Stephen Hawking (41 page)

Like all breakups, theirs caused a great deal of sadness. The Hawking children took the news particularly badly. Robert, then twenty-three, had graduated in physics from Cambridge the previous year and was already embarking on postgraduate work; Lucy, nearly twenty, was at Oxford University, studying modern languages. The two of them, though naturally upset, were old enough to accept the situation and were developing their own lives away from home, carving out their own independence. The separation hit the youngest, Timothy, the hardest. Then barely eleven, he was too young to understand fully the reasons why his father had left their home on West Road.

There is little doubt that the trauma of separation had affected Stephen as much as any of those involved, and reporters claimed that the famous Hawking smile was now rarely seen. Others pointed out that, at the time, he was displaying great emotional swings. He could be outwardly very happy for a while, smiling and joking with his colleagues
and students, and then could fall into a depression, casting a mournful shadow over the atmosphere at the DAMTP.

It is important to remember that, although a great many people go through similar emotional upheavals, the vast majority of them have a number of advantages over Stephen Hawking. There are ways in which their emotions can be diverted and released; ineffectual as these methods often prove to be, they were not available to him at all. He could not scream and shout, go for a run, or indulge in a drinking binge; he could not smoke himself stupid or even speak to friends with ease. And although it was he who made the break, the pain was undoubtedly still there.

Many people who claim to know Stephen Hawking have been overprotective toward him, especially since the announcement of the separation. This attitude is misguided and is usually shown by people who turn out not to know him at all well. Close friends know that Hawking needs nobody to protect him—he is perfectly capable of looking after himself. The same people who try to protect Stephen also make the mistake of attempting to imbue him with feelings and emotions different from those of the rest of us, almost as if, because of his highly tuned intellect, he did not share the same dreams, hopes, and passions that the rest of humanity experiences.

One of his closest friends, David Schramm, knew Hawking for over twenty years and had little patience with those who try to create an image of Stephen as in any way emotionally different from others. He never pulled any punches when it came to his friend's personal life. He once introduced Hawking at a talk he gave in Chicago by saying “. . . [A]s evidenced by the fact that his youngest son Timothy is less
than half the age of the disease, clearly not all of Stephen is paralyzed!” Apparently half the audience was shocked speechless, but Hawking loved it.

Schramm believes that people are scared to face the fact that, in emotional terms, Stephen Hawking is a normal man. Because of the power of his intellect as well as the singular nature of his physical condition, they convince themselves that he does not feel the same way as others. Stephen loves the company of women, he enjoys flirting, and he appreciates physical beauty: why else would he have a poster of Marilyn Monroe in his office? Probably not for her intellect. Hawking's relationship with Elaine Mason was not one based on pity or other such feeble foundations. According to Schramm, who spent a lot of time with the couple, there was a genuine love between them.

Hawking refuses to talk publicly about his private life and makes that a stipulation of any interview these days. The journalists, for their part, continue to speculate on the causes and outcomes of the split. Jane, for her own reasons, has until recently remained equally tight-lipped on the matter (see
Chapter 18
). She turned down repeated requests from the producers to take part in the film of
A Brief History of Time
and agreed to participate in interviews only with journalists she knows personally.

Until some time after their separation, pictures of Jane and the children still decorated Hawking's office at the DAMTP, but the split was without doubt an acrimonious one. Friends claimed that Jane spoke bitterly about it. She was now under no obligation, as one acquaintance put it, to “promote the greater glory of Stephen Hawking.”
⁷
Only a year earlier, Jane
had told a reporter that 1989 had been the year when everything had fallen into place for them, when they had reached a new high point in their lives:

For me the fulfillment stems very much from the fact that we have been able to keep going, that we have been able to remain a united family. The awards were like the sugar frosting on the cake. I wouldn't say that is what makes all the blackness worth while. I don't think I am ever going to reconcile in my mind the swings of the pendulum that we have experienced in this house—really from the depth of a black hole to all the glittering prizes.
⁸

She explained to another journalist that her role was no longer to look after a sick man but “simply to tell him that he's not God.”
⁹

