Wednesday, May 18, 2005
Out of Time
Here's one last take on the MIT time travel convention.
It's been proposed that nobody from our future showed up not because they didn't want to or because humans do not exist in the future, but because they simply couldn't. They were prevented by the many worlds interpretation of quantum mechanics.
Here's how. The MWI basically says that there's an infinitely large set of universes called a multiverse. At every instant, the universe splits off an infinity of other universes. Each of these universes has a copy of every quark, electron and gluon of the original universe, but is completely independent. In a multiverse, anything is possible and everything happens. For example, in one splinter universe you are writing this blog and I'm the reader.
But here's the catch. Two copies of the same particle cannot exist in the same universe without violating the laws of quantum mechanics. Therefore, when time travelers from our future arrived at the MIT campus two weeks ago, the universe immediately sprouted a new branch and re-routed the visitors away from us before we had a chance to debrief them.
The MWI, which was first proposed by English physicist Hugh Everett III in 1957, had some powerful backers like Stephen Hawking and John Archibald Wheeler.
However, they both changed their minds. "It required too much metaphysical baggage to carry around," Wheeler told physicist Heinz Pagels, author of the Cosmic Code. Hawking invoked his "chronology protection conjecture," which states that although quantum particles like photons can theoretically travel in time, "the laws of physics conspire to prevent time travel by macroscopic objects." The chief obstacle here is the second law of thermodynamics, which says that entropy, the measure of messiness of a system, must be growing with time for any closed system, including the universe. Reverse time's arrow and you'll most likely violate this bedrock of physics.
Perhaps the most eloquent rebuttal of the multiverse theory comes from Pagels himself: "But isn't this multi-reality and superspace all a great fanstasy, which although not strictly ruled out by quantum theory, is not required by it? You speak of all those other worlds as if they were real, when in fact, it is only this world - the one we live in - that we can ever know."
It's been proposed that nobody from our future showed up not because they didn't want to or because humans do not exist in the future, but because they simply couldn't. They were prevented by the many worlds interpretation of quantum mechanics.
Here's how. The MWI basically says that there's an infinitely large set of universes called a multiverse. At every instant, the universe splits off an infinity of other universes. Each of these universes has a copy of every quark, electron and gluon of the original universe, but is completely independent. In a multiverse, anything is possible and everything happens. For example, in one splinter universe you are writing this blog and I'm the reader.
But here's the catch. Two copies of the same particle cannot exist in the same universe without violating the laws of quantum mechanics. Therefore, when time travelers from our future arrived at the MIT campus two weeks ago, the universe immediately sprouted a new branch and re-routed the visitors away from us before we had a chance to debrief them.
The MWI, which was first proposed by English physicist Hugh Everett III in 1957, had some powerful backers like Stephen Hawking and John Archibald Wheeler.
However, they both changed their minds. "It required too much metaphysical baggage to carry around," Wheeler told physicist Heinz Pagels, author of the Cosmic Code. Hawking invoked his "chronology protection conjecture," which states that although quantum particles like photons can theoretically travel in time, "the laws of physics conspire to prevent time travel by macroscopic objects." The chief obstacle here is the second law of thermodynamics, which says that entropy, the measure of messiness of a system, must be growing with time for any closed system, including the universe. Reverse time's arrow and you'll most likely violate this bedrock of physics.
Perhaps the most eloquent rebuttal of the multiverse theory comes from Pagels himself: "But isn't this multi-reality and superspace all a great fanstasy, which although not strictly ruled out by quantum theory, is not required by it? You speak of all those other worlds as if they were real, when in fact, it is only this world - the one we live in - that we can ever know."
