Can anything travel faster than light?
Only light can travel the speed of light (since it has no mass). Anything with mass travels slower than the speed of light. We know of nothing that can travel faster than light. It has been hypothesized that a sub-atomic particle, called a tachyon, could travel faster than light. Such a particle would have very strange properties, such as it would travel backwards in time.
There are a couple of caveats to that whole situation. Einstein never said that nothing can travel faster than light. Nothing with mass can travel at the speed of light in vacuum, nor accelerate to it from either direction. That’s why people postulated tachyons; (theoretically, they travel faster than light, but can never slow down enough to cross the threshold). At the same time, Cherenkov radiation is produced by fast neutrons exceeding the speed of light in water. (The individual photons still travel at c, but the propogation of the light as a whole is retarded by the medium.
