A literary clash of the time lords will be in the offing in September when Stephen Hawking's new work hits the book shops.

Professor Hawking's book, co-authored with the former Star Trek writer Leonard Mlodinow, is A Briefer History of Time - a pithier and simpler version of his 1988 bestseller.

The problem is that there is already a "pop science" book of the same name.

And what's more, it is briefer than the offering from Professor Hawking, who is Lucasian professor of mathematics at Cambridge University.

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Eric Schulman, an American astronomer, published his account of the Earth's evolution "from the Big Bang to the Big Mac" under the title A Briefer History of Time in 1999.

And, in what raises the unlikely prospect of one man boasting to another that "mine's shorter than yours", Professor Schulman's work runs to a mere 171 pages, compared with Professor Hawking's 176.

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The two titles can already be found side by side on the Amazon website - Professor Schulman's complete with reviews, Professor Hawking's ready for pre-publication orders.

A spokesman for Bantam Books, which is publishing the Hawking-Mlodinow book, said: "The other book was published six years ago, and Professor Hawking is an international figure - so the editor was fine with it. So no change. The editor was aware of the other book, but I don't know whether Professor Hawking was."

Professor Schulman was unavailable for comment.