Research in General Relativity and Quantum Gravity

这个项目涉及量子引力——量子理论和广义相对论的统一。首席研究员解决这个问题的方法是基于因果集假设，该假设断言时空的深层结构是颗粒状的或“原子”的，其中原子（“因果集元素”）被组织成一个扩展的“家族树”，技术上称为局部有限偏序。该项目将通过推进基础理论来进一步发展这种方法，同时将其应用于宇宙常数等问题，宇宙常数最近被证明贡献了大约三分之二的宇宙有效能量密度。该项目的一个主要焦点将是在量子因果集的情况下，对先前发现的经典顺序增长动力学进行推广。这个问题的解决方案通常会告诉我们在最小的长度尺度上的时空结构，同时，帮助回答为什么宇宙在最大的尺度上是这样的问题。该项目还引导了一种新的理解时间的方式，因为时间是因果集的新元素的不断诞生。所要开发的算法和实现这些算法的代码不仅对离散时空过程有用，而且对包括信息技术在内的组合目的也具有更普遍的适用性。在基础物理学中获得的知识，例如在本项目中学习的知识，也对广大公众有吸引力，并有助于培养受过教育和技术熟练的劳动力。

This project concerns quantum gravity---the unification of quantum theory and general relativity. The Principal Investigator's approach to this problem is based on the causal set hypothesis, which asserts that the deep structure of spacetime is granular or ``atomic'' with the atoms (``causal set elements'') organized into an extended ``family tree'', known technically as a locally finite partial order. The project will develop this approach further by advancing the underlying theory, while at the same time applying it to questions like that of the cosmological constant, which recently has been shown to contribute roughly two thirds of the effective energy density of the universe. A primary focus of the project will be on the development of a generalization of the classical sequential growth dynamics, found previously, to the case of a quantum causal set.A solution of this problem is generally expected to tell us about the structure of spacetime on the smallest length scales and, at the same time, to help answer questions about why the cosmos is as it is on the largest scales. The project also leads to a new way of understanding time as the continual birth of new elements of the causal set. The algorithms to be developed and the codes to implement them are not only useful in connection with discrete spacetime processes but also have a more general applicability for combinatorial purposes including uses in information technology. Knowledge obtained in fundamental physics such as that studied in this project also appeals to members of the public at large and contributes towards an educated and technically skilled labor force.