Dirac particles which behave like massless relativistic fermions have been observed in 3D topological insulators. It is hypothesized that gravitation is mediated by a massless spin-2 particle called the graviton. Even without transfer, graphene on SiC exhibits massless Dirac fermions. Such a theory, for idealized massless quarks, has global chiral flavor symmetry. Technicolor avoids this problem by hypothesizing a new gauge interaction coupled to new massless fermions. The Standard Model of particle physics assumed that neutrinos are massless. Photon energy and gluon energy are also carried by massless particles. Free, massless quantized scalar field theory has no coupling parameters. The massless photon mediates the electromagnetic interaction. The above discussion is valid for massless neutrinos, which are always relativistic. Neutrinos were originally thought to be massless. Current commonly accepted physical theories imply or assume the photon to be strictly massless. This behavior is a direct result of graphene's massless Dirac electrons. The behavior of massless particles is understood by virtue of special relativity. Tension forces can be modeled using ideal strings that are massless, frictionless, unbreakable, and unstretchable.