Uncertain Principles: Pop Quiz: Michelson Interferometer
When there’s no light on the viewing screen, we have light going into the interferometer, but no light coming out. What happened to the light?
It’s important to note a clarification Chad gives in the comments
To clarify (or maybe confuse) things a bit: this is a hypothetical idealized Michelson interferometer in which the beams have zero divergence. Thus, you don’t get a ring pattern, just a single spot of light.
Until reading that I wasn’t liking any of the answers.
Though I didn’t comment, I did choose the right answer.
The underlying principle is that energy has to be conserved — anytime you get destructive interference, there must be some other place that is seeing constructive interference. The key to any configuration is deducing out where that is.