Evidence for Planck Luminosity Bound in Quantum Gravity

Recently, we introduced a non-perturbative quantization of impulsive gravitational null initial data. In this note, we investigate an immediate physical implication of the model. One of the quantum numbers is the total luminosity carried to infinity. We show that a transition happens when the luminosity reaches the Planck power ${\mathcal{L}}_{\mathrm{P}}$. Below ${\mathcal{L}}_{\mathrm{P}}$, the spectrum of the radiated power is discrete. Above the Planck power, the spectrum is continuous and contains caustics that can spoil the semi-classical interpretation of the resulting quantum states of geometry.