The large minimum total filter strength contained in the Great Filter is evidence for larger filters in the past and in the future.
That’s true—but anthropic evidence seems kind-of trumped by the direct observational evidence that we have already invented advanced technology and space travel, which took many billions of years. From here, expansion shouldn’t be too difficult—unless, of course, we meet more-advanced aliens.
Other civilizations may possibly be expanding too by now—SETI is still too small and young to say much about that directly. Probably not within our galaxy, but only because us and them becoming civilised at the same time would be quite a coincidence.
Robin’s use of the Great Filter argument relies on the SIA, which (if one buys it) allows one to rule out a priori the possibility that the development of beings like us is very rare. Absent that, if one’s prior for the development of life is flatter than for things like nuclear war (it would be much less surprising for less than one in 10^100 planets to evolve intelligent life than for less than 1 in 10^100 civilizations like ours to avoid self-destruction with advanced technology) then you get much less update in favor of future filters.
OTOH, the SIA also strongly supports the possibility that we’re a simulation (if we assign a 1 in 1 million probability to sims being billions of times more numerous, than we should assign more credence to that than to being in the basement), which warps the Great Filter argument into something almost unrecognizable. See this paper for a discussion of the interactions with SIA.
Probably not within our galaxy, but only because us and them becoming civilised at the same time would be quite a coincidence.
On a log plot, the difference between the number of stars in the Solar System and the number of stars in the Milky Way is smaller than the difference between the number of stars in the Milky Way and the number of stars that we can reach before the expansion of the universe removes them from our grasp. How much probability mass would you place on alien civilizations within reachable space? Within our galaxy?
Katja says:
That’s true—but anthropic evidence seems kind-of trumped by the direct observational evidence that we have already invented advanced technology and space travel, which took many billions of years. From here, expansion shouldn’t be too difficult—unless, of course, we meet more-advanced aliens.
Other civilizations may possibly be expanding too by now—SETI is still too small and young to say much about that directly. Probably not within our galaxy, but only because us and them becoming civilised at the same time would be quite a coincidence.
Robin’s use of the Great Filter argument relies on the SIA, which (if one buys it) allows one to rule out a priori the possibility that the development of beings like us is very rare. Absent that, if one’s prior for the development of life is flatter than for things like nuclear war (it would be much less surprising for less than one in 10^100 planets to evolve intelligent life than for less than 1 in 10^100 civilizations like ours to avoid self-destruction with advanced technology) then you get much less update in favor of future filters.
OTOH, the SIA also strongly supports the possibility that we’re a simulation (if we assign a 1 in 1 million probability to sims being billions of times more numerous, than we should assign more credence to that than to being in the basement), which warps the Great Filter argument into something almost unrecognizable. See this paper for a discussion of the interactions with SIA.
On a log plot, the difference between the number of stars in the Solar System and the number of stars in the Milky Way is smaller than the difference between the number of stars in the Milky Way and the number of stars that we can reach before the expansion of the universe removes them from our grasp. How much probability mass would you place on alien civilizations within reachable space? Within our galaxy?