NASA Telescopes Set Limits On Spacetime Quantum “Foam”

Source: NASA

At the smallest scales of distance and duration that we can measure, spacetime – that is, the three dimensions of space plus time – appears to be smooth and structureless. However, certain aspects of quantum mechanics, the highly successful theory scientists have developed to explain the physics of atoms and subatomic particles, predict that spacetime would not be smooth. Rather, it would have a foamy, jittery nature and would consist of many small, ever-changing, regions for which space and time are no longer definite, but fluctuate.

The predicted scale of spacetime foam is about ten times a billionth of the diameter of a hydrogen atom’s nucleus, so it cannot be detected directly. However, If spacetime does have a foamy structure there are limitations on the accuracy with which distances can be measured because the size of the many quantum bubbles through which light travels will fluctuate. Depending on what model of spacetime is used, these distance uncertainties should accumulate at different rates as light travels over the large cosmic distances.

A team of researchers used observations of X-rays and gamma-rays from very distant quasars – luminous sources produced by matter falling towards supermassive black holes – to test models of spacetime foam. The authors predicted that the accumulation of distance uncertainties for light traveling across billions of light years would cause the image quality to degrade so much that the objects would become undetectable. The wavelength where the image disappears should depend on the model of space-time foam used.

Chandra’s X-ray detection of quasars at distances of billions of light years rules out one model, according to which photons diffuse randomly through space-time foam in a manner similar to light diffusing through fog. Detections of distant quasars at shorter, gamma-ray wavelengths with Fermi and even shorter wavelengths with VERITAS demonstrate that a second, so-called holographic model with less diffusion does not work.

The X-ray and gamma-ray data show that spacetime is smooth down to distances 1000 times smaller than the nucleus of a hydrogen atom.