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Torricelli's Equation?

I hardly think this is actually a worthwhile "article". It has zero sources, and is just one of the "suvat" equations with an elaborate derivation.

Maybe this can be merged into the section Equations of motion, Constant linear acceleration: mentioning one of the suvat equations was also found (and not "created") by Torricelli?

This has already been suggested here way back in 2005, to no effect... Maschen (talk) 14:53, 16 August 2012 (UTC)

Well, I think the whole thing is of some historical interest and significance; unfortunately, that is not how the article is currently written. The "derivation" should be scrapped, and replaced by historical context: how was the equation found? what did Newton have to say about it? Did it enter the vis-viva controversy, and how? (it surely must have!) For these reasons, I don't think it should be merged, but let it await some kind of historical expansion...linas (talk) 22:35, 17 August 2012 (UTC)

If historical sources aren't presented, can I suggest that this might belong better in the conservation of energy article, as a fairly accessible example of it? Sławomir Biały (talk) 22:45, 17 August 2012 (UTC)

Ok - both points are very true. Let's indicate this on Talk:Torricelli's equation and see what happens (I don't have references btw). Maschen (talk) 23:30, 17 August 2012 (UTC)

Based on personal experience with WP, it may take 5 or 10 years for the desired content to show up. I see no harm in leaving the article as it currently stands, its not getting in the way of anything: its not like every stub has to be merged somewhere. linas (talk) 02:14, 18 August 2012 (UTC)

Speaking of vis viva, is there a misplaced claim about conservation of momentum? See Talk:Vis viva. --Amble (talk) 04:32, 20 August 2012 (UTC)

Magnetic monopole and Yang-Mills theory

Please see here. The magnetic monopoles#appendix section has been copied from this site. Ideally it should be rewritten, although I don't understand Yang-Mills theory so can't do much about that... sorry. Maschen (talk) 12:17, 18 August 2012 (UTC)

The SpringerEOM license allows copying but requires attribution, and so this kind of copying should include a note along the lines of "tis article contains material from Springer EOM, licensed under the CC-by-SA and GFDL..etc." I'm looking to see if we have a template for springer that automatically does this...(we do have one, e.g. for planet math) here Template:PlanetMath attribution we need one for springer ...linas (talk) 14:09, 18 August 2012 (UTC)

Now see Template:SpringerEOM attribution linas (talk) 15:21, 18 August 2012 (UTC)

Excellent - thanks for doing all this. Maschen (talk) 21:34, 18 August 2012 (UTC)

Isospin-1 photon... what?

The photon article states that the isospin of a photon can be either 0 or 1. I thought this was clearly nonsense, but the PDG does list the photon has having either isospin 0 or 1, which is making me question a whole lot of things about what I know about isospin. This post on physics.stackexchange.com seems to say that the PDG is somehow referring to weak isospin, but why in the world would they recycle the I symbol for that when everywhere else it means normal isospin? Can anyone make any sense of this? Headbomb {talk / contribs / physics / books} 15:33, 18 August 2012 (UTC)

Yeah, that sucks. The article should be clarified. In the standard model, and specifically the electroweak subsection of it, the photon appears in a triplet with the W and Z bosons. The Higgs symmetry breaking gives W and Z a mass, but leaves the photon massless. The "weak" isospin refers to the weak force. The recycling of symbols of unfortunate... The bit about isospin 0 or 1 ... I don't remember any more, but perhaps this is the Cabibo angle business, which screws over the mass eigenstates vs. the isospin eigenstates (so that the Z boson is also a superposition of spin 0 and 1, but orthogonal to photon.) Yeah, see weak isospin and especially weak hypercharge for details.) linas (talk) 17:37, 18 August 2012 (UTC)

You mean Weinberg angle not Cabibbo angle. — A. di M.  18:15, 18 August 2012 (UTC)

Yeah, just as I went to fix that, a thunderstorm set in and I lost internet :-) anyway, the electroweak article spells it all out in some detail. linas (talk) 18:30, 18 August 2012 (UTC)

To be clear, the choice of word "isospin" for "weak isospin" is a historical accident/convenience. It simply refers to the idea that there is an SU(2) symmetry in there. Count yourself lucky that its not the word used for all occurances of SU(2) symmetry. of course, integer spin means a triplet or adjoint representation, and half-integer is a doublet or fundamental representation of SU(2) — Preceding unsigned comment added by Linas (talk • contribs) 17:54, 18 August 2012 (UTC)

They used I because the other choice, T, is ambiguous too. Surely it is the weak isospin what the photon may have, not nuclear isospin. But what means an enigmatic notation I = 0,1? There are more thoughts about this. BTW, does I mean I₃ or what? Incnis Mrsi (talk) 18:07, 18 August 2012 (UTC)

Properly speaking, I is a vector operator, with components I_x, I_y and I_z or I_1, I_2 I_3 depending on author. But equally often, it also means the ... um, representation err.. index (the Casimir invariant), of the vector operator so that its integer or half-integer, just like for spin. Thus, the operator I^2 has eigenvalues I(I+1) just like usual. All of this is "generally understood" without explanation; it follows from a general understanding of su(2) which is de rigeur for physics in general. Similarly, the statement that I=0,1 is really a shorthand for the Weinberg angle, and you are supposed to "just know this". Here, in WP, we should clarify at least the last point; we should not have to explain the first part, which follows from a general knowledge of su(2).linas (talk) 18:38, 18 August 2012 (UTC)

Or to be even more precise: the symmetry of electroweak is su(2) x u(1). The weak bosons are in a triplet of su(2) and so have I=1 and I_3 of +1, 0 and -1. There's another thing, called "B" that is an su(2) singlet, with I=0 and I_3=0 It mixes with the I=1, I_3=0 thing to give us the photon and the Z. The electroweak article mostly says this, but it could spell it out in slightly better detail, I think. (Its not terribly hard, once you understand it) linas (talk) 18:49, 18 August 2012 (UTC)

