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March 23

The Universe

1. The universe had a beginning as a tiny point which expanded in the Big Bang. This would seem to suggest to me that there the universe has a size, and therefor an edge. But the Universe article states that the "size of the Universe is unknown; it may be infinite." How could it have expanded from a dot the size of an atom to infinite?
2. If there is an edge to the universe, what would happen if you were in a spaceship traveling toward it?

46.7.249.24 (talk) 00:05, 23 March 2014 (UTC)

If it is infinite, then it would have always been infinite, that dot would have been the bit that expanded to the visible universe we now know. If you were in a space ship then the universe would include you and the spaceship too, so you would not be past the edge. To be beyond the edge, there should be no light or radiation of any form, so no cosmic microwave background, or any cosmic rays or gravitational waves. You would not be able to detect gravity from the part beyond the horizon. Graeme Bartlett (talk) 00:55, 23 March 2014 (UTC)

• No, the universe has no edge, just like you don't fall off the edge of the finite surface of the earth, just in higher dimensions. The Big Bang is posited to have begun with a singularity, not at a point. Our article shouldn't be making silly claims like that the universe may be infinite. That would mean no matter how big it actually is, it's actually bigger. μηδείς (talk) 00:57, 23 March 2014 (UTC)

What are you talking about, Medeis? It wouldn't mean any such thing. Infinite geometric structures may or may not correspond to physical reality, but there's nothing wrong with them logically; they have a perfectly coherent mathematical description. --Trovatore (talk) 05:21, 23 March 2014 (UTC)

Our reference desk editors shouldn't be making claims like that the universe definitely can not be infinite. 88.112.50.121 (talk) 01:38, 23 March 2014 (UTC)

And here I thought there were an infinite number of IP 54 troll addresses available? Perhaps You've not heard of Einstein? The Possibility of a “Finite” and Yet “Unbounded” Universe μηδείς (talk) 03:11, 23 March 2014 (UTC)

88.x is right: you shouldn't claim that the universe definitely can't be infinite. It may be infinite for all we know. He/she didn't object to the claim that it may be finite and unbounded, since for all we know it may be that too. -- BenRG (talk) 05:16, 23 March 2014 (UTC)

The possibility of a finite and unbounded universe does not imply that the universe is actually finite, or actually unbounded. There's simply no observational evidence to suggest that the universe is finite (or that it isn't), and no theoretical reason that it should be one way or the other. --Bowlhover (talk) 05:17, 23 March 2014 (UTC)

You folks are just being silly. If you can coherently define a non-self-contradictory "infinite" model of the universe, feel free both to present it explicitly and give what observational evidence that you have that supports the model. When you actually pay attention to what infinite means ("has no actual total size, stands in no definable mathematical relation to its parts") you find your claims are outside the realms of evidence, science, reason and logic. μηδείς (talk) 19:14, 23 March 2014 (UTC)

Medeis, sorry, that's not what "infinite" means, not at all. Take a baby example, the real line; that is, the set of all real numbers, considered as a geometric object. Do you claim that it "has no actual total size" or "stands in no definable mathematical relation to its parts"? Or do you claim it's finite? --Trovatore (talk) 22:22, 23 March 2014 (UTC)

Medeis is an ultrafinitist. Count Iblis (talk) 15:08, 25 March 2014 (UTC)

I sort of doubt that. Ultrafinitism is a specific form of reaction against the Cantor/Dedekind/Weierstrass/et-alia revolution. I see no indication that Medeis is taking any of those figures into account in the first place. --Trovatore (talk) 15:47, 25 March 2014 (UTC)

Numbers are abstractions, not physical objects. Numbers can in the imagination be extended potentially infinitely, but there is no actually existing infinite number of anything. Potentiality and actuality. That's pretty much Philosophy 101, given it's been know since Aristotle. μηδείς (talk) 06:12, 24 March 2014 (UTC)

On this point, Aristotle was flat wrong. So were a lot of other very smart people for a very long time. It wasn't until Georg Cantor that the notion of the actual infinite really started to come into focus. You really can't cite pre-Cantor thinkers on this point; basically everyone was wrong. --Trovatore (talk) 06:23, 24 March 2014 (UTC)

Out of curiosity, do you also reject out of hand a universe that's endless in time? Because there's not much of a distinction between time and space in general relativity. If it makes you philosophically happier, you can imagine "the machine that runs the universe" not only simulating later times at later meta-times, but also simulating an ever-widening area of the infinite universe, so that although the amount that's being simulated at a given meta-time is finite, any part of the spatially and temporally infinite universe will meta-eventually be simulated. This is like the trick for simulating all Turing machines in parallel on a single Turing machine: first do one step of machine #1, then one step of #1 and #2, then one step of #1, #2 and #3... -- BenRG (talk) 21:10, 23 March 2014 (UTC)

I don't accept a priori answers to anything except the law of noncontradiction. My understanding is there will be a big crunch or a heat death either of which will be a singularity beyond which we can't measure. But the easy answer is that time exists within the universe, not the universe within time. Historico-epistemologically, the answer is that savages have all sorts of beliefs, like the earth being flat and having edge, to spontaneous generation, and animal species being unchanging.

Saying the universe is infinite, meaning I can't imagine hitting a wall, is just as conceptually juvenile. It is entirely possible, using the right math, to describe a finite self-bounded universe, just like the surface of a sphere is finite and self-bounded, without need of a wall or edge or infinite horizon. I'll gladly admit that I can't really imagine a beginning of time or an end to it. But I don't then claim omniscience and say I know it is infinite. μηδείς (talk) 06:12, 24 March 2014 (UTC)

Well, no one here has claimed to know that space is infinite either, or if so, it's escaped my notice. On the other hand, you seem to claim to know that it's finite. How do you know that, exactly?

You said in an edit summary, there's no burden to disprove a self-contradictory statement; it does that for you. Perhaps, but surely there is a burden at least to say what the alleged contradiction is, if it's not evident to others. So far, I have not seen any clear explanation of what you think is self-contradictory. The closest you've come seems to involve using private definitions of "infinite" that don't correspond to what anyone else means by the word. --Trovatore (talk) 06:57, 24 March 2014 (UTC)

Maybe this is where the Friedmann–Lemaître–Robertson–Walker metric comes in. InedibleHulk (talk) 01:04, March 23, 2014 (UTC)

Even if we ignore the metric expansion of space, you still could never get to the edge of the universe, as it's expanding at the speed of light, and you'd have to go faster than that to catch up, which is impossible. However, with the model of multiple big bangs each spawning their own "universe", it's possible another universe's edge could move past us. Depending on the age of that universe, the edge might be very dilute, so we might not even notice it passing. StuRat (talk) 03:14, 23 March 2014 (UTC)

Erm, this seems to contain or risk inducing misconceptions. There is no "universe's edge", however you look at it, only what is called a cosmological horizon, which is another concept entirely. Unfortunately, "universe" is sometimes used to mean "observable universe", which may lead to this misconception. —Quondum 04:26, 23 March 2014 (UTC)

The homogeneous and isotropic dust of galaxies that we find ourselves in could be finite in size and surrounded by something else, presumably whatever provided the initial conditions for inflation or whatever produced our cosmos. That environment would be hostile enough to destroy anything you threw into it, like throwing something into the Sun except more so.

It's not logically impossible that space could literally just end. You are made of fields, and those fields hitting the edge of space would be something like ocean waves hitting a beach. The result would depend on the details of physics at the boundary, but you probably wouldn't survive as an organism. Recently it has been argued (controversially) that space actually does end at a black hole event horizon, so there is precedent for this.

It's also possible for space to wrap around so that it's finite in size and has no boundary, as Medeis said, but there's no evidence that it does.

Finally, it is theoretically possible, I think, for inflation from a small starting region to generate a literally infinite cosmos of galaxies. The picture on the right shows a cosmological model, the Milne universe, which on the one hand expands at the speed of light from a starting point, but on the other hand is spatially infinite at all times after the big bang from a cosmological standpoint, because the cosmological space at a given cosmological time is a hyperbolic surface like the "surface of last scattering" in the image, not a horizontal surface. There's a similar way of fitting an infinite, exponentially expanding flat space (like the future of our universe according to ΛCDM cosmology) into a region of de Sitter space that only expands at the speed of light. If you're willing to accept the possibility of a temporally infinite universe, there's no reason not to accept that it might be spatially infinite also. -- BenRG (talk) 05:16, 23 March 2014 (UTC)

Here's what I think is the "simple" answer to the original question. There was never a time at which the entire universe was a single point, because the so called "moment of the Big Bang" never happened at all.
Note that this doesn't mean the Big Bang never happened. There's ample evidence that the Big Bang theory is correct. But the theory per se really never talks about that time t=0 itself. It'll tell you what we think happened 1 second after the Big Bang, or 1/100 of a second, or 10⁻³⁵ seconds, but not 0 seconds. There simply was never such a time at all.
This will make more sense if you take the logarithm of the time coordinate. Think of t=0.01s as being as long before t=0.1s as t=0.1s is before t=1s. Then you see that the time t=0 is moved back infinitely far (log t=−∞). In this sense, the Big Bang is consistent with the proposition that the Universe has "always existed"; it's only our time coordinate that is limited to values greater than 0. --Trovatore (talk) 05:34, 23 March 2014 (UTC)

I tried this argument with my computer science lecturer relating to the halting problem, by suitably scaling the computation speed, you can solve the problem in a finite amount of time – after all, every 'tick' of the algorithm still takes a finite, nonzero time. No prizes for guessing the response. Roger Penrose takes the opposite tack to yours, suggesting that one can go beyond "infinity" (the big bang into the past, and the infinite expansion into the future, across an innumerable number of big bangs). One should take care of artefacts introduced by the choice of coordinates. —Quondum 06:26, 23 March 2014 (UTC)

Well, actually I don't know what the response was. Given a computer that can run at unbounded speed how much are you selling those for, btw? your answer was quite right; you can indeed perform that supertask in finite physical time, but not in a finite number of steps. If I has been your lecturer, I would have pointed out that your objection was correct, but not directly relevant to the material being discussed. Then I would have called you up after class and mentioned that there are models of hypercomputation where such things are considered. Is that what he did?

