Wikipedia talk:WikiProject Physics/Archive March 2015

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Zero-energy universe

Is there a way to rangeblock Saint-Petersburg out of all astronomy and physics articles? -- 70.51.200.101 (talk) 05:13, 2 March 2015 (UTC)

RFC over at Lift(force)

Should we keep the current quantitative statement on momentum transfer in the second section or replace it with a qualitative version?

Link to RFC.

Comments welcome. Mr. Swordfish (talk) 20:49, 9 March 2015 (UTC)

Draft at AFC needs expert review

Please review Draft:Quantum heat engines and refrigerators, thanks. Roger (Dodger67) (talk) 20:47, 13 March 2015 (UTC)

User is inserting spurious references into various Physics articles

Hi there, I have found a user:

http://en.wikipedia.org/wiki/Special:Contributions/Wdlang

Who seems to be insert many references to his own work into various physics articles. The articles themselves are sparse, and I feel that inserting such specific references is just trying to increase personal notability without adding any value to the article, nor is it making it more accessible as the results are so niche.

I would appreciate comment from someone more intimately familiar with the edits he is making. — Preceding unsigned comment added by 108.240.250.26 (talk) 02:54, 10 March 2015 (UTC)

It's clearly inappropriate material to add, particularly with a COI. If he persists it might be an idea to raise the issue at WP:COIN, Second Quantization (talk) 00:27, 15 March 2015 (UTC)

Gravitational constant / Dimensionless physical constant

Hi, I would like to mention the current discussion there (see revision history) and I would appreciate a few more opinions. User:77.238.218.96 kept adding a reference to an article, got reverted multiple times by different users, got blocked for 3RR, the content got removed, now User:Inorout wants to keep it. Check what Google finds about the author, or check the article itself to decide if that fits into the articles. --mfb (talk) 12:47, 16 March 2015 (UTC)

I believe that User:Inorout, User:77.238.218.96, User:77.238.216.206, and User:217.197.137.140 are all the same editor and is quite likely to be the same as the Bosnian author cited in these edits that have been reverted.

The WP rules are one thing (which the Bosnian editor has run afoul of) and the physics is another. All quantitative physical measures are initially and fundamentally of dimensionless values. Any claim that

G

or

c

or

\hbar

or

\epsilon _{0}

or

k_{\text{B}}

are parameters of the universe (in the same manner that

\alpha

is) are fallacious. And, while the claim that

\alpha

may take on a specific theoretical value makes sense, so far there is no accepted theory that defines

\alpha

in terms of other fundamental constants. It is what it is.

But to make the same kinda claim for

G

(or any other dimensionful physical parameter) is dumber and more crankish. We should stand firm against crackpots trying to use WP to advance such. 73.16.37.124 (talk) 19:43, 17 March 2015 (UTC)

It's simpler than that. If Physical Review publishes that the moon is actually a large tasty blue-cheese, our articles should say so, even if some of us think it isn't tasty. YohanN7 (talk) 19:54, 17 March 2015 (UTC)

Quantal translative momentum transfer

Could someone make an assessment of the article with regard to notability and correctness? There is a section in it devoted to defending its existence, Mainstream accounts of particle diffraction, which makes me think that this may be either OR or just pushing POV. I don't know.

As is usual with this editor, his writings are massively referenced. That said, I have rarely been able to see much correlation between what he writes (because I rarely understand anything of what he is trying to say) and what his references actually say. There is also Hamilton's optico-mechanical analogy and massive additions to a number of quantum mechanics related articles. (When it comes to talk pages, "massive" isn't enough for a description of his posts or the amount of references.) YohanN7 (talk) 10:52, 17 March 2015 (UTC)

It's not unreasonable to have an article saying in general that when diffracting/scattering off a perfectly-periodic structure, wavevector changes by one of the structure's reciprocal lattice vector. (This is a special case of the more general principle: When diffracting/scattering off any structure, wavevector changes by a nonzero Fourier component of the structure.) This statement is sorta mentioned in articles on diffraction grating, Bragg diffraction, Laue diffraction, neutron scattering, etc., but I guess not explicitly and generally anywhere. It may not need a whole article, I think a little section in diffraction would be enough.

