Conduction needs touching particles to pass on vibration, and convection needs a fluid to physically carry heat along with it, but radiation needs nothing at all in between, it can even cross empty space, which is exactly how the Sun's heat reaches Earth through a vacuum. That is only possible because radiation travels as electromagnetic waves, mainly infrared, which do not need a carrier medium the way sound or moving fluid do. Molecular collisions describe conduction, electron transfer describes metallic conduction, and fluid flow describes convection, none of these apply to radiation. So radiation travels as electromagnetic waves.