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June 16

centripetal acceleration

http://www.feynmanlectures.info/

Just wondering, why would the force mv^2/R be directed away from the apex? Wouldn't there have to be a normal force N equaling mv^2/R directed towards the apex ie towards the centre of the circle? —Preceding unsigned comment added by 74.15.138.134 (talk) 00:43, 16 June 2009 (UTC)

You are right. The centripetal force is directed towards the center. I doesn't have to be a normal force. Any force towards the center will do. Dauto (talk) 01:14, 16 June 2009 (UTC)

Then why does the solution treat the force as pointing away from the center? —Preceding unsigned comment added by 74.15.138.134 (talk) 02:08, 16 June 2009 (UTC)

Note: I just realized that the link doesn't take people to where I want them to go. Please, go to exercises and go to "ball and cone". —Preceding unsigned comment added by 74.15.138.134 (talk) 02:10, 16 June 2009 (UTC)

I couldn't find any "ball and cone" problem in the exercise. It would be nice if you could give a direct link. Rkr1991 (talk) 04:44, 16 June 2009 (UTC)

I think (I haven't seen the question yet) the solution would have been in the reference frame of the revolving object, which causes a centrifugal force mv²/R away from the centre, balanced by the normal force, towards the center. A more complete explanation can be given after I see the question. Rkr1991 (talk) 04:48, 16 June 2009 (UTC)

woops, i meant particle in cone, it's the first pdf...and a direct link won't work for some reason. —Preceding unsigned comment added by 74.15.138.134 (talk) 04:47, 16 June 2009 (UTC)

Yes, I think I'm right. The other parts of the solution are self explanatoryRkr1991 (talk) 04:56, 16 June 2009 (UTC)

here's the link Rkr1991 (talk) 04:58, 16 June 2009 (UTC)

Also, don't forget to sign your posts, by typing four '~' marks at the end. Rkr1991 (talk) 05:07, 16 June 2009 (UTC)

Hmmm...well, if you treat it from the reference frame of someone else, it doesn't seem to work. How would you do this from an inertia reference frame? 74.15.138.134 (talk) 05:38, 16 June 2009 (UTC)

Well there isn't much of a difference. If you understand the above solution, that shouldn't be a problem. All you do is forget about that centrifugal force, all the other forces are just the same. The only difference is that in the normal direction, you will be writing sum of all the forces to be mv²/R instead of zero. That's all. So the equations essentially remain the same. And I see you have signed your post.:-) Rkr1991 (talk) 06:20, 16 June 2009 (UTC)

That I get, but where does the force which counters the mgcos(theta) (the force pulling the ball down) come from?74.15.138.134 (talk) 11:44, 16 June 2009 (UTC)

The published solution oddly omits the normal force - possibly because it has no component parallel to the cone's surface, but it would still be nice to see it mentioned. Working in an inertial frame of reference:

1. We have two forces acting on the ball; the normal force N and gravity mg.
2. The particle is not accelerating vertically, so N cos(θ) = mg.
3. The particle is not in equilibrium in a horizontal plane - we require a net centripetal force mv²/R. So N sin(θ) = mv²/R. (Note that centripetal force is horizontal, not normal to the cone's surface, because centre of ball's orbit is in plane of ball's motion, which is horizontal)
4. Eliminate N and you get tan(θ) = v²/gR as in the published solution. Gandalf61 (talk) 12:24, 16 June 2009 (UTC)

Well, what can I say - Gandalf has said it all. Just remember to keep gravity in mind. Rkr1991 (talk) 15:25, 16 June 2009 (UTC)

Damn I realized where I went wrong, I said that N=mgcos(theta)...thanks a lot for clearing things up :) —Preceding unsigned comment added by 64.254.236.120 (talk) 16:08, 16 June 2009 (UTC)

Actually wait. How can the normal force, which is perpendicular to the surface (and hence doesn't have a component parallel to the surface) cancel out the component of gravity parallel to the surface? 64.254.236.98 (talk) 17:08, 16 June 2009 (UTC)

It doesn't. Nothing "cancels" the component of gravity parallel to the surface. Nothing needs to because the ball is not in equilibrium; it is accelerating towards the axis of the cone. The only direction in which the net force on the ball is zero is vertically; this is because the ball's motion is in a horizontal plane, so it is not accelerating vertically. Gandalf61 (talk) 19:17, 16 June 2009 (UTC)

lol i got it now, thanks. 74.15.138.134 (talk) 20:01, 16 June 2009 (UTC)

Humans as Krikkets

So I'm reading the Hitchhiker's series...

There's a race called Krikkets who have spent their entire civilisation unaware of the 'universe'

I'm wondering when Humans first became aware that those twinkly things at night weren't like the clouds, that is, mere pretty decorations on this world (obviously clous are more significant than decoration, but my point is that they aren't off the planet)

When did we realize that whether or not "we're alone in the universe" there's a universe in which to be?192.136.22.4 (talk) 01:44, 16 June 2009 (UTC)

See History of astronomy. Tempshill (talk) 01:50, 16 June 2009 (UTC)

See Ancient and early modern ideas (about Extraterrestrial Life for thinking about "being alone or not". -- 07:36, 16 June 2009 (UTC) —Preceding unsigned comment added by Grey Geezer (talk • contribs)

One of my favorite alternate universes to contemplate is if the Earth was always overcast. This would mean no stars or planets would ever be visible and the Sun (and maybe Moon) wouldn't appear as a circle but only as a bright spot in the clouds. How would astronomy develop ? Would we even figure out that the Earth is round ? (We might still be able to see tall ships drop over the horizon as they sail away, but a continuously foggy condition could obscure even this observation.) StuRat (talk) 13:06, 16 June 2009 (UTC)

I think there'd be significant curiosity in what this difuse glowing object in the sky was. Also cartography would definitely conclude the Earth is round in not so much time. Factor in flight to all this and I don't think we'd be that impared on a cloudy Earth.Aaadddaaammm (talk) 16:50, 16 June 2009 (UTC)

The ability to safely navigate the oceans without astronomical navigation would be quite difficult, and a continuously foggy world would make for constant shipwrecks. As for planes, take-off and landing would be quite dangerous if it was always foggy, although perhaps a water landing could be done safely (but getting back to shore would be another issue). Navigation would also be quite a problem. Gyros and/or radio location beacons would need to be used. Cars would also be dangerous in "foggy world", so perhaps trains (and maybe barges pulled along canals) would be the only reliable form of transportation. StuRat (talk) 19:37, 16 June 2009 (UTC)

Takeoff doesn't require visibility, and from the early days of electronics blind landings have been possible --Polysylabic Pseudonym (talk) 07:10, 17 June 2009 (UTC)

It may be possible to take-off and land blind, but it certainly isn't safe, at least with current methods. For example, how do you ensure that the runway is clear, considering that even a small, flat scrap of metal like the one that crashed the Concord could be present ? Perhaps a runway sweeping device could be utilized between each use of the runway and radar used to detect if any people or animals have wandered out there since. StuRat (talk) 11:17, 17 June 2009 (UTC)

You cannot know that we can observe everything. For all you know, there may be a class of phenomena which we cannot observe that, if observed, would show us a much larger multiverse. Thus the beings that move from dimension to dimension pity us because we are restricted to a single dimensions and we are not even aware of it. Tautologically, this hypothesis is not scientific because it is not falsifiable. -Arch dude (talk) 13:28, 16 June 2009 (UTC)

If that were true - there would have to be an entirely new mechanism for viewing. We've explored the electromagnetic spectrum from end to end - and observed what there is to observe along the way (with varying degrees of precision of course). For there to be more "things" to see - the seeing would have to be with some unimagined energy/information transfer mechanism that's not related to gravity/electromagnetism/weak/strong forces. Also, the energy being transferred by this mysterious means would have to be accounted for in some new way because we're currently able to account for most of the energy involved in physical processes. However, for all of that, it's not impossible that what you say is true. This is what makes the whole 'dark energy/dark matter' business so interesting. It implies that there is indeed some entirely different kind of process going on that we only know about because of "accounting errors" in things we do know about. SteveBaker (talk) 13:59, 16 June 2009 (UTC)

The entirely new mechanism for viewing is here. Tempshill (talk) 15:57, 16 June 2009 (UTC)

That's not a new "mechanism for viewing", or you could say "sense". We can sense electromagnetic radiation (sight and touch/heat), chemical compounds (smell and taste), physical force (touch). This is a pretty small list, there are a whole lot of other things we could sense. Taste and smell don't even factor into the energy calculations so it could be anything. Aaadddaaammm (talk) 16:45, 16 June 2009 (UTC)

In those conditions, humanity still could observe the moon and the planets with powerful radar. And if the world is always foggy, radar would be incredibly useful for other purposes. 65.121.141.34 (talk) 13:07, 17 June 2009 (UTC)

If you mean active radar, where a radio signal is sent out and then reflected back, that certainly wouldn't work to view planets from the surface of the Earth. It might possibly work for the Moon, though. Passive radar, or simply radio telescopes, which detect radio signals emitted from or reflected from objects, would still work well in heavy fog, though, to view the planets and distant stars. So, astronomy would have had to wait until the invention of the radio telescope, in such a world. StuRat (talk) 13:55, 17 June 2009 (UTC)

The Arecibo Observatory does active radar observations of planets (out as far as Saturn, anyway). See Radar astronomy. I'm not sure how you would discover planets using active radar, though, it only really works if you know where to send the signal. Passive radio astronomy would be required to first discover the planets, radar could then be used to study them. --Tango (talk) 00:03, 18 June 2009 (UTC)

chemical potetial

Give me a derivation which show the variation of chemical potential with temperature.chemical potetial of a component of a system drecrease with increase in temperature - is it true ?Supriyochowdhury (talk) 06:54, 16 June 2009 (UTC)

Please do your own homework.

Welcome to the Wikipedia Reference Desk. Your question appears to be a homework question. I apologize if this is a misinterpretation, but it is our aim here not to do people's homework for them, but to merely aid them in doing it themselves. Letting someone else do your homework does not help you learn nearly as much as doing it yourself. Please attempt to solve the problem or answer the question yourself first. If you need help with a specific part of your homework, feel free to tell us where you are stuck and ask for help. If you need help grasping the concept of a problem, by all means let us know. -- Captain Disdain (talk) 07:21, 16 June 2009 (UTC)

I'm not answering this specifically unless it turns out its not homework, but I've never had a problem helping people find the answers to their homework.
Have you tried looking in any of the basic physical chemistry textbooks such as Atkins' Elements of Physical Chemistry? Or perhaps your course textbook may have the information you are seeking. If not, try reading your lecture notes to find the answers in there. It's where I find them more often than not. If all these fail, then try the wikipedia article on chemical potential. However wikipedia articles on subjects such as these often assume chemistry knowledge beyond that assumed by an introductory textbook. If the problem really persists, email the lecturer or if you have a supervisor/mentor/tutor at your college or uni try them. They don't just have academic knowledge, they have teaching knowledge and it can always help to talk through the stages of a problem with someone.

This answer isn't to say that I don't know the answer to this, I just don't think you would gain much by me or anyone else just spouting a few formulae.

Alaphent (talk) 09:51, 16 June 2009 (UTC)

Insect identification?

Could anyone identify the insect in this photo, http://s696.photobucket.com/albums/vv323/bailey-tucker/?action=view&current=IMG_2146.jpg. The image was taken in New Hampshire on 2009-05-04. Thanks --Captain-tucker (talk) 13:21, 16 June 2009 (UTC)

Looks like some kind of mayfly, but IANAE. --Sean 14:04, 16 June 2009 (UTC)

Probably in the Baetidae family.Alaphent (talk) 14:09, 16 June 2009 (UTC)

Aches after exercise

Is myalgia the correct term for the aches unfit people may get the morning after exercising a little too strenuously? If not, what is? --Dweller (talk) 15:14, 16 June 2009 (UTC)

Delayed onset muscle soreness? --Sean 16:30, 16 June 2009 (UTC)

Myalgia usually refers to an underlying disorder or other long term situation (alcohol abuse, medication, RSI) that triggers it off (i.e. not 1 exercise session). Does microtrauma help, although that applies according to how hard you push yourself, not your level of fitness. --87.115.23.15 (talk) 18:02, 16 June 2009 (UTC)

Myalgia as a medical term is a synonym for muscle pain - it's that simple. Similarly, arthralgia is joint pain. --Scray (talk) 20:13, 16 June 2009 (UTC)

What is RVS Steel?

A Google search of RVS Steel reveals many products manufactured from this material (many of them Dutch) but none provides information on what type or grade of steel this is or gives any reference to a national or international material specification.

This site suggests it may be simply a translation of 'stainless steel' or at least a variant thereupon. - Jarry1250 ^{(t, c)} 17:04, 16 June 2009 (UTC)

Indeed, it seems. Stainless steel interwiki links to "Roestvast staal" with "RVS" mentioned. This would suggest the S stands for "staal" i.e. steel. - Jarry1250 ^{(t, c)} 17:09, 16 June 2009 (UTC)

I'm betting that Roestvast is roughly either "rust proof" or "rust free" ie. stainless steel. --Polysylabic Pseudonym (talk) 07:16, 17 June 2009 (UTC)

Can the Lotus position be bad for your knees?

I mean the full lotus position.--80.58.205.37 (talk) 15:48, 16 June 2009 (UTC)

We can't give medical advice, but I think it's safe to say you need to be quite flexible to be able to do this in the first place, and you shouldn't continue if it is painful. Alternate the legs occasionally to avoid discomfort.--Shantavira|^{feed me} 16:20, 16 June 2009 (UTC)

I don't think it is a medical advice request (and isn't "stop if it is painful" advice anyway?). I used to do a lot of meditating, and any position becomes painful after an hour, even after a lot of paractice. I found no lingering ill effect, but always wondered about the effect that long term sitting would have (over a life time). I usually sat kneeling, and i read an article once about Japanese elderly having more knee problems due to a life-time of kneeling. Does anyone know better sources for that?YobMod 10:02, 18 June 2009 (UTC)

Speaking for myself, the full lotus position is bad for my knees. And ankles. And hip joints. I think it depends on the individual. Some people have naturally loose and flexible joints, and other like me don't in spite of doing a lot of stretching exercises. ~Amatulić (talk) 17:17, 18 June 2009 (UTC)

Why are damselflies bright blue?

Many dragon flies have ultraviolet reflective patches on their wings in order to attract prey. Are damsel flies colored to attract prey? —Preceding unsigned comment added by Dranorter (talk • contribs) 16:17, 16 June 2009 (UTC)

Either prey or mates. There's only really three good reasons to be brightly colored: 1) To attract prey 2) To attract a mate 3) To look poisonous so other things won't eat you. Take your pick. --Jayron32.talk.contribs 17:35, 16 June 2009 (UTC)

I would think for advertising strength and virility since only the males are brightly coloured (usually). As an aside, the male dragonflies eyes are larger than those of the females. They actually touch at the top of the head! I would think that is so because he has too always watch for rival males. 67.193.179.241 (talk) 22:53, 16 June 2009 (UTC) Rana sylvatica

Word, botany

What is the word for plants that prefer shadow? "Umbrophilia"? 80.203.110.95 (talk) 20:50, 16 June 2009 (UTC)

Our article Shade tolerance discusses the subject, which seems surprisingly complex; but doesn't offer a Latinesque or Greekesque word to describe the plants that "prefer" shade. Tempshill (talk) 21:55, 16 June 2009 (UTC)

Photophobic. B00P (talk) 21:57, 16 June 2009 (UTC)

When is the Pleiades meteor shower this year?

Oddly, I'm having difficulty getting relevant search results. --Trovatore (talk) 22:06, 16 June 2009 (UTC)

I don't believe a such-named shower exists. Are you sure you aren't after something else in our list of meteor showers? Algebraist 22:13, 16 June 2009 (UTC)

Have you got the right name? Pleiades is a star cluster. Exxolon (talk) 22:36, 16 June 2009 (UTC)

Do you mean the Perseids? As always, they'll peak on the night of August 12-13, and the best time to see them in Toronto (where I live) is around 3 a.m. on August 13. --Bowlhover (talk) 22:55, 16 June 2009 (UTC)

I did mean the Perseids, thanks. Of course the peak is not exactly the same day each year, which is why I was asking. Apparently the morning of Aug 12 will be the best this year, though with interference from the Moon. --Trovatore (talk) 22:58, 16 June 2009 (UTC)

Often the exact time of the peak isn't as important as local factors in determining the best time to go out. It is generally best to view between midnight and dawn, local time, although I can't remember why (something to do with the directions the meteors will be coming in). You also want to view when the radiant is as high in the sky as possible and when the moon is out of the way. --Tango (talk) 23:36, 16 June 2009 (UTC)

Aug 12 - oops! I somehow got the impression that the peak is almost always somewhere around Aug. 13 morning, but I guess that's not true. --Bowlhover (talk) 00:15, 17 June 2009 (UTC)

Yes, unfortunately these are somewhat incompatible this year, as moonrise will be around midnight. But this link suggests there could be a decent show anyway. --Trovatore (talk) 23:39, 16 June 2009 (UTC)

For the Perseids, I find it's best to go out around 3 a.m. because the radiant is high in the sky at the moment, and because going out at 3 a.m. gives plenty of time to observe before dawn. Of course there are advantages to observing earlier: you get to see the slow and long-lasting earthgrazers, the ones that enter the atmosphere at a shallow angle, and this year the Moon won't interfere. --Bowlhover (talk) 00:15, 17 June 2009 (UTC)

Thanks much. I'm hoping to be backpacking in the Sierras that night, and if the weather cooperates we can just lie in our sleeping bags on top of a ground cloth and watch the sky. I did that once as a boy during a meteor shower, and it was unforgettable. --Trovatore (talk) 01:25, 17 June 2009 (UTC)

June 17

Does TeVeS or STVG explain LIGO?

Despite years of operation, LIGO has yet to have a single unambiguous detection event. Meanwhile, TeVeS and STVG have been developed, which can explain galaxy rotation curves without the need for dark matter, and which avoid some of the problems that plagued earlier alternative gravity theories. Does either TeVeS or STVG modify gravity theory at interstellar distances in ways that would explain why LIGO can’t seem to detect gravity waves? Or are TeVeS and STVG both close enough to unmodified general relativity that it shouldn’t affect LIGO? Red Act (talk) 00:16, 17 June 2009 (UTC)

All these modified gravity theory have a hard time explaining some of the evidence for dark matter such as the Bullet Cluster, so they may be part of an explanation but don't preclude the need for some form of dark matter. Dauto (talk) 00:38, 17 June 2009 (UTC)

I don’t know about TeVeS, but the STVG article says that STVG successfully explains the gravitational lensing in the Bullet Cluster, using this as its reference. Red Act (talk) 00:51, 17 June 2009 (UTC)

Does anyone know the answer to Red Act's question abut the gravity waves? I'd be interested also. --Trovatore (talk) 09:43, 17 June 2009 (UTC)

I've just learned that I mispoke a bit in my question, although my intended meaning was clear from context. My question about LIGO is of course referring to gravitational waves, not gravity waves. Red Act (talk) 18:40, 18 June 2009 (UTC)

What is the resonant frequency of fingertips? Is it in ultrasound?

Sagittarian Milky Way (talk) 01:26, 17 June 2009 (UTC)

I would expect it to be at the high end of the audible range, based on intuition. How would you define the resonant frequency? Where is the energy applied? Edison (talk) 02:22, 17 June 2009 (UTC)

A fingertip is a structure of the human body that is constructed of many different tissues. There is no uniform answer to you question. Medical ultrasonography only covers part. There are many other imaging techniques that rely on various resonance frequencies. Most of those do not consider Skin. 68.208.122.33 (talk) 05:29, 17 June 2009 (UTC)

Resting a finger lightly on a loudspeaker cone delivering bass tones may give an impression that the finger resonates slightly at some frequency. However the fingertips are so like rubber that any resonance would be so heavilydamped as to be probably undetectable. Cuddlyable3 (talk) 08:13, 17 June 2009 (UTC)

Edison, applied at the fingerpad, I guess. Cuddyable, true it does feel like that, but then again, I can't touch the wall soft enough to not hear it, so something's vibrating there, and not too obscurely at that. Very short, but not infinately damped.

Maybe because of my age. Old people like 40 or 80 can't hear as high a frequency so if people return negative findings with being able to hear that then it's pretty much confirms the range. Sagittarian Milky Way (talk) 14:15, 17 June 2009 (UTC)

"Resonant frequency" is probably the wrong term; the fingers are so highly damped that they don't resonate to any meaningful degree. If the point of the question is to ask what frequencies we can sense with our fingertips, the main sensors are Pacinian corpuscles and Meissner's corpuscles, which mainly respond to frequencies below 100 Hz, i.e., deep bass. Looie496 (talk) 17:18, 17 June 2009 (UTC)

Yes, they will not resonate, because they are not a nice acoustic simple harmonic oscillator. The frequency response is probably very wide. Nimur (talk) 22:36, 17 June 2009 (UTC)

Why does so little of the energy become sound when objects strike each other?

Sound power says that a jackhammer is only 1W of sound power. You make 2 orders of magnitude more than that just standing still. What is the efficiency ratio? (Joules of kinetic energy dissipated to joules of sound (all frequencies) produced) Sagittarian Milky Way (talk) 02:05, 17 June 2009 (UTC)

Take a look at transverse wave compared to longitudinal wave for help with your question. It looks like homework, so I won't say more other than you can probably get by with simple math. ZabMilenko^{How am I driving?} 04:56, 17 June 2009 (UTC)

If I attached the business end of a jackhammer to a flexible cone of plastic inside a properly designed sound enclosure, the sound output could be orders of magnitude higher. It is designed to break concrete, not to cause air vibrations. Edison (talk) 02:20, 17 June 2009 (UTC)

If you can find the watts of electrical power consumed by the compressor that feeds the jackhammer then you have its overall power ratio regarded as an unintended loadspeaker. Power is also released at supersonic frequencies and as heat. Cuddlyable3 (talk) 08:03, 17 June 2009 (UTC)

Maximum possible impact of one person

Is there any theoretical upper limit on how much of humanity, or of the universe as a whole, one person can ultimately impact in one lifetime? Any lower limit? NeonMerlin 01:52, 17 June 2009 (UTC)

If you're the guy who invented the self-replicating nanobots that end up malfunctioning and consuming first the entire planet for resources to increase their number, then spreading out from there, then 'lots'... ;) --Kurt Shaped Box (talk) 01:58, 17 June 2009 (UTC)

Well, if chaos theory says that the flapping of a butterfly's wing can change the course of a hurricane on the other side of the earth a year later then the amount of change that the least noticable, laziest couch-potato can make in a lifetime is WAY more than that! The theoretical upper limit is determined by the speed of light. If you live for 100 years - the theoretical limit of your influence during your lifetime is a sphere 200 light-years in diameter. But beyond your lifespan...there is no theoretical limit. I strongly suspect the upper and lower limits of influence are pretty similar. But a lot depends on what you mean by "impact". Genghis Khan had a pretty wide-spread influence - he's known for a lot of very specific influence. But the total number of atoms he rearranged as a result of his actions are pretty similar to the "influence" of anyone else. It's a matter of notability. SteveBaker (talk) 02:15, 17 June 2009 (UTC)

I think Steve loves to bring Chaos theory into the picture every opportunity he gets :-)Rkr1991 (talk) 11:04, 17 June 2009 (UTC)

but if you think about it genetically rather than physically Khan is more influential. some ridiculous number of people are descended from him on account of his prodigious reproduction. --173.66.250.169 (talk) 03:21, 17 June 2009 (UTC)

(That's actually the reason I picked him as my example!) SteveBaker (talk) 12:41, 17 June 2009 (UTC)

The theoretical impact would indeed be limited, by cosmic inflation outpacing light speed. --Sean 12:51, 17 June 2009 (UTC)

Taking "impact" literally, presuming a person massing 120kg (because they want to make as big an impact as possible), and travelling near light speed (for the above reason), they'd deliver an impact approaching (0.5 x mass x speed x speed) 5.4 EJ. That's quite an impact. --Polysylabic Pseudonym (talk) 07:44, 17 June 2009 (UTC)

Such a person might well cry "I'll show them all who has guts." Cuddlyable3 (talk) 07:51, 17 June 2009 (UTC)

Very, VERY briefly...yes. SteveBaker (talk) 12:41, 17 June 2009 (UTC)

Superconducting Monkey Collider loses funding. --Sean 12:51, 17 June 2009 (UTC)

Wouldn't their mass increase without limit as their speed approaches the speed of light? — DanielLC 14:38, 17 June 2009 (UTC)

Mass is not a useful consideration, but their energy would certainly increase without limit. --Tango (talk) 17:23, 17 June 2009 (UTC)

An unsourced bon mot by Peter Ustinov gives a hint of the maximum impact to date: "The jews are remarkable for having produced Jesus Christ and Karl Marx who have influenced more people than any others, but had the sense to believe neitherr of them." Cuddlyable3 (talk) 07:49, 17 June 2009 (UTC)

It has been argued that at their peak there were more fans of The Beatles than followers of Jesus...but "influence" is a slippery word and almost any interpretation is possible. SteveBaker (talk) 12:41, 17 June 2009 (UTC)

With 1/3 of the Earth's population being Christian, and counting the Muslims as well (Jesus has an important role in Islam as well) I would disagree with the above sentence. --131.188.3.20 (talk) 22:22, 17 June 2009 (UTC)

Well, you would be wrong. It definitely has been argued. Steve made no statement on whether the argument was correct or not. --Tango (talk) 23:49, 17 June 2009 (UTC)

Is telepathy possible through technology? What is this called?

And how is it done? —Preceding unsigned comment added by 24.118.246.158 (talk) 04:54, 17 June 2009 (UTC)

Take a look at brain waves for older examples, and possibly brain-computer interface. All of this, I believe, falls under emerging fields like cognotechnology. ZabMilenko^{How am I driving?} 05:05, 17 June 2009 (UTC)

It's called techlepathy. —Preceding unsigned comment added by 24.118.246.158 (talk) 05:15, 17 June 2009 (UTC)

Following WP:RS the answer is No. Cuddlyable3 (talk) 07:37, 17 June 2009 (UTC)

What about this? It looks as if synthetic telepathy may be another useful search term. ZabMilenko^{How am I driving?} 08:04, 17 June 2009 (UTC)

Some day, cell phones could be so small that we would be able to have them inside our ear. Does it count as telepathy?--80.58.205.37 (talk) 10:38, 17 June 2009 (UTC)

"Telepathy" is a pretty wide out term. Are you looking to be able to talk to people brain to brain? Because you can't do that. But there, are interesting technologies that allow you to control computer games (Or other computer programs) with your brain. [1] And there's this toy from Mattel that sort of gives you telekinesis. Sort of. APL (talk) 13:49, 17 June 2009 (UTC)

Yes, "telepathy" is not a very precisely defined term. In the sense of direct brain-to-brain communication, it isn't possible to any useful degree with present technology, but there is nothing to rule out future developments making computer-mediated non-linguistic brain-to-brain communication possible. Looie496 (talk) 17:11, 17 June 2009 (UTC)

"Possible" is also poorly defined. Any "Is xxx possible through technology" could be answered with "maybe in the future". Can pigs fly?: maybe in the future! Even proposals that break the laws of physics can be answered so, as there is no way to predict the far future. To my mind, that makes the whole line of enquiry non-scientific, it is instead purely philosophical.YobMod 09:50, 18 June 2009 (UTC)

Anything will fly as long as you give it a means to generate sufficient thrust. Think pig with Cruise missile strapped to back. Large boar ammunition. 65.121.141.34 (talk) 13:12, 18 June 2009 (UTC)

Oils and fluids

What is the difference between an oil and a fluid?

I am an apprentice fitter & turner, 2nd year. I have just started to learn about hydraulic fitting, and my tradesman wants me to find out the difference between an oil and fluid. I have used google and yahoo, but can't find anything. Everyone seems to say they are the same thing, but they are not. So I want to know the difference. All I know so far is that a fluid is used to transmit power, whereas an oil is purely a lubricant. —Preceding unsigned comment added by Thenickoff (talk • contribs) 05:34, 17 June 2009 (UTC)

I have no particular technical training or knowledge, but in terms of hydraulics "hydraulic fluid" and "hydraulic oil" mean the same things - they even point to the same wikipedia page. Hydraulic fluid is generally made of mineral oil. More generally, see oil and fluid - outside the field of hydraulics these terms are very, very, very general. --Polysylabic Pseudonym (talk) 07:32, 17 June 2009 (UTC)

Oil is a fluid, so is water. Thus not all fluids are oil. You seem well aware of the application of oil in particular. There are many applications of fluids in general, including washing, irrigating, drinking, swimming, floating boats on, putting out fires, thermometers (mercury or alcohol - both are fluids), riot crowd control, eye/nose/ear drops, steam engines,... Hydraulic systems are not my field but the article Hydraulic fluid says it may or may not be an oil. Cuddlyable3 (talk) 07:33, 17 June 2009 (UTC)

Scientifically speaking, all gasses, most liquids and a few solids (eg silly putty) are "fluids". Therefore oils are also fluids.

However, in the automotive world, I don't think many people would think of gasses as fluids. People talk about "windshield washer fluid" - which is most certainly not an oil. I don't agree with your idea that fluids transmit power - that's certainly not true of windshield washer fluid! We also tend to use terms like "hydraulic oil" and "hydraulic fluid" interchangeably - so not all oils are for lubrication. The definition of an 'oil' is a bit fuzzy - basically it's a fluid, and it's one that's "hydrophobic" (won't mix with water). But we don't call gasoline an "oil" so that definition isn't precise enough...I think oils have to be more viscous than that. It used to be that all oils were derived from natural biological sources (ie crude oil or vegetable/nut oil) - but with synthetic engine oil - that definition is falling apart.

In your field, I would offer the following simplified definitions:

• Fluid - Any liquid.
• Oil - Any viscous fluid which does not mix easily with water.

SteveBaker (talk) 12:31, 17 June 2009 (UTC)

The on-line etymology dictionary gives:

OIL c.1175, "olive oil," from Anglo-Fr. and O.N.Fr. olie, from O.Fr. oile (12c., Mod.Fr. huile), from L. oleum "oil, olive oil" (cf. Sp., It. olio), from Gk. elaion "olive tree," from elaia (see olive). O.E. æle, Du. olie, Ger. Öl, etc. all are from Latin. It meant "olive oil" exclusively till c.1300, when meaning began to be extended to any fatty, greasy substance. Use for "petroleum" first recorded 1526, but not common until 19c. The verb is c.1440, replacing O.E. besmyrian. The artist's oils (1663), short for oil-colour (1539), are paints made by grinding pigment in oil. Cuddlyable3 (talk) 21:22, 17 June 2009 (UTC)

The above answers seem to be forgetting that this is a domain-specific terminology. The original poster has clearly stated that he wants to know the difference with regard to metal-working. We have an article: Cutting fluid. There is not a significant difference, and the terms are often used interchangeably. (Take a look at Metalworking Fluid Magazine's recommended reading list for some example usage). However, "fluid" is more technically correct (more general), because not all metal-working fluids are petroleum-based (or oils at all, in the chemical sense). Fluids include silicones, petroleum derivatives and true oils, soy-based and organic chemicals, mists, etc. etc. etc. For example, if you were going to be working on a metal fitting joint for an oxidizer system, never use an oil - you must use an oxygen-clean, safe working fluid - because there is a very real risk that residues left behind will combust (catch fire). Krytox is a safe alternative, it is often used for sealing, but it can also be used while working the part. Some machinists will suggest that a good toothbrush cleaning removes all oil residues, but they probably never worked with very strong oxidizers... Nimur (talk) 22:43, 17 June 2009 (UTC)

Determining the Credibility of Research Journals

Until recently I was very naive about research journals, sort of blindly accepting their published results as being peer-reviewed and trustworthy, even if I'd never heard of the journal before. As a writer who is now frequently tasked with reporting on advances in cancer research, this is admittedly foolish. But then I came across Regulatory Toxicology and Pharmacology, and recognized the editor's name as a notorious one in his field, and later read that it receives funding from RJ Reynolds.

