Spatial and observational homogeneities of the galaxy distribution in standard cosmologies

This work discusses the possible empirical verification of the geometrical concept of homogeneity of the standard relativistic cosmology considering its various definitions of distance. We study the physical consequences of the distinction between the usual concept of spatial homogeneity (SH), as defined by the Cosmological Principle, and the concept of observational homogeneity (OH), arguing that OH is in principle falsifiable by means of astronomical observations, whereas verifying SH is only possible indirectly. Simulated counts of cosmological sources are produced by means of a generalized number-distance expression that can be specialized to produce either the counts of the Einstein-de Sitter (EdS) cosmology, which has SH by construction, or other types of counts, which do, or do not, have OH by construction. Expressions for observational volumes and differential densities are derived with the various cosmological distance definitions in the EdS model. Simulated counts that have OH by construction do not always exhibit SH features. The reverse situation is also true. Besides, simulated counts with no OH features at low redshift start showing OH characteristics at high redshift. The comoving distance seems to be the only distance definition where both SH and OH appear simultaneously. The results show that observations indicating possible lack of OH do not necessarily falsify the standard Friedmannian cosmology, meaning that this cosmology will not necessarily always produce observable homogeneous densities. The general conclusion is that the use of different cosmological distances in the characterization of the galaxy distribution lead to significant ambiguities in reaching conclusions about the behavior of the large-scale galaxy distribution in the Universe.Comment: 12 pages, 12 figures, LaTeX. Matches the final version sent to the journal. Accepted for publication in "Astronomy and Astrophysics

Cancer mortality in Portugal

Following Population News, Trends and Attitudes #6 it was possible to identify that, despite circulatory system diseases represent the leading causes of death (COD) in Portugal, the share of deaths caused by neoplasms is increasing with time. Analysing data from 10th International Classification of Diseases available at Statistics Portugal (INE), one can observe that since 2010 mortality associated to neoplasms is the major COD for males. In 2015, males presented almost twice the number of deaths caused by neoplasms when compared to females: 356.0 against 169.9 per 100.000 individuals

Skeptical Fideism in Cicero’s De Natura Deorum

The work of Richard H. Popkin both introduced the concept of skeptical fideism and served to impressively document its importance in the philosophies of a diverse range of thinkers, including Montaigne, Pascal, Huet, and Bayle. Popkin’s landmark History of Scepticism, however, begins its coverage with the Renaissance. In this paper I explore the roots of skeptical fideism in ancient Greek and Roman philosophy, with special attention to Cicero’s De Natura Deorum, the oldest surviving text to clearly develop a skeptical fideist perspective

The Apparent Fractal Conjecture

This short communication advances the hypothesis that the observed fractal structure of large-scale distribution of galaxies is due to a geometrical effect, which arises when observational quantities relevant for the characterization of a cosmological fractal structure are calculated along the past light cone. If this hypothesis proves, even partially, correct, most, if not all, objections raised against fractals in cosmology may be solved. For instance, under this view the standard cosmology has zero average density, as predicted by an infinite fractal structure, with, at the same time, the cosmological principle remaining valid. The theoretical results which suggest this conjecture are reviewed, as well as possible ways of checking its validity.Comment: 6 pages, LaTeX. Text unchanged. Two references corrected. Contributed paper presented at the "South Africa Relativistic Cosmology Conference in Honour of George F. R. Ellis 60th Birthday"; University of Cape Town, February 1-5, 199