26.8 Time dilation

Before you read this, I suggest you read posts 16.12 and 26.7. I introduced the concept of time in post 16.12. However, the special theory of relativity leads to an unexpected property of time – it depends on the state of motion of an observer; time does not pass equally in different inertial frames of reference. The more quickly you move, the slower time passes. We don’t normally notice this effect because it only becomes appreciable at speeds that are comparable to the speed of light in a vacuum, c. This effect is called time dilation. Is there an experimental test of time dilation? Yes. In 1940, the American physicists Bruno B Rossi (1905-1993) and David B Hall (I can’t find anything more about him) measured the rate of decay of a subatomic particle called the muon. They found that muons decayed more slowly when travelling at a speed close to c. What is the explanation of time dilation? The picture above shows a section through two parallel planes that appear as lines containing…