'Big Bounce' behind birth of universe?

Our universe may have 'bounced' into existence from an older collapsing one, rather than expanding from a single point of dense, hot material, according to new study that provides support to the 'Big Bounce' theory to explain the birth of our cosmos.

The universe is currently expanding and it is believed to have burst into existence from a point of infinitely dense and hot material, an event dubbed as the Big Bang.
However, physicists have long debated this idea as it means the universe began in a state of complete breakdown of physics as we know it.

Instead, some have suggested that the universe has alternated between periods of expansion and contraction, and the current expansion is just one phase of this.

This so-called 'Big Bounce' idea has been around since 1922, but has been held back by an inability to explain how the universe transitions from a contracting to an expanding state, and vice versa, without leading to an infinite point.

In a new study, Steffen Gielen from Imperial College London and Neil Turok, Director of the Perimeter Institute for Theoretical Physics in Canada, have shown how the Big Bounce might be possible.

Observations suggest that during its very early life, the universe may have looked the same at all scales – that is the physical laws that worked for the whole the universe also worked at the scale of the very small, smaller than individual atoms. This phenomenon is known as conformal symmetry.

In the present-day universe, this is not the case – particles smaller than atoms behave very differently to larger matter and the symmetry is broken.

Subatomic particle behaviour is governed by quantum mechanics, which produces different rules of physics for the very small entities. The early universe may have been governed solely by the principles of quantum mechanics. The researchers suggest that the effects of quantum mechanics could prevent the universe from collapsing and destroying itself at end of a period of contraction, known as the Big Crunch.

Instead, the universe would transition from a contracting state to an expanding one without collapsing completely. "Quantum mechanics saves us when things break down. It saves electrons from falling in and destroying atoms, so maybe it could also save the early universe from such violent beginnings and endings as the Big Bang and Big Crunch," Gielen said.

Using the idea that the universe had conformal symmetry at its beginning, and that this was governed by the rules of quantum mechanics, researchers built a mathematical model of how the universe might evolve.

The model predicts that the effect of quantum mechanics would allow the universe to spring from a previous universe that was contracting, rather than from a single point of broken physics.

The research was published in the Physical Review Letters.