The Nature of Space and Time [Paperback]

 

 

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I dug deeper into my sleeping bag and looked out into the universe. I was thankful for the Earth's attraction which held me close. The air was so thick with stars I was almost breathing them. Was there an end to the universe? How much stuff was really out there? How did it all begin? Why can't we remember the future or relive our mistakes?

Well, these questions didn't keep me awake for very long that night, but "The Nature of Space and Time" is a step toward answering them. This book, covering several lectures and a final debate between Stephen Hawking and Roger Penrose, provides insight into the prevailing wisdom.

They are two of the greatest minds of our century. Stephen is interested in answers to the extent that they lead toward practical or predictable solutions. Roger is interested in answers to the extent that they lead to a more complete understanding of reality. This difference between them makes the debate a lively and at times amusing one.

Copyright 1997 by Barbara Grant Ashton

Earlier attempts to formulate an answer that takes into account existing theories and observations have failed because of obstacles posed by gravity. The Nature of Space and Time pitts two heavy weights trying to provide a loop quantum gravitational model that successfully merges current ideas, and which may enable us to overcome such difficulties. Stephen Hawking shot to fame in the world of physics when he provided a mathematical proof for the Big Bang theory. This theory showed that the entire universe exploded from a singularity, an infinitely small point with infinite density and infinite gravity. Hawking was able to come to his proof using mathematical techniques that had been developed by Roger Penrose. These techniques were however developed to deal not with the beginning of the Universe but with black holes.

Science had long predicted that if a sufficiently large star collapsed at the end of its life, all the matter left in the star would be crushed into an infinitely small point with infinite gravity and infinite density...a singularity. Hawking realized that the Universe was, in effect, a black hole in reverse. Instead of matter being crushed into a singularity, the Universe began when a singularity expanded to form everything we see around us today, from stars to planets to people. Hawking realized that to come to a complete understanding of the Universe he would have to unravel the mysteries of the black hole.

Hawking and his fellow physicists embarked on an extraordinary intellectual expedition to tame the black hole. Slowly physicists were coming to understand this most destructive force of nature. But Hawking realized that there was something missing from the emerging picture. All work on black holes to that point used the physics of the large-scale Universe, the physics of gravity first developed by Newton and then refined by Einstein's theories of general and special relativity. Hawking realized that to come to a full understanding of black holes, physicists would also have to use the physics of the small-scale Universe, (the physics that had been developed to explain the movements of atoms and sub-atomic particles, known as quantum mechanics.) The problem was that no one had ever combined these two areas of physics before. But that didn't deter Hawking. He set about developing a new way to force the physics of quantum mechanics to co-exist with Einstein's relativity within the intense gravity of a black hole.

After months of work Hawking came up with a remarkable result. His equations were showing him that something was coming out of the black hole. This was supposed to be impossible. The one thing that everyone thought they knew about black holes was that things went in but nothing, not even light itself, could escape. But the more Hawking checked, the more he was convinced he was right. He could see radiation coming out of the black hole. Hawking then realized that this radiation (Hawking Radiation) would cause the black hole to evaporate and eventually disappear. Although Hawking's theories about black hole evaporation were revolutionary, they soon came to be widely accepted. But Hawking knew that this work had far more fundamental consequences. In 1976 he published a paper called 'The Breakdown of Predictability in Gravitational Collapse'. In it he argued that it wasn't just the black hole that disappeared. All the information about everything that had ever been inside the black hole disappeared too.

There are limits to what science can know. For many years no one took much notice of Hawking's ideas until a fateful meeting in San Francisco. Hawking presented his ideas to some of the world's leading physicists. In the audience were Gerad t'Hooft and Leonard Susskind, two leading particle physicists. They were shocked. Both realized that Hawking's 'breakdown of predictability' applied not only to black holes but to all processes in physics. According to Susskind, if Hawking's ideas were correct then it would infect all physics, there would no longer be any direct link between cause and effect. Physics would become impotent. Since that meeting arguments effectively boiled down into two camps. On the one side were Susskind and those who believed that Hawking was wrong: information could not be lost. On the other were Hawking and those who believed that physics would have to be rewritten to take into account the uncertainty about information that Hawking had uncovered. Until a paper emerged by a young mathematician Juan Maldacena. It claimed to be a rigorous mathematical explanation of what happened to information in black holes. It showed that information was not lost. Hawking, it seemed, was on the losing side. But he was not convinced. Hawking set to work with a young research student, Christophe Galfard, to try to pick apart the Maldacena paper. They thought they could use the same mathematical techniques employed by Maldacena to prove that information was in fact lost. But after two years they still could not prove their thesis.

