arXiv subjects

Nicola Bamonti

Publications and source records attributed to Nicola Bamonti.

8 recordsLinked to original sources

arXiv2026

Does DESI Provide Evidence for Dynamical Dark Energy?

Recent results from the Dark Energy Spectroscopic Instrument (DESI) have suggested that dark energy, long considered to be a cosmological constant, may actually be \lq{}dynamical\rq{}. To clarify what follows from these results, we distinguish three claims: (D1) the data disfavour the \LCDM expansion history; (D2) within the phenomenological Chevallier--Polarski--Linder (CPL) parametrisation, the data prefer $(w_0,w_a)\neq(-1,0)$; and (D3) there exist one or more genuine dynamical dark-energy degrees of freedom in the matter-sector, within GR and coupled to the standard sectors only gravitationally, whose dynamics account for the departure from the \LCDM expansion history. We demonstrate that DESI establishes D2, which supports D1, but does not establish D3. The \lq{}designer\rq{} construction in $f(R)$ gravity provides a gravitational realisation of the same background history, so that no observable determined solely by that history can discriminate, even in principle, between its \lq{}matter\rq{} and \lq{}gravitational\rq{} readings. Furthermore, non-minimally coupled models admit regular effective phantom-crossing realisations of the relevant phenomenology, while the selected crossing places additional pressure on a single-component, minimally coupled realisation of the matter-sector reading. We characterise the resulting underdetermination between matter and gravitational interpretations---exact at the level of background history, but breakable beyond it---and draw the corresponding norm for survey reporting.

physics.hist-ph↗

arXiv2026

Reference Frames and the Ontology of General Relativity. Re(l)ality: The View From Nowhere vs. The View From Everywhere

In General Relativity, the genuine observable quantities are gauge-invariant Dirac observables. One well-known method of constructing them is relational, using reference frames. This leaves open an interpretive question: how should we understand two distinct relational observables defined relative to two distinct frames? I argue that this question admits two equally precise answers, corresponding to two distinct ontologies for relational general-relativistic physics, both expressible within a single fibre-bundle vocabulary. Central to the analysis is a distinction -- building on Wallace (2019) -- between frame-independence and frame-freedom, which disambiguates appeals to perspective-'neutrality'. The View from Nowhere treats relational observables as gauge-invariant partial descriptions on one underlying physical situation, typically formalised as a frame-free gauge equivalence class, and articulates within GR Adlam (2024)'s moderate physical perspectivalism. The View from Everywhere takes each relational description to represent the 'most comprehensive' -- as opposed to partial -- physical situation, rejecting ontological commitment to any shared frame-free reality, and articulates Adlam's strong perspectivalism in a non-solipsistic form. I do not settle the choice between them: each is reconstructed with its ontological commitments and costs made explicit. The framework also exhibits a constructive counter-example to a leading objection to strong perspectivalism -- that it cannot underwrite the structural connections between perspectives without frame-free structures -- by showing that a frame-independent inter-frame translation map fulfils the intended connective function. I conclude by suggesting how the results of this works may also shed light on parallel debates in quantum reference frames and relational quantum mechanics.

physics.hist-ph↗

arXiv2025

What is a reference frame in General Relativity?

This work introduces a novel three-fold classification of reference frames in General Relativity, distinguishing between Idealised Reference Frames (IRFs), Dynamical Reference Frames (DRFs), and Real Reference Frames (RRFs). By defining a reference frame as a set of degrees of freedom instantiated by a physical system, the work contrasts this notion with that of coordinate systems-purely mathematical idealisations lacking physical instantiation. This classification addresses two longstanding challenges in GR: (P1) the difficulty of defining local and gauge-invariant observables, and (P2) how to interpret diffeomorphism gauge freedom in physical terms rather than as merely a mathematical redundancy. Overall, this work clarifies the conceptual foundations in classical General Relativity, enhancing our understanding of gauge-symmetries, observers and laying the groundwork for future investigations in both classical and quantum gravitational contexts.

physics.hist-ph↗

arXiv2025

Apples Falling, Buckets Rolling, and Why Inertia Keeps Trolling: Inertial Motion is Not Natural Motion

