Where Is Everybody?

A pile of enormous numbers on one side, and a single word on the other: nothing. Every fact in this lesson works out how big that gap really is, and how much of it is guessing dressed up as calculation.

Before you start. Two ideas carry this story. First, even light takes time to cross space: a light-year is the distance light covers in a year, so a star 10 light-years away is seen as it was 10 years ago (The Night Sky Is a Time Machine). Second, a test that finds nothing only means something if it was likely to find the thing had it been there (The 99 Percent Test That Is Usually Wrong).