Loop Quantum Gravity: from Computation to Phenomenology

在基础物理学的前沿，存在着将量子理论与爱因斯坦广义相对论结合起来的问题。今天，我们有一些试探性的理论试图实现这一目标——或者量子引力理论——但这些理论都没有得到实验或观测支持的检验。我的“发现”项目的目标是开发理论工具，让我们能够检验这些理论。有两个领域，量子引力有望在描述自然中发挥重要作用：黑洞物理学和大爆炸。爱因斯坦的广义相对论无视量子理论，不能可靠地预测黑洞中心会发生什么，或者黑洞在遥远的未来会发生什么。目前正在研究的一种量子引力理论——环量子引力理论认为，这些区域的量子效应决定了将黑洞转变为白洞的转变（隧穿效应），白洞随后可以发射物质。我的研究计划将开发最近制作的计算机程序，用于计算环量子引力中的跃迁概率，目的是将它们应用于确定黑洞到白洞跃迁的参数。然后，它将利用这些结果将理论预测与天体物理观测（如高能宇宙射线或星系外无线电信号）进行比较，以研究这些观测或其他天体物理现象（如暗物质）是否与黑洞到白洞的转变有关。同样的计算机代码也可以被开发出来，用于研究原始宇宙的行为。环量子引力指出，观测到的宇宙爆炸产生了我们所观察到的宇宙，可能是在之前的收缩阶段之后反弹的结果。本项目旨在研究弹跳时预期的强量子引力现象。特别是，它旨在研究当时产生的时空几何的量子涨落，以及这些涨落可能对星系和星系团等宇宙大型结构的形成产生的影响。我们的目标是能够获得更多关于宇宙早期生命的知识元素，并希望在可观测的宇宙现象（如宇宙背景辐射）中找到一些可观测的原始量子引力现象的痕迹。

At the frontier of fundamental physics there is the problem of combining quantum theory and Einstein's General Relativity. Today we have tentative theories that try to achieve this goal -or theories of quantum gravity- but none of these theories is yet tested by experiments or observations support. The goal of my Discovery program is to develop theoretical tools that could lead us to test these theories. There are two domains where quantum gravity is expected to play a significant role in describe nature: black hole physics and the Big Bang. Einstein's General Relativity disregards quantum theory and is not reliable for predicting what happens at the center of a black hole, or what happens to the black hole in the distant future. A quantum gravity theory currently under study, Loop Quantum Gravity, suggests that quantum effects in these regions determine a transition (a tunnelling effect) that transforms a black hole into a white hole, which can subsequently emit matter. My program of research will develop recently produced computer programs that compute transition probabilities in Loop Quantum Gravity, with the aim of applying them to determine the parameters of this black hole to white hole transition. It will then use these results to compare the predictions of the theory with astrophysical observations, such as high-energy cosmic rays or extra-galactic radio signals, to study if these observations, or other astrophysical phenomena such as dark matter, could be connected to the black-hole to white-hole transition. The same computer codes can also be developed and used to study the behaviour of the primordial universe. Loop Quantum Gravity indicates that the observed cosmic explosion that has generated the universe we observe could be the result of a bounce following a previous contraction phase. This project aims at studying the strong quantum gravitational phenomena expected at the bounce. In particular, it aims at studying the quantum fluctuations of the spacetime geometry generated at that time, and the effect that these might have had on the formation of the large structures of the universe, such as galaxies and galaxy clusters. The objective is to be able to get more elements of knowledge concerting the early life of our Universe, and, hopefully, find some observables traces of primordial quantum gravitational phenomena in observable cosmological phenomena such as the Cosmic Background Radiation.