"We may have misunderstood the nature of time," said co-researcher Paul Steinhardt, a cosmologist at Princeton University. "The Big Bang may not be the beginning of space and time, as conventionally assumed. Instead, time may exist forever."
The new theory also provides a role for the mysterious antigravity force known as "dark energy," which seems to be expanding the universe faster and faster over time.
"This opens our eyes to a new and much more complete picture of the universe," said co-researcher Neil Turok, a theoretical physicist at the Center for Mathematical Sciences in Cambridge, England.
Noted physicist Stephen Hawking of Cambridge University has already bet Turok that new cosmic microwave observations, to be made in 2007 by satellite, will prove standard ideas right.
"I have accepted the bet," Turok told United Press International.
Although the idea of a cyclical universe is not a new one, it has been discounted for decades. If matter rushes out in a Big Bang and collapses in a Big Crunch, scientists argue, the universe must be finite in size. But images of cosmic background microwave radiation show the universe is "flat" or infinite.
The standard model of the cosmos, which presumes a Big Bang and an eternal expansion into darkness, contains some cracks as well. For instance, there is no role for the recently discovered "dark energy," which appears to repel gravity and accelerate the universe's expansion.
Dark energy plays a crucial role in Steinhardt and Turok's new model. Their notion is based on string theory, the branch of physics that seeks to unite all ideas about the forces of nature under a "theory of everything" by proposing the existence of extra dimensions of reality beside space and time.
The researchers believe dark energy is one of the many effects caused by the interplay of additional membranes of reality, or "branes," as they naturally contract and expand. Dark energy will spread apart all matter -- such as black holes and other debris -- and dissipate all energy over the course of trillions of years, ultimately emptying out the universe, leaving it in a state of virtual vacuum.
If so, there would be nothing left to prevent one of the universe's extra dimensions from squeezing back in on itself -- contracting in a Big Crunch.
Yet no matter in our universe would actually move.
In this distant future time, Steinhardt explained, "The space between you and me is not shrinking -- it's not like we're coming back together again during this contraction phase. Our space remains infinite. Instead, it's the space between the extra dimensions is shrinking."
As this extra space collapses, the researchers theorize the laws of physics would change. Gravity would strengthen, while the other fundamental forces -- electromagnetism and the two nuclear forces -- would grow weaker or stronger depending on which version of string theory you believe.
In the end, all these changes over uncounted years cause energy and matter to pop in and out of existence faster and faster, followed by a bang or crunch, which restores the fundamental forces of the universe to their original values and resets the cycle's clock.
"Steinhardt and Turok have injected an imaginative new speculation," said Sir Martin Rees, Astronomer Royal of Britain and theoretical astrophysicist at Cambridge University. "Their work emphasizes the extent to which we may need to jettison common sense concepts, and transcend normal ideas of space and time, in order to make real progress."
If correct, the new model requires different observations from the current picture of the universe.
"The conventional picture predicts a yet-unseen spectrum of gravitational waves, and ours does not. Here we have to wait for improvements in experiments in the next few years to decades to decide the issue," Steinhardt told UPI.
The scientists describe their findings in the April 26 issue of the journal Science.