Force carrier

In the study of quantum field theory, a force carrier is a specific type of particle. These particles are responsible for creating forces between other particles. You might also hear them called messenger particles, exchange particles, or intermediate particles. They are actually the quanta of a physical field. A quantum is a discrete unit of energy within that field.

Without these carriers, particles would not be able to interact with one another.

Scientists use two different viewpoints to describe how these forces happen. The first is the field picture. In this view, one particle generates a field that acts upon another particle. The second is the particle viewpoint. This view imagines one particle emitting a virtual particle. This virtual particle is then absorbed by the second particle. During this exchange, the virtual particle transfers momentum from one particle to the other.

This particle view is very helpful for complex math. Scientists use Feynman diagrams to visualize these paths and quantum corrections.

We can find several different types of force carriers within the Standard Model. Each one is an excitation of a specific force field. Gluons are the excitations of the strong gauge field. Photons, W bosons, and Z bosons are excitations of the electroweak gauge fields. The Higgs boson is also a carrier. It is an excitation of the Higgs field. This specific field is what gives mass to fundamental particles.

There are also composite particles like mesons that act as excitations of an effective field.

Gravity is a unique case in our current understanding of physics. Gravity is not currently a part of the Standard Model. However, scientists believe there may be particles called gravitons. These would be the excitations of gravitational waves. The status of the graviton is still considered tentative. This is because our current theory of gravity is incomplete. Additionally, the interactions of single gravitons might be too weak to detect.

The history of these messenger particles spans several centuries. In the 18th century, Charles Coulomb studied electrostatic forces. He showed these forces follow a law similar to Newton's Law of Gravitation. This relationship became known as Coulomb's law. Later, in 1862, Hermann von Helmholtz described a ray of light as the quickest messenger. These early ideas paved the way for modern quantum physics.

In 1905, Albert Einstein proposed that light was made of particles. He did this to answer the question regarding light quanta. In 1923, Arthur Holly Compton provided proof for this idea. During his experiments at Washington University in St. Louis, he demonstrated Compton scattering. This effect can only be explained if light behaves like a stream of particles. Finally, in 1926, Gilbert N. Lewis introduced the term "photon." This name was given to the light particle Einstein had proposed.

We can see these particles in action during processes like beta decay. In beta decay, a nucleon emits a virtual W boson. This W boson then decays into an electron or positron and an antineutrino. This process demonstrates how virtual particles move and change. The description of these forces using virtual particles relies on perturbation theory. However, this theory can break down in certain situations. For example, it fails in low-energy QCD and when describing bound states.