Wikipedia talk:WikiProject Physics/Archive November 2020

Hamiltonian

Hi all, I started a move discussion at Talk:Hamiltonian, which is an unnecessary and confusing DAB page that should redirect to Hamiltonian mechanics with a hat note to the dab page. Not only is the Hamiltonian the only one on the page (other than its quantum counterpart) to be called a Hamiltonian, it gets many more page views and is a much more common term than any of the others. Most importantly, however, it would be confusing to intro physics students trying to look up the Hamiltonian and aren't sure which to pick. WP:PRIMARYTOPIC is pretty clear about what should happen here, but any input is appreciated. Thanks. Footlessmouse (talk) 02:06, 1 November 2020 (UTC)

Units in Curie constant

Is it me or the first formula in Curie's law is not good if it is written in SI units. For it to be consistent with SI units version of C in Curie constant, maybe the formula should read M=CB/(T μ₀). The problem is that the constant should be defined either for the magnetic susceptibility or for a relation between H and M, not B and M. See for example Curie–Weiss_law#Modification of Curie's law due to Weiss field. Do you agree?--ReyHahn (talk) 11:47, 10 November 2020 (UTC)

The issue is that μ₀ is part of the constant, as defined by our generic use of K (which I can't determine if that's supposed to be K or k_b because it's not specific). I would agree that it could probably use some cleaning up to be more consistent across articles, though. Primefac (talk) 12:57, 10 November 2020 (UTC)

Sure, k is Boltzmann constant in the Curie law article, "K" is for kelvins. I am wary to modify the equation because magnetic units are tricky and it is such a standard way to write Curie's law that it would look weird otherwise. We have three options: write it with the μ₀, scrap the SI units and use Gaussian, or write it using the field H. --ReyHahn (talk) 16:20, 10 November 2020 (UTC)

Draft:Heisenberg time

The anon creator of Draft:Heisenberg time asked for advice an my talk page for what was needed for this draft to be acceptable - I gave them some pointers but thought I'd flag here in-case anyone feels like improving it or adding a comment to why it is or isn't notable. Cheers KylieTastic (talk) 16:42, 1 November 2020 (UTC)

I stated on the talk page Draft talk:Heisenberg time that it should be merged into quantum chaos and explained why. 67.198.37.16 (talk) 06:38, 11 November 2020 (UTC)

Invitation to respond to RfC at talk:Introduction to entropy

We have an ongoing disagreement on how to begin the Introduction to entropy article. One side wants the introduction to begin with irreversibility, the other with an order/disorder discussion. Any input would be appreciated. PAR (talk) 03:28, 4 November 2020 (UTC)

Unfortunately, entropy has nothing to do with either irreversibility, or with order/disorder. Both are flawed ideas, and both will only deepen confusion about what entropy actually is. 67.198.37.16 (talk) 07:57, 11 November 2020 (UTC)

Dear 67.198.37.16, I suggest to you that the page Talk:Introduction to entropy is the venue for discussion of the topic of your above comment.Chjoaygame (talk) 08:35, 11 November 2020 (UTC)

Draft:Introduction to entropy

During discussions at Talk:Introduction to thermodynamic entropy, I (unintentionally) wrote something that could be an draft of an outline of an article for Introduction to entropy in full generality, and not just for thermodynamics. I was wondering if anyone here would be interested in collaborating to expand and turn this into a real article? (I wouldn't do this myself, its clear that this would not meet the expectations/approval of some editors here; the headwinds are too strong for go-it-alone, thus a need for collaboration). I copy the comment from the talk page below, its long but I think reasonable.