Hawking was soon back at work, working on a new proof for the information paradox. But he was to defend his long held belief that information was lost in black holes, instead he claimed that he could now prove the opposite. Hawking presented the outline of proof that he hoped would at last solve the problem that he had posed almost 30 years earlier. But despite the bold claims, some physicists remain unconvinced. Over a year has passed and he has still not presented a fully worked mathematical proof to back up his ideas. But Hawking is a stubborn man. If Hawking is going to change his mind on a view he held for almost 30 years then it will be with his own proof, in his own time. In spite of failing health and increasing problems communicating with his colleagues, he is still working on the proof. If he succeeds in completing a proof that convinces his colleagues, he will not only have solved one of the most difficult problems in physics but he will have managed to have produced ground breaking work at the very end of his career. A feat that even his hero Einstein could not accomplish. If not, Hawking will have inspired some future physicist, who will eventually complete the paradox and answer the question 'What happened before The Big Bang?'

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The current understanding of the physical structure of the universe is bipolar. There is Einstein's theory of relativity, which explains the macroscopic behavior of the universe to many places to the right of the decimal point. At the other end of the size spectrum, there is the quantum theory of fields, which explains the observed behavior of fundamental particles to many places to the right of the decimal point. Although one should always be very reluctant to state such a position, the resolution of this bipolar state into a unified one may be the last, great discovery of physics.
The purpose of this book is to present a debate between Stephen Hawking and Roger Penrose concerning the possibility of the issue being resolved, and in what manner. It is a series of six short lectures, three from each man and ends with a brief debate between them. These lectures are not for the general audience, as each lecturer assumes a fundamental understanding of general relativity and quantum theory. Nevertheless, there is a great deal of explanation, including diagrams, in the lectures. Therefore, it is possible to understand the material if you have a basic understanding of the two main topics. Without that, don't bother opening the book.
Of course, the issue is not resolved, as that must wait for a later date. It is interesting that Hawking tends to emphasize the points of difference, while Penrose goes to some length to describe how similar their positions are. Penrose continues with the position of Albert Einstein, in that he argues that quantum mechanics is not a final theory, but only the "gross" appearance of much subtler events. Hawking believes otherwise, arguing that the probabilistic features of quantum mechanics is the way nature does things, and there is no underlying mechanism yet to be discovered that will remove them.
The arguments are strong, yet unconvincing. Not due to their lack of power, but because they are made by two equally strong and forceful personalities. When two such powers collide, there is rarely resolution. Nevertheless, the debate sheds a great deal of light on the current state of thinking in physics, and points out some ways in which it may be resolved.

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2.0 out of 5 stars SAH-WEET ...!!!
After having read "A Brief History of Time", "Black Holes and Baby Universes and Other Essays", "The Cambridge Lectures" and "The Universe In a Nutshell" by the esteemed Professor... Read more

Published on Mar 24 2002 by Todd H. Knight

3.0 out of 5 stars hold on for dear life
This was an early attempt to capitalize on Hawking's commercial success with the Brief History. Roger Penrose, Hawking's PhD advisor, has also written some really fascinating... Read more

Published on Mar 9 2002 by Bryan Erickson

3.0 out of 5 stars Interesting but not Great
In spite of the errors mentioned in another review the discussion was fairly interesting but not as great a "debate" as I anticipated. Read more

Published on July 25 2000 by D. Harp

1.0 out of 5 stars Massive confusion among irreconcilable physical concepts..
Apart from the elementary, undergraduate level errors in thermodynamics, e.g. the first law of thermodynamics on page 24 is NOT the first law, nor is it a combination of the... Read more

Published on Dec 21 1998

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