Standard Model
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The Standard Model of physics is the best idea to say how fundamental forces and elementary particles work. It uses quantum mechanics and special relativity. In physics there are many different particles and forces, the Standard Model says that all particles and forces are only two different types: fermions and bosons.
[edit] Fermions
Fermions are the "matter" particles. They are the particles that join together to make up everything we see. Examples of fermions are the proton and the neutron. Fermions have a number of properties including charge and mass which can be seen in everyday life. They also have other properties such as spin, weak charge, hypercharge and colour charge. These other properties do not usually appear in everyday life. In physics all these properties are given numbers called quantum numbers.
Fermions are particles with spin numbers that are "half-integers" or 1/2, 3/2, 5/2, etc. They are named after a man called Enrico Fermi, who was a famous physicist
Fermions are special because you cannot put two of them in the same place at the same time. This is because the Pauli exclusion principle says that no two fermions can have the same quantum numbers, such as spin numbers, at the same time. Fermions obey Fermi-Dirac statistics. This is different to photons, where you can have many in the same place at the same time.
Most well known fermions have spin of 1/2. Fermions with spin 1/2 are called Leptons. The electron is the best known lepton.
Fermions are either quarks or leptons. There are 12 different types of fermions. The 12 types are called flavors, these are their names:
- Quarks — up, down, strange, charm, bottom, top
- Leptons — electron, muon, tau, electron neutrino, muon neutrino, tau neutrino
Quarks obey physics called Quantum Chromodynamics or QCD which tells how the colour force works. The color force holds the quarks together so that a quark cannot be alone. Leptons do not have color and so they can be alone.
[edit] Bosons
Bosons are the second type of elementary particle in the Standard Model. All bosons have an integer spin (1, 2, 3, etc..) so many of them can be in the same place at the same time. Bosons are what make forces. Every force that acts on fermions is because a bosons are moving between the fermions, carrying the force. An example of a boson is the gluon. Gluons carry the strong force between quarks in a proton.
All of the forces in nature are explained by the four fundamental forces. These four forces are carried by bosons:
- Strong force:
- Weak force:
- The weak force is carried by three different bosons W+, W-, and the Z boson. This force can change the flavor of a fermion and causes beta decay.
- Gravity:
- Gravity is carried by a particle called the graviton. This particle has not yet been found but physicists think it is real and are looking for it.
- Electromagnetic force:
- The electromagnetic force is carried by the photon. This force explains everything to do with electricity and magnetism, light and other electromagnetic waves.
