Using only elementary mechanics, we show that the decomposition of force into parallel and orthogonal components reveals two distinct physical interactions. In idealized systems these components are lossless, but real systems contain constraints that produce dissipation. Since quantum mechanics and general relativity are both constraint-free theories describing a universe full of coupled subsystems, any unification must necessarily incorporate dissipation and the arrow of time. This paper is an introduction to principles that underly the paper Dissipative Quantum Hydrodynamics: A Symmetric Interaction Between QM and GR (https://doi.org/10.6084/m9.figshare.30615254)
Using only elementary mechanics, we show that the decomposition of force into parallel and orthogonal components reveals two distinct physical interactions. In idealized systems these components are lossless, but real systems contain constraints that produce dissipation. Since quantum mechanics and general relativity are both constraint-free theories describing a universe full of coupled subsystems, any unification must necessarily incorporate dissipation and the arrow of time. This paper is an introduction to principles that underly the paper Dissipative Quantum Hydrodynamics: A Symmetric Interaction Between QM and GR (https://doi.org/10.6084/m9.figshare.30615254)
General relativity (GR) and quantum mechanics (QM) resist unification not because one is wrong but because each is a coarse-graining of the same thing, and the two projections discard complementary information. This note makes that claim precise inside Event Density (ED), a framework in which spacetime and its fields are not fundamental but emerge from a discrete, relational substrate — a network of events, their participation, and their commitment - governed by thirteen primitives, one of which is an irreversible arrow of time. We show that both GR and QM are time-symmetric, so each has already coarse-grained the arrow out; what each retains is a different reversible residue of the substrate’s time, the local rate in GR and the global phase in QM. Because both are projections of one arrow, they are not unified by building a bridge between them but by recovering their common source. Concretely, ED identifies the object QM needs as its pointer-basis selector with the object GR needs as its preferred time: they are one primitive doing two jobs, and the standard “problem of time” therefore does not arise. We are explicit about tier: the QM side is a grounded reconstruction with a stated open residual, the weak-field GR side is derived, but the unification itself is an identification at account tier - distinctive, structural, and as yet carrying no falsifiable prediction of its own.
Modern Physics rests on two pillars: General Relativity (GR) and Quantum Mechanics (QM). The former describes gravitation as the continuous geometry of spacetime, based on differential fields. The latter, in turn, operates in a discretized regime, where energy levels, frequencies, and experimental results arise in quantized packets. The tension between both arises because GR assumes absolute continuity of time and space, while QM presents intrinsically discrete phenomena. Historically, the search for a unified theory started from the assumption that one of the two formulations must be modified — either GR should be discretized, or QM should emerge from an underlying continuous theory. In this work, we argue that the conflict is not fundamental: it stems from the traditional interpretation of time in Special Relativity (SR). When analyzed correctly, the proper time of distinct observers does not evolve synchronously, and this produces beating and discretization effects that explain, without additional postulates, many behaviors labeled as "quantum."
The notions of time in the theories of Newton and Einstein are reviewed so that the difficulty which impedes the unification of quantum mechanics (QM) and general relativity (GR) is clarified. It is seen that GR by itself contains an intrinsic difficulty relating to the definition of local clocks, as well as that GR still requires a kind of absolute that can serve as an objective reference standard. We present a new understanding of time, which gives a consistent definition of a local time associated with each local system in a quantum mechanical way, so that it serves the requirements of both GR as well as QM. As a consequence, QM and GR are reconciled while preserving the current mathematical formulations of both theories.
Abstract Two of the most difficult problems in the foundations of physics are (1) what gives rise to the arrow of time and (2) what the ontology of quantum mechanics is. I propose a unified ‘Humean’ solution to the two problems. Humeanism allows us to incorporate the Past Hypothesis and the Statistical Postulate into the best system, which we then use to simplify the quantum state of the universe. This enables us to confer the nomological status to the quantum state in a way that adds no significant complexity to the best system and solves the “supervenient‐kind problem” facing the original version of the Past Hypothesis. We call the resultant theory the Humean unification. It provides a unified explanation of time asymmetry and quantum entanglement. On this theory, what gives rise to time's arrow is also responsible for quantum phenomena. The new theory has a separable mosaic, a best system that is simple and non‐vague, less tension between quantum mechanics and special relativity, and a higher degree of theoretical and dynamical unity. The Humean unification leads to new insights that can be useful to Humeans and non‐Humeans alike.
This work investigates the fundamental connection between quantum mechanics and thermodynamics through the concept of the arrow of time. While the second law of thermodynamics identifies the arrow of time with the monotonic increase of entropy in isolated systems, closed quantum systems evolve unitarily and conserve von Neumann entropy, making the origin of irreversibility less apparent. Here we establish a no-go theorem proving that correlations in unknown states of closed quantum systems cannot be universally removed by any physical operation. This result demonstrates that correlation generation is inherently irreversible, providing a microscopic and universal basis for the arrow of time. In thermodynamic settings, this irreversibility ensures that heat flows spontaneously from hotter to colder subsystems, reproducing the Clausius formulation of the second law. More generally, the irreversible growth of correlations explains entropy increase, the approach to equilibrium, and decoherence as observable manifestations of the same principle. Our findings ground a quantum-mechanical foundation for the second law of thermodynamics and demonstrate the universality of the arrow of time.
Can our extremely complicated world be explained, starting from simple conditions and laws? Such questions easily become metaphysical, but at the same time they have historically served science well by promoting new and fruitful ideas. Of particular interest in this paper is the unification of general relativity and quantum mechanics. It is suggested that a way to find a common basis for these theories could be to view them both as stochastic theories which, among all possible macroscopic developments, promote the simplest ones. But with the difference that general relativity uses real probabilities, whereas quantum mechanics uses complex weights. In a certain sense this approach goes back to the Principle of Least Action, although the perspective on this principle in the present paper is different from the one which is commonly used in contemporary physics. It is also suggested that a more general principle, which applies to both theories and which is beyond both stationarity and minimizing, could give us a better starting point for the unification.