DEEP THOUGHT, the supercomputer created by novelist Douglas Adams, got there first, but now the astronomer royal has caught up. Professor Sir Martin Rees is to suggest that “life, the universe and everything” may be no more than a giant computer simulation with humans reduced to bits of software.

Rees, Royal Society professor of astronomy at Cambridge University, will say that it is now possible to conceive of computers so powerful that they could build an entire virtual universe.

The possibility that what we see around us may not actually exist has been raised by philosophers many times dating back to the ancient Greeks and appears repeatedly in science fiction.

However, many scientists have always been dismissive, saying the universe was far too complex and consistent to be a simulation.

Despite this, the idea has persisted, popularised in films such as Tom Cruise’s Vanilla Sky and The Matrix, starring Keanu Reeves.

It was also the basis for The Hitchhiker’s Guide to the Galaxy, written by Adams, who died in 2001. In the book, Deep Thought creates the Earth and its human inhabitants as a giant calculating device to answer the “ultimate question”.

The BBC’s rerun of the radio version of Hitchhiker finished recently, just as Rees was putting together his contribution to the debate in which he will concede that the depictions by Adams, Cruise and Reeves might have been right after all.

In a television documentary, What We Still Don’t Know, to be screened on Channel 4 next month, he will say: “Over a few decades, computers have evolved from being able to simulate only very simple patterns to being able to create virtual worlds with a lot of detail.

“If that trend were to continue, then we can imagine computers which will be able to simulate worlds perhaps even as complicated as the one we think we’re living in.

“This raises the philosophical question: could we ourselves be in such a simulation and could what we think is the universe be some sort of vault of heaven rather than the real thing. In a sense we could be ourselves the creations within this simulation.”

Rees will emphasise that this is just a theory. But it is being increasingly discussed by other eminent physicists and cosmologists.

Among them is John Barrow, professor of mathematical sciences at Cambridge University. He points out that the universe has a degree of fine tuning that makes it safe for living organisms.

Even a tiny alteration in a fundamental force or a constant such as gravity would make stars burn out, atoms fly apart, and the world as we know it become impossible. Such fine tuning, he has said, could be taken as evidence for some kind of intelligent designer being at work.

“Civilisations only a little more advanced than ourselves will have the capability to simulate universes in which self-conscious entities can emerge and communicate with one another,” he said.

The idea that life, the universe and everything in it could be an illusion dates back more than 2,000 years. Chuang Tzu, the Chinese philosopher, who died in 295BC, wondered whether his entire life might be no more than a dream.

René Descartes, the 17th century French philosopher, raised similar questions. But he famously came down in favour of existence, saying: “I think, therefore I am.”

The idea was resurrected last century, notably by Bertrand Russell, who suggested that humans could simply be “brains in a jar” being stimulated by chemicals or electrical currents — an idea that was quickly taken up and developed by science fiction writers such as Isaac Asimov.

However, some academics pour cold water on the notion of a machine-created universe. Seth Lloyd, professor of quantum mechanical engineering at the Massachusetts Institute of Technology, said such a computer would have to be unimaginably large.

“The Hitchhiker’s Guide is a great book but it remains fiction,” he said.

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