Perhaps in such statements as this, the murmurings of deep-rooted resentments and disquiet can be detected. Yet in the concluding scene of the BBC's
Master of the Universe
program, we see Stephen and Jane looking down on a sleeping Timothy in their house on West Road while Hawking's computer voice declares, “I have a beautiful family, I am successful in my work, and I have written a best-seller. One really can't ask for more.”
¹⁰

Hawking's children have always known that their father can be a difficult man to live with at times. In the late eighties, Lucy, in the
Master of the Universe
documentary, said:

I'm not as stubborn as him. I don't think I would want to be that stubborn. I don't think I have quite
his strength of mind, which means he will do what he wants to do at any cost to anybody else.
¹¹

Such stubbornness was to hold him in good stead as his personal life began to crumble and the pressures of global fame started to impinge seriously upon him. While Hawking was reaching the pinnacle of his success outside science, new complications began to affect him as he made the transition from celebrity to icon.

^*
Horizon
is a science documentary series on British TV.

17

A BRIEF HISTORY OF
TIME TRAVEL

E
ven though Stephen Hawking turned fifty in 1992 (coincidentally, the year in which the first edition of this book was published) and had forecast the death of physics twelve years earlier, he has continued to be involved in scientific research since then. But like many grand old men of science (a description which, against all the odds, is now an entirely apt one for Hawking), in his later years he has turned his attention to ideas at the wilder fringes of scientific
respectability. During the middle part of the 1990s, Hawking's research contributions largely involved the paradoxes and possibilities of time travel—a field he entered not as a pioneer, but following in the footsteps of his old friend and scientific sparring partner Kip Thorne.

You may be surprised to learn that the subject of time travel is a respectable area of research at all, even at the wilder fringes of respectability. If so, you are not alone. When one of us wrote a book about time travel
¹
and it was reviewed in the pages of the astronomical magazine
Observatory
, the magazine received an irate letter from two engineers at the University of Hull, castigating the editors for lending credence to such ridiculous notions by even acknowledging the existence of the book. But everything in that book, and everything we have to tell you in this chapter, is based on solid, respectable science, jumping off from the work of Thorne and the equally eminent Igor Novikov (formerly of the Soviet Union, now working in Denmark)—and, of course, of Hawking himself. Building a time machine may not yet be a practicable engineering prospect, but the possibility that natural time machines may exist is one that an increasing number of scientists are now taking very seriously indeed.

The physical description of a working time machine that has intrigued Hawking and other researchers recently is closely related to the physics of baby universes, described in
Chapter 13
. On that scenario, matter that collapses into a black hole and toward a singularity in our Universe can somehow be shunted sideways in spacetime, emerging to form a new expanding universe, in its own set of spacetime dimensions. But what we did not spell out in our earlier discussion is that
in principle the original black hole and the new baby universe are still connected by the cosmological equivalent of an umbilical cord, a tunnel through spacetime that the cosmologists prosaically refer to as a “wormhole.” In the context of baby universes, such a wormhole would have a diameter comparable to the smallest quantum of length (the Planck length, about 10
^−35
m); and since no information could get out of the black hole marking the end of the wormhole in our Universe, the connection seems to be only of academic interest.

But there is another way of looking at wormholes, one that has long been a favorite of science fiction writers. The equations of the general theory of relativity also allow for the existence of a more modest kind of wormhole, which links two places in our own Universe. Einstein himself, working with Nathan Rosen at Princeton in the 1930s, worked out the appropriate mathematical description of such a wormhole, which is known as an Einstein-Rosen bridge.

The usual problems with wormholes apply to an Einstein-Rosen bridge, which is, in effect, a wormhole linking two black holes in our Universe—a shortcut through spacetime. Such a wormhole could form naturally, the equations say; but the gravity of the black holes at either end of the tunnel would snap the wormhole shut faster than light could travel along it, closing it before there was time for anything to get from one end to the other.

