Stephen Hawking: Physicist who was light years ahead of the Nobel prize

Stephen Hawking was one of the most imaginative and influential physicists of his generation yet he never won the Nobel Prize. He wrote a popular science book that became a publishing sensation, which is arguably the least-read bestseller of all time.

He was cruelly confined to a wheelchair by a disease that progressively paralysed him yet his mind ranged freely across the immensities of the cosmos. These are just some of the paradoxes of what, by any standards, was an extraordinary life.

Hawking was born in Luftwaffe-ravaged London on 8 January 1942, exactly 300 years after the death of Galileo (a fact that greatly appealed to him). Though his father wanted him to be a doctor, he was inspired by a schoolteacher to study physics at Oxford, where he was, by his own admission, a lazy student. From there, he moved to Cambridge to study for a PhD in the then unfashionable field of “general relativity” – Albert Einstein’s theory of gravity, which attributed the force to the unseen warpage of four-dimensional “spacetime”.

Christmas 1962 was a pivotal moment in Hawking’s life. In his final year at Oxford, he had noticed that he was becoming unaccountably clumsy and, when he returned home at the end of his first term at Cambridge, his mother persuaded him to see a doctor.

Exhaustive tests during a two-week stay in hospital led, in early 1963, to the diagnosis of motor neurone disease, a progressive deterioration of the brain cells that are responsible for movement. Although, at first, a person loses control over their voluntary muscles, eventually they also lose control of involuntary muscles that control essential reflexes, which leads to death. Normally the disease runs its course within two years.

Aged just 21, Hawking appeared to face a death sentence. The extraordinary thing is that, although he must have suffered bouts of depression, he did not succumb to total despair. In part, this was due to having met Jane Wilde, with whom he fell in love and married in 1965. Bolstered by her unflagging support, he decided to make the most of his short life expectancy.

The time limit on his life focused the mind of the formerly lazy student and, for the first time, his PhD work began to flow. Even more miraculously, towards the end of the second year of his research, the progression of his disease began to slow. Amazingly, it seemed, he might have more than two years left to him.

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Hawking’s fascination was with cosmology, the science that deals with the origin, evolution and ultimate fate of the universe. Einstein – never one to think small – had in 1917 applied his theory of gravity to the biggest gravitating system he could imagine: the whole universe. Like Isaac Newton before him, he was wedded to the idea of a “static” universe, in which the stars and galaxies hung in space, unchanging, for all time.

He therefore missed the message in his own equations, which was that the universe was inherently restless and had to be in motion. Support for this came in 1929 when the American astronomer Edwin Hubble discovered that the universe was expanding, its building blocks – galaxies of stars like our own Milky Way – flying apart from each other like pieces of cosmic shrapnel in the aftermath of a titanic explosion.

It appeared that the universe had not existed forever but had been born in a “Big Bang”. The Big Bang marked the beginning of time (we now believe the universe began 13.82 billion years ago).

A universe of finite age could be avoided, however, if as the galaxies fly away from each other, new matter fountains into existence out of the vacuum, congealing into new galaxies to fill the gaps.

Despite expanding, the universe can still look the same at all times and so be infinitely old. But this “steady state” theory, championed by British astronomer Fred Hoyle, was dealt a killer blow by the discovery in 1965 of the “cosmic background radiation”, the “afterglow” of the Big Bang fireball.

This then was the scientific background as Hawking embarked on his post-PhD research and made the first of his remarkable discoveries. The big question was: is the Big Bang truly the beginning of the universe? If the expansion of the universe is imagined running backwards like a movie in reverse, it shrinks ever smaller. Squeezing material into a smaller volume, as anyone who has squeezed air into a bicycle pump knows, makes it hotter.

But, according to Einstein’s theory, this process has no limit. As the universe dwindles to a point, its temperature and density skyrocket to infinity. Such a point is known as a “singularity” and is a sure sign that a theory has been stretched into a regime where it is no longer valid. Since Einstein’s theory of gravity broke down in this way, it had nothing sensible to say about earlier times and so the Big Bang had to be the beginning of time.

However, there was still a possibility that a singularity might be avoided in Einstein’s theory and, with it, the identification of the Big Bang with the beginning of time. If the matter of the universe were spread unevenly, this unevenness would become magnified as the backward-running universe shrunk ever smaller.

Different parts of the collapsing universe, instead of all piling up at one point, would miss each other and so not create a catastrophic singularity. Since Einstein’s theory of gravity would not break down, it would be possible to follow the history of the universe to earlier times – before the Big Bang. Perhaps, for instance, the universe had contracted down to a “Big Crunch” from which it had then bounced into the Big Bang.

While working on such matters, Hawking’s officemate, Brandon Carter, happened to mention a talk he had attended in London given by a young mathematician called Roger Penrose. It seemed Penrose was using novel “topological” methods to investigate the formation of another type of singularity, one which formed at the heart of a “black hole” – the region of grossly warped spacetime left behind when a dying star shrinks catastrophically under his own gravity. A black hole singularity was a singularity in space rather than time but it had much in common with the singularity of the Bang; Hawking contacted Penrose and there began one of the most fruitful collaborations in 20th-century physics.

