Wikipedia:Reference desk/Archives/Science/2013 February 5

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February 5

Yellow rain

In December 2012 Sri Lankan towns such as Mineragala and Southern provinces experienced Red rain and towns of Polonnaruwa and Kantale experienced Yellow rain. But the article about yellow rain totally differs from this rain. So natural yellow rain should be also included here. Sri Lanka based researches reveal that this colouration of monsoon rains was due to remains of meteorites. So what is the difference between natural and artificial ones? Source:

• [1]
• [2]
• Rupavahini broadcasting (government's official broadcasting channel)

--G.Kiruthikan (talk) 07:06, 5 February 2013 (UTC)

I fixed the dead links above. Sean.hoyland - talk 07:38, 5 February 2013 (UTC)

Both the red rain and the natural form of yellow rain are actually varieties of blood rain, which is caused by large quantities of dust and pollen in the air (the meteor hypothesis, BTW, has been disproved). "Artificial" yellow rain, however (I put it in quotes because its very existence is unproven) is a hypothetical Soviet chemical weapon allegedly used against South Vietnam by the Vietcong in 1975, which may be composed of various mycotoxins, mustard gas, etc. FWiW 24.23.196.85 (talk) 08:53, 5 February 2013 (UTC)

Law of excluded middle, null hypothesis, and disproof of god

Ok so let's say that the statement "god doesn't exist" is the null hypothesis and "god exists" is the alternative hypothesis. So the null hypothesis can not be proven and is the default position, that directly implies that the claim "god doesn't exist" can not be proven. Let's define god as the being that is described in The Book of Genesis. Since this being has been described as creating humans, that is a demonstrable claim that can be falsified. Evolution has falsified creationism, and therefore the god described in The Book of Genesis has been disproven. According to the Law of excluded middle, two contradictory propositions (i.e. where one proposition is the negation of the other) one must be true. Since the alternative hypothesis has been disproven, it stands to reason that the null hypothesis must be true according to the Law of excluded middle. So my question is, can something be true, without it being proven (using this logic)? ScienceApe (talk) 02:00, 5 February 2013 (UTC)

This is the reference desk. Can you rephrase that as a specific request for research help, rather than a long invitation to debate? μηδείς (talk) 02:13, 5 February 2013 (UTC)

A statement can be assumed true, and thus require no proof. This is the essence of the method by which most religious persons justify their convictions. 72.128.82.131 (talk) 02:38, 5 February 2013 (UTC)

Your argument utilizes the strawman argument and is not a proof; and "using this logic" [sic] one can prove anything. ~:74.60.29.141 (talk) 02:44, 5 February 2013 (UTC):~

Or disprove anything. No believer has ever come up with any evidence that would convince a scientist there is a god, and no scientist has ever been able to cause a believer to doubt there is a god. Then there are scientists who teach evolution but privately are strong believers in the God who created the universe ab initio. Work that out. -- Jack of Oz ^[Talk] 02:53, 5 February 2013 (UTC)

Not to mention that God and evolution are not mutually-exclusive. [I didn't mention that] ~:74.60.29.141 (talk) 03:48, 5 February 2013 (UTC):~

The flaw here is in this line: "Since this being has been described as creating humans, that is a demonstrable claim that can be falsified."...Sadly, that is not the case. God is described as being "omniscient" and "omnipotent" - and that's a major problem for any disproof of his existence. If this is true, then he can do absolutely anything. For example: He could create humans (per Genesis), then completely falsify all of the evidence (planting fake fossils, adding appropriate junk DNA, etc) to make it look to scientists like we evolved from pond-slime...or he could warp the minds of scientists who investigate evolution to make them believe it to be true and to ignore contradictory evidence. Heck, it might be that not one single person in the world believes in evolution but God decided to warp your mind to make you think that it's widely accepted as true. Maybe he allowed evolution to do the work and then faked the creation of the book of Genesis. An omnipotent being has literally no limits...that's why the non-existence of God is unfalsifiable - even by complicated arguments like yours. Of course my claim that there are omnipotent, green, piano-playing aardvarks living on the dark side of the moon is also unfalsifiable - and so are an infinite number of other possibilities. The "God hypothesis" therefore has a statistically infinitesimal (but not zero) probability of being true...so rational beings may ignore that possibility. SteveBaker (talk) 16:17, 5 February 2013 (UTC)

Your final sentence does not logically follow. The premise that there are is an infinite number of possible omnipotent beings does not lead to the conclusion that the probability for each of those possibilities is infinitesimally small, because that requires the unstated (and unproven) assumption that each of those possibilities is equally probable. - Lindert (talk) 16:36, 5 February 2013 (UTC)

Yeah - that's true to a degree - but since these are unfalsifiable hypotheses and none of them (including the "God hypothesis") has any solid evidence to prove them, our best guess has to be that they are equally probable. SteveBaker (talk) 20:41, 5 February 2013 (UTC)

