I find that Minds (https://www.minds.com/?referrer=undisciplined) is even better for discussions that aren't specifically about Bitcoin or economics (for the time being).
Here are some quick thoughts:
It has to be possible to reconcile quantum mechanics and general relativity, although it might require fundamental changes to both theories.
Nothing particularly special happens at event horizons, in the sense that if you crossed an event horizon you wouldn't notice.
Black holes form when a concentration of mass is great enough for gravity to overwhelm the electromagnetic and strong nuclear forces that maintain separation between particles.
There pretty much have to be undiscovered particles or forces, because the ones we have discovered are insufficient to explain the universe we observe.