From the mailbag comes this question.
Dear Professor Briggs,
Thanks for your astutely iconoclastic posts. I’m very interested on your opinion as regards the “there’s an infinite number of planets so there must be more intelligent life” meme. Disclosure: I am an Anti-Dawkins, “meme”-hating big fan of the late Stephen J. Gould, who thought the odds were greatly against anything like us on other planets, based upon the unlikelihood of so many crucial events in our evolutionary history. Thanks.
Hey, me too! I also think memes are stupid, except as synonyms for “goofy ideas du jour“. As a scientific explanation for human behavior, they are at best asinine and useless and at worst a scurrilous, unjustified attack on human intelligence.
And I too enjoyed Stephen Gould’s writing and was with him all the way in his criticisms of the risible just-so stories “evolutionary psychologists” tease each other with.
But to your question. If there were an infinite number of planets, and given what we know about physics and biology as it pertains to evolution and so forth, then there would indeed be an infinite number of planets with life. Whether that life is “intelligent” is a separate question requiring the additional premise that all we (a sample of intelligent life) are is the result of “blind” forces. However, suppose that premise is true for the sake of this argument. Then given the other premises, there would be an infinite number of other planets with intelligent life, with “many” (by which I mean an infinite number) of these planets having life that looks and acts like us.
All this follows easily from simple probability calculus. Let the chance human-like beings evolve from scratch be some number, and let that number be as small as you like as long as it’s greater than zero. (It cannot be infinitesimally small given we already see us.) Then as long as we’re multiplying this small number against an infinite number, we must end up with infinity.
That means we must have an infinite number of planets that look just like ours (but are not ours) which contain beings who look us, who speak and act as we do, who are our doppelgangers in every respect, even to the point that there must exist at least one (other) plant where a being named “Felong” writes to another being named “Briggs” asking him questions about infinity.
There: An argument only a multi-worlds physicist could love. But also a demonstration that infinities are dangerous creatures not to be trifled with.
Anyway, there are not an infinite number of planets; in this universe there are not a infinite number of anything. I leave open the question whether there really are an infinite number of universes (with which no communication is possible). But inside this one, everything is finite. All is countable and limited.
This being so, it becomes crucial to nail the probability with which sentient life evolves. With an infinite number of planets, its size was irrelevant; here, it is everything. We can still say this probability is non-zero, and we can say this because we can say this. It is here that Gould’s observation that we are highly complex becomes relevant.
And we are complex; I’d say indescribably so, or at least incomprehensibly so. By which I mean that no one person can understand all that it is to be human, or can delineate the exact processes which were the causes of our evolution (an event which I do not deny). The best we can say is that there is nothing else like us; no other animal is even similar to us, especially with regards to thinking—and how that thinking relates to our ability to make tools which would make other intelligent life aware of our existence.
Since even identifying the premises which give us the probability our of evolution is difficult (or impossible), we can’t say with any certainty how many other planets with intelligent species exist. This remains true even if we could unambiguously say how many other planets there were which could support life and can support it for some identifiable length of time (for the universe is also finite in time).
The best we can do is to make the numbers up whole cloth, à la the Drake equation and its variants. This of course makes for a certain amount of fun, and for innumerable Star Trek episodes. But that’s about it.