Multiversal success and failure.  Success?   Star Trek TOS episode "Mirror, Mirror," and the 2017 Starz series, "Counterpart."  Failure?  It pains Driftglass to say it, but Robert Heinlein's "The Number of the Beast" is well-known as a massive fail in the multiverse and just plain science fiction novel genre.

And you can hear Patton Oswalt's magnificent Parks and Rec filibuster concerning "multiverses" here.

More at sciencefictionuniversity.com.

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