What Is Relativity?

December 2, 2013
“Black holes don’t suck,” says astrophysicist Bennett (Life in the Universe); in fact, their exotic nature is the perfect way to explore relativity. The special theory of relativity, proposed by Albert Einstein in his 1905 paper, “On the Electrodynamics of Moving Bodies,” says in part that nothing can outrace light, but it’s exactly in that highly accelerated realm where you need to be to observe the extreme weirdness of relativity at work: time dilation, mass increasing, and the shortening of the length of high-velocity objects. Bennett shows how particle accelerators can provide that environment on Earth, making special relativity “one of the most well-tested theories in all of science”—but still incomplete, as far as Einstein was concerned. He sought “an underlying simplicity in the universe”—wherein gravity and acceleration are the same—and he found that in the curved spacetime of general relativity where orbiting objects move “like marbles in a salad bowl,” following the curvature of spacetime along the straightest possible path. From black holes and gravity waves, to wormholes and warp drive, Bennett’s fun book shows readers what relativity means, and what it reveals about our universe.

March 1, 2014

The theory of relativity is one of those areas of science that seems daunting to non-physicists. Although the experts agree that the theory is accurate and eloquent, most literature explaining it is too complex for the lay reader to grasp fully. Bennett (Beyond UFOs), an astrophysicist who has coauthored many science textbooks, tries a different approach. First, he keeps the math out of it. The only equation in the book is E=mc2. Instead he relies heavily on thought experiments. Einstein himself used thought experiments to understand how to make sense of the shortcoming of Newtonian physics. Bennett takes the reader step by step from the special theory of relativity through the broader general theory of relativity. At each step he starts with what is known to us more or less through common sense and then moves slowly into new material. For example, he uses an intuitive concept like the earth being round to help explain how space-time can be curved, a concept that may not be intuitive. A generous dose of graphs and charts also helps illuminate his discussion. VERDICT Bennett does a masterly job of teaching a difficult topic without oversimplifying it. The results are recommended for readers at the high school level and above. A general understanding of Newtonian physics is beneficial.--William Baer, Georgia Inst. of Technology Lib., Atlanta

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