We seem to be awash in exotic physics, an administrative category I created on this site only a couple of days ago to house the trillion-year crunch story and the ‘light in reverse’ work at the University of Rochester. It seems an appropriate time, then, to look at an investigation reported in the Physical Review Letters that takes us, like Alice through the looking glass, into the universe before the Big Bang. Penn State researchers are behind this study, combining quantum physics tools that Einstein didn’t have with general relativity to punch through to a universe on the other side.

So let’s talk again about what might have been there before the Big Bang. This analysis says the previous universe had a spacetime geometry much like our own expanding universe, except that it was a contracting universe. Gravititational forces were pulling the previous universe together until the quantum properties of spacetime caused gravity itself to become repulsive. What follows is aptly described as the ‘Big Bounce.’ Let me quote from a Penn State news release on this work:

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.

Out of which we draw some exotic conclusions. Says Abhay Ashtekar (director of the Institute for Gravitational Physics and Geometry at Penn State):

“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. 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.”

Of course, the idea of one universe feeding into another has been around for a while, and science fiction readers will recall wonderful tales like Poul Anderson’s 1970 novel Tau Zero, in which the runaway ramscoop ship Leonora Christine ends its journey in the only way possible, threading through the lens of gravitational collapse into an entirely new universe. But this is the first time the properties of spacetime geometry in such a universe have ever been deduced. And the big news is that the pre-Big Bang universe this study deduces wasn’t a sea of quantum foam or a matrix of energies indescribable by our mathematics. It was a classical universe, like ours.

Image: The figure represents our expanding universe as the right branch of the arc. Our time now is located at the 1.8 grid mark on the right side of the drawing. According to Ashtekar’s team’s calculations, when looking backward throughout the history of the universe, ‘time’ does not go to the point of the Big Bang but bounces to the left branch of the drawing, which describes a contracting universe. Singh explains, “The state of the universe depicted by its wavefunction is shown in space (\mu) and time(\phi). The big bang singularity lies where space vanishes (goes to zero). Our expanding phase of the universe is shown by the right branch which, when reversed backward in time, bounces near the Big Bang to a contracting phase (left branch) and never reaches the Big Bang.” Credit: Abhay Ashtekar/Penn State.

The paper is Ashtekar, Pawlowski, and Singh, “Quantum Nature of the Big Bang,” Physical Review Letters 12 April 2006, available here.