ABSTRACT
This chapter aims to review ideas on the notion of mass in gravitation theories. The gravitation theory is a theory dealing with attraction of massive bodies. Gravity is a force that makes things move toward each other. In Newtonian physics objects are attracted through the gravitational force. In Einstein-Hilbert's general relativity gravitation is ascribed to space-time curvature instead of a force. In 1967, Sakharov suggested that gravitation might not be a fundamental interaction, but a purely quantum phenomenon that arises due to an interaction with vacuum energy. Basically quantum gravity is subdivided into two branches of practically independent studies: loop quantum gravity and string theory. The inertia and gravitation connection with the vacuum electromagnetic fields was called the quantum vacuum inertia hypothesis, which allowed them to derive the classical Newtonian gravitational force. The energy associated with the fluctuations, Zitterbewegung, is interpreted as the energy equivalent of gravitational rest mass.
