Massive Particle - Bradyons

Bradyons

A bradyon, also known as a tardyon or ittyon, is a particle that travels slower than light. The term "bradyon", from Greek: βραδύς (bradys, “slow”), was coined to contrast with "tachyon", from Greek: ταχύς (tachys, “swift, quick, fast, rapid”), which refers to hypothetical particles that travel faster than light.

As predicted by relativity, since baryons travel slower than light, they can also be defined as particles that have a non-zero rest mass. However, if tachyons exist, then not all massive particles are bradyons, since tachyons are also massive, but with an imaginary rest mass (see Tachyon).