In Episode 12 of Cosmos, the next to last, Carl Sagan investigates one of the big questions. Are we alone?

By far my most lasting memory of this episode is the Drake Equation. Cosmos was my first introduction to this method of estimating how many other civilizations might be out there. I love its combination of hard numbers with wild and hopeful speculation, and the first thing I wanted to do, when I saw it, was try the equation myself, adjust the numbers to my own biases and prejudices, and see if I could come up with a different number.

Sagan used the equation to tell a bit of a morality tale. If civilizations destroy themselves soon after they develop radio astronomy, then there might be a tiny number of civilizations at any one time, maybe ten. If, on the other hand, civilizations learn not to destroy themselves, then there might be millions. The implications are profound. If we listen to the skies and hear nothing, then we are doomed. Or, to be a little more positive, we can conclude that civilizations destroy themselves. Therefore, we should be really, really careful with things like nuclear weapons. But let’s be honest. We’re not likely to be any more careful than anyone else. So probably we’re doomed.

If, on the other hand, there are lots of civilizations out there, then there’s hope. We can survive this dangerous period, learn to live with our differences, and fluorish. So, the implication is, it’s pretty important to listen.

This was a perfect argument for a twelve year old boy living in a Ronald Reagan world. I was completely mesmerized by it. Now I can see some of the flaws, but still I think there is something to this argument. If we did discover an extraterrestrial civilization that had somehow survived and thrived, it might be interesting to learn some lessons from them. How did they manage to overcome things like climate change caused by their own wastes? How did they overcome religious differences? How did they (do they) deal with the unequal distribution of resources?

Still, there are lots of other variables that Sagan sort of glossed over in his argument that really deserve more attention, I think. The biggest is the one that says that one in a hundred planets with life will eventually develop civilization. That now seems to me hopelessly optimistic. The only evidence we have is from our own planet, and here no animal came anywhere near civilization (it seems pretty clear) for well over four billion years. If the Earth had been wiped out by the death of the Sun or a huge collision only a hundred thousand years ago (the blink of an eye for a 4.6 billion year old planet), then the Earth would have ended its run with zero technological civilizations. And yet it certainly seems to be an ideal world for such a development.

Just based on the evidence presented by the Earth, here’s what seems likely to me. Life is common. It took almost no time for life to begin on the Earth. That would indicate to me that given the right conditions life is almost inevitable, the result of just the right chemistry. I would not be surprised if we do find life on Mars (even if now extinct), Europa, and maybe elsewhere. I bet that the universe is brimming with life.

Multicellular life seems a lot harder. It took a long, long time to go from bacteria to even simple animals. Did it really take that long for everything required to develop? I bet not. I bet, instead, that multicellular life was an unlikely accident, much less likely than life itself. Now, once multicellular life got going it proved to be a pretty good idea. But that’s beside the point. The point is, it took a long time to develop. I bet there’s lots of worlds out there where life never gets beyond bacteria.

And again, once life became multicellular, it took a really, really long time before anything like a person came along. Again, I bet there are plenty of worlds with something like animals, but nothing like a creature capable of doing radio astronomy. There might be super-intelligent squid-like creatures or dolphins, but because they’re not likely to build radio telescopes, we won’t know about them until we go there.

If we ever do.

So, the preliminary SETI efforts seem to say that the sky is not, in fact, humming with extraterrestrial signals. We seem to be relatively alone. We don’t know yet. It’s still early. But it’s not that early. Maybe the message is that civilizations do blow themselves up (or maybe choke on their own pollution, or something). But I think it’s more likely that our sort of civilization is just utterly, incredibly rare. Maybe unique.

To me, that makes it even more important that we try to find a way to survive. We are a way for the universe to know itself. Maybe, just maybe, we’re the only way. If we are an endangered species, then surely we’re worth saving. Aren’t we?