According to Einstein's general theory of relativity, the Big Bang represents The Beginning, the grand event at which not only matter but space-time itself was born. While classical theories offer no clues about existence before that moment, a research team at Penn State has used quantum gravitational calculations to find threads that lead to an earlier time. “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,” says Abhay Ashtekar, Director of the Institute for Gravitational Physics and Geometry at Penn State. “Beyond that point, we needed to apply quantum tools that were not available to Einstein.” By combining quantum physics with general relativity, Ashtekar and post-doctoral researchers, Tomasz Pawlowski and Parmpreet Singh, were able to develop a model that traces through the Big Bang to a shrinking universe that exhibits physics similar to ours.

In research reported, the team shows that, prior to the Big Bang, there was a contracting universe with space-time geometry that otherwise is similar to that of our 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,” says Ashtekar. “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.”

While the general idea of another universe existing prior to the Big Bang has been proposed before, this is the first mathematical description that systematically establishes its existence and deduces properties of space-time geometry in that universe.

The research team used loop quantum gravity, a leading approach to the problem of the unification of general relativity with quantum physics, which also was pioneered at the Penn State Institute of Gravitational Physics and Geometry. In this theory, space-time geometry itself has a discrete 'atomic' structure and the familiar continuum is only an approximation. The fabric of space is literally 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," says Ashtekar. "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." >from *Penn State Researchers Look Beyond the Birth of the Universe* . May 12, 2006

related context
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> gravity-modification breakthrough. 'scientists have measured the gravitational equivalent of a magnetic field for the first time in a laboratory. just as a moving electrical charge creates a magnetic field, so a moving mass generates a gravitomagnetic field. a significant step towards the quantum theory of gravity' march 23, 2006
> new satellite data on universe's first trillionth second. 'new evidence for what happened when the universe suddenly grew from microscopic quantum fluctuations to enable the formation of stars, planets and life. according to this picture, researchers say, only 4 percent of the universe is ordinary familiar atoms; another 22 percent is an as-yet unidentified dark matter, and 74 percent is a mysterious dark energy.' march 16, 2006
> gravitational wave research project. 'gravitational waves are ripples in the fabric of space and time produced by events in our galaxy and throughout universe.' july 30, 2004
> quantum universe. 'what is the nature of the universe and what is it made of? what are matter, energy, space and time? how did we get here and where are we going?.' june 11, 2004
> space/time atoms?: quantum gravity-based universe. 'the tiny scale at which the microscopic structure of space and time becomes observable is the planck scale.' february 26, 2003
> oldest light: milestone in cosmology. 'in addition, the new portrait precisely pegs the age of the Universe at 13.7 billion years old.' february 17, 2003
> in search of extra dimensions: beyond the standard model. 'somewhere within the planck scale, or at extreme energy levels, an incredibly small extra dimension may finally combine gravity and electromagnetism.' february 20, 2002
> search for gravity waves. '"gravitational waves are at the frontier of astrophysics. there's no question they exist, but they have not yet been detected directly.' december 10, 2001

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