IN THE SPRING OF 1981 there was a symposium at the Rockefeller Uni-

versity in New York in honor of Andrei Sakharov's 60th birthday. (Sakharov was born in Moscow on May 21, 1921.) It was a memorable occasion because not only were Sakharov's contributions to human rights celebrated but also one was able to get a real sense of what he had done as a physicist. I think that what many of us felt was, as is so often the case, best articulated by the Nobelist I.I. Rabi. As he was leaving, Rabi said to me, "Gee, I had no idea that he was such a good physicist." Since the symposium, I have thought about Rabi's remark a good deal. It catches what may be the real tragedy of Sakharov's current martyrdom in Gorki where he is under house arrest and deprived of the books, papers and scientific contacts that are so necessary to a physicist's working life. The tragedy is that Sakharov may lose his identity as an extraordinarily creative scientist, something which is, I am sure, most precious to him. In the end he may be remembered only as the courageous, martyred figure from Gorki. All of us know, for example, of Galileo's trials with the Catholic Church, but how many of us know the extent of his contributions to science?

For this reason this collection of Sakharov's work--all of it translated into English--is especially valuable. One can really see what the man did, and because of the excellent commentary by some of the best and most active physicists in comparable fields, one gets a sense of how that work fits into recent developments in physics. I found these commentaries extremely useful because, although I am a physicist with a professional interest in some of the areas that Sakharov has worked in, many of his papers are hard going. This is, I think, for two reasons. In the first place, as physicists go, Sakharov tends to be very elliptical in his writing style. Very few results are derived in detail and if one wanted to reproduce them one would have to do Sakharov's calculations for oneself. A mathematics teacher of mine once said "Mathematics is not like The New York Times. We do not give all the 'news that's fit to print.' " Well, some do and some don't, and Sakharov doesn't. In the second place, and this I will discuss in more detail shortly, many of these articles were extremely prescient. Work done, say in 1966, has only now been fitted into the mainstream. Therefore reading these papers is like looking at unframed art. Many of them were completely unappreciated when they were written and even reading them now one is constantly confronted with very modern ideas put in an oddly archaic language. It is almost as if one had done an excavation of one of the Trojan cities and had come across a spaceship.

Sakharov's work covers a very wide range of physics but I will focus on only two groups of papers; those having to do with controlled thermonuclear fusion and those having to do with cosmology. I make this choice for two reasons. In the first place these are the two areas of his work that I understand the best and, in the second place, I think, and, of course, I may be wrong, that his papers in these two disciplines are the most significant of his oeuvre.

Sakharov's work on controlled nuclear fusion was certainly a corollary of his work on the hydrogen bomb. He is credited with having independently discovered the so- called Ulam-Teller trigger--the method of igniting light elements such as hydrogen in an uncontrolled series of fusion reactions, i.e. a hydrogen bomb, by using the energy of an exploding nuclear fission bomb. For this book Sakharov has written a brief autobiography, and it contains the following laconic statement about the Soviet hydrogen bomb project: "We were all convinced of the vital importance of our work for establishing a worldwide military equilibrium, and we were attracted by its scope." Teller and Ulam, at about the same time, were doing the same work here because of fear of the Russians and because, in Oppenheimer's phrase, it became "technically sweet." The British physicist who performed the same job for the British told me he did it partly because of the intellectual challenge and partly because he thought the British were being denied their fair share of our atomic secrets. The French did it, no doubt, for similar reasons and the Chinese did it because of fear of the Russians and ourselves. If only all of these well-meaning individuals could have sat down in a room together before engaging in this exercise and discussed why they were setting out to do what they did, we might all now be sleeping somewhat more soundly.

