Ox ford physicist says time travel is possible

By Charles Arthur, Technology Editor

By Charles Arthur, Technology Editor

19 December 1999

Is time travel possible? It certainly is, according to Dr Neil Johnson, a physics lecturer at Oxford University who insists that a world previously confined to the pages of H G Wells is more than mere fiction.

Dr Johnson has just finished taping this year's prestigious series of five Royal Institution lectures, which will be broadcast to the nation from Boxing Day onwards.

The talks, titled "Time's Arrow", incorporate a huge journey around the complex topic of quantum physics - in language that schoolchildren could understand - and involve dispatching atomic clocks for round-the-world trips and being revisited by a whiskery vision of his future self, courtesy of the BBC's makeup department.

The key to time travel, explains Dr Johnson, is understanding that our intuitive view of the world is actually quite wrong. In everyday life, we usually go along with the view promulgated by Sir Isaac Newton in the 17th century, which is that the speed of everything, even light, is relative.

"Einstein said that it's the speed of light which is absolute, and motion which is relative," explains Dr Johnson. "Where Newton said that time is the same for everybody, Einstein said that time depends on what you are doing." Thus if you are running up and down the room, you age more slowly than if you simply sit slumped in your chair.

The two clocks that demonstrate this effect in the lectures are paired atomic clocks, accurate to a second every few million years. One travelled to Shanghai and back while the other stayed in London - creating what Dr Johnson calls "a timewarp" of a few billionths of a second.

That's one sort of time travel; but a growing number of scientists, including Dr Johnson, now agree that real time travel - the sort of thing that HG Wells wrote about in his novel The Time Machine - is possible.

That's the good news; the bad news is the conditions required to make it happen. Those same scientists who now agree that time travel is possible also agree that you probably wouldn't like to experience it.

The key is "wormholes", which - they hypothesise - could be formed when black holes collapse.

A black hole is the leftover of a huge star that collapses on itself until the force of gravity becomes so great that not even light (which, as Einstein but not Newton realised, must be affected by gravity) can escape. If the black hole collapses on itself further, it might connect with another part of the universe, where instead of sucking in matter, it would spew it out.

So not only would you have to go through a black hole and then be spat out of the other end, you would have to go through the correct part, the wormhole. But in a black hole, which might be miles wide, a wormhole would - according to the mathematics - be only a billionth of a trillionth of a trillionth of a centimetre wide.

And one of the best arguments that time travel, at least in a reasonable form like Wells's time machine, is not possible is the simple and logical one: we have not - as far as we can tell - been visited by anyone from the future.

Details about the lectures can be found on the internet at www.ri.ac.uk/christmas/