the Drake equation

Over the last few weeks I’ve done a couple of gigs with some sixth grade teachers, doing some astronomy — stuff like finding the Moon, measuring the diameter of the Sun via a pinhole projection, touring the universe and so on. One of the pieces I’ve added to this is a discussion and activity where we do a calculation of the Drake equation. It goes like this, more or less:

N = R^{\ast} \times f_p \times n_e \times f_{\ell} \times f_i \times f_c \times L \!

It’s a calculation of the number (N) of possible civilizations out there in our galaxy right now that we could have actual communications with if we were lucky enough. This seems like a semi-silly exercise, kind of fanciful and maybe it’s exactly the kind of thing I’d do just for fun. Well, yes. But also it’s the kind of thing that’s useful to think through because, 1. It mostly sums up all of astronomy, or at least a lot of it, in one capstone kind of discussion; and, 2. It gives you a pretty good indication whether or not you should look up at the sky and think that someone could be looking back at you. This gives you an idea if either wondering or investing time and money into wondering is worth it.

Maybe most important, it tells us something about ourselves. It tells us if we’re really that special or if we’re a funny enigma in the galaxy. Probably we’re both, it turns out. There are enough stars out there and there’s been enough time so that we can be both extremely rare, percentage wise, but also relatively numerous. Maybe.

If you look at the first 5 terms exclusively, you can afford to be an optimist. These each have to do with the number of stars in our galaxy, the number of these with planets, the average number of Earth-esque planets per system, the potential for life on each one, and the potential for evolution into intelligent life. Using ourselves as the data and inferring from there, these numbers all seem to be fairly promising.

However, it’s the last two variables that start to make things interesting, and they’re the most removed from astronomy. Many interesting things are, of course.

fc is the likelihood that life, having evolved to an intelligent state (I’d define this as self-awareness) then creates a technologically advanced society capable of making itself known to other parts of the Galaxy, probably through radio waves. It was when one sixth-grade teacher was contemplating this that she concluded, “Well, I know I could never create that kind of technology myself, so it seems like this requires you to have someone really really smart — so this must be a really low probability,” or something like this. What was striking to me was that she was the sixth grade teacher; she was the person who was educating my future mayor or the person who will cast a deciding vote or a future astronaut or a best selling writer or a chemist or . . . It didn’t bother me that she didn’t think that she could invent an iPod herself, but I suddenly had this soapbox moment where I got to point out that she (and every other sixth grade teacher out there) was responsible for the next iPhone, the next mayor, the next innovation, and the next salvation. This funny “fc” is something that we all create, and the very fact that we have an educational system, a socialized gathering of knowledge and learning, makes this possible.

She’d never thought of it that way.

L is the scary number. It’s the length of time that an average civilization keeps the ability to communicate. Basically, thinking about this number makes you think about how long we’re going to keep ourselves around before we screw something up. So far, we’ve been communicating with radio waves for about a century. When someone estimates that the value for L is 150 years, I at first think that maybe they’re being very wise, but then I think less of them. Really — how do you teach future generations if you see the horizon of our existence? What kind of teaching philosophy do we develop if we think that we’re just biding our time here for a few more years and then, poof, it’s over? I step on a soapbox again for this one, and point out that even if you do have an outlook that looks pretty grim, I really hope that you work to fix what’s going on. In the movie Strange Brew, something I saw when I was in high school, I remember only this one scene: a car heading down a hill, the brakes go out, and the driver lets go of the steering wheel and cries out, “No point in steering now!” It seems to me that we may be having this tendency with regards to our planet, our existence, and one another, and I lose patience with this. Especially if you’re teaching sixth grade.


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