Gravity seminar - Aditya Vaswani Seminar

Abstract: In the context of special relativity, the ultrarelativistic limit is a useful idea to approximate the motion of objects moving close to the speed of light. Can this idea be generalised to curved spacetimes, and will it be useful in describing the motion of point-like particles? In my talk, I will present a perturbative formalism that can, in some sense, capture the behaviour of ultrarelativistic particles. The key ingredient in this formalism is the Penrose limit -- the idea that the metric around a specified null geodesic in an arbitrary spacetime can be made to look like a plane wave metric. Objects whose worldlines remain close to the fixed null geodesic are ultrarelativistic, and their motion is determined by the structure of the plane wave metric. I will present some results about how this formalism can be used to simplify the equations of motion of a point-like particle in arbitrary spacetimes. Finally, I will discuss in what regimes this formalism is expected to hold, as well as when it breaks down.