A buyer’s guide to the Hubble constant

Since the expansion of the universe was first established by Edwin Hubble and Georges Lemaître about a century ago, the Hubble constant $$H_0$$ H 0 which measures its rate has been of great interest to astronomers. Besides being interesting in its own right, few properties of the universe can be deduced without it. In the last decade, a significant gap has emerged between different methods of measuring it, some anchored in the nearby universe, others at cosmological distances. The SH0ES team has found $$H_0 = 73.2 \pm 1.3 \; \;\,\hbox {kms}^{-1} \,\hbox {Mpc}^{-1}$$ H 0 = 73.2 ± 1.3 kms - 1 Mpc - 1 locally, whereas the value found for the early universe by the Planck Collaboration is $$H_0 = 67.4 \pm 0.5 \; \;\,\hbox {kms}^{-1} \,\hbox {Mpc}^{-1}$$ H 0 = 67.4 ± 0.5 kms - 1 Mpc - 1 from measurements of the cosmic microwave background. Is this gap a sign that the well-established $${\varLambda} {\text{CDM}}$$ Λ CDM cosmological model is somehow incomplete? Or are there unknown systematics? And more practically, how should humble astronomers pick between competing claims if they need to assume a value for a certain purpose? In this article, we review results and what changes to the cosmological model could be needed to accommodate them all. For astronomers in a hurry, we provide a buyer’s guide to the results, and make recommendations.

O Ponto Ómega de Teilhard de Chardin. Do Contraponto com o Átomo Primitivo de Georges Lemaître à Projeção em Teorias Cosmológicas

This article focuses on the Omega Point, an essential concept in Teilhard de Chardin’s evolutionary metaphysics. In certain passages about the Omega Point, Teilhard mentions the primeval atom hypothesis, a theory about the beginning of the universe proposed by Georges Lemaître, another contemporary Jesuit priest who was also a scientist. Although Teilhard and Lemaître are essentially evolutionists, besides being Jesuit priests, their evolutionary metaphysics and their philosophies of science are radically divergent, and two important differences are presented here – about the eventual cosmic determinism and about the relationship between scientific knowledge and religious beliefs. This article also shows how Teilhard’s original concept was projected into two cosmological theories in which it reveals an essential transfiguration by losing its initial anthropic and religious matrix – the cosmological anthropic principle, proposed by physicists John Barrow and Frank Tipler, and the Omega Point Theory proposed later by Frank Tipler.

Behavior of Irregularities in the Distribution of Matter: Newtonian Approximation

This chapter examines the behavior of a given mass distribution in the Newtonian approximation. Discussion of how irregularities in the matter distribution behave in an expanding universe is greatly simplified by the fact that a limiting approximation of general relativity, Newtonian mechanics, applies in a region small compared to the Hubble length. The rest of the universe can affect the region only through a tidal field. Though the point was clearly made by Georges Lemaître, it has not always been recognized that the Newtonian approximation is not a model but a limiting case valid no matter what is happening in the distant parts of the universe. Because of the importance of this result, the chapter discusses it at some length.

Homogeneity and Clustering

This chapter traces the history of the development of ideas on the large-scale structure of the universe. Modern discussions of the nature of the large-scale matter distribution can be traced back to three central ideas. In 1917, Albert Einstein argued that a closed homogeneous world model fits very well into general relativity theory and the requirements of Mach's principle. In 1926, Edwin Hubble showed that the large-scale distribution of galaxies is close to uniform with no indication of an edge or boundary. In 1927, Georges Lemaître showed that the uniform distribution of galaxies fits very well with the pattern of galaxy redshifts. The chapter then assesses several questions. The first is whether the universe really is homogeneous. Could the homogeneity of the universe have been deduced ahead of time from general principles? Or might it be a useful guide to new principles? It also asks how clustering evolves in an expanding universe, what its origin is, and what this reveals about the nature of the universe.

From Genesis to Revelation

The expanding universe model was first championed by the Belgian priest Georges Lemaître, who does not always receive as much credit as he deserves. Lemaître showed how the equations of general relativity predict the universe is expanding, but Einstein was sceptical. Lemaître realized this idea could be tested because spectral lines in light from distant galaxies should be redshifted in an expanding universe and this redshift should be proportional to the distance to the galaxies. Henrietta Leavitt discovered that it is possible to determine the distance to Cepheid variables by measuring the period of their variability. Hubble used this technique to determine the distance to various nearby galaxies and compared this to their redshift data and showed that the universe is indeed expanding.