Sorry for posting here so much, but.... those articles also fail to state that the weinberg angle (and the cabbibo angles) are purely experimentally determined. There is no theory that explains what these values should be. (well, I suppose some supersymmetry or string theory attempts to give them a value, maybe... but its an open question) I find this quite remarkable. It really means that we are still waiting for some sharp pencil to explain why these are what they are, presumably garnering a Nobel prize in the process. linas (talk) 19:02, 18 August 2012 (UTC)

Ok so to recap, and make sure I understand things, the strong interaction-related isospin due to the up/down quarks (which I'll call I^ud) of photons is indeed zero, but some other SU(2) symmetry, the weak interaction-related isospin (which I'll call I^W), can be either 0 or 1 (or a mix of 0 and 1?). That is when the PDG writes I(J^P) of say mesons [1], they really mean I^ud(J^P), but when they write the I(J^P) of photons [2] and possibly gluons [3], they really mean I^W(J^P)? Because if so, the PDG should really come up with better symbol use, or make it abundantly clear what I is exactly referring to. Headbomb {talk / contribs / physics / books} 21:53, 18 August 2012 (UTC)

Uhh, no. These are all exactly the same isospin, the weak isospin. There are a whole mess of weak isospin doublets in the standard model: (electron, electrons neutrino) and (u,d) for lowest energy flavors. There are four more doublets for the next set of flavors. These all couple to the su(2) x u(1) gauge field exactly the same way. This gauge field has one vector, and one scalar. The vector is called W, the scalar is called B. The vector W is written as the usual lie algebra: $W^{+}=W_{1}+iW_{2}$ and $W^{-}=W_{1}-iW_{2}$ and $W^{0}=W_{3}$ all of these have weak isospin=1, and the I_3 component is +1, -1 and 0, respectively. The singlet B has I=0 and I_3=0. Now, its impossible that W+ and W- could mix with each other, or with W^0, so they don't. It would be insane to suggest that they could, it defies the logic of su(2), it defies the whole point of having a vector. However, there is no mathematical reason why W^0 and B can't mix, and ... lo and behold, they do. The mass eigenstates are not the same as the isospin eignestates. Just a fact of life, the standard model does not offer any prediction in this regard, one way or the other. No one knows why they mix (why the mas and isospin eigenstates aren't the same) or can explain it. We can explain *how* they mix, this is the Weinberg angle. But why .. big mystery beyond the standard model. The photon and the Z^0 both have I_3=0. Equally irritating, the quarks mix too: the mass eigenstates of the quarks are not the weak isospin eigenstates of the quarks. So, for example, there is an up quark which has a mass, and it is a mix of the weak-quark-up, weak-quark-down, weak-quark-strange, etc. This insane mixture is given by the Cabibbo angles. So you really should be thinking of two different kinds of quarks: those that are weak-isospin eigenstates, and those that are mass eigenstates. They are not the same.

OK so what the heck is the strong isospin? It is the isospin for the MASS eigenstates! If you visualize the weak isospin operator as a 3D vector, pointing in some direction (say, true north), then the strong isospin vector is pointing in some other direction (say, magnetic north). The difference between these two directions is the Cabibbo angles. Again, why the heck these two damn things point in different directions .. is utterly unknown. They just do. However, they are, in this sense, "exactly the same thing", the one and the same isospin, but measured in two different coordinate frames: either the coordinate frame of the mass eigenstates, or the coordinate frame of su(2)xu(1) weak gauge symmetry.

To use a formula I just made up on the spot, we have

${\vec {I}}^{strong}=M{\vec {I}}^{weak}$

where M is (related to!?) the Cabibbo matrix, and the quark mass eigenstates are eigenstates of I^strong while the quark weak eigenstates of I^weak. M really is supposed to be an ordinary rotation matrix, and experimental results seem to agree. I'm glossing over something here, and that is the 3 flavor generations, so the above formula is actually kind-of wrong. So its a little more subtle than that, but not much. At the pop-sci level, its more-or-less correct-ish. Does it all make sense now? linas (talk) 04:00, 19 August 2012 (UTC)

No, in the hadron tables by I they mean the ‘original’ isospin (which together with the strangeness indexes the members of representations of the approximate flavour SU(3)): they list the Ω⁻ baryon as having I = 0 (its weak isospin is −3/2). (Also, the CKM matrix only mixes quarks with the same electric charge.) — A. di M.  09:17, 19 August 2012 (UTC)

The answer why the neutral gauge bosons, the quarks, (and the leptons) mix is really simple: Because they can. Naturalness (physics) requires that all terms that are allowed by symmetry and renormalisation are present in the Lagrangian. The mixing terms are allowed therefore they are non-zero. Now, if these mixing terms were zero, then that would require an explanation! Of course, a valid question is why is there a hypercharge symmetry at all. (We know there is because we see 4 gauge bosons).TR 09:40, 19 August 2012 (UTC)

Hi TR, Yes, but I meant: the actual values of the angles are unexplainable in the standard model.They could be anything.linas (talk) 15:00, 19 August 2012 (UTC)

I just struck everything out above, since its somewhat misleading, I fear. Its almost right, but might give you the wrong idea or confuse you. I am not sure I can give a short, intuitive, pop-sci and yet still technically correct explanation at this point. One really is a global SU(6) flavor symmetry, the other is a local su(2) gauge symmetry of pairs of particles picked out from the su(6) rep, twisted off at a wacky, unexplainable angle. They use the same symbol I for both, since its essentially the same thing, but .. Argghhh. One really has to look at what is happening to those doublets in the Lagrangian, and look at how the mixing is happening. It really doesn't help that I only studied this a very very very long time ago, at the dawn of time, and have forgotten important details. linas (talk) 04:28, 19 August 2012 (UTC)

