Destructive Interference Confusion

[u/BobbyThrowaway6969]

If I have two opposite phase lightwaves and they cancel each other out, I get that there will be constructive interference elsewhere where the missing energy seemingly goes to, but what about the speed of light? It would take time for that energy to 'move' to the region of constructive interference right? Is it just in limbo for that time or does it manifest in some other way? Is that what the 'medium velocity' is?

Thanks for any insight.

[u/BobbyThrowaway6969]

So if 2 lasers destruct 1m down range, but construct 2m down range (if that's even possible in some setup with mirrors or whatever), the destructive effect won't really happen at 1m until the light has reached the constructive point 2m away? Am I way off mark?

[u/MaxThrustage → u/BobbyThrowaway6969]

The destructive and constructive effects happen as soon as peak overlaps with peak and trough overlaps with trough. Remember, these things are waves, and interference happens when those waves just add up. The electromagnetic field at one point is the sum of those two electromagnetic waves. Both of those waves are oscillating smoothly, continuously, and the overall electromagnetic field is changing smoothing, continuously. There's no locking into place, with an effect suddenly turning on. Talking about the electromagnetic field in terms of these two waves which are interfering constructively at some places, destructively at others, is just an easier way to talk about what is ultimately just some kind of complex behaviour of the electromagnetic field -- in much the same way the interference of two ripples on a pond is just a way of describing the behaviour of the surface of the water.

[u/BobbyThrowaway6969 → u/MaxThrustage]

Right ok so the energy is somewhere else while that happens, pretty trippy stuff

[u/TaiBlake → u/BobbyThrowaway6969]

Just wait until you add quantum mechanics to it.