Inertia has long been treated as the paradigm of natural motion. This paper challenges this identification through the lens of General Relativity. Drawing on Norton (2012)'s distinction between idealisation and approximation and analysing key results from Tamir (2012) on the theorems of Geroch-Jang, Ehlers-Geroch, Einstein-Grommer, and Geroch-Traschen, I argue that geodesic motion -- commonly treated as the relativistic expression of inertia -- fails to qualify as either. Rather, geodesic motion is best understood as a useful construct -- a formal artefact of the theory's geometric structure, without real or fictitious instantiation, and excluded by the dynamical structure of General Relativity. In place of inertial motion, I develop a layered account of natural motion, which is not encoded in a single "master equation of motion." Extended, structured, and backreacting bodies require successively refined dynamical formalisms that systematically depart from geodesic motion. This pluralist framework displaces geodesic motion as the privileged expression of pure gravitational motion, replacing it with a dynamically grounded hierarchy of approximations fully consistent with the Einstein field equations. Inertial motion thus emerges not as the universal default of motion under gravity alone, but as a formal construct that stands apart from the pluralistic framework in which natural motion is genuinely realised.

physics.hist-ph↗

arXiv2025

In Search of Cosmic Time: Complete Observables and the Clock Hypothesis

This paper considers a new and deeply challenging face of the problem of time in the context of cosmology drawing on the work of Thiemann (2006, 2007). Thiemann argues for a radical response to the cosmic problem of time that requires us to modify the classical Friedmann equations. By contrast, we offer a conservative proposal for solution of the problem by bringing together ideas from the contemporary literature regarding reference frames (Bamonti 2023; Bamonti and Gomes 2024), complete observables (Gryb and Thébault 2016b; Gryb and Thébault 2023), and the model-based account of time measurement (Tal 2016). On our approach, we must reinterpret our criteria of observability in light of the clock hypothesis and the model-based account of measurement in order to preserve the Friedmann equations as the dynamical equations for the universe.

gr-qc↗

arXiv2024

The Hole Argument for Reference Frames

We exploit the results of Bamonti and Gomes (2024) concerning the dynamical (un)coupling of reference frames to gravity to analyse the role of reference frames in the Hole Argument. We introduce a new possible threat to determinism, which we call Arbitrariness Problem (ARB), resulting from the inherent freedom in selecting a reference frame.

physics.hist-ph↗

arXiv2024

What Reference Frames Teach Us. Part I: About Symmetry Principles and Observability

This paper is an exploration of the nuanced realm of reference frames within the framework of General Relativity. Our analysis exposes a violation of Earman's SP1 principle in scenarios involving fields that are dynamically uncoupled, a common assumption for reference frames. Unlike other violations, we cannot foreclose it by eliminating background spacetime structure. Our analysis also leads us to challenge the conventional notion of partial observables as quantities that are associated with a measuring instrument and expressed within a coordinate system. Instead, we argue that a partial observable is inherently relational, even if gauge-variant, and needs dynamical coupling with other partial observables to form a bona-fide, gauge-invariant complete observables. This perspective allows us to distinguish between being relational and being gauge-invariant, two properties that are often conflated.

physics.hist-ph↗

arXiv2021

Features of the Primordial Universe in f(R)-gravity as viewed in the Jordan frame

We analyze some relevant features of the primordial Universe as viewed in the Jordan frame formulation of the f(R)-gravity, especially when the potential term of the non-minimally coupled scalar field is negligible. We start formulating the Hamiltonian picture in the Jordan frame, using the 3-metric determinant as a basic variable and we outline that its conjugated momentum appears linearly only in the scalar constraint. Then, we construct the basic formalism to characterize the dynamics of a generic inhomogeneous cosmological model and specialize it in order to describe behaviors of the Bianchi Universes, both on a classical and a quantum regime. As a fundamental issue, we demonstrate that, when the potential term of the additional scalar mode is negligible near enough to the initial singularity, the Bianchi IX cosmology is no longer affected by the chaotic behavior, typical in vacuum of the standard Einsteinian dynamics. In fact, the presence of stable Kasner stability region and its actractive character are properly characterized. Finally, we investigate the canonical quantization of the Bianchi I model, using as time variable the non-minimally coupled scalar field and showing that the existence of a conserved current is outlined for the corresponding Wheeler-DeWitt equation. The behavior of a localized wave-packet for the isotropic Universe is also evolved, demonstrating that the singularity is still present in this revised quantum dynamics.

gr-qc↗