Quantum field theory, or QFT, is a generalization of quantum mechanics capable of describing relativistic particles. It is currently the standard mathematical formalism used in particle physics, as well as certain areas of condensed matter and atomic physics. In QFT, fields rather than particles are the fundamental objects. Particles correspond to vibrations of these fields. This formulation puts particles and forces on equal footing, as both are described by fields. An interaction between two particles, which are vibrations in the field that correspond to that type of particle, proceeds through the exchange of the particle that corresponds to a vibration in the field associated with the force. For example, electrons are vibrations of the electron field, and photons are vibrations of the electromagnetic field. When two electrons repel, they exchange photons.