Like many in the community of theoretical physicists, Professor Hawking is after the Grail of science-the Theory of Everything that lies at the heart of the cosmos. He involves us in the attempts at uncovering its secrets-from supergravity to supersymmetry, from quantum theory to M-theory, from holography to duality, and now, at the very frontiers of science, superstring theory and p-branes. He shares his eagerness to "combine Einstein's General Theory of Relativity and Richard Feynman's idea of multiple histories into a complete unified theory that will describe everything that happens in the universe."
With characteristic exuberance, Hawking invites us to be fellow travelers on this extraordinary voyage through spacetime."
What is time? Is it an ever-rolling stream that bears all our dreams away, as the old hymn says? Or is it a railroad track? Maybe it has loops and branches, so you can keep going forward and yet return to an earlier station on the line.
The nineteenth-century author Charles Lamb wrote: "Nothing puzzles me like time and space. And yet nothing troubles me less than time and space, because I never think of them." Most of us don't worry about time and space most of the time, whatever that may be; but we all do wonder sometimes what time is, how it began, and where it is leading us.
Any sound scientific theory, whether of time or of any other concept, should in my opinion be based on the most workable philosophy of science: the positivist approach put forward by Karl Popper and others. According to this way of thinking, a scientific theory is a mathematical model that describes and codifies the observations we make. A good theory will describe a large range of phenomena on the basis of a few simple postulates and will make definite predictions that can be tested. If the predictions agree with the observations, the theory survives that test, though it can never be proved to be correct.
On the other hand, if the observations disagree with the predictions, one has to discard or modify the theory. (At least, that is what is supposed to happen. In practice, people often question the accuracy of the observations and the reliability and moral character of those making the observations.) If one takes the positivist position, as I do, one cannot say what time actually is. All one can do is describe what has been found to be a very good mathematical model for time and say what predictions it makes.
Isaac Newton gave us the first mathematical model for time and space in his PRINCIPIA MATHEMATICA, published in 1687. Newton occupied the Lucasian chair at Cambridge that I now hold, though it wasn't electrically operated in his time. In Newton's model, time and space were a background in which events took place but which weren't affected by them. Time was separate from space and was considered to be a single line, or railroad track, that was infinite in both directions. Time itself was considered eternal, in the sense that it had existed, and would exist, forever.
By contrast, most people thought the physical universe had been created more or less in its present state only a few thousand years ago. This worried philosophers such as the German thinker Immanuel Kant. If the universe had indeed been created, why had there been an infinite wait before the creation? On the other hand, if the universe had existed forever, why hadn't everything that was going to happen already happened, meaning that history was over? In particular, why hadn't the universe reached thermal equilibrium, with everything at the same temperature?
Kant called this problem an "antimony of pure reason," because it seemed to be a logical contradiction; it didn't have a resolution. But it was a contradiction only within the context of the Newtonian mathematical model, in which time was an infinite line, independent of what was happening in the universe. However, as we saw in Chapter 1, in 1915 a completely new mathematical model was put forward by Einstein: the general theory of relativity. In the years since Einstein's paper, we have added a few ribbons and bows, but our model of time and space is still based on what Einstein proposed. This and the following chapters will describe how our ideas have developed in the...
Reviews
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Unlikely as it seems, Hawking means his title literally. This lucid, methodical work summarizes dominant theories in physics. Hawking reviews relativity, quantum physics, the nature of time and space, and explains contemporary research into subatomic particles and fundamental physical laws. Laced with dry humor and references to Hawking's personal life, it makes theoretical physics sound like the most exciting thing in the world. Concluding with speculative chapters about time travel and the future of the human race, it fascinates from beginning to end. Simon Prebble's narration fits Hawking's style well; he delivers technical jargon and bilingual jokes with equal ease. G.T.B. (c) AudioFile 2002, Portland, Maine
St Louis Post-Dispatch ...
"Clear, concise and accessible. And he leavens it further with occasional wry humor."
Time...
"Provocative and informed ... plenty of comprehensible analogies and no small amount of humor, often self-deprecating.... Best of all, the book is liberally sprinkled with well-conceived, gorgeously rendered and frequently whimsical illustrations."
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