There is a theory about time travel called the Novikov self-consistency principle, wherein Novikov asserts that if time travel were possible, it would still be impossible to travel back in time and alter events that have already taken place. If present-day you could return to the past, you could certainly make observations that felt new—observations that had the benefit of real-time hindsight—but you’d be unable to, say, prevent your parents from meeting, since that, by definition, had already happened. To do so, Novikov says, would be as impossible as jumping through a brick wall. Time—the
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