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No end.

Bouncing Branes

A new theory paints a surprising picture of the formation and demise of the universe--a sheetlike "brane" universe that eternally dies and rises from its ashes. This model, published online by Science today, contrasts with the standard notion of a continually inflating universe, and it hearkens back to the long-discarded "steady state" model of a cosmos without beginning or end.

In new model, colliding sheetlike branes stamp out universe after universe. The new idea is an extension of the ekpyrotic or "big splat" theory, which physicists introduced last year as an alternative to the inflation model (Science, 13 April 2001, p. 189). Inflationary theory says that for less than 10-30 of a second, the universe expanded at an incredible rate--an idea that can explain facts such as the astonishing similarity of widely separated regions in space. The ekpyrotic alternative, proposed by Neil Turok of Cambridge University and Paul Steinhardt of Princeton University and colleagues, describes the birth of our universe in the collision of enormous four-dimensional membranes, or branes. Not only did the model make similar predictions for inflationary theory, it got rid of some of the troublesome mathematical aspects of the big bang.

The latest version, proposed by Turok, Steinhardt, and others, is more sophisticated. Two infinite branes--one that becomes our universe and a "mirror universe"--live a tiny fraction of a meter apart. When the branes collide, the resulting energy creates all the matter and energy in our universe. The membranes then bounce apart. The newborn universe, on its brane, evolves and eventually burns out. However, the theorists were surprised to realize that the collide-and-bounce process repeats itself ad infinitum.

The inventor of the inflationary-universe model, physicist Alan Guth of the Massachusetts Institute of Technology, says that the new theory is attractive, but he doesn't feel that the kinks are quite worked out yet--particularly what happens when the branes collide and separate. To Turok, the new model is not only mathematically consistent but aesthetically pleasing. "As soon as I started working on this, I appreciated that time marched on--that there was no beginning of time."

Related sites
Turok's site
Steinhardt's site