Pharyngula

SETI built on GIGO

I’ve never been a fan of SETI, the search for extraterrestrial intelligence. It’s like playing the lottery obsessively, throwing down lots of money in hopes of a big payoff, and I don’t play the lottery, either.

I’d really like to know if Seth Shostak is innumerate enough to play the lottery, though, because his recent claim that we stand a good chance of discovering extraterrrestrial intelligence within 25 years. All right, bring it: let’s see your evidence for such a claim.

“I actually think the chances that we’ll find ET are pretty good,” said Seth Shostak, senior astronomer at the Search for Extraterrestrial Intelligence Institute in Mountain View, Calif., here at the SETIcon convention. “Young people in the audience, I think there’s a really good chance you’re going to see this happen.”

Shostak bases this estimation on the Drake Equation, a formula conceived by SETI pioneer Frank Drake to calculate the number (N) of alien civilizations with whom we might be able to communicate. That equation takes into account a variety of factors, including the rate of star formation in the galaxy, the fraction of stars that have planets, the fraction of planets that are habitable, the percent of those that actually develop life, the percent of those that develop intelligent life, the fraction of civilizations that have a technology that can broadcast their presence into space, and the length of time those signals would be broadcasted.

Reliable figures for many of those factors are not known, but some of the leaders in the field of SETI have put together their best guesses. Late great astronomer Carl Sagan, another SETI pioneer, estimated that the Drake Equation amounted to N = 1 million. Scientist and science fiction writer Isaac Asimov calculated 670,000. Drake himself estimates a more conservative 10,000.

The Drake Equation? That’s it? I hate the Drake Equation. It’s seven arbitrary parameters plugged into a simple formula, of which we have reasonable estimates of one (the rate of star formation), growing evidence of values for another (the number of planets around each star), and the other five are complete wild-ass guesses, most of them dealing with biology and culture, and we’ve got astronomers who know next to nothing of either inserting optimistic values. When biologists amend the values to something more reasonable, the likelihood of intelligent life plummets. Not that their wild-ass guesses are necessarily more accurate (although they are based on the history of life on this one planet), but it does say something that the equation can yield results that vary by six orders of magnitude, depending on who does the calculation.

It’s a useless formula. You can’t calculate anything from a formula in which almost all of the variables are complete unknowns, and it’s also meaningless in that no matter what result we acquire from empirical evidence, it can all be retrofitted to the magic formula. I really don’t understand the appeal of the Drake Equation, except that it turns our ignorance into a pseudo-sciencey string of fake math…but smart people ought to be able to recognize garbage.

I can’t really make a prediction here, unlike Shostak, who seems willing to gamble everything on promises he doesn’t have to worry about fulfilling. He could win the lottery. But I’m not going to place any bets on it.