Time travel and the apocalypse are old friends in fiction. If the world is going to end, the obvious fantasy is to go back and stop it, and the obvious problem is that changing the past tends to break the story. Here is a quick guide to the paradoxes, the best stories that wrestle with them, and the one form of time travel that actually works.
The paradoxes
The grandfather paradox. If you travel back and prevent your own grandfather from meeting your grandmother, you are never born, so you never travel back, so he meets her after all. Stories that change the past have to explain their way around this, usually with branching timelines.
The bootstrap paradox. An object or piece of information loops through time with no origin. A man receives instructions from his future self, follows them, and later sends them back. Who wrote them first?
The self-consistency principle. Proposed by physicist Igor Novikov, it suggests that if time travel were possible, the universe would only allow events that are consistent with the past. You can go back, but whatever you do was always part of history. Applied to the apocalypse, that is a grim thought: your attempt to prevent the catastrophe might be what causes it.
The butterfly effect. Small changes in the past snowball into enormous changes in the future. The term comes from chaos theory and meteorologist Edward Lorenz, who found that tiny rounding differences in weather simulations produced completely different forecasts.
The stories that do it best
- La Jetée (1962). A short French film told almost entirely in still photographs, in which a survivor of a nuclear war is sent back in time. It is haunting, and it’s only about half an hour long.
- 12 Monkeys (1995). Terry Gilliam’s feature inspired by La Jetée, about a convict sent back to gather information on a plague that wiped out most of humanity. A masterclass in self-consistent time travel.
- The Terminator (1984). A machine is sent back to prevent the birth of humanity’s future leader, and a soldier follows to protect his mother. The original is a tight, frightening thriller built around a bootstrap loop.
- Dark (2017 to 2020). A German series about four families, a small town, a nuclear plant and an apocalypse that keeps repeating. Keep a notebook handy for the family tree.
The time travel that actually works
You can’t go back and warn your past self. But you can do the next best thing, which is to act now as if you’d received that warning. Ask yourself what the version of you living through a disaster next year would beg you to do today. Probably: fill the water jugs, refill the prescriptions, write down the phone numbers, charge the power bank, make the family plan. Our list of ten small habit changes is a good place to start.
If you could send one sentence back to yourself a year ago, what would it say? Tell us in the comments.
