Stephen Hawking (45 page)

By this time Jane was living with a classical musician, Jonathan Hellyer-Jones, and her life had moved on in other ways. She had become an author herself and had written a book about converting properties in France called
At Home in France
. But clearly the wounds still ran deep, because despite having rebuilt her life after the separation in 1990, recriminations continued. Jane said of Stephen and Elaine's big day: “I wasn't invited to the wedding and if I had been I wouldn't have attended.” And years later, in 1999, she had published her autobiography,
Music to Move the Stars
, in which she gave a no-holds-barred account of her life with Stephen. Her book painted a far from pretty picture of the Hawking marriage. Meanwhile, David Mason (who had been doubly damaged by the loss of his wife, because much of his computer business was built around Hawking's system) simply commented that Hawking “uses people.”
¹⁷

Even Hawking's mother, Isobel, made a rather dignified public comment about the treatment Stephen and Elaine had received from the press, revealing in an interview that she thought her son's relationship had been misrepresented. “The coverage of the wedding and the barrage beforehand were thoroughly unpleasant,” she said. “The impression was that
Elaine was an interloper—and she is not. There is nothing disreputable about the wedding, as the press suggested. It is quite normal for people who have been together for four years to get married.”
¹⁸

Indeed, the media seemed determined to portray the Hawking wedding as something of a freak show. The occasion was variously dubbed “Best-seller weds,” “Einstein wedding boycott,” and “Genius weds nurse,” and more than one national newspaper journalist wrote condescending features heavy with the whiff of sanctimony.

But perhaps in reflective moments Hawking accepts this furor as the downside of having by now become public property, a figure as much in the public eye as Hollywood actors, pop stars, and royalty. If he is happy to appear in any newspaper commenting upon almost anything, then he cannot justifiably complain too much if the press fails to treat his personal life with due respect. He has never made any form of public complaint over the issue, although his mother's comment on this was that “Stephen and Elaine have never said it has hurt them, but I think it has caused them pain.”
¹⁹

A poignant reminder of Hawking's many-faceted life and career came with the celebration of his sixtieth birthday. A press release announced that there would be “a special birthday symposium photocall and that space for TV crews and photographers would be very limited.” Newspapers around the world covered the story and great attention was given to the fact that the professor was still with us, almost forty years after being diagnosed with ALS and given only a short time to live. But at the same time, “Hawking the scientist” was not forgotten, and he chaired a special four-day symposium at
Cambridge University on “The Future of Theoretical Physics and Cosmology.” On the evening of his birthday, January 8, he hosted a private party to which over two hundred family, friends, colleagues, and former students were invited.

But many more ups and downs lay immediately ahead for Stephen Hawking and those around him. As we will see in the next chapters, there were new scientific challenges in which to participate, while in his personal life he was about to experience some of his greatest traumas and triumphs.

19

GOD AND THE
MULTIVERSE

I
n 1963, shortly after Hawking, still only a Ph.D. student, was diagnosed with motor neuron disease, any suggestion that he might still be making significant contributions to science in the first decade of the twenty-first century would have been laughed out of court. Nearly thirty years later, when the first edition of this book appeared, the suggestion would still have seemed faintly ridiculous, not just because of his illness but because very few scientists make important
contributions in their sixties. But once again, Hawking has proved an exception. Returning to his fascination with cosmology, he has proposed a new explanation for the origin of the Universe, and along the way stirred up controversy by stating dogmatically that God does not exist, to the delight of Richard Dawkins but rousing the ire of Baroness Susan Greenfield.

These new ideas build on the concept of anthropic cosmology and the many-universes (also known as many-worlds) idea that we mentioned briefly in
Chapter 13
. To put them in context, we need to explain the latest version of the many-worlds idea, which now goes by the name of the Multiverse.

There are, in fact, several different versions of the Multiverse,
¹
one of which (the bubble-universes model) we met earlier. The version that Hawking espouses is known as M-theory. The letter “M” here has no significance except as a label—it does not stand for anything, although as it happens it could stand for Multiverse. It is the modern version of the supergravity idea which Hawking liked and others dismissed in the 1980s; in a recent lecture outlining these ideas,
²
Hawking joked that it now “goes under the name of M-theory” to hide the blushes of “those that rubbished supergravity in the eighties.” The key feature of M-theory is that it is a quantum-mechanical theory which includes a mathematical description of every possible universe allowed by the laws of physics, including those with different values of the constants of nature (such as the strength of gravity) and different numbers of spatial dimensions.

One way of thinking about this is in terms of something called the cosmic landscape.
³
Supergravity, or M-theory,
involves universes that are composed of ten dimensions of space plus one of time, making eleven dimensions in all. The space dimensions can roll up in different ways to make different numbers of effective dimensions. In the case of our Universe, as we described earlier, this leaves three space dimensions plus one of time, a four-dimensional Universe for all practical purposes. But according to quantum theory, there is nothing to stop the dimensions rolling up in other ways, to produce universes with different numbers of dimensions—six of space plus one of time, or eight plus one, and so on. This possibility is a particularly intriguing one because it seems that complicated creatures like ourselves can only exist in universes which have three spatial dimensions. With only two dimensions, complicated structures simply cannot exist, as is spelled out in the entertaining book
Flatland
.
⁴
Rather more surprisingly, it turns out that with four or more spatial dimensions, gravity and electric forces would not obey an inverse-square law but would decrease more rapidly with distance. That would make it impossible to have planets orbiting a star in stable orbits, like our Solar System, or even for stable atoms to exist. So if we are interested in life forms like us (not
exactly
like us, but complicated, intelligent creatures), we are restricted to studying the universes which have rolled up to produce three large dimensions of space plus one of time. But that, it turns out, is not very restrictive.

