1. Govert Schilling, “The Chance of Finding Aliens,” Sky and Telescope, December 1998, 36–42.
2. Lamb, 3.
3. Quoted in Dick, The Biological Universe, 537.
4. Edward Purcell, “Radio Astronomy and Communication Through Space,” in Cameron, editor, 121–143.
5. Jack Cohen and Ian Stewart, What Does a Martian Look Like?, Hoboken, NJ, Wiley, 2002, 209.