My point here is mostly that, sure, given a universe that's currently infinite, you have a weird problem if you try to explain the topology of a manifold-like-thingie that is just a single point at one time slice, but then infinite at every other time slice. But that's not really a problem, because the time slice where it's just a single point is not something that we have any coherent description of in any other way either, and indeed there's no reason to think that it corresponds to any actual event in the past. --Trovatore (talk) 06:45, 23 March 2014 (UTC)

I should have guessed that models have tried to go beyond the Church–Turing thesis. I had hoped to spark a bit of a debate with the lecturer (I raised the point after class; she was cute), but only got a dismissive response. This preceded nearly all the dates on references in the articles you linked. The manifold concept is inadequate for explaining a singularity, and we know we're at sea at Planck scales, so for now we can simply acknowledge the lack of coherency. —Quondum 19:17, 23 March 2014 (UTC)

As my fellow ref-deskers have failed to condense this subject into terms that proceed from your question to the understanding of nature and geometry of space-time necessary to understand our best hypotheses on this subject (which, to be fair, is no easy task), and given that by the end I tend to be the most verbose party of all, I've decided in this case to simply link you to Shape of the universe and Observable universe and provide a couple of the briefest quotes from good ol' Carl Sagan, whose gift for reducing these concepts--which are non-intuitive to usual human perception of the physical world, visual and otherwise-- to something digestible was unparalleled (consequently, if you are neophyte to cosmology with a deep interest, you could do a lot worse than to pick up his book Cosmos as a primer):

"[Prior to the Big Bang] all of the matter and energy now in the universe was concentrated at extremely high density...perhaps into a mathematical point with no dimensions at all. It was not that all matter and energy were squeezed into a minor corner of the present universe; rather, the entire universe, matter, energy, and the space they fill, occupied a very small volume. There was not much room for events to happen in.

"In that titanic cosmic explostion, the universe began an expansion that has never ceased. It is misleading to describe the expansion of the universe as a kind of distending bubble viewed from the outside. By defintion, nothing we can ever know about was outside it. It is better to think of it from the inside, perhaps with grid lines--imagined to adhere to the moving fabric of space--expanding uniformly in all directions."

Since the general point of your question comes to how the universe can be finite but unbounded (a concept others have touched upon above) you might find the article General relativity to be of use, as it addresses the basics of space-time curvature, though I think it might be a bit technical, starting from the place of your question. Although better understood in mathematical terms, just try as best you can (or anyone can) to visualize the most common model -- a universe with curved space, such that you can travel indefinitely in it and yet never hit an edge. We don't know for certain what the shape of such curvature would be, so the old suggestion that you could fly off and never change course and eventually end up back where you started is dubiously correct, but a good way to try to get a handle on the concept anyway. Snow (talk) 10:49, 23 March 2014 (UTC)

I have nothing against these quotes but I don't see how they help with the original question. Finite and unbounded models of the universe were historically popular for philosophical reasons, but in modern cosmology they're not theoretically well motivated. If there are finitely many galaxies, they're probably surrounded by something else, not wrapped around. -- BenRG (talk) 21:10, 23 March 2014 (UTC)

According to quantum mechanics, the amplitude of making some particular observation is given as the path integral over all fields and space-time configurations of exp(i S) where S is the action containing both the space-time degrees of freedom and the matter fields. The most important contribution to the path integral comes from the one which minimizes the action, and that then yields the classical equations of motion (The Einstein equations coupled to the equations of motion for the matter fields). Then since you can only ever make a finite number of local observations and you would need to integrate out everything that you don't observe in the path integral formulation, an infinite unverse should be physically equivalent to a finite one where all possible local configurations occur with the correct amplitudes. Count Iblis (talk) 14:50, 23 March 2014 (UTC)

Did you make up this argument or paraphrase it from somewhere? First, I'm not sure how you're going to apply the path integral to observations of the whole universe. What are the ingoing and outgoing states? Second, are there no measurements happening anywhere else in the universe? If you want to allow the possibility that the universe is a show put on for our benefit, you don't need quantum mechanics. You can just say the whole universe is a light year in radius and at the edge are particle-generating machines that mock the appearance of the rest of it. That's a lot of machinery but still much cheaper than making all of those galaxies. -- BenRG (talk) 21:10, 23 March 2014 (UTC)

These are some half baked ideas I have yet to work out in detail. The latter possibility you mention should contribute to the path integral but it will presumably only make a negligible contribution. Count Iblis (talk) 17:23, 24 March 2014 (UTC)

Coherent radar

Various articles use this term in describing particular equipment, but I don't see it defined or its uses or benefits listed. See Journal article about photonics-based coherent radar Jim.henderson (talk) 01:59, 23 March 2014 (UTC)

Wave radar has some information: "Coherent radars measure Doppler-modulation as well as amplitude modulation, while non-coherent radars only measure amplitude modulation. Consequently, a non-coherent radar echo contains less information about the sea surface properties." — A basic understanding of wave phase coherence would be helpful; but a simple analogy would be a laser which utilizes phase-coherent light.  —71.20.250.51 (talk) 04:11, 23 March 2014 (UTC)

You may be interested in the use of the term as it applies to radio demodulation, as it is the same concept. Coherent demodulation allows more detail and information to be extracted from a signal than noncoherent demodulation does, and hence allows transmitted waveforms to be used that require far less power to be used for the same effective received signal. Noncoherent demodulation was used originally, for example, with amplitude modulation receivers, which requires the transmission of a strong carrier for the same demodulated signal quality compared with say double sideband or single sideband that requires coherent demodulation. The advantage of noncoherent demodulation is that the receiver circuitry can be considerably simpler, something that is less of a consideration with modern electronics and techniques. —Quondum 04:18, 23 March 2014 (UTC)

Thanks; that clarifies it somewhat. I should have mentioned that my question was inspired by a news report that tried to hook a radar improvement to the great buzz about Flight MH370. Surely that connection does not warrant attention in a Wikipedia article, but I hope editors who understand the technical issues will add appropriate links among those technical articles and maybe a paragraph or two of explanation based on the above. Jim.henderson (talk) 13:29, 23 March 2014 (UTC)

Coherent detection of a signal buried in Additive white Gaussian noise obtains +3 dB better Signal-to-noise ratio than incoherent (envelope) detection. 84.209.89.214 (talk) 15:47, 23 March 2014 (UTC)

Yup I failed to mention that even for waveforms designed for noncoherent detection, coherent detection does a better job in this sense. —Quondum 19:27, 23 March 2014 (UTC)

The news story sounds like someone riding on a news event to sell their equipment. It's a technology for doing the same job better by replacing the radar electronics. I'm no expert, but I'd be surprised if any modern radar (even the simple Doppler that the cops used for measuring road speeds) is not coherent. —Quondum 19:27, 23 March 2014 (UTC)

...alas, no! There are incoherent scatter radars like the AMISR [1], at the Poker Flat Rocket Range. They are rare, and they are used for special purposes - typically for studying the chemistry and physics of the mesosphere and ionosphere. What makes them "incoherent" is that the radio return doesn't bounce off any specific object: these RADARS detect incoherent returns from the entire ensemble of ions and molecules in the upper atmosphere. Nimur (talk) 15:15, 24 March 2014 (UTC)

Since this "incoherent" applies to the scattering, not the radar system, I see no cause for lamentation. The radar system itself will no doubt still use coherent detection. —Quondum 03:43, 26 March 2014 (UTC)

Here's a tutorial from Haystack Observatory's Millstone Hill ISR: Incoherent Scatter Radar Tutorial. Here's more about AMISR's system description. The phase of the individual radiating elements - AEUs - in the AMISR are controllable (it can be considered a phased array). Nonetheless, an entire community of experts call these "incoherent scatter RADARs" - in contrast to coherent scattering RADARs. I think it's semantics; it's the same machine, whether the adjective "coherent" describes the machine itself, or the physics that the machine relies on. Nimur (talk) 02:38, 27 March 2014 (UTC)

How much greater is gravity on the dark side (away from earth) of the moon than on the light side (facing earth)?

How much greater is gravity on the dark side (away from earth) of the moon than on the light side (facing earth)?68.36.148.100 (talk) 05:06, 23 March 2014 (UTC)

I'm guessing that you think the Earth's and Moon's gravity will add together on the far side, while the Earth's gravity will be subtracted from the Moon's on the near side. This would be true if the Moon was stationary with respect to Earth, but, since it orbits, the apparent centrifugal force exactly cancels this effect, although there may be slight tidal effects left over. Also, "dark side" and "light side" aren't good ways to describe the near and far sides of the Moon, as which side is dark or light changes, while the side facing the Earth doesn't (except for some wobble). StuRat (talk) 05:19, 23 March 2014 (UTC)

If the moon affects the gravity on earth why doesn't the earth affect gravity on the moon?? eg: quote from Moon article:"The tides on Earth are mostly generated by the gradient in intensity of the Moon's gravitational pull from one side of Earth to the other, the tidal forces."165.212.189.187 (talk) 17:39, 26 March 2014 (UTC)

Does the moon truly "wobble" or is it just that we can see more than 50 percent of it simply because of its elliptical orbit? ←Baseball Bugs ^{What's up, Doc?} carrots→ 05:21, 23 March 2014 (UTC)

If one side always faced the Earth, with no wobble, why would an elliptical orbit show us more than half of it ? (I can see why observations from different points on Earth would see slightly different views, including due to the same point on Earth rotating each day, but that's a different issue.) StuRat (talk) 05:28, 23 March 2014 (UTC)

I figured out the answer to my own Q here. The Moon rotates at a constant speed, so this means it would only have one side exactly facing the center if it was also revolving around the Earth at a constant speed, which would require a circular orbit. StuRat (talk) 22:13, 23 March 2014 (UTC)

Does it literally "face the earth", or does it face a focus point of its elliptical orbit? If so, that might allow us to see beyond the conventional edges a bit compared with when its truly facing us, at apogee and perigee. I'm just not so sure the orbit is sufficiently off-circular to explain the percentage we can see. Does it literally rock back and forth (i.e. wobble or oscillate) regardless of where it happens to be in its orbit? ←Baseball Bugs ^{What's up, Doc?} carrots→ 05:49, 23 March 2014 (UTC)

To put it another way, is it wobbling with respect to itself, or only with respect to the view from the earth? Possibly oscillating as the last vestiges of its presumed, ancient rotation before the earth started slowing down its rotation? ←Baseball Bugs ^{What's up, Doc?} carrots→ 05:52, 23 March 2014 (UTC)

Moon wobble (aha, we haven article on it!) is with respect to an Earthbound observer. The article gives a better explanation than I could, so I'll simply leave the link. Someguy1221 (talk) 05:58, 23 March 2014 (UTC)

Perfect. Thank you! ←Baseball Bugs ^{What's up, Doc?} carrots→ 06:58, 23 March 2014 (UTC)

Aye. Thanks, too. Got me humming "Good Librations". The Funky Bunch version, not Beach Boys. InedibleHulk (talk) 20:25, March 23, 2014 (UTC)

If anything gets you humming Marky Mark over Brian Wilson, you have problems I am not allowed to recommend fixes for, per Wikipedia's medical disclaimer. But you still got problems. --Jayron32 22:08, 23 March 2014 (UTC)

I didn't exactly choose it. Just popped into my head. And I wasn't thanking him for the tune, just the info. Bandwise, Beach Boys win. Song-for-song, this one's catchier. But yes, I'm nuts. InedibleHulk (talk) 22:27, March 23, 2014 (UTC)

I diagnose an ear worm, and recommend using mental floss to remove it. StuRat (talk) 22:43, 23 March 2014 (UTC)

Thanks, but it's too late. That article beaned me, and now I can't not confuse my worm with palinacousis. My lobes keep telling me "Come on" and "feel it". I think I'll need more than floss for this. InedibleHulk (talk) 22:55, March 23, 2014 (UTC)

Or get some Brain Bleach from That Other Wiki(tm)... - ¡Ouch! (^{hurt me} / _{more pain}) 11:14, 26 March 2014 (UTC)

The question is about the Dark side of the Moon and you're humming that? ¡Pobre! Wnt (talk) 23:30, 23 March 2014 (UTC)

Great as they are, they don't make good humming tunes. Anyway, I've moved on to this Godzilla melody. Learned a lot about space from that game. InedibleHulk (talk) 01:11, March 24, 2014 (UTC)

Isn't the relevant focus of the ellipse always on the line joining the two bodies? —Tamfang (talk) 00:23, 24 March 2014 (UTC)

I think so; if one mass is negligible compared to the other, one can treat the center of gravity of the heavy body as one focus. On the still far from equal Earth–Moon pair (80:1 IIRC) the common center of gravity, which should be the location of a focus, is still well inside Earth.