Even within each kind of universe, there is enormous scope for variety, because the laws of physics can have different values—different strengths—in different universes. For example, it is possible, according to this idea, to have a universe with three space dimensions and one time dimension,
but in which gravity is stronger or weaker than in our Universe. Another intriguing example comes from the discovery, at the end of the twentieth century, that the expansion of the Universe is beginning to speed up. This acceleration is explained in terms of a “cosmological constant,” which is a measure of the springiness of space. The constant is tiny, but if it were slightly bigger the Universe would have expanded too fast for galaxies, stars, and people to have formed. M-theory says that there must be universes in which exactly that has happened.

So where are the other universes? This is where the cosmic landscape comes in. We are back in the realm of cosmic coincidences and anthropic cosmology, but with a new perspective. Quantum theory tells us that the different universes have different energies (technically, different “vacuum energies”), and the landscape represents this in the same way that a three-dimensional tabletop model can represent the hills and valleys of a region of the Earth's surface. The difference is that the cosmic landscape is a mathematical model rather than a physical model. High peaks in the landscape correspond to high energy, valleys and potholes correspond to lower energy. Quantum fluctuations can produce the seeds of all possible universes, some with more energy and some with less. A universe “born” in a pothole, with a certain number of space dimensions and values of the constants of physics, will sit there quite happily. But a universe “born” on a mountaintop, or on the sloping side of a valley, will roll down, like a ball rolling down a hill, toward the nearest low point, giving up energy as it does so. The energy released in this process drives inflation, setting the universe expanding; and the low value of the
vacuum energy at the bottom of the pothole corresponds to a low value for the cosmological constant. Each point on the landscape corresponds to a possible universe; but the potholes are “sweet spots” where, among other things, there is a low value of the cosmological constant, allowing stars, galaxies, and creatures like us to exist.

The standard version of this idea harks back to the simple version of anthropic cosmology. It says that every pothole in the landscape corresponds to a universe more or less like our own, and that because life like us can only exist in such sweet spots, it is no surprise that when we look around us, we see the Universe we see. On this picture, there is a myriad of other universes containing observers more or less like us, but an even larger number of uninhabited, and uninhabitable, universes. But Hawking's version of M-theory translates it into the language of Richard Feynman's “sum over histories” approach to quantum mechanics and turns the whole argument on its head, with our existence front and center. As he puts it, “top down” rather than “bottom up,” with us at the top.
⁵

Hawking says that the anthropic principle is “essential, if one is to pick out a solution to represent our universe from the whole zoo of solutions allowed by M-theory.”
⁶
He emphasizes that—although the famous singularity theorems that he developed with Roger Penrose back in the 1960s say that if the general theory of relativity is completely correct, then the Universe must have begun as a singularity—what this is really telling us is that one has to allow for quantum gravitational effects close to the singularity, so the Universe had a quantum origin. It is that quantum origin which gives rise to all the
possible universes of M-theory, each described by a set of equations known as a wave function. Hawking developed the implications of this idea with Thomas Hertog, of CERN, and they published a paper, “Populating the Landscape: A Top Down Approach,” in the journal
Physical Review D
in 2006.
⁷

You can get an insight into the thinking behind their approach by thinking about how Feynman's “sum over histories” idea might be used to describe the flight of a ball thrown by someone on the ground through a window on the second floor of a building. According to the sum over histories idea, the ball somehow sniffs out every possible way it can get from the hand of the thrower to the window, but these paths interfere with each other in such a way that everything cancels out except for the “classical” trajectory that we understand from our everyday experiences. Mathematically, this corresponds to integrating the wave functions for the different histories. You start out with a large number of wave functions, and work toward a single “history.” This is what Hawking and Hertog call the “bottom-up” way of looking at things. It corresponds to guessing how the Universe started, and working out from that beginning what it should look like now.

But we don't know how the Universe began! We
do
know what it looks like now. This is as if we are sitting in a room on the second floor and a ball comes in through the window. We know the ball came in through the window at a certain angle and a certain speed, but we don't know how it got there. We can, though, work backward, using the sum over histories method, from the observation of the ball to work out where it came from—which wave functions contributed to its trajectory. This is a small-scale example of Hawking and Hertog's
top-down approach, in which the history of the Universe is traced backward quantum-mechanically to determine which wave functions contributed to its origin. The ball coming in through the window, for example, does not carry the imprint of wave functions corresponding to its having been dropped from an aircraft or thrown from the top of a tree, so many “histories” can be eliminated. Applying this to the Universe tells us how things began.

This, says the team, means that the present, in effect, specifies the past. The other universes which are allowed by M-theory are no longer seen as being physically real, but are ghosts of universes that might have been, like the ghost of Christmas yet to come in
A Christmas Carol
, in the same way that other possible trajectories for the ball are ghost trajectories. Only some of the possible cosmological histories have left an imprint on the world in which we are living. The Multiverse began in every possible way, but all but a few possibilities were soon eliminated. The Universe had many beginnings, but has only one ending—one “now.” This is at once the death of the Multiverse, in its usual form, and the triumph of anthropic cosmology, since we can eliminate all histories that do not allow our existence, such as those with four spatial dimensions or a large cosmological constant. And, combined with Hawking's “no-boundary” condition (
Chapter 11
), it leads him to assert that there is no God. In
The Grand Design
, he concludes that “spontaneous creation is the reason there is something rather than nothing, why the universe exists, why we exist.”