“We must realise that there are other worlds in other parts of the universe, with races of different men and different animals.” That was the Roman poet Lucretius, writing in the 1st century BC.
Only in the past few decades have we grasped the truth of the first part of that statement, thanks to planet-hunters such as NASA’s . Almost 5000 suspected planets have already been spotted outside our solar system, , not the exception. With hundreds of billions of stars in our galaxy alone, that’s an awful lot of worlds.
Surely, then, it’s only a matter of time before we confirm the second part by finding signs of life.
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Perhaps. Life on Earth has required billions of years to evolve organisms capable of asking such questions, and that process has been anything but inevitable. Other life, if it exists, may be nothing like life as we know it.
This is the central dilemma of searches for ET, says of the NASA Ames Research Centre in Moffett Field, California. “You can’t assume nothing because then you don’t even know how to start looking, but if you assume too much then you’re biased and you’re not open to finding a lot of things that might be there.”
So alien life might be carbon-based, and ultimately get its energy from starlight through a process like photosynthesis. Or it might work entirely differently, in which case searches for the metabolic products of carbon-based life in far-off atmospheres – oxygen, methane and the like – will never be a smoking gun.
Perhaps more conscious signals from similarly questioning advanced civilisations are a better bet. “It’s natural to assume that any intelligent civilisation would have that concept of needing to wave a flag,” says Scargle. He is studying Kepler data for signs of “star-tickling”: variations in a star’s brightness induced by aliens using it in some way as a beacon. But as far as decoding any message goes, he’s sceptical: even our idea of what counts as a regular pattern might not be shared by others.
Scargle’s colleague points out that even looking for something like radio transmissions might be assuming too much. “Earth is getting quieter as it gets more advanced, not louder,” she says. And what if we were to pick up an incontrovertible signal of alien civilisation from, say, 10,000 light years away across the Milky Way? That would tell us of something existing 10,000 years ago – a long time by the measure of human civilisation to date. Perhaps even a lively cosmos is a lonely one.
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This article appeared in print under the headline “How to think about alien contact”
