PEOPLE used to think the world was flat. Sail too far and you would drop off the edge.

Then wise men gazed into the cosmos and surmised the Earth was not alone. That out there are millions of stars and planets so that, by the law of averages, some would be bound to support life.

Now, I was surprised to read, scientists believe that while outer space is infinite, so is the space in which we live. Parallel worlds exist, they say, alongside our own.

This theory been used by writers of science fiction and fantasy for generations. But now scientists say it may be fact.

They are investigating the possibility that these other parallel worlds are real.

Worlds where Britain beat the revolutionaries in America so that the New World remains our colony. Worlds where Napoleon won the Battle of Waterloo and we all speak French.

On many of these other worlds, we still exist as individuals, unaware we are living out multiple lives. But in some worlds, we don't exist at all.

Television shows from the Twilight Zone to Doctor Who have used this possibility. Writers from H G Wells to Stephen King have produced “what if” books based on aspects of the theory. I wrote one myself called The Heydrich Sanction in which Hitler won the war.

In the TV series Sliders, travellers used a wormhole to slide between universes.

If wormholes became reality, it might be fun nipping to the world next door to meet yourself for a pint.

There would be drawbacks, of course. Think of all the Christmas cards you'd have to send to yourselves in all the different dimensions.

These other worlds may have been sensed by earlier generations. Perhaps, in the past, folk thought they were inhabited by ghosts, fairies or gods. Maybe ghosts are actually shadows from an alternative earth?

Parallel worlds are part of what scientific believers call the M Theory and there is a suggestion it could lead to time travel. Which would be nice.

I could nip back a few years with the winning Lottery numbers and become a millionaire.

The whole idea is fascinating and thought provoking.

Would religion be the same? Is there somewhere, in these millions of other worlds, that enjoys universal peace? Or is mankind conditioned to permanent war?

Stephen Hawking is open minded about the M Theory.

He says that if it is proven, it will be exciting. And if it is proven not to be true, it will still be exciting, because the body of knowledge about a world we still don't understand will have been increased.

He is not so sure about time travel.

“I gave a party for time-travellers,” he said at a conference in Seattle.

“But I didn’t send out the invitations until after the party. I sat there a long time, but no one came.”

We could be sitting here a long time waiting for proof that we all lead multiple lives in different universes. And would we really want to know?