This result was so well known that for fifty years no relativists bothered to study the equations describing such wormholes in detail. But that didn't stop the SF writers from leaping on the idea and using it as a basis for moving their characters (and spaceships) around the Universe more or less instantaneously.
The idea is that if you had an Einstein-Rosen bridge connecting a region of space near our Sun with a region of space on the other side of the Galaxy, a spaceship could dive in one end and come out of the other end essentially instantaneously, without the bother of covering all the intervening space at something less than the speed of light. But what those SF writers carefully swept under the carpet was the evidence that any such tunnel through space would only be open for a fraction of a second and would in any case only be as wide as the Planck length, so that their spaceships (and any passengers) would be distinctly crushed by their journey.

All of that changed, as Kip Thorne recounts in his book
Black Holes and Time Warps
,
²
in the mid-1980s, when the noted scientist Carl Sagan decided to turn his hand to fiction. Like other SF writers, Sagan wanted to use the idea of a tunnel through space to get around the speed-of-light barrier. But being a scientist, he wanted at least to pay lip service to the problem of the rapid collapse of a wormhole and give his readers some scientific double-talk to provide a fictional “explanation” of why the tunnel they were traveling through did not collapse. He turned to Kip Thorne for advice on how he might provide this necessary verbal camouflage, and Thorne took up the challenge.

At the end of the 1984–1985 academic year, Thorne realized that what would be needed to hold a wormhole open would be to thread it with so-called “exotic matter.” Exotic matter gets its name because it has a bizarre property—negative pressure, or negative tension. If you squeeze ordinary matter, it is compressed; but if you squeeze exotic matter, it expands (it doesn't just resist your squeeze; it really does
expand). You might think that this is hardly a step forward, since nobody has ever seen exotic matter. And yet cosmologists believe that it might occur naturally in the Universe, in the form of what is known as cosmic string.

Cosmic string is hypothetical material left over from the Big Bang, in the form of tubes of energy much narrower than an atom but possibly stretching across the entire Universe. It is a by-product of the era of the Big Bang itself, and the best way to think of it is as a piece of the Big Bang “frozen” and trapped inside a tube with a diameter of just 10
^−14
that of an atomic nucleus. Because the string contains the energy density of the Universe as it was about 10
^−35
seconds after the moment of creation, even though it is so narrow, each centimeter of cosmic string would contain the equivalent of 10 trillion tons of mass. A loop of cosmic string a meter long would weigh as much as the Earth.

There is no direct proof that cosmic strings exist or ever have existed, but there is some circumstantial evidence—such objects could have provided the “seeds” on which galaxies grew when the Universe was young. The gravitational influence of loops of string would make clouds of gas clump together, eventually getting big enough to carry on the job of galaxy formation unaided.

And, you may have guessed, cosmic string has another strange property: it operates under negative tension. If you pull a piece of cosmic string, it will shrink; but if you squeeze it, it will stretch. It is just the stuff to hold wormholes open with; the more the gravity of the black holes involved tries to squeeze the wormhole shut, the more the cosmic string will expand and hold it open.

Sagan was delighted with Thorne's suggestions on how to hold a traversable star gate open, and the explanation duly appeared in his novel,
Contact
, published in 1985. At the time, few readers realized that the “mumbo-jumbo” describing the structure of the wormhole through which Sagan's characters traveled was actually the most up-to-date scientific theory about wormholes, at the cutting edge of research. But what is really surprising, with hindsight, is that neither Thorne nor Sagan immediately appreciated that the equations Thorne had found which allowed for the existence of a traversable wormhole would apply equally as well to time travel as to space travel. The point, of course, is that Einstein's equations of the general theory of relativity describe spacetime, not just space alone. A wormhole (an Einstein-Rosen bridge) can link different parts of spacetime in our own Universe. This means that it can link different regions of space at the same time (allowing instantaneous space travel). It can also link the same place at different times (allowing instantaneous time travel). Or, indeed, it can link different places at different times, allowing the intrepid voyager to travel through both space and time, simultaneously and instantaneously. Thorne only realized the full power of the work he had started out on as a favor to Sagan when he went to a symposium in Chicago in December 1986, and one of the other participants pointed out the implications of the work for time travel.