1. 〈http://en.wikipedia.org/wiki/Drake_equation〉
2. 〈http://en.wikipedia.org/wiki/SETI〉
3. 〈http://en.wikipedia.org/wiki/Astrobiology〉
4. 〈http://en.wikipedia.org/wiki/Frank_Drake〉
5. Probability, Random Variables and Stochastic Processes;Athanasios Papoulis,2002