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Friday, December 14, 2007

"Time to Reexamine Time"

Taking a momentary break from the subprime crisis, the fall in the dollar, the distribution of income and wealth, the Fed, tax cuts, and so on, here's something on the nature of time:

Making Space for Time, by Scott Dodd, Scientific American: ...Many of the world’s top theoretical physicists and cosmologists gathered ... to grapple with the mystery of how time works. New telescope observations and novel thinking about quantum gravity have convinced them that it is time to reexamine time. ...

On the face of it, time seems pretty simple, like a one-way street: eggs don’t unscramble, ... and your grandparents will never be younger than you. But the universe’s basic laws appear to be time-symmetrical, meaning they are unaffected by the direction of time. From the point of view of physics, the past, present and future exist simultaneously.

For more than a century, physicists have proposed any number of explanations for this apparent contradiction, from the psychological (the flow of time is an illusion) to the physical (some unknown property of quantum mechanics reconciles the contradiction). None has proved satisfactory. In 1927 astrophysicist Sir Arthur Eddington coined the term “time’s arrow” for the phenomenon and linked it to entropy: as the universe gets older, it becomes more disordered, following the second law of thermodynamics. But scientists cannot explain why order lies in the past and disorder in the future. ...

Laura Mersini-Houghton, a physicist at the University of North Carolina at Chapel Hill [says]... “It’s been very difficult to make progress over the past 20 years, because there hasn’t been much new to say.” That is all changing thanks to stronger instruments for probing the heavens. The cosmic microwave background radiation, a remnant of the big bang, shows that 380,000 years after its birth, the universe was filled with hot gas, all evenly distributed and highly ordered. Eventually the early cosmos underwent inflation and began to coalesce into the disordered universe of stars and atoms we know today.

What remains puzzling, though, is why the early universe was so orderly—a condition that physicists consider highly improbable—and what caused it to swell so rapidly. “The arrow-of-time problem, once you get down to the nitty-gritty of it, is, Why was the early universe the way it was?” says Sean Carroll, a cosmologist at the California Institute of Technology. ...

Prominent physicists ... invoked string theory, black hole equations and the idea that we live in one of many parallel universes as possible explanations.

The multiverse concept emerged as one of the more favored—or at least frequently talked about—theories for the strange tidiness of the early cosmos. “If you accept the idea that this might be only one of many possible universes, then that makes it more plausible,” Mersini- Houghton says. Universes that started out more chaotic might not have survived or evolved to support intelligent life. So one-way time—and our entire existence, for that matter—could be just a happenstance. ...

    Posted by on Friday, December 14, 2007 at 08:46 PM in Science | Permalink  TrackBack (0)  Comments (13)

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