Alien Odds: The Drake Equation (Part Two)


Welcome back to Alien Month on Rev. Matt’s Monster Science, and our discussion of the Drake Equation – a mathematical means of framing the odds of intelligent life existing on other planets, and its coming to see us. Last week we got through f sub p, which expressed the number of planets in the galaxy, which, as it turns out, is so, so many, you guys. So far, so good; but now things start to get narrower.


Now we’re at the point where we multiply what we have so far by n sub e – and no, I don’t know why we’re picking these letters at this stage – which expresses the number of planets that can potentially support life, per star with planets. And this is our first real stumbling block. Certainly, not all stars have potentially habitable planets; some give out X-Ray pulses that are harmful to life, or are only orbited by gas giants in wildly elliptical orbits, or are made entirely out of nougat, or something. The question is, of course, how many. There are actually names for the sort of polarized arguments here.

One is the Rare Earth Hypothesis, which posits that the conditions that enable life are vanishingly rare; the star has to be exactly the right size, and age, and distance from the center of the galaxy – seriously, they are looking for excuses to make life rare – and the planet has to be the right distance from its star and have the right axial tilt and on and on. Proponents of this are the sorts of scientists who give science in general its reputation for sucking the wonder out of life, even while most of science gives us quasars and mimic octopuses. These are people who can’t watch The Empire Strikes Back without going “Hey, there’s no sound in space!” Oh calm down. Still, they may be right; we don’t know.


On the other end of the spectrum we have the principle of mediocrity, which is horribly misnamed because it is actually the principle of totally awesome, because it holds that our Sun and our planet are more or less typical. The idea here is that 100% of fully observed star systems so far have a planet teeming with life, and that sample size may be exactly one but you work with what you’ve got. Obviously debatable, but good science does work this way sometimes; in paleontology, for example, when you find a single fossil you go ahead and assume that there were more animals just like the one you’ve found, that it’s not a freak of nature, and of course this does hold up. So the principle of mediocrity is actually very well regarded in the scientific community, and has had among its proponents the noted science writer and action hero Carl Sagan.

This is from the comic book “Atomic Robo,” which is the best comic book there is, I am not even kidding, go find it.

Now we multiply this by f sub some kind of squiggly line; here we have the fraction of potentially life-sustaining planets that actually go on to have life on them. This is – look. This is 100%. Because we’re talking about science here. Life occurs because of a physical or chemical reaction. And so when you have the conditions, it happens. When you have vodka and orange juice in the same glass that is a screwdriver 100% of the time. Maybe not a very good screwdriver but that’s not the point, not yet. And geological evidence does show us that as soon as favorable conditions occurred on Earth, life appeared pretty much instantly. This part of the Equation is largely agreed upon by scientists; the only real argument against it is that life does not appear to have generated itself anew multiple times, in spite of the conditions being there. But this doesn’t really go very far, for the simple reason that once life exists, newly formed life isn’t going to get anywhere; newly formed bacteria on a planet already teeming with bacteria are going to be outcompeted and go extinct almost immediately. Vodka and OJ make screwdrivers, but you don’t need a new screwdriver until you’ve finished your first one, wino.


The next thing we multiply by, f sub i, that’s where the actual quality of the screwdriver comes in; that’s the fraction of planets with life that develop intelligent life. And this, unfortunately, is where things turn ugly. But unfortunately our time is up. Tune in, then, for the next episode of Alien Odds, when we will discuss the difficulties of f sub i. There is…there is a lot to say about f sub i. Isn’t there always?