The trick here is that you are defining "god" very narrowly here, as being not merely the god of Genesis but a particular interpretation of that god which is one whose work must leave evidence demonstrably contradictory to evolution. So your proof of "god not existing" is equally narrow. You have not, for example, disproved that there could be a God who created the world as in Genesis, but who subsequently covered up his prior work by some miraculous means to leave only evidence of the natural history implied by our current laws of physics; or who did the creation in a parallel universe and copied and refined it in this one; or who did the work in some sort of Platonic realm of archetypes; etc. Wnt (talk) 05:12, 5 February 2013 (UTC)

I am not personally very interested in not the god-vs-no-god debate - at least, not at face value. I feel that this debate has been rehashed by many intelligent people, and many many more unintelligent people, for many centuries, and in many languages. What I am interested in is the Kolmogorov complexity of their debate, and more importantly, the marginal contribution to that complexity of any new individual's argument. I fear that we are reaching a plateau, where the complexity no longer increases, because the exact same arguments for each side are made, over and over and over again, by people who have chosen not to invest the time to read the earlier parts of the "thread." Now, it's a heck of a lot of effort to expect every Tom, Dick, and Harry to start off with Plato and Thomas Aquinas and Sartre; but by golly, if somebody's interested in the subject, then they really ought to invest the time to read all the prior arguments so that we can make forward progress in the discussion, instead of repeating the same string-literal arguments, without adding to the complexity. (And yes, I posit that in five centuries of English, and five decades of digital texts, somebody has written almost exactly the same string of text as your brilliant idea to prove, or disprove, anything). If only there were a free repository of great classic literature, and short encyclopedic summaries to help guide the interested reader through the denser parts of the prose... I bet each person could expend a little effort to ramp up on "prior art," and there would be much less repetition of the elementary tenets of formal logic, theology, and the general theory of human knowledge. And more to the point, we could then process this digital corpus to estimate the Kolmogorov complexity of the god-vs-no-god debate, giving us an upper-bound of the importance of it, as measured in bits-of-entropy. We could then compare that to the bits of entropy in other observed phenomena. Nimur (talk) 05:28, 5 February 2013 (UTC)

While what you say is valid in many arenas, basic-level questions should be welcome here - we don't tell people to read Schroedinger when they ask about quantum teleportation, for example. Also there may be an argument that in modern society, our unspoken assumptions about God have changed so dramatically that the same arguments may not lead to the same conclusions, because our generalizations may not accurately reflect our actual feelings and the range of potential philosophy under which we might evaluate them. Wnt (talk) 15:24, 6 February 2013 (UTC)

This is not a place for religious debates. Why don't we just hat the whole thing? 24.23.196.85 (talk) 05:39, 5 February 2013 (UTC)

Malala, the girl who survived the Taliban's assassination attempt, today called her survival a gift from God. And there's not a soul on earth who can prove her wrong. ←Baseball Bugs ^{What's up, Doc?} carrots→ 05:47, 5 February 2013 (UTC)

Being nearly assassinated and surviving? I think I'll pass on gifts from God then thank you very much. Dmcq (talk) 10:30, 5 February 2013 (UTC)

The assassination attempt was a "gift" from evil people. If you would prefer not to survive an assassination attempt, that's up to you. ←Baseball Bugs ^{What's up, Doc?} carrots→ 14:46, 5 February 2013 (UTC)

That's the old argument from The God Delusion - why did Our Lady of Fatima not guide the bullet another 20cm that way? Or, more generally, why is there evil in the world? If you assign all evil in the world to "evil people", and all good to god, what stops me from doing the same with communism, or Thor, or the Beach Boys? --Stephan Schulz (talk) 21:47, 5 February 2013 (UTC)

Right, the assassination attempt was by humans because it was evil, whereas the recovery was by God because it was good. Teams of dedicated doctors, sophisticated medical devices, and generous donors obviously had nothing to do with it. Apparently, a 14 year old girl with zero scientific training and minimal scientific knowledge is now the world's sole scientific authority. --140.180.247.198 (talk) 15:51, 5 February 2013 (UTC)

more for us165.212.189.187 (talk) 13:58, 5 February 2013 (UTC)

I would guess the Taleban think they follow God's teaching and British surgeons are in general misguided infidels even, dare I mention it?, atheists and evil has triumphed for the moment in this case by saving her life. Dmcq (talk) 17:10, 5 February 2013 (UTC)

As (it seems to me) usual in these debates, it all hinges on each individual's definition of "God"; and (it seems to me) any such concrete definition can be disproved, the more concrete and specific the easier to disprove. In this case, God defined as the God of the first portion of Genesis. This doesn't lead to any ending, however, if one's definition of God includes transcendence over concrete definition by the human intellect. See Neti neti and Apophatic theology. Gzuckier (talk) 18:09, 5 February 2013 (UTC)

