Long, but fascinating piece describing the relatively (no pun) unknown relationship between Einstein and Gödel.
“Gödel: the union of Einstein and Kafka, had for the first time in human history proved, from the equations of relativity, that time travel was not a philosopher’s fantasy but a scientific possibility. Yet again he had somehow contrived, from within the very heart of mathematics, to drop a bomb into the laps of the philosophers. The fallout, however, from this mathematical bomb was even more perilous than that from the incompleteness theorem. Gödel was quick to point out that if we can revisit the past, then it never really “passed.” But a time that fails to “pass” is no time at all.”