scholarly journals A buyer’s guide to the Hubble constant

2021 ◽  
Vol 29 (1) ◽  
Author(s):  
Paul Shah ◽  
Pablo Lemos ◽  
Ofer Lahav
Keyword(s):  
Cosmological Model ◽  
Cosmic Microwave Background ◽  
Early Universe ◽  
Hubble Constant ◽  
Microwave Background ◽  
A Value ◽  
Expansion Of The Universe ◽  
Edwin Hubble ◽  
The Universe ◽  
Georges Lemaître

AbstractSince 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.

scholarly journals Inflationary universe models and clustering of quasar red shifts

1986 ◽  
Vol 119 ◽  
pp. 509-510
Author(s):  
C. Sivaram
Keyword(s):  
Cosmological Model ◽  
Early Universe ◽  
Hubble Constant ◽  
Matter Density ◽  
Inflationary Universe ◽  
Expansion Phase ◽  
Exponential Expansion ◽  
The Universe ◽  
Inflationary Models ◽  
Universe Models

Recently it has been shown that many of the puzzling features of conventional cosmological models (such as the horizon and flatness problems) could be explained by invoking inflationary models of the early universe with an exponential expansion phase at very early epochs. These models have the added advantage that they are able to make a definite prediction about the present matter density in the universe, i.e. they require that the density be exactly equal to the closure density which in turn can be easily estimated from the Hubble constant now known to within a factor of two. Now if one goes back to an earlier idea that explored the possibility of unusual clustering of quasar redshifts around z = 2 or 3, we get an example of another cosmological model with a definite prediction for the present overall matter density. This is a modified version of the Eddington-Lemaitre type of model which naturally accommodates such features as a clustering of quasars at certain epochs. From these models one can get a prediction for the present matter density which would be an involved function of the Hubble constant and the redshifts at which such clustering occurs. It can be shown that if such clustering had occurred at any z, the present matter density predicted would be substantially smaller than the corresponding closure density. The conclusion is that any clustering of quasar redshifts is incompatiable with inflationary universe models, indirectly providing observational support for these new theories.

scholarly journals The habitable epoch of the early Universe

2014 ◽  
Vol 13 (4) ◽  
pp. 337-339 ◽  
Author(s):  
Abraham Loeb
Keyword(s):  
Cosmic Microwave Background ◽  
Cosmological Constant ◽  
Water Chemistry ◽  
Early Universe ◽  
Liquid Water ◽  
Matter Density ◽  
Microwave Background ◽  
Star Forming ◽  
Rocky Planets ◽  
The Universe

AbstractIn the redshift range 100≲(1+z)≲137, the cosmic microwave background (CMB) had a temperature of 273–373 K (0–100°C), allowing early rocky planets (if any existed) to have liquid water chemistry on their surface and be habitable, irrespective of their distance from a star. In the standard ΛCDM cosmology, the first star-forming halos within our Hubble volume started collapsing at these redshifts, allowing the chemistry of life to possibly begin when the Universe was merely 10–17 million years old. The possibility of life starting when the average matter density was a million times bigger than it is today is not in agreement with the anthropic explanation for the low value of the cosmological constant.

scholarly journals The cosmic distance scale and H0: Past, present, and future

2012 ◽  
Vol 8 (S289) ◽  
pp. 3-9 ◽  
Author(s):  
Wendy L. Freedman
Keyword(s):  
Recent Progress ◽  
Hubble Space Telescope ◽  
Cosmological Parameters ◽  
Hubble Constant ◽  
Future Prospects ◽  
Microwave Background ◽  
A Value ◽  
Systematic Uncertainties ◽  
Near Future ◽  
The Universe

AbstractTwenty years ago, there was disagreement at a level of a factor of two as regards the value of the expansion rate of the Universe. Ten years ago, a value that was good to 10% was established using the Hubble Space Telescope (HST), completing one of the primary missions that NASA designed and built the HST to undertake. Today, after confronting most of the systematic uncertainties listed at the end of the Key Project, we are looking at a value of the Hubble constant that is plausibly known to within 3%. In the near future, an independently determined value of H0 good to 1% is desirable to constrain the extraction of other cosmological parameters from the power spectrum of the cosmic microwave background in defining a concordance model of cosmology. We review recent progress and assess the future prospects for those tighter constraints on the Hubble constant, which were unimaginable just a decade ago.

