What Is the Singularity Problem?

The singularity problem is that deep inside the black hole at the very center, the space time curvature becomes infinite and the density of Mathur also becomes infinite. Infinities are unphysical. So in the case of the fuzzball model, you have a bag of strings. No one knows exactly what inside is there. What would be inside a black hole? Right? And to do that, we will have to crack the puzzle of quantum gravity. We will have to reconcile Einstein's general relativity with quantum mechanics and quantum field theory. It's not been possible to do that yet.