For some reason, in all of this speculation about intelligent alien life we forget about how immense the distances are between stars, not to mention galaxies. If there were only one planet per spiral galaxy inhabited by highly intelligent life, the universe would be teeming with intelligent life. But the distance between them would prohibit interstellar travel and physical contact, and even radio communications would be hit or miss. Of course, that may have happened throughout the universe, but not yet with us. The point is, there are real physical barriers to what science fiction writers have presented to us as intriguing possibilities. But not to despair, because the reality is likely to be far more interesting!