scholarly journals CMB anisotropy science: a review

2012 ◽  
Vol 8 (S288) ◽  
pp. 42-52 ◽  
Author(s):  
Anthony Challinor
Keyword(s):  
Dark Matter ◽  
Cosmological Model ◽  
Cosmic Microwave Background ◽  
Gravitational Waves ◽  
Early Universe ◽  
Critical Role ◽  
Microwave Background ◽  
Fundamental Physics ◽  
Standard Cosmological Model

AbstractThe cosmic microwave background (CMB) provides us with our most direct observational window to the early universe. Observations of the temperature and polarization anisotropies in the CMB have played a critical role in defining the now-standard cosmological model. In this contribution we review some of the basics of CMB science, highlighting the role of observations made with ground-based and balloon-borne Antarctic telescopes. Most of the ingredients of the standard cosmological model are poorly understood in terms of fundamental physics. We discuss how current and future CMB observations can address some of these issues, focusing on two directly relevant for Antarctic programmes: searching for gravitational waves from inflation via B-mode polarization, and mapping dark matter through CMB lensing.

Nonbaryonic Dark Matter

2020 ◽  
pp. 279-299
Author(s):  
P. J. E. Peebles
Keyword(s):  
Dark Matter ◽  
Cosmological Model ◽  
Early Universe ◽  
Particle Physics ◽  
First Generation ◽  
Mass Density ◽  
Rest Mass ◽  
Big Bang ◽  
Expansion Of The Universe ◽  
The Universe

This chapter discusses the particle physicists' considerations of nonbaryonic matter. It takes into account the condition that if this nonbaryonic matter were produced in the hot early stages of expansion of the universe, then its remnant mass density must not exceed that allowed by the relativistic big bang cosmological model (again, assuming the relativistic theory). But it is notable that cosmologists took over the notion of nonbaryonic dark matter before the particle physics community had taken much interest in the astronomers' evidence of the presence of subluminal matter. The nonbaryonic dark matter most broadly discussed in the 1980s came in two varieties, cold and hot. The latter would be one of the known class of neutrinos with rest mass of a few tens of electron volts. The initially hot (meaning rapidly streaming) neutrinos in the early universe would have smoothed the mass distribution, and that smoothing would have tended to cause the first generation of structure to be massive systems that must have fragmented to form galaxies.

Does Gravity Rule the Universe?

1992 ◽  
Vol 10 (2) ◽  
pp. 87-93
Author(s):  
Donald S. Mathewson
Keyword(s):  
Cosmic Microwave Background ◽  
Early Universe ◽  
Spiral Galaxies ◽  
Bulk Flow ◽  
Microwave Background ◽  
Peculiar Velocities ◽  
Sky Survey ◽  
The Universe ◽  
Initial Results ◽  
Great Attractor

AbstractThe initial results of a southern sky survey of the peculiar velocities of 1355 spiral galaxies by a group at Mount Stromlo and Siding Spring Observatories (MSSSO) are discussed against the background of past work in this area. The most important result is that the Great Attractor does not exist; rather, there is bulk flow relative to the cosmic microwave background (CMB) of amplitude 600 km s−1 and scale greater than 130 h−1 Mpc in the Supergalactic plane. This is generated by the assumption that the CMB dipole is Doppler induced by our Galaxy moving at 622 km s−1 relative to the CMB. This may be incorrect, in which case there is no bulk flow and the radiation dipole is cosmological in origin with important implications for the early Universe.

scholarly journals Mapping the Dark Energy Equation of State

2005 ◽  
Vol 216 ◽  
pp. 59-66
Author(s):  
Eric V. Linder
Keyword(s):  
Dark Energy ◽  
Equation Of State ◽  
Energy Density ◽  
Cosmic Microwave Background ◽  
Structure Formation ◽  
Energy Equation ◽  
Microwave Background ◽  
Redshift Surveys ◽  
Expansion Of The Universe ◽  
The Universe

The acceleration of the expansion of the universe has deep implications for structure formation, the composition of the universe, and its fate. Roughly 70% of the energy density is in a dark energy, whose nature remains unknown. Mapping the expansion history through supernovae, mapping the geometry of the universe and formation of structure through redshift surveys, and mapping the distance to recombination through the cosmic microwave background provide complementary, precise probes of the equation of state of the dark energy. Together these next generation maps of the cosmos can reveal not only the value today, but the redshift variation, of the equation of state, providing a critical clue to the underlying physics.

scholarly journals Cosmic Microwave Background as a Thermal Gas of SU(2) Photons: Implications for the High-z Cosmological Model and the Value of H0

