Why Haven't Alien Intelligences Contacted Us Yet?

Experts say any spacefaring alien races we meet must be vastly more advanced than we are. That's because the odds of an alien race, within a reasonable traveling distance, developing spaceflight at the exact same moment as humanity are virtually nil. So any other space-traveling cultures in our patch of the galaxy could well have the technology to come to us. So why haven't they shown up yet? Vote for your favorite explantion.

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Man Of Two Worlds cover from Gems From The Collection.