Does everyone have a doppelganger?

What are the chances of finding your exact lookalike? BBC Future investigates.

It's on your passport. It's how criminals are identified in a line-up. It's how you're recognised by old friends on the street, even after years apart.

Your face: it's so tangled up with your identity, soon it may be all you need to unlock your smartphone, access your office or buy a house.

Underpinning it all is the assurance that your looks are unique.

And then, one day your illusions are smashed.

"I was the last one on the plane and there was someone in my seat, so I asked the guy to move.

He turned around and he had my face," says Neil Douglas, who was on his way to a wedding in Ireland when it happened.

"The whole plane looked at us and laughed. And that's when I took the selfie."

The uncanny events continued when Douglas arrived at his hotel, only to find the same double at the check-in desk.

Later their paths crossed again at a bar and they accepted that the universe wanted them to have a drink.

He woke up the next morning with a hangover and an Argentinian radio show on the phone - the picture had gone viral.

Folk wisdom has it that everyone has a doppelganger; somewhere out there there's a perfect duplicate of you, with your mother's eyes, your father's nose and that annoying mole you've always meant to have removed.

The notion has gripped the popular imagination for millennia - it was the subject of one of the oldest known works of literature - inspiring the work of poets and scaring queens to death.

But is there any truth in it?

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