2017 ◽  
Vol 2017 ◽  
pp. 1-9 ◽  
Author(s):  
Steffen Hahn ◽  
Ralf Hofmann
Keyword(s):  
Dark Matter ◽  
Cosmological Model ◽  
Cosmic Microwave Background ◽  
Cold Dark Matter ◽  
Formal Solution ◽  
Planck Scale ◽  
Low Frequency ◽  
Hubble Constant ◽  
Microwave Background ◽  
Photon Gas

Presently, we are facing a 3σ tension in the most basic cosmological parameter, the Hubble constant H0. This tension arises when fitting the Lambda-cold-dark-matter model (ΛCDM) to the high-precision temperature-temperature (TT) power spectrum of the Cosmic Microwave Background (CMB) and to local cosmological observations. We propose a resolution of this problem by postulating that the thermal photon gas of the CMB obeys an SU(2) rather than U(1) gauge principle, suggesting a high-z cosmological model which is void of dark-matter. Observationally, we rely on precise low-frequency intensity measurements in the CMB spectrum and on a recent model independent (low-z) extraction of the relation between the comoving sound horizon rs at the end of the baryon drag epoch and H0 (rsH0=const). We point out that the commonly employed condition for baryon-velocity freeze-out is imprecise, judged by a careful inspection of the formal solution to the associated Euler equation. As a consequence, the above-mentioned 3σ tension actually transforms into a 5σ discrepancy. To make contact with successful low-z  ΛCDM cosmology we propose an interpolation based on percolated/depercolated vortices of a Planck-scale axion condensate. For a first consistency test of such an all-z model we compute the angular scale of the sound horizon at photon decoupling.

scholarly journals PROBING THE ANISOTROPIC EXPANSION HISTORY OF THE UNIVERSE WITH COSMIC MICROWAVE BACKGROUND

2012 ◽  
Vol 27 (24) ◽  
pp. 1250144 ◽  
Author(s):  
RANJITA K. MOHAPATRA ◽  
P. S. SAUMIA ◽  
AJIT M. SRIVASTAVA
Keyword(s):  
Cosmic Microwave Background ◽  
Background Radiation ◽  
Microwave Background ◽  
Anisotropic Expansion ◽  
Microwave Background Radiation ◽  
Expansion Stage ◽  
History Of ◽  
Density Perturbations ◽  
Expansion Of The Universe ◽  
The Universe

We propose a simple technique to detect any anisotropic expansion stage in the history of the universe starting from the inflationary stage to the surface of last scattering from the cosmic microwave background radiation (CMBR) data. We use the property that any anisotropic expansion in the universe would deform the shapes of the primordial density perturbations and this deformation can be detected in a shape analysis of superhorizon fluctuations in CMBR. Using this analysis we obtain the constraint on any previous anisotropic expansion of the universe to be less than about 35%.

scholarly journals Uniformity of cosmic microwave background as a non-inflationary geometrical effect

2015 ◽  
Vol 30 (35) ◽  
pp. 1530026
Author(s):  
Branislav Vlahovic ◽  
Maxim Eingorn ◽  
Cosmin Ilie
Keyword(s):  
Cosmological Model ◽  
Cosmic Microwave Background ◽  
Light Propagation ◽  
Space Region ◽  
Microwave Background ◽  
Planck Data ◽  
Spatial Geometry ◽  
Geometrical Effect ◽  
Age Of The Universe ◽  
The Universe

The conventional [Formula: see text]CDM cosmological model supplemented by the inflation concept describes the Universe very well. However, there are still a few concerns: new Planck data impose constraints on the shape of the inflaton potential, which exclude a lot of inflationary models; dark matter is not detected directly, and dark energy is not understood theoretically on a satisfactory level. In this brief sketch, we investigate an alternative cosmological model with spherical spatial geometry and an additional perfect fluid with the constant parameter [Formula: see text] in the linear equation of state. It is demonstrated explicitly that in the framework of such a model it is possible to satisfy the supernovae data at the same level of accuracy as within the [Formula: see text]CDM model and at the same time suppose that the observed cosmic microwave background (CMB) radiation originates from a very limited space region. This is ensured by introducing an additional condition of light propagation between the antipodal points during the age of the Universe. Consequently, the CMB uniformity can be explained without the inflation scenario. The corresponding drawbacks of the model with respect to its comparison with the CMB data are also discussed.

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