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A hundred years ago Albert Einstein came up with his theory of general relativity.

It turned him into a global superstar and has informed much of our understanding of the universe ever since.

The United Nations has designated 2015 the International Year of Light because Einstein developed his theory based on what happens to light in different situations.

Professor Ruth Gregory, a specialist in general relativity at Durham University, told Today's Sarah Montague: "We've certainly verified it's predictions at least over a certain range of scales. We know it works in the solar system, we know it works down to roughly millimetre scales."

"We believe it works in the cosmos, we have a very good theory based on General Relativity and our other theories of physics."

"We always like to think there could be something else and it's often quite hard to eliminate the impossible."

First broadcast Today programme 2 January 2015.