Good to be back!

Skeptical Enquirer this month includes a Q&A session from the archives with Carl Sagan. I am not greatly familiar with Sagan's writings, but find it interesting that such an enthusiastic proponent of the idea of the abundance of intelligent life throughout the universe should have been so readily accepted by an organisation such as CSICOP. OK, he may have been an ardent critic of pseudoscience, but his publication of a novel about alien contact must have raised a number of eyebrows among his fellow skeptics. I have never thought of CSICOP as a particularly broad church, but maybe I should think again.

The question of intelligent life elsewhere in the universe inevitably raises its head in the Q&A session, when a member of the audience raises the following question:-

It seems that [for us]as skeptics, there’s an argument that seems very disappointing and maybe a bit persuasive in the Fermi paradox, the idea that if civilizations were to arise at any significant level, that even given a very extremely slow rate of expansion in the galaxy, that there’s been more than enough time for them to have populated the galaxy several times over. What’s your view on the Fermi paradox?

Sagan's answer is as follows:

The Fermi paradox essentially says, as you said, that if there’s extraterrestrial high technology intelligence anywhere they should have been here because if they travel at the speed of light, the galaxy is 100,000 light-years across, it takes you 100,000 years to cross the galaxy. The galaxy is 10 billion years old, they should be here. And if you say you can’t travel at the speed of light, take a tenth of the speed of light, a hundredth of the speed of light, still much less than the age of the galaxy. William Newman and I published a paper on this very point, in which we point out: Imagine there is a civilization that has capable interstellar spacecraft and now they start exploring. What are we talking about? That they’re sending out 400 billion spacecraft, all at once, simultaneously, to every star in the galaxy? Not at all. Interstellar space flight is going to be hard, you’re going to go slow, you’re going to go to the nearest star systems first, you’re going to explore those stars. It is not a straight line but a diffusion question. And when you do the diffusion physics with the appropriate diffusivity, that is, the time to random walk, there are many cases in which the time for an advanced civilization to fully explore the galaxy in the sense of visiting every star system is considerably longer than the age of the galaxy. It’s just a bad model, we claim, the straight line, dedicated exploration of every star in the galaxy.

The Fermi Paradox is indeed a significant stumbling block for those positing the existence of life elsewhere in the galaxy. The Search for Extra Terrestrial Intelligence (SETI), a cause celebre for Sagan, has spent decades scouring the sky for the a tell-tale radio wave which may indicate the existence of remote intelligence, but without success.

Sagan's answer may have some merit, but skips over a number of other (in my mind) more convincing solutions to this puzzle. It is interesting, for example, to think that when SETI began its search, the assumption was made that any intelligent civilisation would be bound to transmit radio waves as part of their communication systems. However, even on earth communications are already rapidly moving towards digital optical networks and away from radio waves. How long will it be before earth itself is undetectable from space? A counter-argument may well be that travel through space would required the use of radio technology, but the idea that remote civilisations will be roaming space is perhaps a romanticised one. It surprises me how scientific supporters of these arguments so readily assume that the limits imposed by the speed of light will be irrelevant to such cultures. If one were to stand on Einstein's side of the fence, there may not be much in the aliens' back yard to be worth exploring after a while.

Perhaps the most depressing, and perhaps most compelling, arguments however relates to the shelf-life of any life-form which has tamed science to such a point where it can use technologies the like of which have been developed on Earth. With the capacity for space travel comes almost inevitably the power of potential self-destruction. Martin Rees, Britain's Astronomer Royal, gloomily gives mankind only around a 50/50 chance of making it through the next 100 years. In a celebrated article in Wired magazine, Sun Microsystems guru Bill Joy argued that the 21st century heralded new unprecedented risks to civilisation. In addition to our old nuclear, chemical and biological bugbears come the novel threats of self-replicating genetic, nanotechnological and robotic apocalypses.

So perhaps civilisations we seek are predominantly snuffed out before we can detect them. In any case, the light years between us would mean that by the time we see each other a response would likely reflect on dusty remains. Still, it would perhaps be of some small consolation before we go up in smoke to discover that we are not all alone after all...