The dark side is facing away from the Sun, and that's not always the same part of the Moon. The side facing away from Earth should be called the back (or the far side) of the moon. The terms where "dark" means "unseen" often cause confusion. Another thing I cannot find the original source for... :(

The center of the Moon should experience no net gravity, in the sense that if there were a small cavity, a body inside the cavity wouldn't be pulled towards any wall. For a BIG cavity, (small) bodies inside would be pulled either towards the side facing Earth or to the opposite side, depending on which is closer. - ¡Ouch! (^{hurt me} / _{more pain}) 15:29, 24 March 2014 (UTC)

There is no gravity inside a central cavity in a spherically symmetric object (assuming no external influences), regardless of the size of the cavity. It is a consequence of the inverse-square law. Hence, the only influence felt would be Earth's tidal force, which would have the effect ¡Ouch! describes (as well as an apparent repulsion from the "equator" between the near and far points). Also, on the Moon's surface, effective gravity would probably lower at the near and far points of the moon, and higher elsewhere. —Quondum 03:31, 26 March 2014 (UTC)

Regarding gravity inside a hollow sphere, see Shell theorem. --Jayron32 13:56, 26 March 2014 (UTC)

Alcohol flush reaction

Why is it that the alcoholic flush reaction common in asian people seems to be more noticeable after 1 or 2 drinks but fades quickly, even if they continue to drink, after an hour or so? 82.132.244.11 (talk) 09:37, 23 March 2014 (UTC)

Does our article on the subject address your question? μηδείς (talk) 10:18, 23 March 2014 (UTC)

Another problem related to thermal imaging

I think every weapons amateur like me knows about thermal camouflage like "Nakidka" , or BAE′s ADAPTIV , I think such camouflage has brought an end to the thermal IR cameras forever - of course in the case of a war between the world greatest armies , not in the case of a war between NATO and Taliban who will not have any thermal camouflage forever also - , so I think we will return to night vision again . Sorry for annoying you about these confusing topics but I like it , and I hate forums . Tank Designer (talk) 11:09, 23 March 2014 (UTC)

No need to apologize; that's what we're here for. However, what exactly is your question? You should know by now we're not here to discuss what you or we think will happen. For that you do need a forum. Rojomoke (talk) 11:28, 23 March 2014 (UTC)

Just because thermal camo exists doesn't necessarily mean it will be widely used. Some possible reasons not to:

1) The expense. Perhaps that money could be better spent elsewhere.

2) The inconvenience/discomfort.

3) Keeping the heat in could cause them to get heat stroke.

4) Presumably they have to keep their entire face covered, which could limit their view.

5) As per the previous discussion, thermal camo would work best when the background temp was close to body temperature. If the soldier is much hotter than the background, he will be a lot harder to hide.

6) If the thermal camo uses a coolant like liquid nitrogen to absorb the heat, it will need to be exchanged for more coolant frequently.

So, I can imagine their use being restricted to commandos and such.

UPDATE: I see this technology is not used on infantry but only vehicles and structures. However, some of the items I listed still apply, like the expense, and infrared cameras are still of value to detect infantry, if nothing else. Also, tank crews seem to often have the hatch open when not in combat, for ventilation, to get a better view, etc., allowing them to be spotted by spy planes. StuRat (talk) 12:59, 23 March 2014 (UTC)

(edit conflict)::The problem with this stuff is the expense of fitting all your vehicles with it. As far as I can see, nobody has actually started the process yet and Adaptiv seems to be still in development. Then there are other IR signatures that can't be hidden, such as exhaust plumes. The M-1 Abrams has a particularly "massive IR signature" although there have been recent upgrades which are supposed to suppress a lot of it; diesel engines have a visible exhaust plume too. Alansplodge (talk) 13:08, 23 March 2014 (UTC)

Thank you so much for your efforts , you ended my worries by your valuable information . Tank Designer (talk) 15:14, 23 March 2014 (UTC) Thanks are not enough , God bless you .Tank Designer (talk) 15:21, 23 March 2014 (UTC) — Preceding unsigned comment added by Tank Designer (talk • contribs) 15:20, 23 March 2014 (UTC)

We have articles about Nakidka and Adaptiv (ADAPTIV is a redlink - if that's a common variant, please make the redirect). I don't know anything about it, but the photos don't look 100% impressive. Question: couldn't you camouflage against IR and night vision simply by dyeing fabric with camouflage patterned India ink (carbon), since aromatic carbon seems to absorb/emit every possible frequency the same way in a manner that depends only on the number of molecular layers and the fine-structure constant? Wnt (talk) 17:27, 23 March 2014 (UTC)

I'm not clever enough to say, but one suspects that if it were that simple, somebody would have already thought of it. Alansplodge (talk) 21:28, 23 March 2014 (UTC)

Yeah, I suppose in the far IR (heat glow) this is kind of like camouflaging a light bulb by wiping off obscuring material. It might confuse that it's a light bulb, but... On the other hand, if you backed your fabric with a space blanket... Wnt (talk) 23:26, 23 March 2014 (UTC)

It doesn't seem thermodynamically possible to hide something for very long. If your human or vehicle is converting an internal energy source into something else - there will be heat generated as a by-product. The heat absolutely has to go somewhere or else the internal temperature will climb. For humans, that would be quickly fatal - and even unmanned vehicles would eventually get hot enough to melt something important. So the heat has to go somewhere. Using a blanket to absorb the IR light will only cause the blanket to heat up and become visible.

Probably the best solution has to be to convert the heat into something else. You can have a reservoir of something cold (liquid nitrogen, for example) and warm it up - but you'll eventually run out of cold places to store your waste heat - and then you're back to being visible again.

Just like visual camouflage, you're not making the object transparent - so it'll still block the background that's behind it - which may yet make it detectable.

I suspect that you could use some of these techniques to hide a warm object for a while - but eventually, it's either going to become visible in IR - or it's going to cook whatever is inside. But modern IR cameras are really amazingly sensitive - and it's hard to imagine that you'd be able to fool one of those. However, from a military perspective, most of the world's combatants won't have access to the very best cameras - so there is certainly some mileage in using thermal camo. It's not going to obsolete IR cameras in the longer term though because the fancy electronics and whatever that you need to push the sensitivities way up will slowly get cheaper and more available - and I very much doubt that the camo technologies can keep up with it, simply because they are fighting the inevitability of the laws of thermodynamics.

SteveBaker (talk) 14:59, 24 March 2014 (UTC)

You forgot emissivity. You can have a surface that has high emissivity at certain wavelengths and low emissivity at others. So, you can choose a surface treatment/cover that has high emissivity at wavelengths that are already present in the environment. This is really the same as colour camoflage cothing but extended into selective infrared wavelengths. Metals and most man made materials have moderately high emissivity at heat wavelengths. But air has very low, near zero, emissivity. So what you can do is use a heat pump and heat exchanger to heat air which you blow through. Because of air's very low emissivity, you can exhaust air at a much higher temperature than you need to keep metal surfaces in order to have the same detectability. 124.178.107.238 (talk) 16:07, 24 March 2014 (UTC)

Convection and evaporation are alternatives to emission. A person could avoid all light emissions and still stay cold with a breeze over sweaty skin. Wnt (talk) 19:05, 24 March 2014 (UTC)

I support SteveBaker′s opinion , but I respect all the contributions . Tank Designer (talk) 21:07, 25 March 2014 (UTC).

Nucleosynthesis

A version of the periodic table indicating the origins – including reference desk/science – of the elements. All elements above 103 (lawrencium) are also man-made and are not included.

Hi all,

Does anyone have a definitive list of the origins of the elements?

After I created this graphic:

https://commons.wikimedia.org/wiki/File:Nucleosynthesis_periodic_table.svg

based on http://www4.nau.edu/meteorite/Meteorite/Book-GlossaryN.html and http://www.daviddarling.info/encyclopedia/N/nucleosynthesis.html , I found that it appears to conflict statements e.g. "Big Bang nucleosynthesis produced no elements heavier than beryllium..." in https://en.wikipedia.org/wiki/Big_Bang_nucleosynthesis#Heavy_elements and "In addition to the above light elements, tritium and isotopes of aluminium, carbon (carbon-14), chlorine, iodine and neon are formed within solar system materials through cosmic ray spallation..." in https://en.wikipedia.org/wiki/Cosmic_ray_spallation .

Who's right?

Thanks, cmɢʟee⎆τaʟκ 17:54, 23 March 2014 (UTC)

• Ah, this is the subject of perhaps the most wonderful non-fiction book I have ever read, P. A. Cox's The Elements; Their Origin, Abundance, and Distribution. It is available used for the cost of shipping, and probablt downloadable at places like scribd for free. μηδείς (talk) 19:06, 23 March 2014 (UTC)

I'd take the .info source above with a grain of salt; it looks quite spammy.

I'd take the Meteorite source with a bucket of salt. Excerpt (from Neutron star, same page):

"This intensifies the magnetic field of the star to around 1012[sic!] times that of the Earth."

If a "scientific" page can't even get its exponents right, I don't trust its claims too much either.

I wonder if large stars can synthesize that many elements heavier than iron without a supernova, and there must be some amounts of lithium from the Big Bang (which is supported by our BBN article), too, and I wouldn't count any elements as purely man-made. The issue is probably that they were synthesized in supernovae but decayed quite quickly. There is even a kind of supernova afterglow that's caused by radioactive decay. - ¡Ouch! (^{hurt me} / _{more pain}) 06:59, 26 March 2014 (UTC)

Oops, I got it wrong; the BBN article mentions not only lithium but also beryllium, and trace amounts of carbon (the latter being so low that it is completely lost in the "noise" of stellar nucleosynthesis, which assembles substantial amounts of carbon, so the BBN carbon cannot be detected).

