ESA/Hubble & NASA
IN 1960, astronomer Frank Drake began an experiment. With a radio telescope, he studied two nearby sun-like stars, hoping to find signals that could only have been generated by life on planets orbiting these stars. He came up blank. In the six decades since Drake started the search for extra-terrestrial intelligence (SETI), astronomers have kept listening, carefully and systematically. Still, we have heard nothing.
One possibility is that there simply are no aliens out there – that we truly are alone. But this seems unlikely, given the vastness of the cosmos, with hundreds of billions of galaxies containing hundreds of billions of stars, most of which have at least one planet orbiting them, at least according to our burgeoning knowledge of exoplanetary systems in our own galactic neighbourhood.
Jill Tarter, co-founder of the SETI Institute in California, says we haven’t listened for long enough or looked hard enough to make any such sweeping statements yet. Astronomers have studied all kinds of electromagnetic radiation – light, radio waves, gamma rays – looking for signals. Such a search has to cover all directions and distances in space, plus the different ways a signal might manifest itself, such as shifts in polarisation, frequency, modulation and intensity. Tarter sees these parameters as a multi-dimensional ocean. “When SETI turned 50, we had explored one glass of water from that ocean. By the time it turned 60 it was more like a small hot tub,” she says. “It’s getting better and faster all the time, but there’s a lot more to explore.”
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