# QUANTUM ELECTRODYNAMICS (QED)

“The probability of an event is always represented by a single final arrow-no matter how many arrows were drawn, multiplied, and added to achieve it.”

-Richard Feynman

**OVERVIEW-**

Quantum Electrodynamics (QED), is a quantum field theory of the electromagnetic force. It is a relativistic quantum field theory that describes the electromagnetic interactions between elementary particles such as quarks and photons at the fundamental level.

QED was born when as an interpretation of Schrödinger’s wave equation which incorporated quantum mechanics and the theory of special relativity. According to the relativistic description of an electron in quantum mechanics, it must possess an antiparticle (Same mass but opposing electric and magnetic properties) partner, known as the positron.

What makes quantum electrodynamics special is that even though so much of quantum theory is incomplete and unknown, QED is in fact, a complete theory. In QED, instead of viewing electromagnetic fields as fields that originally possess electric and magnetic charges, it is taken that charged particles such as photons, electrons, and positrons transmit these charges to one another. However, they cannot be directly observed as it would violate the law of conservation of energy.

## H**ISTORY/TIMELINE-**

The development of quantum electrodynamics largely follows that of quantum mechanics. This is because as quantum mechanics was being refined, there were attempts from various scientists to apply it to certain existing fields in science. It was successfully applied to electromagnetic fields and thus, quantum electrodynamics was born.

1924- Born, Heisenberg, and Pascual Jordan attempted to apply the concepts of quantum mechanics to electromagnetic fields.

1928- Dirac lays the foundation for quantum electrodynamics. By applying the concepts of quantum mechanics to fields rather than singular particles. This allowed him to theorize how an electromagnetic field is quantized.

Late 1940s- Scientists Richard Feynman, Julian Schwinger, and Tomonaga Shin’ichorō (No typos, that’s the proper spelling), fully developed QED into a full-fledged theory.

**PROPERTIES-**

1) Quantization- Paul Dirac quantized electromagnetic fields as a part of quantum field theory.

2) Fundamental Particles- As QED is a part of quantum field theory. As fundamental particles are the constituents of a field in quantum theory, particles such as photons and electrons are the building blocks of QED.

3) Perturbation Theory- It is a set of approximation schemes directly related to mathematical perturbation for describing a complicated quantum system in terms of a simpler one.

4) Renormalization- It is a collection of techniques in quantum field theory, the statistical mechanics of fields, and the theory of self-similar geometric structures, that are used to treat infinities arising in calculated quantities by altering values of quantities to compensate for effects of their self-interactions.

**APPLICATIONS-**

1) Quantum Modelling- It can help provide accurate models of quantum phenomena with no classical analogs, such as the anomalous magnetic moment of an electron.

2) Laser Physics- QED theory can describe the interactions between a laser and a molecule, which is substantially used in the laser industry.

**CONCLUSION-**

Quantum Electrodynamics in itself is a significant theory, being the first complete theory to draw connections between classical and quantum physics. It gives us the first idea of what a complete quantum field theory looks like, paving the way for other field theories such as quantum chromodynamics. While QED is still being better understood, it already has some uses in the real world. With progress in research and development, it will eventually become a vital part of engineering changing the way we view electricity and magnetism for the better.

**GLOSSARY-**

1) Quantum Field Theory (QFT)- It is the mathematical and conceptual framework for contemporary elementary particle physics.

2) Quantum Chromodynamics (QCD)- It is the theory of the strong interaction between quarks and gluons, the fundamental particles that make up composite hadrons such as the proton, neutron, and pion.

**BIBLIOGRAPHY-**

https://science.jrank.org/pages/5604/Quantum-Electrodynamics-QED.html

http://abyss.uoregon.edu/~js/ast123/lectures/lec07.html

https://www.britannica.com/science/quantum-electrodynamics-physics