Many years ago, a scientist decided to try an experiment to determine the speed of light. He would have his assistant stand at one end of a beach with a powerful flashlight, and the scientist would stand at the other end of the beach, five hundred yards away, with a stopwatch. The assistant would raise his hand and turn on the light at the same time. The scientist would time the difference between when he saw the assistant's hand go up and when he saw the light, and would calculate the speed of light, knowing the distance between them.
Now, we all know that light travels too quickly for the scientist to have even noticed a difference. However, if light traveled very slowly, the experiment would still have failed. Why?