Loop Quantum Gravity: from Computation to Phenomenology

在基础物理学的前沿，存在着将量子理论和爱因斯坦的广义相对论结合起来的问题。今天，我们有试图实现这一目标的尝试性理论——或者量子引力理论——但这些理论都还没有经过实验或观察支持的检验。我的发现计划的目标是开发可以引导我们测试这些理论的理论工具。量子引力预计将在描述自然的两个领域发挥重要作用：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，对于预测黑洞中心发生的情况或遥远的未来黑洞发生的情况并不可靠。目前正在研究的量子引力理论“圈量子引力”表明，这些区域中的量子效应决定了将黑洞转变为白洞的转变（隧道效应），白洞随后可以发射物质。我的研究计划将开发最近开发的计算机程序，用于计算环量子引力中的跃迁概率，目的是应用它们来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的预测与天体物理观测（例如高能宇宙射线或银河外无线电信号）进行比较，以研究这些观测或其他天体物理现象（例如暗物质）是否可以与黑洞到白洞的转变联系起来。 相同的计算机代码也可以被开发并用于研究原始宇宙的行为。圈量子引力表明，所观察到的宇宙爆炸产生了我们所观察到的宇宙，这可能是先前收缩阶段后反弹的结果。该项目旨在研究反弹时预期的强量子引力现象。特别是，它的目的是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宇宙大型结构（例如星系和星系团）形成的影响。目标是能够获得更多有关宇宙早期生命的知识元素，并希望在可观测的宇宙学现象（例如宇宙背景辐射）中找到一些原始量子引力现象的可观测痕迹。

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.