OK, I can’t take it anymore! With various pressing tasks on my “to do” list, I didn’t feel I could blog in good conscience. Then, when I did find time here and there, the number of topics I wanted to talk about had grown so large that the idea of sitting and even doing a bulleted list became intimidating. (Silly, I know.)
So, I’m just going to ignore all of that and start from scratch with this topic. Ah, the joys of a clean slate!
Recently (June 27), a Russian scientists declared quite confidently that humanity would detect intelligent alien life in the cosmos within 20 years. It was based on a lot of “castle in the clouds” thinking that is usually associated with such over-confident assertions, and recently Princeton astrophysicist David Spiegel and University of Tokyo physicist Edwin Turner demonstrated very simply just how thin those clouds may be.
Their paper, “Life might be rare despite its early emergence on Earth: a Bayesian analysis of the probability of abiogenesis,” takes a very simple approach, yet — given the incredible popularity of the assumption that intelligent life could arise in any habitable location since, after all, it “arose” here — it reaches a profound, should-have-been-obvious conclusion: Given all we know, it is just as likely that life is extremely rare in the universe. That is, we actually may be alone. (Great, readable article on this here at LiveScience: “Are We Alone In the Universe? New Analysis Says Maybe.” Actual paper submitted to the Proceedings of the National Academy of Sciences downloadable here at arXiv.org.)
The key is that the authors do a proper Bayesian probability analysis. Bayesian probability is an approach I studied as an actuary that seeks to relate probabilities to experience and evidence. As such, it is the logical approach to consideration of what our experience (life on earth) should tell us about the rest of the universe (life elsewhere or not). And it exposes just how dependent the current “life is everywhere” fad truly is on its assumptions (or, as I point out elsewhere, on faith).
Don’t let the fancy name fool you: Bayesian probability is quite sensible. For instance, in learning basic probability in middle or high school, we all learned that the toss of a perfectly fair coin would result in a “heads” with a probability of 1/2. We also learned that tosses are independent of each other, so if that coin produced heads three times in a row, the probability of another heads on the fourth toss is still 1/2 — the previous heads do not affect the next toss, if we are dealing with a perfectly fair coin.
However, what if you’ve tossed the coin 100 times, and each time it came up heads. Do you still have confidence that it’s a fair coin? Shouldn’t reality and evidence be allowed to modify our expectations? That’s where Bayesian probability comes in. It allows you to consider the confidence you should have in prior assumptions or hypotheses in light of experience and actual data. In this coin example, anyone (everyone) would would reasonably begin to question the assumption of the coin’s fairness. In fact, after 100 straight heads, you would be rather justified (all else being equal) in changing your original probability based on the evidence to assuming the probability of getting a head with this coin to be not 1/2 but 1 (or, not 50% but 100%).
This “let’s consider the evidence” approach is what makes Bayesian probability the right approach to consider what we should think about the probability of life spontaneously arising “out there” on habitable worlds based on the observation that life (supposedly) spontaneously arose here.
The conclusion? There is no reason to prefer to think that there are others “out there” as opposed to the possibility that we are essentially alone in the cosmos. The evidence justifies no one concluding that there “must be” intelligent life elsewhere in the universe — or, perhaps, even life, at all, other than here. And this is a conclusion drawn within an Evolutionary/Material Abiogenesis framework. The LiveScience article is a pretty good read on the topic; check it out: “Are We Alone In the Universe? New Analysis Says Maybe.” (The articles offered below cover the same study, I believe.)
Nice work. And hopefully a sobering analysis that will help those of the “Life is Everywhere” Faith to at least admit the existence of that faith.
- Blog – Probability of ET Life Arbitrarily Small, Say Astrobiologists (technologyreview.com)
- Are We Alone In the Universe? New Analysis Says Maybe (space.com)
- Are we alone in the universe? Well, maybe (msnbc.msn.com)