Dreams of Earth and Sky (20 page)

The American space culture as Weinberg articulates it is only half of the truth. The Russian space culture is the other half. If you think as Americans do, on a time scale of decades, then unmanned missions succeed and manned missions fail. The grandest unmanned missions, such as the Cassini mission now exploring the satellites of Saturn, take about one decade to build and another decade to fly. The grandest manned mission, the Apollo moon landing, ended after a decade and could not be sustained. The time scale of a decade is fundamentally right for unmanned missions and wrong for manned missions. If you think as Russians do, on a time scale of centuries, then the situation is reversed. Russian space science activities have failed to achieve much because they did not concentrate their attention on
immediate scientific objectives. Russian manned mission activities, driven not by science but by a belief in human destiny, keep moving quietly forward. There is room for both cultures in our future. Space is big enough for both.

After history and politics, Weinberg’s other main theme is science. He writes about science with the sensitivity of a teacher who has taught courses on Physics for Poets, emphasizing basic ideas and avoiding technical details. In this book there are no equations. Chapters with titles such as “Can Science Explain Everything? Anything?” and “The Future of Science, and the Universe” describe Weinberg’s philosophical conclusions and say little about the tools of his trade.

His philosophy includes a streak of militant atheism. He has a strong aversion to all religious beliefs and a particularly intense dislike for organized religions such as Christianity and Islam. He quotes with approval the mathematician Paul Erdös, who never used the word “God” but instead spoke of the “Supreme Fascist.” He agrees with the statement of Thomas Jefferson: “The Christian God is a being of a terrific character—cruel, vindictive, capricious, and unjust.” After this eloquent condemnation of Christianity, Weinberg’s chapter “A Deadly Certitude” ends with an even sharper condemnation of Islam. The chapter is a review of Richard Dawkins’s book
The God Delusion
(2006). Weinberg concludes:

I find it ironic that Weinberg, after declaring so vehemently his hostility to religious beliefs, emerges in his writing about science as a
man of faith. He believes passionately in the possibility of a final theory. He wrote a book with the title
Dreams of a Final Theory
†
in which the notion of a final theory permeates his thinking. A final theory means a set of mathematical rules that describe with complete generality and complete precision the way the physical universe behaves. Complete generality means that the rules are obeyed everywhere and at all times. Complete precision means that any discrepancies between the rules and the results of experimental measurements will be due to the limited accuracy of the measurements.

For Weinberg, the final theory is not merely a dream to inspire his brilliant work as a mathematical physicist exploring the universe. For him it is an already existing reality that we humans will soon discover. It is a real presence, hidden in the motions of atoms and galaxies, waiting for us to find it. The faith that a final theory exists, ruling over the operations of nature, strongly influences his thinking about history and ethics as well as his thinking about science.

I have profound respect for Weinberg as a scientist. I also have profound respect for his faith, although I do not share it. I accept the possibility that he may be right and I may be wrong. I do not forget the disagreement we had forty-four years ago about a hypothetical particle called the W. In
chapter 21
I tell the story of this disagreement. The letter W does not stand for Weinberg, but it was Weinberg who imagined it before it was discovered. Weinberg believed that the W particle must exist, because he needed it as an essential component of the theory with which he unified the weak forces in nature. I believed that the W particle could not exist because its existence would contradict a mathematical argument that I held dear. His belief was based on physical intuition, mine on mathematical calculation. A few years later the W particle was directly observed. My mathematical
argument turned out to be irrelevant. I was happy to celebrate Weinberg’s triumph, and consoled myself with a quotation from my favorite poet, William Blake: “To be an Error and to be Cast Out is a Part of God’s Design.” Blake had another piece of wisdom, “Opposition is true Friendship,” which made it easy for us to remain friends. As members of the scientific community, we can disagree passionately about facts and theories and still be friends.

Since Weinberg was right about the W particle, why do I not believe that he is right about the final theory? I distrust his judgment about philosophical questions because I think he overrates the capacity of the human mind to comprehend the totality of nature. He has spent his professional life within the discipline of mathematical physics, a narrow area of science that has been uniquely successful. In this narrow area, our theories describe a small part of nature with astonishing clarity. Our ape brains and tool-making hands were marvelously effective for solving a limited class of puzzles. Weinberg expects the same brains and hands to illuminate far broader areas of nature with the same clarity. I would be disappointed if nature could be so easily tamed. I find the idea of a final theory repugnant because it diminishes both the richness of nature and the richness of human destiny. I prefer to live in a universe full of inexhaustible mysteries and to belong to a species destined for inexhaustible intellectual growth.

