When facts are few, speculations are most likely to represent individual psychology
— Carl Jung
Let's go big or go home. Today I will talk about astrobiology, which is the study of the possibility of life outside the Earth. This has been a preoccupation of mine for a long time now, for whenever I tire of human life on Earth, which is often, it is fun to speculate about the existence of technologically advanced alien (extra-terrestrial) civilizations. Astrobiology has been jokingly referred to as the only science without a subject because there is no observational evidence of any kind which suggests that we share the Milky Way (or the observable Universe) with other "intelligent" species. Even the question of whether single-celled bacteria exist on other worlds remains unanswered.
I intend to do a series of articles on astrobiology, and relate it to some of my other writing, so today's post serves as an all-too-brief introduction.
Let's get right to the heart of the matter and focus on Fermi's Paradox (and watch the video below)
The story goes that, one day back on the 1940's, a group of atomic scientists, including the famous Enrico Fermi, were sitting around talking, when the subject turned to extraterrestrial life. Fermi is supposed to have then asked, "So? Where is everybody?" What he meant was: If there are all these billions of planets in the universe that are capable of supporting life, and millions of intelligent species out there, then how come none has visited earth? This has come to be known as The Fermi Paradox.
And from here—
The drive to place humanity at the center of the universe has led to a stream of assumptions that, as facts have been collected, are shown to be ill founded. The Ptolemaic Earth-centered view was replaced by Copernican Sun-centered view which in its time was also replaced. The assumption that we are alone in the universe is also under threat of replacement. One of the more interesting aspects of our apparent aloneness was pointed out by Enrico Fermi and is know as Fermi's Paradox.
Fermi's Paradox may be succinctly stated as: Extraterrestrials should have colonized Earth long ago, but they have not. So where are they? Whether you agree with the point that Earth was colonized or not the fact remains that no concrete evidence has ever been found indicating a visitation of Earth by extraterrestrials. This is in itself is a very significant point...
Let me explain. The Milky Way is almost as old as the Universe itself, with a measured age of roughly 13.6 billion years (with a wide margin of error, 0.8 gya). By some estimates there were enough"metals" (elements more complex than hydrogen and helium) being generated by exploding stars to allow complex life to form by 7 billion years ago. Our solar system and the Earth are 4.6 billion years old. Propagation models suggest that it would only take between 5 to 50 million years for an alien species to colonize the entire galaxy, so there has been ample time for them to do so. These are the sort of calculations Fermi must have roughed out in his head right before he asked his famous question.
There is no positive evidence that aliens have ever visited Earth, nor is there any observational evidence (coming from the Hubble or other instruments) that suggests artificial (non-natural) heat sources or large-scale structures elsewhere in the Milky Way. Outside of old I Love Lucy TV shows, which have propagated to about 60 light years from our location, Earth's human civlization is effectively invisible to aliens who would thus have no reason to look for us. That was the premise of Carl Sagan's book (and the movie) Contact.
We can forestall some objections immediately. As the ever-optimistic SETI people (Jill Tarter, Seth Shostak) are fond of saying, absence of evidence is not evidence of absence. Therefore we can not prove that aliens have never visited the Earth, nor can we infer that they don't exist because of our failure to detect them with our instruments. We can't even prove they aren't watching re-runs of Battlestar Galactica right now from some unknown location in the asteroid belt. (They can't stop laughing.) In fact, you can never demonstrate that aliens don't exist. That's a logical fallacy (a faulty inductive conclusion based on a poor data sample). Just because all the swans you've seen are white doesn't entitle you to conclude that there are no black swans (as we have recently learned).
Even with these objections the existence problem suggested by Fermi's question still stands until some positive data falsifies it. Maybe some genuine evidence will turn up which shows aliens really have visited the Earth. There wouldn't been much to see until about 542 million years ago at the end of the Precambrian. Maybe we'll dig up a monolith on the Moon. Maybe E.T. will call in from his undisclosed Lagrangian orbital point in our solar system. Maybe some nasty aliens are actually on a rampage and they're due to arrive next week so they can blow up the White House. Maybe those illusive UFOs are definitive evidence of a massive government conspiracy (and cover-up) to deploy super-secret technology from outer space.
There are lots and lots of solutions to Fermi's Paradox, and I've heard and considered them all. But I've taken so long to lay out the basics that I'm going to have to discuss them next time. To whet your appetite, I should note that the default (null) hypothesis is that Homo sapiens is alone in the Milky Way, which implies that the evolution of "intelligent" life is extremely improbable. Occam's razor alone tells us this, for that's the simplest explanation for the lack of evidence for extraterrestrial civilizations. Any other explanation requires further elaboration based on guesswork and assumptions which may turn out to be bogus. However, it is still possible to do some highly informed guesswork while making what appear to be reasonable assumptions, which is what makes astrobiology so much fun for oddballs like me. We must of course work with a small, inadequate data sample (of size = 1, us).
Suppose we are alone in the galaxy. If we could somehow prove this conclusion, which we can't, how would that affect the way our species conducts itself? Or what if other "intelligent" extraterrestrial civilizations once existed—this is the teaser—but all of these were extremely short-lived because these aliens ended up destroying themselves or losing their advanced technology—just as we appear to be doing. In short, one solution to Fermi's paradox says that all intelligent species self-destruct, coming into being and then disappearing in far less than the blink of an eye on cosmological time scales.
For the more ambitious among you, watch The Eerie Silence, an hour-long lecture by Paul Davies, Director of the Beyond Center and Co-Director of the Cosmology Initiative at Arizona State University. The best book on the Fermi Paradox is Stephen Webb's If the universe if teeming with aliens—where is everybody? (fifty solutions to the Fermi paradox and the problem of extraterrestrial life). Also see my post Will The Human Species Grow Up?
So stay tuned. I have far more to say about astrobiology.
Bonus Video — Nick Bostrom talks about Fermi's Paradox