The r-process is restricted to a supernova, but the s-process, which occurs in asymptotic red giants, "accounts for approximately half of the isotopes of the elements heavier than iron". so the elements marked as "large stars" are probably accurate. - ¡Ouch! (^{hurt me} / _{more pain}) 06:52, 27 March 2014 (UTC)

agent orange

when to kill foliage how far will the contamination travel? — Preceding unsigned comment added by 47.16.152.38 (talk) 19:31, 23 March 2014 (UTC)

Right down into the roots of the plants it touches, and then it remains in the soil, possibly being washed to other areas. The main danger is if the dead foliage is burned, producing dioxin, but the early production process of "Agent Orange" introduced a very nasty dioxin: 2,3,7,8-Tetrachlorodibenzodioxin. This caused illness even without burning any foliage, and contaminated soils for many years. I used to use these chemicals (2,4,5-T and 2,4-D, sold as "SBK" in the UK, hopefully without any 2,3,7,8-Tetrachlorodibenzodioxin), in small quantities, of course, and I still have some, but now seldom use it. The 2,4-D is usually broken down fairly quickly by soil bacteria, so is still considered relatively safe in some jurisdictions. Dbfirs 22:20, 23 March 2014 (UTC)

Bizarre question regarding McDonalds French Fries

Hey- Whenever I cook oven fries at home, whether they are thick or thin they always let off steam when they are fully cooked. However when I was eating McDonalds French Fries, I could not see any steam at all. These fries were piping hot and just removed from the fryer. Why was there no steam coming from the french fries? I have had this 'query' before in previous McDonalds restaurants. Thanks guys! --TįsILIi Achooo (talk) 19:59, 23 March 2014 (UTC)

I suspect that this could be because the atmosphere at MacD's is already warm and full of moisture so the steam escaping from the French fries doesn't condense into visible mist, but that's really only a guess. Alansplodge (talk) 21:23, 23 March 2014 (UTC)

While warmer air does indeed hold more moisture before it becomes visible water droplets, moist air holds less additional moisture. You want hot, dry air to absorb the most moisture without seeing any steam. StuRat (talk) 22:06, 23 March 2014 (UTC)

"Everything you've always wanted to know about McD's French Fries, but were afraid to ask", can be found in this excerpt from The Atlantic Monthly of: Schlosser, Eric ; Fast Food Nation (Houghton-Mifflin, 2001) — (I haven't read it; don't know if it answers your question) — My guess is that the crust, being extra-crispy, doesn't allow steam to escape.  —71.20.250.51 (talk) 21:41, 23 March 2014 (UTC)

• McD fries are quite thin, so they have much more fried skin outside relative to steamy boiled potato inside. See square-cube law. I suspect their cooking standards also emphasize crispiness through preparation. μηδείς (talk) 01:44, 24 March 2014 (UTC)

• I don't think the speculations above are correct. The actual answer, I believe, is that McDonald's fries, like many restaurant fries, are actually fried twice. First they are fried for a long time at a relatively low oil temperature, which removes a lot of water. Then they are frozen. The pre-frying allows the frozen fries to be cooked quickly and then to stay crisp for a relatively long time after cooking. If your fries come out steaming, then they probably become limp very quickly, even if they initially come out crisp -- that's a result of the high moisture remaining inside. Looie496 (talk) 14:30, 24 March 2014 (UTC)

That's the preparation standards I mentioned. Fries are usually cooed at least twice before serving, and the ones you buy to cook at home have already been cooked. μηδείς (talk) 16:55, 24 March 2014 (UTC)

Do they employ doves to coo at them ? :-) StuRat (talk) 17:09, 24 March 2014 (UTC)

Hehehehehemheheh. μηδείς (talk) 19:09, 24 March 2014 (UTC)

Does space occupy a train carriage as a train carriage occupies space?

Bit hesitant to ask this question, but a friend made me reel when we were watching a train pull up to the station by saying something like, 'Here it comes, bearing the space of its first voyage within it.' Is this in any way true? Does spacetime, defined by the walls of the interior, length by width by height, move along inside the train, or does it move through the train as the train moves through space? Makes me wonder about the qualities of a material that isn't permeable to space...

Thanks for your indulgence...

Adambrowne666 (talk) 22:39, 23 March 2014 (UTC)

Well, when the train first accelerates, it presumably moves out of the space it was in. While it is moving steadily, it is at rest, so the same space it was in. But since it is accelerating against gravity (gravity = acceleration), the space is actually moving down all the time... and accumulating at the bottom of Earth's gravity well? Help, is there a physicist in the house? :) (My guess is that space isn't supposed to be a physical substance, only a geometry, and it's supposed to be the same from all frames of reference and in all locations) Wnt (talk) 23:24, 23 March 2014 (UTC)

get ready to really reel: even "at rest" the train is whipping around the earths surface at 500 mph! 68.36.148.100 (talk) 23:36, 23 March 2014 (UTC)

ha, yes, good point - reeling now - and yes, thought it was likely a category error on my part; i was thinking of space as a thing, or something, whereas it isn't, or something. Adambrowne666 (talk) 23:50, 23 March 2014 (UTC)

Asking if space is moving is kind of like asking time is aging. Is a specific day (say, 12 March 1834) moving in time? Of course it's not. The train is simply moving through space, but if you want, you can think of it as stationary, thus defining a coordinate system centered on the train which moves with respect to the coordinate system of the station. In this sense, space is "moving", though this is misleading, as no observable change (beyond the train's movement) is taking place. Choosing to describe the train as stationary and the train as moving makes no difference in physical reality. If we think of space as a substance, then yes, we could say that the train is still "bearing the space of its first voyage" (just as it's still bearing the first wad of gum to be stuck under one of its seats), but space is most emphatically not a substance, and so that sentence is I'm afraid meaningless. -Anagogist (talk) 14:30, 24 March 2014 (UTC)

@Adambrowne666: here's an approach to your question on another tack: sure, you can think of the car as carrying space along with it. Why not? There are no preferred frames of reference in Newtonian mechanics, or in special relativity. Unless you still believe in Luminiferous_aether, the space encapsulated by the car is ontologically synonymous with the boundaries the car defines in some coordinate system. So this is just a long winded way of saying that the space can be defined with reference to the car, and if you want to think of the car as carrying around that space, that will lead to no problems or non-physical results that I know of. You're just saying that e.g. the top left corner of the car is the same point in space, regardless of where the car may be -- and this is trivially true, with respect to the car's frame of reference. This is really more a question of philosophy than physics though. See also Special_relativity#Lack_of_an_absolute_reference_frame, Preferred_frame, Moving_frame, and Philosophy_of_space_and_time. SemanticMantis (talk) 15:39, 24 March 2014 (UTC)

but it's definitely NOT the same space wrt the CMB. 68.36.148.100 (talk) 21:54, 24 March 2014 (UTC)

• The OP's question isn't so off base in consideration of frame dragging around a dense spinning object, which is sometimes referred to as "dragging space". The conceptual extreme of this is a Tipler cylinder. However, our articles carefully avoid that way of putting it, saying that it "warps spacetime in such a way"... which is a bit different. Wnt (talk) 15:45, 25 March 2014 (UTC)

Thanks, all, for the illuminating and well-written answers, and thanks, too, for the ping, Mantis. So - in my naivety - is there any way that a certain space can be defined aside from coordinates? Is there ever something -- aside, I suppose, from deformations come of gravity - that can distinguish one chunk of space from another? I realise the answer is very likely no.... Adambrowne666 (talk) 23:46, 25 March 2014 (UTC)

March 24

Excess weight being more dangerous for men than for women

Someone previously told me that studies show that excess weight is more dangerous for men than it is for women partly because men store fat around the waist, which squishes the organs, whereas women's bodies are more likely to store fat in the thighs/hip area first. Is this individual's statement in regards to this true/correct/accurate? Futurist110 (talk) 06:54, 24 March 2014 (UTC)

This is unlikely to be true. It illustrates a common fallacy - it purports to explain WHY it is more dangerous for men than women to have excess weight, but without demonstrating that it has actually been shown by some sort of scientific rigor. For example, I might say "sharks that spend most of their time in shallow water close to the coast are smaller than sharks that spend most of their time far out to sea because there are fewer small fish close to the coast and so sharks in this area have a poorer diet." Some people might say "Hey, I didn't know that, but it makes sense. Yes, coastal sharks are smaller than their deep-sea cousins." However, nobody should believe what I wrote. (I confess I just fabricated it for the sake of an illustration.) My fallacy is evident because I made no attempt to demonstrate that there is any objective evidence to suggest that coastal sharks are different in size from deep-sea sharks. I merely stated a plausible explanation that might apply if, in fact, it occurs. (I doubt that it does.)

So having a plausible explanation as to why excess weight might be more dangerous in men than in women doesn't establish whether or not there is credible evidence either way. We need to learn more about the "studies" rather than about the possible explanation. Dolphin (t) 07:12, 24 March 2014 (UTC)

So in other words, this statement can be true, but we can't/don't know for sure without more evidence when it comes to this, correct? Futurist110 (talk) 07:46, 24 March 2014 (UTC)

Correct. "Someone previously told me that studies show ..." We need to be very curious about what these studies were, and what factual information they actually showed. The bit about "... partly because men store fat around the waist, which squishes the organs ... etc. etc." is speculation. It is someone's theory about what might be the cause of this health problem. It isn't factual information.

Critical thinking requires that we always ask ourselves about what sort of information we are looking at - for example, is it objective information (factual) or subjective (someone's opinion). We should always be very skeptical when we are given little or no objective information, and a much greater amount of subjective information, and then encouraged to believe the underlying premise. Dolphin (t) 12:24, 24 March 2014 (UTC)

Also relevant to Dolphin51's discussion is the notion of correlation does not imply causation. Frequently, we get scientific results that show a relationship between two factors (for example, being overweight and premature death in males, just as a possible example). However, that is different than proving a mechanism to explain the correlation. Does being overweight cause premature death? We don't know, because we're not even sure how it might, or how to isolate weight from a plethora of other issues. For things like this, the literature is usually much better at showing relationships between factors but not so good at explaining how (or even if) factor X leads to result Y. --Jayron32 14:30, 24 March 2014 (UTC)

1) I have heard, from multiple sources, one being Dr. Oz, that belly fat is correlated with more health problems than evenly distributed weight.

2) However, "squishing the organs" is not the mechanism, as I've not heard of people dying from that except as a result of impact injuries.

3) It seems that men tend to have more belly fat than women, but I haven't actually seen any studies proving so.

