A new study suggests that, due to the chaotic nature of quantum black holes, an observer falling towards the event horizon would take an infinite amount of proper time to reach it. This finding implies that the black hole interior is operationally inaccessible to any outside observer, marking a significant breakdown in the causal structure of black holes predicted by quantum gravity in the large N limit. The research addresses a fundamental question in quantum gravity regarding whether quantum effects introduce non-trivial structure near black hole horizons and if their interiors are emergent features of this limit.

To model the experience of an infalling observer, the researchers studied the response of a particle detector coupled to a matter field in a 2D quantum black hole background. The results showed a peak in the detector's excitation probability as it enters an infinitely long non-perturbative journey close to the black hole horizon. This chaotic nature of black holes is captured by random matrix statistics of their spectrum, reinforcing the idea that the region near the horizon possesses extreme quantum properties.

This work underscores the importance of considering quantum effects in the description of black holes, especially in the vicinity of their horizons. The operational inaccessibility of the black hole interior, as inferred from this model, has profound implications for our understanding of causality and spacetime structure in strong quantum gravity regimes. The findings suggest that the classical view of a horizon as a surface crossed in finite time might require a fundamental revision when quantum effects are incorporated.