The basic problem of relativity theory arises out of trying to state with mathematical precision what we mean when we use the phrase “at the same time.”

You will probably find the contents of this chapter more difficult to grasp than those of the preceding chapters not because they are mathematically more demanding, but because this chapter, and the next, require that you unthink certain firmly held notions.

Once we understand how the problem arose and why our old notions are inadequate for attacking it, we can appreciate how certain mathematical principles (including the matrix algebra of Chapter 4), used with bold imagination, lead to successful strategies.

The Michelson-Morley Experiment

A. A. Michelson (1852–1931), awarded the 1907 Nobel Prize for Physics, was one of the world's greatest experimental physicists. He is perhaps best introduced by the following anecdote: Asked by a father if his son should be encouraged to continue his studies to become a physicist, Michelson is said to have replied, “No, I advise your son not to study physics. It is a dead subject. What there is to know, we know - except that possibly we could measure a few things to the sixth decimal place instead of the fourth.”

The irony of the story is that Michelson is the man whose experiments led to such a revolution that we have learned more about physics in the last sixty years than in all the preceding centuries.