4) Even if men do have more belly fat, and men have decreased longevity, that doesn't necessarily mean men having more belly fat is the reason. For example, women tend to die more from heart attacks, since they are less able to detect them and get medical help. So, that would tend to make excess weight (a risk factor for heart disease), more of a danger to women. StuRat (talk) 17:19, 24 March 2014 (UTC)

5)Part of the point of the comments above is that "I've heard" isn't a reference. Your point 4)"For example..." in particular is rather useless without a reference. I don't know anything about this subject, but I know what kinds of claims need reference, especially at a -- reference -- desk. SemanticMantis (talk) 19:33, 24 March 2014 (UTC)

Hmm, organ squishing is otherwise knwon as hypertension leading ultimately to lung and heart failure and stroke and heart attack as possible results, no? μηδείς (talk) 23:01, 25 March 2014 (UTC)

See here:

"There are numerous theories as to the exact cause and mechanism in Type 2 Diabetes. Central obesity is known to predispose individuals for insulin resistance. Abdominal fat is especially active hormonally, secreting a group of hormones called adipokines that may possibly impair glucose tolerance. Insulin resistance is a major feature of Diabetes Mellitus Type 2 (T2DM), and central obesity is correlated with both insulin resistance and T2DM itself.[43][44] Increased adiposity (obesity) raises serum resistin levels,[45][46][47][48] which in turn directly correlate to insulin resistance.[49][50][51][52] Studies have also confirmed a direct correlation between resistin levels and T2DM.[45][53][54][55] And it is waistline adipose tissue (central obesity) which seems to be the foremost type of fat deposits contributing to rising levels of serum resistin.[56][57] Conversely, serum resistin levels have been found to decline with decreased adiposity following medical treatment.[58]"

"There is enough evidence in the scientific community where an impaired non-esterified fatty acid (NEFA) metabolism could give way to the insulin-resistant state of individuals with this type of obesity. Hypertrophy of intra-abdominal adipose cells causes it to be in a hyperlipolytic state in which it is resistant to the antilipolytic effect of insulin. The resulting NEFA flux to the liver causes impairment of liver metabolism which leads to over production of glucose in the liver.[61] Individuals with obesity are more likely to develop weakened non-esterified fatty acid (NEFA), which can weaken the metabolism of the liver causing [62] high glucose production. An individual is at a higher risk of developing ischemic heart disease if they have hyperinsulinemia-dyslipidemia while being abdominal obese.[63] Visceral fat, unlike subcutaneous fat, is implicated in many aging-associated diseases. Surgical removal of visceral fat, but not subcutaneous fat, has been shown to extend the mean and maximum lifespan of rodents.[64][65] Abdominal adipose tissue is a major source of increased inflammatory Interleukin-6 (IL-6) associated with aging.[66] Induction of cellular senescence by visceral fat contributes to the inflammation.[67]"

Count Iblis (talk) 19:23, 24 March 2014 (UTC)

sum of a position wavefunction and its conjugate

Hi all,

I was reading Griffith's Introduction to Quantum Mechanics and came across the claim that if $\psi (x)$ satisfies the Time-independent Schrödinger equation then $\psi (x)+\psi (x)^{*}$ is a real valued function.

Trying to show this claim highlighted my lack of a definition of what $\psi (x)^{*}$ for a wavefunction is. (Up until now it was just "replace all $i$'s with $-i$'s" (so $i\sin \left({\frac {ix}{\hbar }}\right)e^{-x^{2}}$ would have a conjugate of $-i\sin \left({\frac {-ix}{\hbar }}\right)e^{-x^{2}}$ but I see now this isn't as rigorous as other definitions.)

My question is what is actually the definition of the conjugate of a (position) wavefunction, does it satisfy the above claim and if so why?

Neuroxic (talk) 10:48, 24 March 2014 (UTC)

In this elementary context, a wavefunction is "just a number" (a more rigorous definition would be $\Psi (x)=\langle x|\psi \rangle$, where $\langle x|$ and $|\psi \rangle$ are vectors in Hilbert space). As a complex number, you can write it in the form $\Psi (x)=Re[\Psi (x)]+iIm[\Psi (x)]$ (where Re[] and Im[] are real), and so its conjugate would be $\Psi (x)=Re[\Psi (x)]-iIm[\Psi (x)]$ as usual. In most cases, simply replacing i with -i does work, and in your particular case, you can see that by using the fact that $\sin(iy)=i\sinh(y)$. I don't see why $\Psi (x)$ needs to be a solution to the TISE though, since $z+z^{*}$ is always real by definition. -Anagogist (talk) 14:02, 24 March 2014 (UTC)

If $\psi$ did not satisfy the TISE then it would be function of t as well as x, so it would have to be written as $\psi (x,t)$, not as $\psi (x)$. Gandalf61 (talk) 16:23, 24 March 2014 (UTC)

The correct question is to show that if $\psi (x)$ satisfies the Time-independent Schrödinger equation that then $\psi (x)$ can be chosen such that $\psi (x)=\psi (x)^{*}$ is a real valued function. Count Iblis (talk) 17:09, 24 March 2014 (UTC)

Yes, however for me the rest of the argument was simple provided that $\psi (x)+\psi (x)^{*}$ was real. (Well, provided you also take $\left({\frac {\partial \psi }{\partial x}}\right)^{*}={\frac {\partial \psi ^{*}}{\partial x}}$ (as you've said below) and a few other things but a definition of $\psi ^{*}$ would have provided these claims anyway.

Neuroxic (talk) 10:20, 25 March 2014 (UTC)

What you need to do then is to show that if $\psi (x)$ is an energy eigenfunction with energy eigenvalue E, then than implies that $\psi (x)^{*}$ is also an eigenfunction with eigenvalue E (Hint: take the complex conjugate of the time independent Schrodinger equation and write that in terms of $\psi (x)^{*}$, the main issue here is to correctly treat the second derivative term). Count Iblis (talk) 17:42, 24 March 2014 (UTC)

isn't this also true? $\psi (x)$ * $\psi (x)^{*}$=1. And multiply both sides by $\psi (x)$ Voila.--DHeyward (talk) 01:42, 25 March 2014 (UTC)

Not quite, the statistical interpretation dictates that $1=\int _{-\infty }^{\infty }|\psi (x,t)|^{2}dx=\int _{-\infty }^{\infty }\psi (x,t)\psi ^{*}(x,t)dx$, not that $\psi (x)$ * $\psi (x)^{*}$=1 for any $x$

Neuroxic (talk) 10:20, 25 March 2014 (UTC)

Factors affecting pyloric sphincter distension

which factors affect pyloric sphincter distension ? does it include CO2/ carbonated drinks. — Preceding unsigned comment added by 182.185.240.247 (talk) 11:08, 24 March 2014 (UTC)

The article Gastric distension does not note any connection with carbonated beverages, but does say that it is commonly caused by air being pumped into the stomach, as caused by CPR. So perhaps... There's also another article titled Abdominal distension which seems more detailed and may help you in your research. --Jayron32 14:25, 24 March 2014 (UTC)

Erasers

How do pencil erasers work? I was hoping to find a more technical explanation than about.com gives. 2001:18E8:2:28CA:F000:0:0:7A27 (talk) 17:40, 24 March 2014 (UTC)

The Eraser article is kind of vague on precisely how it works, but maybe it has some usable references? ←Baseball Bugs ^{What's up, Doc?} carrots→ 18:21, 24 March 2014 (UTC)

The first reference is in Japanese. The second page is a biography of Joseph Priestley. The third is something Priestley wrote that doesn't talk about erasers. The fourth is a Supreme Court of the United States decision about patents. The fifth is link rot. The Eraser: How Products are Made link is a search engine, the JSTOR article is about eraser damage to paper (not to pencil marks), and the Goodyear Rubber History talks about Charles Goodyear, not about erasers. 2001:18E8:2:28CA:F000:0:0:7A27 (talk) 19:04, 24 March 2014 (UTC)

• The "rubber" partially absorbs and abrades the ink or graphite on the surface, and abrades the underlying stained paper as well, the harder you rub. absolution. μηδείς (talk) 19:07, 24 March 2014 (UTC)

A pencil eraser is made of a weakly bound polymer material such as rubber or PVC. When rubbed on paper the action is sacrificial: friction force detaches grains of the polymer exposing molecular bonding sites to which graphite pigment particles attach in preference to remaining on the paper. Non-carbon marks such as wax crayons and coloured pencils make tend to smear rather than be erased. 84.209.89.214 (talk) 20:14, 24 March 2014 (UTC)

Thank you, since I was hoping for this kind of explanation. Do you mean that a chemical reaction occurs? If not, what kind of molecular bonding is involved? 2001:18E8:2:28CA:F000:0:0:7A27 (talk) 20:45, 24 March 2014 (UTC)

For reference, our general articles relevant to 84's description are adhesion and ablation. SemanticMantis (talk) 21:10, 24 March 2014 (UTC)

Wouldn't absorption be more relevant than ablation? In any case, the process is mechanical, not chemical, per se. μηδείς (talk) 23:36, 24 March 2014 (UTC)

I meant that the eraser is being ablated (and perhaps a small bit of the paper as well, if one erases vigorously.) I think that the process of graphite sticking to the bits of ablated rubber is Adhesion#Mechanical_adhesion, but I don't have a ref for that, and didn't want to speculate. I can't rule out Adhesion#Dispersive_adhesion, at least not from first principles. Do you have any refs for that action or your claim? SemanticMantis (talk) 00:17, 25 March 2014 (UTC)

This is rampant speculation, question rather than answer, but I have a suspicion there's some kind of difference between a freshly exposed rubber surface and one which has reacted with air. There are things like Silly Putty that can visibly pull pencil marks off a page on contact, but simply touching the eraser doesn't seem to do anything - until small pieces of it start getting ablated. While they can wear away the paper, I don't think they always do so, depending on the strength of the paper and force of the rubbing. And I recall crummy ones that would actually leave a bit of dye their color and a feeling of themselves in the paper rather than taking the paper away. Wnt (talk) 15:39, 25 March 2014 (UTC)

Here's a reference ('Everyday Chemistry') that says "Erasers are primarily adsorbents." --Heron (talk) 11:03, 26 March 2014 (UTC)

Filling bubbles

Is it physically possible to produce soap bubble filled with a liquid?

I guess it might require using different liquids like soapsuds and oil. Or could it be not soap at all?

