But if we can manage it so people don't have things forced on them that they don't want, I think there's every reason to believe things can settle out in a situation that is recognizably better than the one we're stuck in today.

Plants with leaves no more efficient than today's solar cells could out-compete real plants, crowding the biosphere with an inedible foliage. Tough omnivorous bacteria could out-compete real bacteria: They could spread like blowing pollen, replicate swiftly, and reduce the biosphere to dust in a matter of days. Dangerous replicators could easily be too tough, small, and rapidly spreading to stop - at least if we make no preparation. We have trouble enough controlling viruses and fruit flies.

Likewise nanotechnology will, once it gets under way, depend on the tools we have then and our ability to use them, and not on the steps that got us there.

And that because the moving parts are a million times smaller than the ones we're familiar with, they move a million times faster, just as a smaller tuning fork produces a higher pitch than a large one.

But if we can manage it so people don't have things forced on them that they don't want, I think there's every reason to believe things can settle out in a situation that is recognizably better than the one we're stuck in today.

It's a lot easier to see, at least in some cases, what the long-term limits of the possible will be, because they depend on natural law. But it's much harder to see just what path we will follow in heading toward those limits.

My work at MIT had focused on what we could build in space once we had inexpensive space transportation and industrial facilities in orbit. And this led to various sorts of work in space development.