Our introduction to special relativity in the last chapter covered the basics, but it may have raised more questions for you than it answered. Before reading the chapter, you may have been very happy with the simple idea that everyone would agree on the length of a car, or the time it takes for the hands on a clock to go around once. If so, you have now learned to question these assumptions, that Nature does not really behave like that. If you want to fit these ideas together into a more logical framework, and if you want to learn something about why scientists are so sure that Nature really follows the principles of special relativity, then this chapter is for you. Read on.

1. ▷ The image under the text on this page illustrates length contraction. The top figure is after Leonardo da Vinci's famous drawing. The bottom figure has the dimensions that an experimenter would measure if the experimenter were flying across the original drawing at a speed of 0.9c.

In the previous chapter I listed some important effects of special relativity and gave a brief description of each, such as time dilation and the equivalence of mass and energy.