if there had been a miscommunication at some point in the history of Earth and Moon? (If gravitons had been interrupted at some point, how would we know that.) Thanks. 217.136.92.148 (talk) 16:08, 9 February 2011 (UTC)

In fairness, I think most of the above posts were pointing in much the same direction. Still. I'm glad you accept that byou have an answer to your first question. As to your second question: I don't know. I tend to doubt there would be any forensic evidence we could latch onto. And I tend also to think that the firm expectation is that the laws of physics in this area are well enough proven that no-one is looking for the sort of "miscommunication" which I infer you to be asking about. You might want to read the Evidence of absence article to improve your grasp of this notion of "scientific fact". In my universe, there are hypotheses which have greater or lessor amounts of experimental or observational proof attached to them. These are what amount to "facts". And then there's a whole limitless cornucopia of stuff which is not proven or which cannot be proven, and which falls outside the "fact" category. Your "miscommunication" seems to fall into that bucket ... no one expects such miscommunication, no one is looking for it, there is no proof that it has not happened, but that says little or nothing about whether it has happened. Gravitational theory does not provide any mechanics for it happening. Astrophysics (admittedly to my very limited knowledge) has no examples of this sort of thing going on. On that basis, most of us are content to say "it's never happened & will not happen", but when coming up against a pedant, would add something like "to the limit of current scientific understanding". Does that help? --Tagishsimon (talk) 16:31, 9 February 2011 (UTC)

I think we can safely so that No, there has never been a case of the moon's gravity mysteriously not working. (If it ever did, I think tides would be the least of our worries, actually. It would presumably slip out of its orbit. If it ever happened to the earth-sun gravity we'd really be in trouble.) Tide tables can be calculated far in advance and on days with no wind they're usually spot on.

If gravity is caused by graviton particles, I suppose it's possible that a few of them might decay or otherwise go astray during the earth-moon trip. Perhaps that's what you're asking? But since gravitons aren't known to exist, this kind of speculation is less "theoretical physics" and more "making wild guesses about physics". In any case, that sort of "miscommunication" would be so infinitesimally small as to be completely unmeasurable. APL (talk) 15:23, 9 February 2011 (UTC)

I think the original question is probably based on some kind of bizarre misunderstanding, but it may be worth pointing out that the relationship between tides and moon is pretty complicated. Tides in any given location are generated by a combination of driving by the sun and moon, and the tidal resonance properties of nearby bodies of water. What you get, generally, is a complex oscillation that combines waves with lunar frequency, waves with solar frequency, and waves with local resonance frequencies. Large tides, such as those in the Bay of Fundy, occur when the resonance frequency is a close match to the lunar frequency. Looie496 (talk) 17:28, 9 February 2011 (UTC)

I vote "troll", and that's pretty rare for me. Comet Tuttle (talk) 17:34, 9 February 2011 (UTC)

As TenOfAllTrades already pointed out above, this is a rehash of Bill O'Reilly's brilliant proof of god (and I quote verbatim):"[Sun goes up, sun goes down,] tide comes in, tide goes out, never a miscommunication". What makes this ridiculous argument somewhat remarkable is that O'Reilly has been taped on numerous occasions saying those exact words, and given that "miscommunication" is not exactly an everyday word it makes him sound like he at first rehearsed the argument in front of a mirror or something until he had it down pat, ready to lash it out if the occasion demanded it. TomorrowTime (talk) 17:47, 9 February 2011 (UTC)

The possibility that there would be a "miscommunication" between the moon and the tides is exactly the same, scientifically, as the possibility that there could be a "miscommunication" between your body in the ground, so that you'd wake up hovering three feet above your bed. Scientists, understandably, will look at you slightly strange if you start seriously suggesting that in order to fly, all you have to do is forget to fall. They'll think you're "Looney Tunes". -- 174.24.195.38 (talk) 17:36, 9 February 2011 (UTC)

Why, has that ever happened? If not, I don't really get why you're bringing it up... 217.136.92.148 (talk) 18:11, 9 February 2011 (UTC)

The fact that it has never happened is exactly why the editor brought it up. thx1138 (talk) 19:50, 9 February 2011 (UTC)

It is a scientific fact that Newton's law of gravity (as adjusted by relativity) has never been reliably observed to fail either through lack of communication or for any other reason, either between a human body and the earth, or between the moon and the tides. We don't really get why you're bringing it up... Dbfirs 22:41, 9 February 2011 (UTC)

I'm bringing it up to verify Bill O'Reilly's premise (not his conclusion) about "never a miscommunication". I don't now about his conclusion, but from everything you all have written above, his premise is completely true and valid. Tide goes in, tide goes out, never a miscommunication. 109.128.101.244 (talk) 11:42, 10 February 2011 (UTC)

The art, or rather the knack, to flying is not forgetting to fall, but throwing oneself at the ground and missing. --Tango (talk) 23:34, 9 February 2011 (UTC)

Is natural non-grey hair possible in old age?

