The Scientist as Rebel

by Freeman J. Dyson

  Galison uses the phrase “critical opalescence” to sum up the story of what happened in 1905 when relativity was discovered. Critical opalescence is a strikingly beautiful effect that is seen when water is heated to a temperature of 374 degrees Celsius under high pressure. 374 degrees is called the critical temperature of water. It is the temperature at which water turns continuously into steam without boiling. At the critical temperature and pressure, water and steam are indistinguishable. They are a single fluid, unable to make up its mind whether to be a gas or a liquid. In that critical state, the fluid is continually fluctuating between gas and liquid, and the fluctuations are seen visually as a multicolored sparkling. The sparkling is called opalescence because it is also seen in opal jewels which have a similar multicolored radiance.

  Galison uses critical opalescence as a metaphor for the merging of technology, science, and philosophy that happened in the minds of Poincaré and Einstein in the spring of 1905. Poincaré and Einstein were immersed in the technical tools of time signaling, but the tools by themselves did not lead them to their discoveries. They were immersed in the mathematical ideas of electrodynamics, but the ideas by themselves did not lead them to their discoveries. They were also immersed in the philosophy of space and time. Poincaré had written a philosophical book, Science and Hypothesis, which Einstein studied, digging deep into the foundations of knowledge and criticizing the Newtonian notions of absolute space and time. But the philosophy by itself did not lead them to their discoveries. What was needed to give birth to the theory of relativity was a critical moment, when tools, ideas, and philosophical reflections jostled together and merged into a new way of thinking. Galison would like to put an end to the argument between Kuhnians and Galisonians. In this book he takes his position squarely in the middle: “Attending to moments of critical opalescence offers a way out of this endless oscillation between thinking of history as ultimately about ideas or fundamentally about material objects.”

  The one question that Galison’s metaphor of critical opalescence does not answer is why Einstein discovered the theory of relativity as we know it and Poincaré did not. The theories discovered by Poincaré and Einstein were operationally equivalent, with identical experimental consequences, but there was one crucial difference. The difference was the use of the word “ether.” The wave theory of light, and the theories of electric and magnetic forces that were developed in the nineteenth century, were all based on the idea of ether. James Clerk Maxwell, who unified the theories of light and electromagnetism in 1865, was a firm believer in ether. Electric and magnetic forces behaved like mechanical stresses in a solid medium with suitable properties of rigidity and elasticity. Therefore, it was believed, a solid medium must exist, pervading the whole of space and carrying the electric and magnetic stresses. Light waves must be shear waves in the same elastic medium. The all-pervading solid medium was given the name “ether.”

  The essential difference between Poincaré and Einstein was that Poincaré was by temperament conservative and Einstein was by temperament revolutionary. When Poincaré looked for a new theory of electromagnetism, he tried to preserve as much as he could of the old. He loved the ether and continued to believe in it, even when his own theory showed that it was unobservable. His version of relativity theory was a patchwork quilt. The new idea of local time, depending on the motion of the observer, was patched onto the old framework of absolute space and time defined by a rigid and immovable ether. Einstein, on the other hand, saw the old framework as cumbersome and unnecessary and was delighted to be rid of it. His version of the theory was simpler and more elegant. There was no absolute space and time and there was no ether. All the complicated explanations of electric and magnetic forces as elastic stresses in the ether could be swept into the dustbin of history, together with the famous old professors who still believed in them. All local times were equally valid. In order to calculate with Einstein’s version of relativity, all you needed to know was the rule for transforming from one local time to another. In the competition for public recognition, the clarity and simplicity of Einstein’s argument gave him an overwhelming advantage.

  Poincaré and Einstein only met once, at a conference in Brussels in 1911. The meeting did not go well. Einstein afterward reported his impression of Poincaré: “Poincaré was simply negative in general, and, all his acumen notwithstanding, he showed little grasp of the situation.” So far as Einstein was concerned, Poincaré belonged with the ether in the dustbin of history. But Einstein underestimated Poincaré. Einstein did not know that Poincaré had just then written a letter recommending him for a professorship at the Swiss Federal Institute of Technology in Zürich. Here is what Poincaré had to say about Einstein:

  What we must above all admire in him, is the facility with which he has adapted to new conceptions and from which he knows how to draw the consequences. He does not remain attached to classical principles, and, in the presence of a problem of physics, is prompt to envision all the possibilities.… The future will show more and more the value of Mr. Einstein, and the university that finds a way to secure this young master is assured of drawing from it great honor.

  Poincaré bore no grudge against his young rival. He was still driven by the same generous impulse that made him rush into the coal mine at Magny thirty-two years earlier. A year after the meeting with Einstein in Brussels, Poincaré was dead. Einstein never saw Poincaré’s letter and never knew that he had misjudged him.

