Explaining the Universe

A Brief History of Time: From the Big Bang to Black Holes.
by Stephen W. Hawking.
Bantam Books. 198 pp. $18.95.

The title of Stephen Hawking’s new book is unduly modest. A Brief History of Time is indeed brief, but it is considerably more than a history and it deals with a far wider range of topics than time. What Hawking has written is a concise, firsthand account of current scientific thinking regarding the nature of the universe as a whole, enlivened by his own insights into recent developments in the theories of general relativity and quantum mechanics.

Hawking himself is responsible for many of those developments. One of the world’s premier mathematical physicists, he holds the Lucasian Chair of Mathematics at Cambridge University, a position once occupied by Sir Isaac Newton. Here he shows not only a formidable command of the technicalities of the subject matter, but an ability to communicate that is notable for its nontechnical clarity and accessibility to the lay reader.

This combination of scientific creativity and literary ability, while by no means common, is not unique. What definitely is unique is the incredible degree of struggle that has characterized Hawking’s career. A glance at the book’s cover photo gives a hint of the effort that has been entailed not only in his achieving professional eminence but even in his being able to marry and raise a family. In the photograph, Hawking is shown against the background of a star-filled sky. The wheelchair in which he is seated, his wasted frame, his hunched posture all testify to the effects of amyotrophic lateral sclerosis, the progressively crippling Lou Gehrig’s disease from which the forty-six-year-old scientist has suffered for a quarter of a century. Just the production of this book entailed a staggering effort, for ever since a 1985 bout with pneumonia destroyed his already limited ability to speak, Hawking has been able to communicate with the outside world only by means of a computer.

It is not surprising, then, that much of the attention that has deservedly been paid to A Brief History of Time, Hawking’s most popular work and an atypical bestseller, has focused on the author and his handicap. Nor is this necessarily inappropriate. Even though scientists have traditionally insisted on the subordination of personality to the objective communication of results, Hawking refers frequently in this book to his handicap, often in joking asides; moreover, knowledge of his condition helps us appreciate the personality that lies behind some of the most significant, and surprising, advances in physics in recent years.

Hawking’s central theme is that the dogged pursuit of consistency, both between theory and observation and among different parts of the same theory, will eventually lead to a full understanding of the universe. Indeed, his scientific contributions as a whole have been characterized by an extraordinary intellectual determination to follow ideas to their logical conclusion, no matter how absurd that conclusion may at first appear.

Hawking is keenly aware that even the giants Newton and Einstein failed to pursue some far-reaching implications of their own insights. Newton did not realize that according to his theory of gravitation, a universe that was both infinite and unchanging could not exist: the force of gravity would inevitably cause it to collapse on itself. In fact, it took some 300 years before this was appreciated. And when at last Albert Einstein superseded Newton’s theory with his General Theory of Relativity, according to which the universe would tend either to expand or contract spontaneously, he too assumed that the equations showing this result would have to be modified to allow for a static solution. (Einstein later declared this the worst mistake he ever made.)

According to Hawking, it was Edwin Hubble’s 1929 discovery that the universe was expanding which, by destroying Newton’s long-held assumption, began the modern study of cosmology and eventually led to general agreement that the universe came into existence at a definite time in the past. In simple terms, the beginnings of the current expansion can be traced back to a cataclysmic explosion, popularly known as the big bang. This was the moment of creation, the origin of the universe and of space and time. Depending on how much matter there may be in the universe (an issue of considerable dispute), the resulting expansion may either continue until eternity or reverse itself some time in the future, shrinking the universe until it once again approaches a state of infinite density—the “big crunch”—and the end of time as we know it.

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Until the mid-1960’s, the study of the origin of the universe remained something of a backwater within the field of astrophysics. An inconclusive debate pitted followers of the big-bang theory against others who believed on philosophical grounds that the expanding universe was kept in a steady state of constant average density by the continuous creation of matter at a slow rate. The latter theory was largely abandoned after 1965, about the same time Hawking was starting his career as a graduate student. As he describes it, having already survived longer than the two years’ life expectancy he had been granted when his physical condition was first diagnosed, he had decided to marry and needed a Ph.D. to get a job. He came across an interesting thesis topic dealing with black holes, then a considerably more arcane topic than it was subsequently to become (thanks in no small part to Hawking himself).

Hawking’s adviser, Roger Penrose, had shown that the collapse of a sufficiently massive star, the atomic structure of which was not strong enough to resist its own gravitational attraction, would result in a black hole. This, as devotees of popular science-fiction know, is a gravitational singularity occupying zero volume which is able to absorb anything closely approaching it but from which neither matter nor light can escape. Hawking soon realized that the logic of Penrose’s argument could be reversed. In the first of his notable contributions, he proved that if the universe were indeed expanding, it must have originated in a gravitational singularity: the big bang.

