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Model Suggests Pre-Big Bang Physics

A computer model created this data portrait of the universe going back to the Big Bang. Is the peak in the center pointing to a Big Bounce? Image credit: Penn State University
by Phil Berardelli
University Park PA (SPX) May 14, 2006
Researchers using quantum gravitational calculations are attempting to find threads of data that could lead to an understanding of what happened before the universe was born in the event known as the Big Bang, some 13.7 billion years ago.

"General relativity can be used to describe the universe back to a point at which matter becomes so dense that its equations don't hold up," said physicist and lead researcher Abhay Ashtekar of Penn State University. "Beyond that point, we needed to apply quantum tools that were not available to Einstein."

According to Einstein's General Theory of Relativity, the Big Bang represents the birth of not only matter, but also of space-time itself.

By combining quantum physics with general relativity, however, Ashtekar and colleagues report they have been able to develop a model that describes a transition from a previous universe, through the Big Bang to an expanding universe that exhibits physics similar to the one that exists today.

Reporting in the current issue of Physical Review Letters, the team said their calculations reveal that prior to the Big Bang, there was a contracting universe with space-time geometry otherwise similar to the current expanding universe.

As gravitational forces pulled this previous universe inward, it reached a point at which the quantum properties of space-time cause gravity to become repulsive, rather than attractive.

"Using quantum modifications of Einstein's cosmological equations, we have shown that in place of a classical Big Bang there is in fact a quantum bounce," Ashtekar said. "We were so surprised by the finding that there is another classical, pre-Big Bang universe that we repeated the simulations with different parameter values over several months, but we found that the Big Bounce scenario is robust."

The idea of another universe existing prior to the Big Bang has been proposed before, but this is the first time scientists have developed a mathematical description that systematically establishes its existence and deduces space-time geometry in that universe.

The team used loop quantum gravity, a leading approach to the problem of the unification of general relativity with quantum physics. The concept was pioneered at Penn State's Institute of Gravitational Physics and Geometry, which Ashtekar heads.

In this hypothesis, space-time geometry itself has a discrete atomic structure and the familiar continuum is only an approximation. The fabric of space literally is woven by one-dimensional quantum threads.

Near the Big-Bang, this fabric is violently torn and the quantum nature of geometry becomes important. It makes gravity strongly repulsive, giving rise to the Big Bounce.

"Our initial work assumes a homogenous model of our universe," Ashtekar said. "However, it has given us confidence in the underlying ideas of loop quantum gravity. We will continue to refine the model to better portray the universe as we know it and to better understand the features of quantum gravity."

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Using Soap Bubbles To Study Black Holes
University MS (SPX) May 12, 2006
People use them to get cars, dishes and clothes clean. Children blow them for fun. And now, a University of Mississippi physicist thinks soap bubbles can help scientists better understand the properties of black holes.







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