The Scientist as Rebel (29 page)

Greene said his confidence in our ability to find the fundamental laws is based on the marvelous fact that the laws of nature are simple and beautiful. The history of physics shows that this is true of all the laws that we have discovered in the past. We did not need to do unending experiments to discover the laws. We guessed the laws by looking for equations which had the greatest mathematical simplicity and beauty. Then only a few experiments were needed to test the equations and find out whether we guessed right. This happened over and over again, first with Newton’s laws of motion and gravitation, then with Maxwell’s equations of electromagnetism, then with Einstein’s equations of special and general relativity, then with Schrödinger’s and Dirac’s equations of quantum mechanics. Now with string theory the game is almost over. The mathematical beauty of this theory is so compelling that it has to be right, and if it is right it explains everything from particle physics to cosmology.

Since I am reconstructing Greene’s argument from memory, it is possible that I am exaggerating the claims that he was making for theoretical physics. One thing that I remember clearly is the phrase
“We are done.” I still hear him saying, “We are done,” in a tone of triumphant finality.

I began my reply by saying that nobody denies the amazing success of theoretical physics in the last four hundred years. Nobody denies the truth of Einstein’s triumphant words: “The creative principle resides in mathematics. In a certain sense, therefore, I hold it true that pure thought can grasp reality, as the ancients dreamed.” It is true that the fundamental equations of physics are simple and beautiful, and that we have good reason to expect that the equations still to be discovered will be even more simple and beautiful. But the reduction of other sciences to physics does not work. Chemistry has its own concepts, not reducible to physics. Biology and neurology have their own concepts not reducible to physics or to chemistry. The way to understand a living cell or a living brain is not to consider it as a collection of atoms. Chemistry and biology and neurology will continue to advance and to make new fundamental discoveries, no matter what happens to physics. The territory of new sciences, outside the narrow domain of theoretical physics, will continue to expand.

Theoretical science may be divided roughly into two parts, analytic and synthetic. Analytic science reduces complicated phenomena to their simpler component parts. Synthetic science builds up complicated structures from their simpler parts. Analytic science works downward to find the fundamental equations. Synthetic science works upward to find new and unexpected solutions. To understand the spectrum of an atom, you needed analytic science to give you Schrödinger’s equation. To understand a protein molecule or a brain, you need synthetic science to build a structure out of atoms or neurons. Greene was saying, only analytic science is fundamental. I said, on the contrary, good science requires a balance between analytic and synthetic tools, and synthetic science becomes more and more creative as our knowledge increases.

Another reason why I believe science to be inexhaustible is Gödel’s theorem. The mathematician Kurt Gödel discovered and proved the
theorem in 1931. The theorem says that given any finite set of rules for doing mathematics, there are undecidable statements, mathematical statements that cannot either be proved or disproved by using these rules. Gödel gave examples of undecidable statements that cannot be proved true or false using the normal rules of logic and arithmetic. His theorem implies that pure mathematics is inexhaustible. No matter how many problems we solve, there will always be other problems that cannot be solved within the existing rules. Now I claim that because of Gödel’s theorem, physics is inexhaustible too. The laws of physics are a finite set of rules, and include the rules for doing mathematics, so that Gödel’s theorem applies to them. The theorem implies that even within the domain of the basic equations of physics, our knowledge will always be incomplete.

I ended by saying that I rejoiced in the fact that science is inexhaustible, and I hoped the nonscientists in the audience would rejoice too. Science has three advancing frontiers that will always remain open. There is the mathematical frontier, which will always remain open thanks to Gödel. There is the complexity frontier, which will always remain open because we are investigating objects of ever-increasing complexity, molecules, cells, animals, brains, human beings, societies. And there is the geographical frontier, which will always remain open because our unexplored universe is expanding in space and time. My hope and my belief is that there will never come a time when we shall say, “We are done.”

After Greene’s opening statement and my reply, the debate in Davos continued with additional remarks from us and questions from the audience. His new book and my review are a further continuation of the same debate. In the review, as in the debate, I have emphasized the points on which Greene and I disagree. There is no space here to enumerate the many points on which we agree. For both of us the most important and exciting fact is that during the last twenty years cosmology became an observational science. During the last five years,
the Wilkinson Microwave Anisotropy Probe (
WMAP
) satellite, an orbiting radio telescope designed by my friend David Wilkinson in Princeton, has given us more detailed and precise information about the history and structure of the cosmos than all earlier telescopes combined.

Observational cosmology has now entered its golden age, with the WMAP satellite continuing to scan the sky and with a variety of even more sensitive telescopes under construction. During the next decade we shall learn far more about the cosmos than we know today, and we shall probably find new mysteries to replace those that we shall solve. Greene and I agree that so long as observers continue to explore, cosmology will continue to deepen our understanding of where we stand and how we came to be.

After this review was published, Brian Greene wrote me a friendly letter, thanking me for the review but saying that my recollection of his remarks in the Davos debate was wrong. Since I have no wish to perpetuate errors, I deleted from this version of the review the sentences to which he objected. As a result, what is left of his remarks does not put his case forcefully. To set the record straight, here is an extract from his letter: “What I did say in Davos is that the search for the elementary ingredients making up the universe and the deepest laws governing their interactions may be a search that one day draws to a close. The deeper we look, the simpler and more unified the laws become, and there may well be a limit to this process. However, achieving this goal would only mean that we were done with one fantastically interesting but limited chapter in human exploration, the search for the basic constituents and underlying laws.”