(I have un-hatted this discussion. While some responses have gone off the rails, the question is a valid one and there have been several valid answers.) SteveBaker (talk) 14:14, 6 February 2013 (UTC)

feeling "surreal" or like the world is a fabrication or a simulation

Is this a known symptom of psychosis? This is not a medical question, I just wonder if there are lots of people in society with undiagnosed schizotypal disorders, thanks. 71.207.151.227 (talk) 11:44, 5 February 2013 (UTC)

This is not about the philosophical belief, more like the emotional feeling that people have, i.e. it is a very visceral feeling. 71.207.151.227 (talk) 11:44, 5 February 2013 (UTC)

see Derealization, the reference desk cannot provide a medical opinion or speculation ---- _nonsense ferret 13:00, 5 February 2013 (UTC)

And yes it stands to reason that there are lots of people in society with undiagnosed mental illness. The NIMH found that half of all cases of mental illness begin by age 14, and that " there are long delays — sometimes decades — between first onset of symptoms and when people seek and receive treatment". --TammyMoet (talk) 13:04, 5 February 2013 (UTC)

Why do questions like this make me feel like wikipedia is a potentially endlessly recursive computer platform? μηδείς (talk) 20:44, 5 February 2013 (UTC)

Ask somebody to kick you in the shins, and then get back to us about whether it seemed "real" or not. ←Baseball Bugs ^{What's up, Doc?} carrots→ 23:28, 5 February 2013 (UTC)

Whenever I suggest that people accuse me of being cruel! μηδείς (talk) 23:32, 5 February 2013 (UTC)

I might call it the Three Stooges Experiment. If it's real, it hurts. If not, it doesn't. ←Baseball Bugs ^{What's up, Doc?} carrots→ 04:40, 6 February 2013 (UTC)

Zycosoil

Please help me by telling me what is the generic name for Zycosoil — Preceding unsigned comment added by 188.245.230.38 (talk) 12:35, 5 February 2013 (UTC)

A Google search shows it is a waterproofing agent. --PlanetEditor (talk) 12:57, 5 February 2013 (UTC)

I need to know what is the generic name for Zycosoil that is manufactured in India.

188.245.230.38 (talk) 13:13, 5 February 2013 (UTC)

It seems to be a fairly unusual product and I'm not sure that there is an agreed generic term for it. It is used to protect soil from water erosion so it could be called a 'soil protective' or an 'erosion preventer', You might find this link useful as it has a video demonstrating the action of Zycosoil. This may be a Language Desk question. Richard Avery (talk) 14:32, 5 February 2013 (UTC)

• Organosilicon compound — See also: [3]   ~:74.60.29.141 (talk) 17:05, 5 February 2013 (UTC):~

Chelating?

Has chelating have any other practicle purposes other than medical? Would the removal of rust be called this . . . or has it another name? — Preceding unsigned comment added by Cousin Bruce (talk • contribs) 13:34, 5 February 2013 (UTC)

Our article suggests it has other uses than medical Zzubnik (talk) 13:46, 5 February 2013 (UTC)

One application they missed is hydrometallurgy: for example, chelating agents can be used to extract boron from seawater, or plutonium from a nitric acid solution of spent nuclear fuel (among many other things)... 24.23.196.85 (talk) 05:22, 6 February 2013 (UTC)

Does chemical analysis count as practical? See Complexometric titration. 202.155.85.18 (talk) 08:13, 8 February 2013 (UTC)

Sure it does! 24.23.196.85 (talk) 03:35, 9 February 2013 (UTC)

Vacuum of space

does the vacuum of space exert a negative energy on objects in an outward and perpendicular direction to the surface of the objects?165.212.189.187 (talk) 14:06, 5 February 2013 (UTC)

That's sort of a backwards way to look at it. Any object in space, let's say a human who forget his space suit, has some internal pressure (blood pressure is one form of this). On Earth this is countered by atmospheric pressure. Without this, in space, there is an unbalanced outward pressure which causes the person to swell up. StuRat (talk) 14:23, 5 February 2013 (UTC)

Wikipedia says negative energy is "A plot device in fiction" Zzubnik (talk) 14:24, 5 February 2013 (UTC)

OK a positive energy from the negative mass density of space. so the vacuum of space is not exerting outward pressure on the earth? that only applies to objects with inertial outward pressure, (which the earth does not have)?165.212.189.187 (talk) 14:31, 5 February 2013 (UTC)

"Things" have internal pressure. Vacuum of space does not exert a force at this scale. Zzubnik (talk) 14:39, 5 February 2013 (UTC)

So the gravity of earth prevents its internal pressure from exploding like the human without the suit?165.212.189.187 (talk) 15:26, 5 February 2013 (UTC)

Yes, gravity holds it all together. There's also the effect of the solar wind, which tends to blow off lighter elements at the top of the atmosphere, explaining why there is so little free hydrogen and helium in the air, despite those being the most common elements in the universe. BTW, a human in space doesn't explode, he just swells up. StuRat (talk) 15:48, 5 February 2013 (UTC)

