It turns out that time travel into the past is actually relatively easy. All you need to do is make the universe rotate.
The famous mathematician Kurt Gödel was a friend and neighbor of Albert Einstein at Princeton. He became incredibly curious about Einstein's general theory of relativity, which was and continues to be our modern formulation of the gravitational force. That theory connects the presence of matter and energy to the bending and warping of space and time, and then connects that bending and warping to the behavior of matter and energy.
Gödel was curious as to whether relativity could allow time travel into the past. Einstein's theory purported to be an ultimate framework for the nature of space and time, and as far as we know time travel into the past is forbidden. So Gödel reckoned that general relativity should automatically disallow it.
And Gödel discovered that actually general relativity is perfectly fine with time travel into the past. The trick is to set the universe in motion.
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