# Particles faster than light

1. Feb 17, 2010

### Gerenuk

Why do we take photons as the reference and say they are the fastest?

Could anyone prove that there isn't a particle that is slightly faster than photons?

For example one could probable redo all the relativity argument with that faster particle (gravitons or anything)? Then light would only be second in speed.

2. Feb 17, 2010

### Staff: Mentor

Which "relativity argument" are you referring to?

3. Feb 17, 2010

### Gerenuk

I'm not sure about the correct derivation of spec.rel.

Maybe someone can first outline the derivation and then say why it wouldn't work for particles other/faster than light.

4. Feb 17, 2010

### Fredrik

Staff Emeritus
Those "derivations" don't start with the fastest speed. They start with the existence of an invariant speed, i.e. a speed that's measured to be the same by all inertial observers. If there's a particle that moves faster than the invariant speed, its speed wouldn't be invariant.

5. Feb 17, 2010

### Gerenuk

That's not the answer to my question.

Why in particular are photons supposed to have this invariant velocity?

6. Feb 17, 2010

### Ich

Photons are supposed to have no rest mass, and it can be shown that massless particles must travel at the invariant velocity.
If someday they find that photons have restmass, they'd be supposed to be a bit slower than c. But there are http://pdg.web.cern.ch/pdg/2007/listings/s000.pdf" [Broken] on the photon mass.

Last edited by a moderator: May 4, 2017
7. Feb 17, 2010

### Gerenuk

Ah OK. Thanks for the reference.