AT THE moment of the big bang, our universe emerged from a state of infinite density, a point in space and time so small it had no size at all. This, the standard cosmological story tells us, is the singularity, the seed of creation. Singularities can also serve as seeds of destruction, lurking in the centres of black holes, the final endpoints of total gravitational collapse.
Many physicists, however, believe singularities do not mark the ends of space and time but rather the limits of the theory we use to describe them. That theory is general relativity and, according to Martin Bojowald, it's suicidal. When it jumps off a ledge, physicists need a more fundamental theory to take over, one that incorporates what they've learned about the quantum nature of the world - a theory of quantum gravity.
The majority of physicists have turned to string theory as their quantum gravity theory of choice. But a smaller group of physicists has been working on a theory known as loop quantum gravity. According to LQG, space-time on the quantum scale is not smooth and continuous but discrete, built of tiny loops linked and knotted to form a space-time mesh.
Bojowald was 27 years old when he took the equations of LQG and used them to see what happens to space-time near the big bang's singularity. In doing so, he discovered something amazing, and founded the field of loop quantum cosmology (LQC) in the process. Once Before Time tells the story of Bojowald's discovery and its implications in fascinating, eloquent, even literary prose.
He discovered that as we trace the universe's evolution back in time we find that near the singularity too much energy tries to cram into the finite loops. When the loops can't absorb any more, they expel energy. The effect is a repulsive force that counteracts the inward pull of gravity, preventing total collapse. But there's another, stranger side effect as we continue back in time: the repulsive force swaps space's orientation. Instead of contracting into the would-be singularity, space-time begins expanding again on the other side, creating an inside-out looking-glass universe on the other side of the big bang.
It remains to be seen whether LQC will turn out to be the correct theory of our universe's history - and prehistory. But the answer could come from NASA's Fermi Gamma-ray Space Telescope, which is now collecting light from distant gamma ray bursts. If LQG is correct, light of different wavelengths will move through the loopy space at slightly different speeds - tiny effects, but they could add up to a measurable dispersion over billions of light years of travel.
As Bojowald says, LQG is more than a hypothesis but less than a theory. If it does become a theory, we may get to see the universe on the other side of the mirror.
Author: Amanda Gefter | Source: New Scientist – Culture Lab [November 24, 2010]