Re: In a vacuum?
Vacuum... the problem is that we really don't understand what we consider to be a vacuum actually is. Traditionally it's considered to be absolutely nothing, nada, nothing there at all. Unfortunately sub-atomic particles have a nasty habit of spontaneously forming in a vacuum can there truly nothing there because by definition they have to have come from something? Or is it the case that there is nothing there that we can currently observe and measure? in which case it's not unreasonable to assume that the speed of light may vary.