Clashing with Einstein: Spacetime Becomes Granular below the Planck Scale

One solution to this impasse has now been put forward by Stefano Liberati, SISSA professor, and colleagues in their latest publication. The study was conducted with the participation of researchers from the LENS in Florence (Francesco Marin and Francesco Marino) and from the INFN in Padua (Antonello Ortolan). Other SISSA scientists taking part in the study, in addition to Liberati, were PhD student Alessio Belenchia and postdoc Dionigi Benincasa. The research was funded by a grant of the John Templeton Foundation.

“We respect Lorentz invariance, but everything comes at a price, which in this case is the introduction of non-local effects”, comments Liberati. The scenario studied by Liberati and colleagues in fact salvages special relativity but introduces the possibility that physics at a certain point in space-time can be affected by what happens not only in proximity to that point but also at regions very far from it. “Clearly we do not violate causality nor do we presuppose information that travels faster than light”, points out the scientist. “We do, however, introduce a need to know the global structure so as to understand what’s going on at a local level”.

From theory to facts

There’s something else that makes Liberati and colleagues’ model almost unique, and no doubt highly precious: it is formulated in such a way as to make experimental testing possible. “To develop our reasoning we worked side by side with the experimental physicists of the Florence LENS. We are in fact already working on developing the experiments”. With these measurements, Liberati and colleagues may be able to identify the boundary, or transition zone, where space-time becomes granular and physics non-local.

“At LENS they’re now building a quantum harmonic oscillator: a silicon chip weighing a few micrograms which after being cooled to temperatures close to absolute zero, is illuminated with a laser light and starts to oscillate harmonically” explains Liberati. “Our theoretical model accommodates the possibility of testing non-local effects on quantum objects having a non-negligible mass”. This is an important aspect: a theoretical scenario that accounts for quantum effects without violating special relativity also implies that these effects at our scales must necessarily be very small (otherwise we would already have observed them). In order to test them, we need to be able to observe them in some way or other. According to our model, it is possible to see the effects in ‘borderline’ objects, that is, objects that are undeniably quantum objects but having a size where the mass – i.e., the ‘charge’ associated with gravity (as electrical charge is associated with electrical field) – is still substantial.”

“On the basis of the proposed model, we formulated predictions about how the system would oscillate”, says Liberati. “Two predictions, to be precise: one function that describes the system without non-local effects and one that describes it with local effects”. The model is particularly robust since, as Liberati explains, the difference in the pattern described in the two cases cannot be generated by environmental influences on the oscillator. 

 

“So it’s a ‘win-win’ situation: if we don’t see the effect, we can raise the bar of the energies where to look for the transition. Above all, the experiments being prepared should be able to push the constraints on the non-locality scale to the Planck scale. In this case , we go as far as to exclude these scenarios with non-locality. And this in itself would be a good result, as we would be cutting down the number of possible theoretical scenarios”, concludes Liberati. “If on the other hand we were to observe the effect, well, in that case we would be confirming the existence of non-local effects, thus paving the way for an altogether new physics.”