arXiv subjects

Dag Østvang

Publications and source records attributed to Dag Østvang.

11 recordsLinked to original sources

arXiv2025

Equilibrium Thermodynamics and Neutrino Decoupling in Quasi-Metric Cosmology

The laws of thermodynamics in the expanding universe are formulated within the quasi-metric framework. Since the quasi-metric cosmic expansion does not directly influence momenta of material particles, so that the expansion directly cools null particles only (e.g., photons), these laws differ substantially from their counterparts in standard cosmology. In particular, all non-null neutrino mass eigenstates are predicted to have the same energy today as they had just after neutrino decoupling in the early universe. As a result, the predicted relic neutrino background is strongly inconsistent with detection rates measured in solar neutrino detectors (Borexino in particular). Thus quasi-metric cosmology is in violent conflict with experiment unless some exotic property of neutrinos makes the relic neutrino background essentially undetectable (e.g., if all massive neutrino mass eigenstates decay into "invisible" particles over cosmic time scales). But in the absence of experimental confirmation of the necessary exotic neutrino physics needed to resolve said conflict, the current status of quasi-metric relativity has been changed to non-viable.

gr-qc↗

arXiv2024

Birkhoff's Theorem for Quasi-Metric Gravity

Working within the quasi-metric framework (QMF), it is examined if the gravitational field exterior to an isolated, spherically symmetric body is necessarily metrically static, or equivalently, whether or not Birkhoff's theorem holds for quasi-metric gravity. It is found that it does; however the proof is somewhat different from the general-relativistic case.

gr-qc↗

arXiv2024

A Non-Metric Approach to Space, Time and Gravitation

In this thesis, a non-standard geometric framework, the "quasi-metric" framework (QMF), is used to define relativistic space-time. The QMF consists of a 4-dimensional space-time manifold equipped with two one-parameter families of Lorentzian 4-metrics ${\bf g}_t$ and ${\bf {\bar g}}_t$ parametrized by a (unique) global time function $t$. The global time function represents one extra degenerate time dimension and it defines a "distinguished" foliation of quasi-metric space-time into spatial hypersurfaces. The metric family ${\bf {\bar g}}_t$ is found as solutions of field equations, whereas the metric family ${\bf g}_t$ is found via a local transformation ${\bf {\bar g}}_t{\rightarrow}{\bf g}_t$ and is used in the equations of motion. The role of the degenerate dimension is to describe global scale changes between gravitational and non-gravitational systems. In particular, this yields an alternative description of the expansion of the Universe. In this thesis, a quasi-metric theory of gravity is constructed. Like General Relativity, the field equations have two independent propagating dynamical degrees of freedom. However, a number of non-standard features makes the field equations unsuitable for a standard PPN-analysis. This implies that the experimental status of the theory is not completely clear at this point in time. But the non-metric part of the theory may be tested rather independently. That is, the theory predicts that gravitational fields in vacuum and gravitationally bound bodies made of ideal gas expand like the expansion of the Universe. Several observations suggest this; e.g., the "Pioneer effect", the mean acceleration of the Moon, the spin-down of the Earth, palaeo-tidal records, etc. Thus quasi-metric relativity has experimental support where metric theories fail.

gr-qc↗

arXiv2024

Dark Matter Explanation from Quasi-Metric Gravity

The gravitational field of an isolated, axisymmetric flat disk of spinning dust is calculated approximately in the weak-field limit of quasi-metric gravity. Boundary conditions single out the exponential disk as a "preferred" physical surface density profile. Besides, collective properties of the disk, in the form of an extra "associated induced" surface density playing the role of "dark matter", also emerge. Taken as an idealized model of spiral galaxy thin disks, it is shown that including this "dark matter" into the model as a gravitating source, yields asymptotically flat rotation curves and a correspondence with MOND.

gr-qc↗

arXiv2024

Metrically Stationary, Axially Symmetric, Isolated Systems in Quasi-Metric Gravity

