A Temporal Paradox (aka Time Paradox, or just Paradox) is a problem or contradiction resulting from Time Travel, usually involving broken causality. In general, these result when you go back in time and do prevent something that's documented in the history books from happening. It can also happen if you visit your younger self and interact in a way you had no prior memory of.
Depending on the setting, a paradox might be a minor inconvenience, a painful burden, or even the last thing you did before being wiped out of existence. Time Paradoxes are resisted by Ontological Inertia, and may in fact be impossible thanks to the Novikov self-consistency principle. For all we know, the existence of just one Temporal Paradox might be enough to destroy the entire universe. Caveat Chronotor. :)
There are many types of Time Paradox, many of which are also Time Travel Tropes:
- Butterfly of Doom
- Future Me Scares Me
- For Want Of A Nail
- Grandfather Paradox
- In Spite Of A Nail
- Hitlers Time Travel Exemption Act
- Ontological Paradox
- Set Right What Once Went Wrong
- Stable Time Loop
Movies and films often fail to apply consistent rules of time travel, and thus resolve paradox inconsistently within a single film or episode, per the Timey Wimey Ball Principle. This may or may not work for a role-playing game.
For a great discussion of Time Travel theory, read the Continuum RPG by Aetherco.
Game and Story Use
- A serious time travel game, especially a long-running campaign, probably needs to figure how it's going to deal with temporal paradox and then stick to it's guns. If the laws of time travel change during the campaign, it may erode suspension of disbelief.
- A lighter game, especially a humorous RPG, might be able to get away with fluctuating laws of time travel. It could play paradox up for laughs in one session, and then make it the prime plot motivator a few sessions later. You could start the campaign with the notion that each PC is destined to become their own Grandfather.
- Paradox might summon Clock Roaches or the Time Police
- The above ideas mostly assume there's a relatively few Time Travelers within the setting - if there's lots of people running all over time creating paradoxes left and right, it may well lead to a full-blown Collapse of Causality.
- A lot of paradoxes (paradocies?) may be self erasing - if you travel back in time to prevent something from happening, and suceed, then there was never an incentive for you to do so in the first place … potentially space time loops around on itself and you are returned to the point before you took whatever action created the paradox. If you are lucky, you remember that it did so, otherwise you will probably find yourself caught in a time-loop.