I don't believe in the existence of aliens because no one for many years could not scientifically prove their existence. The astronauts were a long time in orbit did not declare the existence of aliens. The Christian religion denies the existence of aliens. Also none of my relatives and friends have not seen aliens. And anyway, assuming they exist, why so far none of the aliens did not come into open contact with the people. maybe they don't...we are for them something like a lower life form.... besides ,do you seriously believe that the only living organisms live on Earth?