I would dearly love to believe we live in a universe teaming with intelligent life. But I have found my optimism and pragmatism have clashed in a way that has left me feeling a little lonely and misled. Through this wonderful tool posted by the BBC I have been able to play with the famous “Drake’s equation” and have discovered something startling about my assumptions.
In 1961, Frank Drake created his equation for calculating how many planets might exist in our galaxy which could have civilizations sending signals humans might detect. He concluded our milky-way should have more than 18 million planets with intelligent life — and not just any intelligent life, but intelligent life broadcasting signals across the galaxy. How amazing would that be? But if there are 18 million signals cross-crossing the Milky way, why haven’t we detected a single one?
This is the essence of the Fermi Paradox, which predates Drakes equation and posits a contradiction between the presumed high probability of intelligent extraterrestrial life in our galaxy, and the complete lack of evidence to support that belief. Put simply, “If we are not alone, why do we appear alone?” or, as Fermi put it, “Where are they?”
But the Fermi Paradox doesn’t seem like such a paradox when I look more closely at the numbers. Drake’s calculations assumed that an average civilization, once it existed, would last for ten million years, sending signals into space. I find that estimate a little insane. Was he basing his estimate on how swimmingly things were going on Earth?
Keep in mind that, even now, our civilization has been broadcasting into space for less than a hundred years. Even if we don’t blow ourselves up, or clot and choke the planet with pollution, I suspect we will move on from broadcast media before this century it out. That would mean, instead of ten million years of broadcasting, we would be at it for maybe 200.
If I double that estimate, just because, and then round up to 500 years, it yields from Drake’s equation about 900 concurrently existing planets with intelligent life sending out signals. That is 900 planets, spread out in our 100,000 light year wide disc. The average distance between those stars would be about 100 light years. That is really far apart.
900 signals spread across the sky, really hobbles our chances at detecting something. For the sake of optimism, to keep that number from dropping, we might want to ignore that we don’t have any idea what format or content an alien intelligence might broadcast. (We can also ignore the fact that some signals might come from as far 80,000 light years away, since, in theory, the distribution should be roughly the same over time, so some signals would just be very old.) There is, however, some issue with intervening matter absorbing, deflecting or blocking signals, but we don’t have a way to calculate this, so let’s give those signals a free ride too.
This also assumes all stars, regardless of their place in the galaxy, have about the same chance of developing life and sustaining life on one of their planets. But is that so? In a solar system it is generally assumed that life bearing planets will be in a “Goldilocks Zone” where conditions are just right. What about that fat glob in the middle of the Milky Way, where the stars are most dense, concentrated, and in the most turmoil? Where there is more stuff flying about, there are more odds for cataclysmic events, like asteroids and nearby supernovae. And, because this part is the most dense, it has the majority of stars. Surely some places in the galaxy are better suited to life than others. But we don’t have any way to put numbers to a Galactic habitable zone, so we will let that be.
But there is another problem with Drake’s assumptions. He assumed every solar system would, on average, contain two and a half planets capable of supporting life. That seems overoptimistic when you consider the only data point we have is our solar system, which has exactly one planet that supports life. Where did he get the extra planet and a half? He also assumed that every planet capable of supporting life, would! And of those planets he assumed every single one would give rise to intelligent species. Wouldn’t that be swell? It seems Drake wanted the galaxy to be swimming in extraterrestrial signals. Me too, Frank. Me too!
Oh, but I can’t. My numbers are also wild speculation — but not as wild as Drake’s. Not even close. I have to drop the number of theoretically habitable planets per system to an average of one, (though a good case could be made to co lower.)And, while I think it could be possible that every planet capable of supporting life, will give rise to life, its a huge leap to make the assumption that, heh, maybe? I think a more reasonable estimate is 50%. Finally, while we’re loping down the number, I can’t believe all planets with life on them will end up with intelligent life, (let alone intelligent life that broadcasts) so I’m cutting that second number to 50% as well.
Now I’m down to 94 planets in our Galaxy that, in theory, might have intelligent life sending out signals. That really lowers our odds when you consider the area we need to scan and analyze to find a signal. With those odds, it no longer becomes a mystery why we haven’t found anyone else. We’re looking for a needle on a planet of haystacks.
This cleanly resolves Fermi’s paradox, though I wish it did not. It also avoids self-aggrandizing proclamations that human kind is unique and special. (We’ve used that methodology before to find our place in the universe and it has yielded awful results. It is the intellectual equivalent of pulling the covers up over our head and going back to sleep.)
None of this is to say there would not be life all over the place. There should be billions of planets with some sort of aliens oozing, and climbing, and slithering along. There has been life on Earth for 3.5 billion years, but humans have only been here for a small sliver of that time and we’ve only been broadcasting for sliver of that sliver. The main problem appears to be time. By my calculations, we keep missing each other — the tiny periods when we broadcast likely will never align. Unfortunately, this math completely contradicts my desire for and my conception of a universe that is a place teaming with intelligent life. Instead, all the things I’ve dreamt probably were, and likely will be, but are not now. Now, we may not be alone, but there is a good chance we live in a galaxy of trilobites, and dinosaurs and bacterial soup.