Light as a fundamental particle

We take it pretty much for granted that the whole visible world of matter and radiation can be explained, if not in fact at least in principle, in terms of the interactions of a handful of so‐called “elementary particles”: the electron; the proton; the neutron; the quantum of light, the photon; the quantum of gravitational radiation, the graviton, and perhaps also the neutrino. We would like to know why these particles have the properties they have, and therefore why the world is the way it is. Or, if you do not believe that scientists should ask “why,” you can restate the question in this form: What we want to know is the set of simple principles from which the properties of these particles, and hence everything else, can be deduced.

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