Anonymous at Tue, 9 Jul 2024 22:13:40 UTC No. 16275115

>>16275092
>how is this not LITERALLY proof
uh, it's an illustration?

Anonymous at Tue, 9 Jul 2024 22:53:44 UTC No. 16275197

i see three arrows and a squiggly line

Anonymous at Tue, 9 Jul 2024 23:21:47 UTC No. 16275240

>>16275092
>superluminal
it's not very likely to happen

Stop guessing start learning at Tue, 9 Jul 2024 23:23:58 UTC No. 16275242

>>16275092
What in the name of dunning Kruger is this shit?

Anonymous at Tue, 9 Jul 2024 23:27:54 UTC No. 16275250

>>16275092
>What is a virtual particle?

Anonymous at Tue, 9 Jul 2024 23:28:07 UTC No. 16275251

>>16275197
The arrows are a moving electron, and the squiggles are a photon.
The electron emits a photon, outruns it, and then recaptures it. How is that not superluminal??

Anonymous at Tue, 9 Jul 2024 23:29:23 UTC No. 16275254

>>16275250
That's a good question. What IS a virtual particle, in your own words?

Anonymous at Tue, 9 Jul 2024 23:34:59 UTC No. 16275263

>>16275251
Because that’s a drawing and didn’t happen

Anonymous at Tue, 9 Jul 2024 23:37:40 UTC No. 16275266

>>16275263
>Drawings of reality that reflect actual events didn't happen

Anonymous at Tue, 9 Jul 2024 23:42:11 UTC No. 16275273

>>16275254
Temporary field excitations

Anonymous at Tue, 9 Jul 2024 23:45:34 UTC No. 16275277

>>16275254
>That's a good question. What IS a virtual particle, in your own words?
Component quantum waves that have not (yet) superposed to form a particle packet.
Remember, packets are restricted to group velocity, hence the light-speed limit. The component waves, however, can and often do exhibit hyper-light phase velocities. They can travel at any speed up to and including infinity.

Stop guessing start learning at Tue, 9 Jul 2024 23:51:25 UTC No. 16275286

>>16275277
Shut the fuck up faggot you have no idea what the hell your even saying you just looked up some bullshit on gpt and start spewing useless jargon

Anonymous at Tue, 9 Jul 2024 23:52:20 UTC No. 16275289

>>16275266
When did it happen then? And prove that it happened

Anonymous at Wed, 10 Jul 2024 00:26:04 UTC No. 16275345

>>16275277
Okay, so they are part of the electron, and they DO in fact travel faster than light. But somehow that doesn't count as superluminal?

Anonymous at Wed, 10 Jul 2024 00:27:08 UTC No. 16275346

no its the photon that is so fast it catches up with the electron and gets absorbed

Anonymous at Wed, 10 Jul 2024 01:11:16 UTC No. 16275399

>>16275092
because einstein said its not.

Anonymous at Wed, 10 Jul 2024 04:50:47 UTC No. 16275586

>>16275092
Feynman diagrams are just mathematical tools that appear in the perturbative formulation of quantum field theories. This formulation is already an approximation of what "real" QFT is supposed to be but since even the most basic QFTs are terribly ill defined mathematically sometimes it almost seems that this perturbative formulation is really the only thing you can do with the theory (there are non-perturbative techniques and other shit but this is not what you are going to see in a typical basic course and have a lot of issues). When you first define them, you are using them to calculate n point correlation functions which are supposed to contain information about quantum fields evolve and interact. Even at this point everything is ill defined and all terms diverge.
Now the reason why they are connected to some physical processes comes from considering scattering processes which are at the end what QFT is all about. In this context you assume a priori that you start at some time with free particles that don't interact, then assume some interaction occurs, but after that you still end with a free particle not interacting. That is, from the get go you ar fixing what should come "in" and "out" and surprisingly this also translate to type of diagrams you should consider, that is, it should start with your in particles and end with your out particles. But that's it, the internal diagrams can be whatever too.
Again without renormalization (and I would argue even with that you still have plenty of issues) basically all but the simplest Feynman diagrams represent meaningless expressions.