Also, the use of the word "Energy" in the question is completely incorrect. Force would've been a much better choice. Energy doesn't have a direction in space and cannot point outward or be perpendicular. Neither does pressure. Dauto (talk) 16:14, 5 February 2013 (UTC)

Thanks for clarifying. Why doesnt gravity hold the human together the same way?165.212.189.187 (talk) 16:52, 5 February 2013 (UTC)

Gravity doesn't by itself help with holding humans together; a man on the moon experiences gravity, but because the lunar atmosphere is practically nonexistent, he'd swell up as if he were in a vacuum. Launch him back into space inside a spaceship, and he'll be safe because of the air inside the spaceship, even though he's experiencing no gravity. It's simply that Earth's gravity holds the atmosphere that prevents us from swelling up. Humans have their own gravity, simply because all matter does, but we're far far too tiny for that gravity to have any practical effect. Nyttend (talk) 17:23, 5 February 2013 (UTC)

But that doesn't explain why the human will swell and the earth doesn't. Also if the swell is an action in the outward direction then what is responsible for stopping the swell. ...object in motion will stay in motion, no?165.212.189.187 (talk) 19:00, 5 February 2013 (UTC)

The same thing which keeps a balloon from exploding when you inflate it. The membranes are strong enough to withhold a certain amount of pressure, but too much pressure would, indeed, cause both to explode. StuRat (talk) 20:00, 5 February 2013 (UTC)

Gravitational forces are proportional to the mass of the object producing it. A person's gravity is simply to week to hold an atmosphere. Dauto (talk) 01:56, 6 February 2013 (UTC)

We should also state that there are other forces which can cause small clumps of matter to stick together in space. There can be chemical bonds, for example. StuRat (talk) 16:50, 6 February 2013 (UTC)

Intermezzo (zolpidem tartrate)

In the past, medications avoided English words as their names, presumably so the pharmaceutical company could protect the trademark copyright more easily. So, why does this med have an English name ? Has something changed ? StuRat (talk) 15:09, 5 February 2013 (UTC)

Hmmm, is that more English than Allegra? Wnt (talk) 15:37, 5 February 2013 (UTC)

I don't speak Italian, yet know what "intermezzo" means. So, to me, that means it has now become an English word, like "pizza". StuRat (talk) 15:51, 5 February 2013 (UTC)

If they thought that avoiding English words as drug names helps to protect trademarks (note: not the same thing as copyrights - there are no one-word copyrighted works) then they don't understand trademark law. Apple (the computer), Genesis (the band) and Mercury (the car) have no trouble protecting their trademarks. Mostly the name choices reflect style. You can look at the drug names "Dr. Bateman's Pectoral Drops" and "Lipitor" and figure out roughly when they were introduced. --Guy Macon (talk) 18:54, 5 February 2013 (UTC)

Who are "they"? The medications? --Trovatore (talk) 03:13, 6 February 2013 (UTC)

Yes. --Guy Macon (talk) 11:25, 6 February 2013 (UTC)

microbiology

Principles of pregenancy test — Preceding unsigned comment added by 93.186.23.89 (talk) 15:21, 5 February 2013 (UTC)

Information about different types of pregnancy tests and the principles by which they operate can be found in the Wikipedia article pregnancy test. TenOfAllTrades(talk) 15:29, 5 February 2013 (UTC)

Live double-headed eagles

Has a live double-headed eagle (or the body of a dead one) ever been recorded, as far as Reference Deskers know? I know that conjoined twins have been found in multiple non-human mammalian species, and I'm pretty sure that I've read about them in other chordates (amphibians, perhaps?), so I don't imagine that it would be completely impossible for the same phenomenon to appear in birds. Google gave exactly eight results, and they were either "I'll buy you a live double-headed eagle for your birthday!" or lists in which "live" happened to be right before "double" etc. Nyttend (talk) 17:18, 5 February 2013 (UTC)

Gah. I'm sure I saw an exhibit of a double-headed eagle at the Odditorium in Blackpool when I was a child. However, I don't think you can search the "Believe It Or Not" website to try and find it. Maybe someone more computer savvy than I can find it. Anyway, thanks for getting me to a site I'd been meaning to find for some time. I may be some time! --TammyMoet (talk) 18:26, 5 February 2013 (UTC)

A huge number of those kinds of things are faked by clever taxidermists. I don't think "having seen one" really tells us much either way here. SteveBaker (talk) 20:32, 5 February 2013 (UTC)

There are a number of images of two headed birds on the internet which may or may not be genuine. This one looks kosher though. Richerman (talk) 20:45, 5 February 2013 (UTC)

Double-headed eagle is a very well known symbol in European heraldry. It's been on the coats of arms of numerous countries, and is currently on the national flags of Albania, Serbia and Montenegro. Countries tend not to have mythical animals in their symbology, so I'm assuming it had some real basis. -- Jack of Oz ^[Talk] 22:00, 5 February 2013 (UTC)

