system
Given the following post, respond as if you're commenting on Reddit:
human
In a rotating black hole, what is rotating?

Just something that crossed my mind recently, since the horizon isn't made up of anything. What is the rotating. Or is it just a way to allow for the conservation of angular momentum without having to go inside the BH with our current understanding?
gpt
The black hole has angular momentum, it may not make sense to speak of anything rotating (at least in a model where you have a 0d point or 1d ring singularity), just like you don't think of electrons as rotating because they have spin.