This sort of scenario might work if Stage 1 takes a minimum of 12 billion years, so that life has to first evolve slowly in an early solar system, then hop to another solar system by panspermia, then continue to evolve for billions of years more until it reaches multicellularity and intelligence. In that case, almost all civilisations will be emerging about now (give or take a few hundred million years), and we are either the very first to emerge, or others have emerged too far away to have reached us yet. This seems contrived, but gets round the need for a late filter.
It might do, except that the recent astronomical evidence is against that : solar systems with sufficient metallicity to form rocky planets were appearing within a couple of billion years after the Big Bang. See here for a review.
Hmmmm. (ETA: following claim is incorrect) They’re judging that the planets are rocky by measuring their mass, not by noticing that they’re actually rocky.
If you don’t have a Jupiter-sized core out there sucking up all the gas, why would gas planets need to end up as giants? They naturally could do that—that happened with the star, after all, but it doesn’t seem inevitable to me, and it might not even be common.
In that case, the earth-mass planets would be gas planets after all. If you think this is a stretch, keep in mind that these are specifically in systems noted to be low metallicity. Suggesting that they might not be high in metals after all is not much of a stretch.
Actually, Kepler is able to determine both size and mass of planet candidates, using the method of transit photometry.
For further info, I found a non-paywalled copy of Bucchave et al’s Nature paper. Figure 3 plots planet radius against star metallicity, and some of the planets are clearly of Earth-radius or smaller. I very much doubt that it is possible to form gas “giants” of Earth size, and in any case they would have a mass much lower than Earth mass, so would stand out immediately.
Not if evolution of multicellular organisms or complex nervous systems is a random (Poisson) process. That is to say, if the development of the first generation of multicellular life or intelligent life is a random fluke and not a gradual hill that can be optimized toward, then one should not expect behavior analagous to a progress bar. If it takes 12 billion years on average, and 12 billion years go by without such life developing, then such a result is stlil 12 billion years away.
Or why stage 1 is so long.
This sort of scenario might work if Stage 1 takes a minimum of 12 billion years, so that life has to first evolve slowly in an early solar system, then hop to another solar system by panspermia, then continue to evolve for billions of years more until it reaches multicellularity and intelligence. In that case, almost all civilisations will be emerging about now (give or take a few hundred million years), and we are either the very first to emerge, or others have emerged too far away to have reached us yet. This seems contrived, but gets round the need for a late filter.
I don’t get the reason panspermia needs to be involved. Simply having a minimum metallicity threshold for getting started would do the job.
It might do, except that the recent astronomical evidence is against that : solar systems with sufficient metallicity to form rocky planets were appearing within a couple of billion years after the Big Bang. See here for a review.
Hmmmm. (ETA: following claim is incorrect) They’re judging that the planets are rocky by measuring their mass, not by noticing that they’re actually rocky.
If you don’t have a Jupiter-sized core out there sucking up all the gas, why would gas planets need to end up as giants? They naturally could do that—that happened with the star, after all, but it doesn’t seem inevitable to me, and it might not even be common.
In that case, the earth-mass planets would be gas planets after all. If you think this is a stretch, keep in mind that these are specifically in systems noted to be low metallicity. Suggesting that they might not be high in metals after all is not much of a stretch.
Actually, Kepler is able to determine both size and mass of planet candidates, using the method of transit photometry.
For further info, I found a non-paywalled copy of Bucchave et al’s Nature paper. Figure 3 plots planet radius against star metallicity, and some of the planets are clearly of Earth-radius or smaller. I very much doubt that it is possible to form gas “giants” of Earth size, and in any case they would have a mass much lower than Earth mass, so would stand out immediately.
I forgot about photometry.
Not if evolution of multicellular organisms or complex nervous systems is a random (Poisson) process. That is to say, if the development of the first generation of multicellular life or intelligent life is a random fluke and not a gradual hill that can be optimized toward, then one should not expect behavior analagous to a progress bar. If it takes 12 billion years on average, and 12 billion years go by without such life developing, then such a result is stlil 12 billion years away.