I'm aware of the more renowned journals, such as The Lancet, but the List of medical journals is extensive. I assume that over time, familiarity will breed the necessary discretion. Until then, are there methods of determining the credibility of research journals I haven't heard of? Wolfgangus (talk) 06:59, 17 June 2009 (UTC)

Your scepticism of journals funded by vested interests is evidence that you are no longer naive. In reports about a major research field such as cancer it would be wise to look for reliable, third-party, published sources similarly to the WP:RS guideline. Cuddlyable3 (talk) 07:14, 17 June 2009 (UTC)

On Wikipedia there is also WP:MEDRS and the reliable sources notice board, WP:RS/N. In real life, googling the journal and the editorial stuff may help. Looking for red flags is useful. And check Google Scholar to see how often and how widely a given paper has been cited. --Stephan Schulz (talk) 07:21, 17 June 2009 (UTC)

If the result of a study doesn't sound right, you will have to examine the methodology used and make your own conclusions (don't forget to also read the footnote containing any possible conflict of interests of the authors). For pharmacology this can be difficult and sometimes an error will be impossible to spot as it is not noted in the research (see: Retracted article on dopaminergic neurotoxicity of MDMA published in one of the big three journals (Nature, Lancet, Science)). --Mark PEA (talk) 09:20, 17 June 2009 (UTC)

OK- The guidelines in both WP:MEDRS and WP:RS seem sound, I can work with those. Google Scholar I hadn't given thought to, so I appreciate that as well. With regard to the reliable sources notice board here, that page is new to me as well. Does that concern only sources used on Wikipedia? It appears that way. (Oh and thanks so much for your time and assistance). Wolfgangus (talk) 09:39, 17 June 2009 (UTC)

For a relevant case study see the MMR vaccine controversy - research originally published in The Lancet was subsequently discredited, but not before widespread panic had been caused amongst parents fearing the vaccine would harm their child. --Lonegroover (talk) 14:50, 17 June 2009 (UTC)

It's sometimes easier, in my opinion, to gauge the value of an article than of a journal, if the article is a few years old. With high probability, if Google Scholar shows a bunch of citations, and the citations come from papers in journals that you know are good, then the article is a good one. This doesn't work too well with articles published in the last couple of years, though. Looie496 (talk) 17:06, 17 June 2009 (UTC)

Incidently, Nature News discusses a fake (nonsensical) paper submitted to and accepted by an online journal. Arguably this will hurt said publication's credibility. Normal peer review should get around this, but I'm skeptical of journals I've never heard of before. Reputable journals ask for authors to disclose potential conflicts of interest. -- Flyguy649 ^talk 17:43, 17 June 2009 (UTC)

Bentham Open also published a "peer-reviewed" paper by 9/11 conspiracy theorists which supports the notion that the World Trade Center was destroyed by a controlled demolition. The Chief Editor of the journal resigned saying that she never authorized its publication and did not consider it worthy of publication; other editors also resigned as a result.[2]. Bentham Open has been accused by academics of 'spamming' researchers with offers to publish or edit the journal, even where those researchers have no background in the field of study.[3][4]. Bentham Open comes up a lot on articles related to 9/11 conspiracy theories because they think it gives their conspiracy theories scientific credibility. A Quest For Knowledge (talk) 18:18, 17 June 2009 (UTC)

Corporate interests do not necessarily invalidate credibility - they just "modulate" it. Ultimately, the reliability of the research is independent of who paid for it and how it was published - what matters is whether the results were scientifically accurate, and the conclusions were reasonable, and the experimental data is repeatable. Nimur (talk) 22:51, 17 June 2009 (UTC)

The "credibility" of a journal is generally considered to correlate reasonably well with its impact factor (though this is not without criticism). Info on Regul. Toxicol. Pharmacol. can be found here, and that particular jounal appears to be of middling impact factor rank in its fields. — Scientizzle 23:18, 17 June 2009 (UTC)

I somewhat disagree here. Specialist areas may be more trustworthily covered by specialist journals that may have lower impact factors. There is a lot of prestige that goes along with getting in higher IF journals, which can result in rushing, or making exagerated claims. This is clearly seen when Science or Nature rushes to publish extroadinary claims (about cold fusion, homeopathy, human cloning) without good fact-checking, because they want to be first.YobMod 09:42, 18 June 2009 (UTC)

Which is why you consider IF within the relevant field. That's the comparison I linked to in my last link immediately above. IF is only an imperfect, but useful, proxy for determining whether a journal is generally considered credible. For someone completely unfamiliar with a particular subspecialty, IF is a reasonable jumping-off point (as is, say, determining whether the journal is indexed in MEDLINE, and looking at citations patterns). — Scientizzle 15:28, 18 June 2009 (UTC)

Quarternary Structure

I've looked around for this on here. What exactly holds the quaternary structure of a protein together. All I could find on here was that the monomers are not normally covalently linked, then the article talked about many methods of determining the quarternary structure. Any help is much appreciated, thanks...Oh, and while I may currently be doing an assignment on proteins and enzymes, this is actually a personal interest question that has cropped up while doing it. —Preceding unsigned comment added by Alaphent (talk • contribs) 09:53, 17 June 2009 (UTC)

Secondary structure is the general 3D form form of local segments of polypeptides, formed when hydrogen bonding occurs between hydrogens of an amino group and lone pairs of a carboxy group. Disulfide bonds can also contribute to secondary structure. Tertiary structure is the 3D form of the entire polypeptide/protein. Quaternary structure is when multiple tertiary structures come together to form a working complex. Examples include insulin (in some states) and haemoglobin (a tetramer with an iron ion bound). --Mark PEA (talk) 11:15, 17 June 2009 (UTC)

Mark, you didn't exactly answer the question. The OP didn't ask "what is the difference between the structures?", he asked for the force that is holding the quarternary structure together. The answer is: Van der Waals force. In chemistry (and also biology), if it's not covalent or ionic, it is in most cases a van der waals interaction. Even hydrogen bonding is a very strong van der waals interaction, so most biological molecules "assemble" the way they do because of van der waals attractions. Btw: most secondary and tertiary structes are also formed because of van der waals forces, with the exception of covalent disulfid bonds. --TheMaster17 (talk) 12:45, 17 June 2009 (UTC)

Sorry, I think I only skimmed over the question, but I assumed that Alphaent didn't really understand what kept secondary structures together, thus once knowing what kept secondary structures together would know what keeps quaternaries together. TheMaster17, are you sure that the Fe²⁺/Fe³⁺ ion in haemoglobin doesn't contribute to holding the tetramer together using ionic forces? --Mark PEA (talk) 15:47, 17 June 2009 (UTC)

Any of the forces that hold the tertiary structure together can also be found linking subunits in quaternary structure. So Van der Waals, Hydrogen-bonding, ionic interactions, hyrophobic effect. I work with an antibody made of 3 units, 2 of which are linked by disulphide bridges (to the central unit). The important part of the definition is what is being linked - the separate subunits is what differentiates it from 3° structure.YobMod 09:34, 18 June 2009 (UTC)

You two are right, my answer was a bit exaggerated: It is not only van der waals forces, for sure there are all possible forces involved, including ionic bonds (between charged amino acids or other ions). I just wanted to point out that van der waals forces with water are usually the major force between different parts of a protein or a complex in aqueous solution. The protein has very many water molecules to interact with: hydrophobic parts will stay away from the water and hydrophilic parts will be "covered" with water. Without water it won't work in most cases, even if all ions and covalent bonds are in place. Water and its van der waals interaction are required for the parts to fit properly. --TheMaster17 (talk) 09:53, 18 June 2009 (UTC)

why do hurricanes slow down?

what stops hurricanes carrying on exponentially? if there is the energy for them to get to the size they do, why doesn't it carry on increasing? i am not a scientist at all, but i was thinking maybe it has something to do with friction, though i have no idea if this is relevant to air particles. is it to do with air pressure? as it moves into low pressure areas it kind of disperses? cheers

nick —Preceding unsigned comment added by 86.172.240.210 (talk) 11:17, 17 June 2009 (UTC)

Have you read hurricane, especially the topic mechanics? "When a tropical cyclone passes over land, it is cut off from its heat source and its strength diminishes rapidly." directly from the article's text. And concerning the growth of the initial hurricane: it gets larger as long as the feedback process can feed more energy per second into the system. If the cyclone moves into an area with less favorable conditions it will shrink, and grow again if there is enough moisture/temperature gradient in another place it passes through. It's a dynamic process with positive and negative feedback loops, and their balance at any time dictates growing or shrinking of the storm system. --TheMaster17 (talk) 12:24, 17 June 2009 (UTC)

There are three factors that impact hurricanes the most: land, water temperature, and wind shear. The land factor is described in the previous comment. The water temperature factor means that when the sea surface temperature is too low, there isn't enough evaporation to sustain a tropical system. This always happens sooner or later, because hurricanes have a strong tendency to move northward, where the water is colder. The wind shear factor comes into play when low-altitude and high-altitude prevailing winds blow in different directions -- this stretches the circular shape of a hurricane and reduces its ability to spin easily. Looie496 (talk) 17:00, 17 June 2009 (UTC)

Also, another reason hurricanes do not strengthen indefinitely is because they often go through eyewall replacement cycles, which temporarily weaken the hurricane even over warm water (sometimes as much as one category downward). Another inhibiting factor is the Saharan Air Layer, which pulls dry air into the hurricane, dramaticly weakening it. ~AH1^(TCU) 13:00, 18 June 2009 (UTC)

Sticky situation

To start with, I'm not considering doing anything that I talk about here. If a person eats a normal balanced diet and they are not ill. How long could they go without shitting if they delibratly held it in? Is there a point at which it would become dangerous? Heinzcreamofchickensoup (talk) 13:16, 17 June 2009 (UTC)

Sorry - we don't give medical advice. Consult a doctor. Exxolon (talk) 13:53, 17 June 2009 (UTC)

Not a medical advice question, consider it a human biology question, read the first sentence? —Preceding unsigned comment added by Heinzcreamofchickensoup (talk • contribs) 13:57, 17 June 2009 (UTC)

I've chosen to answer under Kainaw's criterion, which I find sensible. --Sean 14:09, 17 June 2009 (UTC)

Probably long enough to give themself a fecal impaction, which if untreated could lead to their never having a bowel movement again. There have been cases where drug mules or others who have swallowed contraband and then been apprehended have tried to avoid having a bowel movement in order to withhold evidence, but I don't know how long they held out or how successful that strategy is. --Sean 14:07, 17 June 2009 (UTC)

I'm not even sure it's possible to "hold it in" indefinitely. I once read that there is nothing that varies so much from one human to another as defacation frequency. For some people, once a week seems to be perfectly normal[5] while for others it's several times a day.--Shantavira|^{feed me} 15:31, 17 June 2009 (UTC)

A 19th century circus freak called the "Windbag Man" had a huge protruding abdomen due to feces retained in the colon.He died in 1892 at the age of 29. He supposedly had only one bowel movement per month. "Holding it in" may have led to a massive dilation of the colon. He may also have suffered from Hirschsprung's disease, a congenital nerve problem lmiting bowel contractions. His colon had 40 pounds of stool in it when he died. His colon, with contents, can be viewed at the Mutter Museum of medical curiosities. Edison (talk) 18:59, 17 June 2009 (UTC)

I once saw a photo of a preserved megacolon. It looked to be about the size of an Alsatian dog. --Kurt Shaped Box (talk) 19:27, 17 June 2009 (UTC)

If it had to be surgically resected, would it leave a semicolon? Edison (talk) 22:11, 17 June 2009 (UTC)

Hahaha, that's REALLY funny!!! ROFLMAO!!! 76.21.37.87 (talk) 05:54, 18 June 2009 (UTC)

Many years ago, when I was about 12 or so, I went to visit some relatives who only had an outhouse. Needless to say, the smell was mighty ripe in the middle of July. The nearest flush toilet was 30 miles away! Being a fussy lad, I refused to use the "rural facility." To make a long story short: I refused to poop for a week and a half. Darn near exploded. Not so fussy any more . . .

human weight

I weigh myself several times a day on the same scale and have noticed that I almost always weigh less in the morning then I do at other times of the day, generally by 1-3%. Do people really fluctuate in that kind of a range, or is it more likely a measurement error because the scale is usually cooler in the morning then at other times? 65.121.141.34 (talk) 14:45, 17 June 2009 (UTC)

Short-term weight fluctuation is well-documented and normal. This article specifically discusses day-to-day measurements, but the same principles hold for morning-to-evening measurements. A couple of simple possibilities include time since your last meal (likely highest at your morning weigh-in) and time since your last toilet use (possibly lowest at your morning weigh-in, depending on your ritual). — Lomn 15:35, 17 June 2009 (UTC)

I would suspect your scales and suggest you try weighing something else (such as a full suitcase) at the same time. Bathroom scales are not very accurate. To ensure consistency, make sure the scale is on a hard level surface (not carpet) and don't move it between weighings.--Shantavira|^{feed me} 15:37, 17 June 2009 (UTC)

That wouldn't explain the measurements being consistently lower in the mornings. Lomn's response is the more likely explanation. --Tango (talk) 15:53, 17 June 2009 (UTC)

Just remember that 1 kg = 1 liter. If you weigh 50 kg and you drink a couple of cups of anything, that already makes 1% more weight.--Mr.K. (talk) 16:31, 17 June 2009 (UTC)

I've experienced the same thing. I assume it was because your body continues to burn calories while you sleep and the fact that you probably haven't consumed too much water in the middle of the night. A Quest For Knowledge (talk) 17:49, 17 June 2009 (UTC)

I don't buy this. I agree you will burn some calories while asleep and thus lose some mass as CO₂, but I'm pretty sure it would be a negligible quantity and within the measurement error of your bathroom scale. Assuming you weigh yourself at night after you've urinated/drunk water/whatever and then reweigh yourself in the morning prior to urinating/drinking water/whatever, the reading should be the same. If it's not, I'd look at the scale (unless you sweat a lot at night). Why might it not be reading the same? I'd bet there's a change in ambient temperature of a couple of degrees C that affects the accuracy/calibration of the scale. The only way to verify that the change is not due to some error of measurement is to calibrate the scale with a fixed mass as suggested above. -- Flyguy649 ^talk 20:38, 17 June 2009 (UTC)

I weighed myself after urinating for both the morning and night. The difference between the two is that you typically don't drink much water while you sleep (at least I don't). So your body processes water you already have in your system before it is replenished in the morning. A Quest For Knowledge (talk) 22:12, 17 June 2009 (UTC)

Don't trust your intuition on this one, even giant redwood trees are literally made out of thin air. However, my guess ist that in humans water loss due to breathing is the main form of mass loss at night. —Preceding unsigned comment added by 84.187.114.219 (talk) 21:56, 17 June 2009 (UTC)

Years ago, I let myself go and was getting fairly chubby. For my News Year's Resolution, I decided to lose about 25 lbs. I went on a diet and worked out regularly. I kept daily records and always used my morning weight because it was a pound or two heavier lighter than my nightly weight - except if I ate something salty which I assumed resulted in water retention. My hypothesis is easy enough to test if you have some weights. A Quest For Knowledge (talk) 22:08, 17 June 2009 (UTC)

Through the magic of Google, searching "overnight human mass loss water", I found this recent study published in "Nature Precedings". In this small study, the subjects lost 300 +/- 68 g overnight, or roughly 3/4 lb. My scale won't reliably see that difference, but I suspect others might. But still a very small difference. -- Flyguy649 ^talk 22:31, 17 June 2009 (UTC)

It's possible the scale's bias changes with temperature, which may partly account for this. Dcoetzee 12:03, 18 June 2009 (UTC)

If you habitually urinate before weighing yourself in the morning then since the bladder holds around 400 to 600 mL of fluid - you could easily see an overall 500g drop. Add to that the water you lose due to sweating and that you exhale in your breath - and the carbon you lose in converting oxygen to CO2. That's easily at the lower end of the "1% to 3%" range that our OP sees. The rest of the variation is probably due to inaccuracies in the weighing machine. Just altering where you stand on the machine can get you a kilogram of difference. SteveBaker (talk) 13:09, 18 June 2009 (UTC)

Prediction market and sport betting

If the mob is almost always right, betting on what the mob chose will be a pretty sure way of making money, isn't it? What about if I go betting for results that the mob consider have odds of 99% of happening? I would earn 1.01 (1%) for every time I bet (2 hours?), much more than any bank account.--80.58.205.37 (talk) 16:23, 17 June 2009 (UTC)

Betting on results that have odds of probably 99% and pay 1% are only a good deal if they happen more than 99.1% of the time or more. It is certainly not a "pretty sure way" of making money. --Mr.K. (talk) 16:35, 17 June 2009 (UTC)

Don't forget the vigorish, which would swallow up your 1% profit. Bookies don't work for free. Clarityfiend (talk) 16:37, 17 June 2009 (UTC)

And how much would you lose when the mob is wrong? For this to be a worthwhile strategy, you need three things. One, the mob has to do better than the books over the long term. This might be the case, and in any event, should be verifiable. Two, you need sufficiently deep pockets to recover from inevitable losses. Three, you need a book that allows large enough bets to recover those losses. Points two and three are unlikely, and comprise the flaw in the Martingale system. As such, books are more than happy to let you try this. — Lomn 16:37, 17 June 2009 (UTC)

Your premise is that the mob is almost always right. I would encourage you to go and find evidence of this claim. Tempshill (talk) 16:46, 17 June 2009 (UTC)

Actually, bookies set the line or the odds in considerable measure exactly by appealing to the wisdom of the mob. They look at where the money is being bet and adjust the terms so that there is roughly equal payout expectation on both sides (plus the house's cut of course). So, the available betting propositions are likely to already track the mob's opinion, and consulting the mob is unlikely to appreciably improve your odds. Dragons flight (talk) 16:55, 17 June 2009 (UTC)

Also, how often do 99% certain bets come along? Certainly not every two hours. Clarityfiend (talk) 18:40, 17 June 2009 (UTC)

Can anyone clarify this ([6]) for me? Quote:

Coral have hailed Sunday's defeat of Rafael Nadal at odds of 1/100 in his French Open match against Robin Soderling as the biggest shock in living memory. Soderling was a 14/1 chance to beat Nadal and Coral laid just a single five pound bet online on the Swedish player, with no recorded bets in the shops or on the phones.

How can the odds be 1/100 (for Nadal to lose) and 14/1 (for Soderling to win)? Anyway, this is clearly an example where the mob was very wrong, and the bookmakers look to have made a very nice profit from it. --Mark PEA (talk) 20:20, 17 June 2009 (UTC)

If you are wondering why the probabilities don't add up to 100%, that's where the bookmaker's profit comes from. --Tango (talk) 22:42, 17 June 2009 (UTC)

The odds weren't 1/100 on Nadal to lose. They were 1/100 on him to go through. I.e. he was a shoe-in. Basically they had thousands of bets on Nadal to go through at 1/100 (awful odds but a considered dead-cert, maybe used in accumulators or by high-volume betters) and so before the game they were standing to lose (probably because they couldn't 'balance' the Nadal-win bets with Soderling-win bets). This continued with the in-game betting where gamblings were expecting a turn-around that never came. Coral made bucket-loads because the favourite-lost. Bookies often make the most money when the favourite loses because they have X-thousand betting on the favourite at low-odds and only X-hundred betting on the outside at high-odds. ny156uk (talk) 22:17, 17 June 2009 (UTC)

Forgot to add - read Mathematics of bookmaking, in particular the intro-section on 'notion of a book and overound' ny156uk (talk) 22:19, 17 June 2009 (UTC)

If they couldn't balance the bets, why didn't they just change the odds to reflect how people were betting? ie. if lots of people thought it was a good idea to bet on Nadal at 1/100, change it to 1/200, then 1/300 and so on until people bet for the two players in the appropriate proportions so that the bookie breaks even (well, makes the amount of profit they always factor into the odds). I thought that was how it worked... --Tango (talk) 22:39, 17 June 2009 (UTC)

That's the theory - you set the odds to drive the customers to end up balancing your books, but that's not necessarily always going to happen. If people are betting at 1/100 in droves putting it to 1/200 might drop-off volume but it's not going to get them betting for the no-chancer. The no-chancer had 14/1 odds, that might sound not very generous but in some events 14/1 is the equivilent of a horse at 100/1. Betting on the outcome of a single game of tennis isn't (if my memory 'serves') will never get you a 100/1 outsider because it's a 2-player, 2-outcomes only game. It's likely that the odds that were offered 1/100 (for Nadal to win) and 14/1 (Soderling) were about as wide as the odds go but still the bookie couldn't balance. This is all a bit of rationalisation, but we can say with certainty that a professional book-making company will have tried balancing the bets within the best of their limits. 15:35, 18 June 2009 (UTC) —Preceding unsigned comment added by 194.221.133.226 (talk)

If people aren't betting on the no-chancer then surely the bookie needs to offer better odds on them. I can't see why a bookie wouldn't be able to balance their books if they tried to. Perhaps they decide to accept some risk in order to get better volume of bets and, thus, better (expected) absolute profit? The odds necessary to balance the books might have been odds that most people would have chosen to simply not bet at all on (an irrational decision, most likely, but humans are often irrational). --Tango (talk) 17:12, 18 June 2009 (UTC)

I think the original questioner is using "mob" to refer to the "Mafia" and is assuming that organized crime has rigged the event. This might not be a correct assessment. Nimur (talk) 23:07, 17 June 2009 (UTC)

I don't think so. "Mob" is a fairly common term to describe the large body of betters. --Tango (talk) 23:45, 17 June 2009 (UTC)

I have but few equals and no betters. Or did you mean "bettors?" Edison (talk) 01:58, 20 June 2009 (UTC)

The OED accepts either spelling. --Tango (talk) 02:15, 20 June 2009 (UTC)

White dwarf stars

Is white dwarf always white, or it can be blue sometimes. Then what is a blue dwarf?--69.229.243.248 (talk) 23:25, 17 June 2009 (UTC)

They are always called "white dwarfs" but I believe they can be hot enough to appear blue. Our article talks about white dwarfs with effective temperatures well above 10,000K, which is about where blue-hot begins. We have a disambiguation page, Blue dwarf, which lists some things that can be called "blue dwarfs". One is a type of galaxy, not star, one is hypothetical and I'm rather suspicious of the remaining one, "An early-type main sequence star.". I've never heard of a blue dwarf as a type of main sequence star - the colour depends, roughly, on the size. Small stars are cool and red, medium sized stars are yellow and big stars are blue. A blue dwarf seems to be a contradiction in terms... --Tango (talk) 23:44, 17 June 2009 (UTC)

A star's color more directly depends on its temperature, though it often corresponds with size as well. Red giants are enormous in size but cool, and according to our article on them, are .5-10 solar masses. Main sequence stars are like our sun—average size and average temperature. White dwarf stars are small in size but hot, and according to our article, are around 1 solar mass (with about 1.4 being the maximum, since they would supernova if they became more massive than that). —Pie4all88 ^{T C} 22:38, 19 June 2009 (UTC)

Sorry, I was talking just about the main sequence. Red giants and white dwarfs are not main sequence stars and behave very differently. On the main sequence, size and temperature (and, thus, colour) are very strongly correlated. --Tango (talk) 22:50, 19 June 2009 (UTC)

Ah, gotcha. My mistake. —Pie4all88 ^{T C} 22:16, 22 June 2009 (UTC)

• Do white dwarf just go straight to black or they slowly fade from white to orange, then brown to black?--69.229.243.248 (talk) 01:31, 18 June 2009 (UTC)

I think that the universe is not old enough for that to have happened yet. Presumably, though, they will slowly fade, becoming redder until they are too cool to produce visible light. Assuming the universe lasts long enough for that to happen. --Trovatore (talk) 02:12, 18 June 2009 (UTC)

We have an article black dwarf. Algebraist 02:15, 18 June 2009 (UTC)

The color of the star is just due to incandescence of the surface. Like any white-hot object that cools, its color will shift through orange and red before it fades to black. --Anonymous, 05:28 UTC, June 18, 2009.

I don't think incandescent bodies are ever brown. The go from blue to white to orange/yellow to red to black (notably, they are never green, although that isn't relevant to this discussion). Brown is kind of a dark orange, but we normally look at these things against the backdrop of a black night sky, so there is nothing for it to be dark relative to. Brown dwarfs are a different thing entirely, and are actually red, I think. I guess the name comes from them being a kind of inbetween star/planet and brown is a kind of inbetween colour in some sense. --Tango (talk) 13:49, 18 June 2009 (UTC)

June 18

Question on the Scientific Method

What's the difference between the Control and the Constant? 71.196.63.33 (talk) 05:29, 18 June 2009 (UTC)

It's unclear without context, but i would guess you mean control as being the comparison experiment in which the indepentant variable in not varied or at a standard level (eg. If measuring the effect of various additives on bacterial growth rates, the control should be a growth experiment with no additive, but the rest of the conditions kept the same.) The constant would then mean the parts of the experiment that always stay the same (eg, no matter what additive is used, the agar growth medium/temparature/pH/time should always be the same).09:16, 18 June 2009 (UTC)

surface tension

what is surface tention? —Preceding unsigned comment added by 218.248.80.112 (talk) 05:48, 18 June 2009 (UTC)

Hi, take a look at surface tension and for some interesting reading, contact angle. ZabMilenko^{How am I driving?} 05:55, 18 June 2009 (UTC)

What causes surface tension, essentially, is molecular attraction among the molecules of a liquid (it could be Van der Waals forces, or hydrogen bonding like in water or in concentrated HF, or ionic interactions, etc.) When a liquid molecule is surrounded on all four sided by other molecules, these forces cancel out; but when the molecule is on the surface of the liquid, it's only surrounded by other liquid molecules on the other three sides, so their molecular attraction results in a net force toward the interior of the liquid phase, which is what causes surface tension. Quite simple, really. :-) 76.21.37.87 (talk) 06:26, 18 June 2009 (UTC)

Battery. 2.3Ah, 3.3V. How many Watt-hours it could hold?

Was never understanding that ampere thing(why it even mentioned? rhetorical question). From search it looks like I need to multiply mAh and Voltage. But, no way, it could not hold 2300mAh*3.3V == 7.59kW·h!!! Sorry. DeadlyPenguin (talk) 08:42, 18 June 2009 (UTC)

No, 2.3 Ah x 3.3 V = 7.59 W·h, not kW·h. --Heron (talk) 09:27, 18 June 2009 (UTC)

... and, in real life, the capacity depends on the rate of discharge (and never seems to achieve the claimed figure). Dbfirs 12:50, 18 June 2009 (UTC)

Points on a plate ...no idea????

hi friends ....

can any one help me how should i model a mathematical problem for the following problem:

a thin metal sheet is supplied with heat from external source (such as a welding machine etc.) and i want the heat at various points in the plate considering one dimensional heat flow only. —Preceding unsigned comment added by Sameerdubey.sbp (talk • contribs) 09:29, 18 June 2009 (UTC)

This can be modelled using the one-dimensional heat equation. Gandalf61 (talk) 10:47, 18 June 2009 (UTC)

hey thanks a lot .. for quick reply ... but i want to consider heating of previous point and next points . —Preceding unsigned comment added by Sameerdubey.sbp (talk • contribs) 11:07, 18 June 2009 (UTC)

I think the heat equation allows you to do that, if you want it done as a series of steps you could use an iterative formula. Elocute (talk) 15:08, 18 June 2009 (UTC)

Hepatic filtering

In case of cyanide poisoning or something similar, is it a good idea to start exerting physically as much as possible before the poison starts acting? I think it could be idea, since it would increase the speed of your blood flow, and therefore the rate at which your liver detoxifies the toxin. Have I overlooked possible negative consequences of exercising while poisoned? --83.56.176.138 (talk) 10:21, 18 June 2009 (UTC)

It would really be a nice possibility to detoxify in this way. But in reality, for most toxins this won't work. By exercising, you are not only speeding up your blood flow, you are raising your overall rate of metabolism. So your liver would probably detoxify a bit faster, but the toxins would also poison you faster, because of quicker distribution and uptake. So your method could only work for toxins whose speed is not limited by distribution in blood and uptake by the cells. These would need another distribution method in the body, which would render the liver rather useless (because the liver detoxifies blood). --TheMaster17 (talk) 11:18, 18 June 2009 (UTC)

Also, exercise will probably cause vasodilation in the muscles, leading to increased absorption there (although I'm guessing vasodilation would also occur in the liver for glycogenolysis). --Mark PEA (talk) 15:31, 18 June 2009 (UTC)

In any case, if you get poisoned with cyanide, the poison will act too quickly for you to do much of anything about it. 76.21.37.87 (talk) 05:02, 21 June 2009 (UTC)

Lightning & thunder

We all know that getting hit by lightning probably is not very good for you, but what about a near miss? Thunder is sound energy cause by the shockwave of the rapid heating of the air the lightning passes through, so if you are close to lightning (very close), could you be hurt by the thunder, even if the lightning itself missed? Ruptured eardrums, etc? 65.121.141.34 (talk) 13:17, 18 June 2009 (UTC)

At a guess, probably not (save perhaps the hearing damage). Mythbusters recently did a bit on breaking windows with sonic booms, which I would expect are comparable to thunder. They had no problem with the hosts standing 200 feet from a supersonic fighter jet (with good ear protection). I would expect similar effects from nearby thunder. — Lomn 13:26, 18 June 2009 (UTC)

Our articles lightning strike and Roy Sullivan don't mention the possibility of ruptured eardrums even from a direct lightning strike, so I doubt there's much risk. Algebraist 13:29, 18 June 2009 (UTC)

While we're usually good, we're not that good. A Google search for ruptured eardrum or ruptured tympanic membrane and thunder will pull in a substantial number of reputable reports and case studies describing ruptured eardrums following a direct lightning strike; a bit of sieving will identify cases caused solely by thunder. TenOfAllTrades(talk) 13:38, 18 June 2009 (UTC)

Absolutely. Any sufficiently loud noise can rupture eardrums, including a clap of thunder. The British Medical Journal reported such cases all the way back in 1864, also noting that it may be accompanied by otorrhagia (bleeding from the ears). TenOfAllTrades(talk) 13:32, 18 June 2009 (UTC)

I can attest to that. I once had lighting strike nearby me (30 yards or so away). I thought I had permanent hearing damage after that, but thankfully it was temporary. ~Amatulić (talk) 17:10, 18 June 2009 (UTC)

Thanks all. Good to know. 65.121.141.34 (talk) 18:08, 18 June 2009 (UTC)

There was an incident when players were playing football on slightly wet grass when the ground was hit by lighting, due to the conductivness of the water on the grass 4-7 players were electrocuted i suppose this could countChromagnum (talk) 13:51, 20 June 2009 (UTC)

Earth sized cyclotron/rail-gun for human relativistic stasis?

