Search arXiv⌕ Search
Home/Archive/arXiv

arXiv · 0907.4109

Archipelagian Cosmology: Dynamics and Observables in a Universe with Discretized Matter Content

Timothy Clifton·Pedro G. Ferreira
View original source ↗Read source document ↗Export metadata ↓

Abstract

We consider a model of the Universe in which the matter content is in the form of discrete islands, rather than a continuous fluid. In the appropriate limits the resulting large-scale dynamics approach those of a Friedmann-Robertson-Walker (FRW) universe. The optical properties of such a space-time, however, do not. This illustrates the fact that the optical and `average' dynamical properties of a relativistic universe are not equivalent, and do not specify each other uniquely. We find the angular diameter distance, luminosity distance and redshifts that would be measured by observers in these space-times, using both analytic approximations and numerical simulations. While different from their counterparts in FRW, the effects found do not look like promising candidates to explain the observations usually attributed to the existence of Dark Energy. This incongruity with standard FRW cosmology is not due to the existence of any unexpectedly large structures or voids in the Universe, but only to the fact that the matter content of the Universe is not a continuous fluid.

Explore related subjects

astro-ph.COgr-qc

Keep this discovery

Explore connections, maps & timelines

BibTeXRIS

Timothy Clifton, Pedro G. Ferreira. 2011-10-07. Archipelagian Cosmology: Dynamics and Observables in a Universe with Discretized Matter Content. https://doi.org/10.1103/physrevd.80.103503

Cite the original work for its findings. Save a collection to share your selection of sources.

KEEP EXPLORING

Related papers

arXiv2026

Angular BAO Measurements with the DESI DR1 BGS Sample

We employ a model-independent approach in both the correlation function estimation and the angular BAO feature estimation by computing the angular two-point correlation function. First, we conducted a series of tests to the available DESI tracers to check their representativeness to angular clustering; the result was that, considering the completeness of the first data release across the footprint, we could only make use of the BGS sample for the effective redshifts 0.21 (BGS1) and 0.25 (BGS2). For a reliable analysis in such low redshift, we use the bootstrap of the data itself to construct a covariance matrix that accounts for systematics. We use a purely statistical method to correct the projection effects and find that our results show reasonable agreement with the $θ_{\rm BAO}$ expected by the CPL parameters obtained by DESI DR1, being BGS1 $12.77 \pm 1.15$ degrees and BGS2 $11.70 \pm 1.21$ degrees. This means a tension at the $2.4σ$ ($2.7σ$) level for BGS1 (BGS2) CPL parametrization, while a $2.84σ$ ($3.02σ$) discrepancy within the predicted by $Λ$CDM. We conclude that, with the current sample available, the use of an angular correlation function serving as the BAO probe, although prefers the CPL parametrization, does not provide conclusive results regarding the best cosmological model.

astro-ph.CO↗
arXiv2026

Dispersion Measure Distribution of Unlocalized Fast Radio Bursts as a Probe of the Hubble Constant

We present constraints on the Hubble constant ($H_0$) derived from the observed dispersion measure (DM) distribution of unlocalized fast radio bursts (FRBs). While localized FRBs with redshift measurements have been used to investigate the Hubble tension, their sample remains limited. Here we demonstrate that unlocalized FRBs---which are far more numerous---can independently constrain $H_0$ without requiring redshift information, as cosmic expansion imprints itself on their DM distribution. Analyzing a selected sample of 2124 unlocalized FRBs from the CHIME Catalog II, we obtain $H_0 = 69^{+17}_{-15}~\mathrm{km\,s^{-1}\,Mpc^{-1}}$ at the $1σ$ confidence level, corresponding to an uncertainty of about 22\%. Disentangling the parametric degeneracy among $H_0$, the FRB spectral index $α$, and the characteristic cutoff energy $E_*$ of the FRB energy distribution would reduce the fractional uncertainty in $H_0$ to 9\%. This work constitutes the first $H_0$ measurement derived solely from the DM distribution of unlocalized FRBs, highlighting their potential as a new cosmological probe. Future joint analyses with localized FRBs promise even tighter constraints.

astro-ph.CO↗
arXiv2026

Illuminating the Local Universe: Large-Scale Structure from ZTF Type Ia Supernovae

Within the volume-limited subsample at $z<0.06$ of the Zwicky Transient Facility (ZTF) DR2 sample, we confirm a statistically significant excess of Type Ia supernovae (SNe Ia) around $z \simeq 0.02-0.04$, previously reported but not explained by survey selection effects. Forward simulations assuming a uniform volumetric SN Ia rate and realistic ZTF detection efficiencies fail to reproduce the feature, rejecting this hypothesis at a $12.2σ$ level for the volume-limited sample. We further detect excesses in the rates compared to our survey simulations at $z \simeq 0.08$ and $0.14$, increasing the significance to $14σ$ when extending the redshift range up to $0.12$. To investigate the origin of these inhomogeneities, we compare the observed SN Ia distribution to constrained reconstructions of the local matter density field from the Manticore project, based on Bayesian forward modelling of the 2M++ galaxy catalogue. While SN overdensities are spatially associated with prominent nearby structures such as the Perseus, Coma, and Hercules superclusters, the amplitude of the SN excesses significantly exceeds that expected from local matter overdensities alone. By reconstructing a redshift-dependent volumetric SN Ia rate, we find that local enhancements can reach factors of three to eight within specific clusters, while the sample-averaged rate remains consistent with previous low-redshift measurements. These results indicate that the SN Ia rate is not a linear tracer of the underlying matter density and suggest a strong environmental dependence in dense structures. We discuss possible physical origins and highlight the implications for low-redshift SN cosmology, including correlated peculiar velocities and additional covariance beyond standard linear corrections.

astro-ph.CO↗