Anonymous at Wed, 10 Jul 2024 04:58:46 UTC No. 16275591

>>16275586
> tl;dr, at this scale shit’s so complicated we are approximating the approximations and using hacky math that just works and gives the right experimental predictions
> einstein was right, we do need to come up with a better philosophical interpretation of this hot mess than the “stfu and do math” we have been teaching phys students for nearly a century

Anonymous at Wed, 10 Jul 2024 05:26:46 UTC No. 16275604

They actually proved that particles can technically go a little faster than light by performing the double-slit experiment with two time-slits instead of two spatial slits.

Anonymous at Wed, 10 Jul 2024 06:16:46 UTC No. 16275638

>>16275591
The problem is with QFT not quantum mechanics as a whole though. Einstein was against quantum theory because of certain predictions that are perfectly rigorous, experimentally verified but "weird". In QFT you never quite sure what the fuck you are calculating and you just develop things by analogy. I cannot really call myself an expert, but I've really tried giving it a chance and I cannot understand why the hell do physicists say they find the theory beautiful or why are they so impressed by it. For me when a physicist talks about a real prediction of the standard model, it is basically post hoc rationalization with really no tangible prediction whatsoever.

Anonymous at Wed, 10 Jul 2024 07:13:31 UTC No. 16275681

https://youtu.be/bHIhgxav9LY

Anonymous at Wed, 10 Jul 2024 08:31:07 UTC No. 16275730

>>16275092
This is just a diagram. The photon is probably actually moving in a straight line and not a curve because curves like that are just conveniences in diagrams so that drawings aren't all superimposed on one another.

Also, so long as the electron is not more than 1 wavelength away from the photon, an interaction is still pretty likely. They don't have to be in the exact same place. The uncertainty principle basically means there is not even such a thing as the "exact" same place.

Anonymous at Wed, 10 Jul 2024 10:41:48 UTC No. 16275815

>>16275730
Yes it is a diagram, no it doesn't say anything about how the photon is moving it is just a computational tool.

Anonymous at Wed, 10 Jul 2024 18:14:29 UTC No. 16276273

>>16275092
Funny, when Feynman tried describing his stuff at the Ponoco Conference, pretty much all the physicists there hated it or didn't understand him. One of his comments was something like, "everyone physicist seems to have their favorite rule, and he was breaking all of them".

Idk what specific stuff he was talking about, but your question might've been one of the stuff they were concerned about, like momentum conservation or speed of light stuff.

Think Dyson was like the only other person who saw value in it, and showed it equivalent to what Schwinger was doing at the conference. (Feynman also has a similar feeling too after talking with Schwinger)

Anonymous at Wed, 10 Jul 2024 18:28:35 UTC No. 16276297

>>16275730
>so long as the electron is not more than 1 wavelength away from the photon,
So you can actually derive a timescale for this kind of thing?
>an interaction is still pretty likely
Aren't the probabilities of every interaction known? Afaik, these aren't just "muh abstrakshuns" but literally a sum of probabilities for each interaction happening

Anonymous at Wed, 10 Jul 2024 18:36:37 UTC No. 16276305

>>16275250
Virtual particles are superluminal. The antiparticles are reaching us from the future due to our descendants utilizing antimatter fusion drives for FTL travel

Anonymous at Wed, 10 Jul 2024 19:04:49 UTC No. 16276323

>>16275266
>Drawings of reality that reflect actual events didn't happen
These reflect virtual particles, which are infamous for not obeying any law of physics. They exist as intermediate states in transmutations, or at least thats how i see them, and cannot be seen alone.
Maybe virtual photons dont move at the speed of light? They are not actual photons, likely nothing real at all. The idea of a virtual particle is a narrative device cooked by Feignman, at heart these are just integrals in the Dyson series.

Anonymous at Wed, 10 Jul 2024 19:06:49 UTC No. 16276325

>>16275254
>What IS a virtual particle, in your own words?
A narrative device by Feignman, who knew people want physics to take the form of a story where particles are cute characters doing things. Each of these "particles" is nothing more than some integral in the dyson series. You could just do the integrals and get an amplitude without giving each one some cute name.

Anonymous at Thu, 11 Jul 2024 00:59:24 UTC No. 16276769

>>16276297
>So you can actually derive a timescale for this kind of thing?
No, even if you where to interpret the diagram asa physical thing, you actually have to send time to infinity to derive the formulas lol.
>Aren't the probabilities of every interaction known? Afaik, these aren't just "muh abstrakshuns" but literally a sum of probabilities for each interaction happening
I mean each diagram contributes something something and you just have to add them up, but they are literally just abstractions.

