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gwern comments on Where I've Changed My Mind on My Approach to Speculative Causes - Less Wrong
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You should probably read Carl's link.
I did. I am not impressed by the statistics quoted in it. In particular, there is a neat trick in transitioning from "NASA reports that all near-earth asteroids larger than 10 kilometers in diameter ... have already been identified" to "This eliminates much of the estimated risk due to {note the glaring empty space here where words "near-earth" used to be} asteroids"
Asteroid impact is mostly a black-swan type of problem: you can identify the risk you see but you have very little idea of the remaining risk from things you do not see.
Near earth asteroids are the primary threat set here, with only a tiny fraction not in that set that have any chance of hitting Earth. That's precisely why they say it eliminates much of the estimated risk due to asteroids.
I think it used to be the primary threat set. The claim is that near earth asteroids are not a threat because we looked at them and established that large ones are not going to hit Earth in the near future. Thus near earth asteroids are not the primary threat set any more.
This seems like an odd use of language which misses the fundamental point: the observation of the near Earth asteroids reduces the estimated risk level by orders of magnitude. Whether the remaining risk is still concentrated in the near-earth case is a secondary consideration and not relevant to what was being discussed.
I don't know why you think this use of language is odd. Saying that "we thought X was dangerous, we looked at it closely and it turns out X isn't dangerous at all" has the same meaning as "we mis-estimated the danger from X and then corrected the estimate".
If your updated belief is that there is little danger from near-earth asteroids, then the original belief that near-earth asteroids were the primary threat set was incorrect.
Because it misses the point that the total risk was from asteroids isn't that high. Yes, of the remaining asteroid threat, more of it is from non near Earth asteroids, but that's not relevant to the discussion at hand. Hence the phrase in the report that you objected to ""This eliminates much of the estimated risk due to asteroids" makes complete sense.
We are talking past each other.
Let me try to reformulate my point. We're talking about existential risk of an asteroid impact (where "asteroid" is defined as anything large enough moving fast enough). Large asteroids have hit Earth before, we have a fairly good idea how often such things happen. The historical record gives us the basis for a guesstimate of the risk.
That risk estimate is, of course, quite low. Still, we went out looking for things which might hit us in the near future. Note the asymmetry here: were we to find something our risk estimate would skyrocket, but were we to find nothing, it wouldn't perceptibly change.
So we looked at near-earth asteroids because, well, they are near-earth. Turned out none of them is on a collision course with Earth in the foreseeable future. This is good, of course, but it does not mean that the estimated risk went down -- what happened was that it did not go up and that's a different thing.
My original objection was to the characterization of asteroid risk as a "solved problem". It is not. Saying this is like looking up, noticing that the ceiling isn't about to collapse, and then on this basis confidently pronouncing that things falling on your head is a solved problem.
I had the impression that the near-earth ones were the ones that, averaged over earth's history, are the bulk of the problem. So if the current crop of near-earth asteroids aren't likely to hit us in the historically-near future, doesn't that mean that our near-future risk of impact is below the long-term average risk?
(I am not an astronomer and do not vouch for "NEAs are the main part of the risk" from personal knowledge.)
Well, IANAAE (I Am Not An Astronomer Either) but I think that with respect to historical record, there are these considerations:
We're pretty sure that large asteroids (defined as above) have struck Earth before. We are not sure where they came from.
With the passage of time the frequency of collisions should decline as Earth sweeps a path free of other space objects. So the future risk of impact is below the historical risk of impact.
The extinction-scale impact risk seems to be very small. In geologically recent times Earth was not bombarded by asteroids.
Yes, it does mean the estimated risk has gone down. It means that the largest set of obvious candidates aren't doing that. If seeing them would make it go up, not seeing asteroids on collision paths must push it down. This is the conservation of expected evidence.
Yes, technically. But I've already been though that in a thread here -- that was the whole thing about how checking your garbage can and not finding a tiger in it happens to be evidence for non-existence of tigers.
I'm willing to grant that not finding any near-earth asteroids on a collision course reduces the probability of an impact during, say, next 50 years, but that reduction is miniscule. In fact I'd call it "undetectable".
To throw in another metaphor, if I'm driving on a highway, look around, and see that no cars are headed straight at me -- technically speaking, that reduces the probability that I'll get into a car accident this year. But it reduces this probability by an infinitesimal amount only. On the other hand, if I see a car that's about to ram me, the probability of getting into an accident this year HUGELY increases.
Risks and dangers here are percieved risks and dangers. In that context, such talk makes sense - obviously percieved risks depend on your current state of knowledge. Maybe god knows whether the bad thing will happen or not - but without a hotline to Him, percieved risks and dangers will remain the best we have.