Unicorns, dragons and phoenixes have all been used in European heraldry. I take it the OP is referencing double-headed snakes? CS Miller (talk) 22:32, 5 February 2013 (UTC)

Huh? I'm looking for members of the family Accipitridae (I suppose I'd accept non-eagles from that family) with two heads, in part because I'd already looked at the article Jack links, and I observed that it doesn't discuss the existence or nonexistence of individual members of this family that appeared to have two heads. Snakes hadn't even come to mind; I can't remember ever hearing of a two-headed snake. Nyttend (talk) 23:00, 5 February 2013 (UTC)

See polycephaly and here. I remember reading or hearing that two-headed carnivores usually attack each other, which would explain the lack of such birds. μηδείς (talk) 23:40, 5 February 2013 (UTC)

This more concise link works equally well, as far as I can tell. —Tamfang (talk) 01:16, 28 October 2013 (UTC)

Two headed carnivores usually attack each other? - you can't be serious! Richerman (talk) 00:40, 6 February 2013 (UTC)

I certainly can be serious that I remember hearing, I think it was about turtles, that they would bite each other. If I had a reference (probably one of those 10 most craziest critters shows) I'd give it but it's not the sort of thing I keep files on, sorry. Lol. μηδείς (talk) 01:05, 6 February 2013 (UTC)

Hmmm - my fault for editing when I've been to the pub I suppose. However, a lot of people believe nonsense like that - you should make it clear with that sort of comment that it's a joke. Richerman (talk) 06:37, 6 February 2013 (UTC)

No, it wasn't a joke. The heads supposedly peck at each other. Did you think I meant various two-headed carnivores seek out other two-headed carnivores to battle? μηδείς (talk) 17:57, 6 February 2013 (UTC)

No, I thought that "it would explain the lack of such birds" meant that the two heads always fight to the death, which sounds rather like something from an ancient Greek myth. Richerman (talk) 18:49, 6 February 2013 (UTC)

That only happens in WWE. μηδείς (talk) 03:49, 7 February 2013 (UTC)

I've heard that such reptiles go hungry because each head tries to keep the other from eating. But among turtles, at least, I wouldn't have thought the necks flexible enough for the heads to fight directly. —Tamfang (talk) 01:16, 28 October 2013 (UTC)

Tangentially, the mythological beast Carebearus, which has three heads and three bodies, and the magical ability to be in three different places at the same time. Gzuckier (talk) 14:41, 7 February 2013 (UTC)

Black sky at night

Given that there are "billions and billions" of stars and that light (obviously) travels at the speed of light, why do we see so much "black" in the night sky rather than filled with starlight? Thank you. Rdhartwell (talk) 21:04, 5 February 2013 (UTC)

Black#Why the night sky and space are black - Olbers′ Paradox --Guy Macon (talk) 21:12, 5 February 2013 (UTC)

More to the point, Olbers' paradox. --Jayron32 21:25, 5 February 2013 (UTC)

The universe is finite and expanding, which explains why it is not infinitely bright in all directions, but it does glow in all directions, see cosmic background radiation. μηδείς (talk) 23:42, 5 February 2013 (UTC)

The universe is not in fact known to be finite. See shape of the universe. (The observable universe is finite, but that's different.) --Trovatore (talk) 03:04, 6 February 2013 (UTC)

Yes, and neither is the Flying Spaghetti Monster not known to exist. There's no evidence its infinite, nor even any coherent way of formulating claims about an infinite universe. μηδείς (talk) 17:51, 6 February 2013 (UTC)

Medeis, that's just completely wrong. There are definitely coherent ways of formulating claims about an infinite universe. In Riemannian geometry, it's no more difficult to talk about an infinite universe than a finite one.

As for evidence: The simplest models having nonpositive curvature are infinite, and there definitely is evidence of nonpositive curvature. Whether that evidence is compelling or not at the current time, I can't speak to, as I'm not really up to date on that. But evidence certainly exists.

Now, there are models with nonpositive curvature that live on a compact manifold (that is, finite universe), but they're weird. They're things like a solid dodecahedron with opposite faces identified. Why the universe should have that topology would be more in need of explanation than why it should be infinite. --Trovatore (talk) 21:09, 6 February 2013 (UTC)

I am quite aware there are models which use infinity as a factor. None of them has a real or concrete interpretation. If the universe is "infinite", then however big it actually is, it is even bigger than it actually is. Among other things that means atoms have no size or charge in relation to the universe. That's fine if you want to play such linguistic games, but there's no evidence for it. μηδείς (talk) 00:27, 7 February 2013 (UTC)

You're not making any sense, Medeis. However big it actually is, it's even bigger than that??? What's that even supposed to mean? If the size of an atom is not as large as any finite submultiple of the size of the universe, then why is that bad? Mathematics is perfectly capable of handling infinities as first-class objects, and it is perfectly plausible that the universe could be an example of such. As for evidence, I already addressed that, and you haven't responded to my specific points. --Trovatore (talk) 01:21, 7 February 2013 (UTC)

Medeis is definitely wrong here. In standard cosmology, the universe is qualitatively different if its total energy density is above, equal to, or below a critical threshold. If it's above the threshold, the universe has positive curvature, and must be finite. If it's at the threshold, the universe has 0 curvature and is flat--that is, its geometry is very nearly Euclidean--which implies an infinite universe If it's larger, the universe has negative curvature and must be infinite. This model holds as long as we assume that the universe is nearly uniform at large scales (the cosmological principle). It is indeed nearly uniform within our observable universe, but whether it's uniform elsewhere is not a testable question. As for how an infinite universe can expand, imagine the set of natural numbers: 1, 2, 3, 4... This set is infinite. Now multiply every element by 2, and you can 2, 4, 6, 8... The set has expanded by a factor of 2, and is still trivial to describe. As another example, imagine a large sheet of rubber that's being stretched in all directions. The distance between any two points on the sheet will increase with time, and even if the sheet were infinite, the expansion would still be perfectly well-defined.

Trovatore is not correct in saying there's evidence of nonpositive curvature. Our best value for the curvature is 0, to within 0.4% (see shape of the universe). The fact that the universe is so remarkably flat, along with a few other problems, inspired inflation theory, which current cosmological experiments are trying to test for. --140.180.247.198 (talk) 03:30, 7 February 2013 (UTC)

My understanding is that there are some surveys that come up with a positive number and others with a negative number, isn't that so? In that case, there is evidence of nonpositive curvature (namely the studies that show the negative number). I never asserted that it was the current best hypothesis that the curvature is nonpositive; I don't need to assert that, because Medeis was claiming there was no evidence the universe is infinite, which is not so. --Trovatore (talk) 03:38, 7 February 2013 (UTC)

Oh, and by the way, zero is nonpositive :-) --Trovatore (talk) 03:48, 7 February 2013 (UTC)

The best available measurements indicate the curvature is 0, to within a small margin of error. That means there's roughly 50% chance of the actual curvature being positive, and 50% of it being negative. Whether you call that "50% evidence that the curvature is negative" or "100% evidence that we don't yet know" is a matter of semantics. --140.180.247.198 (talk) 04:42, 7 February 2013 (UTC)

Yes, but semantics are important, especially in this sort of case. There's a big difference between "there's no evidence that proposition A is true" and "the evidence that proposition A is true, and that it's false, is roughly balanced". --Trovatore (talk) 04:46, 7 February 2013 (UTC)

I agree with Medeis. Surely an infinite universe can be ruled out on account of it's finite age. If as evidence indicates it began 13+ billion years ago in a "big bang" there has not been enough time, even with inflation, for it to have achieved infinite size. An infinite universe is only compatible with "steady state", or at least either infinite age or infinite expansion rate. Desiderata9 (talk) 02:34, 10 February 2013 (UTC)

No, that is not correct. See below. --Trovatore (talk) 02:11, 29 August 2014 (UTC)

Yeah - Olbers' paradox is the answer here. It goes something like this:

• The light from a distant object attenuates as the square of the distance between us...a star at distance 2X is four times dimmer than a star at distance X.
• The number of stars (galaxies, whatever) within a distance X is (on average) four times smaller than the number at distance 2X.

So this growth in the number of stars over distance is exactly compensated for by the reduction in light over that distance...but...

• The amount of dust and gasses attenuating that light is (on average) proportional to the distance to the star ('X') - and therefore the amount of light they absorb is also proportional to X. So the further you get away from here - the less light there is (in total) coming from the stars at that range.

That sounds like it solves the problem...but sadly, no. Things are more complicated than that...

• Those intervening dust and gas clouds are heated by the incoming light - and will eventually heat up and glow - emitting the same amount of energy that they absorb. So, again, we should have an infinitely bright sky.

The resolution of this problem relates to redshift. The universe is expanding - so the frequency of light from distant objects has longer and longer wavelengths - so visible light is converted into microwaves and longer wavelengths. The "cosmic background radiation" is where that light ends up - and the sky is indeed filled with that radiation (although, interestingly, it's kinda patchy).

Stars that are sufficiently far away are retreating from us at faster than the speed of light (because of the expansion of the universe) - so their light can never catch up with us anyway.

SteveBaker (talk) 14:10, 6 February 2013 (UTC)

Steve, you were just fine until your last sentence. Light just doesn't work that way. Even if it was possible for anything to travel faster than light (it isn't in our current understanding of the universe), if you had a flashlight moving away from you at twice the speed of light, it's radiation would still reach you, because the speed of light in a uniform medium is constant. Of course, as you mentioned, it would be very redshifted so your eyes couldn't see it, but it would still be moving at the speed of light. Another example: the light from the headlamp of a speeding train isn't moving any faster than the light from your computer screen, or any other light traveling through air on Earth. —Rutebega (talk) 03:48, 7 February 2013 (UTC)

You're thinking in special-relativistic terms. Light that originates from beyond the horizon of the observable universe, from our point of view, will indeed never reach us. In any local inertial frame containing those photons, sure, they're moving at c, but it doesn't matter because such an inertial frame cannot be extended out to our position. --Trovatore (talk) 04:13, 7 February 2013 (UTC)

First, it's not true that things with a recession velocity larger than c are invisible. The recession velocity of the CMBR is about 3c and we can see it. Second, dust does absorb starlight in the real world. Only in a steady-state universe would it have to be in equilibrium with the starlight (although arguably everything would have to be in equilibrium - I'm not sure how steady-state cosmologies solved that problem).

The size of the observable universe increases with time. If not for the accelerating expansion, light from arbitrarily far away would eventually reach us. In the accelerating universe there is a genuine horizon beyond which nothing is ever visible. However it's far from certain that that model is correct; the universe could still recollapse. -- BenRG (talk) 05:01, 7 February 2013 (UTC)

OK, fair enough. There seem to be two roughly complementary notions that, at least naively, could be called "the observable universe", and I'm probably using the wrong one (i.e. the one not standardly called by that name). --Trovatore (talk) 06:14, 7 February 2013 (UTC)

Surely an infinite universe can be ruled out on account of it's finite age. If as evidence indicates it began 13+ billion years ago in a "big bang" there has not been enough time, even with inflation, for it to have achieved infinite size. An infinite universe is only compatible with "steady state", or at least either infinite age or infinite expansion rate. Desiderata9 (talk) 02:34, 10 February 2013 (UTC)

Just saw this -- normally one doesn't edit archived posts, especially from a year and a half ago, but I think it's a little bit important not to leave this as the last word.

In fact, that doesn't follow at all. An infinite universe is quite compatible with the Big Bang. If it is infinite, then it has "always" been infinite, where "always" means "at any positive time after the Big Bang" (as measured in comoving coordinates.

The reason that this is counterintuitive is that you want to extrapolate back to the actual moment of the Big Bang, where the time after the Big Bang was literally equal to zero. But that's not a useful thing to do. When you read what cosmologists write, they talk about 1 second after the Big Bang, or 10^-10 seconds, or 10^-35 seconds, but never ever ever zero seconds. The way to think of it is, that time simply does not exist. The Big Bang theory is correct, for any positive time after the Big Bang. But it simply gives us no description at all of the exact moment of the Big Bang. --Trovatore (talk) 02:11, 29 August 2014 (UTC)

Economic growth , what curve?

We are constantly told that economic growth is brilliant for us (I think it's to do with GDP?)

However what kind of growth are they implying? Linear? Exponential? Does it head towards a limiting value?

(edit) Also if it IS Exponential won't that be completely unsustainable and almost a joke that economic growth is even talked about as a fact?

Ap-uk (talk) 21:35, 5 February 2013 (UTC)AP

If you get "X" number of economists to answer this question, you're likely to get "X+1" different answers. If economists knew what drove the world economy towards a positive outcome with any certainty, we'd have been there yesterday. --Jayron32 21:37, 5 February 2013 (UTC)

Even if the answer gores someone's ox? —Tamfang (talk) 01:18, 28 October 2013 (UTC)

(from op) If it is exponential and say 3% growth I see a problem with sustaining it now as the Wikipedia article sites 1830 as a start date [[4]] . At 3% we would get doubling every 23 years and it's the old wheat on a chessboard problem [[5]] as we now are getting onto the second row where the next 23years growth must equal the sum of all that has gone before in order to grow.

Except it's not a problem, because 1) nobody's saying exponential growth can continue forever, and 2) due to inflation, you have to distinguish between growth in real and nominal terms. If the inflation rate is 2%, that means all money in the country will be worth 2% less next year. Even if the economy produces exactly the same amount of goods and services next year, its nominal growth rate will still be 2%, even though real growth is 0%. --140.180.247.198 (talk) 23:52, 5 February 2013 (UTC)

Can exponential economic growth (which of course refers to real GDP) continue forever? The answer is unknown, but here are some considerations. Malthusianism was the idea that population grew exponentially while food supply grew just arithmetically, so soon there would be mass starvation that would prevent the population from continuing to grow exponentially. The reason that was wrong (at least up to and including the present) is that it ignored technological change -- the amount of food that we know how to get out of a given amount of land itself grows exponentially. This reality of technological progress applies more generally to our ability to produce the variety of things that go into GDP -- this ability has grown exponentially. The question is whether that can be sustained even in a world with finite resources. The answer to resources running out has so far been to figure out different ways of sustaining and exponentially increasing production by shifting away from the declining resources and into currently plentiful resources. A key example right now has to do with energy: the petroleum is going to run out at some point (though predicting when is enormously difficult), but we are in the process of learning how to use solar, hydrogen fusion, etc.

