Foundations of Physics最新文献

We demonstrate that the internal logical structure of a quantum circuit can leave a distinct thermodynamic signature under progressive decoherence. By comparing deep, conditionally branching circuits with shallow, uniform counterparts—while controlling for overall halting probability and physical resources—we show that branching architectures induce greater entropy flow into the environment. This effect is captured by a logical depth factor (L_d), which quantifies entropy accumulation during environmental interactions. We validate our framework through detailed analysis of two 4-branch quantum circuits, demonstrating greater entropy production with (L_d approx 1.615) for conditional versus uniform architectures. An ancilla-based experimental protocol using controlled-phase gates provides a concrete pathway for detecting these thermodynamic signatures on current quantum platforms. Our results establish logical depth as a physically measurable quantity with implications for circuit design, compilation strategies, and verification protocols.

Scientific realism is the philosophical stance that science tracks truth, in particular in its depiction of the world’s ontology. Ontologically, this involves a commitment to the existence of entities posited by our best scientific theories; metaontologically, it includes the claim that the theoretical framework itself is true. In this article, we examine wave function realism as a case study within this broader methodological debate. Wave function realism holds that the wave function, as described by quantum mechanics, corresponds to a real physical entity. We focus on a recent formulation of this view that commits to the ontology of the wave function while deliberately avoiding the metaontological question of the framework’s truth. Instead, the view is defended on pragmatic, non-truth-conductive grounds. This, we argue, raises tensions for the purported realism of wave function realism and its compatibility with scientific realism more broadly.

The so-called Geometric Trinity of Gravity includes General Relativity (GR), based on spacetime curvature; the Teleparallel Equivalent of GR (TEGR), which relies on spacetime torsion; and the Symmetric Teleparallel Equivalent of GR (STEGR), grounded in nonmetricity. Recent studies demonstrate that GR, TEGR, and STEGR are dynamically equivalent, raising questions about the fundamental structure of spacetime, the under-determination of these theories, and whether empirical distinctions among them are possible. The aim of this work is to show that they are equivalent in many features but not exactly in everything. In particular, their relationship with the Equivalence Principle (EP) is different. The EP is a deeply theory-laden assumption, which is assumed as fundamental in constructing GR, with significant implications for our understanding of spacetime. However, it introduces unresolved conceptual issues, including its impact on the nature of the metric and connection, its meaning at the quantum level, tensions with other fundamental interactions and new physics, and its role in dark matter and dark energy problems. In contrast, TEGR and STEGR recover the EP, in particular in its strong formulation, but do not rely on it as a foundational principle. The fact that GR, TEGR, and STEGR are equivalent in non-trivial predictions, but the EP is not necessary for TEGR and STEGR, suggests that it may not be a fundamental feature but an emergent one, potentially marking differences in the empirical content of the three theories. Thus, the developments within the Geometric Trinity framework challenge traditional assumptions about spacetime and may help to better understand some of the unresolved foundational difficulties related to the EP.

There are two main styles of interpreting the quantum state: either focusing on the fundamentality of the quantum state (a state or wavefunction realist view), or on how projection operators represent observable properties (an observable-first approach). Rather than being incompatible, I argue that these correspond to taking a 3rd person and 1st person perspective respectively. I further contend that the 1st person perspective - and the observable-first approach that goes with it - is better suited to explain measurement, based on the way that the metrology literature characterises measurement through the quantifiable properties of a system. Finally, I show how the 1st person, observable-first approach can emerge in the world through the process of decoherence, hence showing the compatibility of the two approaches and resolving the need to choose absolutely between them.

Sebens (2025) has proposed a semiclassical “precursor” to quantum electrodynamics (QED) in which the electron’s anomalous magnetic moment arises from the self-interaction of an extended charge distribution governed by the Dirac equation. The calculation reproduces Schwinger’s leading-order value only for suitably tuned, spatially extended wave-packets, and thus yields a state-dependent magnetic moment. This paper offers a systematic critique of that result. After reviewing the standard QED derivation—where the anomaly is fixed by gauge symmetry, the Ward–Takahashi identity, and renormalization—we show that the semiclassical model lacks the structural resources that guarantee universality. Drawing on a general distinction between phenomenological dependence and theoretical fundamentality, we argue that Sebens’s construction attains intuitive, mechanical appeal at the cost of explanatory depth: its high phenomenologicality cannot compensate for its low fundamentality. What Sebens treats as a puzzle for QED—how the theory “nails down” a single value of (g-2)—is instead a symptom of the precursor’s incompleteness. The episode illustrates a broader methodological point: in modern physics, structural principles, rather than classical pictures, underwrite genuine explanation.

