In Einstein's equation, time is a river. It speeds up, meanders, and slows down. The new wrinkle is that it can have whirlpools and fork into two rivers. So, if the river of time can be bent into a pretzel, create whirlpools and fork into two rivers, then time travel cannot be ruled out.

I like to engage the public because when I was in high school, I had all these questions about anti-matter, higher dimensions and time travel. Every time I went to the library, every time I asked people these questions, I would get some strange looks. Nobody could answer any of these questions.

Originally, the burden of proof was on physicists to prove that time travel was possible. Now the burden of proof is on physicists to prove there must be a law forbidding time travel.

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