Countless Alternative Worlds May
Actually Have Existed at the Big Bang:
February 05, 2008
http://www.dailygalaxy.com/my_weblog/2008/02/countless-alter.html
How did the Universe begin is one of the most profound questions of all. But to Stephen Hawking, who has perhaps come closer than anyone to answering it, the question doesn't in fact even exist.
Hawking, who holds Newton's Lucasian Chair 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 emerged out of a 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. According to their article in Nature:
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".
In other words, some of these alternative histories have left their imprint behind. This is why Hertog and Hawking insist that their 'top-down' cosmology is testable. Hertog says that the theory predicts the pattern of the variations in intensity of microwave background radiation, the afterglow of the Big Bang now imprinted on the sky, which reveal fluctuations in the fireball of the nascent Universe. These variations are minute, but space-based detectors have measured them ever more accurately over the past several years.
What's fascinating about this theory is that, by extension, it may be transferable to you as an individual observers. By applying a stronger variant of the anthropic principle, one could argue that the cosmos has structured itself around your very own existence.
That, they insist, is the only possible conclusion if we are to take quantum physics seriously. "Quantum mechanics forbids a single history," says Hertog. “Quantum mechanics forbids a single history.”
The researchers' theory comes in response to a problem raised by 'string theory', one of the best hopes for a theory of everything. String theory permits innumerable different kinds of universe, most of them very different from the one we inhabit. Some physicists suspect that an unknown factor will turn up that rules out most of these universes.
But Hawking and Hertog say that the countless 'alternative worlds' of string theory may actually have existed. We should picture the Universe in the first instants of the Big Bang as a river of all these possibilities; like a projection of billions of movies played on top of one another.
Most crucially, Hertog says that "our current Universe has features frozen in from this early quantum mixture".
As the two researchers work out top-down cosmology in more detail, they hope to be able to calculate the spectrum of these microwave fluctuations and compare it with observations.
The theory also suggests an answer to the puzzle of why some of the 'constants of nature' seem finely tuned to a value that allows life to evolve. If we start from where we are now, it is obvious that the current Universe must 'select' those histories that lead to these conditions. Otherwise we simply wouldn't be here.
Now, how cool is that!
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