Speed of light not necessarily the speed limit?

[Fanghur]

I just thought of something the other day. It is common knowledge that the speed of the electromagnetic force (AKA the speed of light) is "C". And experiments with particle accelerators have shown that nothing can travel faster than "C". It occured to me that maybe the reason that no particle accelerator has been able to accelerate particles faster than the speed of light is because the accelerators use electromagnetic fields to accelerate the particles, in other words it would be impossible to accelerate a particle faster than light because it would then be moving faster than the magnetic fields which are accelerating it.

 

In other words if a particle were travelling at superluminal speeds, it would be unaffected by the electromagnetic force, kind of like how a slower runner would be unable to touch a faster runner in a game of tag.

 

I've actually always thought it was kind of stupid to assume that gravity moves at the speed of light even though we know virtually nothing about how gravity works, and since gravity is a completely different fundamental force than electromagnetism.

[Mr Skeptic]

Look up Cherenkov radiation.

[Cap'n Refsmmat]

Cherenkov radiation doesn't involve anything breaking c -- only things breaking the speed of light in a particular medium.

 

We know that nothing can travel faster than c not just because of experiments but because of the theory of relativity, which posits that it should take an infinite amount of energy to accelerate a particle to c, and that it takes more energy to accelerate a particle the faster it's going. Pretty much all aspects of relativity have been tested and shown to be true, so I wouldn't bet on faster-than-light speeds just yet.

 

The speed of gravity has been experimentally tested and the evidence indicates that it's the speed of light, or at least close to it. That's not a certainty, of course, as the Wikipedia article notes, but at least we're not just "assuming."

[Klaynos]

It should also be remembered that in the rest frame of the particle being accelerated the photons are travelling at the speed of light...

[Edtharan]

In other words if a particle were travelling at superluminal speeds, it would be unaffected by the electromagnetic force, kind of like how a slower runner would be unable to touch a faster runner in a game of tag.

But if that faster runner was in a crowd, they would be effected by those that he runs into.

 

If you were moving faster than light, you would still be effected by the electromagnetic force . Yes, you would leave photons behind, but then you would run into the photons in front of you.

[ajb]

General relativity predicts that the propagation speed of gravity (the speed that the metric reacts to a small change in energy-momentum) is c. Also, we need to be a little careful about a fundamental speed limit. It only applies to massive particles and information. You can have the group velocity of a wave packet to be greater than c, for example. Also shadows and light spots can travel faster than c, but no matter or information is carried so this is ok.

 

One thing that strikes me and I think it is an open question is (in the context of special relativity) why are light-cones and causal-cones the same? I.e. why is c the fundamental speed? By this I mean is it possible to change the parameter in the Lorenz group from c to say v with v>c (even just infinitesimally). How does this effect the Casimir operators and the group representations (i.e. the particles!)? Can v>c still agree with experiments?

 

In doing so I presume that the light-cones would be "slightly smaller" than the causal-cones. Meaning that light could not be used to "map" the causal structure.

 

Any thoughts?

Edited June 27, 2008 by ajb

[Farsight]

Look at annihilation. Combine an electron and a positron and you get two 511KeV gamma photons. We do it every days in PET scans.

 

 

An electron can't travel faster than light for a very simple reason. And nor can any other particle either.

[pioneer]

What about quantum jumps between energy states? The electron will get from point A to point B in zero time or does it? Is this limited to C?

[blike]

If you were moving faster than light, you would still be effected by the electromagnetic force . Yes, you would leave photons behind, but then you would run into the photons in front of you

Remember that in the rest frame of the mass, the speed of light is always c. So you wouldn't be running into any photons in front of you. You can't ever "catch up" to them.

[swansont]

What about quantum jumps between energy states? The electron will get from point A to point B in zero time or does it? Is this limited to C?

 

Energy state jumps don't necessarily correspond to physical changes in location. Even so, one must recall [math]\Delta E \Delta t > \hbar[/math]

[Farsight]

What about quantum jumps between energy states? The electron will get from point A to point B in zero time or does it? Is this limited to C?

No it doesn't get from point A to B in zero time, it's isn't at one point, and it's limited to c.

[NeonBlack]

ajb, did you mean the phase velocity can be greater than c?