Why we may not be alone in this universe

It’s an age-old question, as valid for you and me as it was for Giordano Bruno when he wrote about an “infinity of worlds” before being burnt at the stake in 1600.
But 50 years ago last month, a letter to the magazine ‘Nature’ ended the passive, look-up-and-ponder attitude by proposing a scientific, experimental approach. We don’t have an answer yet (or you and I would know), but in the process we have come up with quite a tale to tell.

Giuseppe Cocconi (1914-2008) and Phil Morrison (1915-2005) were both accomplished physicists when they wrote ‘Search for Interstellar Communications’ (Nature, Sept 19, 1959). Cocconi started his life in science doing experiments with the physicist Enrico Fermi and later had a brilliant career at the European Particle Physics Laboratory (CERN) in Geneva. Morrison, professor at MIT, had been a group leader in the Manhattan Project.
Their letter to ‘Nature’ reported the obvious. At the time, they had no evidence of the existence of planets around stars and no clue about life on them, much less on any evolution of technological societies. But if there are intelligent beings somewhere out there, they wrote, they may have established a channel of communication, aimed also at us.

It’s easy to see that such a channel would probably use radio waves as the most efficient way of transmitting a signal. The two men suggested frequencies for us to listen in on, using the new antennas of radio-astronomy, just then coming of age.
They had no clue as to what to listen for, of course. Prime number sequences? Digits of pi? No use guessing, just trust them.

The suggestion of the two physicists fired quite a bit of enthusiasm. Almost immediately, Frank Drake, at the newly created National Radio Astronomy Observatory, started Project Ozma, the first radio search for an intelligent signal. Since then, over 100 search programmes have been carried out, culminating in the biggest of them all, SETI (Search for ExtraTerrestrial Intelligence), still going strong.

All to no avail, of course: not an intelligent peep on any antenna. Does this mean that we are alone in the sky? Not at all. As Francis Bacon wrote, “They are ill discoverers that think there is no land, when they can see nothing but the sea.”
SETI itself, and its predecessors, have prompted a small revolution in science, technology and sociology. Over 50 years, our ability to search for radio signals has increased 10,000 times more than the increase in sensitivity enjoyed by all optical astronomy in the 400 years since Galileo.

SETI has also been able to survive dramatic funding cuts, notably from NASA, and is now thriving on mostly private support. It does so through the extraordinary involvement of the public.

The enormous computer power necessary to process all the radio signals collected from the sky is now enthusiastically supplied by a network of close to a million personal computers. Download SETI software as your (fascinating) screensaver and you could, one day, be the first to spot an extraterrestrial signal — an irresistible prospect to many.

New additions
Meanwhile, astronomy from ground and space has found extra-solar planets. The first was discovered in 1995 around a nondescript local star. Nearly 400 more are now catalogued in one of the greatest leaps of astronomical discovery. We have today a good insight into the existence of planets: We know they are the norm, not the exception, around stars.

With 100 billion stars in our galaxy alone, we have ground for optimism about the emergence of life somewhere else.

Data are accumulating on organic materials in outer space. Some important building blocks of life, such as amino acids and sugars, are now routinely found in meteorites and in extraterrestrial environments. Recently, NASA brought back some amino acids straight from a comet’s tail.

Complex organic molecules just randomly present in the stuff our solar system was made from? Panspermia — the theory that life seeds came from outer space — confirmed? Too early to tell.

The only thing we can safely discard is the ‘directed panspermia’ theory of Francis Crick and Leslie Orgel. In 1973, the DNA Nobel discoverer and his co-author theorised that “organisms were deliberately transmitted to earth by intelligent beings on another planet.” That would require living matter travelling to us from another star. An implausible prospect, we now think.

While we are making palpable progress on the emergence of life, we are definitely stuck on assessing the chances of life forms being capable of sending radio signals. We still have a sample of just one, our own planet. The visible proof of it, from the outside, is a sphere of radio and TV waves expanding in all directions at the speed of light.
In the century that has elapsed since Guglielmo Marconi started sending radio signals, this sphere must have engulfed the many stars surrounding us within 100 light years. Of course, it has become much stronger in recent decades: In Italy, it is affectionately known as the ‘Berlusconi Bubble’.