Stephen Hawking's nurse offers me his hand to shake; it hangs limply as I take it. The devastating impact of the disease that has ravaged his body for almost 50 years is all too apparent. Yet I feel no pity -- only awe.
It was in 1963, then a 21-year-old PhD student at Cambridge, that Hawking was told that he had a type of motor neurone disease (today we know it as an atypical form of amyotrophic lateral sclerosis) and was given about two years to live. His illness was degenerative: it would attack the nerves that controlled his muscles, affecting first his body, then eventually his mood, senses and thinking.
On Sunday, Hawking will celebrate his 70th birthday. While his body was paralysed, Hawking used his mind to journey through the cosmos, glimpsing the origins of space and time. And that, indeed, is the story of his life: he is a man who has defied the laws of medicine in order to rewrite the laws of physics.
His remarkable office at Cambridge University's Centre for Mathematical Sciences is a fitting home for the world's most famous scientist. On his desk, a humidifier containing seashells from his second wife, Elaine Mason (from whom he is now divorced), expels puffs of vapour. There's a letter from Michelle Obama, photographs of Hawking with three popes (he's a member of the Pontifical Academy of Sciences), images of a visit to Easter Island, and of a memorable trip to China, where he was carried aloft by the Beijing wrestling team. And, of course, there's Marilyn Monroe, whom he describes as "an old girlfriend of mine".
On one wall hangs a 'Simpsons' clock, a tribute to his appearances on the show (one of which featured the immortal pay-off: "Your theory of a doughnut-shaped universe is interesting, Homer. I may have to steal it"). He's also made cameo appearances in 'Star Trek' and in the animated sitcom 'Futurama'; his own life has been the subject of a documentary by the director Errol Morris and a BBC drama.
Personally and professionally, Hawking has travelled light years since that original, shattering diagnosis. He has never complained, or shown any signs of self-pity: he initially coped, he says, by listening to Wagner. "Reports in magazine articles that I drank heavily are an exaggeration," he said.
What gave him something to live for was meeting Jane Wilde, a languages student, whom he married in 1965. The advance of his disease slowed, and he threw himself into his research, turning from a brilliant but lazy student into a workaholic.
He first captured the attention of his peers in the late 1960s, working with Roger Penrose on how the laws of physics -- notably Einstein's law of gravity -- sometimes break down, resulting in something called a singularity. If the theory of general relativity was correct, they showed, then such singularities must occur inside black holes -- and, most probably, at the start of the universe. This idea implies that singularities mark the beginning and end of space and time.
One of Hawking's long-standing goals has been to blend the theory of the very big (general relativity) with the very small (quantum theory) to produce an overarching theory known as quantum gravity. In particular, he raised the intriguing possibility that black holes are not as black as once thought.
One strange consequence of quantum theory is that empty space isn't empty at all: pairs of particles are constantly popping into and out of existence. If they appear right on the event horizon -- the point of no return from the gravity well of a black hole -- they may find themselves on different sides, with one sucked in, and the other zooming free as "Hawking radiation".
The same mathematics can also be applied to the splash of residual warmth left over from the Big Bang, and to the way in which a soup of ultra-hot matter crystallised to form the universe that astronomers study today. In spring 1982, Hawking made a bold proposal: that variations in the cosmic background radiation -- the echoes of that initial explosion 13.7 billion years ago -- could be traced back to Hawking radiation, as the tiny seeds around which the structure of the universe coalesced. That summer, this "fluctuation theory" was fleshed out at a workshop organised by Hawking and his colleague Gary Gibbons. Remarkably, their efforts -- and those of two Russians who came up with the same result independently -- predicted these fluctuations in the fabric of the cosmos a decade before a purpose-built satellite observed them.
As Hawking's career was advancing, so was his disease. By 1983, his speech had become slurred and hard to decipher. Soon, a tracheotomy left him unable to speak at all: the only way he could communicate was by raising his eyebrows to select letters as they were held up on cards.
By the time I first met Hawking, in California in 1988, when he was promoting 'A Brief History of Time', he was using the speech synthesiser that has since given him his trademark American accent.
For the past few years, he has operated the device by twitching a cheek muscle -- but it would take him minutes to give prepared answers. His sparkling one-liners -- he wouldn't compare the joy of discovery to sex, he says, but it does last longer -- are as much a product of necessity as is his humour.
His private life, too, has not been entirely smooth. He and Jane had three children -- Lucy, Robert and Tim -- but separated in 1991. Partly, this was down to religious differences: one implication of Hawking's most daring project, quantum cosmology, is that the universe's creation and evolution can be entirely explained by the laws of science, without reference to a creator. Although Hawking has often talked of "knowing the mind of God" by discovering a complete theory of the cosmos, he means it in a metaphorical sense. As he once told me: "You can say the laws (of physics) are the work of God, but that is more a definition of God than a proof of His existence."
It was also extremely difficult for Jane to cope with the pressures of his fame and his disability, or shoulder the tremendous burden of care alone. The two were reconciled in 2006, after the end of Hawking's marriage to Elaine Mason, formerly one of his nursing team.
However, Hawking's life is getting no easier. He tends to arrive in his office in mid-afternoon, and in recent months, he has made more frequent visits to Papworth Hospital. Sometimes he finds it hard to breathe, and needs a ventilator.
An effort is under way to harness his brainwaves to his trademark voice. Intel, which has for many years supplied Hawking's computing and communication devices free of charge, is also working on a way of incorporating in its system the range of facial expressions that he uses.
During the course of Hawking's career, cosmology has risen from a niche subject to being perhaps the most compelling of all the sciences -- not least thanks to his own inspirational contribution.
It has been, he insists, a "glorious time to be alive and doing research in theoretical physics".
A critical ingredient of Hawking's story is harder to convey: the relentless drive that has allowed him to achieve so much despite great suffering. Through his cosmic force of will, he is still defying that devastating diagnosis of half-a-century ago. (© Daily Telegraph, London)
Roger Highfield is director of external affairs for the UK's National Museum of Science