Final answer:
Physicists are searching for the theory of Quantum Gravity to understand quantum mechanics in black holes, which aims to unify quantum mechanics with General Relativity and may be approached through Superstring theory.
Step-by-step explanation:
The theory physicists are seeking that would help them understand quantum mechanics in black holes is Quantum Gravity. Physicists are attempting to reconcile the principles of quantum mechanics with Einstein's theory of General Relativity through this theory.
While quantum mechanics provides probabilities for the behavior of particles, general relativity predicts exact outcomes. The future of quantum gravity revolves around the concept of Superstring theory or String theory, which aims to unify all four fundamental forces and provide a comprehensive theory often referred to as the Theory of Everything (TOE).