For most of history, it has belonged squarely in the provinces of religion and philosophy. In recent decades, however, scientists also have been attracted to the problem in increasing numbers. Fifty-one years ago, a young astronomer by the name of Frank Drake began sweeping the skies with a radio telescope in the hope of stumbling across a message from an alien civilisation. Thus began SETI -- the Search for Extraterrestrial Intelligence -- an ambitious enterprise to survey thousands of sunlike stars in our neighbourhood of the Milky Way galaxy for any signs of artificial radio traffic.
When SETI began in 1960, it was regarded as quixotic at best, crackpot at worst. "A quest of the most adverse odds," was the way distinguished biologist George Simpson expressed it. The prevailing opinion among scientists was that life was the result of a chemical fluke so improbable it would be unlikely to have happened twice in the observable universe. "Life seems almost a miracle," wrote Francis Crick, the co-discoverer of the structure of DNA. It was echoed by another Nobel prizewinning biologist, Jacques Monod, in a bleak assessment: "Man at last knows that he is alone in the unfeeling immensity of the universe, out of which he emerged only by chance.
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