The Varieties of Scientific Experience

CHAPTER FOUR

Questioner: I'm a wee bit skeptical at Drake's equation. It doesn't really indicate how much extraterrestrial life there is. All it indicates is whether the user of it is a pessimist or an optimist. And given this, why do you bother to use it at all?

CS: That's a perfectly good question. And it has a perfectly good answer. And that is, it might have turned out before you went through this exercise that even in the optimistic case the number of civilizations was so low that it didn't make sense to search. But it doesn't turn out that way. There's a sequence of perfectly plausible numbers that lead to a large number of civilizations. It doesn't say it's guaranteed, but it survives the initial test. That's the only function that this has, apart from the very nice fact that there is a single equation that connects stellar astrophysics, solar-system cosmogony, ecology, biochemistry, anthropology, archaeology, history, politics, and abnormal psychology.

Questioner: Oh, this scares the hell out of me. But there's one fact that I think Professor Sagan hasn't brought into account in Drake's formulation. The point is that he's only taken this galaxy into account and not all the other-I don't know- thousands or millions of other galaxies, way back to the big bang 15,000 million years ago. So, I mean, if you're going to take that particular formula, why don't you multiply it by that particular factor?

CS: Again, a good question, and I was merely talking about the justification for the search for signals from advanced civilizations in our galaxy. Clearly you can imagine them in some other galaxy. For their signals to reach us here, they have to have a technology far in advance of ours, but that's perfectly possible. And in fact Frank Drake and I have made a search of just a few nearby galaxies with exactly that idea in mind. We found nothing at the few frequencies we looked at. But, you see, once you start imagining signals coming from another galaxy, then you are into significant power levels and therefore significant dedication by some other civilization to try to make contact with what for them would be a distant galaxy. If you imagine civilizations in our own galaxy, you can at least contemplate that they know that this solar system is a plausible abode for life, even if they haven't visited here to check it out, that there's some way that they could target our particular region of the galaxy for a specific message. There's no way that this could be the case from a distant galaxy, as far as I can see.

This does remind me, though, that I forgot to say something. Very nearby civilizations can detect our presence, and that is because television gets out. Not just television but radar. Radar and television get out. Most of AM radio, for example, doesn't. So let's just look at the television for a moment. Large-scale commercial television broadcasting on Earth begins when? In the late 1940s, mainly in the United States.

So forty years ago there's a spherical wave of radio signals that spreads out at the speed of light, getting bigger and bigger as time goes on. Every year later it's an additional light-year away from the Earth. Now, let's say it's forty years later, so that expanding spherical wave front is forty light-years from the Earth, containing the harbingers of a civilization newly arrived in the galaxy. And I don't know if you know about 1940s television in the United States, but it would contain Howdy Doody and Milton Berle and the Army-McCarthy Hearings and other signs of high intelligence on the planet Earth. So I'm sometimes asked, if there are so many intelligent beings in space, why haven't they come here? Now you know. It's a sign of their intelligence that they haven't come. (I'm just joking.) But it's a sobering fact that our mainly mindless television transmissions are our principal emissaries to the stars. There is an aspect of self-knowledge that this implies that I think would be very good for us to come to grips with.