Revision as of 03:15, 26 March 2014

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

• WP:RD/S

Main page: Help searching Misplaced Pages

How can I get my question answered?

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

How do I answer a question?

Main page: Misplaced Pages:Reference desk/Guidelines

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

• Teahouse
• Help desk
• Village pump
• Help manual

March 22

Capsaicin half-life?

Thanks. Regards. 95.35.51.89 (talk) 00:21, 22 March 2014 (UTC)

Approximately 24 hours, elimination half-life is 1.64 hours. --Canley (talk) 00:31, 22 March 2014 (UTC)

If you're asking about the burning feeling it causes humans, that might be a bit more difficult to figure out, as we also become accustomed to it over time. StuRat (talk) 00:45, 22 March 2014 (UTC)

Referencing to the first answer: What is the difference between the 24 period to the 1.64 period of biological half-life? 109.64.137.68 (talk) 04:04, 22 March 2014 (UTC)

They are actually both elimination half lives. The 24 hour figure is the half life of capsaicin on human skin, whereas the 1.64 hour figure is the half life of capsaicin in human blood plasma. Neither is the half life of say, capsaicin in a pepper, or a bottle of hot sauce, or prepared food. Someguy1221 (talk) 04:15, 22 March 2014 (UTC)

Is it true that all human embryos are initially female?

Someone told me that all human embryos start out with just the X chromosome, and then develop for a period of time, and then hormones and another Y chromosome are added at a later stage of development to make it male. Is this true? ScienceApe (talk) 00:48, 22 March 2014 (UTC)

No. You start out with your full set of chromosomes right from conception. However, it is true that the embryo looks female at the beginning, as the penis doesn't develop until later, and the testicles don't descend until much later, sometimes even after birth. StuRat (talk) 01:01, 22 March 2014 (UTC)

I got carried away with details below, but I should say first: the human egg starts out with an X chromosome, and indeed, it is undeniably female, being part of the female body and being the female gamete. But the sperm carries either X or Y, which quite rapidly fuse during fertilization.

See, oh, Sex determination and differentiation (human), Sexual differentiation, genital ridge, Mullerian ducts, Wolffian ducts. Embryos are sort of female, but then again ... so are men. The only meaningful way to define male and female is by the essence of the embryo, i.e. its future programmed sexual development. That said, the chromosomal type isn't always XX or XY, nor a perfect prediction (see Turner syndrome, testicular feminization, freemartin, SRY. So in order to truly determine the sex of an embryo with perfect reliability... you have to watch it grow up. And even then maybe it's transsexual and it and you still can't make up your mind. :) Bottom line: the sex of an embryo is an abstraction, an imperfect model. You have to simply cite the evidence you have, such as the karyotype or other genetic test, and more than 99% of the time that will be perfectly convincing. Wnt (talk) 01:20, 22 March 2014 (UTC)

Below? In the skyhook thread? Gametes don't have sex, only zygotes do. Otherwise you are of the absurd opinion that all sperm are male, which is obviously false. μηδείς (talk) 03:26, 22 March 2014 (UTC)

Hmmmm... now that's an amusing philosophical question. Clearly sperm can be "female" in that they carry an X chromosome and have a wild aspiration to give rise to baby girls. But even more clearly they are male because they are part of a man's body - I mean, if sperm isn't male, what is? Biology really doesn't have a lot of respect for semantics. :) Wnt (talk) 11:08, 22 March 2014 (UTC)

To say that eggs are female because females produce eggs is like saying cakes are bakers because bakers make cakes. It just doesn't follow. μηδείς (talk) 18:04, 22 March 2014 (UTC)

If the union of sperm and egg isn't a case of male and female joining up, I don't know what is. I mean, if a transsexual impregnates a woman, it goes to show she isn't "fully" female because there's a part of her that's male. I'll tell you one thing, this looks to be a damn sight more amusing than arguing about the chicken and the egg! Wnt (talk) 17:15, 23 March 2014 (UTC)

The SRY gene on the Y-chromosome makes a mammalian embryo develop as a male; without it the embryo will develop as a female. However, before the SRY gene is expressed, there is no difference between a genetically male or female embryo. CS Miller (talk) 11:59, 22 March 2014 (UTC)