Isaac Newton, the scientist who took the biggest single step toward the understanding of nature, saw clearly how far he was from any final theory. “I do not know what I may appear to the World,” he wrote toward the end of his long life, “but to myself I seem to have been only like a boy playing on the seashore, and diverting myself in now and then finding a smoother pebble or a prettier shell than ordinary, whilst the great ocean of truth lay all undiscovered before me.”

Newton wrote more modestly than Weinberg of the ability of the
human mind to penetrate the mysteries of nature. Newton was a devout Christian, as dedicated to theology as he was to science. Newton was no fool.

Note added in 2014: Weinberg wrote in response to the review:

WHY SHOULD ANYONE
who is not a physicist be interested in Paul Dirac? Dirac is interesting for the same reasons that Albert 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 in 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
The Strangest Man: The Hidden Life of Paul Dirac, Mystic of the Atom
, a 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

In Farmelo’s book we see Dirac as a character in a human drama, carrying his full share of tragedy as well as triumph. He is as strange a figure as Einstein. He is less famous because he preferred to fight his battles alone.

The title,
The Strangest Man: The Hidden Life of Paul Dirac, Mystic of the Atom
, is not well chosen. The British edition published by Faber and Faber has a better title, with “Mystic of the Atom” replaced by “Quantum Genius.” Mystic and genius are not synonymous. The phrase “The Strangest Man” is a quote from Niels Bohr, the great Danish physicist who invited Dirac to visit his Institute for Theoretical Physics in Copenhagen in 1926 when Dirac was twenty-four years old. Bohr said many years later that Dirac was the strangest man who had ever come to his institute.

It was true that Dirac’s inner life was well hidden. He did not like to reveal what he was thinking, either about science or about himself. But Bohr did not say that Dirac was a mystic, and it is not true. Dirac was the opposite of a mystic. He worked in a straightforward way, trying out mathematical schemes to describe the way nature behaves. What was strange about Dirac was not mysticism but formidable concentration of attention upon a single problem. He was silent and aloof because he liked to think about one thing at a time. In his choice of problems to think about, he was guided by his ability to set aside irrelevancies, to see clearly what was important and what was not. For him, most of the subjects that people talk about in everyday conversation were irrelevant, and so his conversation was mostly silence.

Although Dirac spoke little about himself, he preserved almost all the letters and papers that he received from his family and friends, all
the way back to his childhood. These papers are now accessible in the Dirac archive at Florida State University. They provide a solid documentary basis for Farmelo’s biography. In spite of Dirac’s legendary silence, we know more about his early life than we know about his more talkative contemporaries. Farmelo also interviewed everyone still alive who had known Dirac, and obtained detailed accounts of rare conversations in which Dirac as an old man talked at length about his youth. The most dramatic of these conversations was reported by Kurt Hofer, a biologist colleague of Dirac at Florida State University. Farmelo places Hofer’s story at the beginning of his biography, emphasizing its importance for the understanding of Dirac’s struggles. The truth of the story is confirmed by other witnesses and documents.

Paul Dirac’s father was Charles Dirac, a Swiss schoolteacher who taught modern languages in the English city of Bristol. He was a capable but harsh teacher. Paul’s mother, Florence, was twelve years younger and dominated by her husband. Paul had an older brother, Felix, and a younger sister, Betty. According to Hofer, Charles made Paul’s life miserable by insisting that he speak only French at home and punishing him when he made grammatical mistakes. Since talking brought punishment, Paul acquired the habit of silence. Charles was habitually unfaithful to Florence, and the pair were barely on speaking terms. Paul was close to his mother, Betty to her father, and Felix to neither. Felix suffered acutely from comparisons with his brilliant brother. When Paul was twenty-three and Felix twenty-five, Felix killed himself. By that time Paul had escaped from the hate-filled home and enrolled with a scholarship at St. John’s College, Cambridge. Paul’s hatred of his father endured until he talked with Hofer more than fifty years later. Paul said, “I never knew love or affection when I was a child,” and speaking of his father, “I owe him absolutely nothing.”

In spite of these inner torments, Dirac had a remarkable talent for friendship. His closest friend at Cambridge was Peter Kapitza, the charismatic Russian experimental physicist who later won a Nobel Prize for discovering the superfluidity of liquid helium. Kapitza then lived and worked in England but spent his summers in Russia. Dirac several times went to Russia for long holidays with Kapitza and other Russian friends, climbing mountains and enjoying the comforts of Kapitza’s country club in the Crimea. Dirac also tried his hand at experimental work in Kapitza’s laboratory.