Albert Einstein's theories of special relativity (1905) and general relativity (1915) revolutionised the way science looks at the world and physicists have been busy ever since working out the implications of these theories. Time-travel is one of the possibilities raised by this new world-view and J. Richard Gott brings us up to date on this topic in this fascinating book.
Gott is eminently qualified to explain this subject as he is a leading researcher in time-travel. He explains the subject simply and elegantly but, make no mistake about it, this book is no quick and easy read. The concepts involved are subtle and deep and call for much pondering. However, taken in easy stages, the book is accessible to all and is a wonderful read.
It begins with an interesting discussion of time-travel in science fiction, ranging from the novel The Time Machine by H.G. Wells (1895) to the film Back to the Future starring Michael J. Fox (1985), and describes how good science fiction provides useful ideas for physicists to test.
In order to underpin his explanation of time-travel, Gott sets the stage by explaining some fundamental physics such as Newton's Law of Gravity, Maxwell's Theory of Electromagnetism, Michelson's and Morley's experiment to detect the ether, and Einstein's theory of relativity. Gott deals competently and clearly with these matters but similar treatments can be found in many popular books on physics.
Time travel to the future is more straightforward and easily understood than travel to the past. Travel to the future is possible because the faster you travel the slower time passes for you. You can visit earth 1,000 years from now by making a round trip from earth to a star 500 light years away travelling at 99.995 per cent of the speed of light. Earth will now be 1,000 years older than when you left, but you will only be 10 years older.
The problem, of course, is how to travel at such enormous speed - at the moment we can make only sub-atomic particles move at such a speed. Perhaps when we develop into a super technical civilisation we will be able to move that fast, but until then, any significant time travel into the future is not a practical proposition.
Time-travel into the past is allowed by Einstein's theory of general relativity but is very difficult, requiring an extreme twisting of space as might occur in wormholes or around rapidly contracting cosmic string loops. Only a supercivilisation could travel to the past . . . one device proposed to allow travel to the past weighs 200 million times the weight of the sun.
The big bang is now the standard model in cosmology. It describes the origin of the universe as a huge explosion at a single point about 15 billion years ago. What was there before the big bang? Gott has an interesting answer based on time travel - the universe existed before the big bang and looped back in time to become mother at its own birth! It had a beginning without having an earliest event (I told you this stuff was deep).
The book is laced with interesting anecdotes - e.g. Einstein chatting with a man at the Institute for Advanced Studies at Princeton. The man suddenly pulled a notebook from his pocket and wrote something down. "What is that?" Einstein asked. "It's a notebook I keep so that anytime I have a good idea, I write it down before I forget it," said the man. "I never needed one of these," Einstein replied. "I only had three good ideas."
Time travel is fascinating to think about but one wonders how useful it would be. On the other hand, a device that would allow us to travel at will to the present would be very valuable, since many of us spend so much of our time worrying about the future or regretting the past.
William Reville writes the Science Today column in The Irish Times
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