But wait, sound in space?
New Scientist: Big bang sound waves explain galaxy clustering
Sound waves that roared through space after the big bang left behind a subtle imprint in the way galaxies are clustered today, reveal two major studies.
New Scientist: Universe started with hiss, not bang
For those worried that you cannot have sounds in space, that is true today, but it was not so in the Universe's infancy...the Universe was small and dense enough that sound waves could indeed travel through it - so efficiently, in fact, that they moved at about half the speed of light.