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Since QED and relativity aren't consistent, and QED says that can photons travel at speeds less than and greater than c, isn't it possible that relativity is ju

Since QED and relativity aren't consistent, and QED says that can photons travel at speeds less than and greater than c, isn't it possible that relativity is just probabilistically true but not "enforced" to be true?

nessus42 14y ago
Since I don't know anything about QED, I'm not equipped to answer this question. What I can say, however, is that much of what we consider to be "causality" is just a matter of probability. There's nothing in the fundamental laws of physics that says that a flower pot that fell off the window sill and broke into a million pieces an hour ago, can't now suddenly put itself back together and then fly back onto the sill, just as if nothing had ever gone awry. The fact that flower pots don't typically tend to do so, is that this turn of events is extremely unlikely. In fact, as far as fundamental physics goes, the forward arrow of time and the backward arrow of time are indistinguishable. I.e., if you were to look at a movie of subatomic particles interacting, you wouldn't be able to tell, if you didn't already know, if the film were being played forwards or being played backwards. (As a slight caveat to this--a caveat that does not detract from what I am saying, but should be mentioned for the sake of completeness--there is one tiny aspect of fundamental particle physics that breaks this time symmetry, but it is a rather subtle one. The physicists who discovered this won a Nobel prize, and as I understand it, why this symmetry should be broken--no matter how subtle the effect--is still a deep mystery.) What we consider to be the forward arrow of time comes completely from thermodynamics, not from fundamental law. E.g., if the Big Bang occurred at the end of time, rather than the beginning of time, we wouldn't be able to tell the difference, because from our point of view, that would end up being the beginning of time anyway.
- jonmrodriguez 14y ago
  Do you think the big bang has universes on both sides of it?
gus_massa 14y ago
QED is consistent with Special Relativity. The standard introduction to QED starts with the successful attempt of Dirac to create a "covariant" version of the Quantum Mechanics that is consistent with Special Relativity (in that process he explained the particle spin and predicted the positrons). Then it's necessary to make the theory more complicated to explain some experiments, but the final QED theory is consistent with Special Relativity (or "covariant" in the jargon). The extensions that involve the weak and strong forces are also covariant and they form the Standard Model (with the slightly hypothetical Higgs boson). Any reasonable extension of the Standard Model is "covariant". And it would be very difficult to make the physic community consider seriously a no "covariant" theory (nothing is impossible). Nobody knows the quantum version of General Relativity, so perhaps there is a very tiny loophole, but I would not be very hopeful about it.

nessus42 14y ago

Since I don't know anything about QED, I'm not equipped to answer this question. What I can say, however, is that much of what we consider to be "causality" is just a matter of probability. There's nothing in the fundamental laws of physics that says that a flower pot that fell off the window sill and broke into a million pieces an hour ago, can't now suddenly put itself back together and then fly back onto the sill, just as if nothing had ever gone awry. The fact that flower pots don't typically tend to do so, is that this turn of events is extremely unlikely. In fact, as far as fundamental physics goes, the forward arrow of time and the backward arrow of time are indistinguishable. I.e., if you were to look at a movie of subatomic particles interacting, you wouldn't be able to tell, if you didn't already know, if the film were being played forwards or being played backwards. (As a slight caveat to this--a caveat that does not detract from what I am saying, but should be mentioned for the sake of completeness--there is one tiny aspect of fundamental particle physics that breaks this time symmetry, but it is a rather subtle one. The physicists who discovered this won a Nobel prize, and as I understand it, why this symmetry should be broken--no matter how subtle the effect--is still a deep mystery.) What we consider to be the forward arrow of time comes completely from thermodynamics, not from fundamental law. E.g., if the Big Bang occurred at the end of time, rather than the beginning of time, we wouldn't be able to tell the difference, because from our point of view, that would end up being the beginning of time anyway.

jonmrodriguez 14y ago
Do you think the big bang has universes on both sides of it?

gus_massa 14y ago

QED is consistent with Special Relativity. The standard introduction to QED starts with the successful attempt of Dirac to create a "covariant" version of the Quantum Mechanics that is consistent with Special Relativity (in that process he explained the particle spin and predicted the positrons). Then it's necessary to make the theory more complicated to explain some experiments, but the final QED theory is consistent with Special Relativity (or "covariant" in the jargon). The extensions that involve the weak and strong forces are also covariant and they form the Standard Model (with the slightly hypothetical Higgs boson). Any reasonable extension of the Standard Model is "covariant". And it would be very difficult to make the physic community consider seriously a no "covariant" theory (nothing is impossible). Nobody knows the quantum version of General Relativity, so perhaps there is a very tiny loophole, but I would not be very hopeful about it.