Supposing a cyclotron rail-gun with a capsule large enough for a terminally ill human was created that circled the Earth. Would it be theoretically possible to accelerate the person to relativistic speeds with present day technology (assuming no funding limits) to slow time down for them until the cure for their disease became available, bearing in mind that surviving cyronic suspension is a highly speculative proposition to say the least? (Trevor Loughlin) —Preceding unsigned comment added by 80.2.205.61 (talk) 13:46, 18 June 2009 (UTC)

In short, no. By my calculations, at light speed, you will circle the earth at a rate of 7,500 times each second. Using the equation for centripetal force, you are talking acceleration on the human in question of 1.44 billion g's of acceleration. Considering that amount of acceleration, I can confidently say that he will be unrecognizable as a living thing long before he gets to relativistic speeds. 65.121.141.34 (talk) 14:05, 18 June 2009 (UTC)

My slide rule, confirmed by a back of the envelope calc, says that if the circumference of the Earth is about 24000 miles, and the speed of light would carry you around it 7500 times per second, then the speed of light would be 180 million miles per second. When did it increase in your universe? Edison (talk) 18:57, 18 June 2009 (UTC)

Did you not get the memo? --Tango (talk) 14:20, 20 June 2009 (UTC)

I agree, the g-forces for that kind of circular path would be prohibitive. If you had unlimited funding, you could probably put them on a space ship and send them at relativistic speeds in a straight line. In order to keep the g-forces reasonable you would need to accelerate fairly slowly (by relativistic standards), so I doubt you could get the proper time elapsed for the patient below a year or two (including accelerating, decelerating, accelerating in the other direction and then decelerating again). The elapsed time for the Earth could be arbitrarily high, though, you just keep going for longer before you turn around. --Tango (talk) 14:13, 18 June 2009 (UTC)

Unfortunately for the straight line relativistic rocket, we find that at high speeds collisions with dust become extremely energetic and resultingly very destructive. Making the practicalities design of such a vehicle out of the scope of modern technology. Elocute (talk) 15:04, 18 June 2009 (UTC)

If money is no object, you can just put lots of ablative armour on the front (give me a minute and I'll try about work out how much). That would dramatically increase the energy requirements, but that's just more money (prohibitively more money in real life terms, but the OP isn't talking about real life). --Tango (talk) 15:55, 18 June 2009 (UTC)

Ok, apparently we're talking about something on the order of 1 atom per cubic centimetre. I'll assume that is actually one proton per cubic centimetre, because that's close enough (it's going to be mostly hydrogen). Let's say we want a time dilation factor of 100, that gives the energy per atom as about 15nJ. That time dilation factor requires a speed of 0.99995c. One square centimetre of the front of the ship would sweep out a volume of 3*10¹⁰ cubic centimetres every second, so would have 3*10¹⁰ collisions per second. That's an energy of 450J per second. So you would need to dissipate 450W per square centimetre of cross section all the time you are at top speed. That is a lot, but not astronomical amounts. Impossible to do with existing technology at any remotely reasonable cost, but I don't think it would be impossible with unlimited funds. (Ablative armour probably isn't the best idea, but it was the first I thought of. Something that can just turn the energy into heat combined with a refrigeration system would probably be better.) --Tango (talk) 16:08, 18 June 2009 (UTC)

Because the guy can't orbit the earth (see above argument about centrifugal forces) - he'd be rocketting away from us at some large fraction of the speed of light in more or less a straight line. When we find the cure and send the message to tell him to come home and get fixed up - the message is going to take an alarming amount of time to get there. At a 100x time dilation factor, (as Tango points out), he has to travel at 99.995% of c - he covers 99.995% of a light-year every year. From our perspective our message (at the speed of light) is only catching him up at a relative speed of 0.005% of c. So it might take a few thousand years for our message to reach him! Then he has to slow down, stop, and fly back to us for another thousand years. Even with the 100x time-dilation factor - he's going to be dead before he can get home. I think it's possible to show that there is no way for him to cheat death no matter how clever the technology is. SteveBaker (talk) 18:16, 18 June 2009 (UTC)

Well, I suppose you don't need to fly the ship in a perfectly straight line. If you flew in a circle with a 1 ly radius, you are only pulling 1.5g, and could get the message in only 1 year, but even 1.5g long term might be really bad for you. (Maybe you would look like the incredible hulk when you were done). 65.121.141.34 (talk) 18:37, 18 June 2009 (UTC)

Make the circle a little bigger and you only need 1g, which would be perfect. No worries about high g-forces and no worries about weightlessness. That requires constant thrust, though, which requires even more fuel. In this money-no-object scenario, though, that's a good option. --Tango (talk) 18:46, 18 June 2009 (UTC)

Hang on... I get the radius required for 1.5g proper centripetal acceleration as a little over 6000ly, not 1ly. Either I can't Google relativistic formulae correctly, or you made a mistake. --Tango (talk) 19:03, 18 June 2009 (UTC)

I was thinking you would just guess how long it would take to figure out a cure, add a little on for a margin of error, and come back at that time. If you come back later than necessary, no great problem (it wouldn't be much later from your perspective), if you are too soon then you could always do it again, although you would need to spend more time accelerating back up to speed. --Tango (talk) 18:46, 18 June 2009 (UTC)

mechanical device

Is there any mechanical device like a gear box of a car,in which the output shaft rotates in the same direction independent of the direction of rotation of the input shaft i.e. the output shaft always rotates in clockwise direction when the input shaft is rotated either clockwise or anticlockwise? —Preceding unsigned comment added by 113.199.184.1 (talk) 15:26, 18 June 2009 (UTC)

how about the gear box of a car? —Preceding unsigned comment added by Alaphent (talk • contribs) 16:02, 18 June 2009 (UTC)

I'm not sure a car's gear box behaves the way you describe (else how else does a car reverse?), but a winch on a boat (like this one) commonly has a ratchet system that behaves this way. — Lomn 16:08, 18 June 2009 (UTC)

Ratchets usually just stop the output shaft turning at all if you turn the input shaft in the wrong direction. You could build a system with two sets of ratchets, one in each direction, with one direction being reversed (that just requires one extra gear). I can't see anything difficult about such a set up. (This may be what some boat winches do, I'm not much of a sailor.) --Tango (talk) 16:13, 18 June 2009 (UTC)

All sailboat winches I've worked with advance the line in one direction regardless of which way the handle is turned. Changing which direction you turn the handle affects the mechanical advantage provided, much like gears on a bicycle. I suppose this means that there are a pair of ratchet setups, but not being a ratchet expert, I opted for the generic "ratchet system" phrase. — Lomn 17:34, 18 June 2009 (UTC)

Ok. "Ratchet system" would be an accurate, if imprecise, description. Having different gearing for each direction would be trivial to achieve in the kind of setup I described. --Tango (talk) 17:56, 18 June 2009 (UTC)

Let the input shaft "jiggle" a Self-winding watch. This is probably what goes on in this watch winder. The output shaft is what turns any of the hands of the watch. Cuddlyable3 (talk) 00:32, 20 June 2009 (UTC)

Need additional scientific quotes

I asked my friend what he was doing and he said he was "just sitting around converting oxygen to carbon monoxide". I thought that was funny and I wanted to think of other quotes to answer him back but I can't think of any. --Reticuli88 (talk) 15:56, 18 June 2009 (UTC)

You shouldn't talk to your furnace. People will look at you weird. 65.121.141.34 (talk) 16:12, 18 June 2009 (UTC)

For your information humans don't breathe out Carbon Monoxide, which is in fact poisonous. We breathe out Carbon Dioxide. See Breathing. Rkr1991 (talk) 16:22, 18 June 2009 (UTC)

Tell him that you're doing your part to increase entropy. Tempshill (talk) 19:42, 18 June 2009 (UTC)

How about these: "I'm just sitting here converting glucose to glycogen" "I'm just sitting around converting glucose to ATP" and if you are going to be drinking "I'm going to put my hardest working enzymes to good use" (alcohol dehydrogenase and aldehyde dehydrogenase "Running around converting glucose to carbon dioxide" --Reticuli88 (talk) 19:46, 18 June 2009 (UTC)

"I'm just sitting here keeping my synapses from weakeining."68.208.122.33 (talk) 21:28, 18 June 2009 (UTC)

There are thousands of things you could say, but one will sum them all up: "Maintaining homeostasis". --Mark PEA (talk) 21:58, 18 June 2009 (UTC)

I am currently resting between hydrous oxide downloads. Cuddlyable3 (talk) 00:19, 20 June 2009 (UTC)

Tell him not to be such an oxygen thief and do something usefullChromagnum (talk) 13:45, 20 June 2009 (UTC)

Fan Displacement

Does anyone have any figures for the average displacement of a desk fan (preferably around 40 cm in diameter), or alternatively, any figures for the revolutions per minute and depth of such a fan, so I can work it out myself? Thanks. --80.229.152.246 (talk) 16:07, 18 June 2009 (UTC)

Desk fans at 40 cm (15-16 inches) are rather rare. 12-13 inches are more common. Size is not necessarily in direct relation to efficiency. The math is rather complex. 68.208.122.33 (talk) 19:07, 18 June 2009 (UTC)

Examples of Thermodynamic Laws

Please give me some practical examples of each of the Thermodynamic Laws: Zeroth, First, Second and Third. I read the Wiki article but having problems on how I would apply it. Thanks! --Reticuli88 (talk) 18:45, 18 June 2009 (UTC)

• The zeroth can be roughly summarized as "if a=b and b=c, then a=c". As a result, we can have meaningful conversations about temperature and energy, since we can discuss common points of reference. Alternately, as Max Planck said, we can construct a thermometer.
• The first law notes that you cannot create or destroy energy, ruling out perpetual motion generators. Rather, energy is transformed.
• The second law notes that energy transformations are inefficient. Over time, the usable energy of a system is lost as waste heat. This rules out remaining perpetual motion machines.
• The third law defines absolute zero as a reference point, but notes that you never actually reach it.

Depending on how much you've read, I'll note that we've got an overview article of the laws of thermodynamics as well as individual articles on each law. However, you may also need to clarify what you don't understand and what sort of applications you're looking for. — Lomn 19:01, 18 June 2009 (UTC)

Let's have a shot at some examples:

• Zeroth law: Take three bits of metal called A,B and C that are at different temperatures. Put A,B and C together until the temperature of A is the same as B - and B is the same temperature as C. I don't think anyone would be surprised to find that A and C are at the same temperature as each other. The Zeroth' law is really just elementary math...it almost doesn't need to be stated. It's so "obvious" that it wasn't really named/stated until about 100 years after the first/second/third laws.
• First law: A refrigerator makes your food colder - it's taking energy out of the food. But the first law says that we can't destroy that energy - it's got to go someplace - so at the back of your fridge - you'll see some exposed metal pipes. These are HOT! The reason being that they are where the energy from your warm food went to as it was cooled down.
• Second law: There is no such thing as a 100% efficient machine - there's always some kind of lossage when you convert energy from one place to another. That's why you have to put electrical energy INTO your refrigerator in order for it to move energy OUT from the food. Some people wonder why you can't use the energy that you take out of the food to run the refrigerator...well, the second law is the problem. The result is even more waste heat coming out of those pipes at the back.
• Third law: Heat energy moves from hot things into cold things...not the other way around. The only way for your refrigerator to make your food colder is to use a coolant that's even colder than the food. However, to get things to absolute zero (where there is ZERO heat energy left) you'd have to get the very last bit of energy out by putting something even colder than absolute zero next to it. But you can't have less than zero heat energy - so there is no way to get to zero.

I've heard it said that the four laws can be summarized as the following depressing look at life:

• First law: You can't win.
• Second law: You can't even break even - except when you have nothing left to lose.
• Third law: There's always something else to lose.
• Zeroth law: You can't even leave the game.

That's a bit of a stretch - but it's memorable!

SteveBaker (talk) 00:55, 19 June 2009 (UTC)

Another version of this (though lacking the zeroth law) is:

1. You can't win, you can only break even.

2. You can only break even at absolute zero.

3. You can't reach absolute zero.

AndrewWTaylor (talk) 17:23, 19 June 2009 (UTC)

why is carbamic acid unstable?

Is it because the OH protonates the NH2 group, making it NH3+COO-, that decomposes into ammonia and carbon dioxide? What is the exact mechanism of decomposition, electron transfer, etc. and how fast and exergonic is the reaction? If there was an alkyl group on the nitrogen (making it a secondary or tertiary amide), would decomposition still occur? John Riemann Soong (talk) 19:53, 18 June 2009 (UTC)

As we discussed in the quesiton about carbamic acid a few months ago, decarboxylation of N-alkyl carbamate is fairly rapid., and is part of the removal of amine protecting groups like t-BOC, Cbz, and Fmoc. I don't remember at what point/rate in actually performing the various methods the CO2 is released, but note that they cover the range of pH, being cleaved under strongly acidic, neutral, and basic conditions respectively. An alternate mechanism could be first protonating the N and then carboxyl collapse/fragmentation to give O=C=OH⁺ (BOC cleavage with neat TFA is often complete within a few minutes). The carbamate page mentions some equilibrium-constant information about carboxylation of amine (i.e., the reverse of the mechanism you propose), but doesn't mention pH effect. Interestingly, solid phase peptide synthesis notes "Fmoc deprotection is usually slow because the anionic nitrogen produced at the end is not a particularly favorable product, although the whole process is thermodynamically driven by the evolution of carbon dioxide." The carboxylate form does exist at least long enough to trap it if you're careful:

RNH-C(=O)-OTBS + TBAF + BnBr → RNH-C(=O)-OBn

and TBAF is usually considered strongly basic, so the fragmentation might be most efficient not under such conditions. DMacks (talk) 21:39, 18 June 2009 (UTC)

Solar radiation

At what distance is the radiance of the Sun still blinding enough to obscure other stars or planets? Is there anything to relate the brilliance of a star to the vastness of the space it is in? (please, if there is no answer, that is good an answer as any) ~ R.T.G 23:57, 18 June 2009 (UTC)

On Earth we can't see stars during the day because the Sun's light gets scattered by the atmosphere. Without an atmosphere, even if you were really close to the Sun, say on Mercury, you would be able to see stars during the day as long as the Sun (or anything lit by the Sun) wasn't in your field of view. So, if you look straight up so you can't see the ground and shield the sun with something then, if you give your eyes time to adjust, you'll be able to see stars (admittedly, you'll be burnt to a crisp, but let's not worry about that!). If you want to be able to see stars while the Sun is in your field of view you have to be quite far away. I'm not sure how far... About 20 times further away from the Sun than Pluto would definitely be far enough, since the Sun there would be about as bright as a full moon here, and you can see stars during a full moon. So it is something less than that, but I'm not sure how much less (it could be a lot less, you may be able to see stars during the day from some planets in the solar system, I'm not sure). Is any of that helpful? I'm not sure I understood the question, so that's my best attempt at answering what I think you mean. If I've misunderstood you, please clarify! --Tango (talk) 00:18, 19 June 2009 (UTC)

Did Armstrong or the others try this on the moon? 65.121.141.34 (talk) 13:10, 19 June 2009 (UTC)

The lunar surface itself is brightly enough lit by sunlight that it is very hard to see stars from the surface of the Moon. There are people who think the lunar landings were faked and one of the bits of "evidence" they cite is that photos taken from the Moon don't show stars. But see item 4 in this section of the article. --Anonymous, 18:45 UTC, June 19, 2009.

Indeed. As I said, you have to make sure there is nothing lit by the sun in your field of view. All the photos taken include large amounts of lunar surface, so it isn't at all surprising there are no stars. Even if they pointed the camera straight up they would need a long exposure to pick up stars, just as you do at night on Earth. --Tango (talk) 21:10, 19 June 2009 (UTC)

20 times farther than Pluto? NASA says that from Pluto, the Sun just looks like a bright star. (It's a kids' page, but, still, a NASA page which I assume is accurate.) Tempshill (talk) 03:44, 19 June 2009 (UTC)

It's angular diameter is very small (so it would look like a point of light), but it is still brighter than a full moon. Apparent magnitude says the Sun is 449,000 times brighter than a full moon. That means for the Sun to appear the same brightness as a full moon you need to be ${\sqrt {449000}}$ times further away. That's 670AU, or just under 20 times more than Pluto's semi-major axis. --Tango (talk) 16:05, 19 June 2009 (UTC)

It's interesting to think about: at Pluto's distance, the Sun appears no bigger than Venus does to us, yet it's still 100 times brighter than the full moon. --Bowlhover (talk) 00:51, 20 June 2009 (UTC)

Actually, it's nearly 400 times brighter. I'd never really thought about it before doing that calculation, it really is an interesting fact. --Tango (talk) 01:17, 20 June 2009 (UTC)

In a total eclipse, you can see stars pretty close to the edge of the sun. That's how Sir Arthur Eddington measured how much the light from a star is bent by the sun's gravity - and thereby was the first to verify Einstein's theory of relativity. In normal daylight conditions, it's impossible to see any stars with the naked eye.SteveBaker (talk) 00:31, 19 June 2009 (UTC)

Impossible, you say? As for the OP's second question, there's the inverse square law: brightness drops off as the square of the distance. A twofold increase in distance corresponds to a fourfold decrease in brightness, for example. --Bowlhover (talk) 03:50, 19 June 2009 (UTC)

Well, technically - you can see Sirius from the top of a tall mountain at just the right time of day and year IF the sky is perfectly clear...but that's an awful stretch - and Sirius is the only star that's anywhere close to being that bright. However, re-reading RTG's question, we're also being asked about planets - and there is no doubt you can see Venus in daylight around dawn or dusk...even when it's pretty close to the sun. SteveBaker (talk) 04:22, 19 June 2009 (UTC)

You can see Venus in full daylight without needing to be at a high elevation, when it's at an angle far enough from the Sun, i.e. near elongation. I've done it. Of course, when it's in such a position, it's not the Sun that's "competing" for your eyes' attention, but only the sky. --Anonymous, 18:51 UTC, June 19, 2009.

I am supposing, so, that even as far as Mars or Jupiter our eyes would be much more able for looking directly at the Sun (correct me if that is wrong!) Thanks. 11:22, 19 June 2009 (UTC)

More able, certainly, but I expect it would still blind you if you did it for too long. Jupiter is only 5 times further away from the Sun than Earth, so the Sun would be 25 times dimmer. That sounds like a lot, but the eye actually works on a logarithmic scale, so really it's just a difference in magnitude of 3.5, which isn't much when you consider than the magnitude of the Sun from Earth is nearly -27. You can look directly at the Sun from Earth, as long as you don't do it for long (I don't recommend you try it, though, because I don't know how long "too long" is - a second would probably be enough to cause at least temporary damage). --Tango (talk) 16:13, 19 June 2009 (UTC)

The statement is actually wrong: it's a fact that the brightness per unit area of a light source remains constant as you move farther away from it -- only its area changes. That means that you wouldn't be able to look at the Sun safely until you are so far away that it appears as a point which the eye can't fully resolve. And that's far beyond the orbit of Pluto. From Pluto, the Sun would be a very small circle, but each point on its surface would look just as bright as it does from Earth. Looie496 (talk) 23:55, 19 June 2009 (UTC)

The angular size of the sun seen from Earth is about 32'. Block that disk and you are left with the corona. In visible light the corona seems insignificant outside twice the sun's radius. That implies that if your view of the sun is blocked by a disk of twice its angular size as seen from wherever you are, and there is no intervening atmosphere, then the sun does not affect star viewing at all. Cuddlyable3 (talk) 00:08, 20 June 2009 (UTC)

Is brightness per unit area the sole consideration? It seems that it should be a consideration, since it determines the amount of light hitting a given part of the retina, but is there no harm done by having a large part of the retina exposed to a level of light that isn't quite enough to harm any part of it individually? (If that made any sense.) --Tango (talk) 00:12, 20 June 2009 (UTC)

Well, if you move your eyes around, the larger the bright area, the more time a given part of your retina is likely to be exposed to it. I didn't mean to imply that size doesn't matter at all. As far as I know there isn't a harmful "total exposed area" effect though, unless you are so close that the sun heats the interior of your eye appreciably. Looie496 (talk) 02:59, 20 June 2009 (UTC)

Okay, now I am thinking that at 100 times the brightness of the moon in the Pluto region, the Sun would still be quite blinding (as regards trying to pick out stars etc.) and also that it is something that is not often calculated. ~ R.T.G 15:46, 21 June 2009 (UTC)

Yes, although it would be so small that it would be very easy to block it out so you could see stars very close to it if you wanted to (as long as there wasn't any illuminated ground in you field of view, as mentioned above). --Tango (talk) 16:28, 21 June 2009 (UTC)

As long as the disc of the Sun can be resolved by the human eye (possible down to about 1 arc minute, corresponding to a distance of about 30 AU), the brightness per unit area stays the same. If you travel farther away, the spot on the retina doesn't become smaller (see Airy disc), and it is roughly the size of 1 cell of the retina. If you multiply the distance at which you can no longer resolve the Sun's disc by the square root of the ratio of the Sun's and the full Moon's apparent brightness (about 384*10³), you get the distance at which the Sun looks as bright as one "pixel" of the full Moon (about 19*10³ AU). Icek (talk) 23:26, 22 June 2009 (UTC)

I can almost smell the cookies now but for me that says 19 multiplied by 1000 (* = computer multiply sign and 10³ = 1000, but I suspect you are saying "Somewhere in the Delta Quadrant"). ~ R.T.G 00:09, 23 June 2009 (UTC)

Writing "19,000" would imply more precision than I want to imply ;-) -Icek (talk) 11:12, 23 June 2009 (UTC)

The square root of 384e3 is 62e1, not 19e3. —Tamfang (talk) 17:48, 26 June 2009 (UTC)

The distance at which the sun cannot be resolved by the eye is 30 AU, not 1 AU ;-) Icek (talk) 07:24, 29 June 2009 (UTC)

Now I see how I didn't read carefully enough. —Tamfang (talk) 15:19, 1 July 2009 (UTC)

June 19

Coefficient of thermal expansion...

Those who are following this list may have spotted occasional references to my current pet project - refurbishing (well, throwing away and rebuilding from scratch) my home-made computer-driven milling machine (essentially, a robotic 2 horsepower router).

I'm thinking about the calibration of the machine. I'm using three precise stepper motors to rotate threaded steel rods that move the cutter up and down, left and right and in and out. The thread on the rod has a pitch of 16 turns per inch - and the stepper motor can move by just 1/200th of a revolution at a time. So, I have a resolution at around 1/3200'th of an inch! (Well, it's not really that good because of backlash etc...but it's not bad).

The problem is that the steel is going to expand and contract with temperature. So I'd need to calibrate the thing every time I turned it on. The drive system has limit switches - so I can move all the way down/left/in until the limit switches all trip - then move up/right/out until the other limit switches trip - and I'll know how many steps there are between the two limit switches.

But the limit switches are mounted onto the MDF (Medium-density fibreboard) frame - which (I'm hoping) doesn't expand and contract anywhere near as much as steel...but is that really true? Our article says: "Subject to significant shrinkage in low humidity environments."

So - to cut a long story short:

• What's the coefficient of thermal expansion of MDF?
• What's the coefficient of humidity-related expansion of MDF?
• Is it really less than steel?

SteveBaker (talk) 12:23, 19 June 2009 (UTC)

Steve (I assume)

Carbon steel is 10.8, other steels, depending on composition, range from 11.0 to 13.00 according to our own article on co-efficients. "The thermal conductivity of MDF varies slightly with thickness with the usual range being 0.05-0.08 kcal/mh°C (0.12 - 0.15 W/m°K). Like natural timber, MDF has a low thermal capacity. Within the normal range of temperature variation, MDF is dimensionally stable" according to this trade datasheet.

Humidity seems to be more of an issue, as 30% humidity at 20C can result in 5% moisture content, rising to 12% at 85% humidity. Moisture causes changes in length about 0.03 - 0.06% for every 1% change in moisture content, and by 0.3 - 0.5% in thickness. If your frame is 2 inches wide, this might come to 1/100th of an inch, which is substantial if you are working to 1/3200th accuracy. - KoolerStill (talk) 08:01, 19 June 2009 (UTC)

(Sorry - I forgot to sign...and for some reason sinebot took a vacation.) The longest distance over which expansion would occur is about a meter. The operating volume of the robot is 1m x 0.5m x 0.25m. So with a range moisture content from 0% to maybe 30%, I might see 30x0.06=2% !! Wow. That is a lot! I hadn't planned to paint the MDF - but now I might...just to control the uptake of water in it! Over (say) a 30 degC temperature range, the steel is going to expand by 30x11=330 parts per million..which is only a third of a millimeter over the longest dimension. So that gets me thinking...if MDF doesn't change size with temperature - and we know that steel doesn't change size with humidity - I wonder if I can have the robot somehow figure out which dimensions are changing. Because the distance between my two limit switches is determined by the moisture content of the MDF and the number of stepper motor steps it takes to move between them is determined by the temperature of the steel...tricky. SteveBaker (talk) 12:23, 19 June 2009 (UTC)

Ah! I think I have it figured out. If I change the design a bit and mount one pair of limit switches on an aluminium bar - then I can count the number of steps to span that pair of switches (which will be independent of humidity) and I should be able to use the difference in thermal expansion rates of aluminium and steel to calculate the temperature and correct for it. Aluminium expands about twice as much as steel - so I'd get maybe a third of a millimeter difference over a 30 degreeC temperature range - which is around 30 steps of my motor - so this would allow me to measure the temperature accurate to about a degree (is it a robotic milling machine or is it an exceedingly silly thermometer?!) Then I can count the number of steps it takes to get between the limit switches in the other axis (where the limit switches are on MDF) - correct for the expansion of the steel and then I'll know how much the MDF has changed size by and I can figure out how all of the dimensions of the machine have changed and correct for that too. That way, I don't have to care whether the MDF changes dimensions with temperature because I'm just measuring the size directly.

This is so much fun! (Well, if you're a serious geek it is...I imagine some people are yawning at this point.)

SteveBaker (talk) 13:02, 19 June 2009 (UTC)

Steve, your whole setup, including the workpiece and jigs, will expand and contract. If you intend to work with materials that all have the save coeffiecients of expansion as you machine, then you can simply ignore the problem. If not, then you need to consider the whole system, not just the machine itself. Perhaps you can invest in a single reference block of invar (or something) and calibrate against it each time. -71.0.188.190 (talk) 13:54, 19 June 2009 (UTC)

That's certainly true - and it's certainly something I've thought about. It's clear that nothing that's made of wood has precise or stable dimensions...and that's mostly what this machine is making. The previous incarnation did a wonderful job of doing wood carving. You could design a 3D pattern of leaves and flowers and stuff by processing a photograph using "shading-to-shape" techniques - then just hit the GO button and about an hour later - you'd have something that looked like someone had spent a month out of their lives carving it. The new version will be much better than that...I'm just exploring the envelope a little here...seeing if I can do yet better without it costing me much. SteveBaker (talk) 14:58, 19 June 2009 (UTC)

Why don't you measure the MDF fittings, buy a chunk of Hardened Steel, rework your fittings, and design or buy a small coolant pump (a tray underneath to recycle the used coolant, picture ;-) none goes down the drain) which will work quite well with only a fraction of the flow shown in that picture. You will have no end of improvement to your finish and be much kinder to your tools. Keep the workpiece cool rather than the machine (when it heats up too much it makes crap out of the piece anyway! How can you properly tighten your fittings to MDF without damaging it? You can't.) Use coolant, settle for a frictionless finish rather than all this messing about with burnable stuff! Coolant is dilutable, oils your stuff and recycles itself. It shouldn't cause any major overhead and is the standard method. ~ R.T.G 14:15, 19 June 2009 (UTC)

Why build a thermometer-machine? can't you put a simple real thermometer/temperature sensor into it? reading that will take less calculation in your already very_tight_on_memory controller chip than having to calculate temperature from relative expansion measurements. It would save having a set-up routine to do the measuring. How are the bars being fixed to allow for this amount of movement without stress or shearing? - KoolerStill (talk) 14:53, 19 June 2009 (UTC)

I don't think you understand what I'm doing. This is a hand-made machine I keep in my garage for making small (mostly wooden) things - with the new setup, I'm hoping to be able to mill copper circuit boards and drill holes for components - maybe mill a occasional aluminium part for a classic car restoration. I can't have pumps squirting stuff all over the place! If the workpiece gets too hot while I'm milling it - I'll just adjust the software to move the cutting head more slowly and shave off thinner layers - maybe pause for a while between tool passes to let everything cool off. Anyway - the machine has been doing great work for several years now - it's just that all of the cheap rollerskate bearings I used are getting worn and other parts are starting to fail and some of the wires have been flexed back and forth one time too many and broke...so I'm refurbishing it. And in the process using chunkier motors with more precision - new computer interfaces - that kind of thing. Since I have much more precision in the new machine than the old one - I thought I'd do a bit of 'due diligance' and check on the size of the thermal expansion error - and see if some simple steps (SIMPLE!) would reduce it. (Before, the errors due to thermal expansion would have been negligable compared to the backlash in the gear boxes, the lack of precision in the shaft-encoders, etc). My entire budget for building the machine is $200 ($120 of which went into the three big-assed stepper motors). I use the shaft encoders from an old USB mouse for figuring out how far the thing has rotated...that kind of thing. This is a "toy" compared to a professional CNC milling machine...but an amazingly useful toy...well worth a few weekends of work and $200. SteveBaker (talk) 14:52, 19 June 2009 (UTC)

Would like to say woodworking and PCB baords can't cause too much heat but can't say. Still be much better for the tools and the piece if you cool it when you are cutting metals. You could set up an open top gallon drum with a tube and a tap, chill in the fridge refill it occasionally, use a well aimed trickle, don't want to short the router either. The powerful gush in the CNC picture is probably the optimum but also the maximum. The coolant is reusable and dilute so isn't the most expensive in itself. Fair play but it seems you are agonising rocket science on what you could just make your own hardened steel fittings for. Good luck with it. ~ R.T.G 15:58, 19 June 2009 (UTC)

You should add it too Wikibooks and Wikiversity unless you are keeping the copies on it. Hardly a mean feat to put together and the motor is as powerful as your average 7-8 foot machine which lasts forever if you replace bits. I guess you are still working out bits for now or even selling the idea. ~ R.T.G 11:09, 20 June 2009 (UTC)

Without seeing SteveBaker's machine, I think using limit switches mounted on wood as a length standard is not a good idea. Not only is wood the least dimensionally stable material in the machine, the switches themselves presumably contain deformable springs. But if you dissect mice then you have light emitters and detectors with which to arrange optically sensed limits of a length standard. See this table of expansion coefficients. If you choose two readily available materials (steel and aluminium) and make an optical length standard based on each material, your software can calculate a temperature-independent length from the observed difference between the lengths of the materials. Cuddlyable3 (talk) 23:46, 19 June 2009 (UTC)

Err . . . you are talking about computer mice, aren't you, Cuddlyable3? I had a brief Girl Genius moment there. 87.81.230.195 (talk) 19:53, 20 June 2009 (UTC)

Why not measure the thermal and humidity related expansions directly with a Strain gauge or two? They are cheap and rather easy to use. Noodle snacks (talk) 12:05, 21 June 2009 (UTC)

remedy or something else?

On an episode of Emergency! before the opening credits, Roy was gargling warm salt water when Johnny and Chet came into the locker room. A minute later, Chet said his mother made him gargle with vinegar and soybean oil when he had a sore throat. Can those two fluids do the same thing salt water does when gargled?69.203.157.50 (talk) 04:25, 19 June 2009 (UTC)

Sore throat in common usage has a wider meaning than Acute pharyngitis. It can range from simple dry mucous tissue to something viral or bacterial among other things. Salt water helps with the hydrostatic pressure of the cell walls. Some bugs are sensitive to acids and the ph of many tissues in the human body is slightly acidic. This environment can be changed in favor of pathogens during an infection. Oil will coat the tissue and help against further drying. It may also keep a couple of the nasties from entering cells. So, depends on what you got if it has much of a positive effect, but at least it doesn't do harm. Unlike some OTC and prescription drugs that can seriously upset your system. (Patients who urge their doctors to prescribe antibiotics ignore the fact that those don't work on viruses.) 71.236.26.74 (talk) 07:42, 19 June 2009 (UTC)

Sustainability

Is it possible for humanity to live in a sustainable global society?

Or are there physical limiations on our global impact in that we will always need to consume more resources than we can replace? TheFutureAwaits (talk) 09:55, 19 June 2009 (UTC)

It's certainly possible - but almost certainly not at anything like the present population levels. If there were (say) ten million people in the world - we would have negligable impact - but at seven billion, I think it's quite clear that it's unsustainable - somewhere between those two numbers is the limit. SteveBaker (talk) 11:54, 19 June 2009 (UTC)

I disagree. It isn't at all clear whether or not the current population is sustainable. For example, if economies were all free markets with good protection of property rights, it is possible that we could support more people using fewer resources and with less environmental degradation. Wikiant (talk) 12:07, 19 June 2009 (UTC)

I'm sorry - but that's incredibly naive.

We can manage less environmental degradation...yes - for sure...but ZERO degradation? That would mean zero use of fossil fuels, zero increase in atmospheric carbon (in fact, a significant REDUCTION in the present levels) - zero mining of metals (100% recycling of every scrap of metal we use...that's insanely difficult!) - zero over-fishing of the oceans. Abandonment of non-recyclable plastics and other chemicals based on fossil oil.

Consider just one case: It's not high on the list of environmental panics - but did you know that the world only has 60 years worth of copper reserves left? Yep - we're going to run out of copper during the lives of some of our younger readers. Even if we go into recycling overdrive - there are no recycling processes that reclaim even 50% of any given resource. So we have 120 years of copper supplies - at most - assuming everyone treats this stuff like gold. Can we do better? Are we geared up to recycling every single scrap of copper we ever use? It's very difficult to do that. Sure - when a building is demolished, we can go in there and salvage all of the copper pipes and electrical wiring - and when a car is recycled, we can pull all of the copper wiring out of the alternator and starter motor. We could stop using copper in coins. But those tiny little copper contacts inside the battery compartment of your kid's toys? Will those get fully, 100% recycled? No - I don't think so. Also, many of the uses of copper require us to mix it with something else - eg to make Brass. You can't get the copper out of brass in order to recycle it without huge expenditures of energy (which - you'll recall - we are also trying to save!)...so gradually, no matter what we do, we cannot sustain the use of copper. We're probably going to run out of copper in industrial quantities within 100 years...the price will rise until it's the price of platinum or something - and we'll have to resort to mining less and less viable mines - resulting in us tearing up yet more of the landscape and consuming yet more energy. Meanwhile - what do we use for conducting electricity? Aluminium works - but it has lots of problems with corrosion in the air and it's not as flexible as copper - so no more bendy wires between your toaster and the wall socket! Silver makes great conductors - but it's kinda rare too.