I think it's probably impossible to give a clear explanation without going through the history. There was an original, empirical isospin SU(2) in nuclear physics, which made sense in the quark model as a symmetry between u and d (including left- and right-handed quarks). This got generalized in two different ways: first by adding flavors, to give SU(3) and eventually six flavors; and second by promoting the symmetry to a gauge SU(2) and including leptons, but no longer acting on right-handed quarks. The latter keeps the name "isospin." I think the meaning is somewhat split by field: to a nuclear physicist, the original strong-force isospin is the isospin, and to a particle physicist, the weak-force SU(2) is the real isospin (while the old strong-force version is a historical note). --Amble (talk) 06:26, 19 August 2012 (UTC)

Perhaps. But regardless of what one personally calls isospin, what I want to know is what is the I the PDG refers to in their reviews. Strong I? Or Weak I? Or is it context dependent? Because, as A. di M. pointed out, the "strong" isospin of an Omega baryon is 0, while it's "weak" isospin is not, and the PDG lists I = 0. But in the case of the photon, it's "strong" isospin is 0, but the PDG lists I = 0,1, which seems to be referring to "weak" isopin. Headbomb {talk / contribs / physics / books} 03:32, 20 August 2012 (UTC)

Aha. You want more accounting, and less philosophy! I believe what the PDG means by this is indeed the strong-force isospin. It's there for an eminently practical purpose: finding out which decay modes are allowed. And this notation tells you that the photon can participate in decays either with I=1, I₃=0, -or- with I=0. That's why, if you look at the decay modes for η'(958), you can find both ρ⁰ γ -and- ω γ. The original η'(958) has I=0, as does ω, but ρ⁰ has I=1. So the photon has to be able to enter the bookkeeping in two distinct ways. --Amble (talk) 04:19, 20 August 2012 (UTC)

OK, that makes sense now. (The way I thought about that until now is that electromagnetic interactions don't conserve nuclear isospin in the first place, so it's pointless to assign nuclear isospin to the photon, but now that I think about it, what the PDG do also make sense.) — A. di M.  10:20, 20 August 2012 (UTC)

Ah I see, I'm more focused on baryons right now [currently finishing a thesis on a new baryon nomenclature and a generalization of isospin to all quark pairs, not just u/d isospin], so I forgot about the stupid truly flavourless mesons. Not saying I understand what the PDG is hinting at, but at least I'll know where to focus my efforts to understand what they mean exactly. Headbomb {talk / contribs / physics / books} 14:25, 20 August 2012 (UTC)

Headbomb: Same thing for baryons. Look at the decays of Λ(1520). It has I=0 and can go to Σ π and Σ⁰ γ (where Σ has I=1), -or- decay to Λ γ (where Λ has I=0). It can't decay to Λ π because that would violate isospin conservation. --Amble (talk) 15:47, 20 August 2012 (UTC)

A. di M.: True: you could also say that EM interactions don't really conserve nuclear isospin in the first place. But they only violate it in certain ways. A photon never goes into the bookkeeping I=2, or I₃=±1, but only I₃=0, I=0,1. So this convention is more informative that just saying "does not conserve isospin" because there are decays you could write down that otherwise look OK but are actually impossible. --Amble (talk) 15:40, 20 August 2012 (UTC)

Hmm... I suppose I'll need to take a closer look at Λ(1520) → Σ + π and other such decays. Is that a strong or EM process? Because that seems to have ΔI = 2, which is both ruled out by my understand of the strong interaction, and which you also seem to rule out via EM processes in the above post. Headbomb {talk / contribs / physics / books} 16:49, 20 August 2012 (UTC)

Strong process. Keep in mind that you can't just add up all the values of I. The isospin acts like a spin, you have to add them in the sense of angular momentum coupling. Alse note the notation Λ(1520) → Σ + π really stands for three different final states: Σ⁰ π⁰, Σ⁺ π^-, and Σ^- π⁺. --Amble (talk) 19:33, 20 August 2012 (UTC)

Right, forgot that you need to add isospins like spins. Not quite sure that that implies, but I'll go over it tonight/tomorrow. Headbomb {talk / contribs / physics / books} 01:28, 21 August 2012 (UTC)

You really really really should read up on the representations of the rotation group SO(3). Sadly, WP is not the place to do it, we don't even have a stand-alone article on SU(2). But once you study angular momentum in depth, I think a lot of this will make a lot more sense. (Its the prototype for all the other SU's and opens the doors to many things) linas (talk) 05:53, 21 August 2012 (UTC)

The problem I have with group theory (and Lie algebra and related things in general) is that it's completely unpenetrable at the most basic of levels and I almost can't make any connections between the maths and the physics. I spent years trying to get a foot in the door, and while I can tell you that [for example] SO(3) is "the group of rotations in ordinary space", for me that's a sentence containing zero information, and I can't do anything useful with that. Luckily, you don't have to do things with group theory, you can do something equivalent with bra/ket formalism and big matrices, or alternatively, bra/ket formalism and the Pauli principle, and dodge group theory entirely. At least as far as SU(N) stuff is concerned. Headbomb {talk / contribs / physics / books} 14:30, 21 August 2012 (UTC)

I recently wrote a section about isospin symmetry: Particle physics and representation theory#Example: isospin symmetry. (I was using it as a simple example of how approximate symmetries give rise to groupings of particles.) I was assuming that isospin related only to up and down quarks, but it sounds like the truth is more complicated. Or maybe that I should clarify the way in which "isospin" is used. I hope someone can take a look and correct any inaccuracies... --Steve (talk) 12:42, 22 August 2012 (UTC)

As Amble explained above, this problem is terminological. Certainly, the strong isospin is a well-defined quasi-symmetry on ⓤ–ⓓ quark flavors. The trouble is about the meaning of the word "isospin" in general, because there are other 2-states (qubit) degrees of freedom to which the analogy to the spin-½ is exploited by certain high-energy physicists. Under just the same name, isospin. There is nothing in these analogies but the fact that all qubits are mathematically identical. This consideration is not a recent invention – it was known, for example, to Richard Feynman, well before all these 21-century quantum computings. A recent trend is to write the word isospin without a required precision, though. Incnis Mrsi (talk) 15:09, 22 August 2012 (UTC)

Electric torque?

