Foundations of Physics最新文献

A central question for the foundations of thermodynamics is which conceptual structures underpin the existence of entropy and temperature. Jauch claimed that entropy and temperature could be derived from a novel conservation law. This paper reconstructs the physics and mathematics of Jauch’s claim and finds that his original proof is not valid. Remarkably, his theorem is still true. We provide an alternative proof using geometric ideas from modern gauge theory, revealing a deep geometric structure in thermodynamics. This result also helps to settle an old debate by showing that entropy and temperature can be defined in a new, conceptually clear way without appeal to an irreversible assumption like the second law.

The thought experiment called “Wigner’s Friend" has experienced a renewal of interest for interrogating the meaning of intersubjectivity and objectivity in quantum mechanics. These new inquiries extend to investigations at the intersection of phenomenology and QBism. Philosopher of physics Steven French argues that QBism does not give assurances that Wigner and friend must agree on the same quantum state or measurement outcomes. In this article, we draw on Wigner’s Friend to argue that an external guarantee for agreement on either quantum states or measurement outcomes is unnecessary. We defend the view that the quantum formalism is already inherently intersubjective in the way required to sustain objectivity. Here we explore the QBist notion of reciprocity, which treats Wigner and friend as physical systems taking mutual actions on each other. The QBist notion of reciprocity leads to a sharper characterization of what it means to objectify quantum systems with the formalism. Drawing on phenomenological resources, we argue that state assignments for quantum systems, including those for Wigner and friend, are a form of objectification. To assign a quantum state is to objectify a phenomenon as a quantum system, to treat something as the sort of object to which the formalism applies. Our argument accounts for why the quantum formalism does not radically change in application for different systems because the systems themselves exceed their formalization.

Decoherence explains why selected quantum histories behave as mutually exclusive alternatives with Born weights, but it does not by itself show that such alternatives are worlds. We formulate this as a geometric representability problem within decoherent histories. A world-bearing branch must support a local physical representation: a compatible spectral and local structure sufficient for spacetime-like observables, stable records, and observer-level description. For a history effect (F_alpha =K_alpha ^dagger K_alpha ) and a positive spectral probe (A), we introduce the branch-resolved heat trace (Theta _alpha (t)={text {Tr}}(e^{-tA/2}F_alpha e^{-tA/2})). Its small-time behavior tests the spectral supply carried by that branch. We prove that identical decoherence data can be realized by branches with inequivalent heat profiles, and that exact decoherent refinement can decompose a spectrally thick branch into probability-bearing but spectrally thin branches. A positive lower-bound theorem then shows that genuine branch-local spectral regularity forces corresponding heat-trace growth. Decoherence remains essential for probabilities, but branch ontology requires structural admissibility beyond decoherence.

In this short note we argue that, even if, as sometimes remarked, a Lorentzian manifold does not model correctly the structure of the continuum of physical events as it is, yet a Lorentzian manifold should describe its macroscopic structure as we experience it. More precisely, theoretically motivated by von Weizsäcker’s chronological relative frequency interpretation of probability, and taking the Diaconis–Mosteller principle (also called the law of truly large numbers) as an empirical evidence in the macroscopic world, we argue that large collections of physical events appear in a composition of two fundamentally different formations, termed as progression and sample here, suggesting, in this framework, to use a Lorentzian-type metric on a manifold to describe matter-filled macroscopic regions of the physical continuum.

Quantum theory implies, and empirical evidence confirms, that while particles can exhibit wave-like behavior in interferometric experiments, this behavior is so limited as not to allow for third- and higher-order interference. The article at hand shows that this possibility-impossibility structure suggests the universal validity of a principle that regulates statistical correlations between spatiotemporally localized events, independently of the nature of the objects that may or may not partake in these events. Roughly, and up to some qualifications, the said principle mandates that any joint influence of m mutually spacelike separated events on another event, be such, that it can be separated by at least (lceil frac{m}{2} rceil) mediating events, and in some cases, by no more than (lceil frac{m}{2} rceil) mediating events. The structure of quantum interference thus teaches us that events can influence each other in a non-separable fashion, but that this non-separability has a certain exactly quantifiable limit. 

The behavior of an electric dipole simple harmonic oscillator is analyzed where the oscillator is located within a nonuniform, static electric field. This system is used to derive the classical electromagnetic zero-point (ZP) radiation spectrum, which is the cornerstone for the classical physics based theory of nature called stochastic electrodynamics. It is shown that a key property of ZP radiation is that it has the only spectrum that results in no heat flow under reversible, isothermal thermodynamic processes. The article considers incident random classical electromagnetic radiation at temperature T acting on the oscillator, resulting in the oscillator undergoing a stochastic fluctuating motion. The incident radiation is assumed to have Fourier modes that are independent random variables with a Gaussian probability distribution. The oscillator is made to undergo an infinitely slow displacement in the nonuniform, static electric field, which here is provided by a point charge held nearby. In a resonant approximation, no heat is found to be radiated into all space, but only if the spectrum of the incident radiation is that of classical electromagnetic ZP radiation, or radiation at temperature (T=0). This result is found without counting the sum of the dipole radiation plus the cross term of the dipole-incident radiation. However, without making this resonant approximation, these two terms do need to be included and a stronger condition is found, with no heat radiated into all space for all frequencies if ZP radiation is present.

Relational Quantum Mechanics (RQM) treats quantum states as observer-dependent facts rather than absolute properties. While this relational stance is conceptually attractive, it raises concerns about empirical confirmation, particularly in multi-observer scenarios. Existing responses within RQM focus on securing agreement between observers by strengthening the status, stability, or accessibility of recorded outcomes. However, they leave open a more basic question: what grounds the persistence of an observer across time? Scientific observation presupposes stable records and the capacity to relate outcomes across successive measurements. We argue that the minimal definition of the observer in RQM as a merely interacting physical system is insufficient to support this requirement. We propose a complementary account of the observer that distinguishes physical interaction from informational coherence, and show how this distinction supports empirical confirmation in Wigner’s friend–type scenarios.

On a mathematically foundational level, our most successful physical theories (gauge field theories and general-relativistic theories) are formulated in a framework based on the differential geometry of connections on principal bundles. After reviewing the essentials of this framework, we articulate the generalized hole and point-coincidence arguments, examining how they weight on a substantivalist position towards bundle spaces. This question, then, is considered in light of the Dressing Field Method, which allows a manifestly invariant reformulation of gauge field theories and general-relativistic theories, making their conceptual structure more transparent: it formally implements the point-coincidence argument and thus allows to define (dressed) fields and (dressed) bundle spaces immune to hole-type arguments.