Force carrier

Gravity is not a part of the Standard Model, but it is thought that there may be particles called gravitons which are the excitations of gravitational waves.

The description of forces in terms of virtual particles is limited by the applicability of the perturbation theory from which it is derived.

This effect is only explainable if light can behave as a stream of particles, and it convinced the physics community of the existence of Einstein's light-particle.

Lastly, in 1926, one year before the theory of quantum mechanics was published, Gilbert N. Lewis introduced the term "photon", which soon became the name for Einstein's light particle.

[6] From there, the concept of messenger particles developed further, notably to massive force carriers (e.g. for the Yukawa potential).