Robert McNees
Paul Dirac's paper on quantum emission and absorption of radiation was submitted to the Royal Society #OTD in 1927. It advanced the first quantum mechanical theory of electrodynamics and is considered by many to mark the birth of ✨Quantum Field Theory✨
This thread is for the quantum gravity folks, and it does not lead where you expect.
https://royalsocietypublishing.org/doi/abs/10.1098/rspa.1927.0039
Robert McNees
Quantum Field Theory is, along with General Relativity, the most precise physics theory ever devised by humans. So this is a pretty momentous paper!
But even though this was the beginning of QFT, and in particular quantum electrodynamics, it was *not* the first attempt to quantize electromagnetic waves.
Born, Heisenberg, and Jordan made an attempt in their 1926 paper "Zur Quantenmechanik. II.”
Robert McNees
BHJ considered a field that depends on time and a single spatial direction x which runs from 0 < x < L. The field is set to zero at the ends, just like the boundary conditions you would use for the displacement of a string on a guitar or violin.
They expanded the field in Fourier modes, wrote the time-dependent coefficients of the modes as creation and annihilation operators, and imposed the usual commutation relations.
It was like they were quantizing the excitations of a string.
Robert McNees
In fact, they *were* quantizing the excitations of a string.
So technically, Dirac’s beautiful paper kickstarting Quantum Field Theory came one year after the introduction of the first two-dimensional string theory 😎
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