Hawking: we'll be able to travel back in time
"One of the consequences of rapid interstellar travel would be that one could also go back in time."
The Sunday Times
by Jonathan Leake and Rajeev Syal
In a U-turn that will send shock waves through the universe, Professor Stephen Hawking, Britain's leading cosmic physicist, has
accepted the possibility of time travel.
Having ridiculed the concept for years, Hawking now says that it is not just a possibility but one on which the government should
spend money.
Three years ago, Hawking, the Lucasian professor of mathematics at Cambridge University, stirred up debate among cosmologists
and astronomers when he dismissed time travel. This came as a growing number of astronomers and physicists were speculating that
Einstein's general theory of relativity might allow for the possibility.
Hawking, however, produced his chronology protection hypothesis, a mixture of advanced science and ordinary logic. Time travel,
he said, would allow people to alter their own pasts. You could murder your ancestors or even prevent your own birth, a possibility
he considered ridiculous. "The best evidence that time travel will never be possible is that we have not been invaded by hordes of
tourists from the future," he said two years ago.
Now, in the foreword to a new book, The Physics Of Star Trek by American astronomer Lawrence Krauss, which is due for
publication next month, Hawking has recanted to the point of adopting the language of "Trekkies". He talked openly of warping
space and of faster-than-light travel. He said: "One of the consequences of rapid interstellar travel would be that one could also go
back in time."
Hawking said yesterday he still thought time travel would probably never be practical, but the seeds of doubt had been sown in his
mind: "If you combine Einstein's general theory of relativity with quantum theory, it does begin to seem a possibility."
He pointed out that research on "closed time-like curves", the technical term for time travel, is going on in a number of universities,
including Cambridge and the California Institute of Technology.
"It doesn't involve much money - what it needs is an openness of mind to consider possibilities that might appear fantastic," said
Hawking.
Scientific debate over time travel goes back to Sir Isaac Newton who, in the 17th century, dismissed it absolutely, claiming that time
and space were fixed and immutable.
His assertions were accepted until Einstein showed that time and space are closely related and that both are affected by gravity. His
theories led to the idea that enormous gravitational fields, such as those found around collapsing stars, known as black holes, could
reverse the flow of time.
Dr. Michio Kaku, a professor of theoretical physics at the City University of New York, who is touring Britain to publicise his new
book, also support time travel - in theory. "Building a genuine time machine will not be as easy as sitting in a chair and twirling a few
knobs. Modern proposals for such a machine face one severe problem: the energy supply," he said.
He believes that the necessary energy will only be found in fuel sources located in outer space, which still leaves the problem of
getting there.
As Hawking says in his foreword: "There is a two-way trade between science fiction and science. We may not yet be able to boldly
go where no man or woman has gone before, but at least we can do it in the mind."
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