QED stands for Quantum Electrodynamics, and it is a quantum field theory that describes the electromagnetic interactions of elementary particles. It is one of the most successful and well-tested theories in physics and is a fundamental component of the Standard Model, which is the current theoretical framework for particle physics.
QED combines quantum mechanics, which describes the behavior of particles at the microscopic level, and electromagnetism, which encompasses the interaction of electrically charged particles and electromagnetic fields. The theory was developed independently by Richard Feynman, Julian Schwinger, and Sin-Itiro Tomonaga in the 1940s and received a Nobel Prize in Physics in 1965.
In QED, electromagnetic interactions are mediated by virtual particles called photons. Charged particles, such as electrons and positrons, interact by emitting and absorbing photons, which act as carriers of the electromagnetic force. These interactions are described mathematically through Feynman diagrams, which represent the possible particle interactions and their probabilities.
QED successfully explains a wide range of phenomena, including the behavior of electrons in atoms, the scattering of particles in particle accelerators, and the emission and absorption of light. It provides precise calculations and predictions that have been experimentally verified with remarkable accuracy.
One of the significant achievements of QED is the calculation of the anomalous magnetic moment of the electron, which has been measured experimentally with great precision, confirming the theory's predictions to an extraordinary degree.
Although QED specifically deals with electromagnetic interactions, it serves as a prototype for quantum field theories that describe other fundamental forces, such as the weak and strong nuclear forces. These other forces are described by similar theories within the framework of the Standard Model, extending the principles and mathematical techniques established in QED.
In summary, QED is a quantum field theory that mathematically describes the electromagnetic interactions of elementary particles, and it has played a crucial role in our understanding of particle physics and the behavior of matter and light at the fundamental level.