Antibubbles do not count. 91.77.161.202 (talk) 21:19, 24 March 2014 (UTC)

Probably not in air, as it would drop like a rock and break apart. However, you can create a "bubble" of one liquid in another, such as oil in water (think lava lamps, although larger spherical bubbles are possible if the fluids are both still). StuRat (talk) 21:35, 24 March 2014 (UTC)

See Micelle and Liposome for examples of these liquid-in-liquid bubbles. 24.5.122.13 (talk) 01:36, 25 March 2014 (UTC)

March 25

Heart disease

Can heart disease cause a rash on the patient's chest (and in particular, a red mark shaped like the letter "A")? Note: this is NOT medical advice (as you can hopefully see from the link). 24.5.122.13 (talk) 01:39, 25 March 2014 (UTC)

Why would you think that it could ? StuRat (talk) 03:21, 25 March 2014 (UTC)

See [2] for more relevant inspiration. Wnt (talk) 04:15, 25 March 2014 (UTC)

True enough -- but do you suppose the Reverend branded himself as a form of penance? 24.5.122.13 (talk) 06:25, 25 March 2014 (UTC)

It's a long blathery tale told from a mad perspective, which doesn't even say exactly what was there, if anything - for all I know he could have imagined it, it might have been supposed to be a divine manifestation, he scratched it into his flesh over and over again with his fingernails, who knows? What I do know is that there's a sternum, a not inconsiderable mass of bone, separating the heart from the skin except in certain cases of congenital malformation. Any relation with heart disease would have to be an incredible Rube Goldberg biological mechanism. Wnt (talk) 15:31, 25 March 2014 (UTC)

Thanks for the answers, everyone! The reason why I asked is because the Reverend's physical symptoms (weakness, unhealthy pallor, chest pains) are unmistakably those of heart disease. However, considering what you told me, and what the book says, the most likely explanation is that his remorse for his transgression (and not just for the act itself, but for seeing Hester suffer public ostracism while himself being unfairly spared from it), and the stress caused by the need to hide it from the public, both exacerbated his heart disease and also drove him to brand himself as an act of penance (among other things such as rigorous fasting, nighttime vigils, self-flagellation, etc.) 24.5.122.13 (talk) 22:53, 26 March 2014 (UTC)

What might happen in a wall wart if connected across a battery?

I made my own dynamo-powered bike light with a very simple circuit which charges some NiCad cells to keep the light on when I stop at traffic lights. Due to a disconnected wire, I used it without input which of course drained the cells. I tried to the charge them in a manner I did once before - by connecting via crocodile jumper leads to a variable wall wart power supply. Now I'm trying to do the same thing but the light on the power supply turns off whenever connected across my cells. What might be happening inside that power supply? Does it short the batteries? I imagine it was never designed for this purpose but it did work once before set at 6 V and at 7.5 V (I have five cells connected to form a ~6 V battery) --129.215.47.59 (talk) 12:04, 25 March 2014 (UTC)

I'd guess the cells are fried. If you lucky one is fried and the others are OK. If you had a multi-meter you could test to see if there is any juice left in them, normal discharged cells will still read 0.1V–1V. If you lucky the power supply has some short circuit protection and its detecting a short and switching off, if your unlucky you have fried the power supply as well. Normally when charging the current is limited to prevent the batteries over heating or over charging, connecting them straight across the power supply didn't have such protection. See Rechargable batteries--Salix alba (talk): 15:06, 25 March 2014 (UTC)

I think a miscommunication occurred. The battery has open circuit voltage 5.9 V and the charger, still set to 6 V is at 6.02 V (plus or minus whatever), according to my multimeter. I didn't leave them charging and come back. I attempted to initiate charge and no current would flow (and the light on the power supply would go out) whereupon I left everything disconnected and posted here. 129.215.47.59 (talk) 17:09, 25 March 2014 (UTC)

It sounds as if your power supply has a current limiter and switches off because it thinks it is being short-circuited. Try putting a small resistance in series with the circuit to limit the current that is drawn. Why not just recharge the cells with your bike dynamo (with the lights turned off)? Dbfirs 17:33, 25 March 2014 (UTC)

....Wall wart?

Magnet motor

Hi, on WP Their is a redirection on Magnet motor to Perpetual motion. Don't magnets lose there magnetism over the years? What do you think of those videos [3] [4] [5]. --YB ^✍ 14:32, 25 March 2014 (UTC)

All videos showing free energy from magnets are fake. There is no exception to this. Magnets can indeed loose their magnetism.217.158.236.14 (talk) 15:07, 25 March 2014 (UTC)

As a general rule, nearly all "science" videos on YouTube are fakes. Sure, there are a few honest people making nice videos of real effects - but they are BY FAR outnumbered by the pathetic fakes and camera tricks. When you see an amazing effect on a YouTube video, it's about 90% certain that it's a fake.

The confusion that nearly everyone who proposes these things has is that they confuse the physics concept of a "Force" with the concept of "Energy" or "Work". Something can exert a force without consuming any energy. If you hang a weight on the end of a chain, the chain is exerting a force on the object (in this case, it's equal and opposite to the gravitational pull of the earth). But nobody thinks the chain is going to lose it's ability to support weight because it somehow "runs down" like a dead battery. Magnets are the exact same deal - they can support a weight against gravity without consuming energy in the process.

However, as soon as you get something moving as a result of a force, some energy had to be expended to make that happen - and once it's gone into moving the object, the energy is lost to whatever set it in motion. Magnets don't contain any special energy source - so they can't be used to "power" a machine. That's why 100% of "magnet motor" videos are faked. These machines cannot possibly work - but it's not because the magnet might "run down" - that's a complete red herring.

Sure, you can use a magnet to pick up (say) a steel ball-bearing from a table...but that's a one-time thing. Once the ball-bearing is stuck to the magnet, you've got to use some energy to pull it away again - and the amount you need is more than the energy that was required to put the ball-bearing there in the first place. So you can't use this to make perpetual motion.

It's just the same as using gravity to do the same job. You can roll a ball down a hill - but to do that a second time, you have to expend some energy to raise the ball back to the top again. You can't make a perpetual motion machine from gravity either.

SteveBaker (talk) 21:30, 25 March 2014 (UTC)

The above lecture contains almost only correct usages of the contraction "it's" meaning "it is". 84.209.89.214 (talk) 00:12, 26 March 2014 (UTC)

Now don't be sad, ’cause six out of seven ain't bad. —Tamfang (talk) 05:30, 26 March 2014 (UTC)

As to how the fakery is done in this case, notice in the first video that the device the magnetic gizmo is attached to is supposed to be a generator, but that isn't what it is. The metal cylinder is suggestive of a generator housing, but it's a plain cylinder of metal, without any heat sink fins or at least air holes to help cool off the windings that one would expect on a real generator of that size. Also, in addition to the expected wires that carry the power from the back end of the "generator", there's also an extra small pair of wires coming out of the rotor end of the "generator", which wouldn't make any sense if that device was really a generator. The other end of that pair of wires, which go to the magnetic gizmo, would also make no sense if the "generator" was really a generator. The magnetic gizmo is supposedly a purely mechanical device (it doesn't contain any windings or other visible circuitry) that produces its own energy, so why would it need power supplied to it from the generator? I think the paper with "challenge to all the engineers" written on it a bunch of times that's wrapped around the top of the "generator" is there to help with the illusion by helping to hide the fact that that metal cylinder really doesn't look all that realistically like a generator. I think the "generator housing" is what contains the batteries that are really powering everything, as well as the motor that keeps the useless but impressive magnetic gizmo in motion. The small pair of wires that don't make sense if you assume the setup isn't fake make total sense if you assume that in reality, those wires are attached to a switch connected to the gizmo housing such that shutting the gizmo housing is what switches on the motor and external circuit.

Hopefully this "explanation" will be adequate for me to get my payment from the free energy suppression conspiracy consortium. Red Act (talk) 05:46, 26 March 2014 (UTC)

Actually, a buried power cable into the base of the fan would also work as the power source, instead of batteries in the motor housing. The fan is never lifted, it's always plugged in while the device is running, and it's sitting on a patch of dirt next to the patio instead of being on the patio like everything else is. Red Act (talk) 06:16, 26 March 2014 (UTC)

The point is that magnet motor should not be called a perpetual movement machine because magnets lose their magnetism after a while.--YB ^✍ 14:56, 26 March 2014 (UTC)

I think the amount of energy stored in a permanent magnet must be small, but how do you calculate it? I'm thinking the magnetic field necessarily contains some energy, but that doesn't speak of the magnet itself. Another way I look at it gets a different result: take two strong magnets sitting on a table at rest. They snap to each other, liberating a small amount of extractable energy in the process. Now in order to demagnetize them, you need to put that energy back in, so when stuck together they actually have less energy than demagnetized magnets... right? But... if you chop up and randomize a magnet into itty bitty pieces, letting them all reassort to neutralize each other, doesn't that get the most energy out of them? Oh phooey, I confused myself this time. But looking at a paper from 1953 there seems to be a formula, based on the idea that a material usually adopts a magnetization state that minimizes its free energy as one would expect; it still needs some unpacking to get to a number though. Wnt (talk) 15:07, 26 March 2014 (UTC)

No, magnets losing their magnetism over time is irrelevant. The phrase "perpetual motion machines" isn't used to describe a set of devices which are actually capable of running literally forever. Instead, it's used to describe a set of devices which are intended by their inventor to be capable of violating the first and/or second laws of thermodynamics. All "perpetual motion machines" would stop functioning eventually due to wearing out in one way or another. But the more important problem that makes such devices be called a "perpetual motion machine" is that they are incapable of violating the laws of thermodynamics as intended even initially, long before wearing out would ever become an issue.

Besides, magnets can hold their magnetism for centuries. A perpetual motion machine that uses magnets would fail due to wear on its bearings long before demagnetization would be the expected failure mode. Red Act (talk) 17:40, 26 March 2014 (UTC)

I think there's some confusion here. Magnets do not contain energy.217.158.236.14 (talk) 16:15, 26 March 2014 (UTC)

E = MC^2. Which implies that Wnt's two magnets will have a (very slightly) greater mass when separated than they do when they come together. (See also this old ref desk discussion on the increase in mass of an alarm clock spring resulting from it being wound up [6]). AndyTheGrump (talk) 16:25, 26 March 2014 (UTC)

And it takes a certain amount of energy to unstick two magnets. But it's not the point.--YB ^✍ 16:39, 26 March 2014 (UTC)

Wow, it would be easy to miss that you tweaked "point" to link to magnetic bearing. However, magnetic bearings would be inadequate to keep a device rotating without energy input until demagnetization became an issue. Magnetic bearings use permanent magnets to provide the bias field, but usually require active control coils for stability purposes, due to Earnshaw's theorem. Those active control coils consume energy due to resistance in the coils resulting in Joule heating. A homopolar electrodynamic bearing doesn't require control coils, but it works due to induced eddy currents. Those eddy currents again cause energy loss due to Joule heating, causing the rotor to slow down until it ultimately stops. Red Act (talk) 03:43, 27 March 2014 (UTC)

Even an electron, which really does spin forever, is not a perpetual motion machine, because a "perpetual motion machine" is a device that violates the first or second law of thermodynamics and not, despite the name, one that moves forever. All this discussion of whether a device made of magnets will eventually spin down seems irrelevant. Getting back to the original question of whether "magnet motor" should link to "perpetual motion", I think it probably shouldn't because the phrase could just as well refer to an ordinary electric motor. -- BenRG (talk) 07:50, 27 March 2014 (UTC)

Amber-colored vertical displays

FCR 1 in 2009 during the STS-128 mission.

What are these vertical, amber-colored displays? What do they do? Why don't they just use normal LCD monitors? -- Toytoy (talk) 16:41, 25 March 2014 (UTC)

The look like old Monochrome monitors from the 1980s. As to why they use them, perhaps they are connected to a system that uses them and has not been upgraded. The principle "if it ain't broke, don't fix it" may apply here. --Jayron32 16:51, 25 March 2014 (UTC)

And it looks like it's only used to display text data, where color isn't all that useful. Also, you don't have to worry about picking colors so the colorblind can still read it properly (unless they do something really stupid, like green text on a red background). StuRat (talk) 16:55, 25 March 2014 (UTC)

Very first Ghit for mission control amber suggests they show the console DVIS panel (Digital Voice Intercom System).--Shantavira|^{feed me} 17:00, 25 March 2014 (UTC)

Yes, they're the DVIS keysets which allow controllers to connect into different voice channels (like a phone conferencing system, where the conferences are on all the time). info. DVIS is the second generation system, consisting of an amber aviation-grade touchscreen; the first generation was VIS, which had a physical button for each channel, and DVIS was replaced with DVICE, which is a more modern LCD touchscreen. Photos of all three are here. -- Finlay McWalterჷTalk 17:16, 25 March 2014 (UTC)

A little bit more about DVIS operation is here. -- Finlay McWalterჷTalk 17:33, 25 March 2014 (UTC)

The display looks a lot like the "plasma panel" invented at the University of Illinois in 1964, later marketed by IBM, which used a flat neon based panel which could both store a display and was touch sensitive. It may be a precursor of today's plasma TV displays( which don't have the touch sensitive feature). Edison (talk) 16:51, 26 March 2014 (UTC)

March 26

Kessler Corporation? A background check.

we can't give legal advice, of which this is a classic case. μηδείς (talk) 03:05, 26 March 2014 (UTC)
The following discussion has been closed. Please do not modify it.
I recently got a patent and it has been published. Lo and behold a couple of weeks later I got a letter from the above firm offering their services (for a substantial fee) to help me to find manufacturers interested in implementing the invention. I have already set different plans in motion and this offer is not on my map but I am still curious. I want to keep various options open. I wonder if anybody heard about the company (positive or negative) and could shed any light. Thank you --AboutFace 22 (talk) 00:47, 26 March 2014 (UTC) You could check with BBB, they have a review: Accredited A+  —71.20.250.51 (talk) 01:06, 26 March 2014 (UTC) If you have a patent you should be seeking advice from a patent lawyer, not some random people on the internet. μηδείς (talk) 03:05, 26 March 2014 (UTC)

Closed per μηδείς (talk) 03:05, 26 March 2014 (UTC) as a request for legal advice.
μηδείς (talk) 03:05, 26 March 2014 (UTC)

What is your reason for treating the question as a request for legal advice? It's not a question whose answer requires knowledge of the law or application of legal principles. --173.49.81.186 (talk) 04:21, 26 March 2014 (UTC)

The BBB is a 501(c)(6) non-profit Accreditation organization. "Background checks" on companies is mostly what they do. In the US, that's the 1st place most people look to check the reputation of a (US) company.  —71.20.250.51 (talk) 05:05, 26 March 2014 (UTC)

I appreciate the comment by the poster who objected to defining my OP as a request for legal advice. It was far from what I had in mind. I want to see if anybody had experience dealing with this company on a practical level. The original issue (obtaining the patent) was perfectly scientific, so this is its extension. --AboutFace 22 (talk) 14:22, 26 March 2014 (UTC)

This is in no way a request for legal advice. It's a request for information about a business, which was prompted by that business contacting the asker in relation to a published patent (itself a legal document, but that's irrelevant). Even if the question was asking for an opinion on a firm of lawyers, it wouldn't be legal advice ("You don't need to talk to an X lawyer about this" - Possibly legal advice, "Y,Z & Q LLP are a terrible law firm, all of their letters were printed on rabid bobcats which made them extremely hard to read" - not legal advice). As it is, the question isn't even related to patent law, just a company offering to help commercialise an invention, and using patent publications to find clients. MChesterMC (talk) 16:47, 26 March 2014 (UTC)

This is a reference desk. Maybe the OP could specify some matter we can help with, like the company's contact numbers, any news they have been mentioned in in the last few years. WE cannot give our own opinions of the company itself (see the section on opinions at the top of this page) or offer original research WP:OR or comment on their reliability or busniess practicess, which my subject us to suit for defamation, or give advice on patents ourselves, since that is indeed legal advice. IP 71 has given a helpful comment. μηδείς (talk) 17:34, 26 March 2014 (UTC)

The OP didn't ask for opinion. (His request was certainly not umambiguously a request for opinion, and arguably not one.) Even if he did, the helpful response would be to tell others to refrain from offering opinion, not to hastily declare the question "closed". Posters of questions may not always phrase the question the best possible way at first; useful answers can nevertheless be provided, not necessarily to the original question as asked, but to the question that the OP should have asked instead. In this case, the OP was really asked for input to help to form an opinion about an entity. What other people may have "heard" need not be subjective opinions, they can be verifiable facts. They can take the form of honors and recognitions, rankings, metrics of past performance, records of criminal conviction/civil penalties etc. --173.49.81.186 (talk) 02:51, 27 March 2014 (UTC)

Dowmo alloy electrical resistivity vs temperature

Does anybody know where I can find information on the resistivity versus temperature characteristics of "dowmo" alloy (tungsten & molybdenum 50:50)? I need it over the range 300 K to at least 1200 K, so Mitchell's formula is unlikely to be accuate. Worthing's formula might be. I found nothing via Google. I know it's about the same as pure tungsten at the high end of the range, so even a single measured value near 300 K would help a lot. 120.145.131.60 (talk) 03:14, 26 March 2014 (UTC)

Light bulb brightness in circuits

Hey everyone, I have two questions relating to physics and electricity. I think I did them right, but I just wanted to double check:

1. A resistor measuring 330Ω and 3.1V, and an LED measuring 190Ω and 1.8V, are placed in series, both with a current of 9.5mA. If another resistor is added in series to the circuit, would the brightness of the LED change? I said no, because if the current is the same throughout the entire circuit in series, there would be no difference if another resistor was added, only the voltage would change.
2. The first resistor and LED (from the above question) are placed in series again, but the two are in parallel to a third resistor. If the resistance of both resistors increases, what would happen to the brightness of the LED? Here I said that the brightness would change because while voltage is equal throughout, and resistance increases, current must decrease throughout the circuit and so the brightness decreases.

Was I right? Thanks everyone. 64.229.204.125 (talk) 03:18, 26 March 2014 (UTC)

The question is incompletely stated. The current and voltage are also determined by the rest of the circuit, so rearranging things can change both the total voltage and current. It is likely that the implicit assumption that you were intended to make (but this reflects badly on whoever set the question) is that the source of the current is a battery or power supply of negligible internal resistance (this should have been made explicit in the question). From the initial setup, this is a voltage of 3.1V + 1.8V = 4.9V. You were then presumably supposed to make inferences about the voltage vs. current characteristics of each component and how this would affect the current in the diode in each new configuration. This gives you different results in the first question. In the second question, while your final answer is correct, the voltage does not stay the same throughout due to the different voltage vs. current characteristics of a LED and a resistor. —Quondum 04:02, 26 March 2014 (UTC)

1. IF the current through the series circuit is constant then you are right that the LED brightness doesn't change. Two problems: a) it's rather unusual to power a circuit from a constant current supply. For example a battery gives a constant voltage and adding a series resistor would reduce brightness. b) Ohm's law applies to the resistor exactly so 3.1V across a 330 resistor causes a current of 9.394mA, not 9.5mA. (A LED has non-linear I-V characteristic so Ohm's law cannot apply to it.) I have provided links to articles in Simple Wikipedia that may be helpful. The same subjects are covered in higher detail in Wikipedia.
2. IF the supply is a constant voltage then the 3rd resistor across the supply has no effect on the current in the LED, and you are correct that the LED brightness decreases when its own series resistor is increased. 84.209.89.214 (talk) 01:14, 27 March 2014 (UTC)

Sorry, I should elaborate on a few details. 1) There are only 2 significant digits to work with, so 330Ω was rounded up. 2) the circuit was completed on a breadboard, with the current being direct, but plugged into a power outlet. 64.229.204.125 (talk) 01:55, 27 March 2014 (UTC)

Military careers

Is the military a good career for people who find desk work stressful? As although military is stressful it's a different type of stress to that of desk work. 82.132.244.5 (talk) 14:11, 26 March 2014 (UTC)

Yes, there's very little chance of being blown up by a roadside bomb if you're merely working at a desk. You might also want to look for numbers on the quantity of combat troops vs. the quantity of support personnel, many of which have... desk jobs. ←Baseball Bugs ^{What's up, Doc?} carrots→ 14:21, 26 March 2014 (UTC)

Different people find different types of careers "stressful" based on their aptitude and personality. That is, while one person may be energized and well suited to something like being a police officer, another person would find it highly stressful and unpleasant. There's no universal set of values for this thing. If you are in the United States and are interested in a career in the U.S. military, it is often recommended that you take the Armed Services Vocational Aptitude Battery test, which is designed to find a recruit's strengths and weaknesses, hopefully to place them on a career track to which they are well suited. I see by the geolocation of your IP that you are in the UK, so perhaps the UK has a similar method of evaluating potential military recruits for jobs they are well suited for. You may want to into that. --Jayron32 16:45, 26 March 2014 (UTC)

What did Folding @ Home accomplish?

I participated in the Folding @ Home program for a few years with a couple PS3s and home computers. The promise was that it might cure diseases and discover new treatments. But did it? --209.203.125.162 (talk) 17:28, 26 March 2014 (UTC)

Have you read Folding@home? It lists several conditions (such as Alzheimer's and Huntington's) where the program has been useful. I don't believe the project is intended to find cures itself, but to provide information that other researchers can use. Rojomoke (talk) 17:51, 26 March 2014 (UTC)

I seem to recall a few instances where it produced homology models that were usable starting points for molecular replacement, but I don't really have any sources for that. Actually, here's a source, although this was actually using data from Foldit not from Folding@home: Nat Struct Mol Biol. Sep 18, 2011; 18(10): 1175–1177. For what it's worth, it still seems like traditional homology modeling has a much higher success rate. (+)H₃N-Protein\Chemist-CO₂(-) 18:28, 26 March 2014 (UTC)

Eating nitrocellulose

What would happen if you eat some nitrocellulose?

