Editing Quantum number (section)

===Connection to symmetry===
As quantum mechanics developed, abstraction increased and models based on symmetry and invariance played increasing roles. Two years before his work on the quantum wave equation, Schrödinger applied the symmetry ideas originated by [[Emmy Noether]] and [[Hermann Weyl]] to the electromagnetic field.<ref name=Baggott40>{{Cite book |last=Baggott |first=J. E. |title=The quantum story: a history in 40 moments |date=2013 |publisher=Oxford Univ. Press |isbn=978-0-19-956684-6 |edition=Impression: 3 |location=Oxford}}</ref>{{rp|198}} As [[quantum electrodynamics]] developed in the 1930s and 1940s, [[group theory]] became an important tool. By 1953 [[Chen Ning Yang]] had become obsessed with the idea that group theory could be applied to connect the conserved quantum numbers of nuclear collisions to symmetries in a field theory of nucleons.<ref name=Baggott40/>{{rp|202}} With [[Robert Mills (physicist)|Robert Mills]], Yang developed a [[non-abelian gauge theory]] based on the conservation of the nuclear [[isospin]] quantum numbers.