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Time travel looks like a one-way journey, renowned physicist Paul Davies says

Going to the future is a ‘done deal,’ but lots of problems with travelling to the past
September 23, 2013
Paul Davies speaks at University of Calgary

Paul Davies is a professor of physics at Arizona State University, and the author of such titles as The Eerie Silence: Renewing our Search for Alien Intelligence, Quantum Aspects of Life, and How to Build a Time Machine. Photo by Dave Brown

Time travelling to the future is scientifically possible and “a done deal” given enough money and technology, says internationally acclaimed physicist and best-selling author Paul Davies.

However, travellers to the future won’t be able to return to their own time given the known laws of physics, he told an audience of more than 700 at the University of Calgary, in a talk and slide show presented last Friday by the university’s new Institute for Quantum Science and Technology.

“This is a one-way journey only,” Davies said in an engaging science presentation leavened with humour.

What is uncertain in the future is “whether Calgary taxi drivers will have finally figured out how to navigate the campus,” joked the professor of physics at Arizona State University.

Just a decade after H.G. Wells’s science fiction book, The Time Machine, was published in 1895, physicist Albert Einstein published his theory of relativity in a 1905 paper which showed that time is “elastic” and that time travel “is indeed possible,” Davies said.

“Time can be stretched or warped,” and the faster you move, the more you warp time, he said, adding that “time moves faster in space.”

It would take a person travelling at nearly the speed of light (300,000 kilometres per second) two years to get to the nearest star outside our solar system, he said. But for a person on Earth, 20 years would have passed.

“There is no absolute universal time. There is only relative time,” Davies noted.

The force of gravity also influences time and warps space, including on Earth, he said.

Measurements by highly precise atomic clocks have shown that “time runs a little bit faster on the roof than in the basement” of a building.

Global positioning systems, which depend on a network of orbiting satellites, have to account for such “relativistic” time differences in order to be accurate.

If a person were able to go to the surface of a typical neutron star – about the size of Calgary but with very dense mass and enormous gravitation force – a clock would tick out only 70 per cent of the time compared with a clock on Earth.

On the surface of a black hole, which Davies called the “ultimate time warp” because it is so dense that light can’t escape, time would stand still relative to time on Earth.

Although travelling to the future is possible, travelling to the past is filled with paradoxes that challenge what is currently known about physics, Davies said.

It might be possible to travel to the past through “wormholes,” if these theoretical structures actually exist in the expanding, three-dimensional universe, or you could buy one from a “friendly alien,” he said.

Wormholes, whose existence is possible under Einstein’s theory of relativity, are “shortcuts” that connect two different parts of space-time.

However, the immense gravitational field in wormholes would cause “spaghettification” – tearing to shreds a person travelling through them, Davies said. “It’s not something you would do lightly.”

One of several paradoxes Davies cited is a man who goes to the past and shoots a young woman – his mother. How could the son have been born if he killed his mother?

Such a “causal narrative” would only be possible if there are, as some scientists theorize, multiple universes with parallel realities, he said. Even if a son time-travels to the past and kills his mother in a parallel universe, in another universe the mother lives and the son is born.

So if all time is relative, what is time, really?

One answer, Davies offered with a smile: “Time is nature’s way of preventing everything happening at once.”

The serious side of Davies’ and other theoretical physicists’ work, including at the university’s Institute for Quantum Science and Technology, is to understand the causal structure of space-time, to unify the theories of quantum physics and astrophysics.

The new institute, launched last week, is the only one of its kind in western Canada and the third of its scope in Canada.

           

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