Question: What is matter?


  1. Matter is anything that has mass and occupies space.

    It however gets a little more complicated. Contrary to the previous view that equates mass and matter, a major difficulty in defining matter consists in deciding what forms of energy (all of which have mass) are not matter. In general, massless particles such as photons and gluons are not considered forms of matter, even though when these particles are trapped in systems at rest, they contribute energy and mass to them. For example, almost 99% of the mass of ordinary atomic matter consists of mass associated with the energy contributed by the gluons and the kinetic energy of the quarks which make up nucleons. In this view, most of the mass of ordinary “matter” consists of mass which is not contributed by matter particles.