Master of the multiverse

Simon Singh talks to Astronomer Royal Martin Rees about promoting British science and the importance of six numbers.

Catching up with the Astronomer Royal proved trickier than imagined. Unlike most astrophysicists, who spend their lives nuzzled up to telescopes or computers, Sir Martin Rees travels whenever possible, extolling the wonders of astronomy and the mysteries of cosmology. In between speaking at a meeting in Sheffield, a Cambridge bookshop and in Barcelona, he managed to spare a moment to meet for tea in Cheltenham, where he was giving a lecture.

The sell-out talk was given in a hall filled with 300 people, ranging from teenagers to dozens of genteel Gloucestershire pensioners. They listened keenly to a vivid explanation of the Big Bang and cosmological evolution, illustrated with snapshots of the most distant galaxies in the universe.

As Astronomer Royal, Rees is in a position to speak out about the issues that concern him. Top of his list at the moment is the scant coverage of British science, a problem compounded by the regular reporting of breakthroughs made in the United States. He acknowledges that this is partly due to the diffidence of British scientists and university press offices, but mainly he blames the British media. "The BBC gives the impression that all the exciting advances are coming from the United States when there are equally articulate and capable people in this country," he says. "To give one example, The Planets series on BBC2 was, rightly, primarily about Nasa's success - but the Cassini mission was a collaboration between the European Space Agency and America, whereas the programme gave the impression that it was an entirely American mission."

Although he would like to influence how science is perceived and conducted, to ensure the United Kingdom maintains its strong astronomical tradition, Rees is well aware that the title Astronomer Royal does not have the same clout as others, such as Poet Laureate. "To some extent it's an embarrassment," he says. "People think it gives me some special influence, whereas in particular with PPARC (the Particle Physics and Astronomy Research Council) I have had frustratingly little influence on many of their decisions, which I feel have been sub-optimal over the years."

Although Rees is one of the world's most eminent astronomers he embarked on his career - which has now spanned four decades - with no great passion for the subject. As an undergraduate, he studied pure mathematics and considered pursuing careers in both statistics and economics. But he was taken under the wing of Dennis Sciama, a Cambridge astronomer responsible for nurturing many of the great figures in modern cosmology. Sciama worked closely with the young Roger Penrose and supervised Stephen Hawking, George Ellis and Brandon Carter before taking on Rees as a PhD student.

The young mathematician soon realised he had stumbled into a rich area of physics, in which revolutionary discoveries were opening up new lines of research. In the 1960s, astronomers discovered quasars, pulsars and the microwave background radiation that is constantly present in the universe, forcing a radical reshaping of astronomical and cosmological models. This heavily discounted the experience of established physicists and created a level playing field for younger researchers.

Quasars and pulsars provided the first real testing ground for Einstein's theory of general relativity, the more accurate successor to Newton's theory of gravity. Newton's law of gravity is satisfactory for describing the orbit of planets in the weak gravity of the Sun and calculating the consequences of the even weaker gravity here on Earth, but the bizarre astronomical objects discovered in the 1960s are held together by such intense gravitational forces that Newton's theory has had to be abandoned in favour of Einstein's.

A pulsar (a form of neutron star) is the super dense core that remains after a large star implodes. The density of a neutron star is such that the force of gravity is a million million times greater than on Earth. This force crushes anything on the surface of a neutron star, so that all mountains are less than one millimetre in height.

However, climbing such a one millimetre mountain would require an immense amount of energy, greater than the energy required to launch a person on Earth into orbit. These gravitational forces can only be explained within the context of general relativity. Prior to the 1960s, general relativity described only hypothetical objects, but now there existed real relativistic objects.

Over the past 30 years, Rees has continued to study the physics of extreme astronomical phenomena, including black holes and active galactic nuclei. Most recently, he has focused his attention on gamma ray bursts, flashes that are incredibly intense when they strike the Earth, even though they originate from far across the universe. They last only a few seconds, and their power is equivalent to the output of millions of galaxies. Rees explains: "We believe that gamma ray bursts are connected with either a peculiar kind of supernova (stellar explosion) or perhaps two neutron stars spiralling together and merging. In either case we are witnessing the formation of a black hole and the energetics of the material falling into it." Typically, astronomers detect one gamma ray burst daily somewhere in the universe.

Rees has also studied broader cosmological questions: the evolution of the universe and the formation of galaxies. He is particularly interested in the so-called Dark Age. Half a million years after the Big Bang, the universe cooled and light shifted to a lower infra-red frequency, which is beyond the visible spectrum. Visible light was created once again roughly a billion years later when the first stars formed and began to shine. Rees is interested in what happened during the intervening phase of darkness - how did a cooling, largely formless universe transform itself into a structured universe with stars?

The evolution of the universe is featured in his new book, Just Six Numbers, in which he points out how every aspect of the universe's evolution depends on the eponymous six numbers. For example, one number, N, reflects the strength of gravity relative to the strength of electrical forces. N is roughly 1036, which means that gravitational forces are a million million million million million million times weaker than electrical forces. This number is important, because had the force of gravity been stronger, then stars would be formed more quickly, and would also die more quickly. Stars in our universe burn for roughly ten billion years, but stars in a different universe, one with gravity that is one million times stronger, would live for only 10,000 years, which is not long enough for life to evolve.

The other five numbers are also critical to the fate of the universe, and the likelihood of life is even more sensitive to changes in these numbers. In other words, if the numbers that define our universe were slightly different, the universe would be a sterile space, which prompts us to ask whether there is some deeper significance to these numbers. Are we simply lucky or is there a creator who selected the numbers in order to create a universe capable of sustaining life?

According to Rees, there is a third possibility. He suggests there are myriad universes, collectively known as the multiverse, each with its own values for the six numbers. Most universes are sterile, but a few can contain life. As we are alive, then we must, by definition, find ourselves in a universe with the right six numbers.

Evidence in favour of the multiverse theory might not be too long in coming. Rees feels that we are in another Golden Age of astronomical discovery, similar to the mid-1960s when he began his research. Physicists are working on superstring theories that might help describe the earliest phase of the universe, while experimentalists are hunting down the so-called dark matter. Ground-based telescopes and the Hubble Space Telescope have observed galaxies farther away and younger than any previously seen, which may provide clues to illuminate the Dark Age.

Regardless of any potential discoveries, Rees is confident there will always be unsolved problems. He is fond of Richard Feynman's analogy between physics and chess: "Imagine you'd never seen chess being played beforeI by watching a few games, you could infer the rules. Physicists, likewise, learn the laws that govern the universe. In chess, learning the moves is just a trivial preliminary on the absorbing progress from novice to grand master. Similarly, even if we knew the basic laws, exploring how their consequences have unfolded over cosmic history is an unending quest."

Simon Singh is a particle physicist turned journalist and author of The Code Book.

Just Six Numbers, Weidenfeld & Nicolson, Pounds 12.99.