How the universe began is one of the most brain-breaking questions you could possibly ask, and the Big Bang is probably the answer most people accept. But what if the infinitely dense point from which the entire universe burst forth wasn't the beginning of everything, but merely the middle of an ongoing cycle? That's the theory of the Big Bounce, which suggests that the universe regularly cycles through periods of expansion and contraction, meaning the Big Bang may have been preceded by an earlier universe collapsing in on itself. A new study details how this might be possible.

The idea of the Big Bounce has been bouncing around since 1922, but explaining just how the universe transitions between expanding and contracting has always been an issue. What's to stop a universe just contracting into a point and collapsing completely? According to researchers from Imperial College London and the Perimeter Institute for Theoretical Physics in Canada, it may be the same quantum mechanics that prevent atoms from deteriorating into nothing.


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In our universe as it currently is, there's an asymmetry between the laws of the subatomic world and those that govern larger matter. Large-scale physics and quantum mechanics exist side-by-side now, but that doesn't mean it's always been the case: back when the universe was young and everything in it was tiny, quantum mechanics may have been the only set of laws in effect, an idea known as conformal symmetry. So the same processes that keep electrons from losing energy as they orbit the nucleus and destroying the atom may have prevented the universe from collapsing into oblivion.

Dr Gielen (left) and Dr Turok (right) discussing the Big Bounce model (Credit: The Perimeter Institute)

"Quantum mechanics saves us when things break down," says Steffen Gielen, of Imperial College London. "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."

With this idea in mind, the researchers built a mathematical model for how the universe might evolve, based on conformal symmetry and other early-universe theories, such as the prevalence of radiation over ordinary matter. The result? It all fit.

"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," says Neil Turok of the Perimeter Institute for Theoretical Physics. "Under these assumptions, the Big Bang was a 'bounce,' in which contraction reversed to expansion."

Further study is being conducted into how things like galaxies, which disrupt the model, can be incorporated into it. The research is published in the journal, Physical Review Letters.

"Our model's ability to give a possible solution to the problem of the Big Bang opens the way to new explanations for the formation of the universe," said Dr Gielen.

We've reached out to the researchers to get the nitty gritty quantum mechanics details on how this all would have happened and will let you know when we hear back.

Source: Imperial College London

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