Stephen Hawking | Critical Review by Robert C. Cowen

This literature criticism consists of approximately 5 pages of analysis & critique of Stephen Hawking.
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Critical Essay by Scientific American

SOURCE: "Cosmic Quarrel," in Scientific American, Vol. 261, October, 1989, pp. 22, 26.

In the following essay, the critic discusses the theoretical disagreement between Hawking and philosopher Huw Price.

Theoretical physicists, equipped with counterintuitive perceptions and a formidable mathematical armory, are considered by philosophers to be armed and dangerous. Their turf—however interesting—is usually avoided. Huw Price, a philosopher from the University of Sidney, belongs to a different breed. He has taken on Stephen W. Hawking of the University of Cambridge, one of the world's leading cosmologists. The rift developed over whether Hawking has, as he claims, found a possible explanation for the arrow of time.

Time occupies a strange place in the cosmological scheme of things. Most physical laws would allow the universe to run equally well forward or backward. The major exception is a relentless tendency for the extent of disorder in the universe, or entropy, to increase. In his best-selling book A Brief History of Time, Hawking argues that the tendency toward entropy underlies the psychological experience that we know as time. He makes the connection by observing that living things can exist and record memories, thus gaining a sense of time, only by overcoming the rising tide of entropy within a local region. To do so, they have to use energy supplied by the sun. So, according to Hawking, the deeper question underlying our perception of time is: Why does the universe at this stage of its evolution contain ordered structures such as the sun rather than just total disorder—random radiation?

Like most cosmologists, Hawking believes the known forces of nature can account for galaxies, stars and other ordered systemsonly if there was a big bang that started the universe expanding rapidly from a very hot, dense and relatively organized state. Hawking and his supporters also think disorder will spread until the universe becomes a bland void that may eventually contract in a big crunch. Hence, for Hawking, the really deep mystery about time is: Why is the universe ordered at one pole of time (the one we call the big bang) but disordered at the big crunch? Why won't nature's epic film run backward?

Hawking finds his answer in a quantum-gravity model of the universe, a theoretical hybrid that combines relativity and quantum physics. He has proposed that cosmologists should focus their efforts on a particular type of quantum-gravity model, one in which the history of the universe is finite in extent and in time but has no boundary. Such a universe lacks an edge or wall because space-time is curved; a straight line eventually meets itself. Hawking calculates that this "no boundary" proposal, together with some other assumptions, leads to the grand conclusion that the real universe is by far the most probable type: ordered at one end of time, expanding to a maximum extent and then, aeons hence, contracting once more, yet becoming more disordered all the while.

At this point Price charges into Hawking's cosmological briar patch. Writing affably in the pages of Nature, he suggests that A Brief History of Time fails to explain how Hawking finds the arrow of time embedded in his no-boundary proposal. The book, according to Price, teases the reader with a mystery that lacks a denouement. "It is as if we are assured that the butler did it, without being told how he overcame the evident obstacles (that he was incarcerated in Wormwood Scrubs at the time, for example)," he writes.

Price argues that Hawking's explanation for the arrow of time assumes what it sets out to show: that one end of time is different from the other. Price maintains that in a discussion about time, external final conditions are just as valid as initial conditions: any explanation for the high state of order at the moment of the big bang that is built into Hawking's model should, he suggests, apply equally to the big crunch. And if Hawking's model assumes some kind of temporal asymmetry, Price says, then it does not explain the arrow of time.

Hawking sticks to his guns. He writes to Scientific American that the no-boundary proposal does indeed explain the arrow of time because it predicts, essentially, that a universe of any given size has two distinct, highly probable degrees of disorder. In the low-disorder state, entropy increases as the universe expands; in the high-disorder state, disorder increases as the universe contracts. Hawking interprets the low-disorder state as belonging to the early history of the universe and the high-disorder state as coming after the universe has started to contract. "He does not have to assume time," one Hawking sympathizer comments. "If he is right, this answers thequestion."

Other cosmologists are not quite so sure. Don N. Page of Pennsylvania State University, who collaborates with Hawking, observes that "it's not clear what fraction of simple models of universes have an arrow of time." If the property of being simple itself predicted an arrow of time, then Hawking's no-boundary proposal might not explain very much.

Nevertheless, Page is confident that further work will clarify the situation. "It may be that Hawking's argument is wrong for other reasons, but I don't think it's because he's smuggling the arrow of time in there," he says. In fact, Page thinks, Hawking may have come on a truly profound insight. "If the time asymmetry is borne out by more complicated models, this would seem to be an amazing fact about the universe that this model might explain…. I know of no previous explanation for the arrow of time."

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This section contains 914 words
(approx. 4 pages at 300 words per page)
Buy the Critical Review by John Barrow
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