What happens to relativity when light is slowed down?

  • #26
Integral
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Yogi,
Your brand of misinfromation has a special place on this board.

We call it Theory Development.
 
  • #27
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Originally posted by yogi
but what are the effects of the electromagnetic fields on photons
Electromagnetic fields don't directly affect photons (to lowest order in perturbation theory, at any rate), but they do affect atoms and their electronic transitions.


what I don't buy is the absorption and release as a physical explanation
Why not? Especially when you clearly know nothing about it.


- take a one meter radio wave photon
Are you under the impression that the wavelength of a photon determines its size? It does not: it determines the wavelength of its wavefunction, i.e., how close together the regions of low probability of finding it and of high probabiliy of finding it are.


- how can it get stored in some kind of atomic configuration and released - yet its velocity will be measured to be slower in a physical medium.
Its effective velocity: you're not measuring the photon's velocity itself, you're measuring how long it takes betwen a wave entering and exiting the medium.

The reason why the G field appeared worth considering was because photons are influenced thereby.
If you'd stop blustering and start calculating, you'd see find that this idea doesn't work. As they say, "talk is cheap": lots of ideas seem plausible until you sit down and actually test them. That's the whole point of science: to provide rigorous methods to compare and eliminate hypotheses.

Whatever a photon is - and whatever part of it is acted upon by matter - it is not unreasonable to investigate whether the forces it experiences as it passes through the atomic field may be determinative of its velocity
Fine. So investigate them and get back to us.
 
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  • #28
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Any calculations necessarily require a lot of assumptions as to the nature of the model - there are many models - and it would involve many assumptions re the interactions - are you really saying a long wavelength radio wave can get wrapped up in a single atom somehow and reradiated - in the first place they do not have sufficient hf energy to trigger electron jumps
 
  • #29
841
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Originally posted by yogi
Any calculations necessarily require a lot of assumptions as to the nature of the model - there are many models - and it would involve many assumptions re the interactions -
You're weaselling.

There are not "many assumptions re the interactions": there is just the standard electron-photon interaction of quantum electrodynamics. You have to put in what atoms you've got --- but this is obvious, since different materials influence the propagation of light differently.

Other than that, tell me what these "many assumptions and models" are.

are you really saying a long wavelength radio wave can get wrapped up in a single atom somehow and reradiated - in the first place they do not have sufficient hf energy to trigger electron jumps
I think I see your confusion.

Real photons propagating through a medium are not always absorbed and emitted; sometimes they just scatter. (This is described to lowest order in perturbation theory by the electron absorbing a photon to produce a virtual electron, which then "decays" to another electron and photon.)

Since they're not propagating directly, they can't traverse the medium as quickly as if the medium weren't there. But the scattering is preferentially opposite the direction of incidence, so the light beam as a whole tends to stay focused, even though the individual photons may be jiggling around. (If the beam travels far enough through the medium, though, it will scatter a lot and diffuse through the medium.)
 
  • #30
russ_watters
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Side note for kartiksg and cucumber - please don't think I was blowing you off, but my knowledge of the nature of light starts to get pretty thin when we get into quantum mechanics. I was hoping someone else would pick up the ball where I left it. Unfortunately...
 
  • #31
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My doubt is deeper than weasling - I have always regarded QED - the notion of virtual photons - as metaphorical - I know - perturbation theory gives extremely accurate predictions for the second order effect (the gyromagnetic ratio) and a lot of other processes - but I do not think virtual photons, gravitons etc represent reality - they are tools for making calculations - extremely useful tools - but any attempt to derive the electron charge or the force between two electrons based upon virtual photons requires many assumptions and the analysis is abstruse (at least all the ones I have read)- one must make postulates about the virtual photon shower in terms of q^2 and make many other assumptions about borrowing momentum (Heisenburg loans) for short periods, - and the list goes on. I am reminded of something Einstein once said about SR "Now that the mathematicians have gotten a hold of it, I am not sure I understand it anymore"

I appreciate that you have a good command of quantum process - but to my way of thinking - forces arise because of stresses in the medium - and these stresses affect the properties of the medium in bulk - this of course is at least partially in conflict with SR because it implies that photons may not travel at c in a stressed spatial medium (but that is another subject in itself). So I will give some thought to how one might model a stress field that has retarding properties that comport with experiment. I will also try to recover a lenghty article that I once read that treated the subject classically.
 
  • #32
841
1
Originally posted by yogi
My doubt is deeper than weasling - I have always regarded QED - the notion of virtual photons - as metaphorical - I know - perturbation theory gives extremely accurate predictions for the second order effect (the gyromagnetic ratio) and a lot of other processes - but I do not think virtual photons, gravitons etc represent reality - they are tools for making calculations - extremely useful tools
Well, many physicists would agree with you on that, but it's really a matter of philosophy, not physics. The whole idea of virtual particles arises as a representation of terms in the perturbation expansion of a quantum field theory. So it's debatable whether a term in a series expansion represents something real. However, quantum field theory itself does not depend on the notion of virtual particles: you can define quantum field theories without reference to a perturbation expansion. The quantum field is the fundamental physical entity, not the virtual particlces.


- but any attempt to derive the electron charge or the force between two electrons based upon virtual photons requires many assumptions and the analysis is abstruse (at least all the ones I have read)- one must make postulates about the virtual photon shower in terms of q^2 and make many other assumptions about borrowing momentum (Heisenburg loans) for short periods, - and the list goes on.
These are not assumptions: they are all derived from the axioms of field theory, not stuck into the calculation to make it work. (You're right if you say that this "Heisenberg loan" stuff sounds ad-hoc, because it is --- it's only a crude way of describing the actual calculation, which is not ad-hoc. But to understand the calculation, you have to understand the mathematics of quantum field theory.)


I am reminded of something Einstein once said about SR "Now that the mathematicians have gotten a hold of it, I am not sure I understand it anymore"
Most theories of physics are not easy to understand. That has nothing to do with their correctness.


I appreciate that you have a good command of quantum process - but to my way of thinking - forces arise because of stresses in the medium - and these stresses affect the properties of the medium in bulk - this of course is at least partially in conflict with SR because it implies that photons may not travel at c in a stressed spatial medium (but that is another subject in itself). So I will give some thought to how one might model a stress field that has retarding properties that comport with experiment. I will also try to recover a lenghty article that I once read that treated the subject classically.
You're of course welcome to formulate your own alternative theories. However, I would strongly recommend seriously learning some quantum field theory --- "abstruse" or not --- to the point of fully understanding the QFT calculation of this effect, before attempting to formulate your own alternative. If there's one thing that the history of science has shown, it's that the only people who ever replace old theories with new ones are those who understand those old theories very well.
 
  • #33
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Yes - all good points - and as I recall, it wasn't obvious initially that Feynman's diagrams were equivalent to the perturbation expansion of alpha (I think it was Dyson's equation). Anyway - I would agree that if one has adequate time - the more one knows about the subject - the better able he is to contribute - but there is at least one counter aspect to that - the new kid on the block enters with a lot of questions - he isn't biased by conventional wisdom - he interrogates what the experts have long dismissed as not worthwhile. In my many years of experience I have found myself on both sides of that situation -

Of course - one must have a little knowledge to know what questions to ask. I tend to think of these forums in that light -
 

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