  Looking back upon this history, I disagree with Galison’s conclusion. I do not see critical opalescence as a decisive factor in Einstein’s victory. I see Poincaré and Einstein equal in their grasp of contemporary technology, equal in their love of philosophical speculation, unequal only in their receptiveness to new ideas. Ideas were the decisive factor. Einstein made the big jump into the world of relativity because he was eager to throw out old ideas and bring in new ones. Poincaré hesitated on the brink and never made the big jump. In this instance at least, Kuhn was right. The scientific revolution of 1905 was driven by ideas and not by tools.3

  1. Norton, 2003.

  2. A.K. Peters, 2002.

  3. The theme of this review, the question whether tools or ideas were dominant in the revolution of 1905, is discussed in a wider context in the chapter “Scientific Revolutions” in my book The Sun, the Genome and the Internet (Oxford University Press, 1999). There I came to the conclusion that the majority of revolutions are tool-driven, the revolution of 1905 being one of the notable exceptions.

  19

  THE WORLD ON A STRING

  IN THE GOLDEN years of the Liberal Party in England, before the First World War, Herbert Asquith was the patrician prime minister and Winston Churchill was an obstreperous young politician. At question time in the House of Commons, Churchill frequently challenged Asquith with provocative statements and awkward questions. After one of these Churchillian assaults, Asquith lamented, “I wish I knew as much about anything as that young man knows about everything.” Reading The Fabric of the Cosmos: Space, Time, and the Texture of Reality,1 this eloquent book in which Brian Greene lays out before us his vision of the cosmos, I feel some sympathy for Asquith. Asquith expresses my reaction to the book precisely.

  I recommend Greene’s book to any nonexpert reader who wants an up-to-date account of theoretical physics, written in colloquial language that anyone can understand. For the nonexpert reader, my doubts and hesitations are unimportant. It is not important whether Greene’s picture of the universe will turn out to be technically accurate. The important thing is that his picture is coherent and intelligible and consistent with recent observations. Even if many of the details later turn out to be wrong, the picture is a big step toward understanding. Progress in science is often built on wrong theories that are later corrected. It is better to be wrong than to be vague. Greene’s book explains to the nonexpert reader two essential themes of modern science. First it describes the historical path of observation and theory that led from Newton and Gali
leo in the seventeenth century to Einstein and Stephen Hawking in the twentieth. Then it shows us the style of thinking that led beyond Einstein and Hawking to the fashionable theories of today. The history and the style of thinking are authentic, whether or not the fashionable theories are here to stay.

  In his book The Elegant Universe, published in 1999, Greene gave us a more detailed and technical account of string theory, the theory to which his professional life as a physicist has been devoted. The earlier book was remarkably successful in translating the abstruse and abstract ideas of string theory into readable prose. Early in his new book he gives a brief summary of string theory as he expounded it in The Elegant Universe:

  Superstring theory starts off by proposing a new answer to an old question: what are the smallest, indivisible constituents of matter? For many decades, the conventional answer has been that matter is composed of particles—electrons and quarks—that can be modeled as dots that are indivisible and that have no size and no internal structure. Conventional theory claims, and experiments confirm, that these particles combine in various ways to produce protons, neutrons, and the wide variety of atoms and molecules making up everything we’ve ever encountered.

  Superstring theory tells a different story. It does not deny the key role played by electrons, quarks, and the other particle species revealed by experiment, but it does claim that these particles are not dots. Instead, according to superstring theory, every particle is composed of a tiny filament of energy, some hundred billion billion times smaller than a single atomic nucleus (much smaller than we can currently probe), which is shaped like a little string. And just as a violin string can vibrate in different patterns, each of which produces a different musical tone, the filaments of superstring theory can also vibrate in different patterns. But these vibrations don’t produce different musical notes; remarkably, the theory claims that they produce different particle properties. A tiny string vibrating in one pattern would have the mass and the electric charge of an electron; according to the theory, such a vibrating string would be what we have traditionally called an electron. A tiny string vibrating in a different pattern would have the requisite properties to identify it as a quark, a neutrino, or any other kind of particle. All species of particles are unified in superstring theory since each arises from a different vibrational pattern executed by the same underlying entity.

  This is a fine beginning for a theory of the universe, and maybe it is true. To be useful, a scientific theory does not need to be true, but it needs to be testable. My doubts about string theory arise from the fact that it is not at present testable. Greene discusses in his Chapters 13 and 14 the prospects for experimental tests of the theory. The experiments that he describes will certainly open new doors to the understanding of nature, even if they do not answer the question whether string theory is true.

  The Fabric of the Cosmos covers a wider field than The Elegant Universe and paints it with a broader brush. There is not much overlap between the two books. Only Chapter 12 of the new book, which summarizes the earlier book and gives us the gist of string theory without the details, overlaps strongly. Greene himself suggests that readers who have read The Elegant Universe should skim through Chapter 12. Except for this chapter, the two books cover different subjects and can be read independently. Neither is a prerequisite for reading the other. The new book is easier, and should preferably be read first. Readers who got stuck halfway through The Elegant Universe may find the new book more digestible.

