Time evolution in string theory

爱因斯坦的广义相对论描述了大型物体之间的引力，比如地球和太阳之间的引力，那些将银河系聚集在一起的力，以及那些决定宇宙大爆炸以来宇宙膨胀速度的力。这是一个准确的理论，它的预测已经在实验和观察中得到了验证。量子力学是关于原子及其组成部分的理论。它支配着半导体、化学反应和基本粒子的行为，从日常的电子到奇异的顶夸克。这一理论与实验的一致性达到了前所未有的精确度。这两种理论似乎没有什么共同之处；然而，对一些对象和现象的研究需要我们两者兼而有之。这包括试图了解黑洞的内部，比如据信存在于我们银河系中心的黑洞。另一个例子是大爆炸后的瞬间，当时我们刚刚诞生的宇宙非常小，密度大，温度高。弦理论是将这两种理论结合在一起的最佳候选框架。在过去的三十年里，弦理论在我们理解引力和量子力学之间的相互作用方面取得了巨大的进步。实验和观察继续挑战这一理论；最近一次这样的挑战是由宇宙学通过测量一个正的宇宙常数而提出的，目前还没有答案。在我的工作中，我专注于那些我认为对回答这一挑战至关重要的问题：弦理论中解决时间演化的方法。我的工作涉及的范围从整个宇宙的演化问题到黑洞如何衰变的问题。

Einstein's theory of general relativity describes gravitational forces between large objects, forces such as the attraction between the Earth and the Sun, those holding the Milky Way galaxy together and those forces determining the rate of expansion of the Universe since the Big Bang. It is an accurate theory and its predictions have been tested in experiment and observation. Quantum Mechanics is the theory of the small: the atom, as well as the atom's constituents.  It governs the behaviour of semiconductors, of chemical reactions and of elementary particles, from the every-day electrons to the exotic top quark.  The theory agrees with experiments with an unprecedented accuracy. These two theories seem to have little in common; however, the study of some objects and phenomena requires us to use of both of them.  This includes attempts to understand the interior of a black hole, such as the one believed to exists at the center of our Galaxy.  Another example is the split-second after the Big Bang, when our just-born Universe was incredibly small, dense and hot.  String theory is our best candidate for a framework in which these two theories can be brought together.  In the last three decades, string theory has made great advances in our understanding of the interplay between Gravity and Quantum Mechanics.  Experiment and observations continue to challenge the theory; the most recent such challenge, issued by Cosmology through the measurement of a positive cosmological constant, has yet to be answered. In my work, I focus on those problems I believe are going to be essential in answering this challenge: the methods for addressing time evolution in String theory.  The implications of my work range from the problems of evolution of the Universe as a whole to the questions of how black holes decay.