Where/ how does light propagate?

Question

The Michelson–Morley experiment proved there is no aether, but we (used to) know that a wave needs a medium in order to propagate. Einstein showed the invariance of speed but assigned no properties to vacuum, even though later he regretted that. Did he ever explain how it propagates without a medium?

Can you tell how is propagation of light explained now, and if QM altered the current view?

"we know that a wave needs a medium in order to propagate" - no it doesn't. That's the point. — John Rennie, May 17 '22 at 09:47
@JohnRennie, does it propagate in space, in a vacuum with no properties? — user157860, May 17 '22 at 09:48
There should be a "we know..." or a "as we all know..." tag... — DJohnM, May 17 '22 at 22:12
@electronpusher, if space is empty (a vacuum) what properties can it have? — user157860, May 18 '22 at 09:04
@user157860 How about dielectric permittivity and magnetic permeability, for starters. The vacuum is not some philosophical perfect void, empty of all substances and impossible to characterize. Quite the opposite. — electronpusher, May 18 '22 at 22:52

score 2 · Accepted Answer · answered May 17 '22 at 10:16

Can you tell how is propagation of light explained now, and if QM altered the current view?

The propagation of light is explained by Maxwell’s equations. They describe how the field behaves. In particular, Maxwell’s equations have vacuum solutions, which describe how the fields propagate through regions without any medium.

QM has not altered this view. What QM does bring is a better understanding of the interaction between light and matter. But the propagation of light through vacuum is largely unchanged.

Where/ how does light propagate?

1 Answers1