This is a pointless "article": three sentences about the torque exerted on water molecule dipoles in food due to microwave radiation in a microwave oven. It doesn't even get the terminology right: "electric torque is the force heating water in the microwave oven". It should be just blanked, redirected, perhaps mentioned in the electric dipole moment article. Maschen (talk) 11:36, 21 August 2012 (UTC)

We already have an article on dielectric heating, which covers the same physics. Redirected. --Amble (talk) 15:02, 21 August 2012 (UTC)

Thanks - I missed that article. Maschen (talk) 15:10, 21 August 2012 (UTC)

Stanislaw Ulam

Stanislaw Ulam has been proposed to be renamed, see Talk:Stanislaw Ulam -- 76.65.128.252 (talk) 04:40, 23 August 2012 (UTC)

Article Feedback

BTW, I noticed recently that you could access article feedback from your watchlist. It's a good way to make a link between the readers of an article, and editors, in that readers will often make suggestions for the article. Unfortunately, most of the feedback is useless, but there are a couple of gems here and there. It would be good for the physics project if people checked their watchlist's feedback every couple of days, and resolve issues as they arise. I'm sure it would greatly improve the quality of a couple of our pages. Headbomb {talk / contribs / physics / books} 17:21, 24 August 2012 (UTC)

I saw that too and have been looking through it occasionally. It's a pity they haven't done a full roll out. IRWolfie- (talk) 22:46, 24 August 2012 (UTC)

I don't think it is realistic to expect issues to be resolved as they arise, any more than we can expect all issues on the talk page to be resolved quickly. It might increase the usefulness of the feedback if some editors copy the good ones to the talk page or a todo list. RockMagnetist (talk) 01:43, 25 August 2012 (UTC)

Stephen Hawking at FAC

The article Stephen Hawking (one of our top importance articles) has been nominated as a WP:Feature article. If you have time, please have a look and leave comments at Wikipedia:Featured_article_candidates/Stephen_Hawking/archive3.TR 12:55, 26 August 2012 (UTC)

Discrete spectrum

Today I looked, at last, to the article which I linked several times, and found an abomination. The meaning from spectroscopy is nothing but a trivial dictionary definition (a discrete emission spectrum or so) with a picture. The meaning from quantum mechanics is the same as in decomposition of spectrum (functional analysis) (mentioned in a hatnote). Of course, discrete emission/absorbtion spectra have a theoretical substantiation in the Hamiltonian's discrete spectrum from atomic physics, but these things are not the same. Should this be converted to a disambiguation page, or ? Incnis Mrsi (talk) 06:48, 27 August 2012 (UTC)

• They are the same. Of course there are some issues why in spectroscopy books they are described differently from how they do it in mathematical physics books, and an elementary quantum mechanics textbook does it in a third way, but in my opinion they should stay on one page (it is best to be rewritten though but not split).--Ymblanter (talk) 07:31, 27 August 2012 (UTC)

  They are not only described differently, they are different. The spectroscopists' "discrete spectrum" is an (observable) phenomenon. The quantum discrete spectrum is an abstraction. There is no 1:1 correspondence between them. The emission spectrum of a light-emitting diode is continuous (as an observable phenomenon), although the electron Hamiltonian's spectrum, theoretically, is discrete – the LED has a finite size, isn't it? On the other hand, the (observable) spectrum of an unmodulated radio wave transmitter is discrete, but where is an operator with a discrete spectrum? Incnis Mrsi (talk) 08:46, 27 August 2012 (UTC)

  We always describe physical spectrum with an abstraction. We know that the Hamiltonian of a bound system has discrete spectrum. What spectroscopists observe is just the consequence of this, given that an electron in an atom is a bound system. There could be of course some details related to spectroscopy, which are best relegated to a different article - for instance, in your example with LED the spectrum is continuous, but there is a linewidth which is greater that the distance between the levels, and this is why the spectrum appears discrete (another way to say the same thing is that LED is coupled to the outside world strongly enough to describe it as infinite). The details on the linewidth may be best described in a separate article. But the principle is the same and should be described in the sense that (a) the spectrum of a bound system is discrete; (b) the way to observe this discrete spectrum is to perform spectroscopy measurements (c) there are some issues which may prevent spectroscopic measurements from yielding discrete spectrum.--Ymblanter (talk) 08:53, 27 August 2012 (UTC)

  The proposal "to perform spectroscopy measurements… to observe a discrete spectrum [of a bound system]" is, generally, a heresy. The spin of many subatomic particles (AFAIK of all less stable than the muon) is known due to parity observations, or by various theoretical assumptions, not due to a direct "spectroscopic measurement" even in a general sense, including NMR or other techniques involving spin precession. Discreteness of the spin in general is only a "theoretical fact". "Spectral observations" of any kind, including such ones as Stern–Gerlach experiment, are not sufficient to support this theory. Incnis Mrsi (talk) 11:24, 27 August 2012 (UTC)

  There is no such thing as a "spectrum of the spin". If we are talking about discrete values which the spin projection assumes, well, this is beyond the scope of the current article, but they can be perfectly measured, for instance, by Zeeman effect. Spintronics is a pretty much experimental field, with a Nobel prize.--Ymblanter (talk) 13:35, 27 August 2012 (UTC)

  Sure, I mean any projection of the (3-dimentional) spin operator. It has 1 + 2s eigenvalues, as you certainly know. It is not outside the scope, because the spectrum of such operator is discrete, and the nuclear magnetic resonance (i.e. a so named "spectroscopic measurement" on the particle those Hamiltonian is perturbed by a uniform magnetic field) is its direct consequence. Incnis Mrsi (talk) 13:47, 27 August 2012 (UTC)

