Editing Schrödinger equation (section)

=== Fock space ===
As originally formulated, the Dirac equation is an equation for a single quantum particle, just like the single-particle Schrödinger equation with wave function {{nowrap|<math>\Psi(x,t)</math>.}} This is of limited use in relativistic quantum mechanics, where particle number is not fixed. Heuristically, this complication can be motivated by noting that mass–energy equivalence implies material particles can be created from energy. A common way to address this in QFT is to introduce a Hilbert space where the basis states are labeled by particle number, a so-called [[Fock space]]. The Schrödinger equation can then be formulated for quantum states on this Hilbert space.<ref name="Coleman">{{Cite book|editor-last1=Derbes |editor-first1=David  |title=Lectures Of Sidney Coleman On Quantum Field Theory |editor-last2=Ting |editor-first2=Yuan-sen |editor-last3=Chen |editor-first3=Bryan Gin-ge |editor-last4=Sohn |editor-first4=Richard |editor-last5=Griffiths |editor-first5=David |editor-last6=Hill |editor-first6=Brian |date=2018-11-08 |publisher=World Scientific Publishing |isbn=978-9-814-63253-9 |oclc=1057736838 |language=en |first=Sidney |last=Coleman |author-link=Sidney Coleman}}</ref> However, because the Schrödinger equation picks out a preferred time axis, the Lorentz invariance of the theory is no longer manifest, and accordingly, the theory is often formulated in other ways.<ref>{{Cite book|last=Srednicki|first=Mark Allen|url=https://www.worldcat.org/oclc/71808151|title=Quantum Field Theory|publisher=Cambridge University Press|year=2012|isbn=978-0-521-86449-7|location=Cambridge|oclc=71808151}}</ref>