OK, this is just a little musing I had and I wonder what anyone who has real physics knowledge thinks about it Now, unless i'm mistaken the speed of sound, i.e kinetic waves in any medium, is based on the medium's density - the denser the medium, the faster the wave propogates. My question is, how dense would the material have to be to travel at the speed of light? My first assumption was it would have to be infinite, but then realized that this would cause the wave to propagate instantaniously... what would stop this from happening? is it that a medium can only ever get to a certain density? what is the speed of 'sound' in a singularity?