The Rare Earth Hypothesis
Contrary to the Copernican Principle and a possible answer to the Fermi Paradox.
The Drake Equation
The Drake Equation, created in 1961 by astrophysicist Frank Drake (1930-2022), was intended to stimulate discussion about the Search for Extra-Terrestrial Intelligence (SETI). Drake never intended it as a precise, or even rough, estimate of actual numbers.
As an aside, Drake was instrumental in the designs of the Pioneer plaque, the Arecibo message, and the Voyager Golden Record. Yet he may be best known for his eponymous equation. Carl Sagan may have been more well-known, but Drake was a giant in astronomy.
For the record (no pun intended), here’s the Drake Equation:
See the Wiki page for an explanation of the individual terms. What matters here — and this is one reason the Drake Equation mustn’t be taken too seriously — is that a bunch of odds are multiplied together to come up with a number, N, representing intelligent galactic species. Specifically, ones trying to communicate.
Many, I think, assign too high a value to one or more of the probability terms. In particular, I think many assign too high a probability to the formation of complex life, let alone intelligent life. The result is a belief in a galaxy teeming with intelligent alien species — a common science fiction scenario.
The Fermi Paradox
As the story goes, before Drake formulated his equation, in the summer of 1950, physicist Enrico Fermi (1901-1945) enjoyed a casual conversation with several fellow physicists about UFOs and faster-than-light travel. Later, Fermi blurted out, “But where is everybody?” (Or words to that effect.)
While the Fermi Paradox predates the Drake Equation, it makes the same assumption that intelligent space-savvy aliens are not just a thing, but common.
Under that assumption, there is indeed a paradox. If the universe commonly supports the generation of intelligent life, then where is everybody?
One thing that leads to this thinking is how common and ubiquitous life is here on Earth. It does seem that, once life gets a hold, as famous said, life finds a way. Cockroaches and dandelions both show the persistence and endurance of life. At the same time, there is an unsolved mystery about exactly how organic chemistry evolves into RNA capable of replication (a process called abiogenesis).
The Copernican Principle
Another driver in assuming intelligent life is common comes from the Copernican Principle. It’s named after Nicolaus Copernicus (1473-1543), the guy who got into so much trouble because he said the Earth goes around the Sun. More to the point, that the Earth wasn’t the center of things.
By extension, the Copernican Principle is the idea that we aren’t special, that we aren’t privileged observers. The universe we observe is somehow normal, and we’re just a tiny (insignificant) part of it.
But this, combined with the observation of apparent fine-tuning in the nature of reality to allow our existence, raises the question of how we can be not-special when the universe itself appears special. This leads to the Anthropic “Principle” (a piece of sloppy thinking that doesn’t deserve name “principle”).
A good analogy is a jackpot winning lotto ticket. If the lotto company printed just one ticket (assuming the usual high odds against winning), and that one ticket turned out to be the winning ticket, you’d suspect a hidden hand. But if the lotto company prints millions of tickets, and just one is a winner, that’s business as usual, perfectly normal. But this is why otherwise sane people not only believe in aliens but multiple universes. The only way to explain this one winner is by assuming millions of losing tickets.
Universes everywhere, why not, and each filled with intelligent (but interestingly shaped) aliens. The only way we’re truly ordinary is if there are lots of other versions of us. Other universes aside, it’s not hard to think not-special implies many other alien species.
The Simple Math
I’d like to suggest what I think is a saner view based on a basic proposition and some very simple math. This is a version of the Rare Earth hypothesis.
The proposition is that for intelligent life to arise at least a half-dozen events or conditions are necessary along the way. Here are some example candidates:
The right kind of star. Not too hot, not too cold.
The right kind of planet. Rocky is likely best. Needs to be stable!
The right size of planet. Too much or too little gravity is a problem.
The right orbit around the star. Not too close, not too far.
Large gas giants (Jupiter and Saturn) in the outer system to shield the inner system from bombardment. They also help clear the inner system from asteroids.
