About This Lesson
How can light bounce off a mirror? Imagine first a tennis ball bouncing off a wall. It has one speed while approaching the wall, then as it hits the wall, the speed rapidly decreases as the ball distorts. At this point, the ball briefly comes to a complete stop. Only a moment later it begins to recoil and pick up speed, flying in the other direction. None of this can be true for light, because an individual particle of light, called a photon, must maintain the same speed both going into the mirror and coming back out. It can’t rebound at less than its original speed, or ever stop.
