If you’ve been reading Letters Blogatory for a while, you know that I am an enthusiast for astronomy and cosmology. I have often surprised people by saying that I hope we do not discover extraterrestrial life, especially simple extraterrestrial life. I get the same reaction I get when I tell people that it is illegal to use, possess, or sell marijuana anywhere in the United States. In this month’s Commentary, astrophysicist Ethan Siegel has an article that bears on my point even though he doesn’t draw the same conclusion.

In the mid-20th century, physicist Enrico Fermi asked, “where is everyone?” That was a laconic way of saying that there are millions of myriads of stars in our galaxy and millions of myriads of galaxies in the universe. The numbers are so large that we should expect there to be lots of civilizations all around us. Our own experience tells us that you don’t need to be fabulously advanced in technology to send out electromagnetic radiation that can be detected across the vast distances of space, given enough time. So where is everyone?

Today we use the Drake Equation to try to formalize Fermi’s intuition. The equation looks like this:

N = R* * fp * ne * f1 * fi * fc * L

Where N is the number of civilizations in our galaxy, R* is the average rate of star formation in the galaxy, fp is the fraction of stars with planets, ne is the fraction of planets that could support life, f1 is the fraction of those planets that actually do develop life, fi is the fraction of those planets that develop intelligent life, fc is the fraction of those planets that develop high technology, and L is the length of time a civilization is detectable from afar. We know a lot now about the number of stars in the galaxy, how many of them are the kind of stars that could support life like us, and how many planets an average star of the right type has. So if we have not encountered intelligent life, and with some caveats that I’ll mention in a moment, we can say that either f1, fi, or fc is very small, or in other words, that it is very hard for life to arise at all, or very hard for intelligent life to evolve from simple life. Or else maybe L is very small, and technological civilization rarely if ever lasts long.

Now, if we discover simple extraterrestrial life in our own solar system—if we dig up a microbe on Mars or find bacteria in a thimbleful of water from Europa—or if we detect the chemical signatures of life using our increasingly excellent techniques for observing exoplanets and their atmospheres, then we will know that it is not difficult for simple life to arise, and the lack of extraterrestrial civilizations that we observe will mean either that it is difficult for advanced life to develop from simple life or that advanced civilizations do not last long. I’m no evolutionary biologist, but it seems to my inexpert understanding that intelligent life is an inevitable consequence of the development of life, given enough time. So it seems to me that if we find that simple life is common, the logical conclusion to draw from the absence of extraterrestrial civilizations that we observe is that technological civilization does not last long when it arises. And so I will feel better about the prospects for the human future if life is very rare, or even if it is unique to the Earth. It’s just math!

The caveats: maybe ET is out there but doesn’t want to be found. Maybe we have met ET but are not smart enough to realize it. And so forth. I nevertheless will continue to say I hope we never meet ET.