Understanding Einstein’s Relativity

by N. David Mermin

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In It’s About Time, N. David Mermin asserts that relativity ought to be an important part of everyone’s education–after all, it is largely about time, a subject with which all are familiar. The book reveals that some of our most intuitive notions about time are shockingly wrong, and that the real nature of time discovered by Einstein can be rigorously explained without advanced mathematics. This readable exposition of the nature of time as addressed in Einstein’s theory of relativity is accessible to anyone who remembers a little high school algebra and elementary plane geometry.

The book evolved as Mermin taught the subject to diverse groups of undergraduates at Cornell University, none of them science majors, over three and a half decades. Mermin’s approach is imaginative, yet accurate and complete. Clear, lively, and informal, the book will appeal to intellectually curious readers of all kinds, including even professional physicists, who will be intrigued by its highly original approach.


“Mermin’s premise is that everyone should know about relativity in order to understand the real nature of time. . . . What is remarkable in his approach is his reliance on developing the reader’s skills to analyze events in more than one frame of reference. This is the key to understanding relativity: being able to translate with ease from one frame of reference (a moving train) to another (a station).”–Simon Mitton, Times Higher Education Supplement

“This is a book full of insight with an engaging style. I recommend it to anyone who has to teach the subject to either [non scientists or undergraduate and graduate students]: it’s a brilliant basis for a set of lecture notes.”–Derek Raine, Nature

“In this highly readable book, Mermin argues that a working knowledge of relativity requires no more than basic algebra and geometry. He makes a valid point. Special relativity is more fundamental, up-to-date and accurate than Newtonian physics, and Einstein’s presence in the classroom may inspire the most uninterested student.”–Amanda Gefter, New Scientist

It’s About Time is a book that should join the very best systematic popular expositions of science written in the last 50 years.”–Peter L. Galison, American Scientist

“There’s a profound difference between knowing about something, and knowing it, and Mermin succeeds at instilling the latter.”–Gilbert Taylor, Booklist

“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, MAA Reviews


Preface: Why Another Relativity Book ix
Note to Readers xiv
Chapter One: The Principle of Relativity 1
Chapter Two: Combining (Small)Velocities 14
Chapter Three: The Speed of Light 19
Chapter Four: Combining (Any)Velocities 28
Chapter Five: Simultaneous Events;Synchronized Clocks 45
Chapter Six: Moving Clocks Run Slowly;Moving Sticks Shrink 58
Chapter Seven: Looking At a Moving Clock 73
Chapter Eight: The Interval between Events 79
Chapter Nine: Trains of Rockets 89
Chapter Ten: Space-Time Geometry 102
Chapter Eleven: E =M2 144
Chapter Twelve: A Bit about General Relativity 171
Chapter Thirteen: What Makes It Happen? 179
Index 187

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