应兰州大学物理科学与技术学院、萃英学院、理论物理交流平台邀请，台湾中央大学James M. Nester教授将来我校进行学术合作交流并做专题讲座，欢迎广大师生参加！

主讲人：James M. Nester教授

题目：Gravity and gravitational energy: a gauge theory and Hamiltonian perspective

联系人：刘玉孝教授/杨捷副教授

讲座简介:

These lectures address two interlinked issues that were of concern for the late Lanzhou U Prof Duan Yi-Shi: (i) gravity as a gauge theory and (ii) gravitational energy. The approach will be largely historical and concerned with fundamental principles.

The evolution of a generally covariant theory is under-determined, this local gauge freedom is deeply connected with the puzzle of gravitational energy. We recount some history of Einstein, Hilbert, and Klein and the novel features of gravitational energy that led to Noether's two theorems. Both under-determined evolution and energy are best revealed in the Hamiltonian formulation.

Gravitational energy is not localizable, rather it is quasi-local. The quasi-local description has two inherent ambiguities: (i) there are many possible expressions, (ii) they are not covariant, they depend on the frame of reference. These issues can be clarified by the Hamiltonian approach along with a geometric gauge theory perspective. From a covariant Hamiltonian formulation we found, for any spacetime region, a certain boundary term expression for the quasi-local energy-momentum (and angular momentum). Recently we found an appropriate way to select the necessary reference frame and discovered that with a best matched reference a large class of reasonable energy expressions yield the same common quasi-local value.

Gravity can be considered as a gauge theory of the local Poincare group. The dynamical potentials of the Poincare gauge theory of gravity are the frame and the connection. The spacetime geometry has in general both curvature and torsion. Torsion naturally couples to spin; it could have a significant magnitude and yet not be noticed, except on a cosmological scale where it could have significant effects.

主讲人简介：

James M. Nester教授是国际知名引力物理学家，广义相对论专家。Nester教授于1977年在University of Maryland at College Park获得博士学位，导师是著名经典广义相对论学者，名著“Gravitation”作者MTW中的M（Charles W. Misner）。Nester教授长期从事广义相对论、引力规范理论、引力场的能量定义与守恒等相关领域的研究。曾获2002年“The Foundation Samii-Housseipour Prize in Sciences (Physics)”奖。Nester教授几十年来教学生动，经验丰富，多次受邀在中科院数学与系统科学研究院讲授《广义相对论》课程。