Quantum electrodynamics (QED) is a well-tested theory explaining how charged particles interact through the exchange of photons. It is a gauge theory that explains electromagnetism and magnetism. QED is difficult to solve and has some theoretical imperfections, but it remains a comprehensive account of electromagnetism. The search continues for a theory that integrates all four forces of nature.
Quantum electrodynamics (QED) is the quantum field theory that explains how electrically charged particles interact with each other through the exchange of photons (the “quanta” of light, or small packets of light). Photons, and therefore interactions in a QED, propagate at the speed of light. QED is referred to as gauge theory, with a mathematically specified gauge field representing the electromagnetic force. The theory also explains magnetism, as magnetism and electricity are two manifestations of the same underlying force, electromagnetism.
QED theory is one of the most well-tested theories on Earth, sometimes giving results accurate to ten decimal places, and was the first quantum field theory to be claimed to be consistent and complete. A prediction made by QED was found to be accurate to 0038 parts per million, probably the most precise and accurate physical prediction ever made. Computing correct solutions for the behavior of systems with larger interacting parts or electronic orbitals becomes exponentially more difficult as the number of components increases, with some calculations requiring literally decades of work to calculate and verify.
Of the four forces of nature—electromagnetism, the weak nuclear force, the strong nuclear force, and gravity—electromagnetism is probably the easiest to explain rigorously, although it took decades of work by many hundreds of scientists to fully explain it. The theory was successfully developed in the late 1940s, thanks to the independent work of Sin-Itiro Tomonaga, Julian Schwinger and Richard Feynman. They received the Nobel Prize in Physics in 1965 for their efforts.
If electromagnetism were the only force of nature operating in the universe, QED would offer a comprehensive account of its exact nature. However, it is not, and the search continues for a quantum field theory that integrates all four forces. Furthermore, solving equations in QED is very difficult, more difficult than conventional quantum mechanical problems, since QED is a generalization of quantum mechanics to special relativity. The most famous images associated with QED are Richard Feynman’s Feynman diagrams, which use straight and wavy lines to analyze the different ways particles exchange photons to physically interact.
QED theory still produces mathematical infinities in certain contexts, and while many of these problems have been resolved, they persist to some degree. Ad hoc renormalization algorithms have been developed to smooth out these theoretical imperfections. These infinities suggest that QED is by no means a definitive theory, leaving the future open to the discovery of a more accurate theory that sees electromagnetism in the context of the other three forces of nature.
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