We don’t know, and may have no way of knowing. There are conjectures that the event horizon is it, that inside the event horizon is a quantum fuzz ball, or strings, or 1D points, or a whole universe. We don’t know, and may well never know. What we do know is that it seems a 2D horizon can encode the information required to describe a 3D volume, and that goes for event horizons, as well certain classes of cosmic horizons in some models. This weirdness is the core of the holographic principle conjecture.
Comments
We don’t know, and may have no way of knowing. There are conjectures that the event horizon is it, that inside the event horizon is a quantum fuzz ball, or strings, or 1D points, or a whole universe. We don’t know, and may well never know. What we do know is that it seems a 2D horizon can encode the information required to describe a 3D volume, and that goes for event horizons, as well certain classes of cosmic horizons in some models. This weirdness is the core of the holographic principle conjecture.