4.1 Time Dilation
[SQUEAKING] [RUSTLE] [CLICKING] PROFESSOR: Welcome back to 8.20. In this section, we're going to talk about time, timekeeping, and how to relate time between two different reference point. Now, let me start with a quote by Albert Einstein. "Everything should be as simple as possible, but not simpler." So let's start with this in mind. And recall that we ended the last section by finding that the wave aether model doesn't really describe electromagnetic waves very well. We see that there is a problem between the experiments, specifically the one by Michelson-Morley, and the theoretical picture people had in mind. So Einstein approached this in an interesting way. He simply postulated the things he thought need to be true. He said, "The same law of electrodynamics will be valid for all reference frames where all laws of mechanics hold good. This is the principle of relativity." The second postulate is that "Light is always propagated in ...