  Yes, I know. So what? The fact that this spectrum is discrete, can be (and in fact was 80 or so years ago) verified experimentally.--Ymblanter (talk) 14:06, 27 August 2012 (UTC)

  So that this example is inside the scope, and its discreteness was experimentally verified for some particles. BTW I do not insist that the article has to be split. I insist only that spectroscopists does not observe operators' spectra. There is a relation with observables in some cases of an emission spectrum. Incnis Mrsi (talk) 15:30, 27 August 2012 (UTC)

• Are you really trying to argue that a spectrum observed by spectroscopist is not an observable? TR 15:36, 27 August 2012 (UTC)

  I am not a QFT expert (maybe, I am a quite ignorant person in that domain) and could say nothing about a hypothetical observable those spectrum is observed in a spectroscope. First, I argue that spectral lines observed by spectroscopists correspond to differences between energy levels of a quantum system, not directly to that levels. Second, there exist spectra of various observables, not necessarily the Hamiltonian (quantum mechanics). Incnis Mrsi (talk) 16:00, 27 August 2012 (UTC)

That article is confused, mathematically speaking. Mct mht (talk) 08:29, 27 August 2012 (UTC)

• This should definitely be covered in a single article, since it is one topic. (One being the theoretical explanation of the other). That article needs a lot of work though.TR 09:33, 27 August 2012 (UTC)

  I have done some basic clean up to the article.TR 09:55, 27 August 2012 (UTC)

  One topic, really? Consider, please, an attempt to refute at least some of my arguments. Incnis Mrsi (talk) 11:24, 27 August 2012 (UTC)

Afaik, in theoretical works; the use of discrete spectrum refers to discretisation of the continuum states and not the physically discrete states. A quick check through google scholar seems to confirm that. IRWolfie- (talk) 14:58, 27 August 2012 (UTC)

So what? The discrete spectrum of, say, a finite-dimensional operator is not a discrete spectrum? Which spectrum is it, indeed? Incnis Mrsi (talk) 15:30, 27 August 2012 (UTC)

(in case people don't remember, this continues a conversation from 6 months ago: Wikipedia talk:WikiProject Physics/Archive February 2012#Special:WhatLinksHere/Quantization (physics).) --Steve (talk)

From a mathematician's perspective: The discrete spectrum of an operator in a Banach space is the set of eigenvalues of the operator (i.e., all $\lambda$ such that $A-\lambda$ is not one-to-one). The continuous spectrum of an operator is the set of $\lambda$ for which the image of $A-\lambda$ is not dense in the space. Note that this is very different from the usage in spectroscopic lore (and Wikipedia), namely that "discrete spectrum" = "spectrum that is discrete" and "continuous spectrum" = "spectrum that is continuous". This is a fallacy from the point of view of a mathematician. Every operator has a discrete spectrum (which might be empty, or not topologically discrete) and a continuous spectrum (which might even be discrete). For instance, acting in the Hilbert space of positive frequency functions on the circle, the operator that multiplies $f(\theta )$ by $e^{i\theta }$ has empty discrete spectrum (mathematician's) and its continuous spectrum (mathematician's) is the set {0}.

I believe that the various parties in the above discussion are talking past one another, seemingly on the grammatical issue of whether the spectroscopist's phrase "discrete spectrum" makes sense interpreted as an adjectival phrase. I contend that it does not: "The Hamiltonian has a discrete spectrum" does not mean the same thing as "The Hamiltonian has a discrete-spectrum"; it means that "The spectrum of the Hamiltonian is discrete". So the only way (that I see) for "discrete" and "spectrum" to form an adjectival phrase (as would seem to be logical for an article by this title) is to adopt the mathematician's point of view. Of course, where we actually go from here should depend on the usual things like sources, NPOV, etc. Sławomir Biały (talk) 23:02, 27 August 2012 (UTC)

I guess this is indeed the point (or very close to the point) which Incnis Mrsi, who is a mathematician, is trying to make. But for me, as a condensed matter physicist, there is no problem to say that let us say the Hamiltonian has continuous spectrum which is observed as such in spectroscopy, or has discrete spectrum which is observed as continuous for a number of reason, or is observed as discrete as it should. In our field, any person doubting that the discreteness of the spectrum has been verified experimentally, would be immediately referred to a textbook. On the other hand, I appreciate of course that mathematicians would like to see it not just verified for many systems, but a proof that it has been verified for all possible systems except possibly a set of measure zero. This is smth experimentalists have difficulties to provide. (I am a theorist for the record)--Ymblanter (talk) 01:31, 28 August 2012 (UTC)

I think you might be missing the point here. The issue is not whether the spectrum is phenomenologically discrete or not. "Discrete spectrum", as a adjectival phrase, refers to a particular thing that may or may not be phenomenologically discrete: it could be continuous, empty, etc. "Continuous spectrum", as an adjectival phrase, refers to a particular thing that may or may not be phenomenologically continuous: it can even be a single point as I have illustrated. Each of these are things that are associated to any operator at all. When you say you have "observed as discrete" or "observed as continuous" or concluded that something has "discrete spectrum", you aren't using the phrase in the same way a mathematician would. It's like you're saying that you have observed a "wet lake", but to Poles "Wet Lake" is actually the name of a particular lake in Poland. So, yes, the lake is wet, but is it Wet Lake? Sławomir Biały (talk) 02:16, 28 August 2012 (UTC)

No, I am not using the phrase in the same way as a matematician would, this is exactly my point. And no physicists would ever do. So what? Is this a reason to have two articles, as suggested?--Ymblanter (talk) 05:11, 28 August 2012 (UTC)

Yes, because there is no relationship between the two different meanings of the phrase. Sławomir Biały (talk) 12:14, 28 August 2012 (UTC)

