The other major event of 2015 was the launch of Russian-Israeli tech billionaire Yuri Milner's 10-year Breakthrough Listen project, which is buying thousands of hours of time on the world's most powerful radio telescopes to search over a million stars for artificial radio or laser signals.
This is “Passive SETI”, and there's certainly no harm in just looking for signs of the existence of other civilisations elsewhere in the galaxy. There is “no bigger question in science,” said the late Prof. Stephen Hawking, who was an adviser to the project. But if you find such a civilisation, an enormous debate will immediately erupt over whether we should reply or not. Hawking thought not.
The Breakthrough Listen project has been up and running for several years now, and in June last year announced that it had so far examined 1000 star systems within 160 light years of Earth but detected no transmissions from alien civilisations.
However, even if there were 10,000 civilisations in the galaxy, the probability that one of them would be within 160 light years of us is very low. Moreover, they would have to be using a very powerful signal aimed specifically at us to be detected at that range. Old television programmes do not travel across the galaxy intact. (Sorry, Galaxy Quest.)
In fact, it is remarkably quiet out there, but that doesn't necessarily mean that there are no other civilisations in our corner of the galaxy. There is a rival hypothesis which suggests that there may indeed be one or more civilisations in our galactic neighbourhood, but that they are observing radio silence.
Why? Because they know or at least suspect that there is something big and bad and dangerous lurking out there in the dark, and they do not want to attract its attention.
This hypothesis is increasingly being called the “Dark Forest Problem”, after the extraordinary success of Chinese science-fiction writer Liu Cixin's “Three-Body Problem” trilogy. It traces the calamitous consequences over 400 years of an alien contact scenario, initiated by well-meaning human beings, that goes desperately wrong.
Nothing in the science we know makes this hypothesis plausible. Interstellar travel is virtually impossible, and neither trade nor conquest would be profitable at interstellar distances even if it did somehow became possible. The energy required and the time taken would simply be too great.
Or so we assume, but our current level of scientific knowledge is probably not the last word on the subject. We still have much to learn even about the basic physics of the universe — the nature and role of “dark matter” and “dark energy”, for example — and distance alone might not be enough to protect us from any ill-intentioned BEMs with a sufficiently high level of technology.
So Dominik is right: we do need to have an international discussion about whether we should make our existence known, should the intensified SETI research yield a positive result. And it would be wise to have it before the media circus that would erupt if we actually found a message.
Another of Milner's programmes, Breakthrough Message, is working on what kind of answer we might send, but its remit is clear. It has pledged “not to transmit any message until there has been a global debate at high levels of science and politics on the risks and rewards of contacting advanced civilizations”.
