Quantum Electrodynamics

Quantum Electrodynamics :
The subfield of physics that explains the interaction of charged particles and light is
called quantum electrodynamics. Quantum electrodynamics (QED) extends quantum
theory to fields of force, starting with electromagnetic fields.
Under QED, charged particles interact by the exchange of virtual photons, photons
that do not exist outside of the interaction and only serve as carriers of
momentum/force.

Notice the elimination of action at a distance, the interaction is due to direct contact of
the photons.
In the 1960's, a formulation of QED led to the unification of the theories of weak and
electromagnetic interactions. This new force, called electroweak, occurs at extremely
high temperatures such as those found in the early Universe and reproduced in particle
accerlators. Unification means that the weak and electromagnetic forces become
symmetric at this point, they behave as if they were one force.
Electroweak unification gave rise to the belief that the weak, electromagnetic and
strong forces can be unified into what is called the Standard Model of matter.
Quantum Chromodynamics:
Quantum chromodynamics is the subfield of physics that describes the strong or
``color'' force that binds quarks together to form baryons and mesons, and results in
the complicated the force that binds atomic nuclei together.

The strong force overcomes the electromagnetic or gravitational forces only on very
short range. Outside the nucleus the effect of the strong force is non-existent.