Tom Hartsfield has a post up at Real Clear Science criticizing both the Drake equation and SETI:
If you like science fiction, you’re probably familiar with the Drake equation. This famous one-line formula solves for the number of intelligent alien civilizations within our galaxy with whom we might be able to communicate. Supporters of the search for extraterrestrial life (SETI) often refer to the expression to bolster their case.
There’s just one BIG problem with the Drake equation. It’s completely useless! In fact, I believe it may actually misrepresent the search for ET and limit our ideas about it.
Hartsfield goes on the discuss the impossibility (at least currently) of knowing the values for each of the variables. Because of this inability to test or observe the various values, he says, the formula is non-scientific.
He then takes aim at SETI (the search for extraterrestrial intelligence):
The worst thing about the Drake equation is that it gives us a false idea of grasping the problem we are trying to solve. A mathematical equation connotes some scientific study or understanding of a subject. But this is misleading: SETI is simply NOT a scientific endeavor. It’s entirely a leap of faith, albeit a leap that uses tools devised by science. It’s like searching for paranormal activity with an electronic sound recorder.
Now, I happen to think that, due to the Fermi Paradox (if there are thousands of civilizations out there, why aren’t any of them here?), the probability of large numbers of civilizations within our galaxy is pretty small. That doesn’t mean there aren’t civilizations in other galaxies, but they may be hundreds of millions of light years away.
That being said, I think Hartsfield is being overly harsh in his assessment. The Drake equation has never been meant to be anything other than a stimulus for discussion. Most people who understand this subject know that it’s essentially just structuring our ignorance. Given its original goal, and given that people still talk about it today, I think it is fairly successful.
Is it scientific? That depends on your definition of science, but I think the variables are things humanity may be able to measure, someday. A scientific theory doesn’t have to be testable immediately in order to be considered science; it just needs to be testable in principle. I don’t know too many people who would actually call the Drake equation a theory, but to what extent it’s modelling the problem might eventually be testable, at some point in the future. I think everyone acknowledges that the Drake equation is almost certainly incomplete, in that there are probably numerous factors that influence the final number that we’re simply not aware of yet, but that applies to many things in science.
I think calling SETI unscientific is simply engaging in polemics. SETI is definitely a long shot. But the search is being conducted carefully and empirically. Saying that the people who are going about it aren’t being scientific, comparing them to paranormal investigators and the like, is just making a value judgment about their enterprise while pretending to be objective.
Now, as I said, I do think SETI is a long shot. There are certain things that have to be true for it to work.
- There needs to be a large number of civilizations out there. Enough that a number of them are close enough for us to detect them.
- Pervasive interstellar travel needs to be impossible, or so monstrously difficult that hardly anyone bothers. Otherwise they would have been here long ago. Even if only 1% of light speed is achievable, that’s still fast enough for a fleet of self replicating probes to colonize the galaxy in 100 million years. (No, there’s no evidence that they’ve been here, despite what the Ancient Aliens people say.)
- They need to communicate in a manner that is detectable with our current technology. If there are civilizations out there, they may be advanced in ways we can’t fathom, and us attempting to listen in on them may be far more fruitless than a primitive hunter-gatherer tribe attempting to listen in on global communications, by watching for smoke signals.
It seems to me that these three constraints make success for SETI unlikely, but not impossible. And nothing about how unlikely it is to be successful necessarily makes it unscientific.
Personally, given 2 above, one strategy to find extraterrestrial intelligence may be to search for probes in the solar system. It may be that there are several already here, laying low. Of course, if they are here and dormant, you have to wonder what they’re waiting for, how far advanced the civilization on the third planet is going to have to be before they initiate contact. And given the vastness of the solar system, if they don’t want to be detected, the chance of us being able to do so seems remote.