Is it possible for this gentleman http://www.bbc.co.uk/news/world-europe-12404554 and other people of similar age to have naturally non-grey etc hair? Or must it be artificially dyed? I recall other politicians in continental europe also have youthful-looking hair. Now I think of it, bald politicians are very rare too. 92.24.185.155 (talk) 13:36, 9 February 2011 (UTC)

Fading of hair colour and loss of hair have a largely genetic component. Some of it is associated with the original hair colour (so blond hair tends to go grey faster than black hair, for example). My own grandfather had a full head of raven hair well into his 60s, while some people go bald or grey in their 20s. 86.164.25.178 (talk) 14:14, 9 February 2011 (UTC)

I know a woman who had dark hair into her 90s; I've not seen her for a few years, but as far as I know, she might still have dark hair. Nyttend (talk) 23:31, 9 February 2011 (UTC)

Quality of 2011 transistor radio v. 1940s top of the range valve radio?

Would the sound quality that I get from a modern cheap transistor radio be better than that of the most de-luxe valve radio of say the 1940s? Allowing for the fact that 1940's AM radio may not have been so crowded or subject to noise as it is now. Thanks. 92.24.185.155 (talk) 14:11, 9 February 2011 (UTC)

For the sake of this hypothetical scenario, are both radios tuning in to the same radio transmission, or should we assume that you want to compare the quality of a 1940s broadcast to a 2011-era broadcast? Modern transistor radios can tune to FM, they can use "digital AM", and so on; so it's unfair to compare different types of transmissions that a 1940 tube radio could not demodulate in the first place. In terms only of noise quality and frequency fidelity between dc and 22 kHz, the best quality 1940s valve radios probably had equal performance to mediocre low-quality AM/FM asic integrated circuit tuner/demodulator/amplifier packages. And to be fair, "transistor radio" is a loosely used term: it historically referred only to those radios that used a single BJT for mixing (demodulating); but may also refer to a transistor power-amplifier, or to a modern fully integrated analog/digital mixed-signal system-on-chip radio and audio-amplifier package. If you want to be very precise, you'll have to specify what exactly you want a comparison between. Nimur (talk) 21:28, 9 February 2011 (UTC)

I don't know about technical sound quality, but I certainly prefer the sound output from a 1940s radio. I find cheap "trannies" annoyingly hissy and tinny, but this is probably a combination of poor reception, cross-channel interference and small loudspeakers. I've never heard a high quality transistor radio, but I expect it would sound better if I rigged up a large aerial to pick up a suitable signal. (Only long wave and satellite digital radio work properly where I live.) Dbfirs 22:32, 9 February 2011 (UTC)

Is that tinny-ness the effect of the radio or the speaker-cabinet? Cheap radios often do have poor low-frequency fidelity; often, a DC-blocking capacitor is added as a "high pass filter" to cut everything below, say, 200 Hz; but this is usually intentional because they are connected to miniature battery-powered speakers that couldn't reproduce those low frequency acoustics anyway. So we've got to compare apples to apples: the actual electrical output from a transistor tuner/amplifier is probably a higher-fidelity signal reconstruction of the original waveform. Post-processing (signal conditioning) can then be applied to make the device more suitable for portable/battery-operated speakers, at the expense of tone quality. Nimur (talk) 22:36, 9 February 2011 (UTC)

Yes, I'm sure you are correct about the circuitry, but for reception and sound output, I vote for the 1940s. There was considerable sound distortion in the decoding and amplifier circuitry in valve radios, but it was a very different distortion, and not nearly so annoying (or is it just that I got accustomed to it?) Dbfirs 22:52, 9 February 2011 (UTC)

Oh, it's a well-known fact among audiophiles that "exact, flawless, perfect recreation of input signal" is not pin-for-pin compatible with "pleasant-sounding." For example, an electric guitar effects-box intentionally adds noise to the signal (in various different ways, depending on the effect), because people like the way that distortion sounds. I happen to like the tone properties of valve amplifiers, myself; there are many aesthetic details of old technology that are very nice. And I still prefer the fades and fuzzes of AM radio, even though this "new-fangled" FM-technology can provide stereo sound. It's fun to hear WSM fuzz out when I'm driving past a mountain or a rainstorm, and there's no thrill like picking up the Nashville stations while I'm driving through West Texas. (Try doing that with an RDS-enabled side-channel stereo FM! Kids today, with their "technology...") But I can't objectively call it "better sound quality." Nimur (talk) 23:10, 9 February 2011 (UTC)

