In particle physics, a massless particle is a particle whose invariant mass is zero. Currently, the only known massless particles are gauge bosons: the photon (carrier of electromagnetism) and the gluon (carrier of the strong force). However, gluons are never observed as free particles, since they are confined within hadrons.
Neutrinos were, until recently, thought to be either massless or have a small mass. Because neutrinos change flavour as they travel, at least two of them must have mass.
Read more about Massless Particle: Massless Particle Description, Special Relativity, Dynamics, Gravitons
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“Experience is never limited, and it is never complete; it is an immense sensibility, a kind of huge spider-web of the finest silken threads suspended in the chamber of consciousness, and catching every air-borne particle in its tissue.”
—Henry James (1843–1916)