1. Ivan Almar, “Analogies Between Olbers’ Paradox and the Fermi Paradox,” Acta Astronautica, Vol. 26 (1992), 253–256; George Musser, “String Instruments,” Scientific American, October 1998, 24–28.
2. Shklovskii and Sagan, 418; Asimov, Extraterrestrial Civilizations, 192.
3. Sullivan, 244–245.
4. Heidmann’s argument was described in Stuart Clark, Life on Other Worlds and How to Find It, New York, Springer, 2000, 156. For other rejections of the paradox, see Koerner and LeVay, 181, Robert A. Freitas, Jr., “There is No Fermi Paradox,” Icarus, Vol. 62 (1985), 518-520, and Robert A. Freitas, Jr., “Fermi’s Paradox: A Real Howler,” Isaac Asimov’s Science Fiction Magazine, 8 September 1984, 30–44.
5. McDonough, 198.