Does the Number of Stars in the Universe Make Other Intelligent Life More Likely?
My recent post on the Fermi Paradox generated many comments on my site and many more on Reddit. I also had an interesting discussion with someone who made a startling claim, assuming I interpreted him correctly. 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 for many years to introduce students to the idea of how certain I assent to 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 there are no round squares or married bachelors anywhere in the cosmos, given that these can only be false if the basic principles of logic are mistaken. About many other issues I might feel 80 or 50 or 20% confident. I feel 50% confident that the next coin flip will be heads or tails. 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. It gives us a reason to believe that such life exists. This is self-evident. To see why consider the following. If we knew there were only 10 stars in the universe, as opposed to the nearly 400 billion in our galaxy alone, that fact would make the existence of otherworldly intelligent life less likely. The reason is that the less planets there are the less likely any one of them would sustain intelligent lie. For example, 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 stars with say 4 trillion planets and moons orbiting them, then we would expect 40 billion planets in our galaxy alone that would support life. (1% of 4 trillion.) And remember there are about 100 billion galaxies in the known universe so that would mean about 40,000,000,000 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 claimed, then whether there are 100 planets or 1024 makes no difference. (This assumes the 1023 stars in the observable universe each had 10 planets and moons orbiting them. This exponential of the number of planets would be written out like this 10,000,000,000,000,000,000,000,000.) His point was whether 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. Moreover 10 x 0 = 0 just as 10 x 1024 = 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 and 1024 x .00000000001. (Assuming the probability of intelligent life arising is vanishingly small.) In the former case there is virtually impossible for the other 10 planets to support intelligent life while in the former case the universe would be teeming with an unimaginably large variety and quantity of intelligent life. 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.
Of course my interlocutor could object and say “but you don’t know the probability of intelligent life is .00000000001%! That is true, but I know it’s not zero. After all, we exist. And if the probability is anything other than zero then intelligent life on other planets is practically certain. The vastness of the universe thus gives us a good reason to believe that there is intelligent life elsewhere. Not a totally convincing reason, since we have no empirical evidence for the proposition, but a good reason nonetheless. Remember the ancient Greeks had good reasons to believe there were atoms 2,000 years before we had empirical evidence of atoms, since the hypothesis provided a solution to the problem of how one thing changed into another.
So while I’m agnostic about whether there is intelligent life, I maintain with Fermi that the vastness of the universe with its countless number of stars and planets increases the chances that life exists elsewhere. And if I had to bet one way or the other, I would bet that there is intelligent life elsewhere. I may be wrong, but I think it is a good bet. Would any thinking person really bet against that? I think not.