@Sławomir Biały

1. The thing you define as the "discrete spectrum" is more commonly called the "point spectrum".
2. It should, of course, read: "all $\lambda$ such that $A-\lambda$ is not one-to-one)"

TR 13:08, 28 August 2012 (UTC)

I have seen it called both in the literature quite often. For instance, most of the top google books hits use it in this sense. Sławomir Biały (talk) 13:32, 28 August 2012 (UTC)

I have gone ahead and made discrete spectrum a disambiguation page, since the two meanings of the term are unrelated. A similar problem was with continuous spectrum that I redirected to decomposition of spectrum (functional analysis). Sławomir Biały (talk) 22:06, 1 September 2012 (UTC)

Astonishing that Sławomir, who appeared to side with me in this dispute, made things even worse with his dab page. Look at his dab page as of September 1:

“

• Discrete spectrum (physics): Refers to an observable whose spectrum is discrete.
• Point spectrum: The set of eigenvalues of an operator.

”

This contrasts observables’ spectra (which, as demonstrated in this discussion and in discussion the half-year ago, is the same as discrete spectral decomposition) to Decomposition of spectrum (functional analysis). BTW Slawekb’s piped link violates WP:MOSDAB #Individual entries. The only thing is missing are spectroscopical discrete spectra, the thing less relevant to spectral decomposition in functional analysis, but not less important in science and much more important historically. I asked here: which observables correspond spectroscopical spectra to? Nobody answered. Certainly, I strongly prefer the discrete spectrum by Ymblanter to the discrete spectrum by Slawekb. Incnis Mrsi (talk) 08:07, 2 September 2012 (UTC)

The discrete spectrum (physics) article begins "In physics, an observable is said to have a discrete spectrum if it takes only distinct values." The first dab entry just reiterates that. Nothing is set in stone about the wording here. Sławomir Biały (talk) 12:10, 2 September 2012 (UTC)

I probably have delusions, but Sławomir apparently dodged the question about the spectroscopy. Namely the confusion between spectroscopy and quantum observables raised my concern in August, as well as Sbyrnes321’s concern in February. Sławomir tried to solve an insignificant problem separating observables from functional analysis, contrary to objections, but bypassed, if not aggravated, a significant one (read the thread from beginning). Is this a Wikipedian way? Does the responsibility exist or not? Incnis Mrsi (talk) 12:32, 2 September 2012 (UTC)

It's true that I solved a different problem than the one you originally objected to, namely the different use of the term in mathematics versus physics. What of it? Is it my responsibility to fix the issue that you raised initially? That's nobody's responsibility but yours. Sławomir Biały (talk) 12:47, 2 September 2012 (UTC)

New editor contributing to and creating physics-related article

Please, could anyone take a look at Special:Contributions/Al126_at_wiki and maybe help the new editor? Some of their contributions have been deleted, and I'm not sure with the rest. Thanks for any assistance. --Vejvančický (talk | contribs) 12:11, 30 August 2012 (UTC)

Antimatter

More eyes are probably needed at Antimatter (edit | talk | history | protect | delete | links | watch | logs | views). Several edits were made by Eternalmonkey (talk · contribs) (from 28 August onward) that IMO could stand vetting. One of the regulars (SpinningSpark) has been monitoring the situation, but we're at a point where a third or fourth look would be helpful, and I'm not in a position to devote the required time myself.

EM has also made related edits to Interstellar travel (edit | talk | history | protect | delete | links | watch | logs | views) that could probably stand review. These edits seem to have been made in good faith, but at first glance might have accuracy issues. --Christopher Thomas (talk) 02:32, 1 September 2012 (UTC)

quantum state tomography

there was an error in the quantum state tomography entry.

the following statement: "a single measurement can be performed repeatedly to build up a histogram which can then be used to express the pure state in the basis of the measurement"

is not true. using repeated measurements you may only get the square of the absolute value of the amplitude in the basis of the measurement. you dont get the phase.

for instance, given the state |+>, if you conduct this tomography in the standard basis, you will get 50/50 chance to get 0 and 1 . if you measure the state |-> you will get the same result. — Preceding unsigned comment added by 46.120.179.153 (talk) 17:08, 1 September 2012 (UTC)

Although the comment seems not to be deeply considered (a quantum system exhibits an unitary evolution, and if the time interval is not very small, compared to steps of the energy spectrum – cf. quantum Zeno effect – then even "the same" measurement will effectively be not the same), but the article quantum tomography apparently needs an expert attention. Incnis Mrsi (talk) 17:32, 1 September 2012 (UTC)

The first sentence in the article indicates that it is talking about the density matrix, which contains only relative (not absolute) phase information. JRSpriggs (talk) 00:41, 3 September 2012 (UTC)

J0651

J0651 has been requested to be renamed to its catalogue entry in the SDSS, see Talk:J0651 -- 76.65.128.252 (talk) 23:19, 5 September 2012 (UTC)

Infinitesimal quibble: L or ${\mathcal {L}}$ for Lagrangian?

Some articles use L and it's script ${\mathcal {L}}$ for the Lagrangian. It doesn't really matter since the literature does also. However for the Lagrangian density, script is almost always used. As long as there is no confusion within an article it's not a problem, although some readers may get confused reading from one article to another article in keeping track which is which...

For notational consistency and zero conflict between these different quantities, throughout WP we should use always use L for Lagrangian and script ${\mathcal {L}}$ for Lagrangian density, agreed?

