Wikipedia:Reference desk/Archives/Science/2016 September 26

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September 26

Sub-Zero Kelvin

Hypothetically speaking, if by absurd even subatomic movement (as opposed to just inter-molecular movement) were to completely and utterly cease, would we reach sub-zero Kelvin ? If so, then what negative value, in Kelvin, would that be ? — 79.118.172.79 (talk) 09:35, 26 September 2016 (UTC)

We have an article about negative temperature. DMacks (talk) 09:43, 26 September 2016 (UTC)

Indeed we do... Unfortunately, what we don't have, is a Physics-to-English interpreter. :-) — 79.118.172.79 (talk) 10:17, 26 September 2016 (UTC)

The misleadingly named physics concept of negative temperature isn't actually about states colder than absolute zero. Rather this concept of negative temperature refers to configurations that are thermodynamically unnatural and unstable in such a way that they will always lost energy when brought into thermal contact with normal systems. As the article says, this means such states are in a sense hotter than all positive temperatures. A system possessing "negative temperature" can be constructed artificially by explicitly manipulating the microstates of the particles, but can never be reached by only adding or removed heat. Dragons flight (talk) 12:04, 26 September 2016 (UTC)

If it is possible to remove energy and further reduce the movement, then you haven't gotten to absolute zero yet. Once you reach absolute zero, it is no longer possible to remove energy via any process. The physical laws of quantum mechanics are such that even at absolute zero the motion doesn't actually cease (the so-called zero point energy), but this residual motion is not something that can be removed. To ask what if "movement... utterly cease" is essentially to ask, "if I did something impossible, what would happen". Its not a question that permits a natural answer. Dragons flight (talk) 12:04, 26 September 2016 (UTC)

I am aware of the fact that such cessation (or deceleration) of motion is not (yet) achievable, but is there really no purely theoretical framework which, when extrapolated to out-of-range values, would yield certain results (as untestable and hypothetical as they might be) ? — 79.118.172.79 (talk) 12:15, 26 September 2016 (UTC)

It would be an explicit contradiction of the uncertainty principle. It is not just "not yet achievable", rather it is explicitly forbidden by the laws of physics as we presently understand them. Dragons flight (talk) 12:28, 26 September 2016 (UTC)

It is debatable whether or not our present understanding of the laws of physics includes the fact that the uncertainty principle holds in the fundamental sense described by the Copenhagen interpretation. If you have a consistent picture of hidden variables, couldn't you argue that this theoretical limitation could be surpassed in the way the OP is looking for. (Although, you would have to negotiate all the other constraints on those theories.) I'm not sure you'd find many physicists willing to bet on this possibility though. 129.234.195.173 (talk) 15:14, 26 September 2016 (UTC)

No, it has nothing to do with one's interpretation of quantum mechanics. All the interpretations predict the same observations in any case. It's a fundamental consequence of the wave nature of matter (let's see if that comes up blue). --Trovatore (talk) 15:18, 26 September 2016 (UTC)

Indeed. As we unfortunately discovered in the preceding discussion, it seems that you can only pick two of three adjectives for the explanation: simple, precise, correct. Two of three, maximum. If you oversimplify, you lose either precision or correctness; if you overspecify, you lose either simplicity or correctness; .... Ultimately, if you want a completely correct understanding, there is no substitute for lengthy, careful, formal study of these topics.

I'm a bit crochety, but I have generally found that as soon as the word "interpretation" appears in a discussion of quantum physics, it is statistically certain that all subsequent discussion is about to rapidly diverge from real, actual science. I'd love to see an equation that captures and quantifies this type of evolution with respect to time.

Trovatore, we have this article: matter wave, to which we might consider redirecting your red link...

Nimur (talk) 15:54, 26 September 2016 (UTC)

Really, you've never heard any physics professors talk about interpretations of quantum mechanics? I take your point that people casually and ignorantly abuse quantum weirdness all the time, but it's not like real scientists don't talk about interpretations. SemanticMantis (talk) 16:52, 26 September 2016 (UTC)

I won't speak for Nimur, but I don't think "real scientists care about it" is the same as "it's really science". Real scientists do, and IMO should, think about metaphysics, but that doesn't make metaphysics "science" sensu stricto.

Among the criticisms of metaphysics is that it's not science, but to me, this is not really a criticism unless you adhere to scientism, which I don't. There are other eliminative approaches to metaphysics, like positivism, but in my judgment none of them are an adequate way of thinking about the world. --Trovatore (talk) 17:04, 26 September 2016 (UTC)

It's a mixed picture within the physics community, the condensed matter people tend to take the view that it's waste of time to discuss interpretations, while the people doing more fundamental research tend to be more open about the relevance of such discussions. The often made statement that the different interpretations of QM are equivalent is not strictly speaking correct. E.g. Bohm Interpretation becomes ordinary QM only after assuming quantum equilibrium, and MWI and Copenhagen Interpretation are not equivalent either, Copenhagen predicts non unitary time evolution for sufficiently large isolated systems, while Copenhagen can be falsified if you could perform a thought experiment contemplated by David Deutsch involving simulating an observer using a quantum computer who performs a reversible measurement. Count Iblis (talk) 17:25, 26 September 2016 (UTC)