And that's just one of a whole bunch of things we're running out of. Helium supplies are dwindling - all sorts of the more exotic metals used in modern electronics come from single-source mines that are unique to a particular place on the planet and have predicted lifetimes measured in decades - not centuries.

We are very, VERY far from living sustainably!

SteveBaker (talk) 13:25, 19 June 2009 (UTC)

Steve makes some great points and I'm really curious about the implications of them. I just don't see how even in theory we can live sustainability given our resource requirements and the difficulty in reusing and recycling these resources. Which also means unless we all move off-world (which is really, really impractical so can we not get into that?) it seems like we're doomed. Maybe to an agrarian culture? Maybe to not exist at all. Am I wrong? TheFutureAwaits (talk) 13:34, 19 June 2009 (UTC)

How is "moving off world" sustainable? All you have done is generalize all resources that we consume into one "planet resource", which you have casually discarded when it becomes easier to go somewhere else. Nimur (talk) 14:56, 19 June 2009 (UTC)

Before we get too much into the carrying capacity discussion I should clarify I'm wondering if it's possible for people to live a 100% sustainable lifestyle and then apply this on a broad scale. In my experience even the greatest green technologies always produce waste. On the other hand when we lived without technology we apparently had major ecological impacts (the death of native species in the Americas and Australia upon our early arrivals comes to mind) so I don't think abandoning technology would offer much of a solution.

So is it possible through the application of technology to live a 100% sustainable life and to apply that on a massive scale? Or are there simply limits to the degree we can minimize our impact? TheFutureAwaits (talk) 13:28, 19 June 2009 (UTC)

We could certainly revert to stone-age existances - but there is no way for seven billion people to live that way! We'd all need stone tools - will the supply of flinty rocks be enough? Are there enough natural caves for us to live in? Would the much lower density of wild animals be able to support such a population without dense farming with fertilizers and irrigation? No! Not by a million miles! For us to revert to a stone-age lifestyle - we'd need a stone-age population density - which means that we would have to wipe out 99.9% of humanity to get down to about 5 to 10 million people (that was the estimated world population in 10,000 BC when farming and such like started). If we did that - then we could live very close to sustainably in the lap of luxury with all of modern technology. Copper would run out in 60,000 years instead of 60 years. Global warming would cease to be a problem - we could all drive gas-guzzling Hummer's and the planet would hardly notice. The problem isn't our technology - it's our sheer numbers. SteveBaker (talk) 13:37, 19 June 2009 (UTC)

I disagree, it seems like population reduction (say everyone had one child for the next several generations) would only delay the inevitable. Sure copper might last 60,000 years instead of 60 but we're just moving the problem further downfield. It seems like eventually, no matter what we do, we're going to hit that wall. That's why I'd like some evidence that we won't; that there is some way to live sustainably at least until the sun runs out of hydrogen. TheFutureAwaits (talk) 13:48, 19 June 2009 (UTC)

Certainly there is no way to consume anything whatever and last forever. Even that stone-age existance with just 1 million people would result in them running out of stone to make tools - eventually. The rate of new rock formation just isn't high enough. We'd have to revert to being great apes with zero technology. That probably requires a genetic change - we'd have to de-evolve back to a more primitive form. But there is a massive difference between having 60 years worth of copper reserves and 60,000 years worth. In 60,000 years we could produce the technology to mine the asteroids - spread onto other planets - build robotic mining machines to dismantle entire planets in search of copper (or whatever). With the resources of the entire solar system and 60,000 years of technological advancement, I have no doubt whatever that we could survive until the extinction of the sun without reverting to pre-stone-age techniques. But there is no way we're going to find a way to mine the asteroids for copper in the next 60 years.

A chinese-style one-child-per-family approach would drop the population by a factor of two in every generation. If we could enforce that world-wide for 10 generations then switch to a two-child-per-family approach, we'd survive this. But that's not such a simple thing to do. Each new generation of workers - has to support two retired people each in addition to themselves...that's tough! But if we could do it - we might be OK. If we take copper as our benchmark (we could choose oil or atmospheric carbon instead) - then in the 60 years it takes the copper to run out - we may have halved our population - which means that we extended the life of the copper reserves by what? 15 years (assuming linear reduction in consumption)...but we can't halve the population again in the next 15 years without killing a lot of people! So the copper is gone...there is nothing we can do to stop that. For oil, I think we could reduce our population faster than we're running out - and for global warming, we could certainly avert disaster by halving our population over the next 60 years.

But applying such draconian measures is tough! China did it only because they were a totalitarian state with relatively compliant people. Could you imagine doing that in the USA?!! It's pretty inconcievable. Religious limitations on birth control would prevent large swaths of the roman catholic world from following that reduction rate. If some countries decided to make the supreme sacrifice and others didn't, you'd find that the sharply decreasing population of the "good guys" would result in them being overrun by the numerical superiority of the "bad guys". Governments would realise this - and we'd never get agreement to do this on a global scale.

Sadly, we're probably doomed.

SteveBaker (talk) 14:08, 19 June 2009 (UTC)

I strongly disagree that asteroid mining in the next 60 years is infeasible. 60 years is a long time, technologically speaking. Think where we were 60 years ago. We were still 8 years away from putting something into orbit. Now trips to LEO are strictly routine and there are serious plans to long-term occupation of the moon (as opposed to everyone assuming there would be such plans sometime next week but nobody actually planning it which has been going on for decades). Manned missions to Mars are intended for sometime in the next 30 years (although 40 might be more likely). Once you can get to Mars, getting to the asteroid belt isn't much harder (near-Earth asteroids are even easier and wholly robotic mining operations might be a better option as well). If the price of things like copper increases as your numbers suggest it will, asteroid mining will easily become economically viable, which means private business will get involved. Private businesses generally move much faster than national space programs since they don't have to contend with massive budget cuts. I wouldn't be at all surprised to see asteroid mining within the next 60 years (although I know better than to make definite predictions that far into the future where technology is concerned). --Tango (talk) 22:53, 20 June 2009 (UTC)

What is sustainability, anyway? How long does something have to be sustainable? After all, our energy comes exclusively from stellar fusion, so we really only need to be as sustainable as the sun.

All life is an energy-intensive process. I make the vague-and-handwavey claim that "higher forms of life are less efficient Carnot engines." In the most basic life-like things on Earth (say, a virus), the energy consumption is near zero until it is time to reproduce. The next steps up on the chain, the autotrophic prokaryotes, are pretty darn efficient - they absorb solar or geothermal energy, and use it to drive a simple chemical reaction and produce complex chemicals. The next few steps upward on the chain of "complex life" move into the realm of multicellular organisms, and the first heterotrophs emerge. These are much less energy-efficient organisms, in that they can't even generate their own energy, but must prey on some other thing. So, solar energy gets concentrated by algae, and then multicellular pondscum comes along and eats on the solar-fed algae. Pond scum, in my naive definition, is thus a "higher form of life," because it has a more complex energy pathway, and uses the excess energy to produce more complicated molecules (like enzymes for digesting the cellulose that they're eating).

As we continue to move up to higher organisms, we see that the total amount of energy for each organism is increasing; and the total efficiency of the food chain is decreasing. When we reach macroscopic organisms like frogs and monkeys, these guys are consuming just enormous quantities of energy compared to the single-celled organisms. So, you need to have billions of algaes so that the pondscum zooplankton can eat them, and millions of zooplankton to feed thousands of fish, and thousands of fish to feed one or two monkeys or frogs ("sustainably"). The root energy supply is still solar, but the ecosystem is getting more towering and the food chain is very sophisticated by this point.

After several million years, some creature decides that this is actually an inefficient way to extract energy from the environment, and begins to develop technology to circumvent the foodchain. They domesticate sheep and cows, and learn how to farm, to speed up the process of concentrating solar energy into usable food. They also develop fire, and waterwheels, and nuclear fission, and petroleum refining. This is a new step up on the hierarchy of "advanced forms of life" - they are able to extract a larger quantity of energy by collecting solar energy that has been stored somewhere for the last millions of years by trillions of algaes. Amazing! Biology has been circumvented with engineering! Now, more energy is extracted, but as always, it is a less-efficient way of using each individual joule of solar energy. This is sort of necessary, though, because thermodynamics teaches us that by physical law, every energy transfer process has some waste. (Maybe somebody who is familiar with thermodynamics can voice their interpretation of the Second Law?)

By extrapolation (making stuff up) it would seem that the most advanced forms of life will continue to consume more and more energy. SteveBaker's robot brains will start to take shape - a server room full of ten thousand blade servers will consume far more energy (in Joules) than the human that it is simulating. But, it will be able to use electricity, instead of trying to digest rice and cow; and it will be able to speed its simulation up or down or whatever. But it's using more energy, which is the only nonrenewable resource.

So, I propose Nader's Law Nimur's Law?: an optimal form of life is the one which matches its energy consumption to the rate of maximum return before the heat-death of the universe. In other words, the pitiful little algaes are extremely energy efficient but their form of life is so primitive and limited that they won't accomplish much. At best, they can hope to make lots of sugar and... sweeten the ocean or something. That's their maximal impact. We humans are successfully changing our atmosphere, launching manmade objects into deep space, building cities and art and pornography, setting fire to cities and art and pornography, raising sheep, developing advanced languages and computers, walking on the moon... so sure, we're not as energy-efficient as the algae, but we do a lot more cool stuff. We've managed to concentrate our resources into a form that is useful for these sorts of tasks - at the expense of some of those resources. Maybe our robot computer replacements will be even better at that sort of stuff with less waste (but I doubt it - they'll find needs for larger energy budgets, with the accompanying extra resource waste). It's entirely possible that some form of life higher or lower than us will actually be more effective, over the cosmological time-scales of our universe, to use energy more efficiently than us to accomplish the same things - but there is a ticking clock - if we don't use the energy up, entropy will dissipate it for us anyway. Nimur (talk) 15:22, 19 June 2009 (UTC)

When human load exceeds supply, something like a Malthusian catastrophe could result. Remember that we'd run out of natural resources if everyone in the world had an ecological footprint as large as that of say, an average American, in fact we'd need about 5 Earths' worth of resources. ~AH1^(TCU) 01:08, 22 June 2009 (UTC)

On Hawaii

When did the first settlers arrive in Hawaii? I'm not talking about americans, mind you, but the original people of hawaii?Drew Smith What I've done 10:46, 19 June 2009 (UTC)

According to ancient Hawaii, it was some time between the third and eighth centuries. Algebraist 10:50, 19 June 2009 (UTC)

Big Bang

Is there a formal name for the big bang theory? or is that all there is? 84.97.254.29 (talk) 10:55, 19 June 2009 (UTC)

It's formally called the Big Bang theory. An earlier name is l'hypothèse de l'atome primitif, if you want an alternative for some reason. Algebraist 10:59, 19 June 2009 (UTC)

Yeah - it's kinda sad. The guy who named it (Fred Hoyle) didn't believe in the theory and was being incredibly sarcastic about it in a radio interview - he pretty much thought up the name on the spot as a way to mock the people who believed in it! So the name of the theory that explains how the entire universe started doesn't get a fancy, grandiose name...but a joke. <sigh> SteveBaker (talk) 13:29, 19 June 2009 (UTC)

Hoyle did coin the name, but I don't think he meant it to be insulting, it was just meant to contrast with "steady state". The articles Fred Hoyle and Big Bang have a couple of sources backing this up. It's better than the earlier names "primeval atom" and "cosmic egg", which are just ridiculous. The problem with all of those names is that they emphasize the wrong thing, the singularity where the model breaks down instead of the well-behaved region where it makes predictions. "Big bang cosmology" is not about a big bang, it's about the evolution of an expanding universe. You might as well call general relativity "the theory of black holes". Of course, "general relativity" is a stupid name also. So is "quantum mechanics". Oh well. -- BenRG (talk) 16:27, 19 June 2009 (UTC)

Why are "general relativity" and "quantum mechanics" stupid names? A Quest For Knowledge (talk) 16:31, 19 June 2009 (UTC)

General relativity isn't a great name because it only makes sense in the historical context of it being a generalisation of special relativity. And, of course, special relativity only makes sense in the context of it being a special case of general relativity. It is something of a circular definition. The only part which has any meaning in itself is "relativity", which offers no suggestion of how it is different to Galilean relativity which had been around for several hundred years before Einstein came on the scene. "(General/Special) invariant speed of light theory" would be more descriptive, albeit it a little less catchy. I don't have any real problem with "quantum mechanics", though, although I would rather name theories by their hypotheses, not their uses. The theory has nothing to do with mechanics, that's just what it is used for. "Quantum energy theory" might be better. --Tango (talk) 16:41, 19 June 2009 (UTC)

I had a professor who said that the name "special relativity" was ironic, because the key point of the theory was that the speed of light *wasn't* relative, but was the same for everyone everywhere. If I remember correctly, Einstein didn"t like "relativity" either, and prefered the term "invariance theory". (Doesn't seem to be mentioned on Wikipedia - Google ("invariance theory" einstein) for references.) -- 75.42.235.29 (talk) 03:26, 20 June 2009 (UTC)

Yes, Einstein later in his life thought it ought to be called invariance theory (because he got sick of people missing the point that the invariances are more novel than the relativity), and on GR he later (following Vladimir Fock) wanted just to call it a "theory of gravitation" or something like that, more straightforward and less emphasis on the relativity. Quantum mechanics was so named to differentiate it from (old) quantum theory. --98.217.14.211 (talk) 18:42, 20 June 2009 (UTC)

Most physicists would probably say "big bang cosmology" rather than "the big bang theory". The latter sounds like a layperson's term (and now like a TV series). You could also call it "Friedmann cosmology" or "Friedmann-Robertson-Walker cosmology". That calls attention to the expansion instead of the singularity. The currently favored version of big bang cosmology is called the "Lambda-CDM concordance model". It's the simplest version of Friedmann cosmology that's consistent with the currently available data. You could also call it "Lambda-CDM cosmology". Lambda-CDM might give way in a few years to another model with a different name which would still be under the umbrella of big bang/Friedmann cosmology. None of these are very good names, but they're a bit more formal sounding. -- BenRG (talk) 16:27, 19 June 2009 (UTC)

Nudibranch (or something)

Hey guys, could some marine enthusiast help me identify this nudibranch subspecies? The picture is from Crete. If the relevant article is in need of a pic, I'll gladly post this one. Thanx! P.S. At least I think it's a nudibranch! PervyPirate (talk) 11:11, 19 June 2009 (UTC)

It's surely a sea slug of some slimy sort, but whether it's a nudibranch or a Cephalaspidea, or a Aglajidae, or a Sacoglossa, or even a Onchidiidae is not clear to me. This website http://www.nudipixel.net/ might help. If they have a forum you could ask there too. (I know the name sounds sketchy but it is a legit site on nudibranchs. It's SFW as long as your boss isn't a gastropod.) Sifaka ^talk 19:28, 20 June 2009 (UTC)

It's probably a polycladida flatworm, maybe yungia aurantiaca, which looks pretty similar,[7] but there's plenty to choose from. Mikenorton (talk) 20:35, 20 June 2009 (UTC)

To Sifaka: What a wonderful site this is! I think I'm gonna start making T-shirts with all those nudibranchs! Unfortunately, the genus I'm looking for is not there... Oh, and my boss kinda behaves like a gastropod, throwing ink at people and looking annoyed if somebody bothers him (Yes, we are both scuba instructors!)
To Mikenorton: YES!! That's exactly the one I've been looking for... I wish we had a relevant article for me to add that picture to.. I guess I'll have to create it myself then.. "Orange flatworm" it is!

Thanx a lot to both of you! PervyPirate (talk) 01:03, 21 June 2009 (UTC)

ADD and stimulants

Hi there. I notice most treatment for ADD/ADHD are amphetamine stimulants like Adderol and Ritalin. How are the actions of those drugs different than say giving someone with ADD 20 cups of coffee? How is one stimulant different than another? --70.167.58.6 (talk) 13:34, 19 June 2009 (UTC)

It has a few side-effects! I think that 20 cups of coffee contains something close to the lethal dose of caffeine for a human. It's LD50 is 150mg/kg of body weight...and a cup of coffee has about 150mg of the stuff - so if you drink one cup of coffee per kilogram of your body weight in a period of a few hours - you have a 50/50 chance of dropping dead. So a 20kg kid and 20 cups of coffee will likely die. A 50kg kid would do better - but it's hardly healthy! One assumes that these other stimulants have much better controlled side-effects. SteveBaker (talk) 13:48, 19 June 2009 (UTC)

I was using hyperbole. ;) I didn't really mean for someone to drink 20 cups. Aren't amphetamines highly addictive? (Valley of the Dolls, Judy Garland, and all that?) --70.167.58.6 (talk) 14:42, 19 June 2009 (UTC)

Really, Steve? How long do you think it would take for you to drink 70 cups of coffee? Quite a bit longer than the ~5 hour half-life of caffeine, I would expect. – ClockworkSoul 16:47, 19 June 2009 (UTC)

In laymen's terms, the neurobiology of ADHD can be simplified in a similar way that depression is simplified. With depression, low serotonin levels cause depressive symptoms, and most antidepressants (TCAs and SSRIs) increase these levels. For ADHD, low dopamine levels cause irritability, lack of focus and lack of pleasure (from tasks such as reading), and most ADHD treatments (amphetamine, methylphenidate) increase these dopamine levels. In reality neurobiology is far more complicated than that (and the "monoamine hypothesis" - which states that low serotonin causes depression - is pretty much obsolete now). --Mark PEA (talk) 18:39, 19 June 2009 (UTC)

Well, I think those statements are somewhat controversial, but the key point is that all stimulants are not created equal. The stimulants that work for ADHD are psychomotor stimulants, which affect the brain's dopamine system. Caffeine operates by a completely different mechanism. (Nicotine, on the other hand, might have some effect, since it partly acts as a psychomotor stimulant.) Looie496 (talk) 00:04, 20 June 2009 (UTC)

Stimulants used to treat ADHD raise the extracellular concentrations of the neurotransmitters dopamine and norepinephrine which causes an increase in neurotransmission. The therapeutic benefits are due to noradrenergic effects at the locus coeruleus and the prefrontal cortex and dopaminergic effects at the nucleus accumbens. Hit up the refs on the Main ADHD page in the management section to find some decent scientific papers on the subject. I suppose you can compare that to the pharmacological effects of caffeine. People with ADHD are more prone to using psychoactive substances which include caffeine. As for how stimulants are different there is info at ADHD management, (the article could use a little cleanup for clarity...) Sifaka ^talk 19:11, 20 June 2009 (UTC)

kineto-baric?? what is this?

Hi

Here are a couple of links to a phenomena called kineto baric effects. Could someone tell me what exactly this is, found a Nasa page on it and mention on a book so Its not something a internet crackpot just made up. Can anyone please tell me exactly what this is??

Kinetobaric effects, a new phenomenon Peschka, W. http://adsabs.harvard.edu/abs/1974DFVLR......603P

http://books.google.co.uk/books?id=zENRkvFO0SEC&pg=PA226&lpg=PA226&dq=kineto+baric&source=bl&ots=qxeQVo7ZB_&sig=SN0aR7fGi9hy1lvD4Puozpjr9bc&hl=en&ei=OJc7SsWhMOeMjAfoxpAg&sa=X&oi=book_result&ct=result&resnum=4

Thanks in advance

Rob —Preceding unsigned comment added by 79.67.246.16 (talk) 13:56, 19 June 2009 (UTC)

It looks like junk-science to me. Your first link doesn't suggest that NASA endorses it - only that it's in their database of science abstracts. This work dates back to the 1970's - if they had truly found a new kind of force - you'd bet that mainstream scientists would have been all over it by now. So your evidence boils down to a 35 year old paper in an obscure German publication - and a reference in a book that's full of crackpot theories. A google search on the term turns up lots of crackpot/free-energy web sites. It's junk. SteveBaker (talk) 14:40, 19 June 2009 (UTC)

I second the vote for junk science, with the caveat that it's equally likely that the abstract has been mangled by poor translation. If you can get your hands on the original, you may be able to get a better translation. Nimur (talk) 15:44, 19 June 2009 (UTC)

The original article is not necessarily junk science—it might just be wrong science, or incomplete science, or premature science. --98.217.14.211 (talk) 18:35, 20 June 2009 (UTC)

Ok thanks guys, just thought I would ask.

Rob —Preceding unsigned comment added by 79.67.246.16 (talk) 18:24, 19 June 2009 (UTC)

I couldn't access one of your links. I had a look around for the German text by W. Peschka [8] His report looks like any other "our experiment has shown this result and we don't have any clue as to why" kind of scratching our heads report. They were re-creating some setup originally done by R. Zinsser during WWII. The effect is described as generating "mechanical energy from an an anisotropic gravitational field" Peschka has a reasonable track record in research at the German Aerospace Center. There doesn't seem to have been much further study since 1974. A followup study in 2004 could not re-create the effect and assumes that the previous results were caused by thermal expansion or air movement [9] However Peschka's report seem to have been adopted by some fans of Fringe science. 68.208.122.33 (talk) 19:04, 20 June 2009 (UTC)

Black rope has musty mildew smell. How to clean?

How can one remove a musty mildewy smell from a colored rope? My first instinct is to dip it in bleach, but that would destroy the color. Are there any color safe ways to remove mildew? --Navstar (talk) 14:35, 19 June 2009 (UTC)

Vinegar would work as well as bleach, and smell better too. Use white vinegar diluted no more than 1:3 with warm water, and move the rope around vigorously to make sure it gets in between the twists. Rinse in plain water. Then dry it in the tumble dryer, as it is residual dampness that causes the growth of mold or mildew.- KoolerStill (talk) 15:48, 19 June 2009 (UTC)

Many things you could do to remove mildew from a rope could reduce its strength, as could the mildew itself. Unless it is just a decoration, how about starting with fresh rope and taking better care to store it is conditions not conducive to mildew? [10] gives some hints on cleaning and caring for rope, and says that bleach weakens it as does battery acid. No mention of vinegar. Here is a 1956 Popular Mechanics article on rope care [11]. Here is a book on rigging with a section on rope care: keep it clean and dry.[12] The sources suggest thay poly rope is not likely to mildew. Is your rope natural fiber? Edison (talk) 18:43, 19 June 2009 (UTC)

Some OR on mildewed poly rope: The fibers themselves are not likely to mildew, but that doesn't mean that stuff can't grow in between the twists. There are a number of products on the market that claim to be safe on fabric. (e.g.[13]) If it's just the smell you want to get rid of, go over to the nearest dive shop. They sell little packets to use on dive gear. I'd second opinions voiced above on not using the rope for anything critical and replacing it sounds like a great idea. 68.208.122.33 (talk) 19:28, 20 June 2009 (UTC)

Fishing in Ontario lake

Was fishing today. Saw clearly a pink, almost red fish swimming around. Fish was big - I would say more then 2kg (umm, relatively big). Looked like oversized aquarium fish(only because of the color). Put fish like bait in front of her - but then realized that predator could not wear such color. Asked two fisherman - both come up with idea that it could be carp fish. Why pinkish red? One said that it could be ill(was not looking like ill one at all) and another one joked that it is too much uranium around... Is there a spice that could look like that? Or it is totally weird fish? I'm really a newbie in fishing(caught my very first fish today, Largemouth bass:)) DeadlyPenguin (talk) 17:42, 19 June 2009 (UTC)

Carp, Goldfish, and Koi are all very closely related species. It's very possible that there can be colored variants in the wild, even with never-domesticated fish. (There was a recent story about a yellow lobster caught from the wild, where there are also blue and white variants.) By the way, carp are omnivores/scavengers, so they would have no problem eating dead fish. -- 128.104.112.114 (talk) 20:38, 19 June 2009 (UTC)

Definitly a carp. As IP said before, carp, goldfish, and koi are all closely related, with the common ancestor being carp. Obviously carp ancestors had to have the light colored pigmentation gene otherwise we would not have such vibrantly colored goldfish and koi today. Selective breeding has beautified, and mangled goldfish completely.Drew Smith What I've done 14:36, 20 June 2009 (UTC)

Might be Chinook salmon if carp doesn't fit your bill. [14] —Preceding unsigned comment added by 68.208.122.33 (talk) 19:37, 20 June 2009 (UTC)

Question on J.J. Sakurai's notation

I've just read through the first chapter of Sakurai's Modern Quantum Mechanics, and I've begun working through the problems. The second problem has totally baffled me with notation. Throughout the chapter the dot, $\cdot$ , is used for explicit multiplication, and the boldface dot, which I'm not sure how to produce with this LaTeX, is used for the inner product. In problem 2 (page 60) Sakurai states

Suppose a $2\times 2$ matrix $X$ … is written as
$X=a_{0}+\mathbf {\sigma \cdot a}$
where $a_{0}$ and $a_{1,2,3}$ are numbers.

where the sigma, dot, and 'a', are all boldface, and he asks

a. How are $a_{0}$ and $a_{k}$ ($k=1,2,3$) related to $\mathrm {tr} (X)$ and $\mathrm {tr} (\sigma _{k}\,X)$?
b. Obtain $a_{0}$ and $a_{k}$ in terms of the matrix elements $X_{ij}$.

Since $X$ is $2\times 2$, clearly $a_{0}=a_{0}I_{2}=a_{0}{\begin{pmatrix}1&0\\0&1\end{pmatrix}}$, right? He uses this implied notation in the chapter. But what is $\mathbf {\sigma \cdot a}$? Clearly $\mathbf {a}$ is a 3-component vector. It seems like $\mathbf {\sigma }$ is also. But, if they're both vectors, and the dot is the inner product, then

$X=(a_{0}+\mathbf {\sigma \cdot a} )I_{2}$

and the questions make no sense…to me, anyway.

One further piece of evidence is that in Problem 3 Sakurai refers to the "determinant of a $2\times 2$ matrix $\mathbf {\sigma \cdot a}$" as well as $\mathbf {\sigma \cdot {\hat {n}}}$ "when $\mathbf {\hat {n}}$ is in the positive $z$-direction".

So, $\mathbf {\sigma \cdot a}$ can be a $2\times 2$ matrix! But how? Even if the boldface dot were an outer product, that would make it a $3\times 3$ matrix, which, in some sense, is even worse of a description!

Does anyone see or know what I'm missing? Thanks! — gogobera (talk) 18:54, 19 June 2009 (UTC)

Does he use the notation σ elsewhere? It might refer to the Pauli matrices which are a triple of 2x2 matrices, so it makes sense to dot them with a vector and get a 2x2 matrix. Algebraist 19:02, 19 June 2009 (UTC)

hmm. He hasn't defined them, yet. On p. 23 he writes "…when we discuss the Pauli two-component formalism in Chapter 3". On the other hand, the book expects some introductory quantum experience. I'll go with your suggestion though, for now, and see what comes out of it. Thanks! — gogobera (talk) 19:09, 19 June 2009 (UTC)

Oh yeah, and I know this is a math question, but it being in a Quantum text, I thought someone here might've had experience with it. I'll cross-post, I guess, but only if necessary. — gogobera (talk) 19:05, 19 June 2009 (UTC)

Is there a list of notation at either the beginning or the end of the book? --Tango (talk) 21:06, 19 June 2009 (UTC)

The $\sigma \,$ are the Pauli matrices, as Algebraist sugested. That's why I don't like Sakurai too much. He doesn't explain things well enough. Dauto (talk) 05:11, 21 June 2009 (UTC)

June 20

Consistancy and Acceleration.

Apologies if this is in the wrong place. I'm still in training.

In many articles e.g. PCC streetcar, the unit of acceleration is given as mph/ps. In other articles, it's given as mphps (f'rinstance Washington Metro rolling stock).

What is meant is "miles per hour per second". So it seems to me that the correct unit would be mphps, without that extra slash(/), since that would be read as "miles per hour per per second".

Since there are over a hundred articles to be changed, it seems rather tedious to post the suggestion in each discussion page. Also, I'm not so sure that I'm correct (actually, I'm sure I am, but I have to maintain an appearance of humility), since it's possible that one use or the other is standard.

What do y'all think, should I be bold, or just let sleeping dogs lie. Bunthorne (talk) 02:30, 20 June 2009 (UTC)

Alternately, there's mph/s. Agreed that "per per second" is incorrect, so I recommend boldness (always worthwhile for obvious errors). — Lomn 02:49, 20 June 2009 (UTC)

I agree, mph/ps is wrong and mph/s is better then mphps. But where the unit occurs just once or twice in a text passage, I'd be inclined to forget abbreviating the seconds and just use "mph per second"; I think more people will easily understand that. --Anonymous, 03:21, June 20/09.

mph/ps is definitely incorrect. Fortunately, that senseless notation only exists in 3 articles. As far as what to change it to, I think mph/s is clearer than mphps, but mphps is used in twice as many articles as mph/s (14 vs. 7), so at first glance it looks like most editors prefer mphps. Red Act (talk) 03:26, 20 June 2009 (UTC)

mph/ps would be "miles per hour per picosecond". That's some serious acceleration.... --Trovatore (talk) 03:52, 20 June 2009 (UTC)

Not if the number before "mph/ps" were 0.000000000000000000000000001, for example. That might apply to the acceleration of a male smail when he sees his girlfriend in all her alluring, sultry seductiveness. -- JackofOz (talk) 07:16, 20 June 2009 (UTC)

Snails are hermaphrodites. (There's a Perry Bible Fellowship cartoon about snail sexism.) As for the units of acceleration, why not use feet per second per second? That way you don't have the confusion of two different time units in one compound unit. AlexTiefling (talk) 11:43, 20 June 2009 (UTC)

Because speeds of cars are usually measured in mph and they generally accelerate for periods on the order of a few seconds, so the odd mix of units is actually the most convenient. You can, for example, easily convert "0 to 60 in X seconds" (a common way of expressing acceleration off the line) to an average acceleration in mph/s. --Tango (talk) 16:56, 20 June 2009 (UTC)

I believe it is correct Wikipedia style to provide the customary unit (which should be mph/s in this context) followed by the appropriate metric unit in brackets (ms^-2) ? So I think you're free to go with mph/s as your customary unit - provided you also give a more "normal" unit for people who are not familiar with streetcars or who don't use "miles" as their natural unit. Think of your confusion if you were to be given the acceleration of an unladen european swallow in teaspoons per acre per square fortnight...you'd be quite justified in demanding to have the number in meters per second in brackets afterwards. SteveBaker (talk) 15:19, 21 June 2009 (UTC)

Notational point: the metric unit you speak of is not inverse square milliseconds. If you must write m/s² without using a slash, you need a space or a centered dot between the m and the s.

But is m/s² the appropriate metric unit anyway? In metric countries vehicular speeds are normally written in km/h, not m/s. This suggests that km/h per second would be more commonly used then m/s² for accelerations, but I don't know if that's true. And if this unit is commonly used, is it commonly symbolized as km/h/s (not proper SI style) or kph/s (also not proper SI style) or km/h s or km/h·s or km/s·h or what? I don't know; I haven't done enough reading of European materials where it might be used.

--Anonymous, 19:18 UTC, June 21, 2009.

What is an SI unit?

I've split out this subthread into a separate subsection. --Anonymous, 22:12 UTC, June 22, 2009.

Yeah, I think when Steve said "metric" he meant "SI". --Tango (talk) 20:18, 21 June 2009 (UTC)

The hour is a non-SI unit, but is accepted for use with the SI and, as I said, vehicular speeds are commonly measured in km/h. --Anon, 21:59 UTC, June 21, 2009.

The SI unit for acceleration is m/s². Are you disputing that? --Tango (talk) 22:08, 21 June 2009 (UTC)

Only the first word. SI includes many units for acceleration: m/s² is one, km/s² is another, and so on. Additional units are accepted for use with the SI. --Anon, 07:52 UTC, June 22, 2009.

