The principle of action plays a central role in both classical and quantum mechanics, yet its physical meaning is often introduced in a purely formal manner. In this work, the concept of action is examined from a scale-based perspective that clarifies its role in the quantum–classical correspondence. By emphasizing the dimensionless ratio S/ℏ, we show that the emergence of classical dynamics can be understood as a consequence of quantum phase coherence rather than as an independent postulate. Within the path integral formulation, classical trajectories arise naturally from stationary-phase conditions when the action associated with a physical process becomes large compared to Planck’s constant. This interpretation provides a unified conceptual framework in which variational principles, quantum interference, and classical determinism are linked through the scale of action. The analysis highlights the role of Planck’s constant as a universal parameter governing the physical relevance of alternative histories, analogous to the function of Boltzmann’s constant in statistical physics. Beyond its theoretical implications, the proposed perspective offers pedagogical value by providing a coherent bridge between classical and quantum mechanics suitable for advanced undergraduate and early graduate physics education.
The principle of action plays a central role in both classical and quantum mechanics, yet its physical meaning is often introduced in a purely formal manner. In this work, the concept of action is examined from a scale-based perspective that clarifies its role in the quantum–classical correspondence. By emphasizing the dimensionless ratio S/ℏ, we show that the emergence of classical dynamics can be understood as a consequence of quantum phase coherence rather than as an independent postulate. Within the path integral formulation, classical trajectories arise naturally from stationary-phase conditions when the action associated with a physical process becomes large compared to Planck’s constant. This interpretation provides a unified conceptual framework in which variational principles, quantum interference, and classical determinism are linked through the scale of action. The analysis highlights the role of Planck’s constant as a universal parameter governing the physical relevance of alternative histories, analogous to the function of Boltzmann’s constant in statistical physics. Beyond its theoretical implications, the proposed perspective offers pedagogical value by providing a coherent bridge between classical and quantum mechanics suitable for advanced undergraduate and early graduate physics education.
We introduce physical phase invariance as a minimal, observer-independent principle capable of unifying quantum theory and relativity. By identifying the physical phase with the classical action measured in units of Planck’s constant, the framework assigns phase a direct operational meaning. Spacetime structure, Lorentz invariance, and quantum probabilistic behavior emerge as effective descriptions of underlying phase dynamics rather than fundamental postulates. Time is defined relationally through phase evolution, and classical motion arises from stationary phase conditions. A simple dynamical equation for the phase field is proposed, while quantum probabilities are shown to result from statistical coarse-graining over unresolved phase degrees of freedom. This approach provides a coherent conceptual foundation linking quantum mechanics, special relativity, and gravitation.
We propose that the unobservability of absolute scale constitutes a foundational principle of physics. Starting from the requirement that physical predictions must be invariant under rescalings of the action, we show that only phase-based quantities remain well defined. This requirement uniquely selects a complex amplitude description, leading directly to the structure of quantum mechanics, including linear superposition, Hilbert space, and the Born rule. Within this framework, the classical notion of action loses absolute meaning, and physical observables arise from invariant phase relations. Quantum mechanics is therefore not postulated, but emerges as the minimal consistent description of systems in which scale cannot be directly observed. The formal structure of quantum theory is shown to follow from this principle without additional axioms. We further demonstrate that the same principle implies the existence of a dynamical scale field, which governs the effective quantum scale and connects naturally to cosmological models with a time- dependent Planck mass. In this way, the structure of quantum mechanics and the large-scale dynamics of the Universe are linked through a common origin. This framework provides a unified perspective in which quantum behavior and cosmological evolution arise from a single underlying principle, suggesting a new approach to the relationship between fundamental physics and cosmology.
Quantum mechanics is traditionally formulated in terms of postulates inferred from experimentalobservations. Here we propose that the statistical regularities of quantum mechanics arise as macro-scopic manifestations of stochastic fluctuations of dynamical parameters in microscopic systems gen-erated by a non-inertial physical background. Although the specific nature of this background mayvary, the universality of quantum statistics is ensured by invariant properties of stochastic dynam-ics - analogous to the role of the equivalence principle in general relativity - and by the existence ofa fundamental action scale, Planck constant h. By extending classical mechanics to include higher-order derivatives induced by non-inertial fuctuations and imposing a stability condition on admissibletrajectories, the minimal action scale h naturally emerges. In this framework quantum mechanicsappears as an effective statistical description of systems embedded in a fluctuating non-inertial envi-ronment while preserving all standard predictions of the theory.
