Ideally, a theory of quantum gravity should be able to describe all gravitational phenomena existing in our reality, including those not foreseen by general relativity. General relativity has been highly successful in describing gravity on macroscopic scales, such as the motion of planets and galaxies, and its predictions have been confirmed by numerous experimental tests. However, there are still open questions and phenomena that lie beyond the scope of general relativity, such as the behavior of gravity at the Planck scale and the nature of singularities.
Quantum gravity seeks to extend our understanding of gravity to the quantum realm, where the effects of gravity become significant on extremely small scales. At these scales, quantum fluctuations of spacetime and matter are expected to play a fundamental role. Therefore, a theory of quantum gravity should be capable of incorporating both quantum mechanics and the curved geometry of spacetime, enabling a consistent description of gravity on all scales.
By successfully unifying quantum mechanics and general relativity, a theory of quantum gravity would ideally provide a framework for understanding phenomena that have eluded our current theories. This could include the behavior of spacetime near black hole singularities, the physics of the early universe, and the quantum behavior of gravity itself.
However, it's important to note that the specific predictions and phenomena that a theory of quantum gravity would encompass are still highly speculative since such a theory has not yet been fully developed or experimentally confirmed. Different approaches to quantum gravity may have distinct features and make different predictions about gravitational phenomena. Ultimately, the true nature of quantum gravity and its ability to describe all gravitational phenomena in our reality remain open questions that continue to be explored by researchers in the field.