Question

How does a non-mechanical wave propagate without a medium?

Answer 1

The actual speed of an electromagnetic wave through a material medium is dependent upon the optical density of that medium. Different materials cause a different amount of delay due to the absorption and reemission process. Furthermore, different materials have their atoms more closely packed and thus the amount of distance between atoms is less. These two factors are dependent upon the nature of the material through which the electromagnetic wave is travelling. As a result, the speed of an electromagnetic wave is dependent upon the material through which it is traveling.