The following is adapted from remarks made by Avi Loeb and Stephen Webb in a Munk Debates podcast, on the topic: Be it resolved, we are not alone in the universe. Listen to the whole episode at: https://munkdebates.com/podcast/we-are-not-alone
When we think about how many alien civilizations might be out there, people tend to use a framework set out by Frank Drake.
Crudely put, we multiply the number of potential sites for life by the probability that life will arise and go on to develop technology that we can detect. And for many people, this question is settled because astronomers now know for certain there is a lot of real estate out there. There could be five billion earth-like planets in our galaxy, but we don’t know whether that’s a big number in this context. Those probabilities are completely unknown.
Take abiogenesis, the creation of life from non-life. Some biologists believe abiogenesis might be a vanishingly rare event. Even more uncertain is the path from unicellular life to a space faring civilization.
Here’s another big number: perhaps five billion different species have lived on earth, but only one can contemplate the question, are we alone? There’s nothing inevitable about the emergence of a species that’s curious about the cosmos. Crows, octopuses, and dolphins are remarkably intelligent creatures, but if humans go extinct, crows are not going to go on to build a radio telescope. Why would they?
I would much prefer to look out there and find intelligent life, and it’s entirely possible we will. And I think the question is so important that we should throw more resources into finding new ways to look into this. Looking and not finding is not the same as not looking. And given what we know about abiogenesis and of the contingency of evolution, I don’t think we should be surprised if we look out and see a silent universe.
The exact same question about alien civilizations was being debated more than half a century ago. Back then, astronomers were convinced contact was imminent, but some of the greatest biologists and evolutionary thinkers of the 20th century, like Ernest Mayr and George Gaylord Simpson, argued that any species here on earth is the result of chance and a quirky process of terrestrial evolution. Cognition isn’t an end goal or a goal at all. It just is. And if we don’t find high intelligence amongst creatures with whom we could share billions of years of evolution, why should we expect to find it among creatures with whom we share nothing but abiotic chemistry?
I’m willing to be convinced otherwise, and I would like to be convinced otherwise. And if there are civilizations out there, or if they were there, they would have been much more advanced than ours. And I think they could disturb the universe in a way that would be visible and convincing.
But 50-60 years on from those earlier debates, we’re still having the same debate. We haven’t made contact. We haven’t seen any of these signs of them out there.