What if the Big Bang wasn't the beginning of the universe, but only one stage in an endlessly repeated cycle of universal expansion and contraction? So suggests mathematical physicist and string theorist Alan Turok. He thinks there may be many universes, at once interpolated but separate, like a mixture of gases. These universes are attracted to each other; every few trillions of trillions of years, they collide, explode, expand and contract, then repeat the sequence all over again.

Title: Cyclic Universes from General Collisionless Braneworld Models Authors: E. N. Saridakis

We investigate the full 5D dynamics of general braneworld models. Without making any further assumptions we show that cyclic behaviour can arise naturally in a fraction of physically accepted solutions. The model does not require brane collisions, which in the stationary case remain fixed, and cyclicity takes place on the branes. We indicate that the cosmological constants play the central role for the realisation of cyclic solutions and we show that its extremely small value on the observable universe makes the period of the cycles and the maximum scale factor astronomically large.

Title: The Spatially Closed Universe Authors: Chan-Gyung Park (Version v2)

The general world model for homogeneous and isotropic universe has been proposed. For this purpose, we introduce a global and fiducial system of reference (world reference frame) constructed on a 4+1 Minkowski space-time that is embedding the universe, and define the line element as the separation between two neighbouring events that are distinct in space and time, as viewed in the world reference frame. The effect of cosmic expansion on the measurement of physical distance has been included in the new metric, which differs from the Friedmann-Robertson-Walker metric where the spatial separation is measured on the hypersurface at a constant time, regardless of the dynamical state of space. The Einstein's field equations with the new metric imply that closed, flat, and open universes are filled with positive, zero, and negative energy, respectively. We have demonstrated that the flat universe is empty and stationary, equivalent to the Minkowski space-time, and that the universe with positive energy density is always spatially closed and finite. In the closed universe, the proper time of a comoving observer does not elapse uniformly as judged in the world reference frame, in which both cosmic expansion and time-varying light speeds cannot exceed the limiting speed of the special relativity. We have also reconstructed cosmic evolution histories of the closed world models that are consistent with recent astronomical observations, and derived useful formulas such as energy-momentum relation of particles, redshift, total energy in the universe, cosmic distance and time scales, and so forth. It has been also shown that the inflation with positive acceleration at the earliest epoch is improbable.

Roger Penrose interviewed about his new model of the universe. From what I understand, he is saying that when our current universe reaches heat death, a new Big Bang is triggered.

A cosmologist has created a mathematical model that he says shows space-time, contrary to common wisdom, did not begin with the Big Bang. Instead, the model suggests a universe pretty much like the one we live in today existed before the event, except it was contracting instead of expanding. If ever proven, the idea could force a complete rethinking of the origins of the cosmos and perhaps even open a doorway to an endless future.

Some cosmologists think that our universe has been cycling through an endless series of big bangs and big crunches. If so, it implies the universe is doomed to repeat the same thing over and over. A new study, however, suggests that with each big bang, the universe mostly forgets its past and starts anew.

Details of what the universe was like before the big bang may be forever lost to us, according to a new analysis. Einstein's theory of gravity, general relativity, describes the evolution of the cosmos but breaks down at the moment of the big bang, preventing researchers from understanding its origins. To glimpse behind the veil, a researcher has applied a speculative theory that treats the universe as pixellated into tiny atom-like units of space and time. His findings suggest that experiments would never be sensitive enough to fully reconstruct the state of the universe before the bang.

"If that is the case, then we're not able to determine the precise origin of the universe. It would always remain a philosophical scenario" - Martin Bojowald, theoretical physicist of Pennsylvania State University in University Park.

Another universe may have existed before the Big Bang. According to calculations using Loop Quantum Gravity, which attempts to reconcile the incompatible theories of quantum mechanics and Einsteins general relativity, our Universe was created after an earlier universe collapsed. Scientists are calling this new theory the Big Bounce.

Title: The return of a static universe and the end of cosmology Authors; Lawrence M. Krauss, Robert J. Scherrer (Version v3)

We demonstrate that as we extrapolate the current CDM universe forward in time, all evidence of the Hubble expansion will disappear, so that observers in our island universe will be fundamentally incapable of determining the true nature of the universe, including the existence of the highly dominant vacuum energy, the existence of the CMB, and the primordial origin of light elements. With these pillars of the modern Big Bang gone, this epoch will mark the end of cosmology and the return of a static universe. In this sense, the coordinate system appropriate for future observers will perhaps fittingly resemble the static coordinate system in which the de Sitter universe was first presented.

We will never explain the cosmos by taking on faith either divinity or physical laws. True meaning is to be found within nature Scientists are slowly waking up to an inconvenient truth - the universe looks suspiciously like a fix. The issue concerns the very laws of nature themselves. For 40 years, physicists and cosmologists have been quietly collecting examples of all too convenient "coincidences" and special features in the underlying laws of the universe that seem to be necessary in order for life, and hence conscious beings, to exist. Change any one of them and the consequences would be lethal. Fred Hoyle, the distinguished cosmologist, once said it was as if "a super- intellect has monkeyed with physics".