Wrong. There could be tons of different things going on inside, absolutely indistinguishable from outside, which only sees mass, electric charge and angular momentum.
Nitpick: this is only true for a stationary black hole. If you throw something sufficiently big in, you would expect the shape of the horizon to change and bulge a bit, until it settles down into a stationary state for a larger black hole. You are of course correct that this does not allow anything inside to send a signal to the outside.
Nitpick: this is only true for a stationary black hole.
Right, I didn’t want to go into these details, MrMind seems confused enough as it is. I’d have to explain that the horizon shape is only determined by what falls in, and eventually talk about apparent and dynamical horizons and marginally outer trapped surfaces…
Nitpick: this is only true for a stationary black hole. If you throw something sufficiently big in, you would expect the shape of the horizon to change and bulge a bit, until it settles down into a stationary state for a larger black hole. You are of course correct that this does not allow anything inside to send a signal to the outside.
Right, I didn’t want to go into these details, MrMind seems confused enough as it is. I’d have to explain that the horizon shape is only determined by what falls in, and eventually talk about apparent and dynamical horizons and marginally outer trapped surfaces…