From the quantum principles, two very different types of fundamental particles are predicted, the fermions and the bosons, which however can be united and become interchangeable under the supersymmetry. The supersymmetry relates first time the internal symmetry of the particles to the symmetries of their spacetime. Consequently, any theory for the local supersymmetry necessarily includes the forces introduced by Einstein's General Relativity and hence we call the forces the supergravity. With the supergravity, the gravitino of spin 3/2 is predicted. In fact it is the simplest theory that can consistently couple a spin-3/2 fermion to the gravity. As the low-energy effective action of strings, the supergravity is an integral part of the string research.

Einstein gravity  /  supergravity  /  quantum mechanics  /  quantum gravity