So, what really makes up the universe?
What is the Standard Model?
The Standard Model of Particle Physics is a theory that describes the most basic building blocks of the universe. These building blocks, known as fundamental particles, cannot be broken down further. These fundamental particles include particles that make up all known matter in the universe and particles that explain three of the four fundamental forces that rule the universe: electromagnetism, the strong force, and the weak force.
Why is it important?
The Standard Model is the current best theory to explain the framework of the universe and has been thoroughly tested. It can combine all known subatomic particles into a singular precise model that can accurately predict a wide range of universal phenomena.
What does the model include?
The Standard Model of Particle Physics is composed of 17 fundamental particles, broken down into four categories: quarks, leptons, bosons, and the Higgs boson.
Quarks and Leptons
Quarks and Leptons (collectively known as fermions) are known as matter particles and make up every piece of matter. Each group consists of six particles, divided into pairs called “generations” based on their stability and weight.
Quarks
The up quarks and down quarks are the most common quarks that constitute normal matter and create protons and neutrons in atoms. Other quark pairs include the charm quark and strange quark, and the top quark and bottom quark, all of which are fairly rare, due to the fact they all quickly decay into up or down quarks. Due to the interactions between quarks, they can never be found in isolation, and are always in groups. Quarks are the only particles that can experience all four fundamental forces.
Leptons
Leptons can either be charged or neutral subatomic particles. Each generation pair of leptons always includes one charged particle and one neutral subatomic particle. The most common lepton is the electron, whose neutral pair is the neutrino. Other lepton pairs include the muon and muon neutrino, and the tau and tau neutrino, which are heavier than the electron. Unlike quarks, leptons cannot experience the strong force.
Bosons
Three of the fundamental forces (electromagnetism, the strong force, and the weak force) are a result of force-carrying particles, known as bosons. When bosons are exchanged between particles of mass, it causes these forces to occur. Each of the three fundamental forces has its corresponding boson: the electromagnetic force is carried by the photon, the strong force is carried by the gluon, and the weak force is carried by both the W and Z bosons.
Higgs Boson
The Higgs boson is the final piece of the Standard Model. Unlike the other force carrier bosons, the Higgs boson does not carry a “force,” but it does give mass to other particles through interaction. This mechanism, known as the Higgs mechanism, can occur due to the Higgs field, which spans the entire universe. When some particles interact with this field, which is made of Higgs bosons, it will generate mass. The Higgs boson answered a crucial question of how some particles have a mass but others do not.
Is the Standard Model the theory of everything?
While the Standard Model of Particle Physics is great, it is incomplete. The Standard Model fails to explain gravity, the last of the four fundamental forces. While the theory can stand without gravity at the subatomic level, gravity becomes important at extremely small and extremely large scales. Scientists have attempted to couple the Standard Model with Einstein’s theory of general relativity, but since both theories use different mathematics and framework, they are unable to work together. Furthermore, the Standard Model does not account for dark matter or dark energy, which composes the majority of the universe.
Future advances in physics may one day discover a way to merge gravity and the Standard Model, but for now, the Standard Model of Particle Physics is a perfectly acceptable theory of almost everything.
Thanks for reading!
Written by Kaylee Barrera
Sources:
Barberio, Elisabetta. “Explainer: What Are Leptons?” Phys.Org, 7 Jan. 2014, phys.org/news/2014-01-leptons.html.
Murayama, Hitoshi, and Kurt Riesselmann. “DOE Explains...the Standard Model of Particle Physics.” U.S Department of Energy, www.energy.gov/science/doe-explainsthe-standard-model-particle-physics. Accessed 6 July 2021.
“The Standard Model of Particle Physics.” Symmetry Magazine, www.symmetrymagazine.org/standard-model. Accessed 6 July 2021.
“The Standard Model.” CERN, 23 June 2021, home.cern/science/physics/standard-model.
Institute of Physics, www.iop.org/explore-physics/physics-stepping-stones/standard-model#gref. Accessed 6 July 2021.
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