Does the universe repeat itself every trillion years? A new cosmological model appears to demonstrate that the universe can endlessly expand and contract, providing a rival to Big Bang theories and solving a thorny modern physics problem, according to University of North Carolina at Chapel Hill physicists. A new view that requires for a new take on our concept of time – one that has more in common with the “cyclic” views of time held by ancient thinkers such as Plato, Aristotle and Leonardo da Vinci, than the Christian Calender and Bible-influenced belief in “linear” time now so deeply imbedded in modern western thinking.
The cyclic model proposed by Dr. Paul Frampton, Louis J. Rubin Jr. distinguished professor of physics in UNC’s College of Arts & Sciences, and co-author Lauris Baum, a UNC graduate student in physics, has four key parts: expansion, turnaround, contraction and bounce.
During expansion, dark energy -- the unknown force causing the universe to expand at an accelerating rate -- pushes and pushes until all matter fragments into patches so far apart that nothing can bridge the gaps. Everything from black holes to atoms disintegrates. This point, just a fraction of a second before the end of time, is the turnaround.
At the turnaround, each fragmented patch collapses and contracts individually instead of pulling back together in a reversal of the Big Bang. The patches become an infinite number of independent universes that contract and then bounce outward again, reinflating in a manner similar to the Big Bang. One patch becomes our universe.
“This cycle happens an infinite number of times, thus eliminating any start or end of time,” Frampton said. “There is no Big Bang.”
Cosmologists first offered an oscillating universe model, with no beginning or end, as a Big Bang alternative in the 1930s. The idea was abandoned because the oscillations could not be reconciled with the rules of physics, including the second law of thermodynamics, Frampton said.
The second law says entropy (a measure of disorder) can’t be destroyed. But if entropy increases from one oscillation to the next, the universe becomes larger with each cycle. “The universe would grow like a runaway snowball,” Frampton said. Each oscillation will also become successively longer. “Extrapolating backwards in time, this implies that the oscillations before our present one were shorter and shorter. This leads inevitably to a Big Bang,” he said.
Frampton and Baum circumvented the Big Bang by postulating that, at the turnaround, any remaining entropy is in patches too remote for interaction. Having each “causal patch” become a separate universe allows each universe to contract essentially empty of matter and entropy. “The presence of any matter creates insuperable difficulties with contraction,” Frampton said. “The idea of coming back empty is the most important ingredient of this new cyclic model.”
Key to Frampton and Baum’s model is an assumption about dark energy’s equation of state -- the mathematical description of its pressure and density. Frampton and Baum assume dark energy’s equation of state is always less than -1. This distinguishes their work from a similar cyclic model proposed in 2002 by physicists Paul Steinhardt and Neil Turok, who assumed the equation of state is never less than -1.
A negative equation of state gives Frampton and Baum a way to stop the universe from blowing itself apart irreversibly, an end physicists call the “Big Rip.” The pair found that in their model, the density of dark energy becomes equal to the density of the universe and expansion stops just before the Big Rip.
One of the most important space probes of the century is the Wilkinson Microwave Anisotropy Probe (WMAP) launched in 2001 to measure the temperature differences in the Cosmic Microwave Background (CMB) radiation -the 14-billion year old Big Bang's remnant radiant heat . The anisotropies then in turn are used to measure the universe's geometry, content, and evolution; and, perhaps most importantly, to test the Big Bang model, and the cosmic inflation theory. WMAP data seem to support a universe that is dominated by dark energy in the form of a cosmological constant.
Perhaps not surprisingly, there is no supporting data to date to confirm the Big Bang theory, although the results aren't sensitive enough to rule out the pervasive Big Bang/inflation model.
The influence of gravitational waves on polarization is different from that of overall energy distribution, so it should be possible to tell from polarization in the WMAP scans whether the variation is coming from contrasting energy density (heat) or gravitational waves that a Big Bang should have produced.
The world's leading astrophysicists are confident that with a sensitive enough probe such as that by the new Planck telescope with its more detailed CMB plots, that they can reduce the level of uncertainty low enough so that they can say definitively whether the gravitational waves that should have been created by the Big Bang as present.
If this next generation Planck Telescope shows that there is no obvious distortions caused by gravity waves, it will rule out the Big Bang plus inflation theory -an add-on theory that explains the phenomenal sudden expansion of space from a tiny point. In it's place will be new models that support what many leading cosmologists see as our universe to be proved to be one of just many in an eternal cycle of birth and rebirth.
Models of the universe that involve a bouncing brane or a Big Crunch rather than a start from scratch Big Bang predict much smaller gravity waves being produced than would come from a Big Bang. If the universe actually went through cycles of expansion and contraction, it is possible that the uneven distributions in the early post-Big Bang universe that resulted in the formation of galaxies were leftovers from the universe before.
Only gravity can't exist soley in a specific brane, but wanders where it will, leaking off our brane into what physicists call "the bulk" -- the rest of space-time. Brane theory offer an fascinating and plausible explanation for why gravity is such a weakling: Maybe it's not any weaker than the other forces, but just concentrated somewhere else in the bulk, or on another brane, providing the key to understanding the dark matter that makes up 90 % of our universe.
If our brane is but a small slice of a much larger cosmos, however, the "dark matter" might be nothing but ordinary matter trapped on another brane. Dark matter is no longer some mysterious unknown, but the force at the heart of the brane-brane interaction. With the brane model the universe goes through an eternal cosmic cycle over a vast timescale of attraction, bounce with a spread out bang, springing apart, and expansion until attraction (gravity) takes over again.Such a shadow world, Hawking speculated, might contain "shadow human beings wondering about the mass that seems to be missing from their world."
Are branes the key to understanding the origin of our universe? "Who knows?" says CalTech's Sean Carroll. "they will have taught us a useful lesson that we should have known all along, which is that we don't have a clue to what's going on."
Alan Guth of the Massachusetts Institute of Technology, creator of the currently accepted model of the Big Bang, said recently "he felt a little like Rip Van Winkle -- picking up his head from a long sleep only to notice that the landscape of physics he thought he knew had suddenly, drastically, changed."
Roger Penrose of Oxford sums up some of the most brilliant new thinking on the big bang in the video below. The summary is the big bang happens after the end of the universe, starting a new one.
Top of Page Image Credit: With our thanks to: Lost in Space by jrtce1.
Image Credit: http://www.csudh.edu/dearhabermas/stringtheory01.htm