British scientist Stephen Hawking has had to miss a symposium to mark his 70th birthday because of ill health.
Professor Hawking was discharged from hospital only on Friday, Professor Sir Leszek Borysiewicz, vice-chancellor of Cambridge University, told the event.
A recorded speech was played to the symposium, at the university, instead.
In it, Prof Hawking, who was diagnosed with motor neurone disease aged 21, urged the continued exploration of space “for the future of humanity”.
He used his talk, entitled A Brief History of Mine, to warn that the human race would not “survive another thousand years” without beginning to colonise other parts of space.
As well as running through his personal history and pronouncements on the future of the human race, he also used the conclusion of the speech to call on people to “be curious”.
“Remember to look up at the stars and not down at your feet. Try to make sense of what you see and wonder about what makes the universe exist,” he said.