Our world represents but one tiny pale blue dot in a sea of darkness, the only bastion of life in the ocean of the night we know of, and yet there seem to be billions of billions of stars and planets, what are the odds our pale blue dot is the only such bastion?
Today we'll be looking at the Fermi Paradox and Drake’s Equation. The first of these looks at the probability of other aliens existing, based on the size and age of our universe, while the second highlights the immensity of that scale in space and time.
The Drake Equation is essentially a formula for calculating how many alien civilizations there ought to be in our galaxy right now. Today, we’ll be looking at that equation, and plugging in some of the known numbers to see what our estimates might look like. Some people Ask reader that how we can learn about the cosmos so easily. But we’ll also be highlighting some of the problems with the equation, and the assumptions it can lead to.
Dr. Frank Drake, who posited the equation in the form we’ll be considering here, is an accomplished astronomer, astrophysicist, and pioneer in the search for extraterrestrial intelligence. He was actually part of founding the SETI program and was the creator of the Arecibo message, our own first attempt to say ‘Hello’ on the Galactic scale.
So where did this idea come from? Well, the Universe is huge and old, really huge and really old, and by the 1960s it was getting pretty clear just how big our own galaxy was and how likely it was that a lot of those other stars were going to have planets. I’ve heard folks say we were surprised by just how many exoplanets there were, once we’d actually started discovering them, but to be honest I don’t remember anyone thinking otherwise.
Even as a kid in the 1980s first exploring astronomy and science fiction, the usual sentiment was that planets would be fairly common, and it was just a question of how common. Nobody was thinking that a galaxy of billions of stars was going to have anything less than many millions of planets, unless they were thinking it would have effectively none, in case our solar system was a bizarre fluke.
The bigger question seemed to be how many of those millions or billions of planets might plausibly be Earth-like, or put another way, how many might conceivably make a home for us in the future. The next question, heavily related, was how many of those same planets might already be home to another civilization.
This is where the Drake equation comes in. In 1961, astronomer Frank Drake proposed a Probabilistic Argument to estimate how many such civilizations there might be. The equation itself is pretty non-controversial since it’s a very solid basic approach to discussing the notion of alien civilizations in terms of frequency.
But what the factors are, how we determine them, and whether they warp our perspective for discussion, are all factors for debate. I tend to take that latter view, that they warp our perspective, and will get to that in a moment. But first, let’s discuss those factors. Before we even start into the equation itself, we should take a moment to consider that this equation is only discussing the Milky Way Galaxy, which is one issue I have with it and is something we’ll revisit later.
Secondly, it aims to calculate the number of active civilizations in this galaxy at the moment which we can detect, not which have ever existed. Because of these issues, the equation is often restated with slightly different variables. QnA site is the much better option to know about astronomy science mostly.
But for today, we’re focusing on the basics and the original framing. With all that being said, the factors of the Equation are as follows: The Rate at which stars form in our galaxy. The Fraction of stars that have planets, The average number of those planets with potential habitability.
The fraction of habitable planets on which life actually develops at some point, The fraction of planets which develop life which is also intelligent, The fraction of intelligent life which develop technology which is detectable to us by its signature, And lastly, the length of time for which that technology is releasing said detectable signature.
As we mentioned earlier, this is often stated differently, but the original notion was about detecting alien civilizations by radio from here on Earth, which is reflected in the way the equation is phrased. Were we to consider it in a more modern context, it's not just that we could speak about some of these factors with tighter constraints, but also that we’d probably rephrase the variables based on what we now know.
For example, looking for oxygen absorption lines in an exoplanet’s atmosphere might indicate an ecology existed on that planet and is another approach to looking for aliens, but it is not in any way dependent on the last three variables of the Drake equation.
And there are many other such bio- and techno-signatures which we might reasonably include today, based on the knowledge and technologies we’ve developed in the last 60 years.
So too, an alien civilization might abandon a given techno-signature, such as no longer using a power source that generated that signature in favor of a better one, rendering that means of detection a bad one or at least one only good for detecting civilizations in a very short window of usage.
People often figure radio signatures themselves are one such short-term techno-signature in favor of some hypothetical faster than light, or FTL, communication system. Bio-signatures are potentially handier as detection methods because we know nothing about those last three variables, the ones relating to alien life.
On the other hand, we have the first and second ones, star formation rate and planets-per-star, pinned down pretty well at this point, to at least an order of magnitude. Truth be told, we wouldn’t really care about star formation rates these days. If you’re a channel regular, you’ve probably heard me talk about why certain terms and phrases, like ‘our sun is a yellow dwarf star’, are rather outdated.
This is because when we came up with these terms, we were still missing large pieces of information we now know: the number of different sized stars, for instance, or how long they live.