I think that space colonization is not on any critical tech paths. In a bit we will probably invent molecular nanotech or superintelligence, and then the game changes. Until then, it doesn't really matter if we expand into space or not. We probably won't get far with current tech, compared with what happens with those techs. I suspect that any attempt at space colonization without enough tech will do little more than fill science news columns. If the ISS had never been made, humanity would be in roughly the same position.

What timescale are you talking about? I guess it's asking "are we going to colonize the solar system before growing a lot here on earth?" I agree that seems pretty unlikely though I'm not sure this is the best argument.

My default expectation would be that humans would be motivated to move to space when we've expanded enough that doing things on earth is getting expensive---we are running out of space, sunlight, material, or whatever else. You don't have to extrapolate growth that far before you start having quite severe crunches, so if growth continues (even at the current rate) then it won't be that long before we are colonizing the solar system.

(Even if people did expand into space before we needed the resources, it wouldn't matter much since they'd be easily overtaken by later colonists.)

I think the argument can be reformulated like this: space has very large absolute amounts of some resources - matter, energy, distance (distance is a kind of resource useful for isolation/safety). The average density of these resources is very low (solar in space is within an order of magnitude of solar on Earth) and for matter it is often low-grade (Earth's geophysics has created convenient ores). Hence matter and energy collection will only be profitable if (1) access gets cheap, (2) one can use automated collection with a very low marginal cost - plausibly robotic automation. (2) implies that a lot of material demands on Earth can be fulfilled that way too on Earth, making the only reason to go to space that one can get very large absolute amounts of stuff. That is fairly different from most material economics on Earth.

Typical ways of getting around this is either claiming special resources, like the Helium-3 lunar mining proposals (extremely doubtful; He3 fusion requires you to have solved lower energy fusion, which has plentiful fuels), or special services (zero gravity manufacturing, military, etc). I have not yet seen any convincing special resource, and while nice niche services may exist (obviously comms, monitoring and research; tourism? high quality fibre optics? military use?) they seem to be niche and near-Earth - not enough to motivate settling the place.

So I end up roughly with Stuart: the main reasons to actually settle space would be non-economic. That leads to another interesting question: do we have good data or theory for how often non-economic settlement occurs and works?

I think one interesting case study is Polynesian island settlement. The cost of exploratory vessels were a few percent of the local economy, but the actual settlement effort may have been somewhat costly (especially in people). Yet this may have reduced resource scarcity and social conflict: it was not so much an investment in getting another island as getting more of an island to oneself (and avoiding that annoying neighbour).

I was a little confused by this post. Is tourism not an economic reason? But I now think the claim is something like "there may not be any benefit to the Earth economy from going to space"

There are multiple different things that we call space colonization that all have a different case.

1) A Mars base

2) A base on earth's moon

3) A base on other moons

4) A base on an asteroid that's for mining the asteroid

5) A base in low earth orbit

6) A base simply floating around in deep space

So what's the economic value of current mining? Well, mining represented 1.2% of world GDP in 2016; but roughly 50% of this is coal, which is mainly used for energy (we'll get to that later). This is a small fraction of the current economy, and one that is in decline (over the century span, if not the decade span).

The noncoal portion is still 375 billion per year. That's a lot of money.

But note "at current prices". Obviously, if we brought down a few trillions of tons of copper, the price of that metal might suffer a slight dip.

That's an argument that can reduce the size of space colonies but not one that leads us to have no space colonies at all.

Is it any easier to design AI in space versus doing it on Earth?

It's plausible that it's helpful to have computers that are stored at a place that can easily be cooled down to very cold temperatures. Maybe someone finds a way to build quantum computer that needs superconductivity.

At a time where our moon isn't used at all, it's the prime place if you want to build a building that needs to cool a lot of things down to temperatures at which superconductivity happens.

If that industry picks up on our moon, the moon will get warmer and there's a reason to go to other moons that are used and still very cold.

It might also be that you have quantum computers that have to additionally be shielded very strongly from radiation and vibrations to work.

I think it is worth noting that the main foreseeable draw for companies, very specifically energy companies to space, in my opinion, is the lack of planning permission. Perhaps that is putting it a little blase but when constructing solar panel arrays, the Earth is expensive for a project that necessarily wide, and on Earth the energy gain is, at a maximum, cut in half due to nighttime. Not considering that the absorption of higher frequency bands such as UV by the atmosphere would be entirely eliminated with a space situated solar-array.

The claims you make seem plausible, but I'd like to see some numbers crunched a bit more. For example:

The attraction of space mining is that we have access to immense resources; but what we need is access to resources at a cheap marginal cost. If space mining doesn't offer that, then we just won't use it, just as there are ways of getting resources on Earth (eg some forms of recycling, distilling resources from the sea, very deep mining) that we are just not using because they're currently too expensive.

My gut tells me the fixed costs of space mining are huge, but once you pay them, the marginal costs will be tiny. Do you have reason to think this is not true? Also, outside view says there are various companies hoping to do some sort of extraterrestrial mining, so that means some experts must think it'll be profitable. And surely they'll have anticipated the objection that the prices will drop once they start producing.