I enjoyed this cute clip where Carl Sagan uses some simple math to estimate how many alien civilizations capable of radio astronomy might exist within the Milkyway galaxy.
Some points of interest:
- At every step, Sagan is able to make a highly conservative estimate (about how many habitable planets there might be, how many with civilizations, etc.) and still retain an excitingly large number -- with one exception. When Sagan attempts to estimate how many civilizations might survive to technology maturity (as opposed to destroying themselves), he finds it takes optimism rather then conservatism to retain any number at all. A fair reminder of how close we have come.
- Sagan uses radio astronomy as the measure, and seems to envision the sort of alien civilizations that have dominated all but the most recent sci-fi. But today, images of enlightened civilizations composed of humanoid artisans and interstellar spaceships seem increasingly naive. Like Sagan, we're able to fuel our imaginations with the science of our time -- modern microbiology, computing, nanotechnology and even the subatomic physics that I understand so poorly. Personally, I find Kurzweil's view both intuitive, and difficult to find challenges for (criticisms of timescale aside). Which leaves my imagination in wondering: What does intelligent matter of astronomical proportions look like? What sort of conditions might allow it to spread explosively rather than gradually? How might we detect this stuff, and if we can't ... what are the implications of that?