Why should anyone who is not a physicist be interested in Paul Dirac? Dirac is interesting for the same reasons that Einstein is interesting. Both made profound discoveries that changed our way of thinking. And both were unique human beings with strong opinions and strong passions. Besides these two major similarities, many details of their lives were curiously alike. Both won the Nobel Prize for physics, Einstein in 1921 and Dirac in 1933. Both had two children of their own and two stepchildren from a wife’s previous marriage. Both were intensely involved in the community of professional scientists in Europe when they were young. Both of them emigrated to the United States and became isolated from the American scientific community when they were old. The main difference between them is the fact that Einstein was one of the most famous people in the world while Dirac remained obscure.
There are many reasons why Einstein became inordinately famous. The main reason is that he enjoyed being famous and entertained the public with provocative statements that made good newspaper headlines. Dirac had neither the desire nor the gift for publicity. He discouraged inquisitive journalists by remaining silent. Einstein has had dozens of books written about him, while Dirac has only two, Dirac: A Scientific Biography by Helge Kragh, published in 1990, and this new biography by Graham Farmelo. The Kragh biography is full of equations and is addressed to experts only. The enormous fame of Einstein and the obscurity of Dirac have given the public a false picture of the two revolutions that they led. The public is aware of one revolution and correctly gives credit for it to Einstein. That was the revolution that changed the way we think about space and time. The new way of thinking was called relativity.
The second revolution that came ten years later was more profound, and changed the way we think about almost everything, not only in physics but in chemistry and biology and philosophy. It changed the way we think about the nature of science, about cause and effect, about past and future, about facts and probabilities. This new way of thinking was called quantum mechanics. The second revolution was led by a group of half a dozen people including Einstein. It does not belong to a single leader. But the purest and boldest thinker of the second revolution was Dirac. If we wish to give the second revolution a human face, the most appropriate face is Dirac. Farmelo writes that “in one of his greatest achievements,” Dirac arranged
what had seemed an unlikely marriage—between quantum mechanics and Einstein’s theory of relativity—in the form of an exquisitely beautiful equation to describe the electron. Soon afterwards, with no experimental clues to prompt him, he used his equation to predict the existence of antimatter, previously unknown particles with the same mass as the corresponding particles of matter but with the opposite charge. The success of this prediction is, by wide agreement …
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