The Debate Over the Probability of Extraterrestrial Life

The Drake Equation is one of the hallmarks of the Search for Extraterrestrial Intelligence (SETI) research movement. It seeks to describe in an equation the probability of technologically advanced civilizations existing outside of Earth. It is named for Frank Drake, a founder of the SETI movement, who came up with the equation during a historic meeting of astrophysicists in 1961. While it was a groundbreaking consideration of the issue, it has been controversial over the years, primarily due to the wide interpretation that can be given to the various parts of the equation. Drake says that the equation suggests there may be 10,000 communicative extraterrestrial civilizations in the Milky Way Galaxy alone.

David Spiegel with Princeton University and Edwin Turner with the University of Tokyo have made headlines this week with a paper in which they take a new look at the question, applying a different mathematical model. The specifics of the Bayesian statistical framework they use are too complicated for me to understand or explain. Please see the paper for details. The conclusion of the piece suggests that estimates for the possibility of extraterrestrial life in the universe may be far too high and from their mathematical model it’s just a probable that we are alone in the universe. Certainly a sobering analysis. However, you need to look closer at the paper to see what they are really suggesting. They state in several places that the search for extraterrestrial intelligence and extraterrestrial biology is the only way to solve the problem. We need to look for these signs to better determine the probability of extraterrestrial life. That seems a bit obvious- if we find extraterrestrial life then it’s more likely there is extraterrestrial life in the universe. The real question is the number of planets with life. With no evidence of life outside of Earth, our current state, the likelihood is low. With the discovery of astrobiology there is a much greater likelihood of widespread life and thus intelligence.

Most extraterrestrial life considerations rely on speculation. Even the best ideas, such as the Drake Equation, rely greatly on speculation. This doesn’t take away from SETI research. A systematic, scientific search of the universe for signs of extraterrestrial life is the only way to get beyond the speculation and work in the realm of fact. That’s what SETI does each day. The exciting NASA Kepler Mission has discovered many planets, some of which could be habitable. This is concrete scientific research at its best. Astrophysicists are pushing the frontier of our knowledge and at breakneck speed. It’s an exciting time to be human.

The rest of the discussion of extraterrestrial intelligence is simply conjecture. This blog is primarily speculation. Many of us will continue to speculate, consider possibilities and offer opinions. There’s plenty of room for that too. Science fiction authors and futurists have offered up ideas on the subject for decades. If there ever is a solid scientific discovery that speculation could be quite valuable to help us create a path to move forward. Spiegel and Turner just have one big message for us: don’t get your hopes up.