I've owned and listened to radios made in the 1920's, 1930's and 1940's. Not all 1940 radios were alike. Some were cheaply made with low output power, only a few tubes and a small cabinet, with a poor quality speaker. Those would be comparable to a modern very cheap and very small radio, which has wonderful signal processing combined with a tiny speaker enclosure which limits bass response and output volume. A premium 1940 radio would have a very large speaker in a large cabinet, engineered for fairly smooth frequency response, and with tone controls which could be adjusted for a limited frequency response for distant or noisy reception, or a wider response for a strong signal. Some radio programs in 1940 were studio presentations with a very low noise level and a good frequency response up to the high frequency limits applicable in the transmitter, to keep the signal within the allowed bandwidth. Premium radios were made to reproduce such broadcasts well. See [15] from 1938, which discusses "high fidelity" premium cost receivers selling for $200. In April 1940 you could buy a Stromberg FM receiver for $295 or less which would sound amazingly high fidelity, as in this ad. Such a receiver would put to shame most modern radios of low or moderate cost. After WW2, the state of the art had obviously advanced even farther. Here is a 1948 article about the quality of FM reception. The best modern radio would still outperform the best 1940's radio, by picking up FM stereo as well as through speaker and electronics advances, but a "cheap" modern radio would fall far short of a good 1940's radio. Edison (talk) 23:34, 9 February 2011 (UTC)

Fantastic links, Edison. "Even if you live next door to a man with an electric razor, your FM radio won't be bothered by it." I suppose I've been selling FM radio short!! Nimur (talk) 23:57, 9 February 2011 (UTC)

A good radio from the 1920's perfectly restored, required the tuning of two RF stages as well as adjustment of the filament voltage, to tune in a station. The sound came from a horn speaker, and was no better than the very cheapest small transistor radio. A late 1940's radio could sound very fine, indeed. Edison (talk) 05:29, 10 February 2011 (UTC)

largest bird egg

Which bird which can fly lays the largest eggs? Googlemeister (talk) 14:45, 9 February 2011 (UTC)

If you allow mythical birds, then the roc would be a contender, (and the ostrich of course for living non-flying birds), but my guess would be a swan. Can anyone think of a larger? Dbfirs 16:23, 9 February 2011 (UTC)

Kori Bustard, Ardeotis kori is quite a bit larger than the swan. Roger (talk) 16:27, 9 February 2011 (UTC)

That's a much better answer. The Argentavis had an egg three times the weight of the swan egg (over a kilogram), but it is no longer around. Dbfirs 16:30, 9 February 2011 (UTC)

The Kori bustard is the heaviest flying bird today (I think), so, yes. But for egg size I might have to check. Crimsonraptor | (Contact me) Dumpster dive if you must 16:41, 9 February 2011 (UTC)

Andean condors have an egg weight of 280 grams or so, and the egg length is around 4 inches. So is that the record, then? Crimsonraptor | (Contact me) Dumpster dive if you must 16:44, 9 February 2011 (UTC)

The swan beats that with an egg weight of up to 340 grams, but I expect the Kori Bustard (paauw, Ardeotis Kori) egg is heavier, and the European Great Bustard ((Otis tarda) would also be a contender. Can anyone find a reference? The eggs of the Elephant Bird, or Vouron Patra (Aepyornis maximus) were the largest ever (bigger than any dinosaur egg), in fact they reached the physical limit of structural integrity for an egg-shape made of shell. Dbfirs 21:53, 9 February 2011 (UTC)

This reply to the condor claim was added after the reply below, but it is also a reply to Quetzalcoatlus claim. Dbfirs 22:17, 9 February 2011 (UTC)

The eggs of Quetzalcoatlus must have been enormous. There has been an increasingly common recent suggestion that modern birds descended from dinosaurs. 2.97.217.143 (talk) 20:22, 9 February 2011 (UTC)

If by "increasingly common recent suggestion" you mean "we're as sure about it as we can be"... It's pretty much established and accepted that birds are descended from dinosaurs. --Jayron32 00:06, 10 February 2011 (UTC)

why is AIDS so hard to cure?

if it's just a virus, a bit of DNA, shouldn't it be really easy to cure instead of really hard? It's not like cancer, of which there are all these different types... it's just a piece of arguably not even living DNA... 217.136.92.148 (talk) 15:12, 9 February 2011 (UTC)

If you read the Article on HIV (AIDS is but an expression of HIV infection in its latter stages) you will see that this simple Virus is firstly attacking one of the vital parts involved in defeating "usual" viruses in the human body secondly has a high genetic variability (Theres all kinds of different kinds), making it very hard to attack by "conventional means". These two among many other things are making this "simple infection" such a challenge to science. The articles are really quite informative. --147.142.185.92 (talk) 15:19, 9 February 2011 (UTC)

