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，我们已经有了试图实现这一目标的试探性理论--或者量子引力理论--但这些理论都还没有得到实验或观测支持的检验。我的探索计划的目标是开发理论工具，帮助我们检验这些理论。量子引力有望在描述自然方面发挥重要作用的领域有两个：黑洞物理学和大爆炸。爱因斯坦的广义相对论忽视了量子理论，对于预测黑洞中心会发生什么，或者在遥远的未来黑洞会发生什么，这是不可靠的。目前正在研究的量子引力理论环路量子引力表明，这些区域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制作的计算循环量子引力跃迁概率的计算机程序，目的是应用它们来确定黑洞到白洞跃迁的参数。然后，它将使用这些结果将该理论的预测与天体物理观测(如高能宇宙射线或银河系外无线电信号)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并用于研究原始宇宙的行为。环路量子引力表明，观测到的宇宙爆炸产生了我们观察到的宇宙，可能是前一个收缩阶段之后反弹的结果。这个项目的目的是研究反弹时预计会出现的强量子引力现象。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结构的形成产生的影响，如星系和星系团。其目标是能够获得更多与我们宇宙早期生活相关的知识元素，并有望在可观察的宇宙学现象中找到一些原始量子引力现象的可观测痕迹，如宇宙背景辐射。

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.