human
I have a question about Einstein's theory of gravity. Where does the mass of an object come from?
assistant
The mass of an object is determined by its energy content. In general relativity, the mass of an object is determined by its energy-momentum tensor. The energy-momentum tensor is a measure of the energy and momentum of an object. The energy-momentum tensor is a 4-vector, which means that it has four components. The components of the energy-momentum tensor are the energy density, the pressure, the stress, and the momentum density.