Interview with Sir Martin Rees

The Times Educational Supplement (Dec 1999)

Catching up with the Astronomer Royal proved to be harder than I imagined. Unlike most astrophysicists, Sir Martin Rees does not spend his entire life nuzzled next to a telescope or sat behind a computer, but rather travels whenever possible, extolling the wonders of astronomy and the mysteries of cosmology to the public. In between speaking at the British Association Meeting in Sheffield, a Cambridge bookshop and in Barcelona, he managed to spare a moment to meet for afternoon tea following his talk at the Cheltenham Festival of Literature.

His Cheltenham lecture, which had been sold-out days in advance, was given in a hall filled with three hundred people, ranging from teenagers attending Cheltenham Ladies’ College to dozens of gentile 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. He presents astrophysics with wit and charm, ultimately giving the impression of a humble man exploring the wonders of the universe, rather than an arrogant master of the cosmos.

As well as giving him a greater opportunity to speak to the public, the title of Astronomer Royal also allows him to speak out about the issues that concern him. For example, he feels that there is some excellent science reporting, but he is currently annoyed by the lack of coverage of British science, a problem that is compounded by the regular reporting of breakthroughs made in the United States. He acknowledges that this is partly the fault of British scientists, who can sometimes be rather diffident, and university press offices, who sometimes be less than proactive, but in the main he blames the British media.

“For instance, the BBC gives the impression that all the exciting advances are coming from the United States,” Sir Martin complains, “When in fact there are equally articulate and capable people in this country who have contributed to the subject. 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, especially, to ensure that the UK maintains its strong astronomical tradition, he is well aware that the title of Astronomer Royal does not have the same clout as other titles, such as Poet Laureate.

“To some extent it’s an embarrassment,” he says. “People think the title gives me some special influence, whereas in particular with PPARC (the astronomy funding committee) I have had frustratingly little influence on many of their decisions, which I feel have been sub-optimal over the years.”

The fact that Sir Martin is a great populariser and politically active within the astronomy community does not mean that he has neglected research. His career has spanned four decades, and he continues to be one of the most respected and eminent astronomers in the world. However, he embarked on his career with no real passion for the subject, and it took an inspirational professor and a remarkable series of astronomical discoveries to make him realise that he should devote his life to exploring the universe.

As an undergraduate, Sir Martin had studied pure mathematics, and upon graduating he considered pursuing careers in both statistics and economics. However, 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, now Sir Roger, and he supervised Stephen Hawking, George Ellis and Brandon Carter, before taking on Sir Martin as a PhD student.

It soon became clear that Sir Martin had stumbled into a rich and vibrant area of physics, in which revolutionary discoveries were opening new lines of research. During the latter half of the 1960s’s, astronomers discovered quasars, pulsars and the microwave background radiation, forcing a radical reshaping of astronomical and cosmological models, which in turn heavily discounted the experience of established physicists and created a level playing field for younger researchers.

Quasars and pulsars were exciting because they provided the first real testing ground for Einstein’s theory of general relativity, the more accurate successor to Newton’s theory of gravity, which has only been useful for three centuries because our experiences have been limited to small gravitational forces. Newton’s law of gravity is satisfactory for describing the orbit of planets in the weak gravity of the Sun, and they are fine for 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 to be abandoned in favour of Einstein’s theory.

For example, a pulsar (a form of neutron star) is the superdense core that remains after a large star implodes in a supernova event. The most spectacular confirmation of this scenario is the Crab Nebula, which consists of debris flying away from a central neutron star, the remnant of a supernova that was observed by the Chinese in 1054 AD. 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. At the time, the astrophysicist Thomas Gold summarised how the community reacted to the emerging field of relativistic astrophysics and the changing role of relativity theorists:

“The relativists with their sophisticated work are not only magnificent cultural ornaments but might actually be useful to science!”

Over the last thirty years, Sir Martin has continued to study the physics of extreme astronomical phenomena, including black holes and active galactic nuclei. Most recently, he has focussed 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. The flashes last only a few seconds, and their power is equivalent to the output of millions of galaxies. Sir Martin explains,

“We believe that gamma ray bursts are connected with either a peculiar kind of supernova 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 per day somewhere in the universe.

In addition to trying to explain the physics of specific astronomical objects, Sir Martin has also studied broader cosmological questions, namely the evolution of the universe and the formation of galaxies. He is particularly interested in the so-called Dark Age, the period between the brilliant early phase of the universe and the moment when stars ignited. Half a million years after the Big Bang, the universe cooled enough so that 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 first stars formed and began to shine. In other words, Sir Martin is interested in what happened during this phase of darkness – how did a cooling, largely formless universe transformed itself into a structured universe with stars?

The evolution of the universe is, in part, the subject of Sir Martin’s 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 strength of electrical forces. N is roughly 10^36, 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 this 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 ten thousand 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, then it 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 Sir Martin, there is a third possibility. He suggests that there is a myriad of universes, collectively known as the multiverse, each with its own values for the six numbers. The vast majority of universes are sterile, but a few of them can contain life. As we are alive, then we must, by definition, find ourselves in a universe with the right six numbers. The book is a digestible and engaging exposition of this astonishing theory,

Evidence in favour of the multiverse theory might be too long in coming, particularly as Sir Martin feels that we are in another Golden Age of astronomical discovery, similar to the mid-1960s when he began his research. For example, 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. Furthermore, ground-based telescopes and the Hubble Space Telescope have observed galaxies that are further away and younger than any previously seen, which may provide vital clues to illuminate the Dark Age.

However, regardless of any potential discoveries, Sir Martin is confident that there will always be a healthy stock of unsolved problems. He is fond of Richard Feynman’s analogy between physics and chess:

“Imagine you’d never seen chess being played before, then 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.”