Suppression of Trapped Surface Formation by Quantum Gravitational Effects

by Ramy Brustein

BGU

at Particles and Fields Seminar

Mon, 29 Dec 2025, 14:00
Sacta-Rashi Building for Physics (54), room 207

Abstract

Classical general relativity predicts that a collapsing, spherically symmetric matter will result in the formation of a trapped region whose outer boundary is an apparent horizon where the gravitational redshift diverges. The incompleteness theorems of Penrose and Hawking then lead to the conclusion that the collapse results in the singular geometry of a Schwarzschild black hole. Both analyses rely on solving Einstein's Equations, which constitute a set of partial differential equations that are valid in the limit that the Schwarzschild radius is finite, setting the Planck length to zero. We keep the Planck length finite, allowing the geometry to fluctuate quantum mechanically, and take the limit of vanishing Planck length only at the end.

We show that the production of particles due to the motion of the shell is large even in the limit of vanishing Planck length. The total number of produced quanta of the gravitational field scales as the Bekenstein-Hawking entropy, while their total energy scales as the mass of the shell itself. Moreover, the quantum width of the would-be horizon scales as the shell's Schwarzschild radius. Furthermore, we show that the expansion parameter does not vanish, implying that an apparent horizon is not formed even when the shell has reached its gravitational radius. This provides the sought-after loophole needed to explain how astrophysical black holes could be compact objects that are completely regular and free of horizons.

Created on 28-12-2025 by Chapman, Shira (schapman)
Updaded on 28-12-2025 by Chapman, Shira (schapman)