“A self-replicating pathogen, whether biological or nanotechnology based, could destroy our civilization in a matter of days or weeks.”

“We can envision a more insidious possibility. In a two-phased attack, the nanobots take several weeks to spread throughout the biomass but use up an insignificant portion of the carbon atoms, say one out of every thousand trillion (1015). At this extremely low level of concentration, the nanobots would be as stealthy as possible. Then, at an ‘optimal’ point, the second phase would begin with the seed nanobots expanding rapidly in place to destroy the biomass. For each seed nanobot to multiply itself a thousand trillionfold would require only about 50 binary replications, or about 90 minutes.”

“Recall that biological evolution is measured in millions and billions of years. So if there are other civilizations out there, they would be spread out in terms of development by huge spans of time. The SETI assumption implies that there should be billions of ETIs (among all the galaxies), so there should be billions that lie far ahead of us in their technological progress. Yet it takes only a few centuries at most from the advent of computation for such civilizations to expand outward at at least light speed. Given this, how can it be that we have not noticed them? The conclusion I reach is that it is likely (although not certain) that there are no such other civilizations.”

“To this day, I remain convinced of this basic philosophy: no matter what quandries we face — business problems, health issues, relationship difficulties, as well as the great scientific, social, and cultural challenges of our time — there is an idea that can enable us to prevail. Furthermore, we can find that idea. And when we find it, we need to implement it. My life has been shaped by this imperative. The power of an idea — this is itself an idea.”