The gravitational field exterior respectively interior to an axially symmetric, metrically stationary, isolated spinning source made of perfect fluid is examined within the quasi-metric framework. (A metrically stationary system is defined as a system which is stationary except for the direct effects of the global cosmic expansion on the space-time geometry.) Field equations are set up and an attempt is made to find an approximate series solution for the exterior part. However, the result is that no stationary solution corresponding to a spinning source can exist when considering terms beyond a certain order in small quantities. That is, except for metrically static systems, axially symmetric systems must necessarily be non-stationary in quasi-metric gravity. However, sufficiently weak, axially symmetric gravitational fields associated with slowly rotating sources, may still be considered as stationary as an excellent approximation. Thus a truncated, approximately stationary solution is found for the exterior field. To lowest order in small quantities, the gravito-magnetic part of the found metric family corresponds with the Kerr metric in the metric approximation. On the other hand, the gravito-electric part of the found metric family also includes a tidal term characterized by the free quadrupole-moment parameter $J_2$ describing the effect of source deformation due to the rotation. This term has no counterpart in the Kerr metric. Finally, the geodetic effect for a gyroscope in orbit is calculated. There is a correction term, unfortunately barely too small to be detectable by Gravity Probe B, to the standard expression.

gr-qc↗

arXiv2024

Classical Electrodynamics in Quasi-Metric Space-Time

The quasi-metric manifold $\cal N$ is equipped with two one-parameter families of metric tensors ${\bf {\bar g}}_t$ and ${\bf g}_t$, each parametrized by the global time function $t$. Moreover, in $({\cal N},{\bf {\bar g}}_t)$ one must define two different electromagnetic field tensor families corresponding to the active electromagnetic field tensor family ${\bf {\tilde F}}_t$ and the passive electromagnetic field tensor family ${\bf {\bar F}}_t$, respectively. The active electromagnetic field tensor family ${\bf {\tilde F}}_t$ couples to gravity. By construction, the norm of the passive electromagnetic field tensor family ${\bf {\bar F}}_t$ experiences a secular decrease, defining a global cosmic attenuation (not noticeable locally) of the electromagnetic field. Local conservation laws for passive electromagnetism imply that ${\bf {\bar {\nabla}}}{\cdot} {\bf {\bar F}}_t=0$ in electro-vacuum, ensuring that photons move on null geodesics of $({\cal N},{\bf {\bar g}}_t)$. From ${\bf {\bar F}}_t$, one may construct the passive electromagnetic field tensor family ${\bf F}_t$ in $({\cal N},{\bf g}_t)$ in the same way as ${\bf g}_t$ is constructed from ${\bf {\bar g}}_t$. This ensures that photons move on null geodesics of $({\cal N},{\bf g}_t)$ as well. As a simple example, the (exact) quasi-metric counterpart to the Reissner-Nordström solution in General Relativity is calculated. Besides, it is found that a classical charged test particle electromagnetically bound to a central charge will participate in the cosmic expansion. But since quantum-mechanical states should be unaffected by the expansion, this classic calculation is hardly relevant for quantum-mechanical systems such as atoms, so there is no reason to think that the cosmic expansion should apply to them. Finally, it is shown that the main results of geometric optics hold in quasi-metric space-time.

gr-qc↗

arXiv2024

Spherically Symmetric, Metrically Static, Isolated Systems in Quasi-Metric Gravity

The gravitational field exterior respectively interior to a spherically symmetric, isolated body made of perfect fluid is examined within the quasi-metric framework (QMF). It is required that the gravitational field is "metrically static", meaning that it is static except for the effects of the global cosmic expansion on the spatial geometry. Dynamical equations for the gravitational field are set up and an exact solution is found for the exterior part. Besides, equations of motion applying to inertial test particles moving in the exterior gravitational field are set up. By construction, the gravitational field of the system is not static with respect to the cosmic expansion. This means that the radius of the source increases and that distances between circular orbits of inertial test particles increase according to the Hubble law. Moreover, it is shown that if this model of an expanding gravitational field is taken to represent the gravitational field of the Sun (or isolated planetary systems), this has no serious consequences for observational aspects of planetary motion. On the contrary some observational facts of the Earth-Moon system are naturally explained within the QMF. Finally, the QMF predicts different secular increases for two different gravitational coupling parameters. But such secular changes are neither present in the Newtonian limit of the quasi-metric equations of motion nor in the Newtonian limit of the quasi-metric field equations valid inside metrically static sources. Thus standard interpretations of space experiments testing the secular variation of G are explicitly theory-dependent and do not apply to the QMF.

