In Ray Bradbury's classic short story "A Sound of Thunder", a character named Lesperance explains why he wouldn't bump in to a time-traveling himself:

Time doesn't permit that sort of mess­—a man meeting himself. When such occasions threaten, Time steps aside. Like an airplane hitting an air pocket. You felt the Machine jump just before we stopped? That was us passing ourselves on the way back to the Future. We saw nothing.

What does this mean? Did the machine/Time somehow hide the previous Lesperance? Does the machine/Time duplicate realities where Lesperance somehow didn't visit while keeping the paint he made onto the dinosaur?

  • 3
    You've probably given the question more thought than Bradbury did. He wasn't writing "hard science fiction".
    – user14111
    Apr 29 at 20:17
  • It is like the Pauli exclusion principle. Time can’t stand to have paradoxes, so it just avoids them.
    – Jon Custer
    Apr 30 at 1:19

1 Answer 1


The way I read it was that the time machine simply won't show up in a period where you already were. Instead, you will wind up a bit before, or a bit after. This fits the rest of the metaphor, The way that, in some systems, it's difficult to actually run into something else because the items repel each other.

  • 2
    If you "wind up a bit before" and just hang around for a bit, you run into yourself? On another note, will Time recognize that you're the same you if you're 7 years older and all your atoms have been replaced? Or what if you just disguise yourself with costume, makeup, fake hair etc.?
    – user14111
    Apr 29 at 22:13
  • How did Lesperance know at what time the dinosaur they killed will be hit by a fallen tree then?
    – Aaron Liu
    Apr 30 at 15:50

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