Figure 12.6 Albert Einstein with Kurt Godel

“Godel en.wikipedia.org/wiki/Kurt_G%C3%B6del was the only one of our colleagues who walked and talked on equal terms with Einstein,” said the physicist Freeman Dyson, then one of the Institute’s rookies, and one of the great mathematical minds of the twentieth century. And as assistant of Einstein’s confirmed : “The one man who has certainly been by far Einstein’s best friend over the past years was Kurt Godel, the great logician. They were very different in almost every personal way [. . . . ] but they shared one fundamental quality: both went directly and wholeheartedly to the questions at the very center of things.” Einstein himself liked to joke: “I go to my office just to have the privilege of being able to walk home with Kurt Godel.” Or perhaps it was not even a joke at all.

. . . . Godel with his characteristic thoroughness, went more deeply into the matter. What had been originally commissioned as a philosophical essay turned into a mathematical theory, and in the process, Godel discovered a truly remarkable new class of solutions to Einstein’s field equations of general relativity.

His work implied that in principle, general relativity allows for rotating universes. Such a universe does not rotate around an axis; it rotates with respect to every local inertial system. It implies that general relativity need not obey with Einstein had called “Mach’s principle,” which he had depended on to motivate his theory. This came as a great surprise. In particular, there would be no absolute time and no global simultaneity in such a world, in contrast to the usual cosmological solutions. But this was not the end of the story.

Indeed, Godel showed that in a rotating universe it is possible, in principle, to travel into the past. It had been known for some time that it is possible to travel into the future. Physicists had gotten accustomed to the idea. But a trip into the past is far more paradoxical, since it plays havoc with causality. For instance, a time traveler could meet with a younger self, “and do something to that person,” as Godel wrote, with a faintly sinister undertone. On the upside of things -- and this was also pointed out by Godel -- when a time traveler lands, time still flows in the usual direction, rather than backward. That is certainly a relief.

Einstein and most other theoretical physicists concluded from Godel’s paradoxical results that travels into the past were ruled out by some as-of-yet-unknown physical principle. Godel, on the other hand, concluded that our notion of time is deeply and fundamentally deluded.

At that time, Bertrand Russell visited Einstein in Princeton, and in the latter’s house he found both Kurt Godel and Wolfgang Pauli. Quite a foursome! Or as Pauli himself might have put it, “Gar nicht so blod” [if I might be so bold - used when you are going to say or ask something that someone might think is rude] In his autobiography, Russell wrote that all three emigrfants had ‘unveiled himself as an unmitigated Platonist” ~ Page 344/345