I got around halfway through. Some random comments, no need to respond:
What is the highest probability of encountering aliens in the next 1000 years according to reasonable choices once could make in your model?
The possibility of try-once steps allows one to reject the existence of hard try-try steps, but suppose very hard try-once steps.
I’m not seeing why this is. Why is that the case?
Sometimes you just give a prior, e.g., your prior on d, where I don’t really know where it comes from. If it wouldn’t take too much time, it might be worth it to quickly motivate them (e.g., “I think that any interval between x and y would be reasonable because of such and such, and I fitted a lognormal”. It’s possible I’m just missing something obvious to those familiar with the literature.
Do you think your conclusion (e.g., around likelihood of observing GCs) would change significantly if “non-terrestrial” planets were habitable?
Typos:
consider three priors on n (should be capitalized, also maybe some text is missing)
The effect of w on NXIC linear (should be “is linear”)
Thanks for your questions and comments! I really appreciate someone reading through in such detail :-)
What is the highest probability of encountering aliens in the next 1000 years according to reasonable choices once could make in your model?
SIA (with no simulations) gives the nearest and most numerous aliens.
My bullish prior (which has a priori has 80% credence in us not being alone) with SIA and the assumption that grabby aliens are hiding gives a median of ~2.5⋅10−6 chance in a grabby civilization reaching us in the next 1000 years.
I don’t condition on us not having any ICs in our past light cone. When conditioning on not being inside a GC, SIA is pretty confident (~80% certain) that we have at least one IC (origin planet) in our past light cone. When conditioning on not seeing any GCs, SIA thinks ~50% that there’s at least one IC in our past light cone. Even if there origin planet is in our light cone, they may already be dead.
Sometimes you just give a prior, e.g., your prior on d, where I don’t really know where it comes from. If it wouldn’t take too much time, it might be worth it to quickly motivate them (e.g., “I think that any interval between x and y would be reasonable because of such and such, and I fitted a lognormal”. It’s possible I’m just missing something obvious to those familiar with the literature.
Thanks for the suggestion, this was definitely an oversight. I’ll add in some text to motivate each prior.
My prior for d, the sum of delay and fuse steps: by definition it is bounded above by the time until now and bounded below by zero.
I set the median to ~0.5 Gy. The median is both to account for the potential delay in the Earth first becoming habitable (since the range of estimates around the first life appearing is ~600 My) and be roughly in line with estimates for the time that plants took to oxygenate the atmosphere (a potential delay/fuse step) .
My prior, LogUniform(0.1Gy,4.5Gy), roughly fits these criteria
My prior for w is pretty arbitrarily chosen. Here’s a post-hoc (motivated) semi-justification for the prior. Wikipedia discusses ~8 possible factors for Rare Earths. If there are Binomial(n=8,p=0.25) necessary Rare-Earth like factors for life, each with LogUniform(0.01,1)fraction of planets having the property, then my prior on w isn’t awfully off.
If one thinks that between 0.1 and 1 fraction of all planets have each of the eight factors (and they are independent) something roughly similar to my prior distribution follows.
My prior for u, the early universe habitability factor was mostly chosen arbitrarily. My prior implies a median time of ~10 Gy for the universe to be 50% habitable (i.e. the earliest time when habitable planets are in fact habitable due to the absence of gamma ray bursts). In hindsight, I’d probably choose a prior for u that implied a smaller median.
The implied distribution of the time at which the ‘early’ universe is x% habitable for x=10,50,90 by my prior on u
My prior for fGC, the fraction of ICs that become GCs:
It is bounded below by 0.01, mostly to improve the Monte Carlo reliability in cases where smallerfGCis greatly preferred
Has a median of ~0.5. A Twitter poll from Robin Hanson ran gave fGC≈0.4 [I can’t find the reference right now].
Lots of the priors aren’t super well founded. Fortunately, if you think my bounds on each parameter is reasonable, I get the same conclusions when taking a joint prior that is uniform on n and log-uniform in all other parameters.
Do you think your conclusion (e.g., around likelihood of observing GCs) would change significantly if “non-terrestrial” planets were habitable?
Good question. In a hack-y and unsatisfactory way, my model does allow for this:
If the ratio of non-terrestrial (habitable) planets to terrestrial (habitable) planets is r, they replace the product of try-once steps w with w⋅(1+r) to account for the extra planets. (My prior on w is bounded above by 1, but this could be easily changed). This approach would also suppose that non-terrestrial planets had the same distribution of habitable lifetimes as terrestrial ones.
Having said that, I don’t think a better approach would change the results for the SIA and ADT updates. For SSA, the habitability of non-terrestrial planets makes civs like us more atypical (since we are on a terrestrial planet). If this atypicality applies equally in worlds with many GCs and worlds with very few GCs, then I doubt it would change the results. All the anthropic theories would update strongly against the habitability of non-terrestrial planets.