Between 1965 and 1970, the pair proved a range of powerful “singularity theorems”. The most important was that, under a wide range of general and highly plausible conditions, the singularity in the Big Bang was unavoidable. It formed no matter how the backward-running movie of the universe went. According to Einstein’s theory at least, the Big Bang must have been a singularity – a true beginning of the universe.

For his next trick, Hawking turned his attention to black holes, at that time still unfashionable; the name was coined only in 1967 by American physicist John Wheeler and the first black hole candidate, Cygnus X-1, was discovered only in 1971 by the Uhuru satellite.

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Along with other physicists, he proved a range of theorems about these cosmic vacuum cleaners out of which nothing, including light, could escape. Most striking was the discovery that, irrespective of what the star that shrunk down to a black hole looked like, the black hole that formed was essentially identical. It was characterised by just two things – its mass and how fast it was spinning.

Black holes are breathtakingly simple objects. As the Nobel Prize winner Subrahmanyan Chandrasekhar observed: “The black holes of nature are the most perfect macroscopic objects there are in the universe: the only elements in their construction are our concepts of space and time.”

Hawking’s next and most famous work built on the insight he and Penrose had gleaned about the Big Bang. The fact that Einstein’s theory broke down did not mean that the beginning of the universe was forever beyond our scrutiny. It simply meant that something better than Einstein’s theory was required in order for us to penetrate to this remote time. That something else was “quantum theory”, the hugely successful theory of atoms and their constituents that had given us lasers and computers and nuclear reactors. The problem was that no one knew how quantum theory and Einstein’s theory of gravity fitted together (in fact, unifying them is, to this day, the outstanding unsolved problem in physics).

Hawking’s intention was to attack the singularity in the Big Bang and at the centre of a black hole, using quantum theory to lift the opaque curtain that the singularity effectively dropped across our view. But that problem was going to be a hard nut to crack. So Hawking decided to practise on an easier problem.

The singularity at the heart of the black hole is actually cloaked by a “horizon”. This marks the point of no return for matter falling into a black hole; pass through the horizon and you can never get out again. It is the horizon which astronomers think of when they talk about the “size” of a black hole. For instance, if the sun were squeezed down to form a black hole, its horizon would define a sphere about four miles across.

Hawking quickly discovered something remarkable – and, to physicists, scarcely believable – about the horizon. To appreciate it, it is necessary to understand what quantum theory says about empty space. Far from being empty, it is actually seething with energy. Specifically, subatomic particles and their antiparticles are continually popping into existence in pairs, something permitted by the Heisenberg Uncertainty Principle.

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Nature turns a blind eye to these particles, not bothering about where the energy to create them comes from, just as long as they meet and destroy, or “annihilate”, each other very quickly. It is a bit like a teenager a borrowing a car from their parent overnight and it being OK as long as it gets in back in the garage the following morning before mum or dad has noticed it’s missing.

But, as Hawking realised, near the horizon of a black hole something interesting happens. There is the possibility that one of the particles of a newly-created pair falls through the horizon into the black hole. The remaining particle has no partner to annihilate with and flies away from the hole along with countless others in the same situation. Contrary to all expectations, therefore, black holes are not totally black. They glow with emitted particles – “Hawking” radiation.

The energy to make particles of Hawking radiation comes from the gravitational energy of the black hole. As it radiates Hawking radiation, it gradually shrinks away. Star-sized black holes have extremely weak Hawking radiation but, as a black hole gets smaller, the radiation gets brighter until, finally, the hole explodes in a blinding flash.

Hawking radiation has never been detected in space and is not likely to be any time soon because, for star-sized black holes, it is very weak. However, in recent years, physicists have used considerable ingenuity to create analogues of event horizons in earthbound laboratories. In 2014, for instance, physicist Jeff Steinhauer at the Technion-Israel Institute of Technology in Haifa created a “sonic event horizon” by trapping sound waves in a fluid chilled to less than one billionth of a degree above absolute zero.

He was able to detect pairs of sound waves as they popped in and out of existence, mimicking, he claimed, particle-antiparticle pairs in the vacuum of space. Some researchers maintain it is still not clear how closely Steinhauer’s laboratory model mimics the event horizon of a black hole, so the jury remains out on whether Hawking’s prediction of Hawking radiation has been confirmed.

One of the black hole theorems Hawking had earlier discovered was that, when black holes merge, the surface area of the horizon of the merged hole is always bigger than the sum of the areas of the two precursor black holes. The Israeli physicist Jacob Bekenstein had speculated that the surface area represents the “entropy” of the black hole.

This is a property that arises in the theory of thermodynamics, the theory of heat and motion which underpins physics and chemistry and many other fields, and it always increases. But it applies only to hot bodies. How could it possibly apply to a black hole?

Hawking had found the answer. Thermodynamics applied to black holes because they were hot! They had a temperature. The proof was that they glowed with heat – Hawking radiation. The significance of Hawking’s discovery was that, at the horizon at a black hole, three of the great theories of physics meet: Einstein’s theory of gravity, quantum theory and thermodynamics. A first tentative step had been made on the road to uniting them: the Holy Grail of physics.

