To travel through time, you can open a wormhole in space-time and step through it. All you need is some “exotic matter,” which is repelled, rather than attracted, by gravity. The problem is, no one knows how to make exotic matter. But New Zealand researcher Matt Visser thinks we’ll learn how to make it soon?then we’ll be ready to travel in time. Wormholes are hypothetical tunnels that connect distant parts of space-time. Einstein’s theory of general relativity says they exist, but in order to stay open, they need exotic matter. Quantum theory says that subatomic particles and their antiparticles pop in and out of existence all the time in the vacuum of space. Exotic matter might be created by suppressing this action.

Astrophysicist Stephen Hawking says that even if we could make a wormhole that was stabilized by exotic matter, we couldn’t go through it to time travel, because even a single atomic particle would destabilize it. Does this mean we’d go back in time and never get home to the present again? But physicists have found a way to solve this problem, using the “time loops” inside a wormhole so we can travel backwards in time without being able to change anything that would alter the future. In other words, we’ll be able to travel back in time, but we won’t be able to kill off our grandparents (which would mean we wouldn’t exist).

One thing Von Braschler learned from his mentor was how to control the flow of time.

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