The question of whether resource constraints will ultimately put a cap on world-wide output is up in the air. But never assume that human ingenuity is going to run out -- it has given us a trend of long-term exponential growth so far, and so far the optimists have been right. Duoduoduo (talk) 15:49, 6 February 2013 (UTC)

An interesting question... I won't pretend I have an answer. I wonder, for example, if there is some kind of "social entropy" that increases over time, so that the GDP can increase despite no real increase in resources. (i.e. Year 1 you own cows, the next year you own cows and iron on the same land with the same resources ... eventually you add shares in a radio station, copyright on a song, a set of collectible trading cards, a digital telephone, a paint-spattered canvas that art appraisers say is worth something, some Bitcoins, an audience of 30,000 following your blog, etc. Yet it's the same land and you still eat the same amount) Wnt (talk) 19:57, 6 February 2013 (UTC)

All of this is assuming humans stay on Earth. Remember that for all practical purposes, the universe has infinite resources, and starlight is a source of infinite energy. --140.180.247.198 (talk) 00:26, 7 February 2013 (UTC)

Burnt stew

I have a 32 quart stainless steel stock pot in which I made some stew from chicken, potatoes, onions, green beans, baby carrots, corn, dried beans, etc. I filled it almost to the top, and boiled it vigorously over an open flame. I left it uncovered, since this prevents boiling over and I don't mind the heat and humidity in winter. Everything went well the first day, and the pot was still half full by night (maybe 1/4 boiled off and 1/4th was eaten). So, I covered it and left it to cool. Early the next morning, it was still warm, and I turned the flame back on. Then I detected a burning smell. So, since the pot was still half full, something must have adhered to the bottom and started to burn. Is there any way to prevent this, other than constant stirring ? Would it have helped if I oiled the pot before using it ? Should I have left the dried beans out ? StuRat (talk) 23:17, 5 February 2013 (UTC)

How does leaving it uncovered keep it from boiling over? ←Baseball Bugs ^{What's up, Doc?} carrots→ 23:22, 5 February 2013 (UTC)

Covering a pot retains the heat that would otherwise be lost as the water vapor leaves the pot, allowing heat to build to a point where it boils over, right after knocking the lid askew. Leaving it uncovered prevents this (of course, an uncovered pot still can boil over, but this requires a significantly higher flame). StuRat (talk) 23:32, 5 February 2013 (UTC)

Put a saucepan nearly full of water on a burner of your stove, turn on the heat, watch it boil, and tell me that it doesn't boil over. ←Baseball Bugs ^{What's up, Doc?} carrots→ 03:30, 6 February 2013 (UTC)

As I said above, there is some level of flame which will cause even an uncovered pot to boil over. It being filled near to the top makes this worse. But, an uncovered pot has a wider range of thermal equilibrium, where more flame leads to more heat being lost from the top, thus keeping the temperature in check.

Incidentally, I have another stock pot, filled with water near the top, which is heated on low flame, uncovered, as a way to add humidity to the house. It has never boiled over (or boiled at all), but likely would have had I covered it. StuRat (talk) 16:41, 6 February 2013 (UTC)

My guess is that after you removed the heat and left it overnight, the ingredients compacted on the bottom and more and more as time went on, with the moisture at the layer touching the bottom of the pot reducing. In the morning when you turned the flame back on you were essentially heating rather dry ingredients which promptly burned. If you had given the pot one thorough stir (as opposed to constant stirring) before turning the flame I think you might have avoided the problem.--Fuhghettaboutit (talk) 23:42, 5 February 2013 (UTC)

Yes, one stir on reheating was all that was necessary. μηδείς (talk) 23:44, 5 February 2013 (UTC)

OK, I'll try that tomorrow. StuRat (talk) 00:15, 6 February 2013 (UTC)

I can confirm the phenomenon that leaving a pot uncovered prevents it boiling over. I always thought this was due to the pressure-cooker effect where higher pressure leads to higher temperature thus faster boiling. (Rhetorically) where do you live? That stew really sounds nice from here!

Detroit. I'll leave a bowl on the porch for you. :-) StuRat (talk) 16:43, 6 February 2013 (UTC)

There is another possible effect of leaving the lid off that would prevent boiling over: reducing the lifetime of bubbles. This is very easy to observe when boiling pasta; with the lid on, the water vapor is retained, keeping the humidity high. The bubbles formed when a protein solution is boiled last longer in a high humidity environment. When you take the lid off, the local (absolute) humidity drops to nearly the same as the room, the bubbles pop much sooner and the foamy layer shrinks. --Wcoole (talk) 22:12, 6 February 2013 (UTC)

Yes, a question of the partial pressure of the water vapor. μηδείς (talk) 00:20, 7 February 2013 (UTC)

Agreed. When you take the lid off a boiling pot of pasta full of foam, the foam collapses immediately. StuRat (talk) 00:23, 7 February 2013 (UTC)

UPDATE: When I fired it up again, I stirred it, and there did again seem to be food adhered to the bottom of the pot. I'm not quite sure why this happens, but it seems to happen every night. I also used a lower flame, and nothing burnt. StuRat (talk) 03:31, 9 February 2013 (UTC)