I don't know what you mean when you say electromagnetic radiation, impossible. Do you mean that light and radio waves are not made up of electromagnetic radiation. Or are you referring to the fact that you think that light waves cannot travel without a medium. If it is the latter, it was once believed that there is a medium called ether that permeated space and it was the medium that light traveled through. The famous Michelson-Morley (not sure I spelled the names right) was unable to detect the ether, Einstein said the the ether is a fiction. It may be that since light has a dual nature, it is both particle and wave, that the dual nature allows it to travel without a medium. Sound does not have a dual nature and needs a medium.

dace