Why do Things Fall?
Leonard Susskind
TL;DR
The paper proposes that gravity, and in particular the inward gravitational attraction toward black holes, can be understood as a quantum-information effect: the universal growth of operator size (complexity) in chaotic quantum systems. By mapping radial momentum growth in the near-horizon geometry to the exponential growth of precursor size in the boundary theory, it shows the Lyapunov exponent saturates the MSS bound, linking Hawking-like acceleration to quantum chaos. It also discusses how stringy corrections can modulate the exponent and identifies regimes where the purely gravitational description remains valid. Overall, the work provides a concrete quantum-information perspective on gravity and black-hole dynamics, with implications for the GR=QM program and for understanding scrambling in holographic systems.
Abstract
This is the first of several short notes in which I will describe phenomena that illustrate GR=QM. In it I explain that the gravitational attraction that a black hole exerts on a nearby test object is a consequence of a fundamental law of quantum mechanics---the tendency for complexity to grow. It will also be shown that the Einstein bound on velocities is closely related to the quantum-chaos bound of Maldacena, Shenker, and Stanford.