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Multiple Beginnings for the Universe?


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#1    Startraveler

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Posted 26 June 2006 - 01:13 AM

Like many, I'm a fan of the late physicist Richard Feynman, a curious character and genius if ever there was one. One of Feynman's great contributions to physics was his path integral formulation (sometimes called sum over histories) of quantum mechanics--basically, to figure out the probability of some event occurring in his formulation you have to sum over every history that includes that event. If you want to figure out the path a particle probably took between two points you'll have to add every possible path it might've taken.

Anyway, this interesting idea is apparently now being used by Stephen Hawking and Thomas Hertog to try and figure out where the univese came from. Interesting article, have a read.

Nature:

Quote

Hawking, based at the University of Cambridge, UK, and his colleague Thomas Hertog of the European Laboratory for Particle Physics at CERN in Geneva, Switzerland, are about to publish a paper claiming that the Universe had no unique beginning. Instead, they argue, it began in just about every way imaginable (and maybe some that aren't).

Out of this profusion of beginnings, the vast majority withered away without leaving any real imprint on the Universe we know today. Only a tiny fraction of them blended to make the current cosmos, Hawking and Hertog claim.

That, they insist, is the only possible conclusion if we are to take quantum physics seriously. "Quantum mechanics forbids a single history," says Hertog.

. . .

He and Hawking call their theory 'top-down' cosmology, because instead of looking for some fundamental set of initial physical laws under which our Universe unfolded, it starts 'at the top', with what we see today, and works backwards to see what the initial set of possibilities might have been. In effect, says Hertog, the present 'selects' the past.

Within just a few seconds after the Big Bang, a single history had already come to dominate the Universe, he explains. So from the 'classical' viewpoint of big objects such as stars and galaxies, things happened only one way after that point. Other 'histories', say, one in which the Earth formed only 4,000 years ago, have made no significant contribution to this cosmic evolution.

But in the first instants of the Big Bang, there existed a superposition of ever more different versions of the Universe, instead of a unique history. And most crucially, Hertog says that "our current Universe has features frozen in from this early quantum mixture". . .



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