Concerning quantum mechanics, a black hole is both very heavy and very light. How can that be? Well, quantum mechanics, which explains much of what happens in space, wasn't a complete explanation. There is also the factor of gravity. So, while quantum mechanics is one part of a black hole, quantum gravity is another part, and together black holes are more thoroughly described. But these are not simple concepts, even for physicist and futurist Michio Kaku who finds the conundrum to be one that is a "nightmare beyond comprehension. Understanding the behavior of black holes is part of many ongoing research studies, but without an explanation how relativity and gravity are at play in the singularity of a black hole, those studies cannot go very far.
It begins with Einstein's theory of relativity, which has to be tweaked a bit to explain the quantum forces. When Kaku tried to combine and calculate the theory of quantum gravity by using the E=MC2 equation, he got a result that made no sense to him, and that is saying something. Quantum mechanics and relativity are not mathematically compatible. Kaku continues to work on the problem, but since black holes exist, he concludes that while physics hasn't figured out the reasoning, nature is "smarter than we are."
