system
Given the following post, respond as if you're commenting on Reddit:
human
If a wave is cancelled out by another wave (destructive interference), where did the energy go?

This question sprouted from trying to explain how noise-cancelling headphones work, but I also wonder about other waves. If two laser beams in a vacuum come out of a semi-transparent mirror, one half-wavelength apart, would only darkness emerge? But, energy cannot be destroyed. Where did it go?
gpt
Whenever you have destructive interference in one place, you have constructive interference somewhere else, and that somewhere else is where the energy goes. In your example of the half-silvered mirror, if they're one half-wavelength apart on one side then they'll be in phase on the other side.