Can we observe fuzzballs or firewalls?

TL;DR

This paper investigates whether fuzzballs or firewalls can be observationally distinguished from traditional black holes, concluding that detecting differences is extremely challenging due to the nature of their surfaces and interactions.

Contribution

It provides a detailed analysis showing that observable signatures of fuzzballs or firewalls are minimal, especially under causality-respecting interactions, challenging the detectability of such objects.

Findings

Reflections off fuzzball surfaces are highly suppressed.

No evidence of firewall behavior in causality-respecting theories.

Large-wavelength photons can be scattered, but few escape back to infinity.

Abstract

In the fuzzball paradigm the information paradox is resolved because the black hole is replaced by an object with no horizon. One may therefore ask if observations can distinguish a traditional hole from a fuzzball. We find: (a) It is very difficult to reflect quanta off the surface of a fuzzball, mainly because geodesics starting near the horizon radius cannot escape to infinity unless their starting direction is very close to radial. (b) If infalling particles interact with the emerging radiation before they are engulfed by the horizon, then we say that we have a `firewall behavior'. We consider several types of interactions, but find no evidence for firewall behavior in any theory that obeys causality. (c) Photons with wavelengths {\it larger} than the black hole radius can be scattered off the emerging radiation, but a very small fraction of the backscattered photons will be able to escape back to infinity.