In 1949, in a festschrift devoted to Einstein, Kurt Gödel published a very short but profound paper titled “A Remark About the Relationship Between Relativity Theory and Idealistic Philosophy.” It has since become well-known as a defense of the possibility in principle of time travel in a relativistic universe. But in fact that is not exactly what Gödel was trying to show. He was trying to show instead that time is illusory. He was using Einstein to revive the timeless conception of reality defended historically by thinkers like Parmenides and McTaggart.
Gödel had discovered solutions for the field equations of the general theory of relativity (GTR) that allow for the possibility of closed causal chains in a rotating universe, where the “backward” part of such a chain can be interpreted as an object’s revisiting its earlier self. As Einstein acknowledged in his response to Gödel in the festschrift, in such a causal chain – in which an apparently earlier event E leads to an apparently later event L, but where L in turn leads back to E – you may with equal justice regard L as the earlier event and E the later. The relations “earlier than” and “later than” cease to be objective features of the situation. Now, as even the B-theory of time acknowledges, the objective reality of the relations “earlier than” and “later than” is essential to the reality of time. Hence Gödel concluded that in a universe of the sort he describes, time is illusory.