  In the history of science there is always a tension between revolutionaries and conservatives, between those who build grand castles in the air and those who prefer to lay one brick at a time on solid ground. The normal state of tension is between young revolutionaries and old conservatives. This is the way it is now, and the way it was eighty years ago when the quantum revolution happened. I am a typical old conservative, out of touch with the new ideas and surrounded by young string theorists whose conversation I do not pretend to understand. In the 1920s, the golden age of quantum theory, the young revolutionaries were Werner Heisenberg and Paul Dirac, making their great discoveries at the age of twenty-five, and the old conservative was Ernest Rutherford, dismissing them with his famous statement, “They play games with their symbols but we turn out the real facts of Nature.” Rutherford was a great scientist, left behind by the revolution that he had helped to bring about. That is the normal state of affairs.

  Fifty years ago, when I was considerably younger than Greene is now, things were different. The normal state of affairs was inverted. At that time, in the late 1940s and early 1950s, the revolutionaries were old and the conservatives were young. The old revolutionaries were Albert Einstein, Dirac, Heisenberg, Max Born, and Erwin Schrödinger. Every one of them had a crazy theory that he thought would be the key to understanding everything. Einstein had his unified field theory, Heisenberg had his fundamental length theory, Born had a new version of quantum theory that he called reciprocity, Schrödinger had a new version of Einstein’s unified field theory that he called the Final Affine Field Laws, and Dirac had a weird version of quantum theory in which every state had probability either plus two or minus two. Probability, as common sense defines it, is a number between zero and one expressing our degree of confidence that an event will happen. Probability one means that the event always happens; probability zero means that it never happens. In Dirac’s Alice-in-Wonderland world, every state happens either more often than always or less often than never. Each of the five old men believed that physics needed another revolution as profound as the quantum revolution that they had led twenty-five years earlier. Each of them believed that his pet idea was the crucial first step along a road that would lead to the next big breakthrough.

  Young people like me saw all these famous old men making fools of themselves, and so we became conservatives. The chief young players then were Julian Schwinger and Richard Feynman in America and Sin-Itiro Tomonaga in Japan. Anyone who knew Feynman might be surprised to hear him labeled a conservative, but the label is accurate. Feynman’s style was ebullient and wonderfully original, but the substance of his science was conservative. He and Schwinger and Tomonaga understood that the physics they had inherited from the quantum revolution was pretty good. The physical ideas were basically correct. They did not need to start another revolution. They only needed to take the existing physical theories and clean up the details. I helped them with the later stages of the cleanup. The result of our efforts was the modern theory of quantum electrodynamics, the theory that accurately describes the way atoms and radiation behave.

  This theory was a triumph of conservatism. We took the theories that Dirac and Heisenberg had invented in the 1920s, and changed as little as possible to make the theories self-consistent and user-friendly. Nature smiled on our efforts. When new experiments were done to test the theory, the results agreed with the theory to eleven decimal places. But the old revolutionaries were still not convinced. After the results of the first experiments had been announced, I brashly accosted Dirac and asked him whether he was happy with the big success of the theory that he had created twenty-five years earlier.

  Dirac, as usual, stayed silent for a while before replying. “I might have thought that the new ideas were correct,” he said, “if they had not been so ugly.” That was the end of the conversation. Einstein too was unimpressed by our success. During the time that the young physicists at the Institute for Advanced Study in Princeton were deeply engaged in developing the new electrodynamics, Einstein was working in the same building and walking every day past our windows on his way to and from the institute. He never came to our seminars and never asked us about our work. To the end of his life, he remained faithful to his unified field theory.

  Looking back on this history, I feel no shame in being a conservative today. I belong to a generation that saw conservatism triumph, and I remain faithful to our ideals just as Einstein remained faithful to his. But now my generation is passing from the scene, and I
am wondering what the next cycle of history will bring. After the revolutionaries of string theory have grown old, what will the next generation think of them? Will there be another generation of young revolutionaries? Or shall we again have an inversion of the normal state of things, with a new generation of young conservatives in rebellion against the elderly pioneers of string theory? My generation will not be around to see these questions answered.

  One of the main themes in Greene’s book is the disconnect between Einstein’s theory of general relativity and quantum mechanics, the two discoveries that revolutionized physics at the beginning of the twentieth century. Einstein’s theory is primarily a theory of gravity, describing the gravitational field as a curvature of space-time, and describing the fall of an apple as the response of the apple to the curvature of space-time induced by the mass of the earth. Einstein’s theory treats the apple and the earth as classical objects with precisely defined positions and velocities, paying no attention to the uncertainties introduced by quantum mechanics. The apple and the earth are large enough so that the quantum uncertainties are negligible.

  On the other hand, quantum mechanics describes the behavior of atoms and elementary particles, for which the quantum uncertainties have a dominating influence, and pays no attention to gravity. The atoms and particles are small enough so that any gravitational fields that they induce are negligible. The two theories divide the universe of physics between them without overlapping, general relativity taking care of large objects from apples to galaxies, and quantum mechanics taking care of small objects from molecules to light-quanta. General relativity is important for astronomy and cosmology, while quantum mechanics is important for atomic physics and chemistry. This division of the universe works well for all practical purposes. It works well because the gravitational effects of single atoms or particles are unobservably small.