Anonymous at Thu, 11 Jul 2024 04:39:10 UTC No. 16276899

>>16275286
Care to enlighten us then or would you just rather throw shit around?

Anonymous at Thu, 11 Jul 2024 14:35:38 UTC No. 16277333

>>16275092
The virtual photons in the electron self energy are just a perturbative way to depict the Coulomb field around an electron. It is nothing deeper than the fact that a charged particle carries an electromagnetic field just as in classical EM.

Similarly virtual electrons in a photon propagator are representing how light interacts with an electron field. This is not exactly like classical EM, because there is no classical electron field, but physically it is very similar to light traveling in a dielectric material. Don't make too much of virtual particles.

Anonymous at Thu, 11 Jul 2024 14:40:32 UTC No. 16277339

>>16277333
>The virtual photons in the electron self energy are just a perturbative way to depict the Coulomb field around an electron
What other way is there to do it, then? And why don't physicists popularize that instead if they know so much

Anonymous at Thu, 11 Jul 2024 15:01:40 UTC No. 16277361

>>16277339
>And why don't physicists popularize that instead if they know so much
I am popularizing it right now on this board. If you search around I'm sure you can find pop sci descriptions of what I am saying since it is correct after all.

FWIW, I'm not saying virtual particle calculations are wrong, I am just saying that the virtual photons are representing the same physical effect as the electromagnetic field carried around by a charge in classical physics. In fact if you consider only diagrams without loops you get the same results for scattering as in classical physics.

Anonymous at Thu, 11 Jul 2024 15:08:12 UTC No. 16277369

>>16277339
>What other way is there to do it, then?
Also there are other ways to it, although they are usually less convenient. For instance if you consider only one spatial dimension, you can completely get rid of the virtual photons (physicists say you "integrate them out") and you are left with an explicit Coulomb interaction between the electrons. (This is easier in 1d because there are no physical photons then)

Anonymous at Thu, 11 Jul 2024 15:15:32 UTC No. 16277381

>>16276323
>virtual particles
jewish-phys shill alert

Anonymous at Thu, 11 Jul 2024 15:35:17 UTC No. 16277415

>>16277361
>>16277369
>I am popularizing it right now on this board
I mean in textbooks and lectures. I've never seen any physics textbook or paper do qed non-perturbatively (i.e. get all the usual perturbation theory results without using perturbation theory)

Anonymous at Thu, 11 Jul 2024 15:46:17 UTC No. 16277430

>>16277369
All coulomb interactions are 1D fyi. At least that's the observed law.
>qed non-perturbatively
No shit. It can't be done. ED can but not QED.

Anonymous at Thu, 11 Jul 2024 15:51:59 UTC No. 16277436

>>16277415
You don't see many non-perturbative results because the theory is not exactly solvable. If you want to see something non-perturbative and exactly sovable, look up the Schwinger model. It is just QED in 1+1d with massless fermions. You can also find lattice results for QED in any dimension. If I recall there is an interesting phase transition to a confining theory if the fine structure constant gets too large.

Of course there are easy non-perturbative things in 3+1d QED that still hold like Gauss's law.

Anonymous at Thu, 11 Jul 2024 15:53:17 UTC No. 16277438

>>16277430
>All coulomb interactions are 1D fyi. At least that's the observed law.
I mean one spatial dimension not three. You didn't understand my post

Anonymous at Thu, 11 Jul 2024 16:44:33 UTC No. 16277488

>>16277438
You didn't communicate very clearly. blame yourself not me dipshit

Anonymous at Thu, 11 Jul 2024 17:45:05 UTC No. 16277568

I dont really understand how static magnetic or electric fields can be represented by virtual photons. I guess it makes sense in a narrative sense that if forces are carried by virtual photons, theres not really "external" fields but only real particles and the force carriers, so at a quantum level theres no such thing as electromagnetic fields.
I dont like this narrative as it seems superfluous, its just something Feynman made up, the physics itself is just the S matrix, why would one need to cook these concepts to do a calculation?

Anonymous at Thu, 11 Jul 2024 19:56:38 UTC No. 16277778

>>16277568
>I dont really understand how static magnetic or electric fields can be represented by virtual photons.
Calculate the scattering amplitude for one charge to scatter off of another. At lowest order in QED (i.e. the "Born approximation") this involves one virtual photon propagator. The Born approximation in non-relativistic QM involves the Fourier transform of the interaction potential. If you do the calculation (it's in Peskin in Schroder for instance) and you'll see that virtual photon propagator is giving you the standard Coulomb potential. If you don't average over the spins of the charged fermions you can see magnetic effects too.

