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?
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?