Stephen Hawking's bet disappears into a black hole

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Professor Stephen Hawking - regarded by some as one of Albert Einstein's intellectual successors - has lost a six-year-old bet with colleagues.

Hawking made a wager with two professors at the California Institute of Technology that "naked singularities" - variations on a cosmological phenomenon believed to lurk at the hearts of black holes - could not exist. Now it seems they might.

The New York Times reported yesterday that Professor Hawking conceded defeat last week "on a technicality" to fellow physicists John Preskill and Kip Thorne. The stake was $164 (pounds 100), plus an item of clothing "embroidered with a suitable concessionary message." Although he could not prove his disbelief in naked singularities, Professor Hawking, the author of the best-selling book A Brief History of Time, proposed his bet at one such meeting in 1991.

Because of its far-reaching theoretical implications, news of the bet spread widely among physicists.

Although no light nor any other kind of signal can escape from black holes, half-dozen or so have been revealed by their gravitational effects on nearby stars. Black holes have also betrayed their presence by sucking in matter from nearby.

Singularities are believed to lurk hidden at the centre of black holes. A naked singularity would be a singularity bereft of a concealing black- hole shell, and therefore visible, in principle, to outside observers.

Professors Preskill and Thorne won the bet because recent computer calculations have shown that naked singularities could, in theory, be created as a star collapsed.

A singularity is defined as a mathematical point at which space and time are infinitely distorted, where matter is infinitely dense, and where the normal rules of relativistic physics and quantum mechanics break down.