Cosmologist and astrophysicist Lord Martin Rees ahead of a press conference on the Breakthrough Life in the Universe Initiatives (© Stuart C. Wilson/Getty Images for Breakthrough Initiatives)

Lord Martin Rees – Astronomer Royal

The prestigious British stargazer and leader of Project Breakthrough tells BBC Focus magazine what alien signals will look like if we find them.

What drew you to Project Breakthrough?


Well, I think SETI (Search for Extraterrestrial Intelligence) is clearly an enterprise where the pay-off from success would be huge. It would be one of the greatest discoveries of all time and would interest a far wider public than other discoveries. But none of us involved would rate the chance of success as more than a few per cent, and I would rate it less than that.

Nonetheless, given that there’s so much public interest, I think it’s hugely welcome that Yuri Milner has offered substantial funding for Breakthrough Initiatives – otherwise the chance of discovering ET in our lifetime would be zero.

What sets this venture apart from SETIs before it?

It’ll be much more sensitive in terms of being able to detect faint signals and in terms of wavelength coverage. So it’ll be a more comprehensive search than has been done hitherto. The initial focus is on radio searches, but we should carry optical searches too, and use all possible techniques as they become available.

Let’s say you pick up a signal – what are the next steps?

There have been lots of suggestions. In fact the International Academy of Astronautics set up the SETI Post Detection Task Group [of which BBC Focus contributor Stephen Baxter is a member] for just this job. Their role is to lay out the first steps towards first contact. The group is led by Paul Davies, who is on our committee.

What might an alien signal look like?

We would be looking for a signal that was not natural. It might have a very narrow bandwidth, or be pulsed. But even if it were clearly artificial, that wouldn’t mean it was a message that we could decode. My guess is that it wouldn’t come from a civilisation of organic beings but from some hyperintelligent machine.

Let’s think what has happened on Earth, and what may happen in the future. Technological civilisation emerged after 4.5 billion years, but within a few centuries it may have been surpassed by machines that spread into space – and they will have billions of years to develop further. So it may well be a fairly brief period in Earth’s history during which intelligence is dominated by organic creatures, and a much longer future when it’s dominated by machines. This therefore suggests that, if alien intelligence has emerged on another planet via a similar route to what happened on Earth, we are unlikely to catch it in the brief organic stage – we’re far more likely to catch it in the far longer post-organic stage.

What could we learn?

Biologists still don’t understand how life began on the Earth. When they do, we’ll learn two things. One is whether it’s a rare fluke or whether we would expect the same thing to have happened in any environment like the Earth.

Secondly, it will probably give us a clue as to whether the chemical basis of life has to be the RNA and DNA that our life is based on, or whether there could be quite different chemistries. But even if simple life were common, the emergence of a complex biosphere harbouring intelligence could be rare.


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