The quantum theory of time: a calculus for q-numbers

TL;DR

This paper develops a calculus for q-numbers in quantum theory, demonstrating that the traditional c-number time is unnecessary in the Heisenberg picture and that physical evolution can be described entirely through a quantum clock's q-number time.

Contribution

It reformulates the Page-Wootters timeless approach in the Heisenberg picture, establishing a calculus for q-number time and removing the need for c-number time in quantum dynamics.

Findings

C-number time is unnecessary in the Heisenberg picture.

A calculus for q-number time is developed based on the clock's algebra.

Physical system descriptors depend on the clock's q-number time.

Abstract

In quantum theory, physical systems are usually assumed to evolve relative to a c-number time. This c-number time is unphysical and has turned out to be unnecessary for explaining dynamics: in the timeless approach to quantum theory developed by Page & Wootters (1983), subsystems of a stationary universe can instead evolve relative to a 'clock', which is a quantum system with a q-number time observable. Page & Wootters formulated their construction in the Schr\"odinger picture and left open the possibility that the c-number time still plays an explanatory role in the Heisenberg picture. I formulate their construction in the Heisenberg picture and demonstrate that c-number time is completely unnecessary in that picture, too. When the Page-Wootters construction is formulated in the Heisenberg picture, the descriptors of physical systems are functions of the clock's q-number time, and derivatives with respect to this q-number time can be defined in terms of the clock's algebra of observables, resulting in a calculus for q-numbers.