Martin Rees is Emeritus Professor of Cosmology and Astrophysics at the University of Cambridge, the Astronomer Royal, a member of Britain’s House of Lords, and a former President of the Royal Society. The interview was conducted at Trinity College, Cambridge, by The Conversation’s Matt Warren.

"Our cosmic horizons have grown enormously over the last century, but there is a definite limit to the size of the observable universe. It contains all the things from which light has been able to reach us since the Big Bang, about 14 billion years ago. But the new realisation is that the observable universe may not be all of reality. There may be more beyond the horizon, just as there’s more beyond the horizon when you’re observing the ocean from a boat.

What’s more, the galaxies are likely to go on and on beyond this horizon, but more interestingly, there is a possibility that our Big Bang was not the only one. There may have been others, spawning other universes, disconnected from ours and therefore not observable, and possibly even governed by different physical laws. Physical reality on this vast scale could therefore be much more varied and interesting than what we can observe."
Opinion: Aliens, very strange universes and Brexit – Martin Rees