Ontological Paradox
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Basic Information

This Time Travel Trope refers to scenarios where items or information are passed from the future to the past, which then become the same items or information that are subsequently passed back. This not only creates a loop, but a situation where these items have no discernible origin. For example, knowing a password because your future self told it to you. Where'd he learn it from? His future self. Where'd he learn it from? See also Stable Time Loop. The paradox raises the ontological questions of where, when and by whom the items were created or the information derived. This paradox is very closely related to the predestination paradox and usually occurs at the same time. See also Novikov self-consistency principle.

Physical items are even more problematic than pieces of information, since they should ordinarily age and increase in entropy according to the Second law of thermodynamics. But if they age by any nonzero amount at each cycle, they cannot be the same item to be sent back in time. Let's say your future self gives you a watch, currently running, and set to say the time is noon. In an hour, when the watch says "1:00" you use your time machine to go back to noon and give the watch to your Past Self. Except, now the watch is an hour older, and it says 1:00 instead of 12:00. The younger you sits around for an hour, during which time the watch advances to "2:00". He then time jumps down to noon and hands off the watch to his younger self. The changing dial of the watch illustrates a problem that happens with any item caught in a time loop - it's slowly aging.



Game and Story Use

  • This sort of paradox is very easy to create by accident. There's a chance of it happening any time an item is moved from The Future to The Past. Depending on the rules governing time travel and temporal paradox in the setting, it might be a minor inconvience or a major hassle.
    • One way of dealing with it might be for the GM to rule that any item passed down in an Ontological Paradox loop immediately and instantly ages to destruction. This still doesn't address the issue of passwords and information coming out of nowhere, but it does have the benefit of keeping the players on their toes.
      • In such a setting, what would happen to PCs caught in a Grandfather Paradox? Would they age away to dust as soon as they started putting the moves on grandma?
    • Another option is to say the item exists only within the loop, and the Law of Conservation of Matter turns out to not apply to Stable Time Loops. The item only passes once through the loop, and does not accumulate entropy. At the moment you time travel back an hour to give your younger self the watch (see the example above), the watch "magically" resets to read noon.
    • Yet another fanciful approach might be to decide the watch now exists in some indeterminate quantum state. The dial is no longer readable. You can know where it is, or when it is, but not both simultaneously.
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