I wasn't trying to imply that interpretation is broadly considered a type of science, sensu stricto, merely that real physicists can and do talk about interpretations and strict science, all in the same paragraph. (Also, "what scientists do" is a perfectly reasonable definition of science that is floated in some contexts, and certainly interpreting mathematical expressions of research findings for real-world implications is a big part of many scientists' jobs these days. ) SemanticMantis (talk) 23:24, 26 September 2016 (UTC)

Many scientists wear socks. Therefore, wearing socks is science. MChesterMC (talk) 08:47, 27 September 2016 (UTC)

Yes, you've found one of the many interpretations and contexts where that is not a useful definition. Likewise, there are contexts where the hypothesis/experiment notions of science are not that useful either, but now we're rather off-topic :) SemanticMantis (talk) 13:10, 27 September 2016 (UTC)

I can only endorse the position that "wearing socks is science" if the method of wearing socks is scientific. Does the wearing of the sock test a falsifiable hypothesis? Does the sock-wearer compare results against a control group who did not wear socks? Are claims confirmed? If claims are refuted, is the sock hypothesis reworked? Does a general consensus gradually emerge amongst professionals who study the results of sock experiment data? Nimur (talk) 14:43, 27 September 2016 (UTC)

I doubt that a large-scale, double blind study has ever been done (and what exactly would a placebo sock look like anyway ?), but there is a general consensus that not wearing socks leads to abrasions and cuts on the feet from rubbing against the inside of shoes. Of course, then the possibility of not wearing shoes also must be considered, but that depends greatly on the weather, ground cover, and activity (fine for walking on a sandy beach, not so good for climbing Mount Everest). StuRat (talk) 16:20, 27 September 2016 (UTC)

So, basically, what you guys are saying is that a drop in temperature would definitely take place, but that its size would be indeterminate because of the uncertainty principle ? — 79.113.230.36 (talk) 18:17, 27 September 2016 (UTC)

No. We are saying that you are talking about something that can't happen. The uncertainty principle is one way of understanding why it can't happen, not a constraint on what would happen if it did. --Trovatore (talk) 18:20, 27 September 2016 (UTC)

Okay, but I already knew that. (It is not as if I am unaware that the movement of subatomic particles cannot be slowed down or stopped). — 79.113.230.36 (talk) 18:32, 27 September 2016 (UTC)

Well, look, I'm a defender of the proposition that counterfactuals are at least sometimes meaningful and useful. Sometimes one can even make sense of "counter-possibles", that change fundamental laws of physics and try to deduce what would happen — one of my favorite questions on an exam in college was what the black-body law would look like if photons were fermions.

But this particular counterfactual, I'm afraid I see no clear way to interpret. Thermodynamics in its microscopic version, quantum statistical mechanics, is so intertwined with quantum mechanics in general that I just see no way of making sense of your question. --Trovatore (talk) 19:04, 27 September 2016 (UTC)

Just out of curiosity, what difference would it make? I don't know how you'd figure out how many photonoids would fit in a space under the Pauli principle, but it seems hard to believe normal light levels would push that limit... Wnt (talk) 03:40, 28 September 2016 (UTC)

Well, I think the point is not how many fit period, but rather how many fit with a given wave number. If they're fermions, the answer is only two (one polarized right, one left, I think). IIRC this results in the minus sign in the denominator of Planck's law changing to a plus sign. But I don't remember the details. I just remember that it was one of the most enjoyable problems I was ever given in an exam. --Trovatore (talk) 03:51, 28 September 2016 (UTC)