Also, viral infections in general are much harder to cure than bacterial infections. See antiviral drug. In general, we only slow the virus down while the immune system adapts itself to do the actual curing. In the case of HIV, the immune system itself is attacked by the virus. --Stephan Schulz (talk) 15:47, 9 February 2011 (UTC)

Is it possible to use nanotechnology to do the actual curing instead? ScienceApe (talk) 17:20, 9 February 2011 (UTC)

That's ridiculous. A virus is a piece of code, exactly the same as a binary executable on Windows, the sole difference being that instead of binary it's in quadrinary - you would need two bits to code each base pair. Now you're telling me that it's polymorphic. Fine. Does Norton etc. give up when a piece of code is polymorphic? No way. You're telling me, however, that we don't do any scanning of virus code whatsoever, in any way. We just slow down execution of it, so that the body's own antivirus can adapt to it! That's ridiculous. Imagine if all "Norton" did was run one very tight loop on all cores, and seek to random parts of the hard-drive, in an attempt to slow down the spread of the virus enough for Windows to catch up to it. That's ridiculous. Give me one good reason the human body couldn't have an artificial antivirus just like Windows can have a third-party one. The idea of having to use the body's immune system is just beyond comprehension for me. Why can't viruses be cured through artificial means -t hey're just a bit of code that, frankly, is not even alive. (Though this is in dispute.) 217.136.92.148 (talk) 16:25, 9 February 2011 (UTC)

Re-writing DNA codes is a very new science, and we cannot even cure the common cold yet. The difference between Norton anti-virus and curing AIDS is that there are millions of copies of the AIDS virus, and we can't (yet) get at all of them, especially in cells deep in the body, so we can't just remove that bit of code from all the infected cells. Dbfirs 16:40, 9 February 2011 (UTC)

If we contuinue to use the (frankly quite ridiculous) computer virus metaphor that the OP seens to have some understanding of: The problem with fighting HIV the way Norton's fights a computer virus is that if HIV was a computer virus the first thing it does when it runs is to delete the Norton's scanning executable. The human body is not a computer so the analogy is seriously limited. Roger (talk) 16:47, 9 February 2011 (UTC)

In addition to the immune system depression, one of the issues with HIV is that it's a retrovirus. That is, it actually incorporates it's DNA into the genome. All DNA looks the same, so once it's incorporated, there really isn't any difference chemically between HIV DNA and Human DNA. You can kill off the existing virus particles, and you might even kill off the cells which are producing virus proteins, but it is hypothesized that there are always "reservoir" cells which contain viral DNA, but aren't producing any viral proteins or RNA (until they are activated later). There's no way you can tell these reservoir cells from healthy cells unless you had a way to read and interpret the sequence of DNA, and we don't currently have ways of doing that, at least while the DNA is still in the cell. All the drugs and treatments we currently have either work on the protein or RNA level, or they attack all DNA indiscriminately, regardless of sequence. Programs like Norton Antivirus work because they have tools which can read the file sequences and compare those to viral signatures. We don't have anything like that for reading and comparing DNA sequences in the body. We have to rely on the natural decoding ability of the ribosome, or the cell's own DNA binding proteins to do sequence recognition. There's hopes that we'll eventually be able to do genome editing with zinc finger nucleases, designed homing endonucleases, or even sequence specific small molecule binders, but we don't have any of those yet. -- 174.24.195.38 (talk) 17:24, 9 February 2011 (UTC)

Actually, we don't know how to cure a single viral disease. We can immunize viral diseases and offer supportive care, and boost the bodies natural defenses but humanity has yet to actually cure viral diseases like we can some bacterial infections. Googlemeister (talk) 17:48, 9 February 2011 (UTC)

Thanks for that informative answer, which means you got my metaphor, unlike the person above you who thought I wanted the antivirus to run on the body's own immune system. So, you say we can't edit DNA in cells. But tell me this: if we could edit DNA in cells, then we could neutralize HIV in 1 cell or 2, or 10, 100, 1000, whatever. In fact, how many cells would have the HIV dna in a real case? Millions? Billions? I remember that there are between 10 and 100 trillion cells in the human body, depending on who you ask. How many of those would have hiv dna in them, in an infected patient? Which kinds of cells would have that DNA? Would cells, like bone cells, or brain neuron cells, have that DNA, which are totally impractical to replace? Or, on the contrary, would all the cells that have that DNA be of a kind that, in theory, you could replace... Thanks. 217.136.92.148 (talk) 18:18, 9 February 2011 (UTC)

There may be an answer,^[16] but developing it means perfecting the most terrible, insidious, and versatile weapon of assassination, mass destruction, genocide, and Orwellian surveillance ever conceived by the hand of man. Then again, the U.S. Army is beginning work on that anyway.^[17] Wnt (talk) 18:58, 9 February 2011 (UTC)

