I found many sci-fi descriptions on many topics, such as Tachions, moving faster than c and so on. Well then I read up on a little on relativity, that holds that the speed of light in a vacuum is a universal constant (c). How are we so sure of this(no math please)? How are we so sure that that vacuum is the universal constant? When I ask this I know it can be answered by special relativity, but i'm thinking more like "what if we could go faster than light"...If Čerenkov radiation exists why cant it exist somewhere else? The sky is the limit(I'd like to think so, that the universe is limitless)... I'm sure someone with more knowlage than me might laugh me out and say "Only in the movies, boy" ect... But I wanted to know how physics stands on this? Thanks for any input.