Klaatu barada niktoOne of the great lines in all of 20th century science was uttered over lunch by Enrico Fermi. In a discussion of the possible likelihood of many advanced civilizations in our galaxy, Fermi said something to the effect of "well, where the hell are they."
I may have taken some liberty in the way Fermi expressed himself, but there’s no doubt that Fermi’s questions is one of the more provocative off-the-cuff statements ever made because of the response that it generated, including immortalization as a named dilemma: The Fermi Paradox.
In 1961, approximately 10 years after Fermi’s lunch-time query, Frank Drake developed an equation that he used to predict the number of advanced civilizations in our galaxy. Upon reading about the Drake Equation many years ago, I was struck by its simplicity and its audacity. Here it is in its full glory. (Read all about the parameters here ) N = R* fp ne fl fi fc L
The equation consists of a chain of probabilities, all multiplied together in the fashion of the probability of a string of independent events. Depending on the values of the individual probabilities, estimates of the average number of advanced civilizations/galaxy range from several thousand to less than one.
Not a very helpful predictor! Although it does keep SETI in business.
Even though the Drake Equation is not the type of predictive rule that would seem to be necessary to be considered a good model, it is still important in a meta-context. The terms in the equation are guideposts to the factors that should most influence the presence of intelligent life in the universe. Thus the terms include such factors as the average rate of star formation, the fraction of those stars that have planets, the average number of planets that can potentially support life, the fraction of these that actually go on to develop life, the fraction of these that actually go on to develop intelligent life, and so on.
One of the best description of the Drake Equation is from The Active Mind: The real value of the Drake Equation is not in the answer itself, but the questions that are prompted when attempting to come up with an answer
So Drake is a model of a modeling process. This is a remarkable achievement for something designed to answer Enrico’s lunch comment.
I was reminded of all of this Drake stuff b/c of a very provocative article just released on Technology Review by Nick Bostrom. Titled (naturally) Where are They?, Bostrom describes how the lace of any ET sightings by SETI suggests the presence of a Great Filter that makes one or more terms in the Drake equation so small that it effectively precludes us from seeing evidence of other civilizations. In what might one day be named The Bostrom Paradox, Bostrom goes on to describe how, if any evidence is found of life on other planets, say Mars, then this would really be bad news. Not only that, but "the more complex the life-form we found, the more depressing the news would be. I would find it interesting, certainly–but a bad omen for the future of the human race. "
Now if these statements don’t whet your appetite for more, then it’s a good thing you weren’t eating lunch with Fermi that day.