Archivi tag: virtual particles

Is our Universe a hologram?

E’ circolata di recente nei media la notizia pubblicata da Nature secondo la quale un gruppo di fisici giapponesi avrebbero formulato una teoria che “potrebbe essere considerata l’evidenza più chiara sul fatto che il nostro Universo sarebbe una gigantesca proiezione“. Nei loro articoli, Yoshifumi Hyakutake e colleghi della Ibaraki University in Giappone spiegano  come la loro idea suggerisca che la realtà fisica, così come noi la concepiamo, potrebbe essere in definitiva un ologramma appartenente ad un altro spazio bidimensionale.

In 1997, theoretical physicist Juan Maldacena proposed that an audacious model of the Universe in which gravity arises from infinitesimally thin, vibrating strings could be reinterpreted in terms of well-established physics. The mathematically intricate world of strings, which exist in nine dimensions of space plus one of time, would be merely a hologram: the real action would play out in a simpler, flatter cosmos where there is no gravity. Maldacena’s idea thrilled physicists because it offered a way to put the popular but still unproven theory of strings on solid footing, and because it solved apparent inconsistencies between quantum physics and Einstein’s theory of gravity. It provided physicists with a mathematical “Rosetta stone”, a ‘duality’, that allowed them to translate back and forth between the two languages, and solve problems in one model that seemed intractable in the other and vice versa (see ‘Collaborative physics: String theory finds a bench mate‘). But although the validity of Maldacena’s ideas has pretty much been taken for granted ever since, a rigorous proof has been elusive.

In two papers posted on the arXiv repository, Yoshifumi Hyakutake of Ibaraki University in Japan and his colleagues now provide, if not an actual proof, at least compelling evidence that Maldacena’s conjecture is true.

In one paper, Hyakutake computes the internal energy of a black hole, the position of its event horizon (the boundary between the black hole and the rest of the Universe), its entropy and other properties based on the predictions of string theory as well as the effects of so-called virtual particles that continuously pop into and out of existence (see ‘Astrophysics: Fire in the Hole!‘). In the other, he and his collaborators calculate the internal energy of the corresponding lower-dimensional cosmos with no gravity. The two computer calculations match. “It seems to be a correct computation”, says Maldacena, who is now at the Institute for Advanced Study in Princeton, New Jersey and who did not contribute to the team’s work.

The findings “are an interesting way to test many ideas in quantum gravity and string theory”, Maldacena adds.

The two papers, he notes, are the culmination of a series of articles contributed by the Japanese team over the past few years. “The whole sequence of papers is very nice because it tests the dual [nature of the universes] in regimes where there are no analytic tests. They have numerically confirmed, perhaps for the first time, something we were fairly sure had to be true, but was still a conjecture, namely that the thermodynamics of certain black holes can be reproduced from a lower-dimensional Universe”, says Leonard Susskind, a theoretical physicist at Stanford University in California who was among the first theoreticians to explore the idea of holographic universes. Neither of the model universes explored by the Japanese team resembles our own, Maldacena notes. The cosmos with a black hole has ten dimensions, with eight of them forming an eight-dimensional sphere. The lower-dimensional, gravity-free one has but a single dimension, and its menagerie of quantum particles resembles a group of idealized springs, or harmonic oscillators, attached to one another. Nevertheless, says Maldacena, the numerical proof that these two seemingly disparate worlds are actually identical gives hope that the gravitational properties of our Universe can one day be explained by a simpler cosmos purely in terms of quantum theory.

Nature: Simulations back up theory that Universe is a hologram

arXiv: Quantum Near Horizon Geometry of Black 0-Brane

arXiv: Holographic description of quantum black hole on a computer

Easy tests in high energy experiments

Tre fisici teorici hanno fatto un passo in avanti per eliminare alcune ambiguità che derivano dalle complesse formule matematiche che vengono utilizzate per studiare le interazioni tra i quark, le particelle più fondamentali della materia che compongono protoni e neutroni, e i gluoni, le particelle enigmatiche responsabili dell’interazione nucleare forte che lega i quark nei nucleoni. Secondo gli scienziati, semplificando questi calcoli è possibile facilitare, per così dire, il lavoro dei fisici per realizzare previsioni più accurate quando vengono eseguiti gli esperimenti di laboratorio.

The theory describing those interactions is known as quantum chromodynamics (QCD), and is an important component of the Standard Model, the reigning theory of the interactions of subatomic particles. “An important goal in high energy physics is to make predictions that are as precise as possible“, said SLAC theoretical physicist Stan Brodsky. “This makes tests of QCD more rigorous. Most important, if QCD doesn’t pass our experimental tests, it could reveal new physics beyond the Standard Model“. In a paper published in Physical Review Letters, Brodsky and his colleagues, Matin Mojaza of CP3-Origins at the University of Southern Denmark and Xing-Gang Wu of Chongqing University in China, have presented a method that will help theorists to automatically eliminate an important theoretical ambiguity of QCD predictions. Particle theorists attempt to put the quantum realm under a mathematical microscope. However, the world of subatomic particles operates according to very different rules than our familiar everyday world. Quantum uncertainties take hold.

On the scale of quarks and gluons, E=mcis not a slogan on a t-shirt, it’s the law of the land, if there’s a possibility for a particular particle to exist, it, and others, will pop into and out of existence, obscuring what lies under the physicists’ calculational lenses.

These “now you see them, now you don’t” particles, called virtual particles, give rise to infinite terms in quantum calculations, a big problem for theorists, who must remove the uncertainty in their calculations caused by these infinities without introducing new ambiguities. This problem has obscured the precision of the theorists’ mathematical microscope. Brodsky and his colleagues have been developing a method called the Principle of Maximum Conformality (PMC) which can focus the mathematical microscope into the quantum world.

Building on this work, in their new paper, Mojaza, Wu and Brodsky show how a novel generalization of a technique that many theorists employ to remove infinities, called modified minimal subtraction, can be used to identify patterns within the calculations.

This, along with PMC, makes the calculations easier to reduce to a form that can be used to make testable predictions, free of ambiguities, the heart of scientific progress. In addition to adding another tool to the theorists’ toolbox and providing testable predictions to experimenters, their technique has another advantage, said Brodsky: “Since the method is systematic, it can be used as the basis of a computer algorithm“, automating the calculations even further.

SLAC: SLAC Theorist Helps Sharpen Tests of Fundamental Theory in High Energy Experiments

arXiv:A Systematic All-Orders Method to Eliminate Renormalization-Scale and Scheme Ambiguities in PQCD