String theory
String conjectures that on the microscopic scale, Einstein's 4D spacetime is a field of Calabi-Yau manifolds, each containing 6 space dimensions curled up, thus not extended into the 3 space dimensions presented to the classical realm.  In string theory, each quantum particle is replaced by a 1D string of vibrating energy whose length is the Planck length.  As the string moves, it traces width, and thus becomes 2D, a worldsheet.  As a string vibrates and moves within the 6D Calabi-Yau space, the string becomes a quantum particle.  With this approach, the hypothetical graviton—predicted to explain general relativity—emerges easily.