In his paper, "Quantum mechanics, matter waves and moving clocks", Müller has suggested that "[The model] has also given rise to a fair amount of controversy. Within the broader context of quantum mechanics... this description has been abandoned, in part because it could not be used to derive a relativistic quantum theory, or explain spin. The descriptions that replaced the clock picture achieve these goals, but do not motivate the concepts used.... We shall construct a... description of matter waves as clocks. We will thus arrive at a space-time path integral that is equivalent to the Dirac equation. This derivation shows that De Broglie's matter wave theory naturally leads to particles with spin-1/2. It relates to Feynman's search for a formula for the amplitude of a path in 3+1 space and time dimensions which is equivalent to the Dirac equation. It yields a new intuitive interpretation of the propagation of a Dirac particle and reproduces all results of standard quantum mechanics, including those supposedly at odds with it. Thus, it illuminates the role of the gravitational redshift and the proper time in quantum mechanics."