I've never heard of units with prefixes being called "an SI unit" they are just "the SI unit with a prefix". --Tango (talk) 14:44, 22 June 2009 (UTC)

I can't help what you've heard. The SI standard defines what units are part of the SI, and that includes the prefixed ones. (The link is to the US edition, but other editions will show the same thing.) By the way, that also includes the four prefixes in between milli- and kilo-; some people have the false idea that those are not part of SI. It is true that certain units are designated as SI base units -- the meter is the base unit of length and the second is the base unit of time -- but that's just a way of stating their definitions, and provides a convention for the construction of named derived units like newtons and watts. There is no base unit for acceleration, as it is derivable from units for length and time. --Anonymous, 22:12 UTC, June 22, 2009.

Which wikiproject would best encompass an Electrical Pollution article.

Hey. I'm starting work on an electrical pollution article on my userpages. How this article doesn't already exist I don't know (Probably because of the electric companies that still try to claim that it's "false science")...

Anyways, I don't feel it's something I can do alone, and want to find some editors that know the subject a bit to help construct it with me. Which wikiproject would best cover this article? Earth Sciences? Natural Sciences? Physics? Energy? Or perhaps just the ol' Wikipedia:Editor_assistance/Requests page would be best for me. What is recommended? -- Floydian ^τ _γ 03:57, 20 June 2009 (UTC)

The content on your user-page article appears to be a less-than-accurate effort to describe Electromagnetic interference. Since we already have this article, any relevant information should be added there. "Electric pollution" is not a term in common use in radio-science or utility electric power. Wikipedia has a strong policy against coining neologisms, described here. If you feel that there are sufficient third-party reliable sources that use such terms as "electric pollution" you should find those sources. The burden lies with you, the editor, to back up such claims with reliable sources. The image you have posted, File:ElectricSineWave.jpg, does not appear to be out of the ordinary - in fact, the electric utilities document the frequency harmonics and phase/amplitude variations, and if you look closely at their technical information you will find that these variations are within the specifications they contractually agree to deliver. It is more likely that those "noise" sources, which you are viewing in the time domain, are due to load variations, not due to electromagnetic interference from cell phones or radio towers. If you don't believe me, consider looking at the frequency spectrum of electric power - there is not a lot of man-made radio activity in there, and when there is, you can clearly see it. Nimur (talk) 06:21, 20 June 2009 (UTC)

Isn't illness due to "electrical pollution" a myth? What's recommended for you is a sixth form/high school physics course......Alaphent (talk) 08:56, 20 June 2009 (UTC)

Please take your negativity and childish insults elsewhere. There are plenty of documents the back it and its effect on humans and animals up. This page lists plenty of research into it. The content on my userpage is a few days of piecing together some small things. It is far from complete and is not being placed here for peer review. I will look into the article you linked and comment later.

EDIT: EMI is a cause. Electrical pollution is an effect. - Floydian ^τ _γ 09:06, 20 June 2009 (UTC)

Maaate, I fail to see where the "childish insult" in Alaphent's contribution there. As for the documents that back it up, there are documents that back anything up - and for that matter there are documents that will refute anything. Just because some "Alternative Medicine Scientists" think that it is a valid effect, it does not neccessarily mean that it is.

Anything you place on wikipedia will be criticised and reviewed, sometimes unjustifiably. Maybe it is slightly arrogant to assume that you can write an article perfectly by yourself? Perhaps consider creating the article and seeing how it goes from there? But here isn't the place for that discussion.Heinzcreamofchickensoup (talk) 09:38, 20 June 2009 (UTC)

After looking at your talk page and contributions, it seems that you have a "thing" about adding controversial unsourced "anti-establishment" information. Governments witholding information about drugs?Heinzcreamofchickensoup (talk) 09:48, 20 June 2009 (UTC)

(outdent). Wikipedia should also have articles on common conspiracy theories and junk science, as long as they are notable, so i see no problem with the concept so long as the article is balanced. There must be tonnes of credible research into this, even if it only debunks the idea. WP:SKEPTIC, WP:Pseudoscience, WP:Environment and WP:Energy all seem appropriate if the article is ever created. It is usually easiest to create the article and worry about projects after, although it is a good idea to get the projects opinions in this case, as we see even a refdesk question causes responses unpleasantly close to incivility and a determination to not answer the questionYobMod 10:52, 20 June 2009 (UTC)

Floydian, please do feel welcome to contribute to Wikipedia. To the other editors, please avoid personal attacks. That being said, a few important issues arise:

• Floydian - if your work is not to be subject to peer review, why are you asking for help? I'm a contributor to the WikiProjects you mentioned - Science, Energy, Physics, ... didn't you come here asking for input or help from these projects? You might not want to completely slough off other editors' suggestions, or they will be less inclined to help.
• Your claim that "EMI is a cause. Electrical pollution is an effect" does not seem to make sense, because EMI is an effect of electric power coupling into places it shouldn't be. It's a symptom of a broad class of phenomena. If you disagree with this concept, you should do the following:
  • Read electromagnetic interference very thoroughly
  • Read about electromagnetism in general
  • Read about electricity distribution
• The claims that your article makes, and your incorrect use of technical language (for example, emf is neither the electric field nor the magnetic field) suggests that you are new to these terms. White noise is not RF interference. Your image of clean and dirty power conveys almost no scientific information, because it is an amplitude-versus-time plot (how about showing us a power spectrum?) Do you know the difference? Do you really feel comfortable to make strong claims about an area you know so very little about?
• If you do, then perhaps you should publish your original research elsewhere, because Wikipedia is not the place to publish new ideas. You must find somebody else's published research and cite it. We will subject that research to fierce debate about whether it is reliable. Your two sources do not appear to be very reliable. Hint: any web page that starts off with an incorrect fact is likely to rank low on the subjective scale of reliability.
• If you still believe that "electric pollution" belongs somewhere in Wikipedia, by all means be bold and add it in.

I can tell you honestly that this article will be edited severely, and probably deleted, because it fails several key criteria (most importantly, the lack of reliable sources; and secondly, the coining/definition of a new term which is not in common use in scientific literature). By submitting your work to Wikipedia, it will be subject to merciless editing, including deletion. If you do not like this idea, then Wikipedia is not the place to publish your ideas. That's why we have our warning on edit-pages: If you don't want your material to be edited mercilessly or redistributed for profit by others, do not submit it. Nimur (talk) 17:11, 20 June 2009 (UTC)

Childish insult: "What's recommended for you is a sixth form/high school physics course". First of all I want to ask which scientists are correct. The ones that are hired, and payed by the companies that want to sell the stuff to come up with "conclusive" research on the topic? Or the ones that do it on their own accord? How about the university of wisconsin, which has been studying the effects of this for 25 years? What defines scientific literature in this case? Who is more credible? The electric company, or the independent not-for-profit study? I can provide well over 30 published and accepted studies that go far more in depth into this subject then a bunch of average people who just feel like slapping a conspiracy theory label on anything that is new to them. I wonder how many people told Darwin that he was a conspiracy theorist?

I am looking for advice on where to ask for help. I'm not asking for people to criticize the 3 sentences that I've written so far. I'm looking for people that actually can back up their claims that this is not real or science.

My research is not original. Everybody that has commented here has made claims without any sort of backup. I'm not sure what you are talking about with my incorrect language use because the article really isn't written and once again isn't being submitted here for review in its current state.

EMI is a cause and Electrical pollution is the effect. This is the case because EMI is a term to envelop any sort of undesired electrical signals, and electrical pollution is the effect that these signals have on our cells and our bodies. —Preceding unsigned comment added by Floydian (talk • contribs) 17:33, 20 June 2009 (UTC)

If you are not going to help me (Or those of you who aren't), then shut up and don't reply - It isn't neccessary. I did not post this to be called arrogant or anti-establishment just because I don't believe everything that I am told, especially when Pfiezer is sponsoring it. -- Floydian ^τ _γ 17:29, 20 June 2009 (UTC)

I tend to believe scientists who follow proper methodologies, irrespective of who funds them. Post your 30 sources, and I'll take a look at them, with an open mind. My professional career is built on doing lots and lots of reading (Why else would I be browsing the Science desk on a sunny Saturday morning?), so it never hurts to throw 30 more papers at me. Nimur (talk) 17:43, 20 June 2009 (UTC)

Firstly, 6 of the 8 studies posted [15] are led by "Magda Havas". I don't know who she is of course (I assume female), but it would be good to check her out for any potential conflicts of interest (although she very loosely states there are none). Secondly, the studies aren't great. The first study contains 8 non-controlled cases. The second one isn't placebo controlled, relies on participant self-reports (instead of doing any objective measurements), and the actual experiments are related to multiple sclerosis and diabetes, yet it is concluded:

"Diabetes, multiple sclerosis, ADD/ADHD, asthma chronic fatigue, and fibromyalgia are all increasing in the population and the reasons for this increase are poorly understood. Dirty electricity may be one of the contributors to these illnesses."

Although she says "may", based on some self-reports (not discussed in the paper) really it is an irrelevant conclusion (as the decrease in pirates may have caused the rise of ADHD/fibromyalgia). Also "Table 1" - which states the symptoms of radio wave sickness - lists almost every common symptom there is. Seems like a case of the barnum effect applied to a disease. Another issue I have is this quote:

"GS filters have been placed in homes, offices, and schools. People report having better sleep, more energy, and less pain. They document cognitive improvements in memory and concentration"

Now there is no reference for this, although a few lines lower it does state something vaguely similar with the ref "Havas et al., 2004". Unfortunately the reference is this:

Havas, M., Illiatovitch, M., Proctor, C. (2004). Teacher and student response to the removal of dirty electricity by the Graham/Stetzer filter at Willow Wood School in Toronto, Canada. Presented at the 3rd International Workshop on the Biological Effects of Electromagnetic Fields, 4–8 October 2004, Kos, Greece.

This is where all the claims fall down for Wikipedia standards. A presentation in Greece is not a reliable source, but I decided to read it anyway (it is on the Electrical Pollution site). From a quick glance over the results, there is no significant difference between GS filters present and absent. In some cases the GS filters caused a reported positive response, whilst in other cases there was a reported negative response. In the bottom right corner of Table 1 it summarises the overall response, and it is clearly insignificant. In all of the results, there is only one case where the GS filters produced a statistically significant improvement, and that is in "unproductive time/class (min) in grade 4 students". Unfortunately it is not stated what statistical test was used, and the sample is still pretty small (18 in GS absent group and 14 in GS present group).

I can't really be bothered to read through any more of this, I'll put my trust in Nimur's conclusions if he/she reads the studies, or I will read for my self any double blind, placebo controlled lab experiments posted in scientific journals (not case studies). --Mark PEA (talk) 19:18, 20 June 2009 (UTC)

Ok people let me put this here plain and simple. I posted this here to find editors to collaborate with. NOT to get opinions. NOT to be told that the scientific body you believe in says it doesn't exist and thus it doesn't exist. NOT to be told I have no qualifications (Because quite frankly, since you are posting to the internet under a pseudonym, qualifications are irrelevent in this discussion. As per WP:NOR, every editor's qualifications are irrelevent). I do not need to prove anything to you, as you are just as qualified as I am.

Secondly, there is not one all-powerful all-knowing scientific body that declares things as fact or fiction. You do not have this power either. Thirdly, the GS filters are something I believe to be BS, and I myself will not introduce that to this article. Fourth, why is a presentation in Greece any less reliable than a presentation in America? You do not know the size or importance of this meeting, and your claim is unfounded. Fifth, lets see proof pointing the other way if you feel so strongly that it doesn't exist. Sixth, objective reports of "I feel sick" are just as valid as having some machine spit out a number that says "This means she is feeling sick". Seventh, 100 years of western medicine doesn't automatically invalidate several millenia of alternative and natural medicine. Eighth, is scientific research done by a company that sells the product it is "researching" proper methodology? By that standard, I should ingest half the pills I see on TV because I have one of the symptoms they list. Almost anything can be made to appear true. I feel myself that research done into a subject matter by a company that makes profit off that subject matter is not as valid as a third party's independent look.

Here are plenty of articles. They are hosted by electrical pollution.org (Which by the way, please back up your claim that this site is not reliable. The publisher is a big part of the studies conducted by the university of WI in Madison.), and each in themselves also reference countless published and reliable articles. I have not read through all of these yet, and only have them selected thus far as potential sources for information. First off, here is the requested power spectrums, published by Dr Martin Graham, Professor Emeritus at University of California in Berkeley. I admit I am not qualified and cannot read them. I'm an editor here though, not a scientist.

• NFAM research article
• Karl Maret (Md, M.Eng) report
• Canadian Human Rights Commision, Margaret E. Sears (PhD, M.Eng)
• Shocking News, a regular newsletter by Dr. Donald Hillman, Professor Emeritus, Department of Animal Science, Michigan State University
• David Stetzer and Magda Havas, World Health Organization workshop on electrical hypersensitivity
• Case study of three minnesota schools with the filters, using dummy filters for control group
• California EMF program final report on effects of EM Fields (Chapter 21 in particular)
• International Association of Firefighters (IAFF) votes to dtudy health effects of cell towers on fire station
• Association for Comprehensive Neurotherapy, report on global problem
• This study is 12 years old and may be slightly outdated

Granted, this is not 30. But again, I do not need to prove myself at this point. The article is not being submitted for review, I am looking for editors that want to collaborate with me and not against me. -- Floydian ^τ _γ 20:12, 20 June 2009 (UTC)

I would be happy to look at a draft. But you would do well to edit the existing articles or section which cover the topic. Right now it seems to be covered in Electromagnetic radiation and health#Health effects of electric power transmission. Additionally, cell phones, radio and television, and wireless broadband could be examined.They are covered in Mobile phone radiation and health Also leakage from microwave ovens, and occupational exposure to radar. There is Wireless electronic devices and health. There is some duplication. There have been many books and journal article published over the last 30 years or so dealing with the question of whether electromagnetic radiation from power lines (and more recently, from cell phones) causes cancer or problems with the immune system. The null hypothesis has seldom been rejected (of no effect). But a principle of "prudent avoidance" has led many to get rid of the electric blanket, and to avoid sleeping in the bedroom with only a brick wall between it ant the distribution line going overhead down the alley. It should be covered in an article, and I expect it is, somewhere. Early studies(Wertheimer and Leeper, 1979) just coded for the presence of power lines without measurements, and noted cancer cases. Later studies did measurements. Lifetime dosimetry of power line EMF exposure is difficult. Incidence of cancer among power company employees tended toward the null hypothesis. See Google book search at [16] for 215 books citing Wertheimer. Some are sensational crap, others are reliable sources. If "the power companies were covering it up" there would not be so many studies looking carefully at the effects. Edison (talk) 20:16, 20 June 2009 (UTC)

There are lots of studies, but many of them contradict the studies published by the power companies. The power companies almost always conclude "there is no such thing", while other studies almost always conclude that there is some sort of effect happening here, but that its not fully understood. -- Floydian ^τ _γ 20:21, 20 June 2009 (UTC)

You are wrong about the studies finding no measurable effect being published by the power companies. Read the articles/sections cited in my post above. Edison (talk) 20:27, 20 June 2009 (UTC)

I never stated that only the power companies publish these studies, I only stated that studies published by the power company (almost) always claim there is no measurable effect, or no noticeable effect on human health. If I am wrong, please link studies and not wikipedia articles for me to decipher and find sources in. My burden of proof doesn't lie on the reference desk, so can we please stop discussing whether or not my article is relevent? I am removing the link to my article in my userpages. It is irrelevent to what I am asking, and it seems that everybody is judging it no matter how many times I state that it is not in any way, shape, or form completed in any sense. It will be at least a C class article before I go ahead and publish it on the encyclopedia. At that point, everyone is free to make whatever comments they wish. -- Floydian ^τ _γ 20:40, 20 June 2009 (UTC)

Fourth, why is a presentation in Greece any less reliable than a presentation in America? You do not know the size or importance of this meeting, and your claim is unfounded.

Firstly, I thought it was quite clear from my sentence that I meant that any presentation is not a reliable source, whether it be in Greece, the USA or on Mars. Wikipedia requires evidence published in a scientific journal, because if not the presentations I've done at University could be cited and I could quack on about anything. Secondly, my claim is not unfounded. The "paper" that was discussed at the presentation was [17], and I discussed (not really 'claimed') its lack of significant results earlier.

Fifth, lets see proof pointing the other way if you feel so strongly that it doesn't exist

The burden of proof is not on me to disprove it. You prove to me that Russel's teapot doesn't exist, along with the Flying Spaghetti Monster.

Sixth, objective reports of "I feel sick" are just as valid as having some machine spit out a number that says "This means she is feeling sick"

No they are not. See: demand characteristics

Eighth, is scientific research done by a company that sells the product it is "researching" proper methodology? By that standard, I should ingest half the pills I see on TV because I have one of the symptoms they list

How would I know without looking at the studies? I have very little knowledge of electricity and "electrical pollution". What I do know is that when someone claims something to exist, they must provide solid evidence of its existence (as mentioned earlier re: burden of proof).--Mark PEA (talk) 11:39, 21 June 2009 (UTC)

Okay, I'm done. I can't take any more. I reviewed as much as I can, and I'm just ... well, did you even read the sources you provided? Three out of three reviewers strongly do not believe that EMF is a universal carcinogen. Half of your papers were self-published. Three apparently centered around an eight-person conference in Kazakhstan, a nation which (according to the conference brief you provided) conducts no research in this area. Nimur (talk) 00:05, 21 June 2009 (UTC)

Also, as I mentioned on your talk page, it is very ironic that you are critiquing "the scientific establishment" at large for conflict of interest, while citing reports that are little more than an advertisement for a bogus commercial "filter thingie". I believe that is the technically correct term for ... whatever this is. Nimur (talk) 00:36, 21 June 2009 (UTC)

The Wikipedia articles I found and cited above, in turn cite reliable sources. It is not reasonable for you to demand that I list the references here because it would be too much trouble for you to read the relevant articles and see what references are cited. Please provide a link to your draft article if you would like commentary and advice. One somewhat dated (from 1973) book I really liked was Power over people[18]," which criticized the EMF that utilities exposed people to, and encouraged ways of minimizing the effects. Edison (talk) 03:29, 21 June 2009 (UTC)

To answer Floydians question(!!!), possibly many projects, from Environment and Ecology to Industry and Electricity, not to mention various other projects this topic would fall under (I've seen four or five projects on a talk page many times), that is to say, so many you will probably just have to pick a couple you feel best, stick their banner on the talk page and invite them to come edit. Try to pick the ones that will gladly read it and wish to edit it, (I would go to Wikipedia talk:WikiProject Environment to ask, "Why is there not (or) which project is, the WikiProject for pollution" and ask more questions from there.) Everything you post on Wikipedia of a scientific or historical nature will be judged by the standard "Is that what they say on the Discovery channel?" (and it's true so don't give me a hard time for saying it) You may be everything from misled and idiotic, to unlearned and unable to speak English (I have heard these things many times but what you have here is certainly mild compared to the process at WP:AFD (deletions) where they won't even insult you, rather, just two or three people will say "don't beleive in it" and delete the whole thing forever, ignoring any arguements and feeling much worse than having some university students telling you to go back to school). There are strong arguements to say that human effects on global warming are about as strong as spitting in the ocean, but, you try to publish that or ask questions about it on Wikipedia you are a) saying the world is flat and b) claiming the holocaust didn't occur. Even articles about quite sensible scientific topics are easily deleted if, for instance, most of the work has been done by one person and he/she is not Albert Eintstein. For scientific theories you can have two things 1) previously published in a major English language/European scientific journal or 2) covered in high-ranking tabloids in a major English language speaking/European country. After that you have a) topics covered in websites that look or sound important (this will not count if the website covers only one topic so, on its own, electricalpollution.org will not withstand a deletion review here) and b) you have the Wikipedia Lottery that even though people ask to delete the topic, nobody wants to because amusing, interesting, signifigant or some other reason (and Electrical pollution will probably get a year or two on that last ticket unless it is truly absurd). I hope this is a helpful preparation for creating articles on more obscure scientific projects. If you can't read what I said, (I wonder sometimes) he said, "They will be more skeptical when they delete it and wont even suggest going back to school, try asking WikiProject Environment." ~ R.T.G 12:49, 21 June 2009 (UTC)

THANK YOU!!! You just did what about half a dozen people were incapable of doing. You answered the question that I actually asked! Thank you very much.

I don't know where in my 2 year absence wikipedia became such a disinclusionist community. Just because every scientist doesn't agree, or hasn't yet, doesn't mean a subject is not notable or that discussion on it can't persist. So many here just right away jump to researching away articles... Kinda defeats the purpose of calling wikipedia the "compendium of human knowledge". Should be changed to the "compendium of important human's knowledge".

And as I haven't released the article, the burden of proof does not lie on me yet. Further to that, I have produced several reports. No matter how much you contest them or their reliability, nobody has provided anything that proves that electricity and electromagnetic fields produces no effect on the environment. -- Floydian ^τ _γ 18:01, 21 June 2009 (UTC)

I beg to differ. RTG's answers are almost always wrong - check back through his history here on the science ref desk. What you really mean is that RTG told you what you wanted to hear...which may make you happy - but won't do you much good. The very first answer to your question was correct - what you are writing is either already covered by Electrical interference - or it isn't a referenceable topic for an article - which will indeed result in it being deleted. Wikipedia has grown up - we have standards - we are actively excluding junk. SteveBaker (talk) 21:59, 21 June 2009 (UTC)

And nobody has provided anything that proves that the Flying Spaghetti Monster, Russel's teapot, the Invisible Pink Unicorn, Steve Baker's Pink Aardvarks and an infinite number of other ideas don't exist, whilst others have produced reports on their existence (hence me mentioning them). That doesn't mean they are suddenly scientific truths. --Mark PEA (talk) 21:21, 21 June 2009 (UTC)

In fact, there is a type of human "allergy" to electrical emissions. It's called electrosensitivity. ~AH1^(TCU) 00:58, 22 June 2009 (UTC)

Getting cancer and our destiny

I apologize beforehand if I am posting this in the wrong section...

I took a workshop a few weeks ago and the teacher mentioned that we choose our own destiny and people that get cancer choose to get it. Even though I don't agree with the second part, I am interested in an explanation to why some people believe this. I know this is not a place for discussion, but can someone please point me to where I can find more information about this? I am having a hard time finding it on my own.

Thanks for your time —Preceding unsigned comment added by 76.166.207.196 (talk) 05:45, 20 June 2009 (UTC)

You are basically asking, "Why does somebody choose to believe patent nonsense?" Some people are just stupid. I wish I had a nicer or more pleasant answer, but it's true. Explaining things scientifically, in simple terms, with factual evidence, building from simple ideas to complex consequences, is not enough to convince some people. These people are just stupid. Nimur (talk) 06:27, 20 June 2009 (UTC)

Yes, Nimur, I think you are largely correct... but those who choose to smoke cigarettes, let's just say, are choosing to increase their risk of a number of cancers unnecessarily. But otherwise, it sounds like the teacher may have been pretty ignorant on the subject of cancer. – ClockworkSoul 06:31, 20 June 2009 (UTC)

Sorry, I may have been a bit harsh. To remedy my harsh language, let me provide some helpful references. Many of our cancer articles have entire sections or at least some content related to misconceptions - I found a lot by searching for this combination. These articles may also point to off-site links, such as Popular Myths about the Causes of Cancer and Myths about HPV. You might find cognitive dissonance and ignorance useful articles. Although not about cancer, we have HIV and AIDS misconceptions; this may illuminate some persistent misunderstandings about health and diseases in general. Nimur (talk) 06:37, 20 June 2009 (UTC)

I believe there may have been a little bit of a misunderstanding about what I meant in my original question. I should have been a bit more clear, sorry for the confusion. When I mentioned people choosing their own destiny and choosing to get cancer, I meant choosing to get cancer in an indirect way, not in a direct way. I am sure no one really "chooses" to get cancer or really wants to get cancer unless they are crazy. I'm kind of having a hard time explaining what I am trying to say. The teacher did not really explain it, he just mentioned it. This was not a topic of the class, it is 2 courses from now, but I wanted to look into it beforehand.

I appreciate the links, I read all that stuff in school, I used to want to become a pharmacist so I have taken several biology courses, so I know all about all that stuff. When the workshop instructor mentioned destiny and cancer I disagreed, but I am very open to other people's opinions so I wanted to look into it. —Preceding unsigned comment added by 76.166.207.196 (talk) 08:49, 20 June 2009 (UTC)

The placebo effect is a real and measurable effect that depends on belief. I can think of no scientific reason that a "negative placebo effect" couldn't cause illness in people based on their beliefs. Psychological states have been shown to effect the immune system (eg. clinical depression), so why can't believing you will get ill do the same? Resisting pseudo-scientific nonsense (of which there is a lot!) does not mean we should ignore real possibilities.

That said, i expect the teacher will actually talk about subconcious changes in life-style that pre-dispose people to certain illnesses, rather than direct psychosomatic effects. YobMod 10:47, 20 June 2009 (UTC)

Your question is pretty meaningless without context (is it a science setting, social, philosophical, religious?) and your offhand response I read all that stuff in school kind of implies that you are not really listening to any kind of answer you get at the science desk. But to have a try at it, possibly the point being made was that everyone arrives at the point they are at in their life due to the decisions they have made on the way. In that respect your decisions are responsible for the situation you are now in whether or not you could foresee, or intended them. But that is little more than a truism and has no scientific value since it is completely devoid of predictive power or falsifiability. SpinningSpark 11:09, 20 June 2009 (UTC)

Re: YobMod's comment about the "negative placebo effect": Here is the article: Nocebo effect. --NorwegianBlue ^talk 13:50, 20 June 2009 (UTC)

Wow, that's a facinating read - many thanks for the link. We have articles on everything!YobMod 14:06, 20 June 2009 (UTC)

The teacher may have been referring to the concept of karma or spiritism, which are not scientific and so don't belong in this section!--TammyMoet (talk) 15:59, 20 June 2009 (UTC)

I saw a bumper sticker that said "Sorry, my karma ran over your dogma." Edison (talk) 03:34, 21 June 2009 (UTC)

mecca

Does the city of mecca really lies on the Golden mean point of Earth??? They claim that the ratio of the distance from the North Pole to mecca and from mecca to South Pole is exactly equal to the Golden Mean Ratio which is supposed to be a standard ratio followed by the Supreme Being in the design of the entire universe. —Preceding unsigned comment added by 121.246.174.130 (talk) 13:38, 20 June 2009 (UTC)

I'm confused - wouldn't every place at that latitude have the same ratio of distances to the poles? For it to be a point, doesn't the longitude have to be defined too?YobMod 14:08, 20 June 2009 (UTC)

Yes, it would be everything on a line of latitude. Let's see, though -- Mecca is at 21°25' N, so it's 68°35' to the North Pole and 111°25' to the South Pole. The Golden ratio is ~1.618. Mecca's latitude ratio, South to North, is 1.624. Close, but not quite. Of course, the ratio of North to South is way off, about .616. So no, this is not true. — Lomn 14:13, 20 June 2009 (UTC)

For what it's worth, we can work out what the latitude of the Golden ratio circle would be -- it's 90-(180/(1+φ)), which is 21°15' S if you want your north-to-south ratio equal to φ. — Lomn 14:15, 20 June 2009 (UTC)

The Chicxulub crater seems to get rather closer though, do you think God is trying to tell us something? SpinningSpark 14:55, 20 June 2009 (UTC)

It might be pointed out that it doesn't matter much if you divide the larger part by the smaller and compare it to φ = 1.618... or divide the smaller part by the larger and compare it to 1/φ = 0.618... Sure, the former is the one that gets the Greek letter, but it's really no more special than its inverse. So saying that 0.616 is "way off" is a little much—it's slightly below 0.618, for the very same reasons that its inverse is slightly above 1.618. (I don't doubt you know this, but the OP might not.) —JAO • T • C 16:01, 20 June 2009 (UTC)

Of course, given enough constants, reference points, units of measure, etc. some sort of cosmological significance can be found for thousands of locations in the world. And if God/Allah was trying to send a message by the location of Islam's holiest city, I don't think it would have really cost Him much more effort to be a bit more precise. 64.252.193.6 (talk) 19:34, 20 June 2009 (UTC)

Maybe he was precise - how much have the tectonic plates shifted since Mecca started being an important place in Islam and in what direction? (I'm clutching at straws here, admittedly, but if you are going to rule it out on grounds of precision it is a question you need to answer (I'd rule it out on grounds of "What would be the point?", personally!).) --Tango (talk) 19:50, 20 June 2009 (UTC)

With respect to the african plate (which is taken as nearly stationary), the arabian plate is moving at about 20 mm/yr to the north, so since the time of Ibrahim (or Abraham) when according to Islamic tradition Mecca was founded around 2000 BC, that's about 80 m north, so not very far. Mikenorton (talk) 20:13, 20 June 2009 (UTC)

I'd prefer it relative to the North Pole. You also need to account for the North Pole moving due to axial shift/precession/whatever. --Tango (talk) 20:18, 20 June 2009 (UTC)

Why has no one mentioned Ley lines in this post yet, are all the fringe theory nutters on holiday today? SpinningSpark 21:16, 20 June 2009 (UTC)

Several independent points, not intended to argue to any conclusion:

• It's not just the whole line of 21°15'N, or more accurately 21°14'46"N, that meets the criteria; it would be equally notable if the two distances were in the reverse ratio, so the whole line of 21°14'46"S qualifies as well.
• The city of Mecca is not a point, so it's not accurate to say that the whole city is "at" 21°25'N. But the city's not so large that it extends to touch the line of 21°14'46"N latitude. Looking at Google Maps satellite imagery, that line of latitude misses the built-up area by about 10 km.
• Because the Earth is not a sphere, there are two different ways to measure latitude. Geographers use geodetic latitude, based on the direction of the local vertical at a place. But it would be equally valid, if less convenient, to use geocentric latitude, based on the direction to the center of the Earth, which gives slightly lower values. According to Latitude#Comparison of selected types, the difference at the latitude of Mecca is about 8 minutes, which means that 21°15'N geocentric latitude just about skims the south edge of the city's built-up area -- I'd need to do a more accurate conversion to be sure whether it hits it or not.

--Anonymous, 23:59 UTC, June 20/09.

