Each of the constraints you name, though plausible, don’t seem to be strong enough to act as a full filter. They appear to filter on the level of full percentage points rather than billionths of percentage points. Without finding dozens more filters of this kind, there would still be human-level life all over the place and hence (assuming no life in the universe) the Great Filter would be ahead of us.
A bunch of tiny filters is an unlikely scenario for explaining “The Great Silence”.
Duncan seems to be just talking about the Earth related constraints. It is possible to have those constraints as well as other constraints. I don’t see Duncan as directly claiming that the Earth filtration issues are the entire filter. His point seems to be more that being in the habitable zone is not the only filtration issue for a planet.
This is true. However, I also think the planetary filters are perhaps easier to evaluate than some of the others. How would I know whether the origin of life is something that’s really unlikely to happen on Earth in half a billion years, or something that will happen in trillions of places all over the planet in under half an hour, given the right conditions? I’m more tempted by the latter thought, but without knowing what the process actually is, or having any suitable examples other than Earth, it’s tough to know what the answer might be. We have no reason for thinking it’s difficult other than that we haven’t replicated it yet, though. That and the great filter question itself—if making intelligent life is easy, why isn’t it everywhere?
It is pretty easy to imagine lots of smallish filters as responsible. If I am doing my math correctly, then 9 filters that each weed out only 9 out of 10 solar systems would reduce the expected population of intelligent life in the Milky Way to just .1 systems. Since we know so much more about star formation I am a lot more comfortable saying “habital planet” will weed out 90% of systems, that is not nearly a big enough filter to account for what we see by itself but as you stack them filters of this size are quite substantial.
edit: er no that’s wrong, off by a few orders of magnitude. So yeah, gosh where is everyone?
Each of the constraints you name, though plausible, don’t seem to be strong enough to act as a full filter. They appear to filter on the level of full percentage points rather than billionths of percentage points. Without finding dozens more filters of this kind, there would still be human-level life all over the place and hence (assuming no life in the universe) the Great Filter would be ahead of us.
A bunch of tiny filters is an unlikely scenario for explaining “The Great Silence”.
Duncan seems to be just talking about the Earth related constraints. It is possible to have those constraints as well as other constraints. I don’t see Duncan as directly claiming that the Earth filtration issues are the entire filter. His point seems to be more that being in the habitable zone is not the only filtration issue for a planet.
This is true. However, I also think the planetary filters are perhaps easier to evaluate than some of the others. How would I know whether the origin of life is something that’s really unlikely to happen on Earth in half a billion years, or something that will happen in trillions of places all over the planet in under half an hour, given the right conditions? I’m more tempted by the latter thought, but without knowing what the process actually is, or having any suitable examples other than Earth, it’s tough to know what the answer might be. We have no reason for thinking it’s difficult other than that we haven’t replicated it yet, though. That and the great filter question itself—if making intelligent life is easy, why isn’t it everywhere?
It is pretty easy to imagine lots of smallish filters as responsible. If I am doing my math correctly, then 9 filters that each weed out only 9 out of 10 solar systems would reduce the expected population of intelligent life in the Milky Way to just .1 systems. Since we know so much more about star formation I am a lot more comfortable saying “habital planet” will weed out 90% of systems, that is not nearly a big enough filter to account for what we see by itself but as you stack them filters of this size are quite substantial.
edit: er no that’s wrong, off by a few orders of magnitude. So yeah, gosh where is everyone?