The Direction of Time

Zack Savitsky

Frank Arntzenius

The frequencies with which photons pass through half-silvered mirrors in the forward direction of time is always approximately 1/2, whereas the frequencies with which photons pass through mirrors in the backward direction in time can be highly time-dependent. I argue that whether one should infer from this time-asymmetric phenomenon that time has an objective direction will depend on one's interpretation of quantum mechanics.

Ruth E. Kastner, Daniel P. Sheehan

Cristian López

Two views on the direction of time can be distinguished-primitivism and non-primitivism. According to the former, time's direction is an in-built, fundamental property of the physical world. According to the latter, time's direction is a derivative property of a fundamentally directionless reality. In the literature, non-primitivism has been widely supported since most (if not all) our fundamental dynamical laws are time-reversal invariant. In this paper, I offer a way out to the primitivist. I argue that we do have good grounds to support a primitive direction of time in the quantum realm. The rationale depends on exploiting the metaphysical and dynamical underdetermination of quantum theories to make a case in favor of primitivism. In particular, primitivism can be grounded in spontaneous collapse theories (e.g., GRW and CSL). The specific sense in which these theories capture a primitive direction of time is that, when the ontology of the theory is seriously taken into account, it does not remain invariant under time reversal. In taking GRW with a matter-density field (GRWm), I will argue that primitivism about the direction of time can be defended in the quantum case.

K. Tamvakis

Jincheng Zhang

This paper proposes a novel mechanism, the Time Direction Generation Mechanism (TDGM), to address the fundamental question of why time appears to flow in one direction only. The prevailing view, rooted in entropy maximization, posits that the second law of thermodynamics dictates the time arrow. However, TDGM argues that this interpretation is incomplete and potentially misleading. Instead, the directionality of time emerges from a deeper, more fundamental process within quantum thermal physics, specifically related to the generation of initial conditions and the inherent asymmetry in quantum measurement. The core concept involves the identification of a measurable quantity, denoted as [At], which represents the fundamental mechanism responsible for generating the temporal direction. This mechanism isn't driven by entropy production but by an underlying process of state preparation and initial condition selection. The paper outlines the theoretical framework, explores the implications for our understanding of time, and highlights the potential for this concept to contribute significantly to the Nobel Prize-winning research in physics. ---