Suppose you have an absolute vacuum, with zero particles, and its container is made of a conductive material, like a metal or something, which is heated. What happens inside the vacuum? Does heat need the medium of air, or will it heat the vacuum? I reason that heat needs a medium (like air particles) to permeate because the particles vibrate, transferring the energy that is registered as heat, but this doesn't seem right. I know that space isn't a perfect vacuum, but it's close enough, and heat from the sun reaches the earth. I guess what I'm ultimately wondering is, does heat (or any form of energy) need a medium to travel through, other than space?