Doctors Fermi, Drake and Strangelove

By now it's well-accepted that there are large numbers of planets in the universe that could plausibly support life more or less as we know it.  From this, it follows that unless civilizations like ours are exceedingly rare on such planets, there must be a great number of them in the universe, if not now then at least over history.  A recent paper argues that "... as long as the probability that a habitable zone planet develops a technological species is larger than ∼10⁻²⁴ [that is, about one in a trillion trillion], humanity is not the only time technological intelligence has evolved".

I've argued elsewhere that numbers like that are beyond our ability to understand directly.  For practical purposes, we can call one in a trillion trillion "zero".  The paper is essentially concluding that, based on what we know now, there (practically) certainly have been other intelligent civilizations in the universe.

In evaluating a statement like that it's important to keep in mind the scales involved.  We're talking about the whole universe here, of which our galaxy is only a tiny part, and we're talking about the entire history of the universe, of which human history is only a tiny part.  The authors make a point of not addressing the question of how many such civilizations there might ever have been in our galaxy, much less close enough for communication with Earth to be practical.

They also make a point of not addressing how many such civilizations there might be right now (regardless of where they might be).  I want to get into the significance of that.


Questions of how many intelligent civilizations there might be generally center around the Drake Equation, which is probably best thought of as a framework for breaking down the problem.  The breakdown is that the number of civilizations we could communicate with must be the product of

• Three factors representing the rate at which planets form that might support life appear (we're assuming here, for better or worse, that life lives on planets)
• Three factors representing what portion of those actually produce life that would put out a detectable signal
• How long those civilizations actually put out a detectable signal (the 'L' factor, for 'lifetime').

We now have a pretty good handle on the first bullet point above.  On the other hand, we don't really know how likely it is that a planet that could support life actually develops life or how likely it is that such life actually puts out a detectable signal.  I've previously argued that, because of the distances involved there's a big difference between "detectable" and "detectable by us" and that the last factor, how long there would be a detectable signal, could be very, very short on a cosmic scale.

The paper I referenced sidesteps these questions by considering everything everywhere and over all time, regardless of whether we could hope to make contact or would even be around to try.  That's fine, but in doing so it shifts from the practical question of "Are we alone?", or Fermi's "Where is everyone?", to the more philosophical question of "Are we unique?".  That's an interesting question, but it somehow lacks the emotional resonance of the other two.

I grew up during the Cold War.  I remember the electricity of the Berlin Wall opening, and the profound feeling of disorientation that came with it.  All my life the East and West had been locked in a permanent stalemate with no sign of an end.  And then it ended.  Now what?

For the most part, life went on.  That's not to say that the transition was smooth, particularly if you had lived in the Soviet Union or its satellites.  My point is more that the "western" developed world, at least, went on more or less as it was.  McDonalds is still McDonalds, Hollywood still makes films, football (or soccer, if you prefer) is still the world's sport, the US still doesn't care greatly that it is, and so forth.  MTV is still the place to go for music videos ... oh, wait ...

Except for nukes.

The amount of nuclear weaponry developed during the Cold War is staggering.  The only two nuclear weapons that have actually been used militarily, the ones dropped on Hiroshima and Nagasaki, yielded under 150TJ (or if you prefer, around 35 kilotons) .  We saw what that did.

Modern nuclear warheads are generally in the thousands of TJ, and tens of thousands of those have been made.  While you can't just multiply numbers and say "Ten thousand times as many bombs each yielding ten times as much means a hundred thousand times as many people killed," it was really no exaggeration, at all, to say that humanity now had the means to cause much, much more destruction than had ever been possible before.

This was a fact of life growing up in the cold war.  My high school newspaper once had a debate in the editorial columns about whether a nuclear war could be survived, at all, and if so whether you should even try.  The bidding started at "The US government would no longer exist" and from there it wasn't far to "Industrial civilization would collapse, bringing about a new Dark Age lasting centuries" or "All humans would die as nuclear winter wiped out agriculture and plunged temperatures by 20 degrees Celsius for decades".  It wasn't completely outlandish to speculate that multicellular life would be wiped out.

This colored our outlook on the world.

Today, not so much, which is interesting since there are still thousands of extremely powerful nuclear weapons in the world and it's not clear that they're as tightly controlled now as they had been.  Just why attitudes might have changed is for another discussion.  For now, let's just take it as a given that "nukes could kill us all" is not nearly as prominent a thought in the early 21st century as it was in the mid to late 20th.

That L factor of the Drake equation represents the amount of time during which an intelligent civilization puts out a detectable signal.  This could be a very short time, on cosmic scales, if only because unless you're actually trying to be detected, putting out radio or other signals that could be detected dozens or hundreds of light years away is a large waste of energy.

If you're streaming video over the internet, for example, no one has to broadcast a signal from a tower.  Even if radio signals are involved they are more likely beamed from one microwave station to another or otherwise narrowly focused.  An intelligent species could quite likely get along just fine for almost all of its existence without producing a detectable signal, if it so chose.

When the Drake equation was first developed, however, this wasn't the interpretation that people tended to use.

At the time, we had no idea whether there were many habitable planets out there, but we had made a few efforts to contact other stars and to listen for signs of life on them (including Drake's own Project Ozma), without any clear success.  That suggested that the factors of the Drake equation must multiply out to a small number.

Since we knew even less then than we know now, most of the factors of the equation were little more than wild guesses.  But we did have at least one data point for an intelligent species (at least by our own definition of "intelligent"), and there was one ready explanation that fit with our understanding of that species and the lack of signs of other species like it: Intelligent species didn't last long.

There was ample reason to believe that.  Perhaps it was inevitable that, at least on the cosmic scale, it would not be long between a species developing technology that could have a major impact on its planet and that species destroying itself.  In 1961, when Frank Drake put forth his equation, it had been less than 20 years since the end of World War II and nuclear weapons testing was in full swing.  It was the most natural thing in the world to wonder if we would make it another 20 years.

Now that we've made it over fifty years since then, it may be more natural to assume that we'll still be here in another fifty, or thousand, or whatever, and either to assume that the L factor could be small for any number of non-lethal reasons or to neglect it altogether on the assumption that we'll be around and detectable forever.  What strikes me here is how much room, within the broad limit that our theories need to be consistent with the facts as we know them, there is for them to reflect who we are at the moment. Then as well as now.