While the definition of quantum field theory is relatively simple, “the mathematical and conceptual framework for contemporary elementary particle physics” (Stanford Encyclopedia of Philosophy), the exciting yet intimidating field of quantum field theory is much more complex than just that. It is the most advanced idea in college theoretical physics, and it can be said to be “the extension of quantum mechanics, dealing with particles, over to fields” (Stanford Encyclopedia of Philosophy). It all comes down to quantum field theory, because it deals with the fields that are the rules for how the universe works. Every idea in physics can come back to quantum field theory. Quantum field theory includes the smaller fields of study of quantum electrodynamics, quantum chromodynamics, and electroweak interaction. Quantum field theory, while often described as the most daunting field of theoretical physics and one that most would not want to approach, can be an exciting study of the smallest particles that make the universe the way it is.
One of the sub-fields of quantum field theory is the study of quantum electrodynamics. This field of theoretical physics is often referred to as QED, and it describes the quantum field theory of an electromagnetic force. This field describes the interaction between electrons as “an exchange force arising from the exchange of virtual photons” (“Quantum Electrodynamics”) and uses Feynman diagrams to describe these interactions. Quantum electrodynamics describes all electromagnetic occurrences at the subatomic level that relate to charged fundamental particles such as electrons or positrons, including, but not limited to electron-positron annihilation, Compton scattering, and pair production. Such electromagnetic phenomena are each their own field of study, and are used to model quantum occurrences, including the Lamb shift. Quantum electrodynamics is often regarded as the first successful quantum field theory, and the development of the theory led to the 1965 Nobel Prize awarded to Richard Feynman, Julian Schwinger, and Sin-itero Tomonaga.
Another quantum field theory is called quantum chromodynamics, and is commonly referred to as QCD. It is defined as “the modern theory of the strong interaction” (“QCD Made Simple”). Quantum chromodynamics explores the interactions between protons and neutrons and their outcomes, as opposed to quantum electrodynamics, which explores subatomic levels of the same mass as an electron. Quantum chromodynamics describes photons and their interactions using two different types of particles: quarks are the matter particles, while gluons are the force particles (“Quantum Chromodynamics”). While quantum chromodynamics can be considered an extension of quantum electrodynamics, and can be slightly easier to understand, most theoretical physics students tend to delve into quantum electrodynamics first. There are six types of quarks with names that in no way relate to their properties: up, down, charm, strange, top, and bottom. Ordinary matter is composed of up and down quarks: protons are up up down, while neutrons are up down down. Delving deeper into quantum chromodynamics may prove it to be more complex than it appears on the surface; however, it is also an exciting and intriguing quantum field theory.
Once one understands quantum electrodynamics and quantum chromodynamics, it is easy to build upon that knowledge to explain electroweak interaction. Electroweak interaction unifies electromagnetism and the weak interaction. While these may seem to be separate entities, weak force particles – W+, W-, and two uncharged particles that mix at low energies – have electromagnetic charges, proving that quantum electrodynamics and weak forces are linked somehow (“Electroweak Unification and the Higgs”). The 1979 Nobel Prize awarded to Abdus Salam, Sheldon Lee Glashow, and Steven Weinberg for the prediction of intermediate vector bosons set the stage for groundbreaking discoveries in this quantum field theory, including the discovery of the W and Z particles in 1983, which made the prediction of Weinberg, Glashow, and Salam a reality (“Electroweak Unification”). The photon, coupled with the W and Z particles, provided the final piece in the unification of weak forces and electromagnetic particles, and thus, this quantum field theory was born.
The exciting and revolutionary quantum field theory includes but is not limited to, three sub-fields of the overall theory: quantum electrodynamics, quantum chromodynamics, and electroweak interaction. All three parts of the theory tie into each other and ultimately go into the bigger spectrum of the whole quantum field theory. What is fascinating about quantum field theory, however, is that it is the basis for string theory and ultimately, theoretical physics, because it explores the properties of particles at the smallest level possible. Not only that, but it can be seen as an offset of string theory, it being a much less general field of study than string theory. Quantum field theory, the essence and basis of theoretical physics, is a complex yet fascinating field of study of the smallest particles present in the universe.
Sources:
"Electroweak Unification." HyperPhysics - Quantum Physics. Georgia State University, n.d. Web.
"Electroweak Unification and the Higgs." Annenberg Learner. Annenberg Foundation, n.d. Web. 24 May 2016.
Kuhlmann, Meinard. "Quantum Field Theory." Stanford University. Stanford University, 22 June 2006. Web. 24 May 2016.
Wilczek, Frank. "QCD Made Simple." Phys. Today Physics Today 53.8 (2000): 22. Web.
"Quantum Chromodynamics." The Physics Hypertextbook. N.p., n.d. Web. 24 May 2016.
"Quantum Electrodynamics." HyperPhysics - Quantum Physics. Georgia State University, n.d. Web.
