Originally Posted by
auctiongroup
At present, one of the deepest problems in theoretical physics is harmonizing the theory of general relativity, which describes gravitation and applies to large-scale structures (stars, planets, galaxies), with quantum mechanics, which describes the other three fundamental forces acting on the microscopic scale. This problem must be put in the proper context, however. In particular, contrary to the popular but erroneous claim that quantum mechanics and general relativity are fundamentally incompatible, one can in fact demonstrate that the structure of general relativity essentially follows inevitably from the quantum mechanics of interacting spin-2 massless particles (called gravitons). Furthermore, recent work has shown that by treating general relativity as an effective field theory, one can actually make legitimate predictions for quantum gravity, at least for low-energy phenomena. An example is the well-known calculation of the tiny first-order quantum-mechanical correction to the classical Newtonian gravitational potential between two masses. Such predictions would need to be replicated by any candidate theory of high-energy quantum gravity.