Matter, in formulas concerning general relativity and cosmology, it is considered as anything that contributes to the energy–momentum of a system, specifically, anything that is not purely gravity. In this view, light and other massless particles and fields are all part of "matter".
- ↑ S.M. Caroll (2004). Spacetime and Geometry. Addison Wesley. pp. 163–164. ISBN 0-8053-8732-3.
- ↑ P. Davies (1992). The New Physics: A Synthesis. Cambridge University Press. p. 499. ISBN 0-521-43831-4. https://books.google.com/?id=akb2FpZSGnMC&pg=PA499. "Matter fields: the fields whose quanta describe the elementary particles that make up the material content of the Universe (as opposed to the gravitons and their supersymmetric partners)."