The common cold is "just" a virus, and we can't even cure that. thx1138 (talk) 19:46, 9 February 2011 (UTC)

The computer virus analogy breaks down on several important levels. First and most importantly: computer code can be stopped, it can be forced to cease execution then operated on discreetly and perfectly. You can't put the human body into a stable 'non-executing code' state, read it, scan it and arbitrarily edit the 'code'. Also key is the fact there's no way to stop the DNA from "executing" short of stopping biological processes entirely, not even killing the patient would do that. Secondly, there's no way to freely, arbitrarily and discreetly remove sections of DNA from a larger strand on-the-fly in vivo, if you could do that AIDS would be an utterly trivial problem yes, but so would death itself. 65.29.47.55 (talk) 01:17, 10 February 2011 (UTC)

A mechanic was removing a cylinder-head from the motor of a Dodge SRT-4 when he spotted a well-known cardiologist in his shop. The cardiologist was there waiting for the service manager to come take a look at his car when the mechanic shouted across the garage "Hey Doc, want to take a look at this?". The cardiologist, a bit surprised, walked over to where the mechanic was working on the SRT. The mechanic straightened up, wiped his hands on a rag and asked, "So Doc, look at this engine. I open its heart, take the valves out, repair any damage, and then put them back in, and when I finish, it works just like new. So how can I make 39,675 a year, a pretty small salary, and you get the really big bucks, $1,695,759, when you and I are doing basically the same work?". The cardiologist paused, smiled and leaned over, then whispered to the mechanic, "Try doing it with the engine running." - manya (talk) 03:50, 10 February 2011 (UTC)

high protein consumption and kidney damage in humans

In humans, what is the correlation and regression curve between kidney damage and the consumption of high levels of protein (200 to 600 grams per day) to meet the basal metabolic rate (BMR)? --Inning (talk) 16:28, 9 February 2011 (UTC)

Please excuse me if I'm wrong, but that has the look of a homework problem. Looie496 (talk) 18:44, 9 February 2011 (UTC)

LOL... was just trying to phrase it so no one would say "We can't give medical advice." Next time just say you need to cover your ass since you do not know the answer to the question. --Inning (talk) 01:14, 10 February 2011 (UTC)

Well, now I'm confused. Do you need some kind of data plot, or do you just want to know how protein-focused a diet needs to be in order to cause kidney damage? Looie496 (talk) 05:02, 10 February 2011 (UTC)

Dirty talk

I have two questions on dirty talk - 1. Psychology of dirty talk, 2. Evolutionary origin of dirty talk.

1. What is the psychology behind dirty talk?

2. According to the article Origin of language, "The development of fully modern behavior in H. sapiens, not shared by H. neanderthalensis or any other variety of Homo, is dated to some 70,000 to 50,000 years ago. The development of more sophisticated tools, for the first time constructed out of more than one material (e.g. bone or antler) and sortable into different categories of function (such as projectile points, engraving tools, knife blades, and drilling and piercing tools) are often taken as proof for the presence of fully developed language". So, how did Homo sapiens did dirty talk before the advent of language? What is the evolutionary origin of dirty talk? --Dolyop (talk) 16:31, 9 February 2011 (UTC)

1. It turns some people on to speak it, it turns some people on to hear it. When those people get together, everyone is happy.

2. There's really no way to know for certain since spoken language (or proto-language) can't fossilize, but giving signals of sexual availability is an extremely ancient and very basic form of communication among animals. Talking dirty would be part of that continuum, so even if we had a time machine it would be tough to draw a line somewhere. Matt Deres (talk) 18:35, 9 February 2011 (UTC)

Teleporting particles

According to the Heisenberg Uncertainty Principle, and Quantum Tunneling, particles like protons and electrons are essentially disappearing from reality and reappearing in reality in a different position. Would it be fair to say that these particles are essentially teleporting? Do neutrons also exhibit this behavior? ScienceApe (talk) 18:55, 9 February 2011 (UTC)

In quantum mechanics there is no underlying "reality" in which every particle has a definite location at every moment. If you drop the concept of "reality", I think you'll find that there is no way even to ask your question. Looie496 (talk) 19:21, 9 February 2011 (UTC)

I think if you drop the concept of "reality", there is no way to even ask any question. 109.128.101.244 (talk) 19:49, 9 February 2011 (UTC)

This usage of "teleporting" would be more confusing than enlightening. In almost every single atom (excepting hydrogen and helium) there are "nodes" where the probability of finding an electron by experiment drops to zero. Do all these electrons "teleport" when they cross these nodes? In your case, you might suppose that the particle doesn't exist inside a barrier of finite width, but in truth the quantum amplitude does penetrate the barrier (see figure in quantum tunneling). It is only that classically, the particle doesn't have the energy to be there. Wnt (talk) 20:35, 9 February 2011 (UTC)

