Two weeks ago, during the world's first CYBER WorldCon, I participated in a panel discussion called "COVID-19: A Great Filter?" The panelists were myself, writer and Coronavirus expert Vylar Kaftan, and astrophysicist Valentin Ivanov. Our topic was the concept of the "Great Filter" and whether a plague like the current Coronavirus outbreak could qualify.
The more I thought about Great Filters, the more I realized there was no way to fit the topic into one 50-minute Zoom panel, or even a single 'blog post. So I'm going to write a series of posts about potential Great Filters, working my way through different types and examining what we know and how plausible they are.
But first: what the heck is a Great Filter?
The term comes from an essay by economist and futurist Robin Hanson, which you can read here. To summarize, we know that technological civilization capable of communicating across interstellar distances is possible, because we exist and could do it ourselves. But if that's the case, as Enrico Fermi famously asked, "Where is everybody?"
Science doesn't like unique phenomena. There should be either multiple technological civilizations, or none. We know it's not impossible because we exist, so . . . where is everybody?
Just to complicate matters, it's unlikely that most civilizations out there would be about the same age as our own. It took billions of years for Earth to produce hominids, and hundreds of thousands of years for humans to develop radio telescopes and space travel. Even a variation of just one percent would mean other civilizations would be millennia, if not eons older than our own. Even at modest rates of growth they should be detectable across interstellar distances even if they aren't deliberately signaling to us.
Frank Drake tried to quantify the probabilities of such civilizations arising in his famous Drake Equation, which you can read about here. He broke apart the likelihood of civilizations existing into a number of sub-probabilities. How likely are stars to have planets? How likely is it for a planet to support life? How likely is it for intelligence to arise? And so forth.
Hanson took that another step. Obviously something keeps the number of technological civilizations very low. How do we know that? Again, because we're here. If civilizations were common, either we'd have heard from them, or seen signs of their existence . . . or we wouldn't exist because a bunch of settlers from the Perseus Arm of the Galaxy colonized Earth right after dropping an asteroid on Yucatan to clear away those pesky dinosaurs 65 million years ago.
The big question is whether the Great Filter — the real bottleneck keeping the number of civilizations vanishingly small — is behind us or ahead of us. In other words, is the origin of life or the origin of intelligence the Great Filter, in which case we've passed through; or is there something about to happen to us which we can't predict or prevent, and which has hit every other nascent civilization in the Milky Way?
As I said, this is a subject too big for a single post, so I'm breaking down the potential filters into categories. First come Stellar Filters: things related to the Galaxy or to stars which make life or intelligence unlikely. Next is Planetary Filters, reasons to think Earth might be extremely rare in some way. Then Life Filters, looking at just how likely it is for life to arise and evolve into something which could become intelligent. After that comes Intelligence Filters, also including issues of language and tool use. Then Civilization Filters, which might make large-scale social systems uncommon in the Galaxy.
That brings us up to the present, and then I'll start looking at Filters we still may have to get through. Disaster Filters are things which might bring down or destroy our civilization. Space Filters are things which might confine us to a single planet or a single star system. Perception Filters are reasons for optimism: maybe we just haven't seen everybody yet. And finally there are Meta Filters, which are essentially ways to reject the entire question.
And so, having finished that long-winded introduction, I will stop here and leave everyone hanging. Next week: Stellar Filters!
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