Unfortunately, if I understand it right, the article is mainly a Trojan horse to argue something like:

Particle diffraction is not evidence of particle-wave duality, because particles can diffract too.

I'm not sure that this is really fringe physics, it seems to me to be more like a trivial complaint about terminology. In quantum mechanics, particles (like electrons) undergo diffraction, everyone agrees about that. Some people describe this by saying "The electron is a wave", others say "The electron is behaving like a wave", others say "The electron is behaving in a way that was traditionally associated with waves (before the advent of quantum mechanics when we learned that particles behave that way too)." I don't think any of these perspectives is really right or wrong, or fringe, or worth arguing about...

Anyway, I would vote to delete the article and replace it with a short section in Diffraction. --Steve (talk) 14:45, 17 March 2015 (UTC)

The wave-particle duality is "explained" by the same editor in Hamilton's optico-mechanical analogy. YohanN7 (talk) 14:55, 17 March 2015 (UTC)

By the way, I didn't put the fringe-template there in "Quantal translative momentum transfer". I did put in in "Hamilton's optico-mechanical analogy" though, because of the wave-particle duality claim. YohanN7 (talk) 15:47, 17 March 2015 (UTC)

I find Hamilton's optico-mechanical analogy to be complete technobabble. It does not even state the analogy it is supposed to be explaining. This editor has a habit of posting cites which do not directly support the content, arguing that "it's obvious" that they mean to. I fear this is a perfect example. — Cheers, Steelpillow (Talk) 16:20, 17 March 2015 (UTC)

My understanding of this editor's thesis is specifically that in diffraction, when the particle's path is bent, momentum is transferred between the lattice and the particle. That is to say, the local direction of the momentum vector is given by the local direction of the particle path. I have been assured by other editors, and in vehement terms, that the momentum transfer model is presented as fact in standard references on crystallography. I confess that surprised me, as I had always understood that no local force was exerted and consequently no momentum was exchanged during diffraction. Can others comment on this issue? — Cheers, Steelpillow (Talk) 16:20, 17 March 2015 (UTC)

From my POV, when now hopefully guessing better what the quantal transfer article is about, it may have a place when pruned off of its POV that is decidedly there. While a pure wave function treatment could be called "semi-classical", QFT would probably have the processes described more along the lines of exchanges of photons, with extra symmetries (apart from the ubiquitous four-momentum conservation) imposed by the symmetries of the lattice. Wave functions are still present in this would-be treatment though. (This is just guesswork.) I don't like the other article in its present form. YohanN7 (talk) 18:45, 17 March 2015 (UTC)

Steelpillow, if you accept that (1) A particle (photon, electron, whatever) has momentum; (2) The particle's momentum changes during scattering / diffraction; (3) Conservation of momentum is true ... Then you have to conclude that there is indeed a momentum transfer during scattering / diffraction. I don't think it's controversial at all. I have frequently heard the specific term "momentum transfer" used in the context of diffraction gratings, and in electron diffraction, and in x-ray diffraction. In the latter, an x-ray has an oscillating electric field which creates a force on electrons in the solid, so there is indeed a local force. :-D --Steve (talk) 20:40, 17 March 2015 (UTC)

I have been told that in quantum mechanics, (2) is false. Because a particle's position is highly constrained by the target, the principle of complementarity dictates that its momentum be equally highly uncertain. For example the Copenhagen interpretation emphasises that it is mere futile metaphysics to speculate on what happens in between the emission and detection of the particle. That is to say, the idea of a billiard ball passing through a hole and then mechanically turning at an angle is no more tenable than the idea of a wave sloshing against a scintillation counter. Is this wrong? — Cheers, Steelpillow (Talk) 08:57, 18 March 2015 (UTC)

No, if QM has such a prediction, it would only demonstrate that basic QM (wave mechanics of a fixed number of particles) alone cannot accurately describe processes where the number of particles is variable - as in actual scattering not modeled by "external potentials". YohanN7 (talk) 10:32, 18 March 2015 (UTC)

