Originally Posted by
EVOEx
Sorry for snipping your quote, I didn't want to fill an entire page with it again. Thanks for your help, guys. It makes sense, except that I don't understand one single part of it: if we would make a photon (or multiple, but let's stay with one for simplicity) bounce back and forth between mirrors, it would make sense, but when the mirrors would start moving (when they're inside a spaceship for instance), the photon wouldn't start moving along with it, would it? So the photon would simply be lost, from what I understand. To make it bounce back and forth indefinitely, would it not have to be sent out diagonally, matched up with the speed of the mirrors, which is exactly what an external observer would see?
What am I misunderstanding here?