The problem of time is a deep paradox in our physical description of the world. According to Aristotle's relational theory, time is a measure of change and does not exist on its own. In contrast, quantum mechanics, just like Newtonian mechanics, is equipped with a master clock that dictates the evolution of a system. This clock is infinitely precise and tacitly supplied free of charge from outside physics. Not only does this absolute time make it notoriously difficult to make a consistent theory of quantum gravity, it is also the underlying problem in establishing the second law. Indeed, contrary to our experience, the Wheeler-deWitt equation --a canonical quantization of general relativity-- predicts a static universe. Similarly, when simply concerned with the dynamics of a closed quantum system, there is no second law because the Von Neumann entropy is invariant under unitary transformations. Here we are mainly concerned with the latter problem and we show that it can be resolved by attributing a minimal amount of resources to the measurement of time. Although there is an absolute time in quantum mechanics, an observer can only establish a time by measuring a clock. For a local measurement, the minimal entropy production is equal to the number of ticks. This lower bound is attained by a black hole.
The problem of time is a deep paradox in our physical description of the world. According to Aristotle's relational theory, time is a measure of change and does not exist on its own. In contrast, quantum mechanics, just like Newtonian mechanics, is equipped with a master clock that dictates the evolution of a system. This clock is infinitely precise and tacitly supplied free of charge from outside physics. Not only does this absolute time make it notoriously difficult to make a consistent theory of quantum gravity, it is also the underlying problem in establishing the second law. Indeed, contrary to our experience, the Wheeler-deWitt equation --a canonical quantization of general relativity-- predicts a static universe. Similarly, when simply concerned with the dynamics of a closed quantum system, there is no second law because the Von Neumann entropy is invariant under unitary transformations. Here we are mainly concerned with the latter problem and we show that it can be resolved by attributing a minimal amount of resources to the measurement of time. Although there is an absolute time in quantum mechanics, an observer can only establish a time by measuring a clock. For a local measurement, the minimal entropy production is equal to the number of ticks. This lower bound is attained by a black hole.
Even though our microscopic physical theories, such as classical or quantum mechanics, are time-reversal invariant, time appears to march forward irreversibly. It is widely believed that effective entropy increase due to the second law of thermodynamics is at the origin of this emergent arrow of time. Any system that is out of thermal equilibrium and produces entropy can thus be used as a clock, be it a melting ice cube or a sophisticated atomic clock. The understanding of entropy in physics has significantly advanced with the advent of information theory in the last century. It has also led to the insight that the amount of entropy a clock produces is linked to how precisely the clock works, and thereby, how much information the clock reveals about the passage of time. In this thesis, we ask: what fundamental limits does the underlying physical theory impose on the precision of clocks within that theory? To rigorously answer this question, we devise a minimal clock model within quantum theory. By consistently modeling all clock constituents as quantum systems, we can ensure we account for all the resources used by the clock. This includes, in particular, the readout. Classically, one can obtain this for free, but quantum mechanically, this has a resource cost associated with it. To this end, we consolidate existing frameworks that describe clocks in both classical and quantum theory. Revising fluctuation theorems from quantum thermodynamics, we demonstrate how such theorems impose limits on the attainable precision of clocks. These precision bounds turn out to be more stringent for classical systems than for quantum ones. Quantum clocks can harness coherence and correlations to suppress fluctuations, allowing them to exponentially surpass precision bounds that hold for classical clocks. We show this separation between classical and quantum clocks by constructing an explicit example that uses quantum dynamics to saturate the quantum precision bounds. Finally, we close the thesis by exploring implications of these timekeeping bounds beyond fundamental science in quantum technologies. We show how quantum clocks can be used to quantify the energetic cost of quantum computation by linking computational fidelity to thermodynamic entropy production.
Time remains one of the least well-understood concepts in physics, most notably in quantum mechanics.A central goal is to find the fundamental limits of measuring time.One of the main obstacles is the fact that time is not an observable and thus has to be measured indirectly.Here, we explore these questions by introducing a model of time measurements that is complete and autonomous.Specifically, our autonomous quantum clock consists of a system out of thermal equilibrium-a prerequisite for any system to function as a clock-powered by minimal resources, namely, two thermal baths at different temperatures.Through a detailed analysis of this specific clock model, we find that the laws of thermodynamics dictate a trade-off between the amount of dissipated heat and the clock's performance in terms of its accuracy and resolution.Our results furthermore imply that a fundamental entropy production is associated with the operation of any autonomous quantum clock, assuming that quantum machines cannot achieve perfect efficiency at finite power.More generally, autonomous clocks provide a natural framework for the exploration of fundamental questions about time in quantum theory and beyond.
