By Ron Cowen
Smaller dots, Georges, please. In their efforts to unify quantum theory and gravity, theoretical physicists have likened spacetime to a Georges Seurat painting, composed of tiny dots or lumps that meld to form a seemingly smooth picture. But if spacetime really does have a grainy structure on the smallest scales, the cosmic painter may need to get finer brushes, a new study reveals.
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The study, published online October 28 in Nature, suggests that the dots that may compose spacetime must be smaller than one-hundred-thousandth of a trillionth of the size of a proton. This new limit on the graininess of spacetime is one-thousandth the size that previous, less sensitive experiments had indicated.
Sylvain Guiriec of NASA’s Marshall Space Flight Center and the University of Alabama in Huntsville and his colleagues used a powerful but indirect method to examine the structure of spacetime. The team measured the relative difference in the speed of two particles of light, or photons, of widely different energies. Both photons were emitted by a cosmic explosion known as a short-lived gamma-ray burst.