[1] Twentieth century experiments showed that the physical description of microscopic and submicroscopic objects moving at or near the speed of light raised questions about such fundamental concepts as space, time, mass, and energy.
A resurgence of interest in evolution parameter theories began in the 1970s with the work of Horwitz and Piron,[11] and Fanchi and Collins.
The development of non-relativistic quantum mechanics in the early twentieth century preserved the Newtonian concept of time in the Schrödinger equation.
From the perspective of Hypothesis I, time must be both an irreversible arrow tied to entropy and a reversible coordinate in the Einsteinian sense.
The problems associated with the standard formulation of relativistic quantum mechanics provide a clue to the validity of Hypothesis I.
These problems included negative probabilities, hole theory, the Klein paradox, non-covariant expectation values, and so forth.
[17][18][19][20][21][22] Relativistic Dynamics is based on Hypothesis II and employs two temporal variables: a coordinate time, and an evolution parameter.