"It's not just the whole line of 21°15'N, or more accurately 21°14'46"N, that meets the criteria; it would be equally notable if the two distances were in the reverse ratio, so the whole line of 21°14'46"S qualifies as well." -- Hey, isn't that the latitude of Rio de Janeiro? 76.21.37.87 (talk) 05:43, 21 June 2009 (UTC)

No. Algebraist 20:09, 21 June 2009 (UTC)

niper-2009

i got 2824 rank in niperjee 2009 n i hav sc reservation n female .......will i get a seat in niper institutions? —Preceding unsigned comment added by 117.195.181.1 (talk) 15:32, 20 June 2009 (UTC)

Googling niperjee only results in 26 matches...if you could be more specific it may helpHeinzcreamofchickensoup (talk) 16:15, 20 June 2009 (UTC)

It seems to be a reference to this. --Tango (talk) 16:48, 20 June 2009 (UTC)

We have an article on National Institute of Pharmaceutical Education & Research (NIPER), and presumably this question is referring to the NIPER Joint Entrance Examination test. You should contact individual schools with regards to their admissions standards, I don't think Wikipedia keeps rigorous statistics on admissions requirements in any of our school or university articles. You should be sure to use proper spelling and grammar when contacting these schools, as informal web-speak is generally not well regarded in the context of university admissions. Nimur (talk) 17:34, 20 June 2009 (UTC)

Sigfigs

As part of a chemistry assignment, I have to do the arithmetic problem 8.937–8.930 to the correct number of significant figures. The obvious answer would be 0.007, which, since leading zeros are not counted as significant, would have only 1 significant digit. Preserving the answer with 4 sigfigs such as both 8.937 and 8.930 have would yield the answer 0.007000, which seems ridiculous. Which one is it, and why? 64.252.193.6 (talk) 17:11, 20 June 2009 (UTC)

Addition and subtraction do not preserve the number of significant digits. They only preserve the accuracy of the result. This can increase or decrease the number of significant digits from the input (for example, consider the exact addition of 3 + 8 = 11. The inputs had 1 digit each, and the output is an exact answer with two significant digits). For more subtleties of the rules regarding significant figures, check the article. Your correct answer is 0.007, with only one significant digit. Nimur (talk) 17:30, 20 June 2009 (UTC)

Significant figures are a pretty useless way of expressing precision (because of problems like this) and are virtually never used at a higher level. For that reason, the "right answer" is simply whatever is on your teacher's answer sheet. --Tango (talk) 17:46, 20 June 2009 (UTC)

Keeping aware of sigfigs is quite important to avoid expressing a result with too many digits. They are always used at "higher levels" by anyone hoping to publish a result without being laughed at by editorial reviewers at a journal. Edison (talk) 20:04, 20 June 2009 (UTC)

No, they aren't used. The actual precision is stated. For example, you may see a value quoted as "4.586(34)" (the number is brackets indicates the precision) or as "1.65 +/- 0.023", or sometimes other notations. You virtually never see a number written with the precision given simply by the number of significant figures. --Tango (talk) 20:26, 20 June 2009 (UTC)

Additional question: for the problem (5.1 + 6.3) * 0.245 (just an example), do you give the answer to 2 sigfigs as in 5.1 and 6.3, or do the addition first, change the equation to 11.4 * 0.245, and give the answer to 3 sigfigs? 64.252.193.6 (talk) 21:47, 20 June 2009 (UTC)

I'd work it out using "interval arithmetic". You interpret 5.1 as 5.1 +/- 0.05, etc. and then work out what the smallest answer you can get is and what the largest is. In this case, that's easy - the smallest is by using the smallest value for each term, so you have (5.05+6.25)*0.2445=2.76285, and the largest is similar: (5.15+6.35)*0.2455=2.82325. You can then say the answer is 2.79305 +/- 0.0302. If you really want it just in terms of significant figures then you find the most figures you can do without giving false precision. In this case, that would be 2 sig figs, or 2.8, since that means 2.8 +/- 0.05, so the smallest possible value is 2.75, smaller than the real smallest value, and the largest is 2.85, larger than the real largest, so we're not stating any false precision. If we added another significant figure we would be narrowing the range too much and it would be false (you can work out the numbers for yourself!). --Tango (talk) 22:29, 20 June 2009 (UTC)

Tango's "interval arithmetic" assumes that the figures in the example problem are quantised approximations. But if that is not stated then it is reasonable to take them at face value. The answer is 2.793. Exactly. Cuddlyable3 (talk) 23:31, 20 June 2009 (UTC)

If we are talking about sigfigs and rounding then obviously we are in the context of uncertain data. --Tango (talk) 23:58, 20 June 2009 (UTC)

Not true that is is un-used past school. I often weigh small amounts to 0.000001 g precision, but i ony report the result down to 3 s.f. as that precision is not needed. Sigfigs usually do not mean the one has uncertain data, just that further precision is useless. This is probably why you do not find them often in other fields - it is often possible in chemistry to measure variables far more precisely than we ever need to: this is not uncertain data. It would be difficult to find any Organic Chemistry Professor that ever reported errors in simple measurments or even had the possibility to calculate them (they would need a full time postdoc position just to continuously calibrate and validate machines), so sig figs are the best one can hope for. Physics is not the only science around! :-)YobMod 12:57, 21 June 2009 (UTC)

You might report your final results to 3sf, but I would hope you either keep the full precision while doing the calculations or keep track of the precision properly. If you don't, you run a very high risk of getting the wrong answers. --Tango (talk) 15:35, 21 June 2009 (UTC)

I keep them, but never use them. Percentage yields are always reported to the nearest percent - so 3 sf is already far more precise than needed when weighing products for example. Keeping track of errors is nice in theory, but practically not possible - i wouldn't even know how to estimate systematic errors produced by the balance, and would not have time to do so even if i could, and any error study would be unpublishable as non-novel. This is the case for a large portion of scientific endevour.YobMod 08:51, 22 June 2009 (UTC)

Sigfigs are a somewhat useful rule of thumb - but they shouldn't be regarded with the same religious furvor that they are taught in most schools. Keeping careful track of error limits is a much better way to manage error tracking. After all - what's so special about base 10? If you're working in base 2, what do you do about preserving significant digits? (You CERTAINLY arrive at a different answer that way!) Very often, the concept of sigfigs goes horribly wrong because of the order of operations - you can get a different "significance" in your answer if you calculate AxB+AxC than if you do Ax(B+C). So the whole concept is very approximate - and should be treated accordingly. Of course if you have to get through a high school exam - do what the teacher says - get your passing grade - and THEN treat this technique with the lack of respect it deserves! SteveBaker (talk) 15:09, 21 June 2009 (UTC)

The error I was referring to above is the obvious one of measuring diameter as 75 millimeters, multiplying it by pi and reporting the circumference as 235.619 mm. That would get a manuscript sent back by return mail, and should get points taken of in a lab or exam. It is a sort of error that became very common among high school and college students in intro science courses after calculators became common, which was rare when all used slide rules (good to about 3 digits). Edison (talk) 18:09, 21 June 2009 (UTC)

Sure, but it's not that you need to quote to an appropriate number of sigfigs, it's that you need to quote to an appropriate precision. If the diameter was measured accurate to the nearest millimetre at 75mm then you would quote the circumference as 235.6(16), or something (in some contexts you may specify a few more decimal places, but I see little point). That is significantly more useful than quoting "240mm (2sf)", which is what you would do if you followed the standard rules taught in schools. --Tango (talk) 20:15, 21 June 2009 (UTC)

That's a really good example - let's do it the proper way - preserving the information we actually have: If you know the diameter is 75mm (plus or minus 1mm) then the circumpherence is 235.619 plus or minus 3.14159 mm). To put it another way, if the diameter is between 74mm and 76mm then we know that the answer lies between 232.4778mm and 238.7610mm. The sigfigs approach says that the answer is 240mm plus or minus 5mm...which is far from the mark! It's unnecessarily increased the error bar at the top end by 2.3 millimeters - implying that the answer could be as large as 245mm (which is in fact impossible) - and at the bottom end, it's saying that the smallest the answer could be is 235mm - when in truth, it could be 2.5mm less than that: 232.5mm! That's very, VERY wrong - completely unscientific - mathematically untenable! By using the sigfigs approach we've widened the error range from it's true value at one end and limited the possible error at the bottom end.

But it's worse than that - we arbitarily decide to round to the nearest DECIMAL digit! Why decimal? Because it's kinda convenient when we're working in base 10...because humans have 10 fingers! That's not good math nor good science. Mathematical statements should be independent of the number base you choose. If we did the math in binary notation and used the "sigfigs" approach, we'd say that the diameter is 1001011mm (rounded to the nearest millimeter). The circumpherence comes out of your pocket calculator as 11101011.100111101mm - which we'd have to round to 7 binary digits: 11101100mm...which in decimal is 236mm. 240mm is 11110000mm in binary. So by choosing to impose these supposedly universal rules - but in a different number base - we get a different answer! If you do the math in hexadecimal (base 16) you get an even more vague answer! This is ridiculous! Science and math shouldn't depend on how many fingers you have! Why is base-10 sigfigs treated as "The Right Way"?

The true and only valid reason to teach this approach is to use as a rough rule-of-thumb to prevent people stating ridiculous amounts of precision - but by codifying these ridiculously complex (and wrong!) rules - you are misleading people into believing that its "The Right Way" to do science...which is far from the truth.

SteveBaker (talk) 21:35, 21 June 2009 (UTC)

How big a population is needed to sustain the current technological society?

If the world's population is too small, a lot of the technologies that we have would be infeasible due to a lack of economy of scale. For example, if the world's population were a mere million, it would be too small to support a space exploration program. There are many other examples I can think of. Has anyone come up with a (well-reasoned) estimate of how big a population is needed to sustain the current state of technology? --173.49.12.233 (talk) 18:41, 20 June 2009 (UTC)

I think it is going to depend on the details. For example, if the population shrank due to wiping out everyone living in sub-Saharan Africa that might well improve the state of technology in the developed world due to the reallocation of resources currently going on humanitarian aid to that region. Another key detail is how spread out the remaining population is. If there are a million people left spread out all over the world, chances are good that they will be unable to remain very technological at all due to an inability to sustain reliable electricity production (a diesel generator per family would work at first, but you would struggle to produce and distribute the diesel). A million people all in one city wouldn't have any problem there at all. --Tango (talk) 19:47, 20 June 2009 (UTC)

Why could a population of a million not support a space exploration program? If they were all the "right" kind of people, like Wikipedia users say, and had access to present-day industrial plants, libraries and an abundance of the resources that 6 billion people consume today they could achieve anything they wanted. Look at it this way: You are the latest of a long line of ancestors none of whom failed to develop, thrive and explore whatever the current population was. Apropos electricity, the Internet could be run on hand generators. Cuddlyable3 (talk) 23:23, 20 June 2009 (UTC)

The cost per person would probably be too high if the only return was scientific development. --Tango (talk) 23:57, 20 June 2009 (UTC)

A keyword here is "specialist" --- one would not be able to have specialist doctors for all sorts of "advanced" diseases, for example, if population was too small. Similar for space engineers, etc (and even carpenters and similar if population becomes very small) Jørgen (talk) 00:45, 21 June 2009 (UTC)

I've searched around the articles on wikipedia concerning societies, civilizations and trying to find models for these. These aren't the fields best covered on Wikipedia, as is understandable giving the intricate models required by even simple questions on the subject. This has already been explained to some extent: Given different factors (population spread or centered), the answer will vary. Until exact numbers are provided, the solution is not... quantifiable, and a mathematical model would be abhorring. For instance, a population requires a constant source of food. Too small a population, and any dent in the agricultural production can have severe consequences. If there is any step back in technology, so to speak, each service's output (agriculture, industry, medicine and so forth) will diminish by a certain bit, and the society can support itself less, possibly spiralling downwards. This is of some importance since you ask "current technological society", which suggests there is a benchmark already to which we can hold all offices and organizations.

One could also add that some industries that exist today rely on multi-million markets (units or buyers) for them to be able to progress financially and thus lend their money to research. The answer to your question, for now, will be that no such thing exists, although I am afraid of answering so absolutely. 90.149.144.31 (talk) 11:10, 21 June 2009 (UTC)

It's a tough question - certainly it took the combined skills of at least a million people to get a man on the moon. Between skills in electronics, software, propellants, engines, aerodynamics, biology, machining, space-suit design, parachute technology, helicopter piloting...you name it! So I think a million people would make that difficult - but perhaps not impossible. Certainly it could be done as a multi-generational thing. We would have to be very careful to preserve knowledge from one generation to the next because it's perfectly possible for one entire generation to have not one single expert in some obscure field like (say) quantum chromodynamics - but you'd want to be sure that such a thing would not be forgotten forever. Education would be very important - and ensuring that we did not have too many people crowding into one area of study to the extreme neglect of another would be tough. But consider it like this...if we imagine that Wikipedia represented the whole of human knowledge (at least in scope, although obviously not in depth) - then with 2.8 million pages and 1 million people - each person would only have to be a 'deep expert' in the subject areas of roughly three articles to have all of human knowledge fully represented. But an awful lot of those 2.8 million pages are things like rock bands, TV shows, movies, descriptions of cities, biographies characters in "The Simpsons"...things that humanity doesn't need to have live, human experts on. We could have a dozen "history of music" people and another dozen "history of TV shows" people who would be able to keep the necessary information "alive" and be available for consultation as needed - so we could still afford to have 1000 mathematicians, 1000 biologists, etc. My guess is that if we considered the topics that are more than mere listings of information (things like math, chemistry, etc) - then we might have less than a million articles that "matter". So one person could be the world expert on (say) Aardvarks - another on Boyles gas laws, another on Xeno's paradox...those are awfully narrow areas of study. So I think the knowledge and skills we need could be retained by a million people. The difficulty with a space mission is that you might need (say) 1000 software engineers to write the software. There might (just) be a thousand software engineers in the world - but could we spare them all on getting a man to mars? I don't think so.

But (since this evidently relates to the earlier sustainability question), I think 1 million people is too few. 10 million or perhaps even 100 million would be a more realistic target. With that number of people, I think humanity could have a few dozen MAJOR projects being worked on in each generation and still have enough people to produce food, repair machinery, etc.

Space missions might become a thing of the past - or they might be considered important enough to be the main work of an entire generation - or something that we'd be happy to take the "long view" of and stretch over 10 generations. Certainly the work of mankind would have to be a more 'focussed' affair - there would be little scope for petty bickering about what would be the work of this generation.

But with no more worries over food shortages, energy shortages - with everyone being able to live on large estates with comfortable lives - with everyone having the responsibility to be THE one singular world expert on something that matters to them - I'd hope that the world would become a more peaceful, relaxed place than it is now. Fighting wars would become exceedingly difficult with so few people spread out so widely! There could probably only be a few thousand soldiers in the world - dropping a nuke on a "major city" might kill a few dozen people. That could be serious in terms of loss of expertise in some key areas - but nothing like the scale of horror such a thing would mean today.

SteveBaker (talk) 14:59, 21 June 2009 (UTC)

If you only have one expert on each area you could keep current knowledge alive, but it would be difficult to develop new knowledge. A lot of academia is focused around collaboration. Without anyone the exchange ideas with, new work would dramatically slow down (by more than just what you would expect from fewer people working on it). I would expect people to live close together, rather than all spread out. You can live a much more comfortable lifestyle that way, so a well placed nuke could wipe out a sizeable portion of the world's population. --Tango (talk) 15:32, 21 June 2009 (UTC)

I think I've mentioned before, but there is a very very bad historical precedent for these sorts of societies, where individuals exist solely because they are "needed." What happens when you have un-needed individuals? Do you euthanize? Even the most effectively planned society will experience environmental and situational changes that will skew the instantaneous need for certain professions and certain individuals. Pol Pot claimed he only needed about one million Khmers for his ideal society; and everyone else was ... well, no loss. All for the benefit of the Planned Society where everyone had a proscribed job and glorious equality among the classes! The idea of having to breed exactly the correct number of individuals, and then forcing them into a particular career path, seems to be a major step backwards in human society. It's important to keep in mind that in our society, even the most unproductive individuals, who are of no "use" to some particular agenda, still have a right to exist. Nimur (talk) 23:36, 21 June 2009 (UTC)

Heating canned goods directly

I seem to remember reading or hearing many years ago that it was a very bad idea to heat canned food directly over a heating element in the can (say a low flame on the range top). Now, mind you, I am not talking about an unopened can! The pressure danger there is or should be evident to most people. Is this true? If so, why? The only thing I can think of is leaching of the metal but most modern store bought cans are made from steel (not mercury or lead etc.)--141.155.143.180 (talk) 19:47, 20 June 2009 (UTC)

Someone asked this question on Yahoo. Hopefully someone here can corroborate the answers. Sifaka ^talk 19:56, 20 June 2009 (UTC)

Someone at Yahoo answers correctly pointed out that it is cooked in the can during the canning process. How would stove-heating be worse, unless it got hotter than at the cannery? Edison (talk) 20:02, 20 June 2009 (UTC)

Assuming the paper label will not be catching fire, then there is the question of any lead in the solder sealing the can, or any chemicals in the coating inside the can which could leach into the food. Many years ago, I recall a vending machine which had cans of chilé and soup kept hot inside and dispensed hot when purchased. Such long-term heating would probably be worse than brief heating on the stove. If steel, the cans are likely coated with tin inside. I have seen some which appeared to be coated with zinc inside, from the mottled appearance. Edison (talk) 20:00, 20 June 2009 (UTC)

Thanks for the answers. I think I'll refrain but I was curious.--141.155.143.180 (talk) 20:35, 20 June 2009 (UTC)

In addition to the can interacting with its contents, the bottom lid is crimped to the side walls. The bottom lid is designed to disburse impact stresses and resist heat expansion of the content at temps. around boiling. It is not designed to deal with the heat expansion caused by direct exposure to temperatures above 1000°F. It is likely to warp, which is in turn likely to put strain on the crimping and the seam on the side of the can. Material failure can be instantaneous and is unlikely to be pretty (launched lunch). The fact that the can not being the right size for your heating element the uneven heat absorption will damage the heating element of your range will probably be the least of your worries. 68.208.122.33 (talk) 21:21, 20 June 2009 (UTC)

This article cites reports that when taken together could imply that the food in 0.5% of tested cans (that's a LOT of cans) contained enough tin to cause nausea, vomiting, and diarrhoea. Heating of acidic food like fruits and vegetables may exacerbate this. Cuddlyable3 (talk) 23:07, 20 June 2009 (UTC)

I do not see how a can of food, with some liquid content, could be heated anywhere near 1000 F on a stove burner. In fact, it is possible to boil water in a paper bag over open flame (Ref: Michael Faraday, Mr. Wizard). The content keeps the container cool. The can should not get much above 212F/100C. Edison (talk) 03:39, 21 June 2009 (UTC)

Agreed. Also about the canning process being far more harsh than any reasonable re-heating method. It seems some canned food may contain tin, but cooking food in the can should do nothing to increase this level significantly. And cans can easily maintain their shape in a camp-fire. Cooking canned beans on the camp-fire is done all the time, and i have never seen any ill effects.YobMod 12:48, 21 June 2009 (UTC)

A can is made of thinner material than a pot. This accentuates any of the contemplated problems above. I doubt there is any problem involved in placing an opened can (of food) inside a pot of water and then heating the water, resulting in the contents of the can becoming heated. Something like a trivet could even be placed beneath the can to further separate it from the source of heat. Bus stop (talk) 13:55, 21 June 2009 (UTC)

But there is no need. A can can easily withstand the direct heat of a typical camp fire. Don't belive me? try it, the same as 1000s of people do every day. Repeated experimental observations surely count for something - any experienced camper should have seen this done, even if they prefer to carry around pots and pans. Camprecipes says it works for any canned food that just needs heating.YobMod 14:26, 21 June 2009 (UTC)

(un-indent)There may not be much of a need. But it is probably best to utilize low heat. And it is probably best to try to endeavor to apply heat in a way that doesn't concentrate it on one spot on the can. Any possible failure in the materials or construction of the can is likely to be exacerbated by both high heat and very unevenly applied heat. Bus stop (talk) 14:40, 21 June 2009 (UTC)

My guess would be that the canning company would use a label saying not to heat in can so that someone does not try heating up an unopened can and sue the company. 65.121.141.34 (talk) 14:26, 22 June 2009 (UTC)

Aren't some cans plastic lined -- to battle the metallic taste caused by direct contact of metal and acidic foods? --70.167.58.6 (talk) 14:38, 22 June 2009 (UTC)

"Homeopathic"?

In the spirit of AGF, I'm going to put this under "Science". I started to feel the symptoms of a cold coming on while visiting my family and my step-mum offered me a treatment that was apparently popular in the US (where she lives). It was some kind of spray that you apply to the back of your throat containing zinc and said on the packaging that is was "homeopathic". My understanding of homeopathy is that the remedies contain (prior to dilution, anyway) organic substances understood to be the cause of the malady. That suggests that this zinc thing wasn't actually homeopathic. In discussion with her, we came to the conclusion that the term in used in the US for any complementary medicine. Firstly, is this true? Secondly, does anyone know what this zinc treatment was and whether there is any evidence to support the claims? --Tango (talk) 20:09, 20 June 2009 (UTC)

The Mayo Clinic says of zinc cold remedies that they "probably don't work", and WebMD says studies are "inconclusive". Still, if you take enough of it, there's some chance you'll develop some kind of super-power, and will fight crime as Rust Resistant Man. 87.115.17.119 (talk) 20:18, 20 June 2009 (UTC)

The article Zinc gluconate cites reports about cold treatments containing zinc and mentions a warning on 16 June 2009 from the FDA about nasal products from Zicam. The Zicam article cites a NY Times report on the same date that the manufacturer has withdrawn Zicam from the US market. It was (or is) marketed as a homeopathic remedy with some additional ingredients. Please see the articles concerned. Wikipedia can only cite reliable sources and will offer no medical advice. Of course you know that but it had to be said. Be cautious and get well soon. Cuddlyable3 (talk) 22:52, 20 June 2009 (UTC)

Thanks for the kind words, but the cold never really materialised (which isn't uncommon for me - I must have a good immune system). I think some of the symptoms were actually caused by dehydration, which I worked out a little latter and treated homeopathicly by drinking lots of plain water! (I would have switched to rehydration salts if necessary, so you don't need to warn me about the perils of rehydrating with only water!) --Tango (talk) 01:20, 21 June 2009 (UTC)

Oh - my - God - Tango. Don't you know that that "plain water" contains the succussive remnants of every other homeopathic remedy ever applied? And they've been getting ever stronger with dilution. This can be simply proved by the fact that water flows to the ocean, which is succussed by gravity waves, so you've clearly crossed the 200C barrier. You're invulnerable to all common ailments now. If there are any actual zinc molecules in the preparation you're spraying in the area of your lungs, you may have a small case of metal fume fever, but I'd recommend you counter that with a dilute application of chromium or vanadium. Remember to use fewer than zero atoms to get the maximum effect though. ;) Franamax (talk) 23:28, 21 June 2009 (UTC)

Homeopathic can mean more than the diluted bit but I have a hard time finding any justification for labeling the zinc treatment as being homeopathic. I agree in this case it seems to be just be a synonym for "alternative medicine" in general. --98.217.14.211 (talk) 01:34, 21 June 2009 (UTC)

"we came to the conclusion that the term in used in the US for any complementary medicine. Firstly, is this true?" No, not as far as I know. It sounds like the term is being misused. I'm surprised that the packaging said this. Perhaps this is just marketing-speak? 'Alternative medicine' is the term we generally use in the US (I live in Chicagoland). A Quest For Knowledge (talk) 02:01, 21 June 2009 (UTC) TC)

Homeopathy does not refer to "alternative medicine" in general but instead has a more precise meaning. An extremely accessible explanation of the origins of homeopathy and the scientific consensus regarding homeopathy is presented here by James Randi. The term is however abused to refer to any complementary/alternative medicine. Whatever you do, do not use a zinc-based "cold remedy" without reading the recent FDA warning regarding Zicam. --71.58.103.112 (talk) 09:42, 21 June 2009 (UTC)

Be careful with that stuff. The FDA recently issued a warning that Zicam may destroy your sense of smell. Guettarda (talk) 14:05, 21 June 2009 (UTC)

Yes. To be clear, according to the FDA, the manufacturers of Zicam have on record complaints from several hundred people who discovered the hard way that Zicam can PERMENANTLY destroy your sense of smell. And since almost all of what most people imagine to be their sense of taste is actually their sense of smell - you can pretty much write off ever enjoying food again - all of the subtle flavors reduce to salty/sweet/sour/bitter/savory. I don't understand how Zicam can be classified as "homeopathic" and still have enough active ingredient to cause this - it seems to me that they must have been abusing the "loophole" that allows homeopathic drugs to get onto the market without adequate testing. The only reason that loophole exists in the first place is because true homeopathic "drugs" are nothing more than water...they are a horrible scam - but they shouldn't be dangerous. If they actually have measurable amounts of (for example) Zinc in them then they aren't homeopathic and they should be undergoing a full swath of clinical trials, etc, etc. If the law allows measurable amounts of active ingredients in homeopathic medicines then they become more than just a scam - you should read that word on the label and mentally translate it to "Completely untested - use at your own risk!" SteveBaker (talk) 14:29, 21 June 2009 (UTC)

I should clarify - I turned down the offered treatment. I know better than to trust anything with the work "homeopathic" on it, regardless of whether it is correctly used or not! This particular treatment was apparently intended to be sprayed on the back of the throat, rather than the nose, which should prevent it destroying your sense of smell. It also would seem to prevent it working if the claimed mechanism regarding mucus membranes in the nose (as described in the pages linked to above) is correct. --Tango (talk) 15:20, 21 June 2009 (UTC)

Mucous membranes. Mucus is a noun, mucous is an adjective. By the way you made the same mistake on phosphorus/phosphorous a few threads back (at least I think it was you). --Trovatore (talk) 22:24, 21 June 2009 (UTC)

I don't remember talking about phosphorus or phosphorous recently, but my spelling has never been ideal. I am far too reliant on spell checkers, so that kind of mistake is quite common for me! I will try and remember the distinction in future, thanks! --Tango (talk) 00:07, 22 June 2009 (UTC)

In US drug regulations "homeopathic" is a specific class of treatments based on homeopathic principles and accepted into the Homeopathic Pharmacopoeia. Inclusion generally requires that the remedy closely follows some traditional alternative medical practice with a long history of use. While they are regulated for safety, and for the kinds of claims they can make, most homeopathic "medicines" are not reviewed for their effectiveness. They are allowed to be sold alongside over-the-counter medications, which can often be confusing. Dragons flight (talk) 22:14, 21 June 2009 (UTC)

• Above, "SteveBaker" said, "Zicam can PERMENANTLY destroy your sense of smell". <-- How did you reach this conclusion? "If they actually have measurable amounts of (for example) Zinc in them then they aren't homeopathic" <-- Is this part of the FDA's regulatory position? "Completely untested" <-- Strange, but the Wikipedia article Zicam cites at least one clinical study that tested the zinc nasal gel and the sales figures suggest that millions of people have used these products. --JWSchmidt (talk) 02:36, 22 June 2009 (UTC)

Well, me not being SB and all, but: "permanently destroy" may come from the same sources the NY Times used when they quoted the FDA director of compliance saying "This disabling loss..may be..permanent..." - would that do? [19] And of course, anyone actually reading the Zicam article can easily ascertain which compounds are claimed to be homeopathic, none of them are zinc, that's just a metal you likely shouldn't be spraying into your respiratory system. And I'd be interested in the peer-review and full text of the clinical study to which you refer (is it one which found damage to health, or the metastudy which suggested that further study is required to verify primary efficacy and doesn't mention side-effects in its abstract?[20]). Oh, and millions of people have used crack cocaine, crystal meth, alcohol, tobacco, asbestos and benzene too, what was your point there? Franamax (talk) 04:00, 22 June 2009 (UTC)

The Wikipedia anosmia article makes it clear that anosmia can be permanent. Infections such as the common cold can cause anosmia, so people who do not use Zicam get anosmia. Who do they sue? Where does the FDA say that Zicam causes anosmia? This is the published study I noticed in the reference list at Zicam. It is certainly wrong to suggest that when you see the word "homeopathy" on a package it means "completely untested". Franamax, I don't know what your point is in mentioning crack cocaine, crystal meth, alcohol, tobacco, asbestos and benzene. Part of the testing of drugs comes after they are introduced into the market and used by large numbers of people. Should we count the number of conventional drugs that have been withdrawn by the FDA only after they were given to millions of people? --JWSchmidt (talk) 14:30, 22 June 2009 (UTC)

June 21

Cockatoos: are they more likely than other birds to go crazy?

It seems as though 3/4 of the cockatoos I see in people's pet videos on Youtube have some sort of psychological problem, whether it's pulling out their own feathers, gnawing strips off of their own flesh or doing that 'rocking around and making repetative noises because I've gone insane' thing. I know that the same thing can happen to most species of parrot but it seems way more prevalent in cockatoos. Is there any particular (known) reason for this? --90.240.20.62 (talk) 00:02, 21 June 2009 (UTC)

There is an article on Feather-plucking but it lacks sources. Sifaka ^talk 00:23, 21 June 2009 (UTC)

Maybe just nobody videos "sane" birds to put onto YouTube? - KoolerStill (talk) 10:32, 21 June 2009 (UTC)

"Enamel strengthening" toothpaste

I see many ads for new toothpaste that proclaim new "enamel strengthening", re-mineralizing, enamel hardening, and other similar claims. Is it me, or is this just new marketing approaches to old fashioned flouride? Are there any new discoveries better than flouride? --70.167.58.6 (talk) 01:14, 21 June 2009 (UTC)

"Waveguide" ultrasonic toothbrushes

Another product I see advertised as being new and different are "waveguide" ultrasonic toothbrushes. Aren't all ultrasonic toothbrushes waveguide -- with the waveguide being the brushing head? A non-waveguide ultrasonic toothbrush could not exist, could it? --70.167.58.6 (talk) 01:23, 21 June 2009 (UTC)

If it's anything like the one described in U.S. patent 7,296,318, then the waveguide is an extra blob of rubber stuck to the brushing head. This is meant to couple more energy into the liquid than you can do by relying on the bristles alone. --Heron (talk) 12:30, 21 June 2009 (UTC)

Interesting. It sounds like a marketing gimmick. At any rate, the company went out of business. [21] --70.167.58.6 (talk) 13:45, 22 June 2009 (UTC)

Range data for Lockheed Electra 10-E?

Hello everyone, sorry to bother y'all about Amelia's plane again, but I seem to be involved in a bit of a dispute about its maximum range (one other editor claims she had barely enough fuel to reach Howland Island, while I'm trying to prove that she had plenty to spare). So I've crunched the numbers a while ago and came up with the following: --Economical cruise speed of ~140 kts. at ~40% power; --Fuel flow rate of ~40 gal./hr. at this speed, giving a maximum range of ~3,850 miles with 1,100 gal. of fuel on board (I know she had exactly 1,100 gallons on board, as it is on the official record).

These figures are pretty close to the range of 3,600 miles that one other source gives, but I'm not sure if they're correct, because (1) I actually calculated the 40% power setting for the Lockheed Lodestar and applied it to the Lockheed L-10 Electra, and (2) I did all the calcs in my head, so I probably introduced quite a bit of rounding error too. So could someone be so kind as to double-check these figures to see if they're correct or not? Thanks!

76.21.37.87 (talk) 06:10, 21 June 2009 (UTC)

I have nothing to say about anything except the calculation: 140 knots X (1100 gallons / 40 gallons/hour) is 3,850 nautical miles. If you were implicitly assuming that "miles" would mean nautical miles in this context, fine. --Anon, 07:21 UTC, June 21, 2009.

Was there a headwind? Remember - your calculations relate to AIRspeed - not GROUNDspeed. There is a huge difference! Also, you use a lot of fuel during takeoff - much more than at cruising speed - particularly if the aircraft is overloaded. Weight is everything here! You also use a lot more fuel if you are changing altitude a lot - eg to get above bad weather or to get low enough to navigate using maps. The amount of power (and hence the fuel consumption) required to maintain level altitude depends on the weight of the plane - so initially, the fuel economy at 140kts would have been much worse than your data suggests. This question (and the previous ones you asked) are extremely bothersome to me. The degree of oversimplification is very worrying. Her plane was not even a standard Electra - and it was not being flown within the manufacturer's original weight restrictions. She'd modified the heck out of the thing...there is no way to know what it's fuel efficiency was - you certainly can't use the data sheets for the standard plane. So IMHO, all bets are off. The answer is "We don't know"...and even..."We will never know". All answers that are other than that are wild-assed guesses and should be treated accordingly. Neither you - nor the person you are disputing with - can possibly have the slightest clue about what you're arguing about! Some mysteries are just mysteries. SteveBaker (talk) 14:15, 21 June 2009 (UTC)

Four towers around rocket gantry

What is the purpose of the four towers shown here: http://en.wikipedia.org/wiki/File:LRO-LCROSS_Atlas_V-Centaur_launching_from_Launch_Complex_41.jpg And do the wires that connect them have any non-structural purpose? 89.242.100.210 (talk) 09:29, 21 June 2009 (UTC)

As it says in the description on the image file, they are lightning towers built to reduce the risk of lightning strikes on the launch vehicle or associated equipment prior to launch. The wires are all part of the system, see this animation [22]. Mikenorton (talk) 10:25, 21 June 2009 (UTC)

should we scale down the internet?

Looking scientifically ....

1) Is there enough future energy to power the servers? [assuming no energy breakthrough]

2) Are we being unbelievably selfish to future generations by depleting energy on websites which are lets face it 99% pointless data?

3) Could a way to remedy this is have a vast archive (like the wayback machine) and delete old pages after a few years?

—Preceding unsigned comment added by 84.13.124.167 (talk • contribs) 11:42, 21 June 2009

Those are interesting questions, but I'm not going to attempt to answer them except to say that I suspect the Internet saves energy in terms of visits to libraries, bookshops, and video rental and other shops, as well as saving on postage and fax costs. Perhaps someone knows of a study into this aspect of the Internet.--Shantavira|^{feed me} 12:11, 21 June 2009 (UTC)

Yes, I agree. The Internet uses a really tiny amount of energy compared to all other human activities - and it certainly saves energy in many ways. Sure - it's possible that in future we'll have insufficient energy to power the thing - but I rather doubt that. Computers don't need much power - and it would be perfectly possible to power the servers using solar panels - particularly because solar panels are getting more efficient and computers are needing less and less power as time goes by. The problems for humanity are in things like cars, trucks, planes and ships which (being mobile) can't take advantage of things like solar power and wind energy - and for large scale industrial activities that need so much power that the amount of area they'd need to be powered from renewable sources becomes a huge issue. But the Internet is far, FAR down the list of things that are problematic.

