Martin Rees earned his degrees in mathematics and astronomy at the University of Cambridge , where he is currently professor of cosmology and astrophysics and Master of Trinity College. Director of the Institute of Astronomy at Cambridge, he has also been a professor at Sussex University.

He has been Britain's Astronomer Royal since 1995. He has modeled quasars and has made important contributions to the theories of galaxy formation, galaxy clustering, and the origin of the cosmic background radiation.

His early study of the distribution of quasars helped discredit the steady state cosmological theory. He was one of the first to propose that enormous black holes power the quasars.

He has investigated the anthropic principle, the idea that we find the universe the way it is because if it were much different we would not be here to examine it, and the question of whether ours is one of a multitude of "universes." He has written nine books.

Through his public speaking and writing he has made the Universe a more familiar place for everyone.

Helen Matsos (HM): Earlier this year our magazine interviewed the Vatican Astronomer, Brother Guy Consolmagno. He discussed how the possible finding of alien life would impact world religions. Do you have any views on that?

Martin Rees (MR): I admire what the Vatican is doing in astronomy. The search for extraterrestrial life is the most exciting quest in 21st-century science. We know too little to say what the odds of success are; we don't know enough to say if it's likely or unlikely. But I think it's a fascinating search.

Of course, there are two parts to the search. One is the search for simple life elsewhere in the solar system, or evidence of a biosphere around an extrasolar planet. The second is the search for complex life.

What is the chance that simple life would get started, and then evolve by Darwinian selection into a biosphere anything like the one we have on Earth, with intelligent beings on it? Many people believe that simple life may be common but that advanced life may be rare.

HM: In your book "Our Cosmic Habitat," you say that a quadrant of the sky seems well suited to human habitability. With the discovery of extrasolar planets, it is now thought that as many as a quarter of the stars in our galaxy have solar systems around them. How do these findings relate to the ideas in your book?

MR: The realization that planetary systems are common around many stars is an exciting development. We don't know what fraction of those stars would have habitable planets, but most of us confidently expect there should be many planets in our galaxy that resemble the young Earth, on which life might have gotten started.

It would be exciting to find any evidence for biological activity on those planets. Within ten to twenty years we could find this. Obviously the detection of any life beyond the Earth would be of great importance. It would show us that the probability of life getting started was not infinitesimally small, that it happened not just once but more than once and probably very many times.

The search for intelligent life is a different problem, and that may fail even if the search for simple life succeeds. Many people would be depressed if the search for intelligent life failed. It would be disappointing if the SETI searches yielded no results. It would make the cosmos seem a lonelier place.

But, I think there'll be some compensations, which I discuss in my book. In particular, I think it would raise our cosmic self-esteem. We could then regard our Earth, tiny though it is, as perhaps being the most important place in the galaxy.

It might be the only place where life has evolved into a complex biosphere, containing creatures with structures like our brains, able to contemplate their origin.

I think another perspective astronomy brings to bear on these issues is that astronomers are aware of the tremendous time span lying ahead of us.

Most educated people are aware that we are the outcome of nearly four billion years of Darwinian selection, and I think many tend to think humans are the culmination of all that. But astronomers know that our sun is less than halfway through its life span.

Our sun will flare up and die six billion years from now, a period of time longer than the sun's history so far. Some people imagine that there will be humans watching the sun's demise six billion years from now, but any creatures that exist then will be as different from us now as we are from bacteria or amoebae.

We should think of ourselves as still in the early stage of the emergence of complexity and intelligence. It's hard to conceive what forms that might take on Earth or far beyond Earth. But I think we should see ourselves as nowhere near the culmination of evolution.

Even if life is now very rare in the galaxy or unique to Earth, that doesn't mean life is forever going to be a trivial afterthought in the cosmos. In the time lying ahead, life from Earth could spread all through the galaxy. The Earth could be cosmically important as the seed from which life spreads more widely.

HM: So we may evolve to a high enough state that we could disperse as an intelligent species throughout the universe. But what about the possibility that life already exists elsewhere?

MR: It's possible that the universe is already teaming with life, but it's equally possible that life is very rare and almost unique to the Earth. In the later case, some people may think that makes life an irrelevant triviality in the cosmos. But if we are mindful of the time that lies ahead, in that far future, life starting from Earth has abundant time to spread through the entire galaxy.

HM: In your book, "Our Final Hour..."

MR: (laughs) It was called "The Final Century" in Britain, but the Americans, with their craving for instant gratification, wanted instant dis-gratification too, and so they called it "Our Final Hour." I was really annoyed about that.

HM: Two countries separated by a common language, I suppose. You say in the book that humans might not survive until the end of this century.

MR: Well I say civilization might not survive. To wipe out all humans is unlikely. But I think a setback as bad as a global nuclear war is quite likely.

HM: And then what happens? How does the story end?

MR: One extreme, pessimistic scenario is that, during this century, we suffer disasters which foreclose all future technological progress and perhaps make it difficult for civilization to survive on Earth.

The optimistic scenario is that, during this century, human communities spread beyond the Earth for the first time. Self-sustaining groups established a hundred years from now would not be destroyed whatever happened to the Earth. That could be the first step towards evolution beyond the Earth.

A feature of this century, which I emphasize in the book, is that not only are traditional technologies changing faster than ever, but the world is changing in different ways.

Humans beings themselves are going to change. For several thousand years, the one thing that hasn't changed has been human nature and the human physique. But in this century we have targeted drugs, genetic manipulation, and maybe even implants in the brain.

This makes it harder to predict a hundred years into the future than it would have been for someone in 1900 to predict our present-day world. That suggests there are greater uncertainties and greater risks facing us now.

But it also suggests that if humans did establish groups beyond the Earth, then it wouldn't take more than a few centuries at most before they evolve into different species. They would be able to use genetic techniques to adjust themselves to survive in a very alien habitat.

HM: What are your thoughts on sending men to Mars and the idea of terraforming Mars?

MR: My view about manned space flight is that, as a scientist and practical man, I'm against it, but as a human being, I'm in favor of it. The practical reason for sending men into space is getting weaker with every advance in robotics and miniaturization.

So it can only be justified as a human adventure. The American public is very risk adverse, even though a 2 percent risk, which is what the shuttle flights have had, is not very high by test pilots standards, and is far lower than the risks that many individuals would take on their own behalf.

I believe the only future for manned space flight is to do it much more cheaply, where private sponsorship or private enterprise can fund it. And also when adventurers are prepared to accept much higher risks.

I believe the first people to go to Mars may go with one-way tickets, but they'd be pioneers. I hope by the end of the century there will be communities on Mars, but I think they will be more in the style of ancient explorers than present-day astronauts.

The Martin Rees interviews on cosmology and biology are serialized in three parts: Our Cosmic Patch (1), Before the Beginning (2), and Our Cosmic Self-Esteem (3).

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