Life out there
The astronomer royal on the—increasingly serious— investigation into extraterrestrial intelligence
Closer than we think: a supposed UFO sighting in the 1950s
MARTIN REES © BETTMANN / GETTY IMAGES
We are used to thinking of extraterrestrial life and intelligence as topics on the speculative fringe. But recent advances on several fronts are rendering them almost mainstream. The transition from complex chemistry to the first entities that could be described as “living” poses one of the most crucial problems in science. Now this problem is being taken seriously. And as it is grappled with, we can begin to think rigorously about whether some of the hundreds of billions of Earthlike planets in our galaxy might also have a biosphere.
Speculations on “the plurality of inhabited worlds” may be newly respectable, but the speculations themselves are anything but new. Indeed, in 200 AD, Lucian of Samosata wrote what we would now call a fantasy novel, about a trip to the Moon where exotic monsters roamed. From the 17th to the 19th century, it was widely suspected that the other planets of our solar system were inhabited. The astronomer William Herschel thought that even the Sun might host life.
The arguments were often more theological than scientific. Eminent 19th-century thinkers argued that life must pervade the cosmos, because otherwise such vast domains of space would represent a waste of the creator’s efforts. The physicist David Brewster (1781-1868), for example, conjectured on such grounds that the Moon must be inhabited. Had it been “destined to be merely a lamp to our Earth,” he wrote, “there was no occasion to variegate its surface with lofty mountains and extinct volcanoes, and cover it with large patches of matter that reflect different quantities of light and give its surface the appearance of continents and seas. It would have been a better lamp had it been a smooth piece of lime or of chalk.”