From the physics point of view, thermodynamic entropy is "explained" by "information" entropy (metric entropy, actually); the explanation is provided by the microstate theory of matter (atoms in a liquid bumping into each other, etc.). The "information" entropy is in turn "explained" by geometry; entropy is a property of geometric shapes, see for example, Morse theory; some textbooks in Riemannian geometry touch on this. The idea of "things bumping into other things" (e.g. atoms bumping into one-another) can be expressed in terms of graphs (say, a vertex for every bump, and an edge from one bump to the next), and so one can express entropy on graphs (a famous example is given by sand-piles; each vertex is a grain of sand, each edge is the other grains of sand that it touches. See Abelian sandpile model. But also the petroleum industry uses percolation models to estimate flow of oil from fraking, etc.). This is not unlike homology, where you can abstract away the common elements of the half-dozen different homology theories, and formulate an abstract version on graphs. After that, it gets interesting: many graphs occur as the results of grammars and languages, and so one can assign entropies to that (this is partly what the biologists were doing, probably without fulling realizing it: DNA encodes 3D structural shapes, which interact based on their shapes, via electromagnetic interactions between the electrons in atomic orbitals. This is called the resonant recognition model of how proteins interact via electromagnetic fields (see resonant interaction). They are "bumping into" one-another, not unlike the atoms in an ideal gas, although the "bumping" is more complicated, because the atoms in an ideal gas are point particles with spherical symmetry, but amino acids are not. So if you want to compute the "thermodynamic" entropy of something that isn't simply round and sphere symmetric, you have to deal with the shape of the thing that is bumping, and you have to deal with non-local forces, e.g. van der Waals forces, and with asymmetric forces, which is what the resonant recognition model does. Oh wait, there's more! Suppose you wish to compute the thermodynamic entropy of a mixture of two different gasses, say helium and neon. You have to adjust for the proportion of each. And so here, different amino acids occur in different proportions. And they float in a soup of water at some temperature. If you wish to deal with the thermodynamic entropy of freon vs ammonia, you have to deal with shapes. If you pull on that thread, you again find that shapes are described by grammars and languages, which, in earlier decades, was the traditional domain of computer scientists and of linguists, respectively. 3D shapes, you could say, are a special case of "language"; in atomic physics, they express the "grammar" of quantum orbitals of atoms. I mean this in a literal sense, and not as a poetic allusion. You can write Backus-Naur forms for how atoms interact; when you do this, you get things like Lindenmeyer systems, and thence onwards to algorithmic botany. (redlink, see algorithmic botany website) So the language and grammar of atoms is fairly well-understood, and the means to compute the "information" entropy of languages and grammars is somewhat understood, How this "information" entropy depends on the analog of "temperature" e.g. similar languages given a Zariski topology, and how this abstract entropy realizes itself in the 3D shapes of molecules is kind-of partly understood, and how to compute the "thermodynamic" entropy of 3D shapes (proteins) in a soup of room-temperature water is kind-of understood. Again, see the resonant recognition model redlink for details. So this is all very pretty, it is a tour of how we go from "entropy as a geometric invariant studied by mathematicians" to "entropy that classifies the motion of things in the spacetime we live in studied by physicists" to "entropy of grammars and languages studied by biologists". When scientists talk about entropy, these are the kinds of things they talk about. These are the kinds of things that could/should be sketched in an "intro to entropy" article.

(And I almost forgot: Axel Kleidon has written lots of fun stuff about production of entropy, see e.g. Axel Kleidon, (2010) "Life, hierarchy, and the thermodynamic machinery of planet Earth", Physics of Life Reviews Elsevier which is available online somewhere. He also has an earlier book on this topic. So, entropy from a fourth perspective.)

67.198.37.16 (talk) 21:31, 13 November 2020 (UTC)

General relativity priority dispute

Could use some expert eyes on this article for notability and whether or not folks here think it's an essay, rather than an article. Thanks. Onel5969 ^{TT me} 21:20, 1 November 2020 (UTC)

I read some earlier version of this, and thought it was fascinating. I'm certain others would think so, too: (undergrad) physics textbooks commonly have historical sidebars, which are either totally fascinating, or completely ignored, depending on one's mind-set (well, they certainly won't be on the mid-term). Certainly, as one gets older, and actually comes to actually master all of the ideas, one develops an interest: "who the heck came up with this stuff? and what were they high on, when they did it?" OK, that didn't come out right, so more politely, "what the heck were they thinking?" Umm, lets try again, "what feverish mental state were they in?"... err. I'm having trouble expressing myself... I think it's fine that its more of an essay. Essays are harder to edit without breaking the flow, but they are more fun to read. 67.198.37.16 (talk) 06:21, 11 November 2020 (UTC)

User:onel5969 It was split from relativity priority dispute. Yes, it definitely reads like an essay, but it has absolutely no notability concerns, given especially that notability is based on what exists and not what is in the article. I had planned on working on it a bunch, but we had a small dispute of our own during the split and everything got put on hold. I will begin working on it again soon and everyone is encouraged to help out where they can. Footlessmouse (talk) 13:12, 15 November 2020 (UTC)

Mass dimension one fermions AfD

I just nominated Mass dimension one fermions for deletion. I figure some of the editors from the Physics project may wish to weigh in. - Parejkoj (talk) 21:25, 14 November 2020 (UTC)

I want to second the canvass; due to the extreme technical nature and the conflict-of-interest issues with the primary editors this needs anybody who has any expertise in quantum physics-related matters. power~enwiki (π, ν) 06:37, 16 November 2020 (UTC)

Equation in Rugate Filter article

I translated Rugate filter from German yesterday, but I just noticed that one of the equations looks really strange:

${\frac {\int _{0}^{d}{n(x)}dx}{d}}d=\left\langle n\right\rangle d={\frac {\lambda _{0}}{2}}$

The left hand side being divided by d and then multiplied by d makes no sense. Does anyone here know what it should look like? --Slashme (talk) 12:29, 19 November 2020 (UTC)

I think it's defining an average index of refraction by

$\langle n\rangle ={\frac {1}{d}}\int _{0}^{d}n(x)dx.$

This is then multiplied by $d$ again to get $\lambda _{0}/2$. It might need rewriting for clarity, but I don't think it's technically wrong. XOR'easter (talk) 17:57, 19 November 2020 (UTC)

Gillespie algorithm

Hey, not sure this is the right place here. Where do you discuss the quality of articles on en:wiki? In any case, could you please have a look at the changes recently performed in Gillespie algorithm? I like the newly added pictures, however I have severe doubts that the software solution also posted on the page is hiding the essence of the algorithm. Prior to the changes the algorithm was shortly presented with this piece of code:

# Main loop
while t < T:
    if n_I == 0:
        break

    w1 = _alpha * n_S * n_I / V
    w2 = _beta * n_I
    W = w1 + w2

    # generate exponentially distributed random variable dt
    # using inverse transform sampling
    dt = -math.log(1 - random.uniform(0.0, 1.0)) / W
    t = t + dt

    if random.uniform(0.0, 1.0) < w1 / W:
        n_S = n_S - 1
        n_I = n_I + 1
    else:
        n_I = n_I - 1
        n_R = n_R + 1

    SIR_data.append((t, n_S, n_I, n_R))

Now the code is much, much longer. Biggerj1 (talk) 00:08, 24 November 2020 (UTC)

The best place to begin these conversations is on the talk page of the article you have a question about. If there are not enough responses to the question you posed, you can post a link in Wikiprojects asking others to join the discussion. It appears as though editors replaced an algorithm outline with a fully functioning python program that implements the algorithm and displays the results using matplotlib. It wraps functionality into a class and calls functions as opposed to inline code that was there before. That is probably unnecessary detail for an article dedicated to the algorithm, but you will have to start a discussion there about it. Thanks! Footlessmouse (talk) 00:37, 24 November 2020 (UTC)

Wikipedia house style generally prefers pseudocode to code and frowns on lengthy examples. Per the Manual of Style, avoid writing sample code unless it contributes significantly to a fundamental understanding of the encyclopedic content. XOR'easter (talk) 00:52, 24 November 2020 (UTC)

Energy quality

Hi all, you may be interested in this strange article (Energy quality) that was nominated for deletion. While it is clearly discussing a physics concept, it was never tagged by this project and it is based on the work of an ecologist. At the very least, the article needs a lot of help. Footlessmouse (talk) 13:07, 15 November 2020 (UTC)

Seems that the result is keep. I do agree, though, that it could use some help. As the section above notes, entropy is important. As well as I know, the usual case is that heat (thermal) energy is low quality. There are limits on how much can be converted to higher quality, such as mechanical or electrical. Gah4 (talk) 06:37, 23 November 2020 (UTC)

Yeah, I don't think AfD was the right venue for that one, I didn't even bother !voting. I just thought it was interesting and wanted to put it here in case anyone else thought it was interesting enough to work on. Footlessmouse (talk) 22:24, 24 November 2020 (UTC)

Weyl and fermions

(I'm not well versed on this, but) is it normal that Weyl equation does not make references to neutrinos at all?--ReyHahn (talk) 15:23, 24 November 2020 (UTC)

It used to be thought that neutrinos were massless, but now it is believed that at most one of them is massless, the others having a very small mass. If they are massive, then the Weyl equation does not apply to them so there is no reason to mention them there. JRSpriggs (talk) 06:21, 25 November 2020 (UTC)

Ok, maybe something should be mentioned still for educative and historical purposes.--ReyHahn (talk) 16:27, 25 November 2020 (UTC)

@JRSpriggs: I tried to be careful and added some historical information on Weyl equation. If you have the time check it is ok. I think there is still word or two that can be added about electroweak theory and left-right decomposition of particles in the introduction, but I do not know if I can describe it correctly. Let me know.--ReyHahn (talk) 09:49, 27 November 2020 (UTC)

By convention, historical information usually goes at the end of the article. Why, I don't know. I'm not sure I care, other than that it allows the first section to be either an "informal explanation" or a short "definition" (so that you find out what it is, before reading about it's detailed history.) Anyway, the more history, the better. Personally, I like historical accounts.67.198.37.16 (talk) 04:38, 28 November 2020 (UTC)