Editing Propagator (section)

{{Short description|Function in quantum field theory showing probability amplitudes of moving particles}}
{{about|time evolution in [[quantum field theory]]|propagation of plants|Plant propagation}}
{{Use American English|date=January 2019}}{{Quantum field theory}}
In [[quantum mechanics]] and [[quantum field theory]], the '''propagator''' is a function that specifies the [[probability amplitude]] for a particle to travel from one place to another in a given period of time, or to travel with a certain energy and momentum. In [[Feynman diagram]]s, which serve to calculate the rate of collisions in [[quantum field theory]], [[virtual particle]]s contribute their propagator to the rate of the [[scattering]] event described by the respective diagram. Propagators may also be viewed as the [[inverse operation|inverse]] of the [[wave operator]] appropriate to the particle, and are, therefore, often called ''(causal) [[Green's function (many-body theory)|Green's functions]]'' (called "''causal''" to distinguish it from the elliptic Laplacian Green's function).<ref>[http://www.mathtube.org/sites/default/files/lecture-notes/Lamoureux_Michael.pdf The mathematics of PDEs and the wave equation], p 32., Michael P. Lamoureux, University of Calgary, Seismic Imaging Summer School,  August 7–11, 2006, Calgary.</ref><ref>[http://www.roe.ac.uk/japwww/teaching/fourier/fourier_lectures_part4.pdf Ch.: 9 Green's functions], p 6., J Peacock, FOURIER ANALYSIS LECTURE COURSE: LECTURE 15.</ref>