To be picky, SRY is a lot, but it's not absolutely everything. XX male syndrome isn't the same as being XY - so far as I know, they're always infertile due to the lack of some important details (especially for sperm-making) on other parts of the Y chromosome. Even in young embryos there may be important unknown differences, and there are technically distinctive known differences such as the X-inactivation in females (though come to think of it, Klinefelter syndrome males also have that...) and well, the presence of the Y chromosome itself. But yes, in the visible aspects known the early genital ridge looks undifferentiated due to lack of SRY expression as you say. Wnt (talk) 13:05, 22 March 2014 (UTC)

Moon winch

How about installing a winch on the moon and hoisting stuff up into space that way? Is that any less feasible than a space elevator? --78.148.110.69 (talk) 02:39, 22 March 2014 (UTC)

If you've got 400,000 kilometers of cable lying around, then go for it. --Jayron32 02:45, 22 March 2014 (UTC)

(edit conflict)One big problem I see is that the Moon isn't in geosynchronous orbit. So the hook at the end of the cable would be moving along the face of the Earth at thousands of miles per hour. Dismas| 02:46, 22 March 2014 (UTC)

While you've got a strong point in general, is that calculation really correct? What is the actual "ground speed" of the moon relative to the earth? It takes about 12 hours for it to get from one horizon to the other, so I would think its ground speed would be in the neighborhood of 1,000 miles per hour. Not exactly slow, but maybe could be used as a space-age equivalent of the old railroad system of a train grabbing a mailbag on the fly. ←Baseball Bugs carrots→ 03:59, 22 March 2014 (UTC)

(edit conflict)It's considerably less feasible. A space elevator has two big advantages over a moon winch: 1) the cable doesn't need to be as long, and 2) the base of the elevator isn't moving relative to the Earth's surface. --Carnildo (talk) 02:47, 22 March 2014 (UTC)

And the reason why long cables don't work is that the weight of the cable is vastly more than the cargo, to the point where the cable can't even support it's own weight and breaks. Even with a long kite string the weight of the string starts to have a drag on the kite, and this is like a million times longer. The space elevator cable may one day be possible, but not the much longer cable to the Moon. StuRat (talk) 14:50, 22 March 2014 (UTC)

Hmmmmmm.... it's possible to make a sort of "cable" by, say, having a steel ball bounce between two steel plates in vacuum, or more realistically, having a rail gun that shoots objects out, which are caught, decelerated to store free energy, and reaccelerated back with that energy by another rail gun at the far end. Such a cable can't mediate an attractive force by any means I know of, but it certainly can induce repulsion. I can kind of picture the Moon being used to "levitate" an object on the far side of Earth by such a stream of exchanged bullets with inspired trajectories, with (hypothetically) relatively low input of fresh energy once it is established. Now if only I had Wile E. Coyote to manage the project! Wnt (talk) 15:04, 22 March 2014 (UTC)

But then it technically won't be a "moon winch", but a "moon gun" or "moon catapult". 24.5.122.13 (talk) 19:50, 22 March 2014 (UTC)

Also, it won't be capable of actually hoisting stuff into space from Earth's surface -- the most it will be able to do is shuttle stuff between low Earth orbit and the Moon. 24.5.122.13 (talk) 19:53, 22 March 2014 (UTC)

True. I think... unless there's some even more lunatic scheme I can devise. :) I suppose that you can boost yourself in something like a sounding rocket or space tourism vehicle to the mesosphere, and then the Captain orders (drumroll) ... "Engage the meteor drive!" The lumps of lunar rock, worked into ceramic heat shields with some robust electronics to control steering fins, pass through the atmosphere almost horizontally, steering to the tiny ship's position and slamming into its momentum receptacle! With blast after blast at incredible speed, the ship gains the crucial momentum to put it into orbit. Except, that is, alas, that it takes quite a bit of energy to redirect a rock from lunar to Earth-grazing orbit, and the energy in this model doesn't plausibly get recycled, so it requires having so much energy on the Moon that it's cheaper than energy taken (with considerable inefficiency) from Earth. Pity. Wnt (talk) 23:29, 22 March 2014 (UTC)

