Editing Quantum mechanics (section)

=== Equivalence between formulations ===
There are many mathematically equivalent formulations of quantum mechanics. One of the oldest and most common is the "[[transformation theory (quantum mechanics)|transformation theory]]" proposed by [[Paul Dirac]], which unifies and generalizes the two earliest formulations of quantum mechanics&nbsp;– [[matrix mechanics]] (invented by [[Werner Heisenberg]]) and wave mechanics (invented by [[Erwin Schrödinger]]).<ref>{{cite journal |last=Rechenberg |first=Helmut |author-link=Helmut Rechenberg |year=1987 |title=Erwin Schrödinger and the creation of wave mechanics |url=http://www.actaphys.uj.edu.pl/fulltext?series=Reg&vol=19&page=683 |format=PDF |journal=[[Acta Physica Polonica B]] |volume=19 |issue=8 |pages=683–695 |access-date=13 June 2016}}</ref> An alternative formulation of quantum mechanics is [[Feynman]]'s [[path integral formulation]], in which a quantum-mechanical amplitude is considered as a sum over all possible classical and non-classical paths between the initial and final states. This is the quantum-mechanical counterpart of the [[action principle]] in classical mechanics.<ref>{{cite book |first1=Richard P. |last1=Feynman |first2=Albert R. |last2=Hibbs |title=Quantum Mechanics and Path Integrals |edition=Emended |editor-first=Daniel F. |editor-last=Steyer |year=2005 |publisher=McGraw-Hill |isbn=978-0-486-47722-0 |pages=v–vii}}</ref>