Diana Kormos Buchwald, the general editor of Einstein’s papers, read this book meticulously and made copious comments and corrections through many drafts. In addition, she helped me get early and complete access to the wealth of new Einstein papers that became available in 2006, and guided me through them. She was also a gracious host and facilitator during my trips to the Einstein Papers Project at Caltech. She has a passion for her work and a delightful sense of humor, which would have pleased her subject.

Two of her associates were also very helpful in guiding me through the newly available papers as well as untapped riches in the older archival material. Tilman Sauer, who likewise checked and annotated this book, in particular vetted the sections on Einstein’s quest for the equations of general relativity and his pursuit of a unified field theory. Ze’ev Rosenkranz, the historical editor of the papers, provided insights on Einstein’s attitudes toward Germany and his Jewish heritage. He was formerly curator of the Einstein archives at Hebrew University in Jerusalem.

Barbara Wolff, who is now at those archives at Hebrew University, did a careful fact-checking of every page of the manuscript, making fastidious corrections large and small. She warned that she has a reputation as a nitpicker, but I am very grateful for each and every nit she found. I also appreciate the encouragement given by Roni Grosz, the curator there.

Brian Greene, the Columbia University physicist and author of The Fabric of the Cosmos, was an indispensable friend and editor. He talked me through numerous revisions, honed the wording of the science passages, and read the final manuscript. He is a master of both science and language. In addition to his work on string theory, he and his wife, Tracy Day, are organizing an annual science festival in New York City, which will help spread the enthusiasm for physics so evident in his work and books.

Lawrence Krauss, professor of physics at Case Western Reserve and author of Hiding in the Mirror, also read my manuscript, vetted the sections on special relativity, general relativity, and cosmology, and offered many good suggestions and corrections. He, too, has an infectious enthusiasm for physics.

Krauss helped me enlist a protégé of his at Case, Craig J. Copi, who teaches relativity there. I hired him to do a thorough checking of the science and math, and I am grateful for his diligent edits.

Douglas Stone, professor of physics at Yale, also vetted the science in the book. A condensed matter theorist, he is writing what will be an important book on Einstein’s contributions to quantum mechanics. In addition to checking my science sections, he helped me write the chapters on the 1905 light quanta paper, quantum theory, Bose-Einstein statistics, and kinetic theory.

Murray Gell-Mann, winner of the 1969 Nobel Prize in physics, was a delightful and passionate guide from the beginning to the end of this project. He helped me revise early drafts, edited and corrected the chapters on relativity and quantum mechanics, and helped draft sections that explained Einstein’s objections to quantum uncertainty. With his combination of erudition and humor, and his feel for the personalities involved, he made the process a great joy.

Arthur I. Miller, emeritus professor of history and philosophy of science at University College, London, is the author of Einstein, Picasso and of Empire of the Stars. He read and reread the versions of my scientific chapters and helped with numerous revisions, especially on special relativity (about which he wrote a pioneering book), general relativity, and quantum theory.

Sylvester James Gates Jr., a physics professor at the University of Maryland, agreed to read my manuscript when he came out to Aspen for a conference on Einstein. He did a comprehensive edit filled with smart comments and rephrasing of certain scientific passages.

John D. Norton, a professor at the University of Pittsburgh, has specialized in tracing Einstein’s thought process as he developed both special and then general relativity. He read these sections of my book, made edits, and offered useful comments. I am also grateful for guidance from two of his fellow scholars specializing in Einstein’s development of his theories: Jürgen Renn of the Max Planck Institute in Berlin and Michel Janssen of the University of Minnesota.

George Stranahan, a founder of the Aspen Center for Physics, also agreed to read and review the manuscript. He was particularly helpful in editing the sections on the light quanta paper, Brownian motion, and the history and science of special relativity.

Robert Rynasiewicz, a philosopher of science at Johns Hopkins, read many of the science chapters and made useful suggestions about the quest for general relativity.

N. David Mermin, professor of theoretical physics at Cornell and author of It’s About Time: Understanding Einstein’s Relativity, edited and made corrections to the final version of the introductory chapter and chapters 5 and 6 on Einstein’s 1905 papers.

Gerald Holton, professor of physics at Harvard, has been one of the pioneers in the study of Einstein, and he is still a guiding light. I am deeply flattered that he was willing to read my book, make comments, and offer generous encouragement. His Harvard colleague Dudley Herschbach, who has done so much for science education, also was supportive. Both Holton and Herschbach made useful comments on my draft and spent an afternoon with me in Holton’s office going over suggestions and refining my descriptions of the historical players.

Ashton Carter, professor of science and international affairs at Harvard, kindly read and checked an early draft. Columbia University’s Fritz Stern, author of Einstein’s German World, provided encouragement and advice at the outset. Robert Schulmann, one of the original editors at the Einstein Papers Project, did likewise. And Jeremy Bernstein, who has written many fine books on Einstein, warned me how difficult the science would be. He was right, and I am grateful for that as well.

In addition, I asked two teachers of high school physics to give the book a careful reading to make sure the science was correct, and also comprehensible to those whose last physics course was in high school. Nancy Stravinsky Isaacson taught physics in New Orleans until, alas, Hurricane Katrina gave her more free time. David Derbes teaches physics at the University of Chicago Lab School. Their comments were very incisive and also aimed at the lay reader.

There is a corollary of the uncertainty principle that says that no matter how often a book is observed, some mistakes will remain. Those are my fault.

It also helped to have some nonscientific readers, who made very useful suggestions from a lay perspective on parts or all of the manuscript. These included William Mayer, Orville Wright, Daniel Okrent, Steve Weisman, and Strobe Talbott.

For twenty-five years, Alice Mayhew at Simon & Schuster has been my editor and Amanda Urban at ICM my agent. I can imagine no better partners, and they were again enthusiastic and helpful in their comments on the book. I also appreciate the help of Carolyn Reidy, David Rosenthal, Roger Labrie, Victoria Meyer, Elizabeth Hayes, Serena Jones, Mara Lurie, Judith Hoover, Jackie Seow, and Dana Sloan at Simon & Schuster. For their countless acts of support over the years, I am also grateful to Elliot Ravetz and Patricia Zindulka.

Natasha Hoffmeyer and James Hoppes translated for me Einstein’s German correspondence and writing, especially the new material that had not yet been translated, and I appreciate their diligence. Jay Colton, who was photo editor for Time’s Person of the Century issue, also did a creative job tracking down pictures for this book.

I had two and a half other readers who were the most valuable of all. The first was my father, Irwin Isaacson, an engineer who instilled in me a love of science and is the smartest teacher I’ve ever had. I am grateful to him for the universe that he and my late mother created for me, and to my brilliant and wise stepmother, Julanne.

The other truly valuable reader was my wife, Cathy, who read every page with her usual wisdom, common sense, and curiosity. And the valuable half-a-reader was my daughter,Betsy, who as usual read selected portions of my book. The surety with which she made her pronouncements made up for the randomness of her reading. I love them both dearly.