Edge is a website that often asks very bright people very interesting questions. Recently they invited 165 intellectuals to write about this question: What Have You Changed Your Mind About. Many of the answers are a bit abstruse, but many are also fascinating. For example, psychologist Martin Seligman, whose reply happens to be the first on their list, says this:
If my math had been better, I would have become an astronomer rather than a psychologist. I was after the very greatest questions and finding life elsewhere in the universe seemed the greatest of them all. Understanding thinking, emotion, and mental health was second best - science for weaker minds like mine. Carl Sagan and I were close colleagues in the late 1960's when we both taught at Cornell. I devoured his thrilling book with I.I. Shklovskii (Intelligent Life in the Universe, 1966) in one twenty-four hour sitting, and I came away convinced that intelligent life was commonplace across our galaxy.
The book, as most readers know, estimates a handful of parameters necessary to intelligent life, such as the probability that an advanced technical civilization will in short order destroy itself and the number of "sol-like" stars in the galaxy. Their conclusion is that there are between 10,000 and two million advanced technical civilizations hereabouts. Some of my happiest memories are of discussing all this with Carl, our colleagues, and our students into the wee hours of many a chill Ithaca night. And this made the universe a less chilly place as well. What consolation! That homo sapiens might really partake of something larger, that there really might be numerous civilizations out there populated by more intelligent beings than we are, wiser because they had outlived the dangers of premature self-destruction. What's more we might contact them and learn from them.
A fledging program of listening for intelligent radio signals from out there was starting up. Homo sapiens was just taking its first balky steps off the planet; we exuberantly watched the moon landing together at the faculty club. We worked on the question of how we would respond if humans actually heard an intelligent signal. What would our first "words" be? We worked on what would be inscribed on the almost immortal Voyager plaque that would leave our solar system just about now - allowing the sentient beings who cadged it epochs hence to surmise who we were, where we were, when we were, and what we were (Should the man and woman be holding hands? No, they might think we were one conjoined organism.)
SETI (the Search for Extraterrestrial Intelligence) and its forerunners are almost forty years old. They scan the heavens for intelligent radio signals, with three million participants using their home computers to analyze the input. The result has been zilch. There are plenty of excuses for zilch, however, and lots of reason to hope: only a small fraction of the sky has been scanned and larger more efficient arrays are coming on line. Maybe really advanced civilizations don't use communication techniques that produce waves we can pick up.
Maybe intelligent life is so unimaginably different from us that we are looking in all the wrong "places." Maybe really intelligent life forms hide their presence. So I changed my mind. I now take the null hypothesis very seriously: that Sagan and Shklovskii were wrong: that the number of advanced technical civilizations in our galaxy is exactly one, that the number of advanced technical civilizations in the universe is exactly one. What is the implication of the possibility, mounting a bit every day, that we are alone in the universe? It reverses the millennial progression from a geocentric to a heliocentric to a Milky Way centered universe, back to, of all things, a geocentric universe. We are the solitary point of light in a darkness without end. It means that we are precious, infinitely so. It means that nuclear or environmental cataclysm is an infinitely worse fate than we thought.
Thinking about Seligman's new thinking on the matter of ETI I'm reminded of an excellent book written by Peter Ward and David Brownlee titled Rare Earth. Ward and Brownlee make it pretty clear that the earth is as close to unique as we have reason to believe and that the conditions necessary for intelligent life might well exist nowhere else in the universe. Anyone who still harbors the Star Wars notion that the uiniverse is probably full of intelligent aliens ought to read Rare Earth.
It is also interesting that Seligman now thinks we live in a geocentric universe. This is an idea that sophisticated people have scoffed at for a hundred years but which now seems to be more likely to be correct in at least one important way than ever before. I talk about why this is here.
You can read the other 164 responses at the link.RLC