Why don't people understand the urgency of colonizing other planets?
Before we colonize anything outside of our own self-sustained gravity well, we kind of need to have a working model of a self-sustained /ecological system/.
Which we noticeably lack.
Let's not forget that, under the criteria of self-sustainment, Biosphere II was a failure, yes? And that subsequent research in ecological systems indicate that we are, collectively, more ignorant than wise as to the mechanics necessary to sustain a fully functional off-world environment.
Yes, we could be wiped out by a kilometer-radius asteroid at any moment. That doesn't mean we actually know what to do about it. Colonizing other planets necessitates /self-sustaining/ colonization - it's utterly pointless, after all, to have a Mars colony doomed to a slow and painful death if its ludicrously expensive supply line to Earth collapses.
If that doesn't convince you, though, /you/ can be the first one to try out a Biosphere-3 on Mars. Go ahead - I won't take your place in line. I promise.
Assuming some worst case scenario, how many people would need to be on another planet for the species to survive? Would 1 million be enough to support the necessary technical infrastructure independent of the Earth?
If it isn't independent of the Earth then what's the urgency? Would having the same number of people on/in Earth, inside an independent ecosystem ("Biosphere III", perhaps?) be sufficient safety net? That would be a lot cheaper.
The presumes that the author's stated goal of species survival is the only goal in advocating the colonization of other planets.
I believe there are gaps and omissions in the text.
"most recent 2 millennia living as farmers" -- that should be about 6 millennia.
"there is no evidence that modern humans have ever gone extinct on a continent or a large island." -- what, the Vikings on Greenland aren't modern enough while 1602 is?
"Detection of a large asteroid on a collision course with Earth would no doubt precipitate a frantic scramble to retrofit existing missiles to deliver a nuclear explosive to deflect it toward a less terrifying trajectory." -- except I thought there were more effective ways than nuking it to another orbit. Nuclear weapons have a lot of energy but not a lot of momentum. A mass driver, or a gravity tow, or a number of other techniques seem more appropriate from what I've read.
"which each killed more than 200,000 people provide powerful reminders of the vulnerability of our species to natural disasters." -- not at all. That's 0.003% of the species. If anything, it shows the vulnerability of an human but the resiliency of our species.
I can even argue that having more people, including those living in dangerous places, means more chances for survival. If we all uniformly lived away from Vesuvius, from tornado alley, from tsunami prone areas, and instead only lived in the safest, then we increase the chances that an unexpected event (asteroid, anyone?) at just the wrong spot can destroy everyone.
That's only hand-waving, which is what the author does all over the place.
When technology problems are sufficiently hard, not working on them is often the right strategy.
The normal progress of science and technology will make more powerful tools available in general, and eventually there will come a point where the solution to the problem is easy because of those new tools.
Better to work on things now that we can actually make progress on, and do research to discover new tools and techniques to expand the range of problems we can deal with.
There is an underlying assumption here that the human species MUST SURVIVE. While my general aim in life is to add to human flourishing, I do feel that people who are obsessed with keeping humanity alive are being a little dramatic.
If an asteroid does hit Earth and destroy most life, is that so bad in the grand scheme of things? If we can come to terms with our personal death, why can't we also come to terms with the death of our species?
Not saying we should all kill ourselves - but that the preservation of our species should take a back seat until we solve more pressing and truly urgent concerns like global poverty, infectious disease, cancer, human trafficking/slavery, etc
Where's the rush? Wait a few decades, let it be profitable and the Moon will be colonized. This timeframe is tiny in the grand scheme of things.
The human race has never been in a better position to ensure its survival and the chances are increasing. I would guess that even a dinosaur-killer (20km) asteroid, while devastating, would not end the human race itself. Thinking about events that happen every few millions of years is not very productive for human beings.
Even if you start spending $1tn. per year, it's doubtful that space exploration can be made profitable; in fact it could be the opposite (public money crowding out private investment).
With that in mind, get NASA to actually search for the multi-km size asteroids that could threaten the Earth.
It seems to me what is most urgent is what is possible now ('the Adjacent Possible')
IMO that is:
Supporting the Seasteaders and Charter Cities; supporting the further development of nuclear technology (all potential forms of fusion and fission); supporting the development of new forms of propulsion technology (e.g. plasma drives).
As an aside, this is an example of what it would take to definitively wipe out humanity:
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if we can't survive here, we can't survive anywhere. there is no urgency to colonize other planets.
Humans suck at reasoning about black swan events, thus the ROI can't compare to more obvious and immediate needs. So blame our brains.