Maybe the reason we seem to be alone in the universe is because we truly are. But this answer to the Fermi paradox only raises more questions: Why us? Why should we be the only intelligent life in a universe 50 billion light years across? Perhaps it turns out that the evolution of intelligent life is actually really, really hard. The Great Filter hypothesis supposes that the universe seems to be empty because there is some do-or-die step between the point where life emerges and where an intelligent civilization spreads out into the universe (where we would notice them) that is so impossible it has thus far killed off every life that’s emerged across the entire universe and throughout all of time. If that’s true, then the reason why humans are the only intelligent life in the universe is because we’re the only life to have made it past that impossible step, the only life to have made it through the Great Filter. And if that’s the case, then we humans have a bright, long future ahead of us and the entire universe is there for the taking to be used in any ways we can dream up. But there’s a catch to the Great Filter hypothesis – that impossible step could also lay ahead in our future. We humans are not quite at that last point where we’ve begun to spread out from Earth and colonize the galaxy. And if there’s something that has killed off every other civilization just before they could spread out from their home planet, then we still face that same impossible trip through the Great Filter too. And if no other life in the more than 13 billion-year history of the universe has made it through, the odds are not in our favor that we will. (Original score by Point Lobo.)
- Robin Hanson, George Mason University economist (creator of the Great Filter hypothesis)
- Toby Ord, Oxford University philosopher
- Donald Brownlee, University of Washington astrobiologist (co-creator of the Rare Earth hypothesis)
- Phoebe Cohen, Williams College paleontologist
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