Original URL: http://www.theregister.co.uk/2012/11/29/penn_state_quantum_loop_universe_theory/

Big Bang bashing boffins ‘Big Bounce’ back to BIRTH OF TIME

The universe before inflation took hold

By Richard Chirgwin

Posted in Science, 29th November 2012 23:54 GMT

A group of Penn State physicists says the universe we now see could have arisen from a "Big Bounce" rather than a Big Bang.

The new work by Penn State, led by professor Abhay Ashtekar, director of the Institute for Gravitation and the Cosmos, proposes ways to apply quantum physics "further back in time than ever before – right back to the beginning," the university says in a release.

We have a pretty good idea of the large-scale structures of the universe when it was only a few hundred thousand years old. That comes from studying the fingerprint of the ancient universe that's visible in the cosmic microwave background radiation (CMB), which has been intensely mapped and studied since its discovery in 1964.

However, the CMB – which marked the "inflationary" period of the universe – poses its own much-argued mystery: why isn't it smooth? How did the "lumps" emerge? (And it's a good thing they did, by the way, since galaxies, stars, planets, and people are all a consequence of those lumps).

The nutshell of Ashtekar's proposal is this: if you can apply quantum physics to the structures of the very early universe, it could explain the structures we now see. And that's what Ashtekar's group believes it has done – it's created a paradigm that uses the emerging field of "quantum loop cosmology" to explain how quantum fluctuations might have created the pre-inflationary structures which, after the universe's inflationary phase, formed the kernels for the universe we know see.

In the period Penn State is looking at, the universe was dense. Very, very dense: where an atomic nucleus has a density of 1014 grams per cubic centimetre, the density of the ancient universe was a staggering 1094 grams per cubic centimetre.

That kind of "stuff" can't be described by the Einsteinian theories that now describe cosmology so well. As one of Ashtekar's collaborators, post-doctoral fellow Ivan Agullo, explains:

The inflationary paradigm enjoys remarkable success in explaining the observed features of the cosmic background radiation. Yet this model is incomplete. It retains the idea that the universe burst forth from nothing in a Big Bang, which naturally results from the inability of the paradigm's general-relativity physics to describe extreme quantum-mechanical situations.

One needs a quantum theory of gravity, like loop quantum cosmology, to go beyond Einstein in order to capture the true physics near the origin of the universe.

In fact, the early universe was so strange that even time would appear different if you could go there and survive the experience. Instead of the strict causality that rules the classical macro universe, the "quantum loop universe" would have been ruled by probabilities. It may even point to a "Big Bounce", in which the universe arises not from "nothing", but from that super-compressed mass that had a distinct history of its own.

It seems almost unimaginable, but those probabilities – the mere chance that in the transition from ultra-dense matter to the inflationary universe, a few quantum particles happened to be clustered rather than uniformly distributed – can, Ashtekar's group claims, explain today's universe.

The combination of the new "loop-quantum-origins" paradigm with quantum cosmology equations, they say, show that "fundamental fluctuations in the very nature of space at the moment of the Big Bounce evolve to become the seed-like structures seen in the cosmic microwave background."

Even better, they assert, their theories demonstrate good agreement with what's observed in the CMB. ®