Similarly for the Hamiltonian H and it's density ${\mathcal {H}}$?... Maschen (talk) 13:04, 7 September 2012 (UTC)

I doubt that it is feasible to enforce consistency across multiple articles. It's enough of a challenge avoiding confusion within a single article - for example, the symbol L is also used for angular momentum, and no doubt for some other quantities. In Lagrangian, we have the statement: "Notice L is used in the case of one independent variable (t) and $\scriptstyle {\mathcal {L}}\,$ is used in the case of multiple independent variables (usually four: x, y, z, t)." In Momentum, I used script for the Lagrangian and Hamiltonian to distinguish them from directly measurable quantities. Also, they look pretty. RockMagnetist (talk) 16:29, 7 September 2012 (UTC)

When something happens like this in a math article, the advice usually given is: "Don't bother changing that unless you have other substantial changes to make to the article." Rschwieb (talk) 19:39, 7 September 2012 (UTC)

Unfortunately, the script ${\mathcal {L}}$ is also used for the Lie derivative which creates a conflict of notation at Noether's theorem#Field-theoretic derivation. JRSpriggs (talk) 19:41, 7 September 2012 (UTC)

Unless they appear in the same article somewhere (do they?!) it's probably not a soluable problem. Pan-Wikipedia consistency, especially between math and physics, is as impossible as it ever was. And if it were then there would always be some mook switching the notation back. Rschwieb (talk) 20:44, 7 September 2012 (UTC)

Oy, they do conflict there! Better break out alternative L's then! Rschwieb (talk) 20:45, 7 September 2012 (UTC)

I don't see any conflict in Noether's theorem#Field-theoretic derivation. The script is used for the Lie derivative and plain type for the Lagrangian. It would only be a problem if someone insisted on changing the symbol for the Lagrangian - but to paraphrase Rschweib's comment: If it ain't broke, don't fix it. RockMagnetist (talk) 20:53, 7 September 2012 (UTC)

Responses in plenty - clearly the answer is to leave things alone and that I raised a false alarm for nothing (not to mention forgetting the Lie derivative notation). Thanks to all. Maschen (talk) 22:10, 7 September 2012 (UTC)

You're pretty hard on yourself today, Maschen. It's a perfectly reasonable question for this talk page. RockMagnetist (talk) 00:14, 8 September 2012 (UTC)

(It sounds silly, but I'm still just becoming acquainted to using these talk pages properly which I never have done till recently, and I'm not being harsh on myself.) Maschen (talk) 00:39, 8 September 2012 (UTC)

Biographical query at BPH taskforce

I've initiated a discussion over among the tumble-weeds at Wikipedia_talk:WikiProject_Physics/Taskforces/BPH#Awards_for_later_discredited_research. John Vandenberg ^(chat) 14:47, 7 September 2012 (UTC)

Forms of energy is frequently IP attacked

This article is frequently attacked by IP's, as you can see from the edit history (some "edits" are pathetic, look back to last year 2011 as well as recently). Shall we lock it from IP's? Maschen (talk) 00:47, 8 September 2012 (UTC)

It looks like there's only been about one questionable edit per month. Semi-protection (which is what you'd be asking for here) is generally only granted when vandalism edits are much more frequent than that (taxing editors' abilities to revert them manually). --Christopher Thomas (talk) 01:18, 8 September 2012 (UTC)

Ok - just thought to let everyone know anyway. Maschen (talk) 01:20, 8 September 2012 (UTC)

image:Birk.jpg

File:Birk.jpg has been nominated for deletion. It's a schematic of the Birkeland currents. -- 76.65.131.248 (talk) 06:25, 8 September 2012 (UTC)

Per similar threads at WT:AST, the person tagging these (Bulwersator (talk · contribs)) has been on an automated or tool-assisted tagging spree for a few days now. People have challenged them on their talk page about it already, without any response visible. Given that quite a few of these were flagged as NASA-derived, and threads on their page refer to other images that had rationales but were marked as "unsourced", it's looking like it's WP:AN/I time. --Christopher Thomas (talk) 06:50, 8 September 2012 (UTC)

Go ahead then. Xxanthippe (talk) 06:52, 8 September 2012 (UTC).

Someone seems to have beaten me to it. --Christopher Thomas (talk) 19:33, 8 September 2012 (UTC)

The person doing it, Bulwersator, has been indef Topic-Banned from XfD at ANI, but given certain leeway at WP:AN for Commons duplication, his own userpages. (though he is active on Commons deletions as well...) -- 76.65.131.248 (talk) 23:16, 12 September 2012 (UTC)

Vetting needed at heat death of the universe

A recent edit by Chjoaygame (talk · contribs) has drastically altered the content of at least one portion of Heat death of the universe (edit | talk | history | protect | delete | links | watch | logs | views). I have doubts about the new content, but I don't have the expertise to vet it. Would anyone with a better thermodynamics background than mine care to do so? --Christopher Thomas (talk) 23:03, 9 September 2012 (UTC)

There might be a valid point in there somewhere, but the added text was argumentative in tone and extrapolated quite a lot from the source. I have reverted for now. --Amble (talk) 07:23, 10 September 2012 (UTC)

They've been editing quite a bit at Thermodynamics, First law of thermodynamics, and related articles, too. I haven't looked at the content of those edits, but if anyone has time on their hands, it might be worth doing so in case they've been similarly aggressive there. --Christopher Thomas (talk) 13:41, 10 September 2012 (UTC)

Talk:White dwarf#I don't think white dwarfs are true stars

The above linked comment is by a registered editor, and comments from people who specialize in astronomy/physics are needed for this discussion. 217.147.94.149 (talk) 02:24, 11 September 2012 (UTC)

Non-dimensionalization and Scaling of Navier-Stokes Equation

I nominated Non-dimensionalization and Scaling of Navier-Stokes Equation for deletion. But it may be of more general interest, since all kinds of equations can and are non-dimensionalized. See the AfD discussion page. -- Crowsnest (talk) 13:05, 11 September 2012 (UTC)

"Lists of quantities/units/symbols (etc)" articles

See also: Wikipedia talk:WikiProject Measurement § "Lists of quantities/units/symbols (etc)" articles

In short: see here.

