The search for extraterrestrial intelligence (SETI) is a collective term for scientific searches for intelligent extraterrestrial life (also called alien life), for example, monitoring electromagnetic radiation for signs of transmissions from civilizations on other planets.
Scientific investigation began shortly after the advent of radio in the early 1900s, and focused international efforts have been going on since the 1980s. In 2015, Stephen Hawking and Russian billionaire Yuri Milner announced a well-funded effort called the Breakthrough Initiatives.
“In the deepest sense the search for extraterrestrial intelligence is a search for ourselves.”
– Carl Sagan, American astronomer
“Our sun is one of 100 billion stars in our galaxy. Our galaxy is one of the billions of galaxies populating the universe. It would be the height of presumption to think that we are the only living things within that enormous immensity.”
– Werner von Braun
“It [the beauty of physics] has nothing to do with human beings. Somewhere, in some other planet orbiting some very distant star, maybe another galaxy, there could well be entities that are at least as intelligent as we are, and are interested in science. It is not impossible. I think there probably are lots. Very likely none is close enough to interact with us, but they could be out there very easily. And suppose they have […] very different sensory apparatus and so on, they have seven tentacles, and they have fourteen little funny-looking compound eyes, and a brain shaped like a pretzel, would they really have different laws? Lots of people would believe that, and I think it is utter balony. … They [the three principles in nature] are emergent properties. … Life can emerge from physics and chemistry plus a lot of accidents. The human mind can arise from neurobiology and a lot of accidents.”
– Murray Gell-Mann
“If it is just us, seems like an awful waste of space.”
– Carl Sagan
“I think the surest sign that there is intelligent life out there in the universe is that none of it has tried to contact us.”
– Bill Watterson
“A time will come when men will stretch out their eyes. They should see planets like our Earth.”
― Christopher Wren
“In very different ways, the possibility that the universe is teeming with life, and the opposite possibility that we are totally alone, are equally exciting. Either way, the urge to know more about the universe seems to me irresistible, and I cannot imagine that anybody of truly poetic sensibility could disagree.”
― Richard Dawkins
“It is possible that the future of human civilization depends on the receipt of interstellar messages.”
– Carl Sagan
“In our time this search [for extraterrestrial life] will eventually change our laws, our religions, our philosophies, our arts, our recreations, as well as our sciences. Space, the mirror, waits for life to come look for itself there. “
— Ray Bradbury
“It is unnatural in a large field to have only one shaft of wheat, and in the infinite Universe only one living world. “
— Metrodorus of Chios
“The key to SETI is to guess the type of communication that an alien society would use. The best guesses so far have been that they would use radio waves, and that they would choose a frequency based on ‘universal’ knowledge—for instance, the 1420 MHz hydrogen frequency. But these are assumptions formulated by the human brain. Who knows what sort of logic a superadvanced nonhuman life form might use? … Just 150 years ago, an eyeblink in history, radio waves themselves were inconceivable, and we were thinking of lighting fires to signal the Martians. “
— David E. Fisher
“Two possibilities exist: Either we are alone in the Universe or we are not. Both are equally terrifying.”
– Arthur C. Clarke
“To consider the Earth as the only populated world in infinite space is as absurd as to assert that in an entire field sown with millet, only one grain will grow.”
— Metrodorus of Chios, 4th century BCE.
“The earth is not alone, it is not like a single apple on a tree; there are many apples on the tree, and there are many trees in the orchard.”
— John Burroughs, The Breadth of Life, 1915.
“A single message from space will show that it is possible to live through technological adolescence… . It is possible that the future of human civilization depends on the receipt of interstellar messages.”
— Carl Sagan, ‘The Quest for Extraterrestrial Intelligence.’ Smithsonian magazine, May 1978.