arXiv subjects

Jan J. Ostrowski

Publications and source records attributed to Jan J. Ostrowski.

21 records · Page 2Linked to original sources

arXiv2013

Virialisation-induced curvature as a physical explanation for dark energy

The geometry of the dark energy and cold dark matter dominated cosmological model (LambdaCDM) is commonly assumed to be given by a Friedmann-Lemaitre-Robertson-Walker (FLRW) metric, i.e. it assumes homogeneity in the comoving spatial section. The homogeneity assumption fails most strongly at (i) small distance scales and (ii) recent epochs, implying that the FLRW approximation is most likely to fail at these scales. We use the virialisation fraction to quantify (i) and (ii), which approximately coincide with each other on the observational past light cone. For increasing time, the virialisation fraction increases above 10% at about the same redshift (sim 1-3) at which Omega_Lambda grows above 10% (approx 1.8). Thus, instead of non-zero Omega_Lambda, we propose an approximate, general-relativistic correction to the matter-dominated (Omega_m =1, Omega_Lambda=0), homogeneous metric (Einstein de Sitter, EdS). A low-redshift effective matter-density parameter of Omega_m^eff(0) = 0.26 pm 0.05 is inferred. Over redshifts 0 < z < 3, the distance modulus of the virialisation-corrected EdS model approximately matches the LambdaCDM distance modulus. This rough approximation assumes "old physics" (general relativity), not "new physics". Thus, pending more detailed calculations, we strengthen the claim that "dark energy" should be considered as an artefact of emerging average curvature in the void-dominated Universe, via a novel approach that quantifies the relation between virialisation and average curvature evolution.

astro-ph.CO↗

arXiv2013

Topological implications of inhomogeneity

The approximate homogeneity of spatial sections of the Universe is well supported observationally, but the inhomogeneity of the spatial sections is even better supported. Here, we consider the implications of inhomogeneity in dust models for the connectedness of spatial sections at early times. We consider a non-global Lemaitre-Tolman-Bondi (LTB) model designed to match observations, a more general, heuristic model motivated by the former, and two specific, global LTB models. We propose that the generic class of solutions of the Einstein equations projected back in time from the spatial section at the present epoch includes subclasses in which the spatial section evolves (with increasing time) smoothly (i) from being disconnected to being connected, or (ii) from being simply connected to being multiply connected, where the coordinate system is comoving and synchronous. We show that (i) and (ii) each contain at least one exact solution. These subclasses exist because the Einstein equations allow non-simultaneous big bang times. The two types of topology evolution occur over time slices that include significantly post-quantum epochs if the bang time varies by much more than a Planck time. In this sense, it is possible for cosmic topology evolution to be "mostly" classical.

astro-ph.CO↗

arXiv2012

A relativistic model of the topological acceleration effect

It has previously been shown heuristically that the topology of the Universe affects gravity, in the sense that a test particle near a massive object in a multiply connected universe is subject to a topologically induced acceleration that opposes the local attraction to the massive object. This effect distinguishes different comoving 3-manifolds, potentially providing a theoretical justification for the Poincaré dodecahedral space observational hypothesis and a dynamical test for cosmic topology. It is necessary to check if this effect occurs in a fully relativistic solution of the Einstein equations that has a multiply connected spatial section. A Schwarzschild-like exact solution that is multiply connected in one spatial direction is checked for analytical and numerical consistency with the heuristic result. The T$^1$ (slab space) heuristic result is found to be relativistically correct. For a fundamental domain size of $L$, a slow-moving, negligible-mass test particle lying at distance $x$ along the axis from the object of mass $M$ to its nearest multiple image, where $GM/c^2 \ll x \ll L/2$, has a residual acceleration away from the massive object of $4ζ(3) G(M/L^3)\,x$, where $ζ(3)$ is Apéry's constant. For $M \sim 10^14 M_\odot$ and $L \sim 10$ to $20\hGpc$, this linear expression is accurate to $\pm10%$ over $3\hMpc \ltapprox x \ltapprox 2\hGpc$. Thus, at least in a simple example of a multiply connected universe, the topological acceleration effect is not an artefact of Newtonian-like reasoning, and its linear derivation is accurate over about three orders of magnitude in $x$.

astro-ph.CO↗