In more detail: does anyone have any objections to absorbing "lists of quantities articles" like:

• List of physical quantities,
• SI electromagnetism units,
• List of common physics notations,
• (possibly but not essentially SI derived unit) etc.

into

• defining equation (physics)
• (else other chemical defs into defining equation (physical chemistry))?

By this I mean combining table styles between the definitions article and the other tables into one:

• common names,
• common symbols,
• defining equations,
• SI units (before each table, emphasis on other more useful units, say Gaussian units, can be made),
• SI dimensions,
• comments/notes/descriptions

Also plan to insert the equations from the radiometry table in the definition article to {{SI radiometry units}}, and create similar templates for collections of common physical quantities (as already collected in the definition article) which would be portable if needed (like {{SI radiometry units}}) and cut the byte size of the definition article.

I can understand most people dislike this article, so need to know if it's fine to merge them... If it is, or no responses in the next couple of months - I will not hold back on merging, it's too much redundancy (content forking) across a few articles... Maschen (talk) 14:23, 11 September 2012 (UTC)

Sorry, Maschen, but I have strong objections. It would not occur to me to look for something like SI electromagnetism units in Defining equation (physics); and the traffic stats demonstrate that it isn't occurring to most other people either (views since 201209):

• Defining_equation_(physical_chemistry) 324
• Defining_equation_(physics) 787
• List of physical quantities 2024
• SI electromagnetism units 952
• List_of_common_physics_notations 6793
• SI derived unit 13512

The defining equation pages already seem to be trying to encompass everything, and they are quite forbidding. I think it would be better to narrow their focus, and if they are really lists they should be renamed so that is obvious. RockMagnetist (talk) 16:39, 11 September 2012 (UTC)

So you mean to do it the other way: split out content from the definition pages? I don't mind if so. Maschen (talk) 16:57, 11 September 2012 (UTC)

Something like that. It would require some thought about the purpose of the page, though. RockMagnetist (talk) 17:05, 11 September 2012 (UTC)

Too easy - the definition pages can be deleted once emptied into already list of physical quantities, SI electromagnetism units Radiometry/photometry tables, etc (see below for more). Maschen (talk) 17:49, 11 September 2012 (UTC)

There is a lot to think about here! It would help if you gave your "related point" its own section. As for defining equation (physics), I would like to know how notable it is. The only direct reference for the definition is to the Physics Encyclopedia, which I don't have access to. If the sources exist, an article on the defining equation might discuss the kinds of defining equation, for example constitutive equations and definitions of SI derived units (in summary form). Otherwise, a merge proposal would be appropriate before splitting the article up. RockMagnetist (talk) 17:05, 13 September 2012 (UTC)

There are many sources in that article (most I added), and all the equations can be found in those books. I didn't inline cite them at the time since that would clutter the names in the tables, but there are some articles (like Laplace transform) which have columns of refs...

The concept of collecting all definitions together, with their common symbols, units, dimensions etc. is notable since physics encyclopaedias (including those cited) do have tables like this, though as things stand this all severely needs rewriting to make it less forbidding.

All I'm basically saying is to leak the definition articles and other long equations-list articles into the focused equations-list articles which already exist, and if need be create new ones/merge content-forked ones along the way.

(As you request the other comments have been moved down below, new section). Maschen (talk) 19:43, 13 September 2012 (UTC)

My reason for mentioning sources is that they might help to determine what should be done with the article after much of the info is moved to other articles (I suggested one idea above). RockMagnetist (talk) 18:21, 14 September 2012 (UTC)

Sorry, which idea? Maschen (talk) 18:47, 14 September 2012 (UTC)

"If the sources exist, an article on the defining equation might discuss the kinds of defining equation, for example constitutive equations and definitions of SI derived units (in summary form)." RockMagnetist (talk) 19:00, 14 September 2012 (UTC)

Related articles...

When spilling content out from any equation list pages in general, these would be the most logical branches of physics (abbreviations for convenience of discussion): Classical mechanics (CM), Analytical mechanics (AM) Special/general relativity (SR/GR), Quantum mechanics (QM) Electromagnetism (EM), Continuum /fluid mechanics (ConM/FM), Wave mechanics (WM), Thermodynamics (TD), Photonics (i.e. radiometry, photometry, geometric/physical optics... Ph) Properties of matter can spill into constitutive equation?

On a related point - the List of elementary physics formulae and whatever else (although not including constitutive equation - a notable topic in its own right) can be similarly split out to articles of fundamental scope:

• List of equations in classical mechanics,
• Table of thermodynamic equations (which should be merged with Thermodynamic equations, no clue why both exist...),
• List of electromagnetism equations (not along the mathematical lines of Classical electromagnetism and special relativity, Covariant formulation of classical EM, Maths of EM field, Maxwell's equations in curved spacetime etc. but the list of relations... from List of elementary physics formulae etc.)
• List of relativistic equations (include general relativity?)

all in the same format as Analytical mechanics - IMO the best format of an equation-listing article, and should set the example...

Does the reversed plan sound better? Maschen (talk) 17:49, 11 September 2012 (UTC)

Edit war at Pendulum

I don't know if this is the right place to mention it, but there is a conflict developing at Pendulum over which large-angle period equation to use. Anyone who wants to stop by and express an opinion would be welcome - it would help build consensus. It's rated a vital article. --Chetvorno^TALK 21:39, 13 September 2012 (UTC)

Please do fix it — but ignore the "vital articles" silliness. It's just a forum to argue about why what's important to me is more important than what's important to you. Should have been scrapped years ago. --Trovatore (talk) 21:49, 13 September 2012 (UTC)

Category:Modern Physics

Category:Modern Physics, which is within the scope of this WikiProject, has been nominated for deletion. If you would like to participate in the discussion, you are invited to add your comments at the category's entry on the Categories for discussion page. Thank you. --BrownHairedGirl (talk) • (contribs) 20:27, 14 September 2012 (UTC)