It'll be difficult to devise something even more lunatic than what is already out there – like in one SF novel where a stream of metallic projectiles was catapulted towards the earth, and used for reaction mass to "climb into space" by the reaction force of electromagnetically accelerating them faster downwards. —Quondum 04:47, 23 March 2014 (UTC)

The "moon catapult" concept was explored in some detail in the Robert Heinlein book The Moon Is a Harsh Mistress. It's a form of Mass driver. --Jayron32 04:55, 23 March 2014 (UTC)

+1 here, a railgun is an incredibly destructive kind of mass driver, in the sense that it damages itself when launching its projectile. "Mass driver" is the broader term, and the one we'd need here.

While we need quite a delta v for the transfer from the Moon to low Earth orbit, the very gravity well that makes the transfer difficult will add to the projectile velocity as they freefall towards Earth. Two weeks ago, we had a topic about how much energy it takes to push the Moon (in its entirety but not necessarily in one piece) into its own circumsolar orbit; this one hints at how much energy we could gain by essentially dropping small pieces of the Moon down Earth's gravity well...

Now we have two topics within one month to combine our moon and mass driver technology; does that make it a "blue moon"? - ¡Ouch! ( / _{more pain}) 06:57, 24 March 2014 (UTC)

Here, we'll need to make that a full moon to make it official. Ѡ Wnt (talk) 19:15, 24 March 2014 (UTC)

The Moon's orbit isn't perfectly circular, so the distance between the Earth and Moon isn't constant. I suppose, if all the other problems were magically fixed, this could actually be an advantage, as you could snag cargo at the low point and release it at the high point, some 42 thousand km up. StuRat (talk) 15:20, 22 March 2014 (UTC)

A related problem is pumping water from well. Suction (i.e. vacuum) will only lift water a finite difference (about 32 feet). But a submerged pump can push up water from a much larger depth. A cable not only has to lift the object, bur the cable itself. The weight of the cable is significant. --DHeyward (talk) 06:12, 24 March 2014 (UTC)

A better analogy is a rocket needing to not only lift the payload but also the rocket, fuel, etc. It's better because you need additional (thicker) cable to support the weight, which in turn adds it's own weight, and the rocket needs more fuel to lift the fuel, and that in turn adds more weight which requires more fuel. In the pump case you may need a bigger pump and thicker pipe to contain the higher pressure differential, but that doesn't add to the weight you need to pump.

Ultimately the solution for a rocket requires using an external power source, such as in a solar sail. StuRat (talk) 17:30, 24 March 2014 (UTC)

Abiogenesis mark 1

A few weeks ago I read an article about traces of multi-celled “organisms” which had been discovered around 2004. The article (from a nonscientific, but otherwise reliable source) implied that these “blobs” were the only “survivors” from abiogenesis mark 1 and significantly older than any of the primitive life forms discovered in Australia and elsewhere.
It seems, that these “blobs” became extinct and life disappeared from our planet for a few hundred million years (?) until abiogenesis mark 2 kicked in some 3.5 billion years ago.
I remember looking up the term used in the en:WP and found no article. Does anybody know what I might be talking about? Unfortunately, I recorded no bookmark, can´t remember more details and Googling gets me nowhere.
Thank you.--Cookatoo.ergo.ZooM (talk) 06:34, 22 March 2014 (UTC)

I assume you've checked out our abiogenesis article — there's plenty of blob-like stuff there. Your description almost sounds like Thermotoga maritima, except they're not extinct. ~:71.20.250.51 (talk) 06:49, 22 March 2014 (UTC)

It's been suggested that life may have arisen during the Hadean era prior to the giant impact hypothesis that created the moon. Such an impact would have wiped out all evidence of prior life, so there is no way to prove it. Someguy1221 (talk) 07:17, 22 March 2014 (UTC)

OP here: I managed to locate the report (in German). The blobs are called Gabonionta (discovered in Gabon). They are about 2.1 bio years old and measure about 35mm). Still, there is no article in the en:WP, indeed, all references I can find are either in German (but a red link in the de:WP) or in French (no article either). Thank you for your help.

--Cookatoo.ergo.ZooM (talk) 08:11, 22 March 2014 (UTC)

PS: Some additional data can be checked here. --Cookatoo.ergo.ZooM (talk) 08:18, 22 March 2014 (UTC)

citric acid Extracellular/Intracellular?

citric acid is a extracellular product or intracellular? --84.108.213.48 (talk) 10:45, 22 March 2014 (UTC)

It's produced in the Krebs cycle, which occurs in the mitochondria -- any guesses as to whether the mitochondria are inside or outside the cell? 24.5.122.13 (talk) 19:48, 22 March 2014 (UTC)

X chromosome inactivation in male mammals

In female mammals, one of her X chromosomes is deactivated at random in each cell. This is because in XY males, the Y chromosome has most (but not all) of the genes missing, and expressing genes from both chromosomes in females, and not in males can cause problems, due the doubled expression. My questions are

1. For the genes that are shared between the X&Y chromosomes, are both sets of genes expressed in males?
2. In females, is the deactivated X chromosome completely deactivated, or is the area conserved on the Y-chromosome still expressed?
3. If both sets of genes are expressed in males, and not in females, does this cause any problems?

CS Miller (talk) 12:14, 22 March 2014 (UTC)

The article you linked and pseudoautosomal region both talk about it a little. By and large, any statement in biology is at least a bit true and at least a bit false, and this is no exception. Gene by gene there are known exceptions to both X-inactivation and to the lack of inactivation on the pseudoautosomal region. When you start looking at it closely, there are structural boundaries but these boundaries are not that simple and not that easy to study. By and large, I think it's fairly reasonable to say that "there is no X-inactivation in males" and "the pseudoautosomal region is spared from X-inactivation". Wnt (talk) 14:31, 22 March 2014 (UTC)

Claudius Ptolemaeus on the year

What did Ptolemy believe to be the origin of the year: different amounts of sunlight in different seasons, or Persephone, or something else? Nyttend (talk) 15:22, 22 March 2014 (UTC)

It seems to me that the different amount of sunlight in the different seasons is absolutely obvious, as is the fact that sunlight warms the Earth. Both can be determined by direct observation. Now why the Earth gets more sunlight at times than others is a bit trickier, being mostly due to the Earth's tilt with a minor component due to the Earth's elliptical orbit. StuRat (talk) 16:03, 22 March 2014 (UTC)

Ancient astronomers, including Ptolemy, were well aware that a year was the time taken by the sun to complete one circuit of the ecliptic and that the tilt of the ecliptic with respect to the celestial equator was responsible for the varying amounts of daylight at different times of year. It never ceases to amaze me that modern folk assume that the ancients were oblivious to easily observable phenomena. Ptolemy may have been mistaken about which body was stationary with respect to the other, but he was no fool. Deor (talk) 18:06, 22 March 2014 (UTC)

The problem is that I wasn't paying attention when I wrote the question, and shouldn't have included the different amounts of sunlight. I meant to ask about the astronomical background: why is a year related to the changing amounts of sunlight? Why does the sun go through the ecliptic once per year? I'm looking for a theoretical basis for the observations, analogous to the theory of epicycles necessary to explain the retrograde motion of some of the planets. Nyttend (talk) 03:01, 23 March 2014 (UTC)

I'm still not sure that I understand your questions, but (ignoring some refinements, such as the eccentric and epicycle he assigned to the sun) Ptolemy viewed the whole heavens as revolving once a day from east to west around the earth. In addition, each of the "planets", including the sun and moon, had a slower motion in the opposite direction, accounting for their movements relative to the background of fixed stars. In the sun's case, this motion produced its yearly movement along the ecliptic, from one vernal equinox to the next—the equinoxes being the points at which the ecliptic intersects the celestial equator. (Some information about the data on which P. based his value for the exact length of the year is at Hipparchus#Apparent motion of the Sun.) The differing amounts of sunlight a point on the earth's surface receives at different times of year is, as I said, a result of the obliquity of the ecliptic (the inclination of the sun's path with respect to the celestial equator). Is that any help? Deor (talk) 15:03, 23 March 2014 (UTC)

Bowel cleaning

How does a human organism clean the bowels from feces' internal traces and residue after defecation?--93.174.25.12 (talk) 16:20, 22 March 2014 (UTC)

