[InclinedPlane]

I hate replying to myself but I think this point is worth following up on re:space. Consider that by current estimates the global economy will be at a level of around a quadrillion dollars per year within the next 100 to 150 years. Now, let's say that developed countries put a priority of space science exploration and manned spaceflight at around 1 part per thousand of GDP, which is fairly close to what the G8 nations spend today. Assuming that the future world retains such a priority it would mean spending of a trillion dollars a year just a century or so out. Now think about that over centuries, hundreds of trillions of dollars of investment into space. I think that means that at a minimum you'll have self-sufficient off-Earth colonies with populations of millions. And that's without assuming breakthrough technologies.