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.