It doesn't, feces is produced by the body, it's not purely a waste product. It contains bacteria that help the body digest foods and keep harmful bacteria away. Some people who have certain types of intestinal infections can be cured by putting feces of healthy people in their bowels. Count Iblis (talk) 16:35, 22 March 2014 (UTC)

Note that for certain medical procedures, like a colonoscopy, it is important to clean the bowels. In that case, a clear fluid is ingested which also causes defecation to occur, and the patient refrains from consuming anything but clear fluids for a day or so. This largely cleans the bowels. StuRat (talk) 17:44, 22 March 2014 (UTC)

The fluid in this case is Polyethylene glycol and the procedure is called Whole bowel irrigation. The procedure is done solely so that the physician performing the colonoscopy can see everything clearly; i.e. there's no feces obscuring the view of the colon. Otherwise, for a healthy person, there's usually no reason to "clean" ones bowel after defecation. External cleaning is done often with toilet paper and/or a bidet. But there's no need to clean one's insides out after defecation. There's a bit of quackery that is sold to the uneducated public as Colon cleansing or sometimes "colonic irrigation", which is mostly hoakum, so don't believe what you hear from people trying to sell you on such stuff. But no, you don't have to clean feces out of your colon after defecation. --Jayron32 23:39, 22 March 2014 (UTC)

I doubt Jayron means to be offering a medical opinion, but I would suggest looking at articles like constipation, diverticulosis, and irritable bowel and so forth before assuming all such issues are bunkum. I do agree healthy people shouldn't be going to non-medical clinics for what sounds like medical treatment, and that people who think they are sick should phone their doctor. μηδείς (talk) 01:28, 23 March 2014 (UTC)

What is the SI definition of 1 litre?

litre says " 1 cubic decimetre (dm), 1,000 cubic centimetres (cm) or 1/1,000 cubic metre ", which are of course all the same. But what is the SI definition. My guess is 1/1,000 cubic metre, but I haven't found a definitive statement. -- SGBailey (talk) 16:55, 22 March 2014 (UTC)

Our article on the International System of Units don't mention the litre, and the article on SI derived units states that "Some other units such as the hour, litre, tonne, and electron volt are not SI units, but are widely used in conjunction with SI units." So the straight up answer is that there is no SI definition of 1 litre, but a litre is defined in relationship to an SI unit - something which is also explained in the second paragraph in the article on the ]. WegianWarrior (talk) 17:06, 22 March 2014 (UTC)

See also Volume#Units. The nontrivial thing here is the SI definition of the metre, which is defined in terms of the second (by defining the speed of light). The second is by definition the duration of 9192631770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium 133 atom. This ultimately how the SI unit of length and derived quantities like the litre is defined in terms of physical quantities. Count Iblis (talk) 17:08, 22 March 2014 (UTC)

The Official brochure for the International System of Units, on page 141 of the English version, states that the 12th General Conference on Weights and Measures (CGPM) abrogated the former definition of the litre, the volume of 1 kg of water under specified conditions, and "declare that the word 'litre' may be employed as a special name for the cubic decimetre". The CGPM has jurisdiction over all metric units, including those that are part of SI, and those, like the litre, that are not. Jc3s5h (talk) 17:28, 22 March 2014 (UTC)

I think we've progressed far enough to where we can say "the amount needed to fill a one-litre bottle to the point such bottles are typically filled". That's what I'm going with, anyway. InedibleHulk (talk) 17:37, March 22, 2014 (UTC)

I think Jcs has given the answer I was seeking: 1L = 1 cubic dm. Thanks -- SGBailey (talk) 23:24, 22 March 2014 (UTC)

Or in proper SI notation: 1 L = 1 dm³ (put a space after the number and don't mix words and symbols). ("1 l" instead of "1 L" is also correct, but harder to read.) See the "official brochure" already cited above; specifically, sections 5.1, 5.2, and 5.3.3. --50.100.193.30 (talk) 04:06, 23 March 2014 (UTC)

No, that is wrong, the deci applies to the m³, not to the m so using that notation it should be 1 L = 1 mm³ ( 1 milli "cubic meter"). -- SGBailey (talk) 12:12, 23 March 2014 (UTC)

What? No, that is not how the notation works. dm³ means a cubic decimetre in standard SI notation. It's a common unit in engineering contexts, and so this isn't a hypothetical. mm³ would be a cubic millimetre, of which there are a billion in a cubic metre. If this was actually intended as a joke (I cannot be sure), you might consider following the convention of enclosing it in <small tags. 86.157.148.65 (talk) 15:28, 23 March 2014 (UTC)

Do any kind of vitamin/mineral/nutrient overdoses cause tics/muscle spasms ?

