A new analysis is getting some attention, one claiming to have refined the old Drake equation and produced firmer numbers, leading to this conclusion:
Under the strictest set of assumptions – where, as on Earth, life forms between 4.5bn and 5.5bn years after star formation – there are likely between four and 211 civilisations in the Milky Way today capable of communicating with others, with 36 the most likely figure.
Whenever I see these types of analyses, I’m always interested in two questions. What new data is available? And what remaining assumptions are being made? The new data is likely all the exoplanet information that has come out in recent years, which makes sense. But the assumptions include a major one:
“Basically, we made the assumption that intelligent life would form on other [Earth-like] planets like it has on Earth, so within a few billion years life would automatically form as a natural part of evolution,” said Conselice.
The assumption, known as the Astrobiological Copernican Principle, is fair as everything from chemical reactions to star formation is known to occur if the conditions are right, he said. “[If intelligent life forms] in a scientific way, not just a random way or just a very unique way, then you would expect at least this many civilisations within our galaxy,” he said.
It might be reasonable to assume that given the right conditions, life will arise. It started early enough on Earth to make that a defensible assumption. We might even get away with assuming photosynthesis (for a biosphere exposed to a sun) is inevitable.
But the further we go along the evolutionary timeline, the more contingent the developments get. How inevitable was the development of eukaryotic life, which may have been based on a single chance event? Or of sexual reproduction? It’s worth noting that Earth was 86% of its current age before complex life evolved, an event that required all the above plus high oxygen levels, which itself was dependent on numerous prior events in Earth’s history, both biological and geological.
And a civilization producing species requires more than just intelligence, but a body plan that allows manipulation of the environment, at various scales, including fine detailed workmanship. In other words, the hand is as important as the brain, and its development was based on numerous contingencies in our evolutionary history.
Of course, there are likely alternate paths to the same capabilities. But just blindly assuming that it’s inevitable is simply ignoring our own evolutionary history, which makes this analysis vacuous, just astrophysicists publishing their opinion on matters that are broader than the scope of their expertise. As PZ Myers notes in his own scathing assessment, they really need to include a competent evolutionary biologist in their collaboration.
These assumptions also have to include one of a couple of starkly pessimistic ones. First, that interstellar travel is impossible, even for uncrewed probes, or so monstrously costly that no one bothers. If even one civilization in the 13 billion year history of the galaxy accomplished it, they should be everywhere within 100 million years. Or second, that civilizations destroy themselves before they are able to spread. That might be a true tendency, but assuming zero civilizations escape it is pretty dark.
If we modify their assumptions to take the probability of a civilization developing on a planet like ours down to 1%, which given all the chance events seems warranted, then we’re alone in the galaxy. Dropping it lower increases the distance to our nearest neighbors accordingly. Throw in Fermi’s paradox (which looks less paradoxical when we’re realistic in our assumptions), and we get convergence that intelligent life is more rare than these folks want to admit.
Unless of course I’m missing something?