Massless particles, such as photons, gravitons, and gluons, are confirmed to travel at the speed of light (c). Gravitons, which are theoretical and yet to be discovered, are also expected to be massless and travel at c. Gluons, while massless, primarily exist within atomic nuclei and do not travel freely in the same manner as photons. It is important to distinguish between "rest mass" and "invariant mass," as photons possess energy but no rest mass.
PREREQUISITESPhysicists, students of particle physics, and anyone interested in the fundamental properties of massless particles and their implications in modern physics.