The h Bar

@Amit There is nothing particularly interesting or difficult about this. Just apply conservation of energy and momentum, akin to how you work out the rocket equation. You have to take a LOT of battery energy-mass with you.

I wasn't talking about accelerating using the light right?

Fifty Years of Quantum Chromodynamics - ICTP Colloquium

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This looks good too

10:10 PM

It isn't difficult in hindsight. But I guess one finds it weird, that at least I don't know of any direct way to derive special relativity from QM

Intuitively it seems to me SR needs to boil down to some innate property of photons?

Instead we usually derive SR just from symmetry arguments, Idk if there's another way

Doesn't make sense to derive SR from QM to me, QM is a theory, in this theory you choose your symmetry group, if it's the Galilean symmetry group you have NRQM/NRQFT, if it's the Poincare group you get RQM/RQFT, if it's the diffeomorphim group you get madness

lol

But arguments from symmetry are so unphysical aren't they? :)

Keep thinking about it and it will eventually click as unavoidable

Q: What crystal structures are predicted for the crystalline phase of matter inside crystalizing white dwarfs? Does it depend on the carbon/oxygen ratio?

I mean, just maybe it covers up something deeper that we never tried to pin down, just because the symmetries work so nicely

Oh, it is unavoidable that may be exactly part of the reason we don't dig deeper

uhoh

2

The abstract of Venner et al. (2023) A Crystallizing White Dwarf in a Sirius-Like Quadruple System includes the following: The location of HD 190412 C on the 𝑇eff − mass diagram implies it is undergoing crystallization, making this the first confirmed crystallizing white dwarf whose total age c...

10:15 PM

@Amit still not difficult

It really reduces to the classical situation, a wave function $\psi$ takes the form $\psi \approx e^{iS/\hbar}$ in the quasi-classical limit, and we fix S by the usual classical arguments (which immediately reduces to asking what is the symmetry group of $S$ distinguishing one between non-relativistic and relativistic physics), a time derivative of $\psi$ gives you the Hamiltonian (being careful about what your time variable is),

a spatial derivative the momentum operator etc... from this you've fixed everything

@Amit It is not covering up anything. bolbteppa correct told you that these are independent topics and thus there is no way to get one from the other

I guess that I am asking whether any attempt was made to find a mechanism for the observed effects that we derived from SR. Currently, subject to correction, it seems to me that the explanation is one by symmetry, which is very beautiful and elegant, but there is no real mechanism involved

@Amit How would one go about finding any mechanism for "Nature is deliberately hiding this information from everybody"?

@naturallyInconsistent Hiding what information?? :) Sry, I don't follow

10:20 PM

Because it is better stated as "Nature Herself does not allow for this information to be kept track thereof"

@Amit in the case of SR, it is "absolute position and rapidity"

The fundamental difference between SR vs Newtonian mechanics amounts to asking whether interactions are instantaneous or whether it takes a finite amount of time for them to transmit, all SR is saying is that it takes a finite amount of time for them to transmit. The implications of this lead to all the weirdness. Every weirdness aspect traces back to this simple point ultimately, it's not magical

@bolbteppa I specificially avoided stating it as velocity because if you do, then you have to insert the special effect of trying to make the velocity limit invariant.

Right, I'm assuming the other part of SR that the physics is the same in all reference frames which implies the velocity limit is the same in all frames

That is actually the harder part. I think people are perfectly fine with "effects take time to propagate". They have difficulty with "velocity limit is the same in all frames"

Writing it as rapidity, however, and you get back infinity as the limit, and so yay

or maybe sinh of that would do too

I can't even imagine how to picture things if they weren't the same in all frames, would things even be invertible I'm not sure

10:27 PM

I have trouble with "velocity limit must be the same in all frames because otherwise we get inconsistencies" -- you see I accept the first part of that sentence wholeheartedly. But the reason -- that otherwise we get inconsistency, seems a bit weak to me.. I realize in practice whether there's a deeper reason or not, may mean nothing for the practical calculations we make, but then again maybe it will

The statement is that the laws of physics are the same in all inertial reference frames, you intuitively know dropping a ball is the same in all inertial frames, why would the speed of light or any other interaction be any different, this is just one of the laws of physics

@Amit Called it. The solution to that is to ask you to go and find an inconsistent theory with velocity limit changing when transformed. Go, and bother us no more.

I don't want the velocity limit to change

I want to know why it doesn't change, lol

Technically you barely even know what an inertial frame is intuitively

@Amit And then this is the part that I was also answering: "Nature Herself does not allow for this information to be known."

10:31 PM

Okay okay, I don't want to bother

If I am in frame A and the speed of light is one speed, and it is moving with constant velocity, then the frame reaches position B, why would it change

This is why it takes years just to learn the basics of physics, even simple things take ages to really get

I would have put it as this:
1) We agree that Maxwell's equations say that speed of light is so and so in our inertial reference frame.
2) All laws of physics are the same in all inertial reference frames.
Therefore, speed of light is the same in all inertial reference frames

And maxwell's equations are derivable from QM! :D

@Amit They are manifestly not.

Soooo what was that paper Freeman Dyson published where he reiterated such a derivation that Feynman once showed him?

10:36 PM

I don't know what light is or what Maxwell's equations are, I want to introduce/'derive' Maxwell's equations as the first non-trivial application of SR via introducing a potential into the SR action, I'd frame 1 in terms of 'velocity of propagation of interactions' rather than light or mentioning Maxwell (though we're all thinking of it)

@Amit This is just another source of confusion and a way to pretend everything is equivalent to everything, what he's doing is basically saying if $F$ takes the form of the Lorentz force, then we get Maxwell's equations

If $F$ takes the form of the Lorentz force, you can immediately get the SR+EM action and then get Maxwell's equations

Why is $F$ taking that form? It reduces back to symmetry groups...

@Amit Was he starting from QFT that already had Maxwell's equations assumed in it, and trying to derive classical electrodynamics?

This paper has the derivation included

No, definitely not from QFT from what I see

@bolbteppa Even better

@naturallyInconsistent I consider "math for physicists" stuff the greatest sin of human kind

Why delete? Anyway this is the original paper where it was published

Some of those books have things no mathematician will ever know

10:49 PM

Content-wise, yes

Especially those Russian Math books

Methoden der mathematischen Physik

Methoden der mathematischen Physik (Methods of Mathematical Physics) is a 1924 book, in two volumes totalling around 1000 pages, published under the names of Richard Courant and David Hilbert. It was a comprehensive treatment of the "methods of mathematical physics" of the time. The second volume is devoted to the theory of partial differential equations. It contains presages of the finite element method, on which Courant would work subsequently, and which would eventually become basic to numerical analysis. The material of the book was worked up from the content of Hilbert's lectures. While Courant...

Is simply insane, even the ways of thinking about simple things in there are incredible

@bolbteppa In that case we have two outstanding mathematicians writing it :P

I was referring to the fact that often the "math for physicists" books tend be sloppy or not really compelling

Yeah I can think of a few

Q: Can you identify this space travel related equation?

And rely on intuition rather than serious proofs

uhoh

4

Does anyone recognize the equation carved on this object? The only hint I have is that the back side has the word "orbit" carved into it. It may be incomplete or incorrectly copied. My best interpretation in MathJax: $U_eR_o\sqrt{\frac{2g}{(R_ôh)}}$ My grandmother carved the object. She had a ...

orbital-elements

old question in Space Exploration SE, just bountied

10:52 PM

NPC (meme)

NPC (; each letter separately; also known as the NPC Wojak), derived from non-player character, is an internet meme that represents people who do not think for themselves or do not make their own decisions; those who lack intrapersonal communication. The NPC meme, which graphically is based on the Wojak meme, was created in July 2016 by an anonymous author and first published on the imageboard 4chan, where the idea and inspiration behind the meme were introduced.The NPC meme gained widespread attention and in October 2018 was covered in numerous news outlets, including The New York Times, The Verge...

books

uhoh

@Mr.Feynman the best books do that :p

Might be true, but as my intuition lacks I prefer to compensate with (sometimes unnecessary) rigor where I can

That's exactly why you need to avoid the rigor and keep working on the intuition, rigor wont help when things get messy especially in physics it's nothing but a burden

Oh, I'm talking about Math right now

In Physics you can't do what I said above. What would rigor even mean?

10:56 PM

Fair enough, in math it depends on the situation yeah