Canonical quantization applied to closed systems leads to static equations, the Wheeler-deWitt equation in Quantum Gravity and the time independent Schrödinger equation in Quantum Mechanics. How to restore time is the Problem of Time(s). Integrating developments are: a) entanglement of a microscopic system with its classical environment accords it a time evolution description, the time dependent Schrödinger equation, where t is the laboratory time measured by clocks; b) canonical quantization of Special Relativity yields both the Dirac Hamiltonian and a self adjoint "time" operator, restoring to position and time the equivalent footing accorded to energy and momentum in Relativistic Quantum Mechanics. It introduces an intrinsic time property τ associated with the mass of the system, and a basis additional to the usual configuration, momentum and energy basis. As a generator of momentum displacements and consequently of energy, it invalidates Pauli's objection to the existence of a time operator. It furthermore complies with the requirements to condition the other observables in the conditional interpretation of QG. As Pauli's objection figures explicit or implicitly in most current developments of QM and QG, its invalidation opens to research the effect of this new two times perspective on such developments.
Time remains one of the least well-understood concepts in physics, most notably in quantum mechanics.A central goal is to find the fundamental limits of measuring time.One of the main obstacles is the fact that time is not an observable and thus has to be measured indirectly.Here, we explore these questions by introducing a model of time measurements that is complete and autonomous.Specifically, our autonomous quantum clock consists of a system out of thermal equilibrium-a prerequisite for any system to function as a clock-powered by minimal resources, namely, two thermal baths at different temperatures.Through a detailed analysis of this specific clock model, we find that the laws of thermodynamics dictate a trade-off between the amount of dissipated heat and the clock's performance in terms of its accuracy and resolution.Our results furthermore imply that a fundamental entropy production is associated with the operation of any autonomous quantum clock, assuming that quantum machines cannot achieve perfect efficiency at finite power.More generally, autonomous clocks provide a natural framework for the exploration of fundamental questions about time in quantum theory and beyond.
In quantum gravity there is no notion of absolute time. Like all other quantities in the theory, the notion of time has to be introduced "relationally", by studying the behavior of some physical quantities in terms of others chosen as a "clock". We have recently introduced a consistent way of defining time relationally in general relativity. When quantum mechanics is formulated in terms of this new notion of time the resolution of the measurement problem can be implemented via decoherence without the usual pitfalls. The resulting theory has the same experimental results of ordinary quantum mechanics, but every time an event is produced or a measurement happens two alternatives are possible: a) the state collapses; b) the system evolves without changing the state. One therefore has two possible behaviors of the quantum mechanical system and physical observations cannot decide between them, not just as a matter of experimental limitations but as an issue of principle. This first-ever example of fundamental undecidability in physics suggests that nature may behave sometimes as described by one alternative and sometimes as described by another. This in particular may give new vistas on the issue of free will.
Overview Schrödinger Dynamics supplies the quantum first-response result within the gravity–quantum unification program. The manuscript begins with closed, determinate quantum standing on the standard smooth projective-Hilbert carrier and asks: What is the unique minimal continuous dynamical law compatible with projective quantum identity, reversible norm-preserving continuation, and lawful time translation? Within the manuscript’s declared regular comparison class, these requirements force unitary evolution, a self-adjoint Hamiltonian generator, and the Schrödinger equation as the corresponding first-response quantum normal form. The completed Wheeler–DeWitt ARC is also an upstream dependency of the manuscript’s hardened realized/export presentation. Its certified WDW–Schrödinger handoff supplies constraint-native realization and quotient-level data to the Schrödinger-side export. This does not replace or circularly ground the original first-response derivation, which remains a projective-Hilbert theorem of this manuscript. Central Result The paper derives the abstract Schrödinger evolution equation The Schrödinger equation is therefore recovered as the minimal Hamiltonian first-response projection of closed quantum standing, rather than introduced as an unexplained primitive law. Principal Contributions Specializes AASC governance to the standard smooth projective-Hilbert quantum carrier. Treats physical quantum states as rays rather than arbitrary vector representatives. Distinguishes standing-bearing projective content from phase, normalization, basis, and coordinate skin. Classifies lawful projective transformations through the applicable Wigner structure. Uses continuous time evolution to select the unitary branch relevant to connected continuation. Applies Stone-type generator structure to obtain a self-adjoint Hamiltonian. Derives the abstract Schrödinger equation as the resulting infinitesimal evolution law. Recovers the scalar nonrelativistic Schrödinger operator within the declared local comparison class. Separates closed predictive evolution from measurement-record formation and exchange-extended processes. Supplies the quantum dynamical projection paired with Einstein dynamics in the structural-unification theorem. Receives a certified upstream Wheeler–DeWitt export in its hardened realized Schrödinger