My apologies for failing to understand, but your reply uses so few of the words that I did, I cannot relate it to my question. Do you mean "No, (2) is not false", or "No, this is not wrong"? — Cheers, Steelpillow (Talk) 12:12, 18 March 2015 (UTC)

Perhaps I use few words to hide my own ignorance

Ignorance revealed: I mean "No, (2) is not false". The way scattering processes are calculated in QFT is by calculating their S-matrix elements (and subsequent "standard" calculations of cross-sections from the S-matrix elements). The S-matrix elements are the Hilbert space inner product between "in" states and "out" states. The "in" and "out" states are states that in the distant past and the distant future have the appearance of free particle states with definite quantum numbers, including momenta,

S_{\beta \alpha }=\langle \Psi _{\beta }^{-}|\Psi _{\alpha }^{+}\rangle

(Here

α

and

β

are compound indices, referring to all out and in particles respectively.) If no quantum number changes, i.e.

β = α

, then one has what is called "forward scattering". Such a scattering event cannot be detected far off from the forward direction (but maybe a little bit due to HUP). The "in" and "out" states are assumed to be complete, so that every (mass-shell) momentum is considered. In more detail, one may have

S_{p_{1},p_{2};p'_{1},p'_{2}}

being the probability amplitude that incoming momenta

p' 1, p' 2

are detected as outgoing momenta

p 1, p 2

. These momenta correspond to different directions. It may be that the average expected change in momentum is zero, but once a particle is detected, then one can conclude that there was in fact a momentum change due to that the directions in which the particles were found must be accompanied by a momentum change. A detailed calculation involve more and more complicated Feynman diagrams, each corresponding to an exchange of virtual particles, and an experimental finding cannot tell which Feynman diagram represents what actually happened during the scattering process since they all contribute coherently. At least this is my interpretation of what is going on in the scattering processes of QFT. YohanN7 (talk) 13:43, 18 March 2015 (UTC)

In the calculation of any Feynman diagram, wave functions are still involved. They are associated with the external lines (incoming and outgoing particles). The conclusion in the article in question that diffraction (scattering in general?) can be described without resort to wave functions is questionable. QFT has been proved to be extremely accurate and employs wave functions. YohanN7 (talk) 11:27, 18 March 2015 (UTC)

Introduction to eigenstates

An edit request was submitted for the Introduction to eigenstates article, but it's not really an edit request. If someone has a chance, would you mind looking at Talk:Introduction to eigenstates#Read with caution? Thanks so much.--CaroleHenson (talk) 09:22, 19 March 2015 (UTC)

"Nova"

The meaning and title of the article and pagename "Nova" is under discussion, see talk:Nova -- 65.94.43.89 (talk) 20:57, 21 March 2015 (UTC)

"Leverage" listed at Requested moves

An editor has asked to change the use of Leverage, for the discussion, see talk:Leverage (disambiguation) -- 65.94.43.89 (talk) 21:16, 21 March 2015 (UTC)

Gearing listed at Redirects for discussion

An editor has asked for a discussion to address the redirect Gearing. Please participate in the redirect discussion if you have not already done so. -- 65.94.43.89 (talk) 21:16, 21 March 2015 (UTC)

Thanks for the notification, but a correction: the Gearing discussion is at this March 17th RfD discussion. --Mark viking (talk) 22:14, 21 March 2015 (UTC)

"carbon fiber"

Wikipedia talk:Articles for creation/Bethe Center for Theoretical Physics

Hello again ... I'll leave it to the physics experts to decide if this old AfC submission should be kept and improved, deleted as a stale draft, or redirected somewhere. —Anne Delong (talk) 21:52, 25 March 2015 (UTC)

Migration of {{cite arxiv}}

The {{Cite arXiv}} template is being updated to be more consistent with other citation templates. This is likely to introduce some red error messages in existing Cite arXiv templates that use unsupported parameters or that should be converted to {{Cite journal}}. Please see this discussion. – Jonesey95 (talk) 15:01, 31 March 2015 (UTC)