http://www.quora.com/What-are-some-theories-on-why-we-arent-visited-by-aliens-yet
http://listverse.com/2014/09/30/10-reasons-that-we-still-havent-found-aliens/
http://io9.com/11-of-the-weirdest-solutions-to-the-fermi-paradox-456850746
http://skepchick.org/2012/01/where-are-all-the-aliens/
http://praxtime.com/2013/02/03/so-where-are-all-the-aliens/