'sound' waves at the speed of light

[hazhar]

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?

 

[Aaron Barnard]

That is a good question! The speed of sound is based on the medium’s density, but the speed of light is an absolute constant and is not dependent on the medium it is traveling through. It is actually impossible for any material to travel at the speed of light, since the speed of light is always going to be faster than anything else. The closest you could get would be in a vacuum, where the speed of light is the absolute maximum speed possible. In a singularity, the speed of anything would be indeterminable due to the immense gravitational forces present.