presentation. Place in the Unification Program The universal AASC kernel and the singleton-interior result of Unus Solus Possibilis Est remain general machinery imported by the unification program. Arc-specific development begins with the physical and gravitational specialization of Gravity as Structural Necessity. The relevant dependency structure is: Non-Degenerate Construction and the Kernel of Admissibility — establishes the universal kernel governing non-degenerate determinate construction. Unus Solus Possibilis Est — establishes the singleton-interior result used by the broader program. Gravity as Structural Necessity — establishes the necessary physical constraint role. Wheeler–DeWitt ARC — carries the realized gravity–quantum architecture through canonical projection, faithful redescription descent, constrained refoliation, matter occupancy, configuration-space differentiation, quantum-constraint survival, and certified physical realization. The mature WDW export — supplies the certified quotient-level WDW–Schrödinger handoff feeding into the realized Schrödinger presentation. Einstein Dynamics — derives the unique minimal first-response metric projection. Schrödinger Dynamics — derives the corresponding minimal Hamiltonian quantum projection. Structural Unification — proves that the gravitational and quantum descriptions are projections of one admissible physical interior. Modules A–D and Complete Certificate Closure — complete the operational source, mass–charge, common-continuation, and certificate-fibre realization architecture. The present manuscript supplies the quantum half of the paired first-response dynamical input used by Structural Unification. Its original theorem does not create a second physical interior alongside gravity; it derives the lawful quantum projection later situated within the common upstream architecture. The Wheeler–DeWitt dependency concerns the certified realized/export layer of the completed presentation. It strengthens the relation between the Schrödinger and constrained gravity–quantum realizations without making Wheeler–DeWitt theory a premise of the original projective-Hilbert derivation. Relation to Einstein Dynamics The Einstein and Schrödinger results occupy parallel but nonidentical positions: Einstein dynamics is the minimal local metric first-response projection. Schrödinger dynamics is the minimal Hamiltonian first-response projection of closed quantum standing. The Einstein branch concerns geometric response and conserved source attachment. The Schrödinger branch concerns projective identity, unitary continuation, and Hamiltonian generation. Neither branch independently exhausts the physical interior. Their common origin and lawful compatibility are established by the structural-unification and certificate constructions. The program therefore does not combine two primitively independent ontologies. It derives two distinct dynamical normal forms and proves that both descend from one prior admissibility-bearing physical interior. Wheeler–DeWitt Upstream Certified Input The Wheeler–DeWitt ARC provides a later constraint-native realization of the already established gravity–quantum architecture. Its completed export feeds into the realized Schrödinger presentation through a certified quotient-level handoff: This handoff is not a retroactive premise of the paper’s original first-response theorem. Rather, it provides an additional certified realization-level route into the Schrödinger-side structure, preserving the distinction between the direct projective-Hilbert derivation and the later constrained gravity–quantum realization. Closed Prediction and Record Formation A central distinction is maintained between closed quantum prediction and physical record production. The Schrödinger equation governs reversible Hamiltonian continuation of the closed quantum state. It does not, by itself, construct an irreversible measurement record, select a realized outcome, or complete the compatibility architecture required for entanglement and exchange. Those additional roles are supplied through the wider AASC record and compatibility machinery and incorporated into the later realization architecture. Irreversible fixation is therefore not silently attributed to unitary evolution itself. Scope and Nonclaims The manuscript does not claim: an independent rederivation of the universal AASC kernel; uniqueness outside its declared regular projective-Hilbert comparison class; derivation of every possible nonlinear, nonunitary, relativistic, or field-theoretic quantum evolution; that vector normalization or global phase carries primitive physical standing; that the Schrödinger equation alone solves the measurement problem; construction of an irreversible measurement record from closed unitary evolution; derivation of a unique potential, initial state, boundary condition, or interaction history; completion of relativistic quantum field theory; primitive unification of quantum mechanics with gravity; derivation of common gravitational and inertial mass; or independent closure of the later source, continuation, certificate-realization, or Wheeler–DeWitt realization problems. These questions either lie outside the theorem’s declared comparison class or are addressed by other components of the program. Conceptual Significance The paper changes the explanatory status of Schrödinger dynamics. The Schrödinger equation is not treated as the primitive foundation of quantum physical reality. It is obtained as the minimal lawful evolution of a closed quantum projection once projective identity, continuous reversible continuation, and Hamiltonian generation are imposed together. The completed Wheeler–DeWitt ARC subsequently provides a certified constrained realization whose quotient-level export feeds into the hardened Schrödinger presentation. The program is thus upstream rather than additive: gravity and quantum dynamics descend from common standing-bearing architecture, and their later certified realizations remain linked without collapsing their distinct theorem roles.