Another thing - the amount of data on a server has little or nothing to do with the energy it takes to run it. Data exists as little magnetic zones on a hard drive. If you power down the hard drive when nobody is accessing it - you can have as much data on the server as you want and it costs zero energy to maintain it. The only cost is when somebody ACCESSES that data and the drive has to spin up to speed, copy the data into main memory and ship it off down the wires. So the fact that 99% of it is "pointless" is not relevent. If you need something to complain about - it should be the number of people who are accessing that "pointless" stuff. However, most of us would argue that if someone feels the need to access it, it's probably not pointless at all.

Deleting pages is actually a wasteful activity because you have to power up the hard drive to do it - and that takes energy. (I should explain a small caveat here: It does take energy to manufacture a hard drive - so I guess there is an initial cost to storing "pointless" data - but very, very few websites need more than one hard drive to store everything - so the cost is the same whether the drive is empty or full.) SteveBaker (talk) 14:03, 21 June 2009 (UTC)

Also, even if the wasted enery came anywhere near that of, for example, cars - i think many people would already prefer to lose the car than the internet. Pointless car journeys (or 5-7 people-carrying cars with only one occupant) far out-number those we need, so eliminating those would be a higher priority in an energy shortage. Why target the internet, but not older industries?YobMod 14:13, 21 June 2009 (UTC)

The free market is capable of working these things out. We would leave fossil fuels in the ground if there weren't better investments, so we're safe in saying that we're not being selfish by using too much energy (though we may be selfish in having too high a prevailing interest rate). As for if we should scale down the internet, the cost of power is part of the maintenance costs. The higher the costs, the fewer webpages will be made. The whole "scaling down the internet" will happen continuously. — DanielLC 17:21, 21 June 2009 (UTC)

"The free market" only works properly if all costs are internalized. See tragedy of the commons. --Stephan Schulz (talk) 00:08, 22 June 2009 (UTC)

They are. There's no way to get energy that doesn't involve owning whatever you're getting the energy from. Or are you referring to environmental costs? — DanielLC 15:07, 22 June 2009 (UTC)

Environmental cost, of course, and political cost - arguably the price of oil is kept artificially kept low by political pressuring and operations like the war in Iraq. For a long time coal-mining has received massive subsidies in Germany (and I'd bet other places). Nuclear power has received not only massive research funding, but so far is not paying market price for safe waste disposal and insurance against possible environmental risks. --Stephan Schulz (talk) 15:14, 22 June 2009 (UTC)

NOTHING

I was just having a discussion with a friend about NOTHING - meaning try to explain nothing in refrence to the univers is expanding into nothing; the idea you can go to the end of the univers and then it stops but whats on the other side. Is there just a quantum theory for this or a mathamaticle one? or is there anybody that could offer a no nonsense explanation for Nothing...a bit about face the question but i am sure you will get my meaningChromagnum (talk) 12:56, 21 June 2009 (UTC)

The word "universe" means "everything". If it had an "edge" and there was something on the other side - then the something on the other side would just be a part of the universe and the "edge" would be some unusual feature running through the universe - not the end of it. But I think you misunderstand how the expansion of the universe works. Space itself is expanding. It's not like there is a bunch of solid objects moving outwards into otherwise empty space...it is the space itself that's growing. Either space is (and always was) infinite - or it curves back around on itself in some fourth spatial dimension - or a couple of other variations on that. But there isn't going to be an "edge". It's best to think of the two-dimensional rubber sheet analogy. Imagine 2D beings living in 2D space...for them, there is no third dimension. Their universe could be a super-stretchy rubber sheet with a grid of lines drawn on it. If space is infinite - then they live on an infinitely large flat sheet...but even though it's already infinite - it's still stretching outwards. If you watch closely, the grid lines around your position on the grid are gradually getting further and further apart. Off in the far distance - the grid lines are moving away from you really quickly - but nearby, the movement is so slow, you can hardly see it happening. That's a valid 2D analogy for what we're seeing happening in 3D. However, there is another possibility. These 2D beings might be living on the surface of a 3D balloon that's slowly being inflated. They can walk around on the surface of the balloon - and the grid-lines on the surface of the balloon will gradually be moving apart - but their universe is still 2D. It has no edge - and it's expanding. In theory, they could travel off in one direction around the balloon in what seems like (for them) a dead straight line - and they'd arrive back at the starting point. However, because the balloon is expanding faster than the speed of light - they could never actually do that in practice - so the universe is larger than they'll ever be able to see.

But in neither case did their rubber sheet universe have an "edge"...and neither does ours. So there is no "nothing" out there that the universe is expanding "into"...space itself is stretching. It's a hard thing to get your head around...but that's how it is. SteveBaker (talk) 13:52, 21 June 2009 (UTC)

I think it is simpler to say we don't understand. If we can't get our heads around something perhaps we should admit that we are stymied by a question. I accept neither that the universe is finite or infinite. I don't understand. That is simpler to say. And I think the same is true of time. I cannot contemplate how time can be infinite, and I cannot contemplate how time can be finite. I'm not trying to stall debate and questioning and contemplation of possibilities. For myself though, I just want to say that I find this unanswerable at this time. Bus stop (talk) 14:21, 21 June 2009 (UTC)

Steve isn't saying he knows the answer, he is just reporting very well-known conjectures that appear in journals. The Flatland comparison is in some UK A-level curriculum - there is no need to deny these theories exist, all becasue we cannot know their validity.YobMod 14:33, 21 June 2009 (UTC)

I don't think it's a good idea to talk about the universe being curved in a "fourth spacial dimension". While things like String Theory and Kaluza-Klein theory posit extra spacial dimensions, that is very different to General Relativity's description of the universe as curved. In mathematics there are two distinct concepts of curvature - extrinsic curvature which describes how a space is embedded in a higher dimensional space, and intrinsic curvature which describes how the space is curved from the point of view of the space itself (eg. what the angles in a triangle in that space add up to). When we talk about the universe being curved we mean the latter, there is no need to consider it being embedded in a higher dimensional space. --Tango (talk) 15:05, 21 June 2009 (UTC)

I'm not denying that any theories exist. I didn't think I was denying anything. On the contrary I am affirming something. I am affirming my own ignorance. I am asserting my inability to cope with such a question as to whether space and/or time is infinite and/or finite. I personally find the questions unanswerable, and even un-addressable. But I don't mean to prevent or discourage others from addressing such questions. Bus stop (talk) 15:04, 21 June 2009 (UTC)

So why the heck are you posting? If there is a question who's answer you don't know or don't understand, the best strategy is to sit quietly in a corner and read the answers. It's pointless to post your own failure to understand. It may be simpler to say "we don't understand" - but we can do much better than that. SteveBaker (talk) 21:03, 21 June 2009 (UTC)

To some extent, it is not exactly correct to call these questions "unanswerable". There are observable consequences to many of the hypotheses about the universe and its shape and curvature. You can read a bit about them here. The effect of having a closed universe, as opposed to an open universe, shows up in many advanced cosmological observations. The math is very hard and I don't pretend to follow all of it, but simply put, there are falsifiable consequences to any hypothesis we make about the nature of the universe. It may show up as a doppler shift on the cosmic microwave background, or a certain flavor of gravitational lensing, or some other subtle effect. This is the point of modern cosmology. It's insufficient just to "think about the unanswerable" - cosmologically inclined physicists must mathematically demonstrate an observable consequence of some theory; or, observe some evidence of somebody else's theory. This is what separates cosmology physics from "wild speculation" or "philosophy." Nimur (talk) 15:11, 21 June 2009 (UTC)

You said "we" not "I". While you may not have the training necessary to truly comprehend these matters there are experts that do. --Tango (talk) 15:16, 21 June 2009 (UTC)

Granted, I said "we," not "I." But I have an expectation of an explanation that I can grasp, on some level, and that has not been forthcoming. It may be a function of the seeming simplicity of the question posed that makes me think someone ought to be able to explain it to an untrained person such as myself. Bus stop (talk) 15:37, 21 June 2009 (UTC)

I think Steve's answer is pretty understandable to the layman. Perhaps you could explain what it is about it you don't understand? --Tango (talk) 15:46, 21 June 2009 (UTC)

It is a non-answering of the question. It is the diverting of a question concerning 3 dimensionality into a 2 dimensional realm. Two-dimensionality is an abstract construct. Three-dimensionality applies best to our understanding of the world, and it is what the original question inquires about. I have to admit, I don't even understand the explanation posed. I only accept analogies so far. And then I want further explanations. The so-called 2 dimensional beings are inconceivable. And even the comparison to a rubber sheet is merely conceptual, because such a rubber sheet would have thickness. I find the question to persist, at the end of the explanation. I still find myself asking if a 3 dimensional universe is finite or infinite. I don't think analogies to 2 dimensionality are answers to problems concerning 3 dimensionality. And again, the same problem, as I see it, applies to time. Is time infinite, or is time finite? I am not trained in these things. I will not rule out that answers are known, concerning these questions, by those more knowledgeable than myself. But I have not seen any that seem realistic. That is all I'm saying. I know I'm repeating myself. Sorry. Bus stop (talk) 16:44, 21 June 2009 (UTC)

It's not a non-answering. It's a means to try to explain a tricky concept by analogy. I don't, personally, have a problem imagining the 3D version of an infinite of a finite-but-wrapped-around universe. But you are kinda stuck with the word "universe" meaning "absolutely everything" - so if there is an "edge" and something "beyond the edge" then it's a part of the universe by definition. If you want to talk about something smaller than everything (like a galaxy or a galactic cluster) then we can - but if we're talking about "everything" then you can't go around asking "what's beyond the edge of everything" - because whatever that is would be a part of everything. Hence, if we are discussing "the shape of absolutely everything" - we have to start to accept infinities and wrapping-around-ness. SteveBaker (talk) 21:03, 21 June 2009 (UTC)

So, you are saying the universe is infinite? And you are saying that we have different understandings of what infinite means? And that "wrapping-around-ness" is an aspect of your understanding of an infinite universe? Bus stop (talk) 22:01, 21 June 2009 (UTC)

I'm pretty sure that was a typo on Steve's part - he means "infinite or a finite-but-wrapped-around universe". As far as I'm aware, modern science hasn't been able to determine which of those options is the correct one (I think we have some lower bounds on the size of the universe, but that's all). --Tango (talk) 22:05, 21 June 2009 (UTC)

What is the scientific definition of "nothing" and in what form can it or has it been found? ~ R.T.G 15:25, 21 June 2009 (UTC)

I don't think there is one. There is vacuum, if that is any help. --Tango (talk) 15:46, 21 June 2009 (UTC)

The problem is that a vacuum is proving to be anything but nothing - quantum foam and virtual particles and the concept of false vacuum. There are a lot of interesting things going on in this supposed nothingness. Also, even if vacuum somehow fitted your definition of nothingness - there is no such thing as a sizeable volume of hard vacuum - even in deep intergalactic space - there are measurable number of hydrogen and helium atoms. Worst still, even the hardest of hard vacuums still has photons and neutrinos and all manner of other exotic things flying through it - so do describe it as "nothing" is a tough sell. SteveBaker (talk) 21:03, 21 June 2009 (UTC)

(Intrinsic curvature has not yet been written.) ~ R.T.G 15:26, 21 June 2009 (UTC)

Try Curvature of Riemannian manifolds, then. It's rather technical, though. --Tango (talk) 15:46, 21 June 2009 (UTC)

To agree with you, Tango, I quote : "In mathematics, specifically differential geometry, the infinitesimal geometry of Riemannian manifolds with dimension at least 3 is too complicated..." :o~ R.T.G 15:49, 21 June 2009 (UTC)

RTG - please stop answering questions...you have no clue about the things you're talking about. Quoting that half-sentence out of context is EXCEEDINGLY misleading. SteveBaker (talk) 22:23, 21 June 2009 (UTC)

You can easily get into trouble talking about "nothing", as in the old syllogism "Nothing is better than eternal happiness; a ham sandwich is better than nothing; therefore a ham sandwich is better than eternal happiness." When you say the universe is "expanding into nothing", you may be making a similar error, treating "nothing" as a concept on the same footing as "empty space" or "green cheese". That will get you into trouble. If space does end, then it just means there's no more space beyond that point. If you ask what's beyond that point, you're implicitly imagining that there's space beyond that point that something could be in. What would happen at the edge? Well, there would be a set of two-dimensional physical laws governing the boundary. It's impossible to know what those laws would be without a better understanding of space than physicists have now, although we have some ideas from studying two-dimensional quantum systems theoretically and in the lab. (This turns out to be a surprisingly deep and interesting subject. Topological quantum computers are one example of new physics that exists only in two dimensions.) Or maybe the edge would be like a black hole event horizon, in which case you wouldn't necessarily need a separate set of laws. Either way, you have physics in space (called the "bulk"), and physics on the boundary, and that's all.

That said, the universe that we see could be expanding into a preexisting vacuum or preexisting cheese. Neither hypothesis seems very likely to me, but they are mathematical possibilities and they're consistent with what we observe. We simply don't know what's out there beyond the limited distance that we can see. -- BenRG (talk) 21:06, 21 June 2009 (UTC)

Pakistan

Does that country of pakistan have any indigeneous missile technology ???I heard it has stacked up the missiles thrown away by N.Korea and China!!! —Preceding unsigned comment added by 121.246.174.130 (talk) 14:48, 21 June 2009 (UTC)

Are you talking about nuclear missiles or missiles in general? Pakistan has had superior weapons technology to N. Korea for some time, I believe, so I doubt they are using N. Korean weapons. It is possible they have bough Chinese weapons, though. --Tango (talk) 14:58, 21 June 2009 (UTC)

This 1999 Unclassified CIA Report discusses Pakistan in particular. According to this report, Pakistan has a well-developed internal nuclear program but their missile infrastructure seems to be largely imported from China and North Korea. Specifically, the CIA claims that the North Korean Rodong-1 inspired (or is) the Pakistani Ghauri_(missile). From a cursory survey, it would seem that missile technology is imported while warhead technology is indigenous to Pakistan. Nimur (talk) 15:17, 21 June 2009 (UTC)

By the time of this 2003 report, Pakistan is no longer considered "developing" a program, and is classified as having a "well-established" program. Nimur (talk) 15:20, 21 June 2009 (UTC)

Well what about the war head technology???Is it superior to it's neighbour India??? —Preceding unsigned comment added by 121.246.174.130 (talk) 17:44, 21 June 2009 (UTC)

It's unclear, but the fact that they have been cooperating with the Chinese on their warhead development suggests that they possibly could be (as China is far more advanced from a nuclear standpoint than India). --98.217.14.211 (talk) 16:29, 22 June 2009 (UTC)

One notices that the anonymous OP refers asymetrically to "that country of pakistan" (not capitalised) and India (properly capitalised). Does the hearsay that N.Korea and China throw away missiles for another country to collect come from a credible source, perhaps overheard in a Calcutta bar ? Cuddlyable3 (talk) 19:20, 22 June 2009 (UTC)

Seems to be from Mumbai. NotAHen (talk) 22:41, 22 June 2009 (UTC)

With a wide range of interests. NotAHen (talk) 22:43, 22 June 2009 (UTC)

Race and brain size/characteristics.

This might be a bit controversial, but here it goes. I'm looking for information regarding correlations, or lack thereof, between race and brain size/characteristics. For example, do blacks have smaller brains than whites? If true, would that affect their intelligence? Is it true that the brains of whites and blacks are "wired" differently? Links such as this one would be helpful too. Thanks in advance, ― Ann _{( user | talk )} 15:25, 21 June 2009 (UTC)

File:Ele-brain.png

Human, dolphin and elephant brains up to scale

As a start, why don't you read about Intelligence and brain structure in normal individuals, and then you can develop a baseline for comparison? This is a really complicated issue, and it sounds like you want to boil it down to an "IQ vs. mass" plot, or a "race vs. brain size." This is too simplistic and will not possibly capture any meaningful scientific conclusion. Brain structure is very vaguely correlated to mental acuity. Race and ethnicity is only vaguely correlated to brain structure, if at all. Different definitions of "race" will skewer any sort of meaningful comparison studies. Nimur (talk) 15:48, 21 June 2009 (UTC)

See Race and intelligence. WP:WHAAOE! --Tango (talk) 15:56, 21 June 2009 (UTC)

We also have several other articles relating to this topic, including Neuroscience and intelligence, Brain size and intelligence, and Heritability of IQ. Before plunging too deeply into this topic, though, here is a question you should think about: suppose when you look up the data you find that black people have larger brains than white people. What conclusion would you draw? Looie496 (talk) 18:13, 21 June 2009 (UTC)

That you've got the "wrong answer" so your methodology must be flawed, of course! --Tango (talk) 18:26, 21 June 2009 (UTC)

...What to speak of elephants and dolphins.--Shantavira|^{feed me} 07:21, 22 June 2009 (UTC)

Though to be more clear nobody actually asserts it is just large size but large brain size relative to overall body mass. So elephants do better than some animals but are not nearly in league with humans. --98.217.14.211 (talk) 16:27, 22 June 2009 (UTC)

The conclusions that the OP seeks are much more than "a bit" controversial. Measuring comparative intelligence is fraught with controversies, such as what different IQ test results really mean, and whether it is even defensible to postulate black and white as different human races. It seems everyone has a vested interest here, for example I don't think I am alone in viewing favourably the idea that I belong to an excellent race with impressive intelligence. The OP must expect accusations of bias connected with any answers to the questions asked, that can be defended only by very conservative labelling of whatever evidence exists. Cuddlyable3 (talk) 19:08, 22 June 2009 (UTC)

Brain size/exercise

Can anyone correlate brain size to exercise? Bruce Lee (see Bruce_lee#Death) died of a swollen brain which various doctors said was caused by either trace amounts of cannabis or normal painkillers but the urban legend is that he trained so hard his brain swelled inside his head (the painkillers and cannabis were both disputed as causes of death). ~ R.T.G 16:05, 21 June 2009 (UTC)

Brain size is primarily determined by skull size, I think. What you want to look for is a correlation between intracranial pressure and exercise. --Tango (talk) 16:24, 21 June 2009 (UTC)

It's hard to do the experiments properly, damn ethics committees, if some people need to be sacrificed it would be for the greater good ;-) From Dance and health "A study in New York in 2003 has shown that cognitive activities like crosswords help ward off dementia but, except for ballroom dancing, most physical activities do not". It seems you need to use your brain to exercise it, raising weights in the gym won't make you any smarter. Dmcq (talk) 16:38, 21 June 2009 (UTC)

I had heard that physical exercise did increase your IQ, by increasing the blood flow through your brain. My non-scientific personal experience supports that idea. 78.146.242.171 (talk) 12:58, 22 June 2009 (UTC)

To my knowledge, there is no correlation between brain size and intelligence, so whether or not it makes you smarter doesn't answer the question. — DanielLC 17:09, 21 June 2009 (UTC)

I expect there is a correlation within humans between adult brain size and intelligence, if you do not exclude persons with Microcephaly. Also in animals and humans, other genetic causes or trauma can cause stunted brain size with diminished mental ability. Additionally, with extreme age or with many diseases or conditions, the brain often shrinks and mental ability decreases. Also across primate species, there is likely a correlation between brain size and intelligence [23]. "Encephalization" normalizes brain size compared to body size, and thus primates have about twice the relative brain size as other mammals [24]. Sternberg says the brain size, after adjusting for body size, is a measure of information processing ability and thus a measure of intelligence. Scholars debate how to normalize brain size versus body size to make a fair comparison. The relative brain size of higher primates, our ancestors as well as dead end higher primates, have shown higher encephalization over the past several million years [25] page 769. Only if you restrict the range to "normal adult humans" will the correlation disappear, as is usually the case when only the center part of an x-y distribution is used in a correlation calculation. Some research indicates that mental activity can decrease the loss of cognitive ability with age. So it is probably true that whatever "intelligence" is, it does not correlate with absolute brain size in normal humans. As for exercise affecting the structure of the brain, many animal studies have shown that experience and environmental richness affects the brain structure in terms of microscopic structure complexity, as well as cortical size [26] page 47. Edison (talk) 17:35, 21 June 2009 (UTC)

A "swollen brain" such as supposedly killed Bruce Lee is not caused by growth of the brain, but by a build-up of fluids as a result of damage. It happens for the same reason your skin or muscles swell when you get a bruise. There is some evidence that exercise or other types of experience can affect brain structure, making certain parts of the brain slightly larger, but that wouldn't come into play here. We have an article, brain fitness, that deals with some of these factors, but unfortunately it isn't a very good article at the moment. Looie496 (talk) 18:04, 21 June 2009 (UTC)

It's a bit unfair because Bruce Lees life was given to philosophy and to suggest that he stretched his physique more than his mind is unfair at least. Could you fault a man if he stretched that muscle? Well its fair due to say that. ~ R.T.G 12:47, 22 June 2009 (UTC)

Low doses of radiation protecting against cancer?

I have read people saying that low doses of radiation provides a measure of protection against cancer. Is that the case? Unomi (talk) 17:40, 21 June 2009 (UTC)

See radiation hormesis. -- BenRG (talk) 17:50, 21 June 2009 (UTC)

We do not give medical advice. But taking the question as just a request for referenced information, a recent publication from the National Research Council (US) says (p 89[27]) that "low dose radiation acts primarily as a tumor-initiating agent." It says there is no expectation of a low dose threshold below which it does not initiate tumors. On page 10 they conclude that there is a linear relationship between radiation dose and cancer risk down to the lowest doses, with no threshold below which the added risk is zero. Edison (talk) 17:59, 21 June 2009 (UTC)

Thank you, it was not meant as soliciting medical advice, merely a query regarding a statement here: http://news.bbc.co.uk/2/hi/health/3554422.stm that I found 'curious'. I found http://www.radscihealth.org/rsh/Papers/FrenchAcadsFinal07_04_05.pdf to be pretty interesting reading regarding their opinion on low levels of radiation. Unomi (talk) 20:10, 21 June 2009 (UTC)

I think that that paper quoted by Edison doesn't really reflect the best understanding about the action of low radiation doses. This[28] paper, for instance, shows a different point of view. Figure 3 suggests that doses as high as 10000 mGy/year may be considered be considered beneficial. Dauto (talk) 21:47, 21 June 2009 (UTC)

I tend to agree with the paper that Dauto linked. The Linear-No-Threshold model seems almost unscientific; I'm not sure if I believe in a benefit of low-doses, but extrapolation of risk by linear model to low-dose seems sloppy in the absence of strong data. Nimur (talk) 23:14, 21 June 2009 (UTC)

It reads as though the posited mechanism of hormesis is by causing enough damage to encourage apoptosis and/or stimulating DNA self repair mechanisms? Also, for general purposes is 1 sievert equivalent to 1 gray for EM radiation ?

no, a sivert is not a unit of EM radiation... its a unit of biological damange... 1 sv = 1 J/kg = 100 Rem... 1 Gray = 100 Rads... a dosage in rems = dosage in rads * QF... the QF depends on the type of radiation (Gamma, Beta, Alpha)... for gamma QF = 1, but alpha has a higher linear energy transfer and QF = 20... 70.71.22.45 (talk) 00:54, 22 June 2009 (UTC)

Ok, but from Sievert it says (as far as I can tell) Sv * Q * N = gray and that a 'human' has an N of 1 and that EMR has a Q of 1, is that a correct interpretation? Unomi (talk) 01:35, 22 June 2009 (UTC)

There are huge differences between saying "low level radiation is tolerable", "low level radiation may be good for you" AND ""Low levels of radiation are probably essential for life itself." The BBC reports Professor Zbigniew Jaworowski stating the latter. Without evidence that sounds like the unscientific adage "The blow that doesn't break my back makes it stronger." I suspect the BBC may have misunderstood the professor if he actually meant that some level of radiation was historically essential to the evolution of life. Cuddlyable3 (talk) 18:18, 22 June 2009 (UTC)

Phone sound

Why is sound quality from phone speakers so poor compared to anything else I've ever heard? Vimescarrot (talk) 19:05, 21 June 2009 (UTC)

Probably for several reasons. First, they are commodity devices and are designed to reduce cost before all other requirements. Next, the telephone system (whether it is POTS or a modern digital wireless system) does not even use high fidelity signal - it is usually found that about 1.5kHz to 3 kHz is sufficient to understand voice and conversations with minimal distortion. So, because the sound played over the speaker is rarely "hi-fi", there is no reason to use a hi-fi speaker. The form-factor of a telephone makes it difficult to have a nice resonant cavity, so the result is a poor signal, poor transducer, and poor acoustic properties - cumulatively, a less than top-notch audio quality. Nimur (talk) 20:02, 21 June 2009 (UTC)

And the reason none of these systems is improved is because of cost? Vimescarrot (talk) 20:12, 21 June 2009 (UTC)

Yeah, pretty much. However, that's a fairly trivial conclusion. Most anything could be further improved if you were willing to spend more for it. — Lomn 20:26, 21 June 2009 (UTC)

Most people who are using their phones as music players are using headphones - it would be hard to justify the size/power/cost of a decent speaker in a phone. SteveBaker (talk) 20:38, 21 June 2009 (UTC)

Just in case you were thinking otherwise, I was specifically thinking of conversation, not music. Vimescarrot (talk) 21:05, 21 June 2009 (UTC)

Well, as others have pointed out, speech is quite comprehensible with just a few kHz of bandwidth. Providing better speakers would help very little because the data simply isn't there. The higher frequencies are chopped off by the microphone - then by any line filtering, then again by the telephone exchange...voice transmitted via phone would sound pretty much like it does even if you had really high quality reproduction. SteveBaker (talk) 22:06, 21 June 2009 (UTC)

Because the frequency range is limited I sometimes find it hard to understand people with accent I am not used to, but understand them much better on VOIP (e.g. Skype). My guess is that VOIP supports a wider range of frequencies. NotAHen (talk) 22:39, 22 June 2009 (UTC)

They could send the signal encoded in MP3 and fit a relatively power-hungry speaker but the batteries wouldn't last very long. My own phone is roughly twice the size of most ordinary phones and yet, the one I had ten years ago was roughly 3 times the size again but the battery size is only about one quarter or less even though it lasts much longer. The Sony Walkman is probably the first well known example of the miniaturisation craze but certainly, your computer is as powerful as one that would have filled a whole building half a century ago. ~ R.T.G 13:01, 22 June 2009 (UTC)

Landlines wouldn't have to worry about power consumption so much, would they? Vimescarrot (talk) 13:16, 22 June 2009 (UTC)

Sure they would. Imagine a million phone calls per day on a companys lines. Power would be one of the main factors in cost and as folks are saying, even a top class speaker system (which you can hook up to your phone) would only recieve a certain quality of signal. (you could hook up as decent a signal as you like over the internet if that is what you are looking for) ~ R.T.G 13:38, 22 June 2009 (UTC)

No - I used to design telephone exchanges - the land lines don't consume much power. The reason relates to bandwidth - and compatability with a trillion phones out there. You can't use MP3 encoding because it's a compressed format - you'd end up with a second or more of latency between speaker and listener. The computer inside a cellphone is considerably more powerful than even the largest computer from 1959. The IBM 7080, for example - released in 1960 - only had 160kbytes of RAM. SteveBaker (talk) 16:52, 22 June 2009 (UTC)

The primary goal of telephone design is intelligibility. Good intelligibility is obtained by restricting the sound bandwidth to, say, 300 - 3200 Hz. However minimal distortion is not necessarily a goal. It is common in avionic and amateur radio communication to limit (clip) the voice waveform. This is a deliberate distortion that actually improves voice intelligibility especially over background noise. It is also a crude way of reducing the dynamic range of the voice signal amplitude that varies with different speakers and mouth-to-microphone distances.

Modern mobile telephones use a variety of voice digitising methods, such as the CELP coding used in GSM networks, that provide data compression while introducing acceptably small delay for natural conversation. MP3 encoding is popular for music i.e. wide bandwidth sound at relatively high data rate; however it uses a masking algorithm that gives poor results for voice bandwith at low data rate, as well as the long latency that SteveBaker mentioned. Cuddlyable3 (talk) 17:56, 22 June 2009 (UTC)

And finally; is sound quality for conversations in phones likely to improve in the future? Vimescarrot (talk) 18:03, 22 June 2009 (UTC)

The technology to improve telephone conversation sound fidelity could be used tomorrow but there is little motivation to make that happen. Most telephony is mobile these days. Mobile networks represent large investments in particular data- and sound bandwidths and codecs while the telephones themselves are overweighted with the features that users are willing to pay for. Examples of these features are music storage, inbuilt camera, GPS, SMS, handheld computing, e-mail, Internet access... But hi-fi voice is not on the investment horizon. Cuddlyable3 (talk) 18:31, 22 June 2009 (UTC)

Bacteria-based stain remover

This product and others like it say that they use "nonpathogenic bacteria" and "natural enzymes" to destroy stains and odors. I notice the ingredients list also includes isopropyl alcohol, though, which I'd think would kill all the bacteria. Does anyone know how this solution works? What bacteria are being used to magically destroy the sources of the bad odors? Tempshill (talk) 20:25, 21 June 2009 (UTC)

It probably works the same way as any biological detergent does. Detergents contain enzymes, not live cultures. However, there are bacteria that help remove odors, too. A freshwater aquarium nitrogen cycle is a good example. --Dr Dima (talk) 21:27, 21 June 2009 (UTC)

Oh, and regarding your question on isopropyl alcohol, it really depends on concentration and on duration of contact which bacteria are killed and which survive. --Dr Dima (talk) 21:33, 21 June 2009 (UTC)

June 22

Binary stars orbiting a planet

Would it be theoretically possible for a pair of binary stars to orbit a planet that sat between them? For that planet to be Earth-like? NeonMerlin 01:25, 22 June 2009 (UTC)

I don't think that would be stable. If the planet moved slightly towards one star it would accelerate towards it. There are several known stable solutions to the three-body problem, but I don't think that is one of them. It's very similar to L1, which isn't a stable equilibrium point. (It may be exactly like L1, I can't remember what the requirements for ratios of masses are...) --Tango (talk) 01:55, 22 June 2009 (UTC)

Something very close to what is being asked is possible. Although the L₁ Lagrangian point is nominally unstable, it’s possible to find stable periodic orbits around these points (called "halo" orbits), in the restricted three-body problem. Also, although the L₄ and L₅ Lagrangian points aren’t between the two stars, they are stable if the ratio of masses of the two stars is at least about 25, and would be reasonable good places for a planet to hang out without large variations in gravity or light. Red Act (talk) 02:12, 22 June 2009 (UTC)

According to [29], the answer is "sometimes" (specifically, 40% to 50% of observed binary systems). For the case of α Centauri, according to [30], the answer is yes. Someone42 (talk) 04:33, 22 June 2009 (UTC)

I don't believe that's the question being asked. Your links are about forming planets around one member of a binary pair. I believe the original question is whether a planet can exist at a stable point created by the combined gravity of both stars. Dragons flight (talk) 07:52, 22 June 2009 (UTC)

With a binary pair of stars - there must be stable lagrange points at which a planet could exist...in theory, it's a three body problem - and therefore, unstable - but providing the planet has negligable size compared to the stars, it's OK. But that's not quite what's being asked because the planet isn't "between" the two stars - it would be off to one side - and the stars aren't orbitting the planet. But given the right setup, I think the planet could possibly be somewhat earthlike. SteveBaker (talk) 15:21, 22 June 2009 (UTC)

If there is a big difference between the size of the stars (Red Act says above that the required ratio is at least 1:25, which rings a bell), then you could have the planet at L4 or L5 and there is no problem. If the stars are similar in size, which I think is what the OP is thinking of (although I may be wrong), then I'm not sure what stable solutions there are... I know of stable solutions for 3 similar sized bodies (there's a great one where they all follow a figure-of-eight), but not one for 2 similar sized large bodies and one small one. If there were a solution where the planet was just sat at the barycentre (which I think is what the OP is thinking of) then the planet could be Earth like, but it would be a little different due to constant daylight. If the planet rotated relative to the stars (which I actually suspect it wouldn't, I would expect it to be tidally locked) then you would get sunsets and sunrises, but there would be no night inbetween since when one sun sets the other rises. That would have some effect on the weather, but probably not anything that would completely rule out life as we know it. If it were tidally locked, then it is a little more difficult, but with the right kind of atmosphere the temperature variations wouldn't be too bad. --Tango (talk) 16:44, 22 June 2009 (UTC)

horsepower and cc

Is there any conversion factor between horsepower and cc of a motor car?? can these be relation in any such numerical figure?? or are these two different things?? —Preceding unsigned comment added by 119.153.21.132 (talk) 06:22, 22 June 2009 (UTC)

They are related, in that all other things being equal, a larger engine produces more power than a smaller one. However, many things are unequal, including bore, stroke, ignition, compression, fuel,... In general, modern engines with higher compression and direct injection get much more horsepower per volume of engine displacement than older, carburetor-based designs. --Stephan Schulz (talk) 06:53, 22 June 2009 (UTC)

There certainly isn't a direct conversion factor - there are too many clever ways of getting more HP from the same cc. To give you a concrete example: My wife's car (a MINI Cooper) has an identical engine (same cc's, same everything) as mine - but mine (A MINI Cooper'S) has a turbocharger, a free'er flowing exhaust system, and different settings on the engine management computer. I don't recall the exact numbers - but mine has about 50% more peak horsepower than hers. There is another version of the exact same car (the MINI One) that's sold only in Europe that's tuned for better fuel economy - it gets even less horsepower than my wife's car - and there are race-tuned versions that get 50% more horsepower than mine...so from the most extreme fuel-efficient version to the race-track version of the exact same car with the exact same engine - you get probably a 2:1 or maybe 3:1 difference in horsepower for the same number of cc's. SteveBaker (talk) 15:17, 22 June 2009 (UTC)

As Stephan and Steve said, there is no direct ratio of cc to hp. However, that doesn't stop people from measuring it. This guy, for example, has compiled an interesting table. It shows cc/hp ratios ranging from 1 (F1 engine) through about 12 to 15 for a production car, up to more than 40 for some unidentified industrial engines. I would be interested to know if there is a theoretical lower limit for this ratio. I guess it must be limited by the speed at which fuel can burn. --Heron (talk) 19:43, 22 June 2009 (UTC)

Is time finite or infinite?

Is time finite or infinite? Bus stop (talk) 07:41, 22 June 2009 (UTC)

The answer to your question isn't known. The solid consensus among scientists is that a Big Bang occurred, so time for sure has a finite beginning. However, there isn't a solid consensus regarding the ultimate fate of the universe. If it turns out that there will be a Big Crunch, then time also has a finite ending, so time is finite. But if there is a Big Freeze, then time will continue indefinitely, and time will be infinite. Red Act (talk) 08:06, 22 June 2009 (UTC)

I'm going to hedge my statement even further. There actually isn’t even a complete consensus as to whether the Big Bang marks the beginning of time. Although I don’t think the idea is widely favored, one possibility under consideration by some cosmologists is that the Big Bang was actually a Big Bounce. Red Act (talk) 08:15, 22 June 2009 (UTC)

I think a big crunch has been pretty much ruled out now. That would require the expansion to be slowly fairly quickly, it is actually measured to be speeding up. --Tango (talk) 14:40, 22 June 2009 (UTC)

Just to confuse things still further it may not even be 1 dimensional at the smallest scales though that's getting very speculative. See Spacetime and Multiple time dimensions. Dmcq (talk) 11:53, 22 June 2009 (UTC)

I agree with everything that's been said already - but I'd say that on balance, the smart money is on time having a finite beginning at the moment of the big bang - and no ending (ie it's infinite) - although when the overall entropy of the universe gets small enough, nothing will be "happening" so it would be hard to measure the progress of time. But there are other possibilities that have not yet been entirely discounted. 15:10, 22 June 2009 (UTC)

Don't you mean when entropy (absence of ability to complete work) gets large enough? Or am I missing something? —Anonymous Dissident^Talk 15:18, 22 June 2009 (UTC)

Actually, I'd suggest that many physicists believe that some form of time and space existed before the Bang, but that our theories and experiments are simply inadequate to understand what came before the apparent singularity. Quantum gravity, whatever form that ultimately takes, will almost certainly eliminate true singularities and create a path to considering space-time before the Bang (though that space-time may be structurally very different than our present reality). Dragons flight (talk) 16:01, 22 June 2009 (UTC)

I think most physicists consider "what happened before the big bang" to be an unscientific question since it is impossible for us to know. The big bang wipes the universe clean, so to speak, so there is no information left from that time for us to observe. If we can't observe something then, from the point of view of science, it doesn't exist. --Tango (talk) 16:48, 22 June 2009 (UTC)

There is a difference between an unanswered question and an unscientific question. No one has evidence of extraterrestrial life, and yet there are many theories for what could exist out there based on our understanding of chemistry and terrestrial life, and someday those theories may be tested. Similarly, there are theories (e.g. Big Bounce, brane collisions, "true" vacuum) for what might have come before the Big Bang. We don't know how to test those ideas today, but that doesn't mean that they will never be tested. For example, most quantum gravity proposals lead necessarily to the conclusion that there was a "before the Bang". If we ever validate one of those proposals as likely correct for the modern universe, then it would be indirect evidence of what the universe may have been like before the Big Bang. Nor is it necessarily true that the Big Bang wipes the universe clean. In the speculative brane collision cosmologies, there could be remnants of before the Bang imprinted on the distribution of dark matter. (That no one has found evidence of this doesn't make it uninteresting to look.) As a physicist, I would suggest that most other physicists see it as a largely intractable question, but not an intrinsically unscientific one. Dragons flight (talk) 17:24, 22 June 2009 (UTC)

Inverted vertical tube manometer

Why the pressures within an inverted vertical tube manometer is being substracted..? —Preceding unsigned comment added by Sreekanth awh (talk • contribs) 08:26, 22 June 2009 (UTC)

Beam of light

Is there an angle that you could cast light at (in a beam) where the circle iluminated would appear the same size at all distances? Say if you shon it at a wall a foot away from you and held a ruler a couple of inches away from your eye the circle of light would appear 4" wide, and it would also appear that if you stood 10 feet away from the wall, due to perspective. Gunrun (talk) 08:43, 22 June 2009 (UTC)

I would think so. The apparent radius of a circle goes like 1/d with d the distance between you and the circle. The actual radius of the illuminated circle is proportional to d. You might want to have a look at http://en.wikipedia.org/wiki/Gaussian_beam

You'd need a "collimation" lens or mirror which makes the incoming light exit in a parallel beam. SteveBaker (talk) 15:06, 22 June 2009 (UTC)

Help with project

My friends and i are trying to do a project in the summer, which would keep us engaged, and at the same time learn something new. We are all first year undergraduate students. The basic idea is this: You have a (computer) mouse which eats light, that is, goes to the brightest area it can. It can do cool things like following the light from a torch, etc. In addition, whenever it collides with an obstacle, it veers back a couple of meters and then zooms off in some other direction. It isn't wired. This is to be done with basic electronics. We are following this book, and you can find the circuit diagram and other details in the link. But the thing is, we are facing multiple problems, and in need of help. The first problem is the IR emitter thingy. The book says the IR emitters (removed from an old mouse) will sense the incoming light, and hence act like the "eyes" of the mouse. It has given clear instructions on how to desolder the emitters and all. My question is, how can IR emitters possibly detect light? Shouldn't you use detectors? This can't be a printing mistake, he's used it several times. Then comes another problem. According to his illustrations, his emitters have 2 terminals, whereas our emitters have 3. What do we do? Worse, our detectors have four! Are there various types of emitters/detectors used in a mouse pcb,and are we stuck with a different kind? If that is the case, would the correct IR emitters/detectors be available in any electronics shop (The major electronics hub in the city is quite some distance away)? I think we are seriously in need of help... Rkr1991 (talk) 09:13, 22 June 2009 (UTC)

You really want to talk with some robot building enthusiasts, there's lots of them around on the web and they're very happy to help with newcomers. You might even find a club nearby if you're lucky. Just google for things like robots builders enthusiasts. Dmcq (talk) 12:13, 22 June 2009 (UTC)

It would be nice if someone could give me a direct link of one such site that's really good... Rkr1991 (talk) 13:07, 22 June 2009 (UTC)

I guess from what you are saying that your university does not have a robotics course or club, that would be best but you can always found one. You really do need to get to grips with searching the web, for instance you have to look at electronics catalogues like Maplin if you are going to strip things down and use the bits. Did you try a google and look at the top few entries for clubs? Wikipedia has articles on robotics from Portal:Robotics but it tends to be more institutional stuff rather than how-to and friendly. You have to suck it and see and sometimes just put the blue smoke down to a learning experience. Dmcq (talk) 14:14, 22 June 2009 (UTC)

Well, there are two kinds of mice:

1. Mechanical (the kind with a ball underneath)
2. Optical (the kind with LED's underneath)

• The mechanical kind do have light sensors in them - but they'd be hard to use. If you pull the mouse apart, you'll see that the ball rolls against a pair of rollers - and if you dismantle the mouse enough - you'll see that each roller connects to a slotted disk that sits inside a U-shaped black box. That box has an LED light and a light sensor - one on each side of the disk that count the number of times the disk interrupts the light beam. But to use the light sensor in your application, you'd have to somehow get it out of the black plastic enclosure without damaging it. Maybe you can do that - but it's not something I've ever tried.
• The optical kind uses a camera that looks down at your desktop and watches it slide past - measuring the speed that it moves. This is a very low-resolution camera (I vaguely recall it's a monochrome 64x64 pixel gizmo) - and the lens it looks through is focussed to produce a sharp image at a distance roughly equal to the thickness of the little rubber feet on the mouse! So you aren't going to be taking any photo's with it! However, technically - I guess you could remove the lens and let it see an amazingly blurry view of the world - which would certainly give you an overall idea of the light level. However, interfacing to the camera might take some fancy electronics...and I don't know how fancy you want to get!

I've built a robot just like you're describing - but I cheated and used Lego Technics - which lets you build such a thing in about an hour - and get the software working in a couple of hours. It can certainly be done. My son and I actually built two of them - put IR LED's on the top of each one and programmed them to play "Tag" - one robot is programmed to seek light and the other to avoid it - they each have a 'skirt' with microswitches as a 'bump' sensor - when one robot hits the other, it changes from seeking light to avoiding it and vice versa. The one that's set to seek light doesn't start moving for 10 seconds in order to give the other one time to escape - and (theoretically) they change sides. It's actually a little bit more complicated than that - they send each other messages via IR to be sure it was a legal "Tag" and not a collision with the wall or something. Anyway - it's hilarious to watch - and an interesting programming challenge to have two people each program their own bot and run it as a competition. SteveBaker (talk) 15:04, 22 June 2009 (UTC)

By the way my favourite book on this sort of thing is Hardware Hacking Projects for Geeks by Scott Fullam. Rather self identifies I guess :) With projects like for instance how to hack a furby (rather a difficult one that). or turn yourself into a Borg. Dmcq (talk) 21:04, 22 June 2009 (UTC)

Wisdom Tooth Extraction After effects

This question has been removed. Per the reference desk guidelines, the reference desk is not an appropriate place to request medical, legal or other professional advice, including any kind of medical diagnosis, prognosis, or treatment recommendations. For such advice, please see a qualified professional. If you don't believe this is such a request, please explain what you meant to ask, either here or on the Reference Desk's talk page. Algebraist 09:47, 22 June 2009 (UTC)

This question has been removed. Per the reference desk guidelines, the reference desk is not an appropriate place to request medical, legal or other professional advice, including any kind of medical diagnosis or prognosis, or treatment recommendations. For such advice, please see a qualified professional. If you don't believe this is such a request, please explain what you meant to ask, either here or on the Reference Desk's talk page. Algebraist 09:47, 22 June 2009 (UTC)--~~~~

Reaching the lowest possible temperature

How can we reach the lowest possible temperature? If something is 0 C, I can put something -5C and cool it a little. But since the absolute zero temperature does not exist, how can be cool something until the lowest existent temperature, there is nothing cooler than it...--Mr.K. (talk) 09:56, 22 June 2009 (UTC)

Bringing an object in contact with a cooler object is not the only way of cooling it. see for example http://en.wikipedia.org/wiki/Laser_cooling

Or even have a look at fridge, have you wondered how that works? Dmcq (talk) 12:25, 22 June 2009 (UTC)

For all that though, an object reaching absolute zero is not possible, because the laws of thermodynamics will insist that some energy enter your sample, which will raise the temperature above 0K. You would need a way to perfectly isolate your sample, and that is not possible. How close you get to 0K will depend on that factor. 65.121.141.34 (talk) 14:01, 22 June 2009 (UTC)

Although we have got remarkably close to it; see absolute zero.--Shantavira|^{feed me} 15:28, 22 June 2009 (UTC)

Even more remarkably, using the technical definition of temperature given by statistical thermodynamics, it is actually possible to have objects with negative absolute temperatures -- and such things have even been created in the laboratory. The way it works out, though, is that negative temperatures are hotter than infinity, and such a system will always lose heat to any system at a positive temperature that it is in thermal contact with. It remains true that no system can be at perfect absolute zero -- systems at negative temperatures cool by dropping to negative infinity and then dropping from positive infinity. Looie496 (talk) 16:58, 22 June 2009 (UTC)

Telescope on the moon

OK, forgive my lack of comprehension of science. As I understand it, because light moves extremely fast, but not infinitely quickly, whatever you see took place a fraction before you actually noticed it. And furthermore, the further away the incident is, logically, the longer ago the incident took place. So I wondered, (Q1) what happened if someone had an improbably powerful telescope and was on the moon, looking at Earth. How long ago would whatever he saw actually have taken place?

Q2 What about if the person with the telescope was even further away, say in some high-tech capsule that allowed him to survive and also get a good view from Alpha Centauri?

Q3 How far away would you need to be to see, say, the Romans invading Britain?

If there's a flaw in my logic, please point it out. --Dweller (talk) 10:13, 22 June 2009 (UTC)

The moon is about one light-second away, so an observer sitting there "now" (scare quoted because that doesn't quite make sense: see relativity of simultaneity) would see events on Earth that took place about a second ago. Similarly, Alpha Centauri is about four and a half light-years away, so an observer there would see events four and a half years ago. To see the Romans invading Britain, you'd have to be about two thousand light-years away (more or less depending on which invasion you want), perhaps somewhere near NGC 6826. Algebraist 10:20, 22 June 2009 (UTC)

Thanks for that (and that's a very pretty picture in your link). Is there some kind of 2D map of [our bit of?] the universe that I can look at that'd show me where we're talking about, to contextualise with other objects even I might have heard of? And, if I might throw yet another question, can I assume that an object c.2,000 light years away is about 500 times further away than something about 4 light years away, or is it some kind of non-linear scale? I'd assume it is, but one thing I've learned is not to make too many assumptions in ignorance. --Dweller (talk) 10:39, 22 June 2009 (UTC)

As the article states, 'light-year' is just a fancy (and shorter) way of saying '9,460,730,472,580.8km', so it's a perfectly linear scale (up to the usual quibbles involving relativity). The best map of the universe I know is this (but note that it is not linearly scaled). I can't find a decent linearly-scaled map of nearby space at present. Algebraist 10:50, 22 June 2009 (UTC)

Interesting, thanks. I can't really understand the map properly (I get that it's a log scale) - why is it rendered as a column, not (as I expected) a square? Presumably, the real universe is roughly spherical from whatever its central point is... so I expected a 2D rendering to resemble the 2D renderings we do of Earth. --Dweller (talk) 11:17, 22 June 2009 (UTC)

I think it's that shape largely so it makes a good wallchart, though the paper may contain other reasons (I read it a while ago and can't remember). The question of the Shape of the Universe is a complicated one on which I am not competent to pronounce. Algebraist 11:43, 22 June 2009 (UTC)

Maps of the Earth's surface usually only attempt to show the two dimensions of longitude and latitude. Drawing a map of the universe presents the challenge of presenting the three dimension of right ascension, declination (the astronomical equivalents of longitude and latitude) and radial distance in a two-dimensional format. The solution adopted in the case of the "column" map is to simply throw away one dimension - it does not attempt to represent declination. The vertical axis is, as you say, a logarithmic distance scale and the horizontal axis is right ascension (there is a further simplification for objects within the solar system which do not have a constant right ascension - they are placed at an arbitrary horizontal co-ordinate a horizontal co-ordinate that corresponds to their right ascension at a specific date and time). So, for example, the Andromeda Galaxy (M31) is shown almost directly above the Small Magellanic Cloud (SMC) because they have similar right ascensions, even though their declinations are very different - the SMC at a declination of -72^o is a southern sky object, whereas M31, at a declination of 41^o, is a northern sky object. To see how the universe is mapped onto the rectangular column, imagine that all the objects shown are projected onto a disc around the celestial equator centered on the Earth; cut a small hole in the middle of the disc and make another cut from this hole out to the edge of the disc; then fold the sides of the cut disc together (like closing a fan), until you have the column shown. Gandalf61 (talk) 12:06, 22 June 2009 (UTC)

They're not shown at arbitrary right ascension, they're shown as they were at 0448 UT on the 12th of August 2003. Algebraist 12:17, 22 June 2009 (UTC)

Ah, yes - thank you - fixed in my post above. Gandalf61 (talk) 12:28, 22 June 2009 (UTC)

The galaxies from the Sloan Digital Sky Survey are actually close to the equatorial plane, so the top part of the diagram is a slice rather than a projection. As for why it's a column instead of a disc: if you just plot a scale model of the equatorial plane then a lot of small-scale structure is invisible because each pixel of the image is millions of light years across. If you logarithmically scale the radial distance then you can fit in small-scale and large-scale structure, but shapes are distorted. To avoid distorting shapes you have to rescale the angular direction also, and it turns out the rescaling that's needed is to make it a fixed width at all distances. This is familiar as the fact that the complex logarithm (which is conformal, i.e. "shape-preserving") repeats at a fixed interval of 2π in the imaginary direction. The mapping they used is actually the complex logarithm with the imaginary part plotted horizontally. The authors compare it to this famous New Yorker cover. -- BenRG (talk) 13:57, 22 June 2009 (UTC)

It's probably impossible to see the romans invade britain now though, unless you're at the planet already, because to get there to see it you'd have to travel faster than than the speed of light. The invasion of the romans is moving away from our planet at light speed! Gunrun (talk) 10:46, 22 June 2009 (UTC)

Yes, I got that. If you could travel faster than light, I suppose you wouldn't need to travel to NGC 6826, you could just go to Kent! --Dweller (talk) 11:14, 22 June 2009 (UTC)

Assuming the age of Earth to be 5 billion years, at what distance in the universe would one have to be to see Earth being "born," and is there enough distance in the universe to get far enough away from the Earth to get this view, or is the universe just too small for this? And if the universe is too small to find a sufficiently distant vantage point from which to see the Earth being born, where does the light go to when it runs out of "universe" in which to travel? In fact, if I can ask one more question, where in general does light go when it reaches the outer limits of the universe? 12:07, 22 June 2009 (UTC)

Now we're into large enough scales that general relativity becomes unavoidable. To be looking at an event here 5Gyears ago, an observer would have to be five billion light years away in terms of light travel distance, but not in terms of more commonly used measures such as comoving distance or cosmological proper distance. See Distance measures (cosmology) for a discussion. Light does not reach the outer limits of the universe, because no such limits exist. Algebraist 12:13, 22 June 2009 (UTC)

You'd also need a pretty big telescope to see these things. To see the Romans invade Britain at 25 frames per second and be able to see individual Romans, the width of the mirror would have to be um well I haven't worked it out but I'd guess quite a bit bigger than the earth. Dmcq (talk) 12:34, 22 June 2009 (UTC)

We need Stephen Hawking here. Is Stephen Hawking in the house? Bus stop (talk) 12:37, 22 June 2009 (UTC)

A back-of-an-envelope calculation, ignoring all possible technicalities, suggests we're talking about an optical telescope about the size of the orbit of Pluto. Algebraist 12:40, 22 June 2009 (UTC)

Perhaps rather than one stationary large mirror we could have a series of smaller, rapidly moving mirrors that gather up light in the course of their journeys, interpolating data at convenient intervals. Bus stop (talk) 12:52, 22 June 2009 (UTC)

The light that reached that galaxy would also be a different shape, right? They'd have to decode it in some complicated way as well, right? ~ R.T.G 13:14, 22 June 2009 (UTC)

Chaps, you sound like a group of ancient scientists laughing about how many horses you'd need to tether together to get an object to move fast enough to fly. Any technology good enough to be able to get a clear view from the surface of a star is probably capable of making a telescope that doesn't depend on massive mirrors. --Dweller (talk) 13:20, 22 June 2009 (UTC)

Well, yes, but that wouldn't be nearly as much fun. Algebraist 13:51, 22 June 2009 (UTC)

That's big. But it is an opportunity. Any sufficiently advanced civilization then that was interested in what was going on round them would build telescopes the size of the orbit of Pluto. It must be possible to spot one of those I'd have thought :) Dmcq (talk) 13:48, 22 June 2009 (UTC)

One way to avoid improbably large lenses and/or mirrors would be to use gravitational lensing. Since gravity bends light - if you position your camera on the opposite side of (say) some suitably gigantic black hole - then you can use it as a lens. Of course you've just exchanged the problem of building a lens the size of the orbit of pluto for the inconvenience of having to fly your camera out to the right place (which might take a few thousand years) - and wait another few thousand for the photos to get back...but it would certainly be cheaper if you're not in a hurry. SteveBaker (talk) 14:47, 22 June 2009 (UTC)

Even cheaper if you don't pay for one hour processing. NotAHen (talk) 22:35, 22 June 2009 (UTC)

re a map of the universe, it seems mandatory that this should be linked from here. Jørgen (talk) 15:38, 22 June 2009 (UTC)

Apparent contradiction?

According to the article on Thymine, the molecular formula of this nucleoside is C₅H₆N₂O₂. However, in the image to the right I can only see two hydrogens and no carbons at all. Where are the four missing hydrogens and the five missing carbons? --83.34.187.22 (talk) 12:00, 22 June 2009 (UTC)

See skeletal formula. Algebraist 12:04, 22 June 2009 (UTC)

Rain in the East Coast, USA

Is there a scientific reason why the East Coast is getting so much rain in the past few weeks? --Reticuli88 (talk) 13:23, 22 June 2009 (UTC)

Farthest blue-shifted object?

Large-scale movement of the universe is dominated by the metric expansion of space, making further objects recede faster. But what is the farthest object that does actually travel towards us? More generally, what it the object with the largest difference between expected and observed red shift (either way)? --Stephan Schulz (talk) 14:59, 22 June 2009 (UTC)

I don't think anything outside the Virgo Supercluster (or Local Supercluster) is blue-shifted. If it is, then it's just a fluke. According to our article on the Virgo Cluster (which is the largest cluster in the local supercluster), its gravity only slows our recession from it by 10%, so nowhere near enough for us to be moving toward it. So I suspect the farthest blue-shifted galaxy will either be in the Local Group (in which there are plenty) or in a group very nearby in the Local Supercluster. --Tango (talk) 16:54, 22 June 2009 (UTC)

We have several blue-shifted galaxies listed in the M81 Group. I can't find any blue-shifted galaxies in other nearby groups, so I'm going to put my money on the furthest away one in that group, which I can't determine (the distances don't seem to be listed anywhere, maybe because they aren't known very precisely). --Tango (talk) 17:01, 22 June 2009 (UTC)

Colours of night sky objects?

Is there an online database that lists the apparent or observed colours of night sky objects to the human eye using some sort of scientific scale? For example, Mars and Betelgeuse are redder. I know Rigel is blue in absolute terms, but is it blue to the naked eye from a human perspective? I want a version of the Hertzsprung-Russell_diagram using observed data from the human eye on Earth rather than absolute data out there in space. --Sonjaaa (talk) 16:53, 22 June 2009 (UTC)

I saw something like this a while ago but I can't find it now. If you want to search around a little, try looking up the photography technique using long exposures and movement so that stars appear as smears which makes their apparent color much more noticeable than when they are just points. Sifaka ^talk 18:37, 22 June 2009 (UTC)

The Cambridge Star Atlas [31] classifies stars by their visual appearance and presents them in color right on the charts. Will Tirion also did Sky Atlas 2000.0 [32]. It's open to interpretation as different eyes respond differently to very low levels of light, but they're the best I know of. Acroterion _(talk) 21:19, 22 June 2009 (UTC)

Mold on mushrooms

I often make spaghetti with different kinds of spaghetti sauces, and it seems that the mushroom sauce gets mold much more often than the tomato-only sauce. I can't imagine why, since both are the same brand, bought in the same amounts, stored in the same type of jar in the same place in the same refrigerator; the only difference between the types is the presence of cooked chunks of mushrooms. Obviously the mushrooms and the mold are different species, so it's not as if the mushrooms are manifesting themselves as mold, but realistically is there any possibility that the mold grows more readily on the mushrooms themselves, and/or that the presence of the mushrooms makes the sauce a better host for mold? Nyttend (talk) 17:49, 22 June 2009 (UTC)

My guess would be that the acidity of the tomato sauce retards mold growth. The mushrooms floating at top might provide a low-acidity area for mold growth to start. It could also be that the recipes are different regarding the sauce itself, for example one saltier than the other. Or, well, who knows? Looie496 (talk) 18:07, 22 June 2009 (UTC)

(Post e.c.)There are quite a few fungal species that specifically parasitize other fungi including mushrooms, the genera of which are escaping my memory right now; however, I strongly doubt that those are the fuzzy culprits in this case. Most likely what is infesting your sauce is similar to what infests your fruit, bread, cheese, or other items. My intuition is that your mushroom sauce has a more favorable environment for growth. The process of preparation or different ingredients may change the pH or solute concentration of the sauce to a more favorable range for instance or if it includes cooking may deactivate some of the natural preservative compounds in the tomato sauce. It could also very well be that mushrooms may be a good host for mold the same way that certain items tend to fuzz over before others do. Hope this helps. Sifaka ^talk 18:26, 22 June 2009 (UTC)

I can confirm that the mold on the mushroom sauce looks the same as the mold on the non-mushroom sauce. What I meant by "cooking" was the preparation that Hunt's puts into before I buy it — between opening the can and actually preparing the pasta, the only thing I do with the sauce it putting it into the jar. Nyttend (talk) 21:16, 22 June 2009 (UTC)

chicken eggs

Are chicken eggs sterile (free of bacteria) before the shell is opened? 65.121.141.34 (talk) 18:31, 22 June 2009 (UTC)

There are bacteria all over the surface of the shell which are there before the egg is opened. According to Egg (food)#Contamination, if the egg is laid by a healthy chicken then yes they are sterile inside, but according to this source, some very few eggs do have bacteria in the interior. Sifaka ^talk 18:48, 22 June 2009 (UTC)

Oops accidentally posted here.. removed!--87.113.12.133 (talk) 20:00, 22 June 2009 (UTC)

I see, the article says that about 1/30,000 chicken eggs in the US is contaminated with salmonella. Now I can accept the risk of eating raw cookie dough (homemade, not sold in the store, because who know how many eggs are in 1 batch). 65.121.141.34 (talk) 20:09, 22 June 2009 (UTC)

Eradicated bacteria on a space station

If we were to create a substantial population in a space station (something like Babylon 5) and ensured that the construction and all people sent there were free of all bacteria/viruses would it remain sterile indefinitely or would the human flora be likely to eventually mutate into forms that cause illness? Thanks :-) --87.113.12.133 (talk) 19:58, 22 June 2009 (UTC)

Not quite addressing the original question here, but I would like to point out that the people who lived on such a space station long term, and eventually left would probably have the equivalent of a compromised immune system, and it would not be advisable for them to leave. 65.121.141.34 (talk) 20:06, 22 June 2009 (UTC)

Human gut flora already causes illness if it colonises places other than the gut. Always wash your hands - especially in space. 86.4.190.83 (talk) 20:48, 22 June 2009 (UTC)

star diameter

Do we know of any stars whose diameter is larger then the orbit Pluto would make (at maximum distance, assuming its eccentricity was 0.0000)? What would be the angle we would be able to see if it was at the distance of Alpha Centari (sp?)?65.121.141.34 (talk) 20:53, 22 June 2009 (UTC)

Guess: No. Too big. No star could be that big. (Just a guess.) Bus stop (talk) 20:57, 22 June 2009 (UTC)

Any star even remotely that big would have long since become a black hole. To be that big and not be a black hole, you'd have to have a density of less than 3 kilograms per cubic metre (about twice that of air), and I'm pretty sure you couldn't make a star with such low density. Algebraist 21:05, 22 June 2009 (UTC)

And for the easy part: an object that big at the distance of Alpha Centauri would have an angular size of about 1.25 arcminutes, twelve times smaller than the full moon. Algebraist 21:07, 22 June 2009 (UTC)

Interesting, I got 0.98', did you use Pluto's aphelion distance or something? --Tango (talk) 21:15, 22 June 2009 (UTC) No, I lost a factor of two, it's more like 0.49'. --Tango (talk) 21:18, 22 June 2009 (UTC)

I used the aphelion, as suggested by the OP's 'at maximum distance'. Pluto's aphelion is about 50AU, so the diameter is 100AU. Alpha Centuari is about 4.4 light years away, which according to Google is about 278255AU, so the angle is 100/278255 radians, which (according to Google again) is about one and a quarter arcminutes. Algebraist 21:23, 22 June 2009 (UTC)

I was right the first time, I actually lost two factors of two in different directions. The difference is simply because I used the semi-major axis. I didn't read the question carefully enough! --Tango (talk) 21:26, 22 June 2009 (UTC)

What were you doing with another factor of two anyway? Algebraist 21:28, 22 June 2009 (UTC)

I guess strictly speaking it was the same factor of two twice. I managed to get very confused about whether I was using the radius or diameter of Pluto's orbit. --Tango (talk) 21:38, 22 June 2009 (UTC)

(ec) I believe Antares is one of the largest stars we know of and its diameter is between those of the orbits of Mars and Jupiter, so quite a long way short of Pluto. I don't know if it is impossible for a star to be much bigger than that, but I would be surprised if any were a big as Pluto's orbit. Pluto's orbit at the distance of Alpha Centari would span just under 1 arcminute, if my calculations are correct. That's about the angular diameter of Venus when it is at its closest. I've just fixed an error, I get about half an arcminute. --Tango (talk) 21:15, 22 June 2009 (UTC)

We have List of largest known stars, of course. If the data is correct, VY Canis Majoris's diameter is twice that of Betelgeuse and four times that of Antares, and it would extend out to about the orbit of Saturn. Still a way to go to Pluto, though (and the more boring theory puts it at only 600 solar radii). --Stephan Schulz (talk) 21:34, 22 June 2009 (UTC)

I took a look at Pluto, Stellar classification, and List of largest known stars and found some cool stuff:

1. Star diameter is measured in solar radii (R_☉) (1 R_☉ = 69,550 km = 0.004652 AU)
2. Plutos orbit: 4,436,824,613 km (about 30 AU) at perihelion and 7,375,927,931 km (about 49 AU) at aphelion
3. A star would therefore have have to be 6,379 R_☉ to extend to the closest point to the sun in Pluto's orbit, and 10605 R_☉ to extend to its furthest.
4. The largest known star (though that size is disputed), is the hypergiant VY Canis Majoris, at between 1,800 R_☉ and 2,100 R_☉, not even close to the orbit of Pluto, but extending to somewhere around the orbit of Saturn.

Stuff I didn't know yesterday. Hope that helps! – ClockworkSoul 21:59, 22 June 2009 (UTC)

Small stars/planets

In reading about small stars (due to an earlier question here), I found this quote: "The relatively puny body weighed in at 96 times Jupiter's mass - above the threshold of 75 Jupiter-masses required for a bona fide star, which must also burn hydrogen." So, are there hydrogen-burning planets, considered planets simply because they are less than 75 Jupiter-masses? -- kainaw™ 22:19, 22 June 2009 (UTC)

Objects around the boundary between stars and planets are called brown dwarfs. There is no generally agreed upon definition of where to draw the line between planets and brown dwarfs and between brown dwarfs and stars. What elements they fuse is a key factor in most proposed definitions, but it doesn't seem to be quite that simple. --Tango (talk) 22:21, 22 June 2009 (UTC)

Also, once an object begins to fuse hydrogen, its radius expands from the outward pressure. Take a look at brown dwarf, in particular the sections "Distinguishing high mass brown dwarfs from low mass stars" and "Distinguishing low mass brown dwarfs from high mass planets". – ClockworkSoul 22:24, 22 June 2009 (UTC)

Thanks for that article, Kainaw. Bus stop (talk) 22:26, 22 June 2009 (UTC)

Talk:Liquid crystal display

There are accumulating unreplied remarks on that page and, of course, there is probably a bunch of you who could answer them. (is mainstream isn't it?) ~ R.T.G 22:32, 22 June 2009 (UTC)