Does light need a medium in order to travel?

12 August 2012

Question

Does light need a medium in order to travel?

Answer

Dominic - This has to do with two theories of physics called quantum mechanics and special relativity. And the question that was troubling physicists about 100 years ago was whether light is a particle or a wave. The problem is, you can describe some properties of light as being like particles and some properties such as diffraction and refraction in terms of a wave-like motion. And what physicists decided was that in fact, it's both at the same time. So light is made up of particles that we call photons, but it's also made up of waves of electric and magnetic fields which are electromagnetic waves.

The question is, do those waves move through some medium like ripples on top of a pond, or do they just move through the vacuum of space?

If they're like ripples in a pond then if you travel at some speed with respect to that medium then you should see light traveling at different speeds. And experiments have determined that light travels at the speed of light, however fast you're traveling in whatever direction. And so, that suggests there is no medium through which light travels.

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