The universe is in a constant state of expansion and the general consensus is that this began as a ‘Big Bang’ – the universe bursting into existence from a point of infinitely dense and hot material.
However, a study of the early universe has revealed it could have been formed from an older collapsing universe, rather than being brand new.
Physicists have long debated this idea as it means the universe began in a state that goes against the laws of physics as we know and understand them. Instead, some have suggested the universe has switched between periods of expansion and contraction.
This so-called ‘Big Bounce’ theory has been around since 1922 but has been held back by the fact physicists have been unable to explain how the universe moves from a state of contraction to one of expansion, and vice versa, without leading to an infinite point – until now.
Dr Steffen Gielen from Imperial College London and Dr Neil Turok, Director of the Perimeter Institute for Theoretical Physics in Canada, have shown how this Big Bounce might be possible.
Research suggests that in its early days, the universe would have behaved the same way at all scales; physical laws that worked for the whole structure of the universe also worked at a smaller than atomic level. This idea is known as conformal symmetry.
In the modern universe, particles smaller than atoms behave differently to larger matter causing this symmetry to break. Subatomic particles are governed by so-called quantum mechanics, for example.
In the early universe, as everything was incredibly small, it may have been governed solely by the principles of quantum mechanics, rather than the large-scale physics we also see today.
Using the idea the universe had conformal symmetry at its beginning, and that this was governed by the rules of quantum mechanics, Dr Gielen and Dr Turok built a mathematical model of how the universe might evolve.Read more: Physicists say Big Bang theory revelation may be premature
This model predicts 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.
In particular, the researchers suggest 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, or the Big Rip. Instead, the universe would transition from a contracting state to an expanding one without collapsing completely.
Dr Gielen said: “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.”
“The big surprise in our work is that we could describe the earliest moments of the hot Big Bang quantum mechanically, under very reasonable and minimal assumptions about the matter present in the universe,” added Dr Turok. “Under these assumptions, the Big Bang was a ‘bounce’, in which contraction reversed to expansion.”
The researchers are now investigating how this simple model can be extended to explain the origin of perturbations to the simple structure of the universe, such as galaxies.
The study is published in Physical Review Letters.
This article was originally published by WIRED UK