In recent years, Hawking has had more to say about black holes. Having shocked the world of physics by claiming that black holes are not black but emit Hawking radiation, in 2014, Hawking stunned the world again. This time he claimed that event horizons do not exist, which means that, strictly speaking, neither do black holes!

The collapse of an object such as a star to form a black hole is violently chaotic and, rather than a horizon, all that forms, claimed Hawking, is a boundary of extreme spacetime turbulence. Information can leak out through such an “apparent horizon”. Hawking’s conclusion was dramatic. “The absence of event horizons mean that there are no black holes – in the sense of regimes from which light can’t escape to infinity,” he wrote. “There are however apparent horizons which persist for a period of time.” Black holes, in other words, are not what we thought they were.

So is the horizon around a black hole the point of no return everyone thought it was? Or is it merely an apparent horizon, as Hawking maintained, leaking stuff from inside the hole? The matter could be settled in only a few years’ time when the “Event Horizon Telescope”, an array of radio dishes scattered across the globe, creates the first image of Sagittarius A*, the black hole with a solar mass of 4.3 million, 26,000 light years away at the centre of our Milky Way.

But the singularity at the beginning the universe, Hawking’s ultimate goal, remains. A quantum theory of gravity, which Hawking did not have, would dissolve it. The question was: what could be said about the beginning of the universe in the absence of such a theory? Well, quantum theory describes atoms and so on by a “wave function”, a mathematical device that encapsulates all that is known about an atom.

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Working with Jim Hartle of the University of California at Santa Barbara in the early 1980s, Hawking tried to write down a wave function for the entire universe. Soon, they made a striking discovery. Einstein’s theory of gravity can be reformulated so that instead of having three dimensions of space and one of time, it has three dimensions of space and one of “imaginary time”. Imaginary time is a mathematical concept but the key thing is that it behaves just like space. Hawking and Hartle showed that the wave function of the universe, which today exists in space and time, could have started out in space alone.

The significance of this is that the singularity exists in time. Removing the time removes the singularity. The question “What happened before the big bang?” is transformed into a spatial question exactly like “What is beyond the North Pole?”. Hawking and Hartle, with their so-called no-boundary condition, had answered the ultimate question by sidestepping it and showing that it was meaningless.

The work with Hartle coincided with another extraordinary development in Hawking’s life – one which did not concern scientific research directly. In 1984, he had begun writing a popular book. In 1988, it was published as A Brief History of Time. A publishing phenomenon, by May 1995, it had been in The Sunday Times bestseller list for a record 237 weeks, a feat which earnt it an entry in the 1998 Guinness Book of Records. Hawking, like Princess Diana, was catapulted into the mega-league of global stardom, previously the preserve of Chaplin and Einstein.

Hawking’s mechanical voice – he had lost his voice after an emergency tracheostomy in the summer of 1985 saved his life – was instantly recognisable across the world. In 1993, he appeared in Star Trek: The Next Generation as a hologram of himself, playing poker with Data and holograms of Newton and Einstein (he is the only person to have played himself in a Star Trek film). He appeared in The Simpsons Halloween Special on 29 October 1995, with Homer Simpson saying: “There’s so much I don’t know about astrophysics. I wish I read that book by that wheelchair guy.”

He became an international phenomenon, the best-known and most recognisable scientist on the planet. What caught the public imagination was the contrast – the man paralysed in a wheelchair whose mind wrestled with the biggest mysteries of the universe, everything from the nature of black holes to difficulties of time machines to the origin of the universe. Since 1979, Hawking had been the Lucasian Professor at of Mathematics at Cambridge, a chair previously occupied by Newton and Charles Babbage, the father of the computer.

What also impressed people was his courage, his incredible determination in the face of adversity. He had three children. He divorced Jane Wilde, then in 1995 married again – his nurse, Elaine Mason, the ex-wife of the man who had given him his computer voice – then divorced again. In 2006, he even flew on Nasa’s KC-135A plane, the “Vomit Comet”, which simulates weightlessness, and moved free of his wheelchair for the first time in decades.

What all the publicity has done is magnified in the public’s imagination Hawking’s scientific achievements. Nevertheless, his contributions are important. The reason he has not received the Nobel Prize is that the Nobel committee like to see supporting observational or experimental evidence of theories. Although black holes litter the universe, with every galaxy, including our own Milky Way, harbouring a “supermassive” version in its heart, no one has ever seen Hawking radiation. Nevertheless, as already mentioned, people are building black hole analogues in laboratories around the world, uncrossable boundaries that mimic a black hole horizon. It is only a matter of time before Hawking radiation is seen on Earth. A case, if ever there was one, for a posthumous Nobel Prize?

Stephen Hawking, theoretical physicist, cosmologist, born 8 January 1942, died 14 March 2018

Marcus Chown is author of ‘What A Wonderful World: Life, the Universe and Everything in a Nutshell’ (Faber & Faber)