The discovery several years ago of acceleration and the underlying dark energy came as a surprise to scientists because the standard model did not predict such features.
The new model offers a streamlined alternative. It treats the Big Bang not as the true moment of creation, but as a transition between two cycles in an endless process of cosmological rebirth.
According to the model, the Big Bang is followed by a period of slow expansion and gradual accumulation of dark energy. As dark energy becomes dominant, it stimulates cosmic acceleration. The current era is near the transition between these stages, Steinhardt said.
As accelerated expansion proceeds over trillions of years, matter and energy are gradually stretched thin across the universe.
Eventually, matter, radiation, and even black holes become so stretched out that they are dissipated to almost nothing, leaving behind a massive universe that is virtually empty, Steinhardt explained.
At this point in the cycle, particles of matter are so far apartand moving away from each other so rapidlythat they cannot interact and are effectively separated into distinct universes.
Steinhardt and Turok call this vacuum-like stage the "big crunch." The vacuum triggers dark energy to materialize into matter and radiation in another Big Bang, refreshing the cycle of expansion.
Other scientists are intrigued by the new model, but it hasn't won them over yet.
Kirshner credits Steinhardt and Turok with assembling the new model to be consistent with what is known about the universe. "They've been careful to account for the known facts," he said.
The new model, Kirshner said, "is highly speculative, but it's not unthinkable."
Rigorously testing the two theories against each other will take some time. Steinhardt already has some ideas about how it could be done.
For example, gravitational waves, a feature of the universe predicted by general relativity, would take a different form in these two models. There would not be long-wavelength gravitational waves in a cyclic universe, whereas there would be in an inflationary universe.
Efforts are underway to measure and characterize gravitational waves, but it will likely take at least several years to gather useful data. The Planck satellite scheduled to be launched by the European Space Agency about 2008 may help settle the question, Steinhardt said.
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