I see the Past, Present and Future existing all at once... -- William Blake For us believing physicists, the distinction between past, present, and future is only an illusion, even if a stubborn one. -- Albert Einstein For Einsteins 70th birthday, the mathematician Kurt Gödel gave him the gift of eternity, but Einstein never knew quite what to make of it. Gödel had been invited to contribute an essay to a volume celebrating Einstein as a philosopher-scientist. In his essay, Gödel used Einsteins equations for the general theory of relativity to construct a universe in which it was possible to travel backward in time. Gödels universe was far different from the one we inhabit, but he reasoned that the same properties of space-time must apply everywhere, meaning that time-travel is theoretically possible in our own backyard. Gödels work has given rise to flights of fancy by physicists and science fiction writers alike, all of whom have ignored his main conclusion. For Gödel, the possibility of traveling backward in time means that the past is somehow always present, proving that time doesnt flow. Just as Einstein had dismantled Newtons universe of absolute time and space, Gödel now used Einsteins own theory to show that time as we normally understand it doesnt exist. During the 1940s and 1950s, Einstein and Gödel were on the faculty together at the Institute for Advanced Study at Princeton. Einstein was a world-renowned physicist, while Gödel was generally regarded as the preeminent mathematician of his day and arguably the greatest logician since Aristotle. They were both German-speaking refugees from Nazism. Each was eccentric in his own way: Einstein sociable and unkempt, wandering around town with his trademark flyaway hair and no socks; Gödel dapper and reclusive, given to wearing heavy overcoats even in summer. They became fast friends, notwithstanding the fact that they sometimes disagreed profoundly on important scientific matters. The paper that Gödel presented as a birthday gift must have tested their friendship, even though this was not the first time Einsteins colleagues had advanced his theories in a direction he would have preferred not to go himself. He had previously discounted the possibility of gravitational collapse (so-called black holes) and major tenets of quantum mechanics, all of which were derived from relativity theory and are now regarded as mainstream science. He likewise had unwittingly opened the door to Gödels relativity-derived theories on time, only to hang back once again at the threshold. Its not hard to see why Einstein was reluctant to endorse Gödels conclusions, or why they have largely been ignored by the scientific community. Notwithstanding Gödels equations, our intuitive sense is that time must be real, because we can feel it passing. Yet imagine how we might experience the world if we had no short-term memory, as is the case with certain severe neurological disorders caused by damage to the hippocampus. We would find ourselves frozen in the present moment, with no memory of the prior moment and therefore no sense of time flowing. Things would presumably change from moment to moment, but each moment would be experienced without reference to any other. Does time then exist in nature, or is it merely the persistence of memory? Philosophers as various as Parmenides, St. Augustine and Kant argued that time was essentially a psychological phenomenon long before Gödel came up with the equations to prove it couldnt be anything else. And yet, isnt a succession of moments precisely what time is, whether we remember them or not? That depends on what you mean by succession of moments. If Gödels conception of space-time is correct, each moment exists forever. The river of time cant flow if its frozen. A moment that exists forever isnt time; its eternity.
Posted on: Tue, 18 Mar 2014 13:30:00 +0000
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