A couple of years ago, the Department of Homeland Security hired a bunch of science fiction writers to come in for a day and think of ways terrorists could attack America. If our inability to prevent 9/11 marked a failure of imagination, as some said at the time, then who better than science fiction writers to inject a little imagination into counterterrorism planning?

I discounted the exercise at the time, calling it "embarrassing." I never thought that 9/11 was a failure of imagination. I thought, and still think, that 9/11 was primarily a confluence of three things:...