October 31, 2009 | David F. Coppedge

Can SETI Be Quantified?

What is the probability of finding intelligent life on other planets?  In 1960, Frank Drake attempted to quantify that question with his famous Drake Equation (see MSNBC and NOVA, which allows you to estimate the probability with an interactive meter).  Trouble is, Stanley Miller and Leslie Orgel of primordial soup fame thought it was meaningless.  In The Origins of Life on Earth (Prentice-Hall, 1974), p. 214, they displayed a table showing conservative and optimistic answers using the equation, ranging over 11 orders of magnitude.  Then they joked, “Also included in the table is space for the reader to put in his own numbers.  These can be considered as reliable as the other two estimates.”
    Alan Boyle wrote in his Cosmic Log today at MSNBC that astrobiologists are trying to come up with a new equation.  This one will be more conservative than Drake’s, because it will not go the distance to speculate on intelligent life – just the probability of habitable planets.  Still, it has SETI implications: “The exercise could help future generations figure out where to look for aliens – or where to settle down.”  Even that question is daunting.  “To be honest, it’s really difficult to find a way forward here,” said Axel Hagermann (The Open University, Britain) at the European Planetary Science Congress this week in Potsdam, Germany.  Whatever they arrive at will probably just specify the necessary conditions, not sufficient ones.  In other words, it will rule out unlikely habitats – not find aliens.  Water, energy and chemicals that allow for complex combinations are usually considered prerequisites.  The hard part is putting numbers to the separate factors and assigning meaning to resultant probabilities.  I.e., If a planet gets a probability of 0.001 for habitability, what does that mean?  The problem is “getting more and more complicated, and more and more interesting,” Hagermann said.
    Here’s what SETI Institute Director Seth Shostak thinks about these exercises.  “It’s a good thing to try to do, and if nothing else, it confronts you with the difficulty of doing it.  Which tells you something.”  The now-elderly Frank Drake also weighed in on the discussion: “Once we learn more, we can start to do this seriously.  Right now, our information is so incomplete that we can’t do a good job of coming up with something like a habitability index.”
Drake told Boyle this statement that wins the coveted SEQTW prize: “Any planet that’s like Earth is going to produce it.  There are so many pathways to the origin of life that it’s going to happen. … If you knew a system had planets with bodies of water on them, that would be a habitability index of 1.

You can play this game with anything you know nothing about.  Remember how we speculated about the probability of gnomes? (09/17/2008 and 04/21/2008 commentaries).  Does it make the speculation better to invent jargon like “gnomic index”?  If one tries to argue that gnomes are mythical but aliens are not, ask on what basis that is true.  We know nothing about aliens.  SETI researchers often speculate that they could be built on an entirely different chemistry.  They might even be creatures made of pure energy, some of them say.  At least gnomes breathe the same air and drink the same water as we do on this one-and-only known habitat for life.
    Frank Drake has had 50 years to try to start to get ready to begin to commence to do this seriously.  By his own admission, he and all the others have failed to even “come up with something.”  This can only be construed to mean they are not doing it seriously.  What’s the opposite of serious?  Foolish.  Alan Boyle should therefore title his article, “Comic Log.”

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