Over on SSC, Nick D. and Rob S. wrote an article about whether we should colonize other planets as part of an existential risk mitigation strategy. They both think that having "lifeboats" of people in case of human extinction level disasters will help to allow humans to recover. This seems like a great idea, but I found their assertion that closed system lifeboats were the best mix of cost, feasibility, and effectiveness to be hilariously optimistic.
N&R describe a lifeboat as a place where "a few thousand humans survive in their little self-sufficient bubble with the hope of retaining existing knowledge and technology until the point where they have grown enough to resume the advancement of human civilization, and the species/civilization loss event has been averted."
What Makes a Lifeboat?
There are three requirements to this lifeboat idea:
1. closed off from the outside world
3. able to retain existing technology (presumably at the current level)
Each of these three requirements could be satisfied partially. They aren't yes/no options.
At one extreme, a closed system could just be a town with strict immigration control. Not letting new people in dramatically drops the possibility of an external plague infecting the town. At the other extreme, something like Biosphere 2 is closed off in air, water, and natural resources as well. A lifeboat could be made anywhere in that range.
Similarly, lifeboats could have varying levels of self-sustenance. A lifeboat at the high end would be capable of producing all of its own food and energy, processing all of its waste, and fixing all of its equipment as fast as it breaks. This is a _very_ high bar, but that lifeboat could last indefinitely. The other end of the spectrum is basically what most preppers have: a cache of supplies that will be drawn down steadily until sustenance is no longer possible.
Finally, retaining existing technology is actually very hard. Unless you have an active semiconductor fab, you aren't maintaining existing technologies. This is why there are only about 5 groups in the world today that are maintaining our current level of technology. That's the number of fully industrialized nations that are able to rebuild their own technology stack. All the other countries in the world just import (making them even less closed systems).
Without being able to make everything you use, at best you're just keeping the knowledge alive by teaching people about it. At worst you have a bunch of books and manuals that you'll have to puzzle over as you try to put technologies back into practice after everyone who had worked with them has died off.
My main issue with Nick and Rob's article is that they assumed they wanted the most extreme form of each of the lifeboat requirements, but they didn't take seriously the difficulty of achieving them. Their discussion of lifeboat options assumes complete self-sustenance and (generally) complete closure.
This is most evident in their (lack of) discussion about retaining technology. They seem to assume that as long as you have a copy of wikipedia stored somewhere, you'll be able to retain the current standard of technology. The problem with that is that so much of current human technology depends on experiential knowledge that is difficult to transmit. Youtube is actually helping a lot with this, but it remains a huge problem.
Space colonies are interesting because, in such a harsh environment, you need an enormous amount of technology to survive. This means that a self-sustaining space-colony is able to retain existing technologies by default. If they weren't, they couldn't maintain their quality of life. Space colonies also are closed by default, and have to make an active effort to take in resources from the rest of humanity.
Contrast that with a farmer in kansas. That farmer can just keep farming, even if they lose the ability to make an iPhone or synthesize polymers. A Martian growing hydroponics would die if their society lost the ability to synthesize polymers. Casey Handmer discusses this at length in his excellent book "How to Industrialize Mars."
Elon Musk wants to create a society on Mars that is self-sustaining, retains modern technologies, and only has contact with Earth every two years. In order to do this, he plans to send over a million people to Mars. That's larger than most cities. It's three times the size of the city I live in now. One million people is the minimum needed to make the Mars colony self-sustaining. All of those people will be working different jobs: farming, mining, making solar panels, programming, caring for children, etc. Fewer people means the Mars city isn't self-sustaining anymore. Fewer people means that everyone dies if the shipments from Earth stop.
Closure on Earth
Later on in the article, N&R seem to implicitly abandon the idea of fully self-sustaining or fully tech-retaining lifeboats. They describe a couple of options for single building city-states that could be populated primarily by programmers. These city states could be easily sealed in case of disaster, thus saving the human race. They wouldn't maintain our current technical standard, but they'd be closed and (mostly) self-sustaining.
N&R helpfully do some math, and show us that a building like the Pentagon could easily house 4000 families in space that's equivalent to a 2 bedroom apartment per family. And if a 2 bedroom apartment is only 500 to 1000 square feet, then that's true. But I have a question for them: what happens to all of the residents' crap?
Literally: when the residents crap, where does that crap go? And where do they get their food? Let's assume amazing solar panels on the roof can solve the electricity problem, but how do they fix those solar panels when they break? The Pentagon only works as a building because it has the infrastructure of a nation behind it.
The cost of a lifeboat
Nick and Rob don't consider the vastly different costs of achieving their lifeboat requirements. At some point in their article, N&R arbitrarily say that they would only send 16000 to a hypothetical Mars lifeboat. The only argument they give for this is that it allows an "apples to apples" comparison with their terrestrial lifeboats. This is a horrible idea.
Let's say you want to buy a drill, but you're not sure if you want a battery powered drill or a drill with a cable. N&R would tell you to take the motor out of the battery-powered drill so that the two weigh the same amount, and then compare prices after that.
When buying lifeboats, as when buying drills, you want to identify the specs for each option along with the prices. Arbitrarily changing some parts of the option is going affect the specs, as well as the price. You need to take that into account.
I think that cost comparisons for lifeboats are likely to be deceptive until there are concrete designs. Even once realistic designs are available, apples to apples comparisons won't be helpful. Different designs will be able to meet different levels of closure/sustenance/tech-retention. Trading off just on cost doesn't let you make good decisions about what you're really buying.
I don't want to harp on Nick and Rob too much. I think having lifeboats is a really good idea, and I think space based lifeboats are worth thinking critically about. But I worry that the article they wrote together will give people an overly rosie picture of the prospect of "backing up" human civilization. Doing so is hard, and we're not going to get a backup that has perfect closure, self-sustenance, and tech-retention.
Instead of trying to get a bunch of perfect lifeboats in every country, I'd rather we focus on having lifeboats that fall on many different places in the closure/sustainability/retention parameter space. Perhaps there are a few different designs, each of which would hedge against different types of threats. More closure would hedge against plague and nuclear fallout. More self-sustenance would hedge against large-scale economic collapse or war. More tech-retention would hedge against luddism (a la the Khmer Rouge).
Say you want all three. Say that you want perfect closure, perfect self-sustenance, and perfect tech retention. In that case, I think your only choice is going to be a Mars colony. Building such a Mars colony will take us an enormous amount of money. Getting it to self-sustaining will probably take at least 100 years of concerted effort. I think that's something to work towards, but let's go for the lower hanging lifeboat fruit first.