Spacetime: A smoother brew than we knew

January 9, 2013, Michigan Technological University

Spacetime may be less like foamy quantum beer and more like smooth Einsteinian whiskey, according to research led by physicist Robert Nemiroff of Michigan Technological University being presented today at the 221st American Astronomical Society meeting in Long Beach, Calif.

Or so an intergalactic photo finish would suggest.

Nemiroff and his team reached this heady conclusion after studying the tracings of three photons of differing wavelengths recorded by NASA's Fermi Gamma-ray in May 2009.

The photons originated about 7 billion light-years away from Earth from a gamma-ray burst and arrived at the orbiting telescope a mere millisecond apart.

"Gamma-ray bursts can tell us some very interesting things about the universe," Nemiroff says. In this case, those three photons recorded by the Fermi telescope may be validating 's view of smooth spacetime into the realm of . In other words, spacetime may not be not as foamy as some scientists think.

In his , Einstein described space and time as smooth, deforming only under the weight of matter and energy. But according to some theories of , which deal with matter and energy at the smallest scale, spacetime is made up of a froth of particles and possibly even that pop in and out of existence over infinitesimally small moments at the so-called Planck-length scale, which is less than a trillionth of a trillionth the diameter of a hydrogen atom.

The "bubbles" in this foam—should they exist—are so small as to be almost undetectable. However, scientists have theorized that photons from gamma-ray bursts should be able to track down the bubbles' signature.

Here's why. The wavelengths of gamma-ray burst photons are some of the shortest distances known to science—so short they should interact with the even smaller bubbles of quantum foam. And if they interact, the photons should be dispersed—scattered—on their trek through frothy spacetime.

In particular, they should disperse in different ways if their wavelengths differ, as in the case of Nemiroff's three photons. Imagine a Ping Pong ball, a bowling ball, and a softball taking alternate paths down a gravely hillside.

Furthermore, few things can delay gamma-ray photons like these, so they might travel for unimaginably long distances unimpeded. You wouldn't notice the scattering over short distances, but across 7 billion light-years, the quantum foam might knock the light around enough to notice. And three photons from the same gamma-ray burst might not have crashed through the Fermi telescope in a dead heat.

Bolstered by the evidence garnered from the three photons, Nemiroff's analysis supports earlier indications but takes them clearly below the Planck length: "If foaminess exists at all, we think it must be at a scale far smaller than the , indicating that other physics might be involved," he says.

"There is a possibility of a statistical fluke, or that spacetime foam interacts with light differently than we imagined," Nemiroff said.

"If future gamma-ray bursts confirm this, we will have learned something very fundamental about our universe," says Bradley E. Schaefer, professor of physics and astronomy at Louisiana State University.

For now, at least, this looks like another win for Einstein. Perhaps it calls for a toast.

Explore further: Physics team finds new constraints on how lumpy space-time can be

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5 / 5 (3) Jan 10, 2013
Must admire Nemiroff &co. Think about it: three single photons stumble upon a satellite, and our technology and science let us write entire articles about them, their origin, and the structure of the cosmos. Pretty darn amazing, IMHO.
not rated yet Jan 10, 2013
Bursts can last from ten milliseconds to several minutes. -- Wikipedia

It would have been nice to see an explanation as to how the authors could make millisecond inferences from such potentially long sources.
5 / 5 (2) Jan 10, 2013
This couples to inflation I think, since there is no such spacetime and/or gravity fluctuations blown up from around Planck scales. (Or below, in eternal inflation.) Just the inflation field primordial fluctuations themselves.

@qwrede: It's just an observation so far.

From the arxiv paper: "Is this arrival pattern of remarkably brief doublets separated by long pauses significant? Do these 3 brief pulses define the finest time scale yet? We argue that such "rhythm" is, most likely, not spurious."

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5 / 5 (2) Jan 10, 2013
gwrede, I think the idea is that over the distances involved, the "foaminess" of spacetime would stretch the distribution of photons from a single burst so that they would reach us over a much longer period than the milliseconds or minutes of the original burst, and thus 3 photons reaching us at the same time is statistically extremely unlikely if that scattering is occurring, thus the result is not consistent with the existing theories of "foamy" spacetime and how it interacts with light.
not rated yet Jan 13, 2013
I explained already there, that the distant gamma ray burst arrive as homogeneous not because the space-time is homogeneous, but because it is so inhomogeneous, it homogenizes them. This explanation is supported with the fact, the short distance gamma ray bursts are significantly more inhomogeneous, than these long distance ones.

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