I think there's no conundrum if you recognize that the wave function isn't the particle. The wave function is only a theoretical description that models certain aspects of the particle's behavior. "Where is the particle" is not word-for-word interchangeable with "where is the value of $|\Psi ^{2}|$ nonzero." The conceptual paradox of "teleporting" across energy barriers is only a problem if you try to equate "particle position" and "wavefunction" in a classical sense. Nimur (talk) 21:33, 9 February 2011 (UTC)

This would be less confusing if they simply weren't called particles. If they were called waves, the uncertainty principle and tunneling wouldn't be so surprising, because they also show up in classical wave theories. This page (which I found with a five-second Google search and haven't carefully examined) describes the classical frequency-time uncertainty principle for sound waves. An example of classical tunneling is the leakage of light between two fiber-optic cables separated by a small amount of air, even when the light is totally internally reflected. This is called evanescent wave coupling or frustrated total internal reflection, but it might as well be called tunneling (or the quantum version might as well be called evanescent coupling). Quantum mechanics is a unification of classical wave and classical particle theories. The unification is new, but practically every quantum phenomenon shows up in one or the other type of classical theory. The wave phenomena are the ones that are usually called "weird", but that's an arbitrary judgment. -- BenRG (talk) 04:53, 10 February 2011 (UTC)

Other phases of ice at room temperature

At room temperature, ice I will melt. Will any of the other forms of ice not melt at room temperature (as diamond does not)? 128.223.222.68 (talk) 19:51, 9 February 2011 (UTC)

What do you mean by "other forms of ice"? Water has a melting point of 0 °C (at sea level). Diamonds are made of carbon, which has a melting point of 3500 °C. thx1138 (talk) 19:54, 9 February 2011 (UTC)

http://en.wikipedia.org/wiki/Ice#Phases may be usefull to you 83.134.177.191 (talk) 20:12, 9 February 2011 (UTC)

According to our article, Ice_VII can remain solid at high temperatures. Also "...ice VII has the largest stability field of all of the molecular phases of ice"... Vonnegut's 'ice 9' notwithstanding. SemanticMantis (talk) 20:23, 9 February 2011 (UTC)

Of course, to have Ice VII, you would need to have a means to exert 10 gigapascals of pressure. Googlemeister (talk) 20:55, 9 February 2011 (UTC)

There is also the FICTIONAL Ice-nine. Dauto (talk) 23:28, 9 February 2011 (UTC)

I interpret this question as asking what solid materials would melt at room temperature (using "ice" in a looser sense as a crystal solid of some type). The answer is of course anything that's liquid at room temperature will melt at room temperature if you take a solid block of it out of the freezer. Mercury (element), for example, as in this video. Pure "Glacial" Acetic Acid's melting point is just below room temperature (16 C/62 F), and will indeed melt if brought into a warm room in a frozen state. It actually looks pretty similar to water ice: [18] Perhaps 128.223 needs to clarify their question. Buddy431 (talk) 00:00, 10 February 2011 (UTC)

I thought the question was clear. It is asking, if you start with water and apply suitable pressure and temperature to convert it to a different phase (such as ice VII), is it possible to achieve a phase that will remain solid at room temperature and (I presume this was intended) ordinary pressure? (Just as you might convert graphite to diamond and the diamond remains stable.) As I understand it the answer is no; water phases like ice VII will not remain stable when the pressure is removed. --Anonymous, 06:10 UTC, February 10, 2011.

Natural hazards and natural disasters humid continental climate

Which natural hazards and natural disasters are associated with Humid continental climate? —Preceding unsigned comment added by 65.95.106.36 (talk) 20:29, 9 February 2011 (UTC)

Since this has the look of a homework question, I'll respond by suggesting that you look at our article on humid continental climate and ask yourself what bad things can happen in the places it shows. The fact that you live in one of them should be helpful. Looie496 (talk) 20:50, 9 February 2011 (UTC)

Metabolism of alcohol

I am trying to figure out how the body is able to get so much caloric value from ethanol. the way that I understand it is that the body absords it directly into the blood stream unchanged. Alcohol is then converted to acetaldehyde by alcohol dehydrogenase. From there is it further metabolized to acetate and then to CO2 and water. Most of the alcohol is methabolized in the liver, and I have read that some of the metabolic conversons are very exothermic. How does the liver make use of these exothermic reactions to give alcohol so many dietary calories per gram?--160.36.38.218 (talk) 20:36, 9 February 2011 (UTC)

I think you're missing the most important step. As our ethanol metabolism article explains, acetic acid is metabolized to acetyl-CoA, which can be used as an energy source in many parts of the body via the citric acid cycle. Looie496 (talk) 20:57, 9 February 2011 (UTC)

