More about physics than I expected (maybe more about tensors than I expected), and a bit slow-starting, but a worthwhile history of science book that recounts the fascinating and controversial history of an idea we take for granted. The end of the book comes up short in the way many general audience science books do — I just don't know how it could be possible to explain the tensor calculus of relativity in a few chapters, at least to me, anyway — but overall a satisfying and enlightening read.