I DIVIDE THIS
chapter into three parts, the first about J. Robert Oppenheimer as a scientist, the second about Robert as an administrator, the third about Robert as a poet. To make the story complete there should be a part about Robert as a statesman, but that would require another chapter as long as this one. I won’t stick rigidly to these boundaries. I want to let Robert speak for himself as much as possible. The best part of the chapter will be direct quotes from Robert and others, telling us the story of his life as they saw it.

I begin in September 1938 with a story told by Robert Serber, the same Serber who appears in the movie
The Day After Trinity
. I owe this story to David Trulock, a friend of mine in Texas. The two Roberts, Serber and Oppenheimer, were at a meeting of theoretical physicists in Vancouver. The entertainment during the meeting included a boat ride among the islands offshore. The day was foggy, and navigation among the islands was done by the pilot blowing a whistle and listening for the echo. Someone asked what the consequences for physics would be if this boatload of theorists sank. Oppenheimer instantly replied, “It wouldn’t do any permanent good.”

One year later, on September 1, 1939, Hitler invaded Poland and started the Second World War. On that day, issue number 5 of Volume 55 of the
Physical Review
was published, containing two papers of historic importance. The first was entitled “The Mechanism of Nuclear Fission,” by Niels Bohr and John Wheeler, twenty-five pages long, containing a complete and thorough theoretical explanation of the process of nuclear fission that had been discovered in Germany only nine months earlier. The second was entitled “On Continued Gravitational Contraction,” by J. Robert Oppenheimer and Hartland Snyder, only four pages long, containing an equally thorough theoretical explanation of the objects that we now call black holes.

Here is the abstract of the Oppenheimer-Snyder paper, with some technical details omitted:

The paper is written in the same unsensational style as the abstract. Oppenheimer and Snyder did not conclude their paper by saying, “It has not escaped our notice that these collapsed objects may play a fundamental role in the dynamics and evolution of the universe,” as Francis Crick and James Watson similarly said fourteen years later at the conclusion of a similar paper.

Black holes are familiar objects to modern astronomers. We know
that they exist all over our own galaxy and in the central regions of other galaxies. We see them as sources of X-ray radiation emitted by gas as it falls into them and is heated to temperatures of millions of degrees by their overwhelmingly strong gravity. At the center of our own galaxy we see a black hole weighing as much as a few million suns, with massive stars orbiting around it like moths around the flame of a candle. Black holes are not rare, and they are not an accidental embellishment of our universe. They are a fundamental driving force of its evolution. They are a dominant source of energy. For every ounce of matter consumed, they yield more than ten times as much energy as the nuclear reactions of fusion and fission that cause our sun to shine and our hydrogen bombs to explode. To a modern astronomer, a universe without black holes makes no sense.

To a modern physicist, black holes are also objects of transcendent beauty. They are the only places in the universe where Einstein’s theory of general relativity shows its full power and glory. Here, and nowhere else, space and time lose their individuality and merge together into a sharply curved four-dimensional structure precisely delineated by Einstein’s equations. If you imagine yourself falling into a black hole, your local perception of space and time will be detached from the space and time of an observer watching you from outside. While you see yourself falling smoothly into the hole without any deceleration, the outside observer sees you coming to a halt at the horizon of the hole and remaining forever in a state of permanent free fall. Permanent free fall is a situation that can only exist by virtue of the distortion of space and time predicted by Einstein’s theory.

This is the central paradox of Robert’s life as a scientist. His theoretical prediction of black holes was by far his greatest scientific achievement, fundamental to the modern development of relativistic astrophysics, and yet he never showed the slightest interest in following it up. So far as I can tell, he never wanted to know whether black holes actually existed. I tried sometimes to talk with him about
the possibilities for observing black holes and testing his theory. He impatiently changed the subject and talked about something else. I also met Hartland Snyder from time to time at the Brookhaven National Laboratory where he spent most of his life. He too was uninterested in black holes. He had a distinguished career as a designer of accelerators.

We now know that the Oppenheimer-Snyder calculation is correct and describes what happens to massive stars at the end of their lives. It explains why black holes are abundant, and incidentally confirms the truth of Einstein’s theory of general relativity. And still, Robert was not interested. The question remains: How could he have been blind to the importance of his greatest discovery? I have no answer to this question. It remains as a paradox in the life of a genius. Perhaps if the Oppenheimer-Snyder calculation had not happened to coincide in time with the Bohr-Wheeler theory of nuclear fission and with the outbreak of World War II, Robert would have paid more attention to it.

I do not have much firsthand experience of Robert as administrator. My chief witness here is Lansing Hammond, a friend of mine who worked for the Harkness Foundation. In 1947, when I came to the United States from England, Hammond was in charge of programs and placements for the Commonwealth Fund Fellows. In those days, Commonwealth Fund Fellows were young Brits who came to America to study at American universities with fund support. I was one of them, and Hammond made the arrangements for me to come first to Cornell University and then to the Institute for Advanced Study at Princeton. Thirty years later, in 1979, Hammond wrote me a letter about Oppenheimer. I replied to his letter, “It is sad that in the official
memorials to Robert there was never anything said or written that gave such a fine impression of Robert in action. I hope there may still be a chance sometime to make your story public.” Hammond died a few years later. Here is his story: