The formal time symmetry of the quantum measurement process is extensively discussed. Then, the origin of the alleged association between a fixed temporal direction and quantum measurements is investigated. It is shown that some features of such an association might arise from epistemological rather than purely physical assumptions. In particular, it is brought out that a sequence of statements bearing on quantum measurements may display intrinsic asymmetric properties, irrespective of the location of corresponding measurements in time t of the Schrödinger equation. The situation of an observer performing two measurements in two opposite directions of t is eventually investigated. Essential differences are found between two descriptions of this situation: the internal one (taking only into account what is recorded in the observer's memory) and the external one (whereby the observer is considered as a quantum system ruled by the Schrödinger equation). Finally, a method allowing several observers to establish a correspondence between their memory sizes is analyzed. The most important facts that usually lead to the associating of a preferential temporal direction with quantum measurements may be inferred from this correspondence.
The formal time symmetry of the quantum measurement process is extensively discussed. Then, the origin of the alleged association between a fixed temporal direction and quantum measurements is investigated. It is shown that some features of such an association might arise from epistemological rather than purely physical assumptions. In particular, it is brought out that a sequence of statements bearing on quantum measurements may display intrinsic asymmetric properties, irrespective of the location of corresponding measurements in time t of the Schrödinger equation. The situation of an observer performing two measurements in two opposite directions of t is eventually investigated. Essential differences are found between two descriptions of this situation: the internal one (taking only into account what is recorded in the observer's memory) and the external one (whereby the observer is considered as a quantum system ruled by the Schrödinger equation). Finally, a method allowing several observers to establish a correspondence between their memory sizes is analyzed. The most important facts that usually lead to the associating of a preferential temporal direction with quantum measurements may be inferred from this correspondence.
Time is used in non-relativistic quantum theory as a classical concept. On the one hand, time is the parameter entering Schrödinger's equation and measured by an external laboratory clock. But it could be considered that time also plays the role of an observable when a given event occurs (e.g., when a particle crosses through a potential barrier), and one would expect that like every observable, it should be represented in the theory by an operator whose properties are predictors of the outcome of time measurements made on physical systems. Several time operators have been proposed in different publications, but still, there is not a widely accepted consensus. That subject, among others concerned with time in quantum mechanics, is analyzed in the present chapter, where we focus on the analysis of time-reversal symmetry in non-relativistic quantum systems. The search for symmetries in Physics helps to study the structure of theories. Briefly speaking, a symmetry is a transformation that does not change the structure of the theory. We start with the analysis of Schrödinger’s Equation verifying that for obtaining a time-symmetric description of the dynamics of a particle, the operation of time-reversal must include conjugation represented by the action of an antiunitary operator acting over a wave function. In particular, we analyze quantum systems whose evolution is determined by a set of external parameters varying cyclically, discussing how even though these parameters return to their initial values, the state of the system acquires a geometric phase, which depends on the path followed by the external parameters in the parameter space and which in general can be associated with the lack of the time-reversal symmetry of the system.
Abstract This chapter discusses how one might add a physical quantity to the usual quantum-mechanical state description in order to account for the determinate measurement records. It explains that the value of this quantity in effect chooses exactly one Everett branch as actual, which is the branch describing an observer as recording the measurement results that he in fact records. In addition, it describes two essential ways of branch selection — stipulating a single preferred physical quantity as always determinate, something like particle configuration in Bohm's theory, or stipulating a rule, like the rules provided by different modal theories intended to select a determinate property for each physical system at each time given the quantum-mechanical state. This chapter also provides a description of the surreal trajectories and the persistence of memory. It discusses the incompatibility of Bohm's theory with relativity and other physical quantities, as well as the theory's limiting properties.
Abstract We investigate two types of temporal symmetry in quantum mechanics. The first type, time symmetry, refers to the inclusion of opposite time orientations on an equivalent physical footing. The second, event symmetry, refers to the inclusion of all time instants in a history sequence on an equivalent physical footing. We find that recent time symmetric interpretations of quantum mechanics fail to respect event symmetry. Building on the recent fixed-point formulation (FPF) of quantum theory, we formulate the notion of an event precisely as a fixed point constraint on the Keldysh time contour. Then, considering a sequence of measurement events in time, we show that both time and event symmetry can be retained in this multiple-time formulation of quantum theory. We then use this model to resolve conceptual paradoxes with time symmetric quantum mechanics within an ‘all-at-once’, atemporal picture.
