In this study, a new concept is introduced - gravitational cells. The body of a black hole consists of a huge number of such cells. This hypothesis from particle physics has been organically built into string theory. As a result of this addition, using the Schwarzschild radius formula and the Coulomb formula, a formula for the gravitational constant in the region of black holes was obtained on the basis of two fundamental constants. Its value has been determined, and the value of the usual gravitational constant has been confirmed. In this study, the mass of the gravitational cell of a black hole was obtained.

The introduction of the hypothesis of gravitational cells into string theory allowed us to apply Planck's formula to gravitational interaction. As a result, the formula for the quantum of the gravitational field was obtained, the frequency of vibrations of gravitational strings was determined. It was proved that the ratio of the energy of the gravitational quantum to the fourfold value of the Planck constant is directly proportional to the ratio of the masses of the electron and the proton inside the gravitational cell (inside the atom). On this basis, a formula for the mass of an electron was obtained on the basis of three fundamental constants. The electron mass calculated by the formula coincided with the known experimental value. Also, a formula was obtained for the dependence of the gravitational constant on Planck's constant, the magnitude of the mass of an electron and a proton, and calculations confirming this formula were made.