The putative accidental collision with Thea is thought to have added to our iron core insuring a strong magnetic field to shield Earth from Solar radiation that would otherwise scour it clean and dry as it did Mars.
A large moon and the resulting tidal pools may have been instrumental in life’s transition from sea to land (and eventually to intelligence). The daily dry/wet cycling of tidal pools encourages the ability to deal with dry land.
Our position in the galaxy, in particular our proximity to ancient supernovae gave us important heavy elements that life appears to need. It also gave us radioactive elements that help keep the Earth’s core warm.
Dinosaurs roamed the Earth for 165 million years without developing sapience. Plants don’t need it at all. Apparently complex life doesn’t necessarily evolve to intelligent life, so it doesn’t seem required by evolution.
Any of the Paradox-resolving so-called Great Filters that block or terminate intelligence. Nuclear war seemed a good candidate for a while. Global warming seems more likely to kill us off right now. Disease is another candidate. COVID-19 took a healthy swing at us (killed over seven million). Great Filters could easily comprise their own list.
The list isn’t exhaustive by any means. Note how most of these conditions are also necessary for just biological life to arise (let alone intelligent life). There are likely dozens or hundreds of factors that combined in our existence.
What I suggest here is that for intelligent life to arise, for us to be here asking this question, at minimum a half-dozen (6) of these have odds of at minimum one in ten thousand (1:10,000).
This does not seem a big ask to me. If you agree consider the consequences:
Six occurrences of 1:10,000 odds gives us 1:1,000,000,000,000,000,000,000,000 odds.
That’s one septillion to one (at least) against us being here to discuss this.
And here’s a remarkable thing about this result. Our Milky Way galaxy has roughly one-hundred billion (10¹¹) stars.1 And the visible universe has about one-hundred billion (10¹¹ again) galaxies. That means the visible universe has roughly:
That’s two orders of magnitude less than the number of stars required to make intelligent life — as calculated by the above odds — a reasonable certainty. In other words, in all the visible universe, we might be the only ones who beat the odds.
Making us the one winning lottery ticket.
In particular, in this galaxy with only 10¹¹ stars, the odds of 10²⁴ for intelligent life make it incredibly unlikely there is any alien life in this galaxy. Given the distance between galaxies, even if other galaxies, even the closest ones, harbor intelligent life, they are effectively completely out of reach.
As an example, our closest big neighbor, the Andromeda Galaxy, is 2.5 million light years away (a mere 150,000,000,000,000,000,000 miles).
The Bottom Line
So, if you accept the simple premise about events and conditions necessary for intelligent life, and accept at least six have odds of at least 1:10,000, then there is a strong conclusion that intelligent life is extraordinary and extraordinarily rare. And given the 10¹¹ stars in this galaxy, it requires serious reduction of odds or events required to close the thirteen orders of magnitude difference.
Very likely SETI is doomed to failure because we’re likely it. Not that they should stop or that looking isn’t a good idea. Science always looks. That’s its deal.
We are very likely what passes for intelligent life in this whole galaxy.
The Copernican Principle applies to our observation of the universe — it is homogenous everywhere we look, and physical law is universal — but that we exist to make that observation is, it appears, rather special.
But contrary to the Copernican Principle, we are, in some sense, truly the center of the universe, especially if it is true we are the only intelligent observers. (If only we learned to act like it.)
The answer to the Fermi Paradox is that the Drake Equation severely underestimates the situation. The Paradox is based on the false assumption that intelligent life is common. It seems far more likely that that it is extremely rare.
An interesting coincidence, the human brain has about one-hundred million neurons.
I also liked Contact, and you're right about Judy Foster. Especially after seeing Tarter in flesh and bones, but also the rest of it, the mind. I guess Foster did her job well, whatever the director asked of her. I can't even remember who the director was.
Pfft, Drake, schmake. I barely started reading.