Differences between optical focuses of electromagnetism and magnetism

WP:COMPETENCE
The following discussion has been closed. Please do not modify it.
What are the differences between optical focus of electromagnetic fields and optical focus of magnetic fields and also optical focuses of magnetic and electromagnetic induction?--79.139.159.41 (talk) 09:47, 26 September 2016 (UTC) This question makes no sense. You're going to need to find a website that uses your native language and ask the question there. You're use of English is too poor for anyone here to be of use to you. --Jayron32 11:12, 26 September 2016 (UTC) You're ?? AllBestFaith (talk) 18:33, 26 September 2016 (UTC) I think that it is depends from what kind of work do atom or nucleus of atom, that is electromagnetic or magnetic work.--79.139.159.41 (talk) 13:11, 26 September 2016 (UTC) Did a photoelectric effect being a magnetic or electromagnetic effect?--79.139.159.41 (talk) 14:15, 26 September 2016 (UTC) I take the question to be the differences in how you focus an optical camera and a magnetic field camera: [1]. That "camera" says in the specs it has "Sensor-surface distance: 0.3mm". I take that to mean it has no way to focus on different depths, but only senses magnetism at that distance. To develop a true 3D map of a magnetic field, it would therefore be necessary to repeat the scan at different distances. The 3D maps they show may just reflect the strength of the magnetic field at one 2D scan (with the Z-axis being added for the strength). The analogy with an optical camera would be if you cut an object into sections and photographed each, which has been done with brain sections, etc. Still, an MRI machine does seem able to focus on different depths, using magnetism (plus radio waves and field gradients), so it must be possible, although again it may just move the sensors closer and farther, rather than using a method akin to an optical focus. StuRat (talk) 15:10, 26 September 2016 (UTC) Thanks. It seems to me that if magnetism and electromagnetism as also and magnetic and electromagnetic induction has optical spectrums, so that they may be has optical focuses.--79.139.159.41 (talk) 15:32, 26 September 2016 (UTC) You can focus an electron stream, as is done in a cathode ray tube, but, unlike visible light, where you have photons bouncing off of everything, normally, just due to sunlight, you don't normally have electrons doing the same. An exception is a scanning electron micrograph. StuRat (talk) 17:36, 26 September 2016 (UTC) I wish to add that I determine an optical focus as an optical force of all optical environments, and I must to say that if it is could and seen in optical mechanics so that it is could and saw in quantum mechanics and in others. Of course, I think that work of atom as also work of nucleus of atom could do as magnetism and as also electromagnetism. For example I think that in my country the USSR-Russia was decided that magnetism always do a work of atom as also a work of nucleus of atom.--79.139.159.41 (talk) 18:50, 26 September 2016 (UTC) This exchange is persistence by Alex Sazonov (as IP 79.139.159.41) in the behaviour on which he has received warnings [2]. Unfortunately Alex is obdurate to the classical electromagnetic theory that has been unified in Maxwell's equations (that describe how electric and magnetic fields are generated by charges, currents and changes of each other). This theory has stood for over 150 years and it is well documented in Russian schoolbooks which I have advised Alex to study instead of attaching his incoherent historical claims about soviet Russia to Ref. Desk answers. [3] [4] [5] [6] [7] and more. AllBestFaith (talk) 20:02, 26 September 2016 (UTC) I think that in all situations is always do a mechanical work, regardless of what it is being.--79.139.159.41 (talk) 20:32, 26 September 2016 (UTC) The user, who claims to be a Russian speaker, can't even speak broken Russian, let alone comprehensible English. μηδείς (talk) 20:41, 26 September 2016 (UTC)

Galapagos Rift and Chemosynthesis

In "Mapping the Deep" by Robert Kunzig, the author gives credit for the discovery of the Galapagos Rift and first observation of chemosynthesis to G Evelyn Hutchinson in 1979. The Wikipedia article on the Galapagos Trench doesn't mention its discovery. The article on Hutchinson doesn't mention the Galapagos Rift. The article on chemosynthesis gives credit to Colleen Cavanaugh for its discovery and doesn't mention Hutchinson. Was Kunzig writing fiction?Bobgustafson1 (talk) 16:19, 26 September 2016 (UTC)

The 1979 expedition included Childress, Ballard, and Karl, according to Karl's bio at PNAS. I can't be sure Hutchinson wasn't there. Cavanaugh proposed the mechanism, and later showed it to be accurate. That's not really what I mean by "discovery", but designating who gets credit for a discovery is always a bit murky.

Here [8] is a research paper from 1982 summing up the state of the art at that time. If nothing else it has a highly relevant ref list. Note the key citations to Childress, Cavanaugh, and Karl, while Hutchinson is cited only for a more general paper.

But 1979 can't be the discovery of the rift: Hydrothermal_vent#Discovery_and_exploration tells us Jack_Corliss led an expedition there in 1977. SemanticMantis (talk) 16:44, 26 September 2016 (UTC)

I am not sure that such a rift exists. Ruslik_Zero 19:34, 26 September 2016 (UTC)

Why does your surety matter? You are not a reliable source... --Jayron32 20:06, 26 September 2016 (UTC)

Here's some more evidence that nobody discovered the Galapagos rift in 1979. A 1976 research article says

“ ...the Galapagos Spreading Center (originally identified and named the Galapagos Rift Zone by Raft[1968] and Herron and Heirtzler [1967]) [9] ”

Herron and Hertzler (1967) is a Science paper that says

“ ... anomaly suggest that a type of sea-floor spreading occurs near the Galapagos Islands... it is suggested that the area be called the Galapagos Rift Zone. [10] ”

Emphasis mine, but I think that's a good indicator that Hunzig got some important bits wrong, or worded the claims confusingly.

It seems much more reasonable that the 1977 submersible mission was the first time a human looked at a critter that was using chemoautotrophic endosymbionts. Here [11] is a web version of 25th aniversary CD put out by WHOI, so it will be a pretty reliable reference on the topic. It lists several members of that mission, Hutchinson not included. Tellingly, it says "No one imagined any need for a biologist on board." In 1977, Hutchinson was one of the leading ecologists in the world, and had he been present, I think he'd have been mentioned.

In sum, this indicates to me the Kunzig book either has some serious factual errors or very bad wording, without a direct quote, it's hard to say. SemanticMantis (talk) 21:36, 26 September 2016 (UTC)

Thank you SemanticMantis and others for your comments and referencesBobgustafson1 (talk) 13:16, 28 September 2016 (UTC)