I add this resource to the sci-fi section in the hope that it will inspire others to start adding similar resources too.
This is only a few links revolving around the so called Fermi paradox, and it's possible explanations every (hard) sci-fi author should be familiar with.
What is the paradox?
The universe is huge and old. Incredibly huge and incredibly old, containing somewhere between 10^22 and 10^24 stars in total. That is 10,000 times the estimated number of "grain of sand on every beach on Earth".
Yet we do not see any sign of intelligent life out there. This was pointed out by Fermi with the question "Where is everybody?"
More details :
A very good article on the topic :
Search for extraterrestrial intelligence :
(no, not SETI. This is the enhanced version)
Where is everybody? (the aliens)