Why Nobody Should Mention the Drake Equation
“Howard: Are you familiar with the Drake Equation?
Sheldon: The one that estimates the odds of making contact with extraterrestrials by calculating the product of an increasingly restrictive series of fractional values such as those stars with planets, and those planets likely to develop life? N equals R times FP times NE times FL times FI times FC times L?
Howard: Yeah, that one.” – Big Bang Theory
Although the purpose of the Drake Equation is to estimate the number of alien civilisations with which we could potentially make contact, in truth we have absolutely no idea how many alien civilisations are out there.
The Drake Equation looks like this:
One can obtain an estimate for N by coming up with sensible estimates for each of the parameters to the right of the equals sign.
The original estimates Drake and his colleagues calculated back in 1961 varied wildly. At the minimum, it was estimated that 20 contactable civilisations existed in our galaxy. At the most, Drake estimated there to be 50,000,000.
Astronomy, Astrophysics, and Biology have all come a long way since the time when the Drake equation was thought up, but despite new, modern estimates for each of the parameters in the Drake equation, the overall estimate still varies wildly.
There are two main reasons why I think the Drake equation should never be used to argue for how many alien civilisations exist in our galaxy.
First of all, the disagreement over the values for each individual parameter means that the estimates produced by the equation have a ridiculously large range. If our estimates fall into such a large range, it’s clear we really have no idea what sort of value is correct.
Secondly, there are obviously important considerations that haven’t been made – there are terms missing in the equation.
A Range of Estimates is No Estimate
One might’ve thought that in the 57 years since the Drake Equation was concocted, we would’ve obtained more definite values for the parameters in the Equation. Whilst this may be true for some of them, on the whole the modern estimates for N actually vary more than they did in 1961!
Some parameters have become more fixed in the modern day: NASA have a fairly fixed estimate for the rate of star production now, putting it at 1.5-3 stars produced in our galaxy per year.
Several of the parameters however are extremely controversial. The proposed value for the fraction of planets that can go on to support intelligent life varies from about 10^-9 to 1. This is an astronomical disagreement – 10 whole orders of magnitude difference. To put this into perspective, this kind of disagreement is like the difference between the length of a bacterium and the circumference of the entire Earth.
The difference in opinion comes from putting emphasis on different things to do with how we evolved on planet Earth. Those who give fi a low value make the argument that seeing as we’re the only intelligent form of life to have evolved on an Earth that has supported countless other species, the probability of intelligent life forming must be very low. Those who give fi a value close to 1 (certainty) maintain that evolution creates more complex life over time and that it’s inevitable that intelligent life will form on a planet already harbouring life.
It will come as no surprise, given this discrepancy, that the estimates for N vary from about 10^-10 (meaning there are virtually no alien civilisations) to 15,600,000 civilisations in our galaxy.
I don’t think I’m saying anything controversial here when I claim that this shows we have absolutely no idea how many alien civilisations are out there.
We Have No Idea How Fast Evolution Occurs
The Drake equation may contain a parameter for the fraction of planets that develop intelligent life, but there’s nothing in the Drake Equation to account for how long it may take intelligent life to form.
The truth is that we have no idea how quickly on average intelligent life develops. We know how quickly we developed, but we are just a single data point – you can’t extrapolate from a single datum.
It could be the case that we’ve evolved exceptionally fast, far faster than expected, meaning we may be the first intelligent civilisation to have existed ever. On the flip side, we may have taken a much longer time to evolve than the average and so there may be thousands of advanced civilisations out there ignoring us because we’re too primitive.
Whatever the case may be, until we’ve met a few civilisations, there is no accurate estimate we can make for how long it takes civilisations to evolve, and hence we can make no accurate estimate for the number of civilisations in our galaxy.
It shocks me that anyone still takes the Drake Equation seriously. It was a nice first estimate back in 1961, but in reality we have absolutely no idea just how many aliens are out there, we don’t even have a reasonable guess.