My bullish prior (which has a priori has 80% credence in us not being alone) with SIA and the assumption that grabby aliens are hiding gives a median of ~2.5⋅10−6 chance in a grabby civilization reaching us in the next 1000 years.
The possibility of try-once steps allows one to reject the existence of hard try-try steps, but suppose very hard try-once steps.
I’m not seeing why this is. Why is that the case?
″
Because if (say) only 1/10^30 stars has a planet with just the right initial conditions to allow for the evolution of intelligent life, then that fully explains the Great Filter, and we don’t need to posit that any of the try-try steps are hard (of course, they still could be).
I got around halfway through. Some random comments, no need to respond:
What is the highest probability of encountering aliens in the next 1000 years according to reasonable choices once could make in your model?
I’m not seeing why this is. Why is that the case?
Sometimes you just give a prior, e.g., your prior on d, where I don’t really know where it comes from. If it wouldn’t take too much time, it might be worth it to quickly motivate them (e.g., “I think that any interval between x and y would be reasonable because of such and such, and I fitted a lognormal”. It’s possible I’m just missing something obvious to those familiar with the literature.
Do you think your conclusion (e.g., around likelihood of observing GCs) would change significantly if “non-terrestrial” planets were habitable?
Typos:
consider three priors on n (should be capitalized, also maybe some text is missing)
The effect of w on NXIC linear (should be “is linear”)
Thanks for your questions and comments! I really appreciate someone reading through in such detail :-)
SIA (with no simulations) gives the nearest and most numerous aliens.
My bullish prior (which has a priori has 80% credence in us not being alone) with SIA and the assumption that grabby aliens are hiding gives a median of ~2.5⋅10−6 chance in a grabby civilization reaching us in the next 1000 years.
I don’t condition on us not having any ICs in our past light cone. When conditioning on not being inside a GC, SIA is pretty confident (~80% certain) that we have at least one IC (origin planet) in our past light cone. When conditioning on not seeing any GCs, SIA thinks ~50% that there’s at least one IC in our past light cone. Even if there origin planet is in our light cone, they may already be dead.
Thanks for the suggestion, this was definitely an oversight. I’ll add in some text to motivate each prior.
My prior for d, the sum of delay and fuse steps: by definition it is bounded above by the time until now and bounded below by zero.
I set the median to ~0.5 Gy. The median is both to account for the potential delay in the Earth first becoming habitable (since the range of estimates around the first life appearing is ~600 My) and be roughly in line with estimates for the time that plants took to oxygenate the atmosphere (a potential delay/fuse step) .
My prior, LogUniform(0.1 Gy,4.5 Gy), roughly fits these criteria
My prior for w is pretty arbitrarily chosen. Here’s a post-hoc (motivated) semi-justification for the prior. Wikipedia discusses ~8 possible factors for Rare Earths. If there are Binomial(n=8,p=0.25) necessary Rare-Earth like factors for life, each with LogUniform(0.01,1)fraction of planets having the property, then my prior on w isn’t awfully off.
If one thinks that between 0.1 and 1 fraction of all planets have each of the eight factors (and they are independent) something roughly similar to my prior distribution follows.
My prior for u, the early universe habitability factor was mostly chosen arbitrarily. My prior implies a median time of ~10 Gy for the universe to be 50% habitable (i.e. the earliest time when habitable planets are in fact habitable due to the absence of gamma ray bursts). In hindsight, I’d probably choose a prior for u that implied a smaller median.
My prior for fGC, the fraction of ICs that become GCs:
It is bounded below by 0.01, mostly to improve the Monte Carlo reliability in cases where smallerfGCis greatly preferred
Has a median of ~0.5. A Twitter poll from Robin Hanson ran gave fGC≈0.4 [I can’t find the reference right now].
Lots of the priors aren’t super well founded. Fortunately, if you think my bounds on each parameter is reasonable, I get the same conclusions when taking a joint prior that is uniform on n and log-uniform in all other parameters.
Good question. In a hack-y and unsatisfactory way, my model does allow for this:
If the ratio of non-terrestrial (habitable) planets to terrestrial (habitable) planets is r, they replace the product of try-once steps w with w⋅(1+r) to account for the extra planets. (My prior on w is bounded above by 1, but this could be easily changed). This approach would also suppose that non-terrestrial planets had the same distribution of habitable lifetimes as terrestrial ones.
Having said that, I don’t think a better approach would change the results for the SIA and ADT updates. For SSA, the habitability of non-terrestrial planets makes civs like us more atypical (since we are on a terrestrial planet). If this atypicality applies equally in worlds with many GCs and worlds with very few GCs, then I doubt it would change the results. All the anthropic theories would update strongly against the habitability of non-terrestrial planets.
Thanks!
Don’t you mean 1-that?
″
I’m not seeing why this is. Why is that the case?
″
Because if (say) only 1/10^30 stars has a planet with just the right initial conditions to allow for the evolution of intelligent life, then that fully explains the Great Filter, and we don’t need to posit that any of the try-try steps are hard (of course, they still could be).
Right, thanks