Researchers are still desperately seeking a theory of quantum gravity, and while many intriguing ideas have been proposed, hard evidence is lacking. Now, however, they might have found a glimpse from the depths of the very vacuum of space.
Italian researchers report in Nature Astronomy the observation of a peculiar signal in both neutrinos and photons emitted by powerful gamma-ray bursts. The signal appears to be consistent with a concept called quantum foam, which is a proposed explanation of space-time at the microscopic level.
Quantum foam is expected to generate minuscule dispersions of light and neutrinos. These particles follow space-time, and if spacetime is not as smooth as traditionally thought, the little bumps will have an effect. The effect is too small to be observed on terrestrial scales, but it could be detectable at cosmic distances.
Gamma-ray bursts are one of the most energetic events in the universe, and their photons and neutrinos travel for billions and billions of years. This means that if the quantum foam is creating a dispersion, they are affected by it. The signal appears to be there and the researchers think that at present it's not likely that it's accidentally created by other mechanisms.
This has the potential to be a big deal, but it is still very early days. Gamma-ray bursts are few and far between, and only a handful of their neutrinos and gamma-ray bursts are actually detected. A lot more detections are necessary and the team expects to have a better idea of quantum foam, and even which model of it might be correct, in the next four to five years.
"The statistical evidence at present is still rather weak, and if we were talking about a more familiar area of physics, there would not be much to get excited about," lead author Professor Giovanni Amelino-Camelia, from the University of Rome La Sapienza, told IFLScience. "However, for the first time, we see a small but tangible probability that we might leap into the quantum-gravity realm, which is far beyond the current horizon of physics."
The new study adds to 15 years' worth of astronomical research on quantum foam. So far, these observations have put a constraint on how granular space-time could be. The fabric of the universe is smooth and uniform down to lengths that are 1,000 times smaller than the diameter of a hydrogen atom.
Researchers have actually come up with a cute analogy to explain the difficulty of measuring quantum foam: If you have a glass full of sand, it might be difficult to see if it is a solid or a liquid from a distance. Things look different when we zoom in and see the actual grains of sand.
So physicists need to zoom in. Unfortunately, the energy to do that in particle laboratories and atom smashers is still beyond what we can achieve. Therefore, an answer to the mystery of space-time might as well come from the sky.