Editing Yang–Mills theory (section)

=== Gauge theory in electrodynamics ===
All known fundamental interactions can be described in terms of gauge theories, but working this out took decades.<ref name=oraifearthagh>{{Cite journal |last1=O’Raifeartaigh |first1=Lochlainn |last2=Straumann |first2=Norbert |date=2000-01-01 |title=Gauge theory: Historical origins and some modern developments |url=https://link.aps.org/doi/10.1103/RevModPhys.72.1 |journal=Reviews of Modern Physics |language=en |volume=72 |issue=1 |pages=1–23 |doi=10.1103/RevModPhys.72.1 |issn=0034-6861|url-access=subscription }}</ref> [[Hermann Weyl]]'s pioneering work on this project started in 1915 when his colleague [[Emmy Noether]] proved that every conserved physical quantity has a matching symmetry, and culminated in 1928 when he published his book applying the geometrical theory of symmetry ([[group theory]]) to quantum mechanics.<ref name=Baggott40/>{{rp|194}} Weyl named the relevant symmetry in [[Noether's theorem]] the "gauge symmetry", by analogy to distance standardization in [[Track gauge|railroad gauges]].

[[Erwin Schrödinger]] in 1922, three years before working on his equation, connected Weyl's group concept to electron charge. Schrödinger showed that the group <math>U(1)</math> produced a phase shift <math>e^{i\theta}</math> in electromagnetic fields that matched the conservation of electric charge.<ref name=Baggott40/>{{rp|198}} As the theory of [[quantum electrodynamics]] developed in the 1930's and 1940's the <math>U(1)</math> group transformations played a central role. Many physicists thought there must be an analog for the dynamics of nucleons. 
[[Chen Ning Yang]] in particular was obsessed with this possibility.