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The cooler side of the Big Bang

Can ‘Quantum graphity’ (not gravity) be tested?

Quantum graphity – not gravity – is a fairly recent and, as far as I can tell, quite obscure angle on cosmology, but some University of Melbourne and RMIT researchers are proposing a test for the theory, and at the same time, proposing a different model for the formation of the universe.

According to the group of theoretical physicists, it’s feasible that rather than an explosive start to the universe, physics should search for a cooling down – a “big freeze” since it’s mandatory to provide an opposite to the big bang – and that evidence of this cosmological condensation could be testable by observation.

“Quantum graphity” arises from papers like this one at Arxiv, which proposes a mathematical model for the universe which tries to resolve the discrepancies between classical and quantum models [author’s warning: what follows is a dangerously abbreviated attempt to summarize in language something that probably needs maths].

One such problem is that it’s hard to demonstrate how characteristics we observe in the current universe like General Relativity actually come into being – to put it more simply, it’s hard to tell how the highly disordered universe immediately after the big bang became a place where General Relativity can exist.

To quote directly from the original Canadian paper by Tomasz Konokpa, Fotini Markopoulou and Lee Smolin:

“In the high temperature, or disordered phase, notions of geometry and perhaps even dimension and topology are useless and the physics must be described in purely quantum mechanical terms. In the low temperature phase, the system becomes ordered in such a way that it can be described in terms of fields living on a low dimensional spacetime manifold with metric obeying Einstein’s equations”.

The point of quantum graphity is an attempt to use geometrical models to try and describe how the phase transition gives rise to the universe – and how the transition might be observed.

Back to the University of Melbourne / RMIT research. To quote from the release: "Think of the early universe as being like a liquid," said lead researcher James Quach. "Then as the universe cools, it 'crystallises' into the three spatial and one time dimension that we see today. Theorised this way, as the Universe cools, we would expect that cracks should form, similar to the way cracks are formed when water freezes into ice."

The large-scale structures of the early universe – which we already know are observable in, for example, the microwave background radiation – could either validate or disprove the quantum graphity model.

Quantum physics specialist Associate Professor Andrew Greentree says if these “condensation structures” (my metaphor) exist, they might be observable acting as lenses that change the path of light or other particles. ®

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