Wikipedia talk:WikiProject Physics/Archive February 2023

PROD candidate

Should I nominate Propagation of light in non-inertial reference frames for WP:PROD? It does not seem to be a topic, per se. —Quondum 21:16, 2 February 2023 (UTC)

Yes, definitely PROD. PianoDan (talk) 21:55, 2 February 2023 (UTC)

Yes, it looks like WP:OR. Xxanthippe (talk) 22:06, 2 February 2023 (UTC).

Thanks, done. —Quondum 22:54, 2 February 2023 (UTC)

Project-independent quality assessments

See Wikipedia:Village pump (proposals)#Project-independent quality assessments. This proposes support for quality assessment at the article level, recorded in {{WikiProject banner shell}}, and inherited by the wikiproject banners. However, wikiprojects that prefer to use custom approaches to quality assessment can continue to do so. Aymatth2 (talk) 20:31, 6 February 2023 (UTC)

MfD nomination of Draft:Orbiting-particle system force that is pulled straight inwardly into infinity.

Draft:Orbiting-particle system force that is pulled straight inwardly into infinity., a page which you created or substantially contributed to, has been nominated for deletion. Your opinions on the matter are welcome; you may participate in the discussion by adding your comments at Wikipedia:Miscellany for deletion/Draft:Orbiting-particle system force that is pulled straight inwardly into infinity. and please be sure to sign your comments with four tildes (~~~~). You are free to edit the content of Draft:Orbiting-particle system force that is pulled straight inwardly into infinity. during the discussion but should not remove the miscellany for deletion template from the top of the page; such a removal will not end the deletion discussion. Thank you. –LaundryPizza03 (dc̄) 08:44, 7 February 2023 (UTC)

Is this the right template for this page? PianoDan (talk) 17:04, 7 February 2023 (UTC)

I don't know of any alternatives except for plain text with a link. –LaundryPizza03 (dc̄) 17:10, 7 February 2023 (UTC)

Good article reassessment for X-ray crystallography

X-ray crystallography has been nominated for a good article reassessment. If you are interested in the discussion, please participate by adding your comments to the reassessment page. If concerns are not addressed during the review period, the good article status may be removed from the article. Onegreatjoke (talk) 21:31, 7 February 2023 (UTC)

Good article reassessment for Atomic theory

Atomic theory has been nominated for a good article reassessment. If you are interested in the discussion, please participate by adding your comments to the reassessment page. If concerns are not addressed during the review period, the good article status may be removed from the article. Onegreatjoke (talk) 21:14, 7 February 2023 (UTC)

This led me to Plum pudding model, which needs more care than I can give it at the moment. Large chunks seem to have been written with a weak grasp of the English language, and some phrases read like they were copied from elsewhere ("Being an astute and practical scientist"?). XOR'easter (talk) 20:38, 8 February 2023 (UTC)

Talk:Plum pudding model

If others could chime it at Talk:Plum_pudding_model#Example_of_damaging_false_and_misleading_information, that would be much appreciated. Headbomb {t · c · p · b} 13:24, 9 February 2023 (UTC)

Axial current

I tagged this new article with Template:Expert needed. The sources currently cited in the article don't appear to include the term axial current. Is the content legit? —Alalch E. 17:04, 9 February 2023 (UTC)

Definitely legit, and I'd be surprised if the listed QFT textbook DOESN'T include the term, but were you actually able to check that one? Could certainly use some cleanup from a native speaker. (of both English, and of QFT)

PianoDan (talk) PianoDan (talk) 18:06, 9 February 2023 (UTC)

Peskin and Schroeder definitely do use the term. I could have sworn I had a copy on the office shelf just in front of me, but I can't find it now, and the Google Books preview isn't quite extensive enough for me to figure out which pages are best to cite; I added a pointer to Zee's textbook for good measure. XOR'easter (talk) 19:47, 9 February 2023 (UTC)

Thank you both. —Alalch E. 22:47, 9 February 2023 (UTC)

Good article reassessment for Electricity

Electricity has been nominated for a good article reassessment. If you are interested in the discussion, please participate by adding your comments to the reassessment page. If concerns are not addressed during the review period, the good article status may be removed from the article. Onegreatjoke (talk) 00:16, 16 February 2023 (UTC)

Good article reassessment for Albert Einstein

Albert Einstein has been nominated for a good article reassessment. If you are interested in the discussion, please participate by adding your comments to the reassessment page. If concerns are not addressed during the review period, the good article status may be removed from the article. Onegreatjoke (talk) 18:06, 17 February 2023 (UTC)

Good article reassessment for Universe

Universe has been nominated for a good article reassessment. If you are interested in the discussion, please participate by adding your comments to the reassessment page. If concerns are not addressed during the review period, the good article status may be removed from the article. Artem.G (talk) 18:21, 6 February 2023 (UTC)

Well, I finally had some time to work on this today, but it was delisted while I was in the middle of referencing. XOR'easter (talk) 18:54, 13 February 2023 (UTC)

