[ad_1]
There modern physics it rests on two large pillars, both cast in the first half of the last century. There quantum mechanicswhich with its laws describes the behavior of waves And particles on microscopic spatial scales, and the general relativitywhich explains the behavior of the severity in terms of a kind of deformation of the space time, the four-dimensional structure in which we are immersed. Separately, quantum mechanics and general relativity work perfectly, and both have been (and continue to be) experimentally verified with ever greater precision; the problem is that when physicists try to fit them into a single theoretical framework, to harmonize them into a more general theory that also describes gravity in quantum terms, things stop working. At the moment, the quantization of gravity is one of the most important unsolved problems in physics: which is why every small step in this direction is greeted with great enthusiasm by the physics community. That’s what just happened to the detector IceCubea huge device built in the ice of theAntarctica to capture and analyze particles arriving from Space, the so-called cosmic neutrinos: the scientists working on the experiment (an international collaboration that also includes Italy), in fact, have just shown that cosmic neutrinos can be used to infer information on the theory of quantum gravity. The details of the research were published in the journal Nature Physics.
Before trying to go into the details of the work – which are, as it is easy to guess given the theme, quite technical and complex – let’s take a look at the state of the art. One of the most promising avenues currently to build a theory of quantum gravity predicts the existence of some kind of spacetime foam: this is a prediction common to many theoretical models, according to which space on microscopic scales would not be continuous, but would have, precisely, a foamy nature. We can clarify this with an analogy: our current geometric description of space-time is somewhat reminiscent of the geometry of an ideal sheet, a sheet that responds to stresses (for example to a mass resting on it) by bending or becoming more taut. but still remaining smooth, or more precisely characterized by a continuous geometry. The “foam” hypothesis predicts that continuous geometry is only a first approximation, a rough image, of space-time: in a more accurate microscopic description, the sheet should be in a certain sense “porous”, just like a foam. The porosity of this grain should change rapidly and dramatically as spatial distances get very small. And the problem lies precisely in this: the size of the elements that make up this foam is too small to be measured directly, and one must (try to) access it indirectly, for example by studying if and how other particles (such as photons) interact with it. He has dealt with it, among others, Giovanni Amelino-Cameliaprofessor of theoretical physics atUniversity of Naples and among the leading experts in quantum gravity: “Until 15 years ago – he told us – being able to observe the texture of space-time seemed impossible, now we have shown that it can be done. And we realized that the foam is even more intangible than we thought “.
What does all this have to do with neutrinos and with IceCube? “Cosmic neutrinos – he explained to us Piera Sapienzaresearcher ai Southern National Laboratories ofInstitute of Nuclear Physics (Lns-Infn) and one of the founders of Km3Neta similar (and somewhat “competing”) experiment by IceCube, which studies cosmic neutrinos with a detector placed 3500 meters under the sea, off Capo Passero in Sicily – they are particles capable of traveling for very long distances and reaching us with very high energy, bringing very precious information on cosmic phenomena that would otherwise be unfathomable. Today we know that there are three “types” of neutrinos, which we call “flavors”: the electron neutrino, the mu neutrino and the tau neutrino, and that neutrinos can “oscillate” between these flavors, transforming into one another. The “classical” theory foresees that the neutrinos that reach the detectors such as IceCube or Km3Net are equalized between the three flavors; if not, it would mean that there is an anomaly due to a physics that we do not yet know, including possible effects of quantum gravity“. In short, the idea is that quantum gravity could have an effect on the oscillations of cosmic neutrinos, and that we might be able to measure this effect. Or rather, just some types of quantum gravity: “The IceCube study – specifies Amelino-Camelia, who among other things carried out two analyzes of the IceCube neutrinos (this And this) with a different approach than the article just published – it has to do with the possible effect of a particular subgroup of quantum gravity models on neutrino oscillations, the so-called non-universal models, that is, those that predict that the effects of quantum gravity are different on different particles “.
Thus we arrive at the results: the new data (which are not very many: 60 events in over seven and a half years of observation, which gives the idea of how difficult it is to study phenomena of this type) found no anomalies in the neutrino equivocation potentially associated with new physics and in particular with quantum gravity effects. It may sound disappointing, but it’s not at all: “Perhaps the most relevant aspect – says Wisdom again – is a further demonstration of how cosmic neutrinosnormally used to investigate extreme cosmic phenomena, may also prove important in the study of particle physics, revealing itself as a sort of ‘bridge’ between astrophysics and particle physics. Furthermore, an apparently ‘negative’ result is actually very important, because excluding something helps theorists to take another path, indicating a direction by exclusion “. Amelino-Camelia also shares the same opinion: “The study just released by IceCube – concludes – it is very significant, especially for the power of the experimental limit obtained on the ‘non-universal’ effects “.
.
[ad_2]
Source link
