Tag: QED
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Ward–Takahashi Identity
Introduction The Ward–Takahashi Identity, named after physicists J.C. Ward and Y. Takahashi, is a key result in quantum electrodynamics (QED) and quantum field theory (QFT). It ensures the conservation of electric charge in QED, and more generally, the conservation of current in QFT. Statement of the Ward–Takahashi Identity Identity The Ward-Takahashi identity can be written…
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Casimir-Polder Force
Introduction The Casimir-Polder force is a physical force arising from quantum fluctuations of the electromagnetic field in vacuum. It was first described by Dutch physicists Hendrik Casimir and Dirk Polder in 1948, who were investigating the interactions between molecules and a dielectric body. Quantum Electrodynamics and Vacuum Fluctuations Quantum electrodynamics (QED) tells us that even…
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Quantum Electrodynamics (QED)
Introduction Quantum Electrodynamics (QED) is a quantum field theory that describes how light and matter interact. It is the first theory where full agreement between quantum mechanics and special relativity is achieved. QED mathematically describes all phenomena involving electrically charged particles interacting by means of exchange of photons and represents the quantum counterpart of classical…
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Quantum Field Theory (QFT)
Introduction Quantum Field Theory (QFT) is a theoretical framework that combines the principles of quantum mechanics and special relativity to describe the behavior of quantum particles and fields. It is the basis for our understanding of elementary particle physics, and it underpins the standard model of particle physics. Basics of Quantum Fields In QFT, particles…