Aug 8, 2007
Prof Amos Ori has set out a theoretical model of a time machine which would allow people to travel back in time to explore the past.
The way the machine would work rests on Einstein’s theory of general relativity, a theory of gravity that shows how time can be warped by the gravitational pull of objects.
Bend time enough and you can create a loop and the possibility of temporal travel.
Prof Ori’s theory, set out in the prestigious science journal Physical Review, rests on a set of mathematical equations describing hypothetical conditions that, if established, could lead to the formation of a time machine, technically known as “closed time-like curves.”
In the blends of space and time, or spacetime, in his equations, time would be able to curve back on itself, so that a person travelling around the loop might be able to go further back in time with each lap.
In the past, one of the major challenges has been the alleged need for an exotic material with strange properties - what physicists call negative density - to create these time loops.
“This is no longer an issue,” he told The Daily Telegraph.
“You can construct a time machine without exotic matter,” he said.
It is now possible to use any material, even dust, so long as there is enough of it to bend spacetime into a loop.
Even though Prof Ori, of the Technion-Israel Institute of Technology, believes his new work strengthens the possibility of a real Tardis, he would not speculate on when a time machine would be built, or even if it would ever be possible.
“There are still some open questions.”
The main remaining issue is the stability of space time, the very fabric of the cosmos, in time travel scenarios.
But overcoming this obstacle may require the next generation of theory under development, called quantum gravity, which attempts to blend general relativity with the ideas of the quantum theory, the mathematical ideas that rule the atomic world.
Time travel has long been a fascination, HG Wells grappled with the scientific issues in his 1895 science fiction classic, The Time Machine, Dr Who is still fighting the time war and Hollywood insisted all that was needed for time travel was a De Lorean and a good flash of lightning.
But more serious work on general relativity first raised the astonishing possibility of time travel in the 1940s.
In the half century since, many eminent physicists have argued against time travel because it undermines ideas of cause and effect to create paradoxes so that a time traveller could go back to kill his grandfather so that she is never born in the first place.
In 1990, the world’s best known scientist, Prof Stephen Hawking proposed a “chronology protection conjecture”, which flatly says the laws of physics disallow time machines.
Three years later, Prof Ori concluded that the possibility of constructing a time machine from conventional materials could not be ruled out.
Prof Hawking then fought back with his Cambridge University colleague Michael Cassidy and they concluded that time loops are extremely unlikely.
Tongue in cheek, Prof Hawking added that there is experimental evidence that time travel doesn’t exist: “We have no reliable evidence of visitors from the future. (I’m discounting the conspiracy theory that UFOs are from the future and that the government knows and is covering it up. Its record of cover-ups is not that good.)”
But now, in Physical Review, Prof Ori has provided some more advanced solutions to the problems of time travel outlined by the likes of Prof Hawking, helping to realise an idea that dates back millennia and appears in 18th century literature, Harry Potter, Dickens, sci-fi movies and much more besides.