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It's About Time: Understanding Einstein's Relativity

N. David Mermin
Princeton University Press
Publication Date: 
Number of Pages: 
[Reviewed by
Kara Shane Colley
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In writing It's About Time, N. David Mermin followed "the rule (widely attributed to Einstein) that the exposition should be as simple as possible, but no simpler than that."  This is what I most appreciate about Mermin's book on relativity.  Too often, popular math and science books are dumbed down for the public.  Mermin's book is certainly not dumbed down — he presents relativity without glossing over the details, giving the reader the chance to delve deeply into the physics. 

On the other hand, Mermin contends that the book is intended for "people with no training in physics, and none in mathematics beyond very elementary geometry and algebra."  Readers without a background in science will probably find Mermin's book a challenge if they try to read it on their own.  They will need motivation and determination to push through when the reading becomes tough.  Most likely, it will be necessary to re-read sentences, sections, or even whole chapters in order to understand the ideas. Still, though the non-science person might not understand every detail, careful readers will be rewarded with a substantial understanding of relativity.  Perhaps the best place for this book is in a college class on relativity for non-science majors.  Having a physics professor nearby would help to clear up any difficulties that arise while reading the book. 

It's About Time covers the major aspects of Einstein's Theory of Special Relativity, briefly touching on General Relativity at the end of the book.  The author explores the concepts of adding relativistic velocities, simultaneous events, length contraction, time dilation, the constancy of the speed of light, and the infamous equation E = mc2.  I particularly enjoyed the chapter on Minkowski's space-time diagrams.  Though I studied physics in college, I had not seen these diagrams before.  They are a compact and enlightening way to see different frames of reference in one illustration.

The best parts of the book are the examples and accompanying diagrams.  First off, his examples are more like stories because they involve people, usually Alice and Bob.  For example, Alice rides by on a train while Bob sits at a train station.  If Alice emits two photons in opposite directions from the middle of the train car, will the photons reach the ends of the train car at the same time?  Consider first what happens in Alice's frame of reference and then Bob's frame of reference.  Rather than saying "Frame A" and "Frame B", this simple trick of using real names brings a bit more life to the examples.  Also, because Mermin can use the pronouns "he" and "she," it makes the examples easier to follow. 

Mermin has taught relativity for 40 years and has clearly thought about the best way to teach the subject.  It's About Time offers a serious, yet accessible approach to relativity.

Kara Shane Colley studied physics at Dartmouth College and math education at Teachers College.  She has taught math and physics to middle school, high school, and community college students in the U.S., the Marshall Islands, and England.  Currently, she is living aboard the Halfmoon, a replica of Henry Hudson's ship.  Contact her at

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