Rules of Time Travel

            In fiction, there are three main concepts for time travel. Each of them have their own rules that must be followed in order to maintain consistency.

            One of these methods is the constant timeline. This is the theory that events throughout time cannot be changed at all. Characters can travel backwards or forwards in time, but anything they change was already accounted for and had been changed for them. A perfect representation of this is in Harry Potter and the Prisoner of Azkaban, where the characters travel back in time in order to save some lives, only to discover that they had done so all along – one of them had even caught sight of themselves before they knew they were traveling back.

            Next is the theory that time is fluid. In this theory, a time traveler can go through time, changing whatever they want – and, in turn changing the future, sometimes with disastrous results. This is sometimes tempered by a rule that history will work itself out, such as in the Dr Who series where the Doctor and his companions are constantly saving people and changing things without altering the course of history.

            Thirdly, we have the dimensional theory. In this case, as in the fluid one, time travelers can change the course of events, but each change branches off a new dimension of reality. The changes are there for the people moving through time, but the other dimension (where the time travelers came from) usually remains unchanged. I some cases, if a big enough change is made, this method allows some branch dimensions to be erased, or at least cut off from the other dimensions. An example of this can be seen in the Back to the Future movies, were the main character nearly causes himself to have never existed – and later finds himself in an alternate timeline that is nearly apocalyptic.

            Now, it really doesn’t matter which theory of time travel is used for any particular work of fiction. It needs to be chosen to fit both the story and the world well. The important part is that once a rule set is chosen, it gets stuck to. Every story – or series – needs to follow the same rules, without jumping from one rule set to the other. As soon as the established rules are broken, the internal consistency is broken and the believability of the story falls to pieces.

            So, if you use time travel, choose and choose well. Then stick to it, no matter what.

            This semi-ranting blog has been inspired by Harry Potter and the Cursed Child – an good story, except for the part where the internal mechanics do not match those established earlier in the series.

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If there's any subject you'd like to see me ramble on about, feel free to leave a comment asking me to do so.