So it is this step that makes it 1/3 better store of energy than sugar?--69.245.43.176 (talk) 21:41, 9 February 2011 (UTC)

I haven't checked your number with the biochemistry, but it seems plausible. High calorie fats or fossil fuels are typically -(CH2)- repeatedly with no oxygen added. Ethanol is CH3CH2OH - one oxygen per two carbons. Sugars are generally -(CHOH)- over and over, in other words, there is already one oxygen combined with each carbon. Now two oxygens per carbon is CO2. So you can think of ethanol as being (very roughly) gasoline that is 1/4 burnt, and sugar as gasoline 1/2 burnt; take (3/4 left) / (1/2 left) and you have your 3:2 ratio. (I omit in this that ethanol has an extra H2 at the ends, because it is short, and that fats sometimes omit H2s when unsaturated, etc. - to do this precisely you have to go through glycolysis, the Krebs cycle, oxidative phosphorylation and related processes in painstaking detail, and it turns out that you often won't get one single certain number even if you do!) Wnt (talk) 22:38, 9 February 2011 (UT

If you look at the energy budget of metabolizing glucose through glycolysis and oxidative phosphorylation, you see that only 2 ATPs are produced per molecule of glucose in glycolysis, but 30-36 ATPs are produced by the oxydative phosphorylation of the two acetyl-CoAs that are formed per glucose molecule and the NADH formed during glycolysis. One molecule of ethanol is turned into one of acetyl-CoA, and the alcohol dehydrogenase and aldehyde dehydrogenase create enough NADH to balance those formed by glycolysis. Two ethanol molecules thus only lose 2 out of 32-38 ATPs that are formed from one molecule of glucose. Because they are lighter than one glucose molecule, the calories per gram figure works out to be about the same (if not a bit higher for ethanol). -- 140.142.20.229 (talk) 23:05, 9 February 2011 (UTC)

Largest phytosaur

I've been doing a bit of research for an illustration I'm making, which has a large phytosaur in it. In fact, quite large. This page from the UCMP website states the largest grew up to 12 metres (39 ft), which nails my illustration, but doesn't give the species. Could anyone here help, because most of our articles don't give a size estimate? Thanks! Crimsonraptor | (Contact me) Dumpster dive if you must 22:35, 9 February 2011 (UTC)

Why does snow melt on cold days?

I've always been puzzled that snow melts on sunny days when the temperature is below freezing. It's 13°F today, how is the sun making the snow melt? --68.102.163.104 (talk) 23:00, 9 February 2011 (UTC)

When snow is in direct sunlight, it can melt even when the air temperature is lower than freezing. --T H F S W (T · C · E) 23:01, 9 February 2011 (UTC)

Agreed, sunlight can raise the temperature of snow or ice several degrees. Sunlight can also reflect off a building and increase the intensity on the snow. If the snow is on the sidewalk or street, the dark color of the concrete or asphalt may cause it to heat up above the freezing point. If ice melter or road salt has been spread, that greatly lowers the melting point of the snow or ice and causes it to liquify and thus hastens its evaporation. Sublimation can take snow directly from its solid form to vapor form. Edison (talk) 23:21, 9 February 2011 (UTC)

A similar effect can be seen in Auto-defrost freezers (pretty much every freezer on the market these days), even thought the temperature IN the freezer never goes above freezing, the freezer creates conditions (mainly by circulating dry air) where unsealed ice cube trays will eventually sublimate away to nothing. Vespine (talk) 23:33, 9 February 2011 (UTC)

Where should post this? I am NOT happy with the physics sections of wikipedia.

Wikipedia needs a lock down on its basic definitions of physics after a thorough review by PhD professionals.

The articles are MISLEADING and students interested in physics are getting bad advice.

I am re-interested in physics and science after studying it many years ago and see many errors between my degree level textbook and basic definitions that are in Wikipedia.

For example the "conservation of mass" article starts to fall apart on the second paragraph, and the reader is left with the impression of a vague law that doesn't really work. There is a huge tendency to lump in classical, special relativity and quantum theory all in the same article which is really confusing to the layman ESPECIALLY when it is in the SECOND paragraph.

