For many decades, many theoretical physicists have been trying to unify quantum mechanics and general relativity to develop a unified theory. Quantum mechanics deals with quantum scales. These scales are so small that a human being cannot experience any event taking place in the quantum realm. General relativity is used to study large-scale structures. The theory includes propositions like that mass is derived from energy and gravity is defined by the curvature of space-time. Quantum mechanics and GR work on different scales with different mathematical frameworks. 

Several theories have been proposed, including emergent gravity, loop quantum gravity, and string theory. String theory proposes that the fundamental particles are nothing but tiny strings vibrating in higher dimensions. Loop quantum gravity introduces an approach where space-time is quantized and is a way to understand the quantum nature of gravity. The Emergent Theory summarizes gravity as a quantum field rather than a force. 

The unification of quantum mechanics and general relativity would change the course of physics and unravel many mysteries about the universe. However, one should note that, with current technology, it is not possible to find scientific evidence for the above-proposed theories via experiments.