Recently, a counter-argument has been presented regarding the invalidity of the Pusey-Barrett-Rudolph (PBR) theorem (Cabbolet, Found. Phys. 53, 64 2023). This claim has sparked a debate, with some authors defending the PBR theorem (Hofer-Szabó, Found. Phys. 54, 36 2024), but the proponent of the claim has insisted on his argument (Cabbolet, Found. Phys. 54, 69 2024; Cabbolet, Found. Phys. 54, 48 2024). Moreover, the author claimed to have proved that the PBR theorem is incorrect by a generic counterexample (Cabbolet, Found. Phys. 54, 48 2024). In this paper, we contribute to the discussion with some new arguments. We demonstrate that the PBR theorem contains no errors and remains intact.

Perspectivist positions have been proposed in physics, notably in order to address the interpretive difficulties of quantum mechanics. Recently, some versions of perspectivism have also been proposed in general philosophy of science to account for the plurality of scientific practice. Both kinds of views share the rejection of what they metaphorically call the “view from nowhere”. However, beyond this superficial similarity, they are very different: while quantum perspectivism entertains a concrete notion of perspective associated with individual agents or systems or concrete contexts, perspectival realism adopts a more abstract notion associated with explanatory aims or conceptual schemes. The aim of this paper is to clarify what is at stake with perspectivism in general. The general notion of a perspective, as well as the various attitudes one can entertained towards them, are characterised using the concepts of harmless contradiction and cross-perspectival accessibility. A taxonomy of positions ranging from absolutism to relativism is proposed on this basis. Then the framework is applied to quantum perspectivism and perspectival realism to show its fruitfulness. Finally, I argue that abstract versions of perspectivism are bound to be metaphysically weaker than concrete versions.

The multiplicative Lagrangian and Hamiltonian introduce an additional parameter that, despite its variation, results in identical equations of motion as those derived from the standard Lagrangian. This intriguing property becomes even more striking in the case of a free particle. By manipulating the parameter and integrating out, the statistical average of the multiplicative Lagrangian and Hamiltonian naturally arises. Astonishingly, from this statistical viewpoint, the relativistic Lagrangian and Hamiltonian emerge with remarkable elegance. On the action level, this formalism unveils a deeper connection: the spacetime of Einstein’s theory reveals itself from a statistical perspective through the action associated with the multiplicative Lagrangian. This suggests that the multiplicative Lagrangian/Hamiltonian framework offers a profound and beautiful foundation, one that reveals the underlying unity between classical and relativistic descriptions in a way that transcends traditional formulations. In essence, the multiplicative approach introduces a richer and more intricate structure to our understanding of physics, bridging the gap between different theoretical realms through a statistical perspective.

Causal Set Theory (CST) is a promising approach to fundamental physics that seems to treat causation as a basic posit. But in exactly what sense is CST causal? We argue that if the growth dynamics is interpreted as a physical process, then CST employs relations of actual causation between causal set elements, whereby elements bring one another into existence. This is important, as it provides a better sense of how CST works, highlights important differences from general relativity—where relations between spacetime points are typically seen as cases of mere causal connectibility rather than actual causation of the relevant type—and points toward a specific understanding of the emergence of spacetime within CST.

This work presents an alternative approach to obtain the quantum field equations in curved spacetime, considering that sufficiently small particles follow stochastic trajectories around geodesic. Our proposal is based on a stochastic differential equation in which the noise term experienced by the quantum particles is a consequence of the stochastic background in spacetime. This fact allows the particles to describe erratic movements and locally the universe exhibits characteristics akin to a lake with gentle ripples rather than a flat unyielding surface. Building upon this foundational understanding, we investigate the influence of this background on quantum-scale particles without considering the metric to be stochastic, rather we let test particles move randomly around the geodesic of macroscopic particles. Their behavior aligns with solutions to the Klein-Gordon (KG) equation specific to this curved spacetime. As the KG equation, in its non-relativistic limit within a flat spacetime, reduces to the Schrödinger equation, consequently, we propose a compelling connection: the Schrödinger equation may emerge directly from a spacetime lacking local smoothness.