The main story " Splitting Time from Space—New Quantum Theory Topples Einstein's Spacetime," describes recent excitement over a quantum theory of gravity proposed by physicist Petr Hořava of the University of California, Berkeley. Testing theories of quantum gravity in the laboratory is not possible, but computer simulations may offer the next best thing—and they seem to be lending support to Hořava gravity.
Jan Ambjørn of the Niels Bohr Institute at the University of Copenhagen and his colleagues have been using computer simulations to model quantum gravity based on spacetimes built from self-organizing "motes" that fall into place naturally.
So far, they have succeeded in creating a stable four-dimensional spacetime, when viewed at large distances. But when they zoomed in to small distances, they found a strange result—their universe seems to drop two dimensions. So where did the missing dimensions go?
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Hořava believes that this dimension drop marks the point at which general relativity emerges in his theory of gravity. In his model, the shackles that force time and space to stretch in unison are removed at high energies and short distances. In a paper published in Physical Review Letters in April, he explains that within this regime, space stretches only a third as quickly as time. "The three spatial dimensions effectively mimic just one normal relativistic dimension," he says, making it look as though two dimensions have vanished.
