How should we assess evidence of aliens or intelligent life? MSNBC’s Ari Melber interviews astrophysicist Neil deGrasse Tyson and former CIA director John Brennan about that challenge in the wake of a new Pentagon report. Brennan says the U.S. must “try to understand what is unexplainable,” while Tyson expounds on his steep skepticism of the evidence offered while encouraging believers to “go catch the aliens” if they can. (This conversation is one part of a broader special report.)

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