
Fermi paradox
http://en.wikipedia.org/wiki/Fermi_paradox
Zoo hypothesis
http://en.wikipedia.org/wiki/Zoo_hypothesis
Wow! signal
http://en.wikipedia.org/wiki/Wow!_signal
Exotic Civilizations: A Possible Answer To Fermi’s Paradox
http://astranaut.org/library/exotic-civilizations-beyond-ka.php
Drake equation
http://en.wikipedia.org/wiki/Drake_equation
SETI and the Cosmic Quarantine Hypothesis (Where is Everybody?)