Like our people, and the British, Sakharov's colleagues began thinking about using the same reactions in a controlled way to produce energy. This work, which was done in secret by all the countries concerned, was declassified in 1958 and for the first time we, and the Russians, were able to see what each other had been up to. In an extremely lucid commentary to Sakharov's articles on fusion Harold Furth, the director of the Princeton Plasma Fusion Laboratory, notes the "remarkable degree of resemblance" among the different fusion programs revealed by the declassification. The Soviet effort was summarized in a three-part paper written jointly by Sakharov and his teacher I.E. Tamm. The part reproduced in the book was written by Sakharov alone and it outlines what is now considered to be the most promising fusion reactor--the so-called tokomak, which, one gathers, Sakharov must have invented. In devices like this a "plasma" (i.e. aagas consisting of atomic nuclei and electrons) of light elements is confined by suitably shaped magnetic fields and heated to something like 100 million degrees centigrade. (For comparison the interior temperature of the sun is "only" about 14 million degrees.) In Sakharov's device the plasma is confined in a doughnut-shaped vacuum chamber. If the plasma can be held together long enough--a fraction of a second--it will begin to "burn" by the nuclear fusion reactions, and this energy can be siphoned off to make, for example, electricity.

What is most impressive about Sakharov's paper is that not only did he think up the idea of confined hot plasmas within such a torroidal chamber but he also realized what was wrong with the idea and how to go about fixing it. It was as if he was playing a game of mental chess with himself. What is wrong with the naive idea is that the plasma particles will leak out to the surface of the doughnut, cool off and the whole reaction will come to an abrupt stop. To deal with this problem Sakharov proposed using the plasma particles themselves as a sort of electrical conducting wire which would produce a second magnetic field and so confine the plasma. This idea seems to work and machines using it are now available, especially at Princeton, which bring the prospect of practical fusion if not within hailing distance, at least somewhere on the horizon. It is possible, given the intense activity in this field of physics, that someone else would have come up with these ideas sooner or later but the fact remains it was Sakharov and his teacher Tamm who did come up with them.

The second area of work I want to describe is about as far removed from "practical" physics as it is possible to imagine. This has to do with Sakharov's contributions to modern cosmology--the study of the origin and evolution of the universe. At the present time this is one of the most active disciplines in all of physics and astronomy. Since the discovery in 1965 by Arno Penzias and Robert Wilson of the Bell Labs of the so-called background radiation which is, one believes, a "fossil" left over from the Big Bang which took place some 12 billion years ago, there has developed what is known as a "standard cosmology." The physics of this cosmology uses almost everything we have learned from Einstein's general theory of relativity to the modern theory of the quark. It attempts to deal with such questions as why, out of any average 100 atoms in the universe, about seven are helium atoms. Remarkably, standard cosmology can give a very good account of this seven and explain why it is not 14 or 31.

An even deeper question is why is there any matter at all. A much more naturally symmetric situation would be one with an identical amount of matter and anti-matter. But in the early universe the matter and anti-matter would have been in a dense compressed state and would have annihilated into radiation. This is very nearly what did happen, since the amount of radiation in the universe is about a 100 billion times as great as the amount of matter. In some sense, that we are here at all seems like a sort of an accident. It was to explain this "accident" that Sakharov wrote a brief but remarkably far- seeing paper in 1966. The paper set out the essential ingredients for the solution of this problem. Among them was the idea that particles like protons, which were always thought to be the absolutely stable building blocks of matter, might in fact spontaneously disintegrate, but at a very slow rate. At the time, this and the other parts of Sakharov's solution, seemed so arbitrary that his paper was largely ignored. However, in recent years a whole theoretical context has developed --what are known as "grand unified gauge theories"--in which all of Sakharov's ideas fall naturally. What he had done was to enumerate the necessary conditions for solving the problem and then in the next decade or so a theory was found that fulfilled his general scheme. Experiments are now under way to see if the proton actually does decay.

To have seen what was needed before there was such a theory is, in my view, a totally remarkable demonstration of scientific imagination. It is somewhat comparable to Von Neumann's enumeration of what would be necessary to solve the problem of biological heredity-- from his work on self-replicating automata--before the structure and function of DNA and RNA were revealed.

In 1979 Sakharov wrote a paper in which he brought his ideas up to date and recast them in the modern idiom. He appended to this note a brief addition written, presumably, for this volume. To complete this addition he needed a reference to a book. He writes, "I do not remember the exact name of the book, and in Gorki I have nowhere to look." What the Soviet Union has to gain by keeping this great scientist locked up in Gorki without the use of a decent library, and all the rest, one cannot begin to imagine. It is the act of a mean spirited, primitive society. At the very least let the man emigrate. His continued imprisonment in Gorki does nothing but bring continued disgrace to the country of his birth.