Is it poisoning, or would it be much like eating regular cellulose? 91.77.188.8 (talk) 17:43, 26 March 2014 (UTC)

I am assuming that you are asking what would happen to a typical adult human being when he eats nitrocellulose? 140.254.227.69 (talk) 17:57, 26 March 2014 (UTC)

According to the encyclopedia britannica, nitrocellulose is used in gunpowder and explosives. Hmmm... I don't think you want to ingest that, because that sounds like smoking a cigarette. A pack of toxins into your bloodstream. 140.254.227.69 (talk) 18:02, 26 March 2014 (UTC)

Being explosive doesn't automatically mean it's not edible. Nitroglycerin, for example, is ingested as a heart medication. See Nitroglycerin#Medical use. StuRat (talk) 00:55, 27 March 2014 (UTC)

I must add that safeness of chemical compounds has nothing to do with the name. The name is just used to describe the chemical structure or components. In order to identify the safeness of a compound, you may want to look up Material safety data sheet. 140.254.227.69 (talk) 18:12, 26 March 2014 (UTC)

According to the Nitrocellulose Safety Data Sheet, there are several problems associated with even getting close to the substance, let alone ingesting it. Always handle unknown chemicals with care. Wear gloves and goggles and maybe a lab apron, though, in most cases, you probably don't need a lab apron. (I never used one, and gloves are usually appropriate in a biomedical lab that deals with biohazards and stuff.) 140.254.227.69 (talk) 18:26, 26 March 2014 (UTC)

Nitrocellulose paper is very commonly used in western blots as a substrate onto which to transfer protein from an SDS gel, and although it is (obviously) flammable if exposed to an ignition source, I don't think it's quite so super hazardous to handle as long as you don't set it on fire. To answer the OP's question though, no, you shouldn't eat it. FYI, that's the answer to virtually every question that starts with "Is this [random thing I found in lab] safe to eat..". The answer is always "no". (+)H₃N-Protein\Chemist-CO₂(-) 18:40, 26 March 2014 (UTC)

Indeed, "should I eat it?" should always be followed with the question "is it food?" If the latter is "no" a safe assumption is that the former should be "no" also. --Jayron32 23:13, 26 March 2014 (UTC)

Is it possible to return the pulse by CPR when having Asistola in the heart?

Someone told me that the pulse can not return by CPR if the heart has total asistola. He told me that when the pulse return it's say that had only a few contractions before, and that the reason why the pulse returned (about 10 for a minute). Is it right or not? 213.57.123.85 (talk) 18:48, 26 March 2014 (UTC)

CPR (but not defibrilation) is still indicated in case of asystole. Recovery, while unlikely, is still possible. Ruslik_Zero 19:20, 26 March 2014 (UTC)

I know that CPR (without defbriliation) is still indicated in case of the asystole. But it's definitely not the question... The question is What had been under the chest before you returned the pulse. Was it total asystole or was it few contractions. I hope I explain myself well, because English is not my mother language. 213.57.123.85 (talk) 19:54, 26 March 2014 (UTC)

The masses and tensions of violin strings

I've been trying to find masses and tensions for a real life violin string, so that I can make realistic physics problems about the wave speed and frequencies. All I can find in web searches are physics problems posted to sites like answers.com. They give masses on the order of ~0.500 grams. Is that realistic? That tends to lead to tensions on the order of hundreds of Newtons. Are violin strings really under tensions that huge?Inkan1969 (talk) 19:27, 26 March 2014 (UTC)

Basic physics of the violin points us to this chart which gives tensions. -- Finlay McWalterჷTalk 19:42, 26 March 2014 (UTC)

Thank you for the link. I couldn't find an article like that.Inkan1969 (talk) 19:48, 26 March 2014 (UTC)

This (which assumes equal tension on each string) gives corresponding gauges in metres, and this table (from the same folks) gives gauges and mass per metre - note that these are for natural gut core strings; steel core strings will surely be quite different. -- Finlay McWalterჷTalk 20:10, 26 March 2014 (UTC)

These are tensions in the 40 to 80 N range, so not quite in to the hundreds. Guitar strings are tensioned to about double that. A pretty thorough list of tensions for various strings (for guitars and related instruments) is here. -- Finlay McWalterჷTalk 20:28, 26 March 2014 (UTC)

Clean burning

Are there any solids that burn entirely without leaving any leftovers on the surface they have been ignited at.

I know some liquids like alcohol might have such properties, but it what about solids? 91.77.160.11 (talk) 20:04, 26 March 2014 (UTC)

A thought in the right direction but not a full response. In order to leave no leftovers the combustion reaction would have ideally have to be a complete combustion, where all the reaction products are gas, which then disperses.

One class of solid materials which as far as I know undergo complete combustion to gas are explosives, However they do so sufficently quickly that they also take out the ignition surface.Sfan00 IMG (talk) 22:56, 26 March 2014 (UTC)

I agree that leaving no left-overs implies the reaction products are solely gases, but that's quite common: for example pure sulfur (solid) burns in oxygen to give sulfur dioxide (gas). Incidentally, some solids can completely dissociate into gases without burning: ammonium chloride (solid) becomes ammonia (gas) and hydrogen chloride (gas). --RexxS (talk) 23:09, 26 March 2014 (UTC)

Diamond, though again the fire will damage the fireplace. Jim.henderson (talk) 23:03, 26 March 2014 (UTC)

Nitrocellulose comes pretty close. Magicians use it as "flash paper" because after burning it leaves almost no visible ash or smoke. Nitrocellulose was also used as the basis for early types of smokeless powder, the lack of solid particulate in the combustion process is what makes the smokeless (since smoke is basically solid combustion products dispersed in air). --Jayron32 23:11, 26 March 2014 (UTC)

If you burn them hot enough, the solid hydrocarbons will produce only carbon dioxide and water vapor. (If you can't manage a hot enough flame, you get soot.) --Carnildo (talk) 02:59, 27 March 2014 (UTC)

Regarding the comment that only gases should be produced: I agree, but keep in mind that they may not be gases at room temperature, only at the combustion temperature. Water vapor is a good example, but there may be other products which are either liquids or solids at room temperature, but are vapors when they leave the fire. Of course, solids that then redeposit when they cool may not meet your standard for "clean burning", but liquids which recondense might, if they are clear and harmless, like water vapor. StuRat (talk) 03:12, 27 March 2014 (UTC)

As long as it's partial pressure remains below the vapor pressure, the water vapor produced during hydrocarbon combustion remains a vapor at ambient temperature as well. It wouldn't start condensing unless the air was locally at 100% relative humidity for the ambient temperature. --Jayron32 08:43, 27 March 2014 (UTC)

Reversible cycle

A classic method of showing that the Carnot cycle has the maximum efficiency between two given temperatures depends on its reversibility.: If a more efficient heat cycle existed, the reversible Carnot cycle can be used as a heat pump to pump all the heat lost by the more efficient engine out of the heat dump and either use it as work or return it to the heat reservoir. But the two engines combined then form a 100% efficient perpetual motion machine. A more detailed explanation of that scenario is shown here. The Carnot+better combo can also be used to make heat flow from the colder dump to the warmer reservoir without any work.

Now a reversible cycle can be represented as a well defined closed loop on a P-V graph. Here's the Carnot graph. But what confuses me: Isn't ANY cycle that can be represented as a well defined closed loop on a P- V diagram a reversible cycle? Like the Otto cycle and the diesel cycle? Then is reversibility actually a property not exclusive to the Carnot cycle? Further, couldn't I then join a Carnot cycle with a less efficient but reversible cycle (with a well defined closed loop) to make a perpetual motion machine? Thank you in advance.Inkan1969 (talk) 20:22, 26 March 2014 (UTC)

Our article at Otto cycle states that this cycle comprises four distinct processes - two of them reversible and the other two occurring at constant volume but not reversible. Therefore I don't think it is correct to assume the Otto and the Diesel are reversible. Dolphin (t) 22:03, 26 March 2014 (UTC)

Clearly Otto is reversible, while Diesel is not, giving us leseiD if we attempt to reverse it. :-) StuRat (talk) 01:42, 27 March 2014 (UTC)

Wouldn't any cycle which starts with a chemical fuel need to produce that chemical fuel again in order to be fully reversible ? StuRat (talk) 01:42, 27 March 2014 (UTC)

The air standard cycles, such as Otto and Diesel, disregard the practicalities of where the heat comes from. In order to determine a thermodynamic efficiency, they simply postulate that there is an increase in temperature and pressure at a constant volume. An increase in temperature and pressure at a constant volume won't be reversible. (Good point about the palindrome.) Dolphin (t) 05:52, 27 March 2014 (UTC)

I thought Palindrome is the other name for Wasilla Airport? ;-) 24.5.122.13 (talk) 06:33, 27 March 2014 (UTC)

March 27

Meth addicts

Whenever you see photographs of meth addicts, they usually have scabs all over their face, as if they pick at their skin. Why is that? Thanks. Joseph A. Spadaro (talk) 05:02, 27 March 2014 (UTC)

According to this, they pick their skin obsessively due to a sensory hallucination of bugs crawling beneath the skin. The technical name for that is delusional parasitosis, also known as "crank bugs". Red Act (talk) 05:24, 27 March 2014 (UTC)

Angle of penis

Links in this question are NSFW.

The article Erection provides a table with the distribution of erect penis angles. But what does it tell us, how is the angle measured? Few penises are completely uncurved. Take the image in the article: at the root it has an angle of about 70° while at the glans it has an angle of about 35°. Which of the values is the correct one? Or does one have to draw an imaginary line through root and glans and measure the angle of this line?

I have no access to the original paper. Does anybody know or can look it up in the paper?

Also asked on Talk:Erection#Angle a few days ago, but with no answers so far. --31.16.110.207 (talk) 10:26, 27 March 2014 (UTC)

How do coil cords get kinked up the way they do?

Here's a link to a YouTube video on how to untangle a coiled cord [7]. My question is: how does a coil cord seemingly suddenly develop a "reversal turn" in the middle of the cord in the first place? I have a hard time visualizing it happening, because the cord on either side of the "turn" looks normal, and certainly nobody did anything like the opposite of the procedure in the video to put the "turn" there. Is there a better way than what's in the video to fix the problem? I fixed a coil cord once by shifting the "reversal turn" to one end, one turn at a time. But the thing is, the cord didn't look quite the same afterward. The length of the cord where the shifting of the "reversal turn" has passed through became visibly less tight than before. --96.227.60.84 (talk) 11:50, 27 March 2014 (UTC)

weights and rest

I heard that weight training (doesn't matter what part of body) shouldn't be done more than two days in a row i.e the third day should be resting or cardio if needed. Is it scientifically sound to say that even if i give rest to my body parts and concentrate on different part the next day still my whole body needs a day of rest ??