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The conference, entitled The State of the Universe, has been charting the theoretical frontiers of black holes, cosmology and fundamental physics, but the event is also a tribute to a career that many feared would be short-lived after Hawking was diagnosed with motor neurone disease at the age of 21.

The birthday bash began on Thursday, though Hawking was unwell and unable to appear in person. Those gathered were assured he was there in spirit and were urged to be on their best behaviour: Hawking was watching online, said Peter Haynes, head of the university's department of applied mathematics and theoretical physics.

The celebrations culminate on Sunday when the man himself is due to deliver a rare public lecture entitled A Brief History of Mine." Warm-up acts include Lord Rees,the astronomer royal, and Saul Perlmutter, who won the Nobel prize in physics last year for the co-discovery of dark energy, the mysterious substance said to drive the expansion of the universe.

"The particular topics we're discussing here are very close to Prof Hawking's heart, and in many cases he's made conjectures or worked in these subjects, so it's an assessment of where we stand today," said Gary Gibbons, a long-term collaborator at Cambridge.

Asked what lay behind Hawking's success as a scientist, Gibbons said: "His great character and imagination, and his desire to get to the bottom of things. In physics, that's the thing that will really characterise you. He made bold conjectures, some of which have turned out to be correct, and he's relentless."

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