Foundations of Physics最新文献

We explore the dynamical behavior of two f(T, B) gravity models with a scalar field: 1. (f(T,B)=T-gamma logbigg [frac{psi B_{0}}{B}bigg ]) and 2. (f(T,B)=eta T+frac{zeta }{B^{n}}), using the potential (V(phi )=V_{0}(alpha +e^{-beta phi })^{-delta }) and an interaction term (bar{Q} = epsilon H dot{phi }^2). A phase space analysis reveals four fixed points in Model 3.1 (three stable, one saddle) and five in Model 3.2 (four stable), indicating transitions from matter to dark energy dominance. With interaction, Model 3.2 exhibits seven fixed points, including five stable, one unstable (stiff matter era) and one saddle point. Evolution of the deceleration parameter q and the total EoS parameter (omega _{tot}) confirms sustained cosmic acceleration, with present values (q_{0} = -1.005) and (omega _{0} = -0.556) (Model 3.1) and (q_{0} = -1.245) and (omega _{0}=-1.0404) (Model 3.2). Comparisons of our observationally constrained parameters with (Lambda )CDM show strong consistency, supporting the viability of these models in describing the late-time accelerated expansion of the Universe.

Relational Quantum Mechanics posits that facts about the properties of physical systems are relative to other systems. As recently pointed out by Adlam, this gives rise to the question of the relationship between the facts that obtain relative to complex systems and the facts that obtain relative to their constituents. In this paper, I respond to Adlam’s discussion of what she calls the Combination Problem. My starting point is a maximally permissive default view according to which any collection of systems counts as a new system and composites inherit all facts that obtain relative to their constituents. Subsequently, I advance three main claims: First, that Adlam’s arguments in favour of a more restrictive approach are not compelling. Second, that even if they were, she is wrong to claim that a ‘tamed’ version of RQM with postulated links between perspectives is in a better position to support such a restrictive approach. And third, that the possibly most difficult aspect of the Combination Problem in fact pertains to the combination of quantum states and probabilities. While significant challenges for the permissive solution arise here, I argue that they are likely to arise for any plausible response to the Combination Problem. More tentatively, I propose a strategy to mitigate the difficulty based on the observer-dependence of relative quantum state assignments. Along the way, I address crucial foundational issues in Relational Quantum Mechanics, from cross-perspective communication to the link between relative facts and experiences to empirical adequacy.

Given two parties performing experiments in separate laboratories, we provide a diagrammatic formulation of what it means for the joint statistics of their experiments to satisfy local realism. In particular, we show that the principles of locality and realism are both captured by a single commutative diagram in the category of probability-preserving maps between finite probability spaces, and we also show that an assumption of such a diagrammatic formulation of local realism implies the standard CHSH inequality associated with dichotomic random variables. As quantum theory is known not to satisfy local realism, our formulation of local realism in terms of commutative diagrams provides yet another way in which the notion of non-commutativity plays a fundamental role in quantum theory. We note that we do not assume any prior knowledge of category theory or quantum theory, as this work is intended for philosophers, mathematicians and physicists alike.

We provide novel, metatheoretical arguments strengthening the position that the naturalness problem of the light Higgs mass is a pseudo-problem: Under one assumption, no physics beyond the standard model of particle physics is needed to explain the small value of the Higgs boson. By evaluating previous successes of the guiding principle of technical naturalness, we restrict its applicability to non-fundamental phenomena in the realm of provisional theories within limited energy scales. In view of further breaches of autonomy of scales in apparently fundamental phenomena outside particle physics, the hierarchy problem of the Higgs mass is instead reinterpreted as an indication of the ontologically fundamental status of the Higgs boson. Applying the concept of robustness of theoretical elements under theory changes by Worrall and Williams justifies this seemingly contradictory attribution within the effective theories of the standard model of particle physics. Moreover, we argue that the ongoing naturalness debate about the Higgs mass is partly based on the adherence to the methodology of effective theories (often claimed to be universally applicable), for which there is no justification when dealing with presumably fundamental phenomena such as the Higgs mechanism, even if it is embedded into an effective theory.

We propose our account of the meaning of local symmetries. We argue that the general covariance principle and gauge principle both are principles of democratic epistemic access to the law of physics, leading to ontological insights about the objective nature of spacetime. We further argue that relationality is a core notion of general-relativistic gauge field theory, tacitly encoded by its (active) local symmetries.

Some authors in the quantum gravity community endorse, explicitly or implicitly, a radical relationalist view of time which states that the ordinal structure of time is not needed even in our classical theories, especially in general relativity. In this article I analyze this position and the arguments supporting it, and I argue that there are some serious concerns with some of the radical relationalists’ arguments which make it an unattractive position. In this sense, I conclude that the chrono-ordinal structures of our theories play important theoretical and explanatory roles and that they can be taken to be part of the empirical content of our theories.

Recent results have shown that singularities can be avoided from the general relativistic standpoint in Lorentzian-Euclidean black holes by means of the transition from a Lorentzian to an Euclidean region where time loses its physical meaning and becomes imaginary. This dynamical mechanism, dubbed “atemporality”, prevents the emergence of black hole singularities and the violation of conservation laws. In this paper, the notion of atemporality together with a detailed discussion of its implications is presented from a philosophical perspective. The main result consists in showing that atemporality is naturally related to conservation laws.

We present a comparative study between classical probability and quantum probability from the Bayesian viewpoint, where probability is construed as our rational degree of belief on whether a given statement is true. From this viewpoint, including conditional probability, three issues are discussed: (i) given a measure of the rational degree of belief, does it satisfy the axioms of the probability? (ii) Given the probability satisfying these axioms, is it seen as the measure of the rational degree of belief? (iii) Can the measure of the rational degree of belief be evaluated in terms of the relative frequency of events occurring? Here we show that as with the classical probability, all these issues can be resolved affirmatively in the quantum probability, provided that the relation to the relative frequency is slightly modified from the Laplace law of succession in case of a small number of observations. This implies that the relation between the Bayesian probability and the relative frequency in quantum mechanics is the same as that in the classical probability theory, including conditional probability.

In most day-to-day physics, one is modelling other systems and it is possible to maintain a provisional separation of subject and object, or of investigator and system being investigated. Ultimately, though, we are part of the universe. The fact that we act in the domain that we are representing can make it impossible to stabilize certain facts or features of the world as objects of knowledge. I’ll suggest that this casts light on the sense in which the universe is participatory and use differences in the way that the effects propagate to distinguish the classical and quantum worlds.  

The ultimate extension of Penrose’s Spin Geometry Theorem is given. It is shown how the local geometry of any curved Lorentzian 4-manifold (with (C^2) metric) can be derived in the classical limit using only the observables in the algebraic formulation of abstract Poincaré-invariant elementary quantum mechanical systems. In particular, for any point q of the classical spacetime manifold and curvature tensor there, there exists a composite system built from finitely many Poincaré-invariant elementary quantum mechanical systems and a sequence of its states, defining the classical limit, such that, in this limit, the value of the distance observables in these states tends with asymptotically vanishing uncertainty to lengths of spacelike geodesic segments in a convex normal neighbourhood U of q that determine the components of the curvature tensor at q. Since the curvature at q determines the metric on U up to third order corrections, the metric structure of curved (C^2) Lorentzian 4-manifolds is recovered from (or, alternatively, can be defined by the observables of) abstract Poincaré-invariant quantum mechanical systems.