Afterword

During the 1950's, Physicist Enrico Fermi was renowned for asking hypothetical questions over lunch at the Fuller Lodge in Los Alamos. One afternoon, Fermi casually asked, “Don't you ever wonder where everybody is?” The scientists present, including George Gamow and Edward Teller, immediately knew what Fermi was talking about, and a discussion started in earnest about the prospect of intelligent life in outer space.

The basis for Fermi's question was the realization that the advent of interstellar travel would allow an intelligent alien race to colonize the entire galaxy in roughly a hundred million years, following the law of geometric expansion. This would be a mere afternoon in cosmological time.