We know that planets rotate, but what about the universe as a whole? No, the universe doesn't appear to rotate; if it did, time travel into the past might be possible.
Although people throughout antiquity had argued that the heavens rotate around the world, in 1949, mathematician Kurt Gödel was the first to provide a modern formulation of a rotating universe. He used the language of Albert Einstein's theory of general relativity to do so, as a way of honoring his friend and neighbor at Princeton, Einstein himself.
But this process of academic "honoring" went in a different direction than you might suspect, because Gödel used the example of a rotating universe to show that general relativity was incomplete.
Gödel's model of a rotating universe was rather artificial. Besides the rotation, his universe contained only one ingredient: a negative cosmological constant that resisted the centrifugal force of that rotation to keep the universe static.
But the artificial nature of that universe didn't bother Gödel. Instead, his main point was that general relativity allowed for the possibility of a rotating universe at all. And Gödel used his rotating universe to show that general relativity allowed for time travel into the past, which should be forbidden.
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