I may have mentioned this before several years ago, but the diagram (see In this diagram, time passes from left to right, so at any given time, the universe is represented by a disk-shaped "slice" of the diagram.) of the universe's expansion is seriously misleading. There is no sudden drastic deceleration of the expansion followed by a long period of almost static size. At a minimum, the caption should be altered to clarify this. JRSpriggs (talk) 23:46, 14 February 2023 (UTC)

Good observation. A logarithmic scale for the diameter might be useful (I don't know what scale applies in the diagram), but the growth behaviour of the universe certainly could be made more understandable, one way or another. —Quondum 01:53, 15 February 2023 (UTC)

JRSpriggs, this figure is widely used, including as the lead image on the level 1 vital article Science, so this seems like an important one to get right. I'm no expert in the expansion of the universe; could you point me to a source that explains how it really happened (and why this picture is misleading)?      — Freoh 00:59, 16 February 2023 (UTC)

Freoh, a comparable image that seems to pay attention to scale and is potentially much more accurate is here, also in Expansion of the universe. The Hubble time linearly extrapolates the current rate of expansion to the age of the universe; that it corresponds within 5% to the estimated age of the universe immediately implies that the image in question is grossly distorted (from the image, the Hubble time would have been maybe double the age of the universe: follow the cone that is tangent to the diagram at the present time backwards). So, you can take it as given that the "diameter" over time in the image is not "to scale". As JRSpriggs said, without drawing this to the reader's attention in the caption, this image is potentially highly misleading. —Quondum 02:15, 16 February 2023 (UTC)

Assuming that the universe is spatially flat (as it appears to be), we can infer from the second equation in Friedmann–Lemaître–Robertson–Walker metric#Newtonian interpretation that the scale factor of the universe a is

$a=\exp \int {\sqrt {8\pi G\rho \over 3}}\,\mathbf {d} t.$

Actually, it is more like sinch during the inflationary period when pressure is − ρ c². Then it enters a radiation-dominated period when pressure is about (1/3) ρ c². Followed by a matter-dominated period (pressure = 0) which is just ending and will be followed by another inflationary period (with a much lower rate of inflation). In any case, there are no negative terms to reduce the rate of growth.

OK? JRSpriggs (talk) 10:09, 16 February 2023 (UTC) Corrected by a factor of 3 as suggested below by PaddyLeahy. JRSpriggs (talk) 16:14, 20 February 2023 (UTC)

Umm, no. That curvature k apparently refers to the curvature of spacetime, not of a comoving spacelike section, which is to say, it is presumably Λ. Anyhow, responding with something that someone without a GR background will not follow is unhelpful. It is clear that there was period of deceleration of expansion, and so the diagram is not in error because it shows deceleration, only because the shape is very far from the estimated trajectory. I did link to a diagram with a better shape above. —Quondum 01:40, 17 February 2023 (UTC)

JRSpriggs, I think you lost a factor of 3, but apart from that your integral is right but not useful. ($k$ in the Friedman equation really is the curvature of space, not space-time). To do the integral you need to know $\rho (t)$, but $\rho$ is directly a function of $a$, and to get the $t$ dependence you need to re-arrange the whole thing. Getting back to the diagram, the real problem is that the universe is 1000 times bigger now than at recombination, so a properly scaled diagram would be illegible. The NASA PR diagram under discussion is self-evidently a schematic and it does get most of the qualitative things right. I've seen it used in dozens of professional talks. PaddyLeahy (talk) 00:08, 20 February 2023 (UTC)

PaddyLeahy, would you be able to suggest a description in the caption that would allow (the nonlinearlity of) the scale factor in the diagram to be understood by the average reader? —Quondum 00:38, 20 February 2023 (UTC)

Well, I tried. Caption now seems over-pedantic. If you read the labelling in the diagram you can see that the time axis represents the first 375,000 years as about 5% of the 13,800,000,000 year total age, which is obviously not to scale, so I don't see why anyone would think the space axes were any more realistic! PaddyLeahy (talk) 01:04, 20 February 2023 (UTC)

Thanks, that includes enough information to make it understandable. I may tweak it for conciseness. I have just realized that I'd missed the time-scale nonlinearity – by three orders of magnitude! :( —Quondum 01:30, 20 February 2023 (UTC)

To PaddyLeahy: Thanks both for the correction to my formula and for correcting the caption of the diagram at Universe. JRSpriggs (talk) 16:23, 20 February 2023 (UTC)

I kinda think this diagram might work well with a log–log scale. Incidentally, the integral formula above seems to imply that contraction is impossible in a "spatially flat" universe, which is rather counterintuitive. —Quondum 16:56, 20 February 2023 (UTC)

A log-log scale would need to go to minus infinity on the time axis and through minus infinity on the x & y axes. A truncated version would work OK for a 1D plot but not for a pseudo-3D picture. The point of this picture is to give some idea of how the contents of the universe change with time, it is not intended to convey in any quantitative way how the universe expanded. PaddyLeahy (talk) 17:47, 20 February 2023 (UTC)

There is no need to go beyond the Planck scale. And no need to stay strictly log–log. It is just that this diagram is so horribly crudely scaled that it throws intuition for a loop; it is "glossy" while being bad at conveying what it could do more effectively, even without being properly quantative. Something much closer to log–log might just do so better at the same job. —Quondum 21:27, 20 February 2023 (UTC)