This chapter completes the physical groundwork of the thesis by examining quantum mechanics, the second of the two theories that the following chapters interpret philosophically. Rather than offering an exhaustive mathematical treatment, it selects the concepts required to follow the two transversal principles identified in Chapter 3: causality and the principle of stationary action. It presents the emergence of the quantum of action, the formal structure of the theory (states, observables, Born’s rule, Schrödinger dynamics, superposition and entanglement), the double-slit experiment, the uncertainty principle, the measurement problem, and the sequence formed by the EPR argument, Bell’s theorem and its experimental tests. Using the three senses of causality distinguished in Chapter 3, the chapter shows that Heisenberg’s 1927 attempt to refute the law of causality did not succeed: unitary evolution preserves dynamical determination at the level of the quantum state, while the no-signalling condition and relativistic microcausality preserve causal precedence and causal propagation, even though Bell-local models fail. It then shows that action, present at the very birth of the theory as Planck’s quantum of action, governs quantum dynamics through Feynman’s path integral and Schwinger’s quantum action principle, and that the classical principle of stationary action re-emerges in the classical limit. The principal result, restricted to physics, is that causality and stationary action are transversal to classical, relativistic and quantum physics, although their mathematical formulation changes. Ontological conclusions are reserved for the following chapters.
The emergence of quantum mechanics from classical world mechanics is now a well-established theme in mathematical physics. This book demonstrates that quantum mechanics can indeed be viewed as a refinement of Hamiltonian mechanics, and builds on the work of George Mackey in relation to their mathematical foundations. Additionally when looking at the differences with classical mechanics, quantum mechanics crucially depends on the value of Planck's constant h. Recent cosmological observations tend to indicate that not only the fine structure constant α but also h might have varied in both time and space since the Big Bang. We explore the mathematical and physical consequences of a variation of h; surprisingly we see that a decrease of h leads to transitions from the quantum to the classical. Emergence of the Quantum from the Classical provides help to undergraduate and graduate students of mathematics, physics and quantum theory looking to advance into research in the field. Readership: Undergraduate and graduate students of mathematics and physics, interested in analysis and differential equations, probability and statistics, geometry and topology and mathematical physics.
A fundamental tenet in the study of organization in inanimate and living matter is the quantization of energy. In inanimate systems where temperature is a critical organizing parameter, the quantum of action is an atomic-level phenomenon described in terms of Planck’s constant, first defined as the ratio of the photon energy to the frequency of its electromagnetic wave. In living systems, where the cycle time of metabolic processes is the organizing variable, the quantum of action is a cell-level phenomenon described in terms of an analog of Planck’s constant, namely the ratio of the metabolic energy to the frequency of the enzymatic or mitochondrial oscillators. This chapter elucidates the relation between these two measures of quantum action. We review the role of Planck’s constant in physics, first, as a fundamental parameter for explaining the empirical laws of black body radiation, and its more modern developments. We also describe the theoretical and empirical rationale for the cellular-level quanta. We exploit this analysis to elucidate how energy transformation in physical processes, where temperature is the organizing parameter, relates to energy transduction in biological processes, which are essentially isothermal. We then link the cell level to the organismal level of metabolism and obtain a scaling relationship for the biological Planck quantum of action as a function of the size of the biological system studied. Finally, we discuss these ideas in light of quantum-like processes in biological organisms and systems: identifying generalized quantum principles that apply not just at microscopic levels but also at macroscopic levels, relevant to biology, where we used to consider classical physics alone to be relevant. This chapter provides a direct analogy between quantization of energy in solids first demonstrated by Debye and biochemical energy production in cellular mitochondria. The Planck constant proved to be a fundamental constant of matter as it appeared both in the Schoedinger equation and the Heisenberg uncertainty principle. Recently, quantum biology has garnered major scientific interest, but so far it has only focused on physical quantum effects in biological systems, such as photosynthesis, not truly biological quantization. We point to metabolism, as an indispensable process that underlies all life forms’ existence, and show that its quantization can be better understood in terms of a corresponding quantum of action. We estimate its value, compare it to Planck’s quantum of action in physics and explain their different scales. We hypothesize that energy quantization of metabolism in biological systems is an important conceptual advance that can provide insights into both healthy and pathological physiology.