But we must invest merely in the cost of the initial generation of probes. It would take, the double-domes think, ten to a hundred million years for the colonization of the Galaxy to be completed in this manner. Once started, the process will be self-directing, self-financing. Our ships will spread along the spiral arm, along lanes rich with stars, farming the Galaxy for humankind. The volume covered by the probes will grow rapidly, like the expansion of gas into a vacuum. The probes will reach new targets and again, more probes will be spawned, and fired onward. More probes will be built and launched from each of the first wave of target stars. There's nothing an entrepreneur likes more than the sound of the wordfree. Such resources are useless for any other purpose, and are therefore economically free to us. We can therefore anticipate massive exploitation of the system's resources, without restraint, by the probe. A target system, we assume, is uninhabited. When the probe reaches a new system, it phones home, and starts to build. The first wave will be slow, no faster than we can afford. But it may be cheaper for the probes to manufacture humans in situ, using cell synthesis and artificial womb technology. One percent of the helium-3 fusion fuel available from the planet Uranus, for example, would be enough to send a giant interstellar ark, each ark containing a billion people, to every star in the Galaxy. We'll probably start as we have in the Solar System, with automated probes. We might use ion rockets, solar sails, gravity assists. Want me to tell you how? Turns out it's all a question of economics.

Or we could be on our way to populating the Galaxy. We could all choke to death, be extinct in a hundred years. You don't need me to stand here and tell you that. Tonight I want to tell you why I care so much about this issue that I devoted my life toil.

I've bored you with that often enough already, right? So tonight I want to look a little farther out. In fact, in the past I've tried to get you to pay for such things. You know I've campaigned for, among other things, private mining expeditions to the asteroids. To two space cadets: My nephew, James Baxter Kent Joosten, NASA

Stephen baxter manifold trilogy