Elegant, But Untestable: On the Unscientific Nature of the Drake Equation

By Adam J. Pearson


Fig. 1.1 – the Milky Way Galaxy, the home of our solar system.  The Drake equation claims to be able to predict the number of detectable extraterrestrial civilizations within the Milky Way.

The Drake equation, which was developed by Frank Drake, Emeritus Professor of Astronomy and Astrophysics at the University of California, Santa Cruz, is an equation used to estimate the number of detectable extraterrestrial civilizations in the Milky Way Galaxy.

The Drake equation states that:

N = R^{\ast} \cdot f_p \cdot n_e \cdot f_{\ell} \cdot f_i \cdot f_c \cdot L

where:

N = the number of civilizations in our galaxy with which communication might be possible;

and

R* = the average rate of star formation per year in our galaxy
fp = the fraction of those stars that have planets
ne = the average number of planets that can potentially support life per star that has planets
f = the fraction of the above that actually go on to develop life at some point
fi = the fraction of the above that actually go on to develop intelligent life
fc = the fraction of civilizations that develop a technology that releases detectable signs of their existence into space
L = the length of time for which such civilizations release detectable signals into space
(Source: “PBS NOVA: Origins – The Drake Equation.” Pbs.org. Retrieved 20 February 2012) 

This seemingly impressive equation has been at the root of controversial debates within the scientific community. SETI, the Search for ExtraTerrestrial Intelligence takes the equation very seriously and uses it in their attempts to locate extraterrestrial life in the Milky Way Galaxy.


Fig. 1.2 – Michael Crighton 

However, the foundation of all science is critical questioning and we must ask: is the Drake equation an example of science? My own position on this issue is in complete agreement with that of Michael Crighton, which he succinctly expressed in a lecture at Caltech delivered in 2003. In the lecture, Crighton states that:

The problem, of course, is that none of the terms [in the Drake equation] can be known, and most cannot even be estimated. The only way to work the equation is to fill in with guesses. […] As a result, the Drake equation can have any value from “billions and billions” to zero. An expression that can mean anything means nothing. Speaking precisely, the Drake equation is literally meaningless...”

Crighton goes on to argue that the Drake equation “has nothing to do with science. I take the hard view that science involves the creation of testable hypotheses. The Drake equation cannot be tested and, therefore,” he concludes, is not science. The reason that the equation cannot be tested is that we have no reliable way of developing values for its parameters that are grounded in empirical data; at best, we can only make guesses, and the guesses that various scientists have put forward for these values range wildly. Which estimates are correct and which are way off the mark? We simply do not have the necessary data to answer this question.

As interesting and ostensibly powerful as the Drake equation may seem at first glance, in the absence of reliable empirical data, it simply remains an interesting subject for an intellectually amusing guessing-game. It cannot be regarded as providing testable hypotheses and, therefore, it is pseudo-scientific at best and, at worst, should not be considered science at all.

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