About 40 years ago, I became acquainted with the Drake equation, which was created sin order to estimate the number of alien civilizations capable of communicating with other civilizations in the galaxy. This happened by my watching Cosmos (Carl Sagan’s original series rather than Neil DeGrasse Tyson’s more recent series). Here’s a clip of his discussion of the equation:
Here’s the Drake equation (though the first factor is slightly different from what Sagan gives above) with each of its factors explained:
Back in the days of the old Cosmos, except for the number of stars in our galaxy, each of the factors used by Sagan is somewhere between an intelligent guess and a blind guess. This was because there were no data. Nobody had any definitive way to detect planets around other stars, much less determine if life in any form had arisen, and so on.
Well, times have changed. Astronomers now do have techniques to detect planets orbiting other stars. For example, it is possible to track the subtle motion of a star due to the presence of an orbiting planet. (We think of planets orbiting stars, but in reality, they are both orbiting around their center of mass. Because the star is usually much more massive than the planet, the center of mass is very close to the star, but never exactly at the center of the star. So when there’s a planet orbiting around it, a star does actually move, and with sufficiently sensitive measurement, the motion can be detected.) Also, if a planet in its orbit passes between the star and the observer, the amount of light observed drops slightly, suggesting the presence of a planet. This latter method is what the Kepler spacecraft, launched in 2009, uses to find exoplanets (the term used for planets that orbit stars other than the Sun). As of May 10, 2016, Kepler had verified the existence of 1,284 exoplanets.
Hence, we now have data! Now it is possible, finally, to come up with reasonable estimates to at least a few of the early factors in the Drake equation. Indeed, a recently published paper provides an estimate for a combination of them, specifically the number of planets in the galaxy orbiting a star that’s good for life (like our own) in the star’s habitable zone (see above), and of the right size (between 0.75 and 1.5 of the Earth’s diameter) for our kind of life to develop and evolve. The bottom line is that there are an estimated 10 billion such planets. That sound like a lot, but it’s actually one-twentieth of Sagan’s estimate in the clip.
I would loosen the constraints a bit, myself. We are only acquainted with one type of life, after all, and there may be other ways life would develop in other environments. There has been speculation regarding life in the atmosphere of Jupiter, where complex organic chemistry is clearly occurring. Life in the hydrocarbon oceans of Saturn’s moon Titan may not be out of the question either, though it’s environment is very cold. As such, I might increase that estimate by a factor of 2.
Of course, the rest of the factors in the equation are still unknown. Again, because we are only familiar with one instance of the development and evolution of life, intelligence and technology, trying to come up with probabilities for these factors rests on sheer speculation. Myself, I think Sagan’s estimated for these terms are optimistic. He estimated around 100 million technological civilizations in the galaxy; with our updated number of habitable planets, this number would be adjusted to 5 million. IMO, given the highly contingent nature of evolution, I would put that estimate well below one percent of that number, i. e. 100,000, using my increased estimate of habitable planets. (Call me a pessimist on this item, but I think that the late paleontologist Stephen Jay Gould would agree with me on this.)
That brings us to the last factor, and that is a true enigma. The time that Sagan made that clip was near the height of the Cold War, and there was a continuous palpable fear that a nuclear war could end human life, and possible all life, on the planet. Forty years later, the chances of nuclear war have been reduced significantly, but now we are facing a climate crisis that threatens to endanger the survival our species as well as thousands of others. As a species, we keep making really poor choices. As evolution favors individuals, the winners may have a tendency toward sociopathy, and that’s bad for the environment. Being that this is built into the process of evolution itself, any civilization is going to have this problem. If we use Sagan’s optimistic estimate of one percent on those 5 million technological civilizations, that leaves us with as many as 50,000 such civilizations with which communication may be possible. This is well below his previous optimistic number of “millions,” but its still a healthy number. On the other hand, if you use his pessimistic number, you get a result much less than one, suggesting that we are in fact alone—not even the 10 civilizations of his estimate.
Again, everything in the last two paragraphs is speculation. Until we actually start finding alien life, there’s no way to know how common it is.
But now, at least, thanks to the data from the Kepler space telescope, we have some hard numbers to put in the Drake equation.
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Top Comments (August 16, 2019):
From MikeTheLiberal:
Okay, so I was busy with Anime Club Movie Night, and didn’t see this excellent comment from mohistory2, responding to my very short comment in ohamaker’s diary I’m a racist. Can we talk about it? until today. It’s thought out, and well done. I hope everyone reads this and ponders this; it really hits the core of our national racism.
From Neeta Lind
I am submitting this comment from FogCityJohn, from Meteor Blades’s terrific diary on a plan by Elizabeth Warren and Debra Haaland to fulfill our obligations to native peoples. (Ed. note: Please read Mr. Blades’s diary, too!)
Highlighted by DoctorCorey:
This comment by koNko regarding Obama’s greatness and imperfections, from DoctorCorey’s post on Joe Biden.
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This comment by BeadLady on Jeffrey Epstein’s treatment in prison prior to his demise, from Meteor Blades’ front page post on the Medical Examiner’s report.
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