is the contradiction between the lack of evidence and high probability estimates for the existence of extraterrestrial civilizations.
Huh? Why is the solar system, galaxy, universe so large if we (humans) are the only ones?
How about this:
*** We have been in contact but it is not on a global scale.
***We haven’t broken the interstellar travel record (FTLT) yet – like in ST First Contact
There could be AND are a number of reasons why they haven’t just shown up on your doorstep.
***Perhaps their Prime Directive prevents them?