This question already has an answer here:
Just looking for a quick, non-mathematical answer.
So the speed of light (c) is the fastest that anything can travel. Is c defined as the speed of light or is c a universal constant that nothing (including light) can travel faster than? Is the speed at which photons travel the limit, or is the limit something else that also limits the speed at which photons travel?
So if in some alternate universe, light travelled at 50% of the speed it did in our universe (for some hand-wavium reason, all other things being equal), would we also be limited to this new speed of light or would the maximum speed be the same as in our universe?
the questions: Is it light that we cannot go faster than or some universal constraint which also constrains light?