These seven sci-fi shows have flawless time travel rules and apply them consistently. Ever since H.G. Wells' novelThe Time Machine popularized the concept, time travel has become a staple in science fiction media. While the idea of moving back and forth through time seems simple to write, it's anything but. If unconstrained, time travel becomes a catch-all deus ex machina. As such, great time travel stories require rules and restrictions to keep things interesting. Maintaining those rules takes meticulous planning and forethought.
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