Meanwhile, researchers in other branches of physics were also looking more closely into the early behavior of the universe. According to theories emerging in the 1960’s and 70’s, the subatomic particles—protons and neutrons—known since the early days of nuclear physics, were in fact made up of still more fundamental entities—quarks—which had the disconcerting property of being undetectable in isolation. To prove these new theories, it would be necessary to observe what happened to such subnuclear particles at extremely high energies, when (it was predicted) the considerable differences observed in their behaviors under normal conditions would disappear. Unfortunately, as Hawking remarks in one of his driest asides, an accelerator powerful enough to test the new theories “would have to be as big as the solar system—and would be unlikely to be funded in the present economic climate.”

But there could be a substitute for such an experimental test: one could predict the composition of today’s universe by making calculations on the basis of what should have happened immediately after the big bang, when both the density and temperature of the universe were sufficiently high. Considerations along these lines led to an ever growing acceptance both of the big-bang theory itself and of the unified theories of elementary particle physics.

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In the 1970’s, Hawking, who sometimes seems to be the Indiana Jones of mathematical physics, moved on to even less charted territory, the no-man’s land between the theory of relativity, which deals with the universe on the largest scale, and the theory of quantum mechanics, which deals with the most microscopic aspect of reality. A reconciliation of these two theories, which in their present forms are inconsistent, is a prerequisite for a uniform theory covering all the laws of nature, the ultimate goal of physics.

There is a fundamental point of difference between classical physics, with its assumption of a strictly deterministic relationship between present and future, and quantum mechanics, where even in principle our knowledge can be no better than statistical. That point of difference is closely related to the Uncertainty Principle enunciated by the 20th-century German physicist Werner Heisenberg. To invoke the most familiar illustration of that principle, we cannot exactly specify both the position and the momentum of a particle: in other words, the more certain we are of the location of an object at one instant, the less we know about where it will be the next. Another less well known but equally surprising consequence of the Uncertainty Principle is that even a perfect vacuum is full of rapidly fluctuating electric and magnetic fields.

In the course of a dispute over thermodynamics, Hawking took note of this second consequence, and he was led by it to the totally unexpected, indeed shocking, conclusion that black holes, which supposedly can only absorb matter and energy from the outside world, actually spontaneously emit particles, with the greatest rate of emission coming from the least massive black holes. In terms as clear and simple as possible, and with the frequent use of witty and enlightening analogies, he explains in the book the reasoning that led him to this and other discoveries—discoveries that propel him to believe that “we may now be near the end of the end of the search for the ultimate laws of nature.” Should we achieve this goal, he writes, the next step will be “the discussion of why it is that we and the universe exist. If we find the answer to that, it would be the ultimate triumph of human reason—for then we would know the mind of God.”

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What does Hawking mean by knowing “the mind of God”? Earlier, he has given us a clue to his own mind on this question when he cites the concept of imaginary time, a mathematical construct (obtained by multiplying time by the square root of minus one) frequently used by physicists. In the world of real time, experienced by real people, the universe, Hawking writes, “has a beginning . . . at which the laws of physics break down. . . .” But, he goes on, “maybe what we call real is just an idea that we invent.” In such a case, the universe, though finite, “would be completely self-contained and not affected by anything outside itself. It would be neither created nor destroyed. It would just BE. . . . What place, then, for a creator?”

But if “what we call real is just an idea that we invent,” what Hawking has given us here is not so much an insight into the “mind of God” as an explanation of why we cannot expect to have such an insight. His explanation is akin to a more familiar one given often by philosophers, though in his case it comes couched in the language of physics. Some may find it no more satisfactory for that.

“In all your ways, know Him,” the Book of Proverbs tells us. Those ways extend beyond the intellectual. In particular, the “mind of God” may be thought to contain answers to two overwhelming questions touching upon the nature and purpose of the universe.

The first is implicit in a paradox expressed most pithily by Rabbi Akiva: “All is foreseen, but free will is granted.” The reason that no merely human mind can fathom the answer to this paradox has to do with our necessarily imperfect knowledge of time. The second and more agonizing question is that of Job, and it concerns the justification of evil and suffering. To that question, our answer must lie in acceptance, which is not the same thing as resignation—and also in wonder at the example set for us by, among other marvels of the universe, the suffering and triumph of such as Stephen Hawking.

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