Wikipedia:Reference desk/Archives/Science/2017 December 22

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December 22

Hawking radiation

I have read the article about Hawking radiation. I did not understand why it exists. The description is that pairs of particles and anti particles are created by quantum theory and one escapes while the other is caught by the black hole. However which particle escapes seems to me to be random. Therefore, there should be an equal number of particles and anti-particles. Those should annihilate each other yielding no escaped particles. Where am I wrong? Is there some preference to which type of particle escapes?

Thanks, Avi. — Preceding unsigned comment added by 79.180.140.132 (talk) 03:00, 22 December 2017 (UTC)

Even if they annihilate the energy that they have is still outside the hole (as EM radiation, generally). The particles that are caught are stranger still: they have an effectively negative energy, and reduce the mass of the hole that incorporates them. --Tardis (talk) 03:50, 22 December 2017 (UTC)

(ec) There are a number of factors, some of which are implied at Hawking radiation.

• The rate of particle emission for massive (non-primordial) black holes is rather low, and it's just plain unlikely that a particle and a corresponding antiparticle would appear at the same point and mutually annihilate.
• Relatedly, some radiation will be in the form of particles with ridiculously tiny cross-sections – e.g. various neutrinos – that almost never interact with anything.
• Some radiation will be in the form of uncharged particles – e.g. neutrons – which have the same charge as their antiparticles, and so won't suffer from fatal electrostatic attraction.
• Some radiation will be in the form of particles that are their own antiparticle – bosons – and which can't mutually annihilate.
• Even if there is a particle-antiparticle annihilation event, the product isn't nothing. Depending on the situation, you get anything from a couple of photons up to a whole shower of particles, photons, and decay products. Some or all of those products can still escape.

Consider the simplest case: an electron–positron annihilation taking place just outside the event horizon, involving particles with a relatively small amount of kinetic energy. Their mutual annihilation will result in a pair of gamma ray photons. Significantly, for conservation of momentum reasons, those photons will be emitted in opposite (antiparallel) directions. (This handy property makes positron emission tomography possible.) No matter how you orient that emission, at least one photon will be pointed away from the black hole and can escape. TenOfAllTrades(talk) 04:08, 22 December 2017 (UTC)

OP, it's hard to make sense of a lot of quantum phenomena, because they are solutions to equations, looking for an explanation in more familiar terms (particles, waves, antiparticles etc.), rather than the other way around. Consider for example that the existence of black holes has only recently been confirmed, while the solution to the equation (a compact massive object having a surface escape velocity greater than c) dates back to John Michell. 78.1.153.199 (talk) 04:51, 22 December 2017 (UTC)

Does being drunk increase the smallest earthquake you can feel?

Just a little or multiple Mercalli scale numbers? 107.77.161.11 (talk) 05:23, 22 December 2017 (UTC)

Unlikely. In my very limited experience (ahem) an alcohol level >0.05% does not make one more sensitive to anything. Including troll detection. Greglocock (talk) 07:28, 22 December 2017 (UTC)

A few drugs can increase sensitivity but most, including alcohol, do the opposite. However many drugs also cause illusions, including a feeling of increased sensitivity. --Kharon (talk) 11:49, 22 December 2017 (UTC)

Sure. When you're drunk enough, you can feel earthquakes that don't even exist. Looie496 (talk) 13:17, 22 December 2017 (UTC)

And while there aren't all that many earthquakes in Cincinnati, there's plenty of drinking. ←Baseball Bugs ^{What's up, Doc?} carrots→ 15:44, 22 December 2017 (UTC)

Increase as in make the limit bigger so you'd miss one you wouldn't miss sober. 107.77.161.11 (talk) 14:56, 22 December 2017 (UTC)

Fundamentally, the question is asking how well we can detect an unexpected acceleration when drunk versus when sober. I managed to find this 1995 abstract from Aviation, Space, and Environmental Medicine that doesn't look at earthquakes, but does look at how sensitive their test subjects were to angular acceleration. (In context, the experimenters were interested in how well pilots could sense – 'by the seat of their pants', if you will – changes in the orientation of a simulated aircraft.) They found that even modest alcohol consumption was sufficient to cause markedly worse performance in their test. At a blood alcohol concentration of 0.037%, the subjects' sensitivity was about 30% worse—that is, it took an acceleration about 30% greater to be perceptible.

