My recent post on the Fermi Paradox generated many comments on my site and more on Reddit. I also had an interesting discussion with someone who made a startling claim, assuming I interpreted him correctly. He claimed that the unimaginably large number of stars and planets does not increase the likelihood of their being intelligent life on other worlds!
The Fermi paradox is the apparent contradiction between the high probability of the existence of extraterrestrial intelligence given the unimaginably large number of stars and planets in the cosmos, and the complete lack of evidence for extraterrestrial life. Hence Fermi’s question, “Where is everybody?”
Interestingly I have used this paradox to introduce students to the idea of distinguishing the likelihood of various proposition. For example, I am about 99.99999% certain that human animals evolved from lower life forms over billions of years, given the overwhelming evidence for the proposition. And I am 99.99999% sure that it is not the case that there are round squares or married bachelors anywhere in the cosmos, given that if there are such things then the basic principles of logic are mistaken. About many other issues I might feel 80 or 50 or 20% confident. For example, I am 50% confident that the next flip of a coin will be heads. Regarding the existence of intelligent life on other worlds, I am agnostic. I just don’t know.
However I believe that the unimaginably large number of stars, planets, galaxies, (and perhaps universes themselves) makes the probability of life on other worlds more likely. The vastness of the universe gives us a good reason to believe that such life exists. To see why consider the following. If we knew there were only 10 stars in the universe in addition to our own, as opposed to the nearly 400 billion in our galaxy alone, that fact would make the existence of otherworldly intelligent life less likely for the simple reason that there would be less planets to sustain intelligent life. So if 1 in 100 planets on average support life, then in a universe of 100 planets we would expect life to exist on 1 of them. But if there were 400 billion planets (1 for each star), then we would expect 4 billion planets in our galaxy alone that would support life. (1% of 4 billion.) And remember there are about 100 billion galaxies in the known universe so that would mean about 4,000,000,000 x 100,000,000,000 planets with intelligent life.
But my interlocutor questioned all this. Since we don’t know the probability of life arising on a given planet, he said, then whether there are 100 planets or 1024 planets makes no difference. (This is written out like this: 100,000,000,000,000,000,000,000,000.) His point was when we multiply 10 or 1024 by an unknown quantity we don’t know what the result will be because we don’t know what we should multiply by. (That all the probabilities in the Drake equation in the video are unknown.) Moreover, 10 x 0 = 0 just as 1024 x 0 = 0. So for all we know there is no other intelligent life anywhere.
Now it’s true that if we multiply by 0 the result is the same. And it is also true that we don’t know the value of the multiplier, since we don’t know how common life is. But if we multiply by any other possible number besides zero the result is vastly different. (Thus the power of the Drake equation.) If we multiply by 1, assuming that all planets have intelligent life then 10 x 1 yields a vastly different number of planets with intelligent life than 1024 x 1. But most importantly the difference is astonishing when we multiply 10 x .00000000001 as opposed to 1024 x .00000000001. (Assuming the probability of intelligent life arising is vanishingly small.) In the former case it is virtually impossible for any of the other 10 planets to support intelligent life, (because 10 x 10-10 =10-9) while in the latter case the universe would be teeming with an unimaginably large variety and quantity of intelligent life (because 1024 x 10-10 = 1014 That is why there is a paradox. On the one hand we have no evidence of extraterrestrial intelligence, on the other hand the number of possibilities for there to be life is so large that it seems almost unimaginable that there is not intelligent life elsewhere. And this holds no matter how small the probability is for intelligent life to arise and survive unless that probability is zero. The universe is that big!
Of course my interlocutor could object and say “but you don’t know the probability of intelligent life arising is .00000000001%, it might be .0000000000000000000000000000 .00000000000000000000000000000000000000000000000000000000000000000000001%! That is true. If there are 1024 planets but the chances of life arising on one of planets is 10-50 then there is small chance that any of those planets support intelligent life. But note that no matter how vanishingly small the chances are of life arising in this latter case, they are still greater if there are 1024 planets than if there are 10 planets (because 1024 x 10-50 is greater than 101 x 10-50.)
Thus the vastness of the universe and the stars it contains give us a good reason to believe that there is intelligent life elsewhere than if the universe contained less stars. Not a totally convincing reason, since we have no empirical evidence that intelligent life exists elsewhere (sorry alien encounter/abductor fans), but a good reason nonetheless. Remember too that we often have good reasons to believe in hypotheses that lack empirical evidence because they play explanatory or predictive roles. For instance, the ancient Greeks had good reasons to believe there were atoms 2,000 years before we had empirical evidence of atoms. Similarly we do have a good reason to believe there is intelligent life elsewhere in the universe–we have discovered that it is a very big place!
So while I’m agnostic about whether there is intelligent life elsewhere in the cosmos, I maintain with Fermi that the vastness of the universe with its countless number of stars and planets increases the chances that life exists on other worlds. And if I had to bet one way or the other, I would bet that there is intelligent life out there. I may be wrong, but I think it is a good bet.