报告题目 (Title)：From bending of light to positive mass: a non-PDE perspective（从光线偏折到正质量定理：一个非偏微分方程的视角）
报告人 (Speaker)：吴小宁 研究员（中国科学院数学研究院）
报告地点 (Place)：腾讯会议（ID：593 914 798）
Penrose et al. investigated the physical incoherence of the spacetime with negative mass via the bending of light. Precise estimates of time-delay of null geodesics were needed and played a pivotal role in their proof. In this paper, we construct an intermediate diagonal metric and make a reduction of this problem to a causality comparison in the compactified spacetimes regarding timelike connectedness near the conformal infinities. This different approach allows us to avoid encountering the difficulties and subtle issues Penrose et al. met. It provides a new, substantially simple, and physically natural non-PDE viewpoint to understand the positive mass theorem. This elementary argument modestly applies to asymptotically flat solutions which are vacuum and stationary near infinity.