There is neither a beginning nor an end of time, just endless cycles of expansion and contraction, this is the universe in the eyes of a pair of US-British scientists, who published their theory on Thursday in the journal of Science.

The new picture of universe, envisioned by Princeton University physicist Paul Steinhardt and his British colleague, Neil Turok of Cambridge University, differs from what many scientists have accepted as the standard explanation of how the universe evolves.

The current standard model for the universe starts with the Big Bang, sometime about 13 billion to 14 billion years ago, followed by a short period of extremely fast expansion and cooling, which is called inflation and continued to spread out at varying speeds until the present day.

Under this model, time would begin but never end.

The scenario combining a Big Bang and inflation can account for several important features of the universe, such as the fact that it looks the same in all directions, the distribution of galaxies and is infinite in extent, or "flat."

However, the standard model of the universe "has some cracks" and does not account for recent discoveries of accelerated expansion and gravitationally repulsive "dark energy," Steinhardt and Turok argued in their paper.

"The recent discoveries of cosmic acceleration and gravitationally self-repulsive dark energy were not predicted and have no particular role in the standard model," they said.

So to patch some of the theoretical cracks, Steinhardt and Turok propose a model in which Big Bangs occur repeatedly, followed by the usual formation of matter and radiation. Then the universe slowly expands, driven by dark energy, over trillions of years or more.

According to their new theory, the matter, radiation, and black holes are diluted away, leaving the universe smooth, empty, and flat. It then begins to contract in a "big crunch," and the cycle begins again.

(People's Daily April 26, 2002)