Physicists are indeed searching for a "Theory of Everything" (TOE) to unify general relativity and quantum mechanics. While both general relativity and quantum mechanics are highly successful theories in their respective domains, they have different frameworks and describe the universe at different scales.
General relativity provides a framework for understanding gravity and the behavior of large-scale objects, such as planets, galaxies, and the overall structure of the universe. It describes gravity as the curvature of spacetime caused by mass and energy. However, at extremely small scales, such as those encountered in subatomic particles, the effects of quantum mechanics become significant.
Quantum mechanics, on the other hand, describes the behavior of particles at the microscopic level and provides a framework for understanding the fundamental forces and particles of nature. It introduces concepts like wave-particle duality and quantized energy levels. Quantum mechanics is incredibly successful in describing phenomena at the quantum scale, but it doesn't include gravity in its framework.
The challenge arises when attempting to reconcile these two theories because they employ different mathematical formalisms and have inherent incompatibilities. At extremely small scales, where quantum effects dominate, the effects of gravity become important, and a consistent framework that incorporates both theories is currently lacking. A theory of everything aims to provide a unified framework that encompasses both quantum mechanics and general relativity, allowing for a consistent description of the universe at all scales.
By finding a theory of everything, physicists hope to resolve the current inconsistencies and unanswered questions in our understanding of the fundamental laws of nature. This includes explaining the behavior of black holes, understanding the nature of dark matter and dark energy, and providing a more complete understanding of the early moments of the universe, among other fundamental questions.