If I drop a rock into a pond, a wave will propagate through the water from the location where the rock made contact. The wave will travel at a speed dependent on the density of the medium. As far as I understand, the crest and trough of the wave are caused because the still water in the path of the wave has inertia which in turn causes the water to “buckle” as the energy of the wave pushes against it before it moves. This is also the reason why the speed of the wave is dependent on the medium.

So, when light travels through a vacuum at top speed and in some way acts as a wave with a crest and trough, is it because the medium through which it travels is “buckling” in the same way?

  • 2
    $\begingroup$ That kind of thinking leads to the dead end known as æther theories. $\endgroup$ Oct 19, 2023 at 16:16
  • $\begingroup$ What would the medium be in a vacuum? $\endgroup$
    – user45664
    Oct 20, 2023 at 17:55
  • $\begingroup$ Light can also be measured and described as a particle. Individual photons move as a particles the collective behavior of photons is described using wave theory. $\endgroup$ Oct 21, 2023 at 16:19

1 Answer 1


I don't think that this is a useful analogy. The idea of space "buckling" will lead to many incorrect statements. For example, since space is the distance between points, this would imply that the distance between points will change whether there is a EM wave propagating between them or not. It would also give the idea that the distance that the wave travels is longer than it does because of the extra distance that it has to go along the buckling. This would lead to the erroneous conclusions that light moves faster than the speed of light.

In electrical circuits you can make an analogy between circuit elements and mechanical objects. In that analogy you can relate either a capacitor or an inductor with a mass. So you could think of those as having "inertia". However, this is definitely more relevant to circuits than to a signal propagating in free space.

  • $\begingroup$ When we measure the speed of a wave in water we don’t measure the distance along the buckle we measure the speed at which the crest of the wave travels between points. So it is not the water that is moving at that speed but the wave. The water is moving up and down. Similar would be light in that light is the wave and the “medium” is oscillating figuratively beneath it it. The wave moves at the same speed. $\endgroup$
    – shane
    Oct 21, 2023 at 15:46
  • $\begingroup$ Also, maybe my question using “inertia” is poor choice. Perhaps the real question is if there is some resistance to propagations through an EM field which could produce such “buckling” and therefore impose a limit on the speed of light. Thanks for your time and thought! $\endgroup$
    – shane
    Oct 21, 2023 at 15:49
  • $\begingroup$ @shane I am just telling you the sort of misconceptions that you can expect with this analogy. I have literally worked with a student who made that exact mistake. I believe your analogy would make that mistake more common. I think it will cause more problems than it resolves $\endgroup$
    – Dale
    Oct 21, 2023 at 15:52
  • $\begingroup$ I think the assertion that EM waves do not move through a medium at all requires more than an a priori mathematical definition of space. $\endgroup$
    – shane
    Oct 22, 2023 at 15:16
  • 1
    $\begingroup$ @shane yes, I agree completely with that last point $\endgroup$
    – Dale
    Oct 22, 2023 at 17:11

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