If so, at what level ? And the same Q for deficiencies. StuRat (talk) 18:03, 22 March 2014 (UTC)

Eating too much Hypericum perforatum will lead to Serotonin syndrome. Count Iblis (talk) 18:44, 22 March 2014 (UTC)

"...supplementing too much of the wrong nutritional remedies ... have a lowering effect on calcium levels ..." — See also: Electrolyte ~:71.20.250.51 (talk) 19:28, 22 March 2014 (UTC)

Thanks so far, good info. StuRat (talk) 13:26, 23 March 2014 (UTC)

Another gravity "related" question

When Sandra is spinning in space: would she eventually get used to it. And observe the universe as spinning around her, the way we observe the sun "go around" the earth. — Preceding unsigned comment added by 2601:C:3600:4AC:4DAA:466F:9A53:2D46 (talk) 19:34, 22 March 2014 (UTC)

Well, she'd feel the blood rushing to the far points, such as her arms if spinning about her spine, or her head and feet if spinning about her hips. If rotating slowly enough, this might not be noticeable. StuRat (talk) 19:46, 22 March 2014 (UTC)

The Semicircular canals would still detect rotational movement due to centrifugal force acting on the fluid in them, so she would always be aware that she was spinning. However, it is hard to know how your brain would interpret which was moving - you or the rest of the universe. And of course, the answer to that really depends on your frame of reference.Richerman (talk) 19:55, 22 March 2014 (UTC)

Yes, but the semicircular canal article also tells us Sandra would "eventually" become habituated to the feeling. I guess from the context that the habituation only takes a few seconds. If so, then I expect she would then see the stars as spinning round although she would obviously know this was wrong. As for the physics rather than the physiology, I found the article Mach's principle not so easy to grasp and Absolute rotation gives a gentler ride. Thincat (talk) 20:46, 22 March 2014 (UTC)

Re: habituation:  There is a (somewhat tangential) experiment regarding Perceptual adaptation — Uhmm... This might be a better link:.  —:71.20.250.51 (talk) 21:55, 22 March 2014 (UTC)

As with many optical illusions such as "old woman, young woman" here it's possible the brain would constantly flip from one model to another so sometimes she would feel she was turning and other times she would feel the stars were moving. Richerman (talk) 22:16, 22 March 2014 (UTC)

Does the Friedmann–Lemaître–Robertson–Walker metric figure into anything here? InedibleHulk (talk) 23:18, March 22, 2014 (UTC)

I assume you're talking about the scene early in Gravity (film) where Sandra Bullock's character goes spinning off after detaching herself from the ruins of the space shuttle. She appears to be spinning head over heels with a period of about 2 seconds, which would make the centrifugal force at her head and feet about 1 gee (in opposite directions). This would be very noticeable, but I don't know if it would feel like spinning. If she flailed around she would also feel the Coriolis force, which might be something like the odd sensation you get when trying to turn a spinning gyroscope.

I would think that anyone who's trained to be an astronaut could give you a definitive answer to this question, but some quick googling failed to turn up anything. -- BenRG (talk) 21:55, 23 March 2014 (UTC)

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 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):

" 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 Misplaced Pages 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 , 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)

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)

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 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 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 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 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 Misplaced Pages'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 from That Other Wiki(tm)... - ¡Ouch! ( / _{more pain}) 15:29, 24 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! ( / _{more pain}) 15:29, 24 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

Hi all,

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

After I created this graphic:

https://commons.wikimedia.org/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/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/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)

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)

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

• Pages automatically checked for accidental language links
• Misplaced Pages resources for researchers
• Misplaced Pages help forums
• Misplaced Pages reference desk