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The Metaphysics of Timeline Branching: People

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One approach to time travel is to embrace timeline branching: when someone travels in time and changes something (which is inevitable), then a branch grows from the timeline. This, as was discussed in the previous essay, allows a possible solution to the grandfather paradox. But it also gives rise to various problems and questions, such as the need to account for the creation of a new universe for each timeline branch. The fact that these universes are populated also creates a problem, specifically one with personal identity. Since I used the grandfather paradox as the context previously, I will continue to do so. Suppose that Sally and Ted travel back in time and Sally kills her grandfather Sam. Ted does not murder his grandfather. Assuming the timeline branching solution to the grandfather problem, Sally creates a new timeline branch in which Sam is killed. While Sally does not exist (one assumes) in the new timeline, Ted does. There would be at least two Teds now: one that is in the original timeline and the Ted in the new timeline. In fact, anyone who was alive for the creation of the new timeline would presumably also in the new timeline—the entire population of the universe would be replicated. This raises some obvious questions about how this would work and issues within the context of personal identity. For the sake of simplicity, I will focus on Ted as my example—but this would also apply to anyone who ends up being branched. To keep it simple, let us suppose that Sally and Ted are the first time travelers, so there have been no time branches. When they travel back, they create the first branch. While Sally will not exist in the new branch (and her act of murder might result in other people not existing or even new people existing), Ted will exist in both. So how would this work? One option is to take the time splitting metaphor literally: the universe and the people in it are split into two. Think of this as being like an amoeba dividing. This does raise. . .

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News source: A Philosopher's Blog

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