In one of the episodes of the podcast Rationally Speaking, Julia Galef and Massimo Pigliucci* cover a topic that he covered in his book, Nonsense on Stilts: is the Search for Extra-Terrestrial Intelligence (SETI) a pseudoscience?
Massimo's book is about various forms of woo and mysticism and how they cloak themselves in the language of science to ward off criticism. I don't know if he's in the book, but Deepak Chopra is one of the worst offenders in this regard. He uses scientific buzzwords, usually from quantum mechanics, to sell his brand of "alternative medicine"**. When pressed, he admits that he's just speaking metaphorically and doesn't mean to imply that his quackery is based on the actual meaning of those words. However, when challenged on the mystical woosense of it, he reverts to using the scientific language, saying it's not mysticism, it's SCIENCE! Fuck Deepak Chopra.
Anyway, Massimo places SETI in a murky gray area on the edges of pseudoscience. It is a scientific enterprise: it follows all the rules of science and is done by scientists (astronomers), and doesn't ever pretend to be more than it is. However, it lacks any data confirming its hypothesis (that there is more than one technological civilization in the universe) and one of the attributes that is generally held to make an enterprise scientific; falsifiability.
For example: what would falsify evolution? As myth puts in the mouth of JBS Haldane, "Rabbits in the precambrian". The theory of evolution predicts that more complex forms arise from simpler forms, and not the other way around, and not without precursors. Thus rabbits in the precambrian, far more complex than their time allowed and without precursors, would violate the theory and require a new explanation. Or, more simply, what would violate gravity? A heavy thing floating. What would falsify the god hypothesis?
SETI isn't falsifiable. It's rather akin to the god question, or Russell's teapot; the only way to prove there's no life anywhere in the universe is to search the entire universe simultaneously. However, it's in a gray area because it's a question with a definite answer and there's no reason to believe that there is or is not life; we have absolutely no evidence. That said, none of the SETI scientists claims that their hypothesis is true, merely that it's worth investigating.
If the hypothesis isn't falsiable, is it testable? Absolutely. That's what they're doing now; they're scanning the sky for signals. If they got a signal, it would confirm the hypothesis in a heartbeat. But they've been at it for 60 years with no answer. What if they scan for another 500 years with no answer; would that still not confirm a lack of life? There would still be no negative, there. Julia raises a good point here; if you search for long enough and get no answer, that's fairly good evidence that there isn't life out there, and the longer you search without an answer, the stronger the evidence gets that we're alone. Of course, life may be incredibly rare and we might just miss a rare broadcast (our broadcast from the moon only went out once... so much for that).
One of the arguments people make in favor of SETI is essentially the Drake Equation. No matter how improbable intelligent life is, the universe is so incomprehensibly big that there must be an incredibly large number of other civilizations. In fact, the Fermi Paradox shows up in a few science fiction books***: if there are so many civilizations out there, why haven't we found them? Massimo argues that the principle of mediocrity is very flawed. The principle says that there's nothing special about us (we're not unique), if one advanced civilization exists and isn't special, that means there must be more (or, even with low probability, a large volume of space and time guarantees it will happen many times). To which Massimo replies, "Skateboarding is a normal behavior here, does that mean it happens everywhere?" There's no reason to suspect that our civilization is unique, because we also have evidence of a unique phenomenon. The universe only happened once. All we have is evidence of a technological civilization. We can't assume anything else, not that we're unique, not that we're common, nothing.
They spent some time discussing the Drake Equation and raised some good points: the complete lack of evidence we have about life and planets in the rest of the galaxy goes double for most of the equation. We just don't know anything about it. They also raised a really good argument against anything about SETI; nothing has changed about it in the fifty years it's been in existence. That is pretty damning. Even if they're not gaining new evidence about the existence of life themselves, the many developments in the last five decades in physics and astronomy really, really should have influenced the theory and work of SETI.
Though they spent a lot of time discussing the likelihood of life on other planets, they didn't really raise any significant objections to SETI that convinced me it borders on pseudoscience. Since Massimo is a philosopher of science, I expected he would have spent more time talking about the conflict between its evidence-based nature and the fact that it is, in all practical ways, unfalsifiable. Instead it was a long discussion of our absolute ignorance of extrasolar conditions. Maybe he didn't want to spoil too much of his book. :) I think it's a fully scientific endeavor, but one whose scope is so broad and the odds so slim that it will never achieve its goal. However, the discovery of standard candles occurred by accident, so who knows what SETI will come up with? The act of systematically scanning the sky with radio telescopes is a good thing in itself. Of course, I say that about all science, so what do I know?
If you're curious, my personal stance on extraterrestrial life is that I think it's common. Not necessarily intelligent life, but life in general. I base this on the thermodynamics that makes chemical bonding prolific, and complexity inevitable. I also suspect that our current estimates of the goldilocks zone where life can exist is too conservative. I don't have any evidence, of course; this is all just cherished private suspicions. The complete absence of evidence on conditions outside of our solar system means that I must be, officially, agnostic.
Also for the curious, NASA's estimate for the answer to the Drake Equation: 2.3. That is to say there are either two or three civilizations capable of broadcasting in the galaxy. And we're one of them.
* Quick rules for a Rationally Speaking drinking game:
Drink whenever Julia complains about common misconceptions about reason or skepticism.
Drink whenever Massimo says, "and so on and so forth".
Drink whenever one of them says, "Well, it depends on what you mean by..."
Finish your drink if Julia disparages the value of philosophy.
** What's it an alternative to? Medicine.
*** Like Variable Star, put together in notes by Heinlein and written by Spider Robinson. Good book, clearly the separate work of two great writers.