It is a great mystery to bewildered astrophysicists that Mankind, in its push into the heavens, has not made contact, formal contact ,with  extraterrestrials .   The scientific community has deemed it a fact that, extraterrestrials must exist, as a mere consequence of mathematical probability, like an actuarial chart.   How could, with so many stars, trillions of them, and planets, only Mankind seemingly has produced a high civilization capable of reaching into the frontiers of space?   Where are the Klingons?   With all these trillion of stars racing around out there, there must be one which has produced a caliber of technological life capable of contacting Mankind.   NASA scientists have been working on this conundrum.   They have offered up THE GREAT FILTER THEORY aka HANSON'S THEORY, to explain.  This Blogger will explore the four main theories which try to explain why Mankind has not met extraterrestrials in the final frontier. Those four theories are: HANSON'S THEORY, GR