How do we know we--or anyone else--is an alien?  Oddly enough, many people ask this question, wondering aloud whether we are really aliens in disguise or whether aliens are in fact running the earth.  People like to wonder about aliens.
     Consider the 2001 movie K-Pax.  This movie presents the earthly appearance of a person (name of "prot") who claimed to be from K-PAX, a planet with two suns in the constellation Lyra.  This person, played by Kevin Spacey, seems to know things about interplanetary travel and motion that even the brightest and most sophisticated astronomers do not, and produces, with little apparent effort, complex mathematical calculations describing such things.  Yet the psychiatrist, played by Jeff Bridges, who is treating him continues to believe that "prot" is merely wrestling with a trauma from his past and, given time, will "snap" out of his delusion.
     As the movie progresses, the psychiatrist discovers what he believes to be "prot's" real identity and concludes that he is very close to resolving the case.  Then, as he promised he would do, one morning "prot" appears to vanish in a beam of light, and taking, it seems, another patient with him.  But the body he apparently "used" remains.
     So really happened?  Was "prot" a visitor from another planet?  Did he just inhabit this other person's body to help him find himself?  And what about the other patient who disappeared?  We are left hanging.
     So, I thought, suppose someone who claimed to be, for instance, God appeared on earth.  Would we believe this person to be who he claimed to be?  What proof would we require?  What if this person did things that we would expect a God to do, like perform miracles and summon the forces of nature at will?  What if this person said things, things that seemed wiser than anything else we had heard before?  And what if this person disappeared without a trace, with no earthly explanation?  We might have to really think about whom that person really was.
     But like the people who knew "prot," in the end, we would need to settle for less than a full explanation.  We would always be wondering what really happened.  Whatever we decided, we'd need to do so without really knowing everything about it.  We'd need to exercise faith.
     For faith, like it or not, is the only way that we will ever settle the question of God:  if God is something we fully understand, what's the point?