If someone could find an equivalent study involving linear accelerations, that would be better, but I frankly wouldn't expect the result to be qualitatively different. TenOfAllTrades(talk) 02:33, 23 December 2017 (UTC)

• Having lived in California for many years, I can tell you that detecting weak earthquakes is very tricky. Quite a number of times I have felt an odd sensation and thought, hmm, was that an earthquake? Sometimes it was, most often it wasn't. I think it would be very difficult to answer this question in any sort of rigorous way. However, given that alcohol impairs balance, I think it must make it harder to detect the sort of subtle swaying that is often the only indication of a weak and distant earthquake. Looie496 (talk) 13:48, 23 December 2017 (UTC)

Religious views on Pre-Columbian trans-oceanic contact theories

Besides Mormonism, are there any other religious systems that make specific claims about pre-Columbian contacts? I.e., not what is implied by young earth theories, but actual claims of specific peoples or events? Thanks. μηδείς (talk) 21:33, 22 December 2017 (UTC)

Your question better fits in Wikipedia:Reference desk/Humanities. --Kharon (talk) 21:35, 22 December 2017 (UTC)

No, because I want people familiar with science to bring forth specific falsifiable-type claims with scientific implications if they are aware of them. Not literature. I don't want Tower of Babel, or Noachic stories or the like. μηδείς (talk) 21:56, 22 December 2017 (UTC)

Are you talking about Jesus coming to America, or Leif Ericsson coming to America? ←Baseball Bugs ^{What's up, Doc?} carrots→ 22:54, 22 December 2017 (UTC)

If you know of the Church of Leif Ericsson, please provide a link. I know we have a user who regularly posts the Jehovah's Witnesses' view of various issues, they may have some information. μηδείς (talk) 23:01, 22 December 2017 (UTC)

I'm just a little confused because the cited article appears to be about regular explorers. Or are you trying to find claims similar to what the Mormons claim? ←Baseball Bugs ^{What's up, Doc?} carrots→ 23:09, 22 December 2017 (UTC)

I am trying to find out if there are any other religious/ideological groups besides the Mormons making what are scientifically investigable claims. There is an intersection here between the humanities and science, but I don't want to hear about Turtle Island or September of 4,004 BC and so forth. μηδείς (talk) 23:47, 22 December 2017 (UTC)

Roger. Sorry for being denser than usual. :) ←Baseball Bugs ^{What's up, Doc?} carrots→ 00:01, 23 December 2017 (UTC)

It is posited that Central American natives used African religious symbolism and African linguistics: Paul A. Barton (February 28, 2001). "The Olmecs: An African Presence in Early America". www.theperspective.org. —

Possibly Musa I of Mali? "Africa's 'greatest explorer'". BBC. 13 December 2000. —2606:A000:4C0C:E200:B8D8:3FE9:323E:5312 (talk) 23:35, 22 December 2017 (UTC)

Interestingly the article posits a Chinese influence on the Olmecs, given a jade mask which is illustrated there. I'll read the Musa article out of simple curiosity--but again what I am looking for is some set of "believers" who make a "falsifiable scientific claim". The closest I can come to in my mind is the insistance of some Objectivists that American natives were savages without the concept of land ownership or private property, and hence were rightfully subjugated by the civilizing forces of European colonizing states. But that's not a claim about pre-Columbian contact, just a myth some people still insist on. μηδείς (talk) 23:47, 22 December 2017 (UTC)

Thanks, IP 2606, that was interesting reading. I wish Will Durant had done a book on African Civilization comparable to his on Rome, Greece, and The Age of Faith. I'll have to comb the library's African History section next time I am there. μηδείς (talk) 00:05, 23 December 2017 (UTC)

I'm not sure whether this is the sort of thing you're looking for, but see Ten Lost Tribes#Native Americans for a theory that at least implies a pre-Columbian migration to the Americas. As I recall, Frankie Ballou in Cat Ballou was a proponent of some such theory, repeatedly speaking to his hired man, Jackson Two-Bears, in Hebrew. Deor (talk) 12:23, 23 December 2017 (UTC)

Yes Deor, thanks! That is exactly the sort of thing I am looking for. μηδείς (talk) 16:36, 23 December 2017 (UTC)

I considered mentioning the 'ten tribes' (i.e: Tribe of Ephraim), but you specified "besides Mormonism". However, evidently, the concept of Jewish tribes arriving at a fourth place in a New World, predates Mormonism. See:

• "Jews Come to America - Judaic Treasures". www.jewishvirtuallibrary.org. American-Israeli Cooperative Enterprise. —2606:A000:4C0C:E200:B8D8:3FE9:323E:5312 (talk) 17:59, 23 December 2017 (UTC)