Anonymous at Thu, 11 Jul 2024 20:03:22 UTC No. 16277783

>>16277568
>so at a quantum level theres no such thing as electromagnetic fields.
A field is just a collection of smaller parts, like photons

Anonymous at Fri, 12 Jul 2024 14:36:07 UTC No. 16278811

>>16277783
Smaller parts of what?

Anonymous at Fri, 12 Jul 2024 15:25:19 UTC No. 16278871

>>16275286
His assertions have been experimentally verified.
https://www.scribd.com/document/208319/NEC-Time-Travel-Experiment-in-2000
>Inb4 quackery
The truly odd thing about this experiment is that a massive plasmonics excitation is traveling an order of magnitude faster than actual photons would over the same distance of vacuum. Regardless of the semantics, if your probe beam has the same 'information' as the exit pulse after passing through the medium as a plasmonic excitation, which happens to be moving FTL, did you violate Bell's Theorem? This is an actual question.

Anonymous at Fri, 12 Jul 2024 16:00:31 UTC No. 16278909

>>16277778
Why the fourier transform of the propagator the coulomb potential? I think i have seen that calculation. Is it something to do with momentum-representation vs space-representation?
The usual simpler calculation of scattering has electrons with some fixed momentum, which means they are very delocalized in space, it can be hard to associate that with a force depending on position (potential inversely proportional to the distance) when theres no clearly defined distance
On the same topic, the typical calculation of anomalous magnetic moment, the one that is lauded as being accurate to many digits, made first by Schwinger, has an electron being deflected by a virtual photon, representing an external field.
How did Schwinger made that before there were Feynman diagrams? And how is this magnetic moment actually measured in real life?
Part of me thinks it could be measured by spectroscopy, like the electron would have some energy levels associated with the magnetic field (u*B), typical magnetic dipole energy, and there would be two values for particles with spin up and spin down, so you'd see two close spectral lines and they would widen with a bigger magnetic field... but i dont know if thats how it gets measured. Somewhere i heard its done with particle accelerators.

Anonymous at Fri, 12 Jul 2024 17:01:20 UTC No. 16278978

>>16278909
>Part of me thinks it could be measured by spectroscopy
Yes I think this might be right. If you consider Feynman diagrams which involve a ladder of an arbitrary number of photon propagators between two charges, this will have poles where the bound states of the two charges are, and you can see how the energy levels are affected by the spins of the charges. If you have not just a ladder of photon propagators but also loop corrections to the vertex where the photon propagator attaches to the charged particle lines, then that would give the anomalous magnetic moment correction to the energy levels. This is not my specialty though so I don't know what they do in practice.

>How did Schwinger made that before there were Feynman diagrams?
There was still perturbation theory and the Born approximation so I think it is not such a leap. If you want to see how QED was understood in the era of Schwinger, maybe try reading Landau and Lifschitz's book on QED, it is sort of old-fashioned but it is clear that there was a lot of physical insight back then that has not survived in modern textbooks.

Anonymous at Fri, 12 Jul 2024 17:58:04 UTC No. 16279045

>>16278909
>The usual simpler calculation of scattering has electrons with some fixed momentum, which means they are very delocalized in space, it can be hard to associate that with a force depending on position (potential inversely proportional to the distance) when theres no clearly defined distance
There is no clearly defined distance but as usual in QM an eigenstate of the relative momentum p between the particles is an integral over all relative positions r weighted by an e^{ip.r} factor. Naturally the first order perturbation theory will involve the potential sandwiched between these momentum eigenstates
<p' | V | p>= \int dr <p' | r> V(r) <r| p>
= \int dr e^{i (p-p').r} V(r)
and roughly speaking (read a textbook to fill in the blanks) that's where the Fourier transform comes from.

Depending on the gauge, the photon propagator ends up being something like 1/p^2, and up to mathematical niceties this is proportional to the Fourier transform of 1/r in three dimensions.

Anonymous at Fri, 12 Jul 2024 18:39:30 UTC No. 16279103

>>16275345
superluminal propagation is allowed below the compton length