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OU on the BBC: Background Brief - Time Travel: The Story So Far

Updated Tuesday, 8th August 2006

We explore the science that suggests time travel could be a possibility rather than mere science fiction

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Paul McGann as Doctor Who Copyrighted  image Icon Copyright: BBC

You cannae change the laws of physics .... but could physics actually enable us to travel through time?

It might sound crazy, but according to Einstein’s theories, there’s no logical reason why time travel isn’t possible - and there are now scientists looking into it as a serious scientific proposal, at least at a theoretical level.

Many science-fiction ideas from the past have subsequently become scientific realities.

Take space exploration, for example. In the 1950s this was just a fantastical idea that few people would have dreamt could actually happen. Now it’s such a part of modern life that the latest blast-off of a spacecraft, or the discovery of a new planet often doesn’t even make the national news...

Time travel is clearly a trickier proposition than space travel though. And prior to Einstein, it would have been deemed utterly impossible (as opposed to highly unlikely!)

Albert Einstein as a young man Copyrighted  image Icon Copyright: NASA
Albert Einstein

That’s because the old idea about time was that it was like a cosmic metronome keeping a regular and constant beat throughout the universe.

And it was thought to move in one direction only (this is the idea of "time’s arrow" - time can go forwards but never backwards).

However, what physicists now know is that time is rather more flexible than the old ’Clockwork Universe’ idea had it. And it was Albert Einstein who set the cat among the pigeons.

Clockwork [Image: Serenae under CC-BY-NC-SA licence] Creative commons image Icon Serenae via Flickr under Creative-Commons license
Clockwork [Image: Serenae under CC-BY-NC-SA licence]


The theory of relativity

Put simply, Einstein’s idea was that every object in the universe has it’s own ’time’, and these vary as objects move. The faster an object moves, the slower its time is, compared to the time of a slower moving object.

The extreme situation would be if an object could move as fast as the speed of light - in which case its time would be completely halted. But whatever an object - or person’s - time is, it’s only evident in contrast to other objects. In other words, it’s all relative.

Hence the famous Theory of Relativity.

Testing the theory

Einstein’s theories about time and space were revolutionary. He became a celebrity - and not just in scientific circles. But it’s only since he published his theories that scientists have been able to demonstrate that space and time really behave the way he said they did.

In 1971, way after Einstein’s death, two scientists were able to carry out a crucial experiment. They used two atomic clocks, synchronised them, and placed one on a plane, while the other stayed in the same location on Earth. The plane then flew around the world for 80 hours.


By Einstein’s theory, the clock on the plane would be expected to have lost time, due to being in motion over 80 hours compared to the clock on the ground.

Atomic Clock [Image: Darwin Bell under CC-BY-NC licence] Creative commons image Icon DarwinBell via Flickr under Creative-Commons license
Atomic Clock [Image: Darwin Bell under CC-BY-NC licence]

When they brought the clocks together and made a comparison, the clock on the plane was indeed a few nanoseconds slower than the other clock.

The experiment was replicated in 1996 with advanced technology, and it was proved again - with an even bigger time difference this time. Which proves that not only is time ’warp-able’, but Einstein was arguably the greatest thinker the world has ever seen.

What does this mean for time travel?

So. Time is warped - and this opens up the possibility that we might be able to somehow manipulate it as a mode of travel one day.

Already one scientist has published a paper in which he detailed how to build a time machine. And there’s another current possibility for potential chrononauts: travel by wormhole.


If it were possible however, it would present some pretty knotty paradoxes... For example, what if someone or something travelled back in time - and changed the ensuing future? (Films like Back to the Future and Terminator play with this idea).

Model of the DeLorean used to time travel in Back To The Future [Image: Clarksworth under CC-BY-NC-ND licence] Creative commons image Icon Clarksworth via Flickr under Creative-Commons license
Model of the DeLorean used to time travel in Back To The Future [Image: Clarksworth under CC-BY-NC-ND licence]

And - wackier still - have you heard the one about the time traveller who dots back and forward in time and by means of various medical technologies is able to be his own father AND mother?!

The philosophy of time travel

And besides, if time travel is possible, where are all the people from the future - surely they’d want to come and meet us poor stranded 21st century beings?

These may seem innocent enough brainteasers, but they really bother the philosophers - some of whom think that possible scenarios like this go to prove that time travel isn’t do-able.

It’s got physicists scratching their heads too though. Few of them believe that time travel’s a real possibility either - but then again neither are they keen to rule it out.

Because after all, a time portal might open up in your living room tomorrow to reveal your great-great-great-great-great-great-great-grand-daughter ....

First broadcast: Friday 15 Oct 1999 on BBC TWO





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