gr-qc↗

arXiv2024

Quasi-Metric Relativity

This is a survey of a new type of relativistic space-time framework; the so-called quasi-metric framework. The basic geometric structure underlying quasi-metric relativity is quasi-metric space-time; this is defined as a 4-dimensional differentiable manifold ${\cal N}$ equipped with two one-parameter families ${\bf {\bar g}}_t$ and ${\bf g}_t$ of Lorentzian 4-metrics parametrized by a global time function $t$. The metric family ${\bf {\bar g}}_t$ is found from field equations, whereas the metric family ${\bf g}_t$ is used to propagate sources and to compare predictions to experiments. A linear and symmetric affine connection compatible with the family ${\bf g}_t$ is defined, giving rise to equations of motion. Furthermore a quasi-metric theory of gravity, including field equations and local conservation laws, is presented. Just as for General Relativity, the field equations accommodate two independent propagating dynamical degrees of freedom. On the other hand, the particular structure of quasi-metric geometry allows only a partial coupling of space-time geometry to the active stress-energy tensor. Besides, the field equations are defined from projections of physical and geometrical tensors with respect to a "preferred" foliation of quasi-metric space-time into spatial hypersurfaces. Moreover, a number of non-standard features make the field equations unsuitable for a standard PPN-analysis. This implies that the experimental status of the theory is not completely clear at this point in time. The theory seems to be consistent with a number of cosmological observations and it satisfies all the classical solar system tests, though. In additon, in its non-metric sector, the new theory has experimental support where General Relativity fails or is irrelevant.

gr-qc↗

arXiv2024

Fully Extended Quasi-Metric Gravity

The original theory of quasi-metric gravity, admitting only a partial coupling between space-time geometry and the active stress-energy tensor, is too restricted to allow the existence of gravitational waves in vacuum. Therefore, said theory can at best be regarded as a wave-less approximation theory. However, the requirement that the weak-field limit of the contracted Bianchi identities should be consistent with the Newtonian limit of the local conservation laws, forbids a full coupling between space-time geometry and the active stress-energy tensor. Nevertheless, in this paper it is shown how it is possible to relax the restrictions on quasi-metric space-time geometry sufficiently to avoid these problems. That is, the original quasi-metric field equations can be extended with one extra field equation, without having said full coupling and such that the contracted Bianchi identities have a sensible Newtonian limit. For weak fields in vacuum, said extra field equation has a dynamical structure somewhat similar to that of its counterpart in canonical general relativity (GR). In this way, the prediction of weak GR-like gravitational waves in vacuum becomes possible. Moreover, exact results from the original quasi-metric gravitational theory are recovered for metrically static systems and for isotropic cosmology. This means that the current experimental status of the extended quasi-metric gravitational theory is the same as for the original theory, except for the prediction of weak GR-like gravitational waves in vacuum.

gr-qc↗

arXiv2012

Interpretations of Cosmological Spectral Shifts

It is shown that for Robertson-Walker models with flat or closed space sections, all of the cosmological spectral shift can be attributed to the non-flat connection (and thus indirectly to space-time curvature). For Robertson-Walker models with hyperbolic space sections, it is shown that cosmological spectral shifts uniquely split up into "kinematic" and "gravitational" parts provided that distances are small. For large distances no such unique split-up exists in general. A number of common, but incorrect assertions in the literature regarding interpretations of cosmological spectral shifts, is pointed out.

physics.gen-ph↗

arXiv2002

An Explanation of the "Pioneer Effect" based on Quasi-Metric Relativity

According to the socalled "quasi-metric" framework developed elsewhere, the cosmic expansion applies directly to gravitationally bound systems. This prediction has a number of observable consequences, none of which are in conflict with observation. In this paper we compare test particle motion in the nonstatic gravitational field outside a spherically symmetric source (as predicted by a quasi-metric theory of gravity) to test particle motion in the Schwarzschild geometry. It is found that if one incorrectly uses the Schwarzschild geometry (to the relevant accuracy) to represent the nonstatic quasi-metric model, the largest errors result from the mismodelling of null paths. One consequence of this is that using electromagnetic signals to track the motion of a non-relativistic particle results in the illusion that the particle is influenced by an anomalous force of size cH (where H is the Hubble parameter) directed towards the observer. This result naturally explains the apparently anomalous force acting on the Pioneer 10/11, Galileo and Ulysses spacecraft as inferred from radiometric data.

gr-qc↗