We examine the assertion that the "reduction of the wave packet," implicit in the quantum theory of measurement introduces into the foundations of quantum physics a time-asymmetric element, which in turn leads to irreversibility. We argue that this time assymmetry is actually related to the manner in which statistical ensembles are constructed. If we construct an ensemble time symmetrically by using both initial and final states of the system to delimit the sample, then the resulting probability distribution turns out to be time symmetric as well. The conventional expressions for prediction as well as those for "retrodiction" may be recovered from the time-symmetric expressions formally by separating the final (or the initial) selection procedure from the measurements under consideration by sequences of "coherence destroying" manipulations. We can proceed from this situation, which resembles prediction, to true prediction (which does not involve any postselection) by adding to the time-symmetric theory a postulate which asserts that ensembles with unambiguous probability distributions may be constructed on the basis of preselection only. If, as we believe, the validity of this postulate and the falsity of its time reverse result from the macroscopic irreversibility of our universe as a whole, then the basic laws of quantum physics, including those referring to measurements, are as completely time symmetric as the laws of classical physics. As a by-product of our analysis, we also find that during the time interval between two noncommuting observations, we may assign to a system the quantum state corresponding to the observation that follows with as much justification as we assign, ordinarily, the state corresponding to the preceding measurement.
Time as the Hidden Variable of Quantum Mechanics: An LTST Interpretation Description This preprint presents an interpretive framework for quantum mechanics from the standpoint of LTST — Local Time Synchronization Theory. The central idea is that quantum uncertainty may arise not from an intrinsic randomness of nature, but from a mismatch between the observer’s external time scale and the local time of the physical process itself. The work does not reject the mathematical formalism of quantum mechanics. Instead, it proposes a different ontological reading of its core concepts. In this interpretation, the wave function is understood as a space of possible local-temporal synchronizations, superposition as incomplete synchronization, collapse as the fixation of one admissible configuration, and quantum instantaneity as the compression of a process’s internal local duration into a single manifested event on the observer’s time ruler. The preprint also introduces a correspondence table between standard quantum-mechanical concepts and their LTST interpretation, and outlines possible directions for testable consequences, including the role of measurement apparatus as an active observation mask and the search for pre-collapse synchronization structures. Abstract Quantum mechanics is an exceptionally successful computational framework, yet its interpretation remains tied to an external time parameter associated with the observer, laboratory frame, or measuring apparatus. This preprint proposes an LTST interpretation in which quantum uncertainty is understood as a symptom of mismatch between the observer’s time ruler and the local time of the process itself. From this perspective, a physical event does not occur merely because external time has passed. It appears when local times enter a compatible synchronization regime. The wave function is interpreted as a space of possible local-temporal synchronizations; superposition corresponds to incomplete synchronization; collapse is the fixation of an admissible configuration; and quantum instantaneity is not necessarily the true instantaneity of the process, but the observer’s lack of access to the process’s internal local duration. The proposed interpretation does not invalidate the mathematical apparatus of quantum mechanics. Rather, it changes its ontological status: quantum mechanics is treated as an effective description of processes whose local time is not directly revealed in the observer’s temporal scale. LTST therefore reframes quantum uncertainty as a projection effect caused by mismatched temporal architectures, rather than as final evidence of fundamental randomness in nature. Keywords LTST; local time; quantum mechanics; temporal uncertainty; wave function collapse; superposition; observer; measurement problem; hidden variable; local-temporal synchronization
This paper is concerned with the description of the process of measurement within the context of a quantum theory of the physical world. It is noted that quantum mechanics permits a quasi-classical description (classical in the limited sense implied by the correspondence principle of Bohr) of those macroscopic phenomena in terms of which the observer forms his perceptions. Thus, the process of measurement in quantum mechanics can be understood on the quasi-classical level by transcribing from the strictly classical observables of Newtonian physics to their quasi-classical counterparts the known rules for the measurement of the former. The remaining physical problem is the delineation of the circumstances in which the correlation of a peculiarly quantum mechanical observable A with a classically measurable observable B can result in a significant measurement of A. This is undertaken within the context of quantum theory. The resulting clarification of the process of measurement has important implications relative to the philosophic interpretation of quantum mechanics.