The universe and all that

There was a university press release that got a lot of publicity recently, about "quantum graphity" - rather a bad name by whoever came up with it, I thought.

Anyhow, ars technica has a cynical look at the PR exercise, and as I expected, there is probably less to this than it seems.

Of more interest, I think, is this story about measurements indicating that spacetime is pretty 'smooth':

Some theories of quantum gravity say that the universe is not smooth but foamy—made of fundamental units called Planck lengths that are less than a trillionth of a trillionth the diameter of a hydrogen atom. Planck lengths are so small that there's no way to detect them, except via photons like those that make up gamma-ray bursts. Here's why.

The wavelengths of these photons are some of the shortest distances known to science—so short they should interact with the even smaller Planck length. And if they interact, the photons should be dispersed—scattered—on their trek through Planck length–pixilated spacetime.

 In particular, they should disperse in different ways if their wavelengths differ, just as a ping pong ball and a softball might take alternate paths down a gravely hillside.

 You wouldn't notice the scattering over short distances, but across billions of light years, the Planck lengths should disperse the light. And three photons from the same gamma-ray burst should not have crashed through the Fermi telescope at the same moment.

 But they did, and that calls into question just how foamy spacetime really is. "We have shown that the universe is smooth across the Planck mass," Nemiroff said. "That means that there's no choppiness that's detectible. It's a really cool discovery. We're very excited."