Saturday science subject: The big bounce

— 11:51 AM on December 13, 2008

What was there before the big bang? Conventional wisdom would tell you, "nothing," because the big bang theory says time itself emerged from the same singularity as everything we know. But what if everything didn't actually emerge from a singularity?

That's exactly the question an international team of researchers are asking themselves after using a new model, loop quantum cosmology (LQC), to simulate the early universe. As New Scientist reports, LQC is "the first tangible application of another theory called loop quantum gravity, which cunningly combines Einstein's theory of gravity with quantum mechanics." LQC suggests our universe might have actually been born from a big bounce:

If LQC turns out to be right, our universe emerged from a pre-existing universe that had been expanding before contracting due to gravity. As all the matter squeezed into a microscopic volume, this universe approached the so-called Planck density, 5.1 × 1096 kilograms per cubic metre. At this stage, it stopped contracting and rebounded, giving us our universe.

"You cannot reach the Planck density. It is forbidden by theory," says [Parampreet Singh]. According to [Martin Bojowald], that is because an extraordinary repulsive force develops in the fabric of space-time at densities equivalent to compressing a trillion solar masses down to the size of a proton. At this point, the quanta of space-time cannot be squeezed any further. The compressed space-time reacts by exerting an outward force strong enough to repulse gravity. This momentary act of repulsion causes the universe to rebound. From then on, the universe keeps expanding because of the inertia of the big bounce. Nothing can slow it down - except gravity.

LQC itself isn't completely new—Bojowald reportedly came up with it in 2000. However, New Scientist writes that the model is now "poised to make predictions we can actually test."

Over the next two years, Singh and his colleagues plan to study the universe's cosmic microwave background to see whether they can find evidence that validates LQC. "Already there are hints that LQC might predict something different from classical cosmology," New Scientist says. Their work will be aided by the ESA's Planck satellite, which will launch next year and offer "the most detailed view of the microwave background to date."

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