...on the slipperiness of time:
It was the sacrifice of absolute time that was most stunning. Isaac Newton believed that time was regulated by a sort of cosmic grandfather clock. “Absolute, true, mathematical time, of itself, and from its own nature, flows equably without relation to anything external,” he declared at the beginning of his “Principia.” Einstein, however, realized that our idea of time is something we abstract from our experience with rhythmic phenomena: heartbeats, planetary rotations and revolutions, the ticking of clocks...[T]here is no universal now. With different observers slicing up the timescape into “past,” “present,” and “future” in different ways, it seems to follow that all moments coexist with equal reality.
Other physicists marvelled that time travel, previously the stuff of science fiction, was apparently consistent with the laws of physics. (Then they started worrying about what would happen if you went back to a time before you were born and killed your own grandfather.) Gödel himself drew a different moral. If time travel is possible, he submitted, then time itself is impossible. A past that can be revisited has not really passed. And the fact that the actual universe is expanding, rather than rotating, is irrelevant. Time, like God, is either necessary or nothing; if it disappears in one possible universe, it is undermined in every possible universe, including our own.
Gödel’s conclusion went almost entirely unnoticed at the time, but it has since found a passionate champion in Palle Yourgrau, a professor of philosophy at Brandeis. In “A World Without Time: The Forgotten Legacy of Gödel and Einstein”, Yourgrau does his best to redress his fellow-philosophers’ neglect of the case that Gödel made against time. The “deafening silence,” he submits, can be blamed on the philosophical prejudices of the era. Behind all the esoteric mathematics, Gödel’s reasoning looked suspiciously metaphysical. To this day, Yourgrau complains, Gödel is treated with condescension by philosophers, who regard him, in the words of one, as “a logician par excellence but a philosophical fool.” After ably tracing Gödel’s life, his logical achievements, and his friendship with Einstein, Yourgrau elaborately defends his importance as a philosopher of time. “In a deep sense,” he concludes, “we all do live in Gödel’s universe.”
“To those of us who believe in physics,” [Einstein] wrote to the widow of a friend who had recently died, “this separation between past, present, and future is only an illusion, if a stubborn one.”
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