Alien Odds: The Drake Equation (Part Four)


And now: The thrilling conclusion of our discussion of the Drake Equation! The links to the three prior Monster Science posts on this matter should be around here somewhere, but clicking links is super hard so we’ll briefly recap.


Here’s the Drake Equation. The N is the number of civilizations in the galaxy with which communication might be possible. The R is the average yearly rate of star formation in the galaxy, which makes the Equation a function of time, which will pay off later, oh man, just you wait. f-p is the number of those stars what have planets, which appears to be 100%; n-e is the number of those planets that can support life, which is really the first place where these numbers might fall off, and there are two schools of thought about this but that’s all in the second episode, you should go read it, it is super interesting. Then we come to our old friend f-squiggly-line, which describes the incidence of planets that can support life actually developing it, which is 100%, for real. And then the climactic f sub i, which describes the number of life-bearing planets that develop intelligence, and this one got a whole post to itself because it is problematic, both in terms of observable odds, and epistemologically – people bring a lot of baggage to this one.


Okay! Almost to the end. This brings us to good old-fashioned f sub c, the fraction of intelligent species that release detectable signs of their existence into space. And here is where our Equation, in spite of its lovely, science name, starts getting philosophical, whether we like it or not. I mean, on the surface of it, this works like the last couple of factors; modern humanity has been a species for 100, maybe 150 thousand years, and we’ve had radio for less than 200. Bad odds once again, and that’s not even factoring in the pre-modern human forms that almost certainly had some variety of sentience. But does the development of technology work like evolution does? Is it a purely practical reaction to changing conditions, or is humanity compelled to continue to improve its lot – not merely adapt, but progress? And even if we are, how strong is this compulsion? If modern humanity is 100,000 years old, that’s still 90,000 years before anyone got around to agriculture or anything. And if this drive is there, is it a necessary component of intelligence, or might it be unique to the human variety thereof? Or might we call it a defining aspect of sentience – the unceasing impulse to build, to invent, to create, aww man, I miss the science.


Related to this factor of the Equation is the Fermi Paradox, which is an extra fancy title for the question: If there is intelligent life out there, why haven’t we seen evidence of it? Why hasn’t it tried to contact us? Some people regard this as a damning indictment of the idea of extraterrestrial intelligence’s existence. Other people regard it as a fair to middling exercise for a beginner-level science fiction writer’s club. Because, of course, there are dozens and dozens of answers to this question. A lot of them have to do with the thought that maybe the aliens haven’t contacted us because we suck. I mean, we’re very dangerous and do a lot of stupid stuff. My favorite answer I’ve heard to the Fermi Paradox is that the spacemen hate us so much that they’ve actually constructed an artificial universe enveloping the Earth, and that everything we see in the night sky is a lie. Whoa, whoa, aliens! Calm down! I mean, I know we could do a lot better, but dang.


But this idea, that humanity is dangerous, actually brings us to the final part of the Drake Equation, the mighty capital L. This is where time comes back into our figurings, as previously tantalizingly promised: This L expresses the lifespan, in years, of a communicative civilization. Our number has likely gotten pretty small before this point – though it bears mentioning that it refreshes every year, with the new star formation at the beginning – but here at least we get to multiply it by a number that is presumably greater than one. Can you imagine a civilization developing radio and then immediately destroying itself? That is a civilization that means business. And here we go into pure philosophy, pure speculation, because we don’t even have our own example to look at, really, because we haven’t completed this part of the equation by coming to the end of our lifespan. Some say that a sufficiently advanced society cannot go extinct, that is becomes everlasting, but since nothing else in the entire universe is eternal then that’s ridiculous. Some say that we’ll go extinct ourselves, oh, just any minute now – a communicative lifespan of less than two centuries. Some even say that it is the nature of intelligence to consume its surroundings and to destroy itself.

Maybe. Maybe not. I hope not. If the Drake Equation, the search for extraterrestrial intelligence, means anything, then surely it must be the search for something that makes a little more sense than we do.