User talk:Sbyrnes321/Archives/2019

Mathematical equivalence in the moving magnet and conductor problem

Your addition showing the mathematical equivalence in the moving magnet and conductor problem appears to be incorrect so I removed it. Please double check, thank you — Preceding unsigned comment added by Legit War Articles (talk • contribs) 12:31, 24 February 2019 (UTC)

The last time I touched that article was here. I don't know if it's changed. I do think the article would be improved by deleting 80% of it. I thought that when I first read it in 2008, and I still think that now. Perhaps the article would be improved even more by deleting the last 20% as well. I don't think there's anything in this article that isn't explained better in other electromagnetism articles.

But whatever.

I am interested in your specific complaint. You suggested that in the magnet's rest frame, there is a constant magnetic field along z, and the conductor is moving along x. So electrons in the conductor get a Lorentz force along y. In the conductor's rest frame, there is an electric field along y, from E'=v×B. Seems consistent. So what's the problem?

Hmmm. Maybe you're hung up on

$\mathbf {\nabla \times E} '=-{\frac {\partial \mathbf {B} '}{\partial t}}.$

Maybe you think that, since the right-hand-side is zero, that means E' has to be zero too. But it doesn't mean that at all. Lots of fields have curl of zero! Not just the zero field. Constant-in-space fields are one example. The gradient of anything whatsoever is another example.

You need the correct derivative and the correct boundary condition. And that leads to E'=v×B, not E'=0.

Sorry if I'm misunderstanding you. --Steve (talk) 03:07, 25 February 2019 (UTC)

No, sorry, that wasn't my concern. My concern is whether this formula is correct:

${\frac {\partial \mathbf {B} '}{\partial t}}=(\mathbf {v} \cdot \nabla )\mathbf {B} =\nabla \times (\mathbf {B} \times \mathbf {v} )+\mathbf {v} (\nabla \cdot \mathbf {B} )$

I think both sides are zero. Why, what do you think? --Steve (talk) 16:20, 26 February 2019 (UTC)

I’m not sure about the numerical values, it’s meant to be analytical anyway, and there is supposed to be an induced EMF.

I believe the derivation is incorrect also. — Preceding unsigned comment added by Legit War Articles (talk • contribs) 11:28, 28 February 2019 (UTC)

What do you mean when you write "it's meant to be analytical anyway"?

When you say "there is an induced EMF", yes this is true, we all agree about this. Why do you bring it up? Is there a problem?

If you think "the derivation is incorrect", can you explain why, or better yet can you give a specific example where the two sides are not equal? --Steve (talk) 18:20, 28 February 2019 (UTC)

Analytical or algebraic, not depending on specific numerical results.

If there’s an induced EMF then dB’/dt can’t be zero.

Earlier you mentioned x, y and z axes, though I assume the formula is general and non-specific to any particular axis.

I tried working it out and it doesn’t seem to add up. How about you show the full, intermediate derivation? — Preceding unsigned comment added by Legit War Articles (talk • contribs) 01:20, 1 March 2019 (UTC)

Now I'm very curious: can you tell me an example of a physics formula that IS "meant to be analytical", and an example of a physics formula that IS NOT meant to be analytical?

You wrote "If there’s an induced EMF then dB’/dt can’t be zero." Why not? --Steve (talk) 01:45, 1 March 2019 (UTC)

All formulae are by definition analytical. What I meant was we didn’t have to speak in numerical terms.

Ok, maybe not, but there must be some changing magnetic flux somewhere to induce an EMF.

Anyway, what’s the intermediate derivation? I believe it is incorrect but I’m not qualified enough to prove it one way or the other.

Sure you can have an EMF without a changing magnetic flux. See Homopolar generator for example. --Steve (talk) 14:37, 1 March 2019 (UTC)

But this is the primed frame we’re referring to, the rest frame of the conductor. Also, the derivation? — Preceding unsigned comment added by Legit War Articles (talk • contribs) 02:36, 2 March 2019 (UTC)

Right, in the rest frame of the conductor, there's an electric field pushing the charges around. The B field isn't doing anything. (I wouldn't call it an "EMF", but the E field certainly would create a current in the conductor). I'm a bit busy to start talking you through the derivation. (Maybe ask again in a couple months.) If you think the formula is wrong, maybe you can come up with an example where the two sides actually evaluate to different numbers? Or by all means, just delete it if you don't like it. Or even nominate the whole article for deletion. --Steve (talk) 23:36, 2 March 2019 (UTC)

Hey Steve, the derivation is correct. However, it only proves that E' and vxB share the same curl, not that E' = vxB. — Preceding unsigned comment added by Legit War Articles (talk • contribs) 04:57, 14 March 2019 (UTC)

FYI File:FrequencyAnimation.gif nominated for deletion

greetings

A file you originated. File:FrequencyAnimation.gif has been nominated for deletion.

There is a claim that it caused someone to commit suicide.

Seems bogus to me. Constant314 (talk) 10:13, 2 March 2019 (UTC)

Suggestion for contribution to Density Matrix page

It looks like you're the most prolific contributor to the Density Matrix page, so I wanted to offer a few recent works related to that, but I'm not sure where best they might go. Perhaps just extra citations in the related works, or maybe some new section. I'm none of the authors below with no connection to them, in fact I'm not even a physicist (computer science, FWIW), which is why I'm not even attempting to make edits. I found their work after an office debate around the new Hulu show Devs. I'm mainly interested in QM interpretations that show progress getting away from Copenhagen and many-worlds. I think the papers from Barandes and Kagan would work as a contribution to the section on Systems and Subsystems, but that's just a guess. According to Weinberg's paper, he became aware of Barandes and Kagan's parallel work after they both published within the same year. Without further ado: - Quantum Mechanics Without State Vectors - A Synopsis of the Minimal Modal Interpretation of Quantum Theory - The Minimal Modal Interpretation of Quantum Theory - Measurement and Quantum Dynamics in the Minimal Modal Interpretation of Quantum Theory 108.44.250.167 (talk) 12:58, 29 March 2020 (UTC)Greg

Sorry but I have more-or-less quit editing physics wikipedia pages. Too busy with other projects. Good luck! --Steve (talk) 13:01, 29 March 2020 (UTC)