Also check out the opening paragraph of "energy", nice examples ? easy to understand? — Preceding unsigned comment added by 92.17.89.69 (talk • contribs)

The physics wikiproject would be better than here, but please remember that we are all volunteers and that if you find something unsatisfactory, the simplest thing to do is to fix it yourself. If you get stuck on something I'm sure there are plenty of people who can help you. SmartSE (talk) 23:14, 9 February 2011 (UTC)

I will also point out that Wikipedia seeks to be an encyclopedia. As such, it is not a replacement for a physics textbook or a physics class. Are you looking for a physics textbook? We can recommend numerous different authors, subjects, and depth-levels, depending on your need. Nimur (talk) 23:19, 9 February 2011 (UTC)

You should write a letter to their offices and request a refund, citing your dissatisfaction. You could also leave a negative review of the encyclopedia on Amazon, to discourage others from buying it. In the meantime, you should go to their competition, Britannica. 109.128.101.244 (talk) 23:28, 9 February 2011 (UTC)

Please don't bite the newcomers. Nimur (talk) 00:09, 10 February 2011 (UTC)

If you'd like to improve the article, please do — anyone, even you, can improve any article on Wikipedia. Comet Tuttle (talk) 23:39, 9 February 2011 (UTC)

It is our policy for the introduction (or lede) of an article to summarise the whole article. That means the introduction to the article on conservation of mass does need to cover classical mechanics as well as relativistic mechanics, so they are both important enough topics to be covered in the article. --Tango (talk) 00:13, 10 February 2011 (UTC)

Yeah, Tango, but the OP still has a point. Just because the lede has to summarize the whole article doesn't mean that it can't do so in a way that is easy to read and understand. The physics and other technical artilcles at Wikipedia are basically impenetrable for anyone without advanced training; which is kinda silly since the articles are often written so that the only people who can understand the article are people who don't actually need to read it because they already understand the concepts being discussed! I fully understand the OP's frustration because I share that frustration. Take a look at Magnetization for example. Lets say you were an English major in college, but still want to know a bit more how magnetization works. That article does you no good. Which is not to say that the techinical detail could not also be in those articles. It absolutely should be. Its just that there needs to be more attention given towards explaining concepts like conservation of mass and magnetization to people who may actually want to learn something from the articles. --Jayron32 01:02, 10 February 2011 (UTC)

I agree. I think wikipedia has a few excellent physics articles, true, but it also has many that are not directed to the general public and if the reader doesn't already understand the topic, he is unlikely to learn anything new. Dauto (talk) 02:29, 10 February 2011 (UTC)

clay

is it true that ceramic dinner plates have crushed glass added to the clay?--Tomjohnson357 (talk) 02:33, 10 February 2011 (UTC)

Some might. --Jayron32 03:49, 10 February 2011 (UTC)

Well, by that reasoning, "some might" have just about anything added to the clay. We do have an article on Ceramic which seems to indicate that crushed glass is not a necessary, or even common component of ceramic. In fact, it also states that for modern ceramics, even clay is not a necessary component. The relevant article is Ceramic materials which further states Glass by definition is not a ceramic because it is an amorphous solid (non-crystalline). Vespine (talk) 04:04, 10 February 2011 (UTC)

Or are you asking if plates that are "advertised" as ceramic sometimes adulterated with crushed glass? I have no answer for that question. Vespine (talk) 05:26, 10 February 2011 (UTC)

On the other hand the Ceramic article states: "Ceramic materials may have a crystalline or partly crystalline structure, or may be amorphous (e.g., a glass)". And Porcelain directly attributes some of the properties of porcelain to glass formation.

Also, is it even relevant for the finished product whether the original mixture included glass powders? If I understand correctly, the components of the body will partially melt and re-crystallize during firing anyway, and the final structure generally consists of crystalline particles held together by a glassy matrix.

The soft-paste porcelain article mentions that ground-up glass has been used in porcelain formulations. –Henning Makholm (talk) 10:32, 10 February 2011 (UTC)

crude oil

why price gap between WTI crude oil and BRENT crude oil is widening ?? —Preceding unsigned comment added by 121.245.239.36 (talk) 09:06, 10 February 2011 (UTC)

The ansewer is in the field of Economics, not Science, your question is in the wrong place. Roger (talk) 09:17, 10 February 2011 (UTC)

Yeah, that's why they call Economics the "dismal humanity". 109.128.101.244 (talk) 11:39, 10 February 2011 (UTC)

Price for quantitative analysis of chemical elements

Say I have 1g of a substance and I want to know which elements are contained in what quantities. I'm not interested in molecules or cristall structures or such. As result, I want to have a list that reads, for example, like this: C 400mg, O 150mg, N 30mg, H 20mg, S 3mg, Si 2mg, .... Ni 3µg, As 1.2µg etc. . How much would such an analysis cost and which methods would be used? 77.3.134.134 (talk) 10:20, 10 February 2011 (UTC)

Depending on the accuracy you need it could be very cheap. Energy-dispersive X-ray spectroscopy would be the trick for every thing in down to the 1% range. Going down to ppm it is expensive.--Stone (talk) 10:32, 10 February 2011 (UTC)

Five percent for each amount (factor 0.95 to 1.05, not percent of the total sample mass) would be fine. What, approximately, would mean "cheap" in this context? 77.3.134.134 (talk) 10:52, 10 February 2011 (UTC)