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Cosmological Parameters 2000

Joel R. Primack

TL;DR

This review addresses the problem of pinning down the fundamental cosmological parameters by synthesizing constraints from multiple observational probes within FRW and ΛCDM frameworks. It combines relative-distance indicators, fundamental-physics methods, CMB data, and large-scale structure to estimate $t_0$, $H_0$, $\Omega_m$, $\Omega_b$, $\Omega_\nu$, and $\Omega_\Lambda$, finding broad concordance on a nearly flat universe with $t_0 \approx 13$ Gyr, $h \approx 0.65$, $\Omega_m \approx 0.3$–$0.4$, $\Omega_\Lambda \approx 0.6$–$0.7$, and a nonzero hot dark matter component $\Omega_\nu \gtrsim 10^{-3}$. The work highlights that SN Ia and CMB measurements are particularly powerful for constraining flatness and dark energy, while cluster baryon fractions and Lyman-α forest data inform $\Omega_m$; it also notes model-dependent tensions in arc statistics and lensing results. The significance lies in demonstrating cross-method consistency and outlining a path for tighter constraints with upcoming CMB missions and improved distance calibrations, enabling sharper insights into dark matter and dark energy physics.

Abstract

The cosmological parameters that I emphasize are the age of the universe $t_0$, the Hubble parameter $H_0 \equiv 100 h$ km s$^{-1}$ Mpc$^{-1}$, the average matter density $Ω_m$, the baryonic matter density $Ω_b$, the neutrino density $Ω_ν$, and the cosmological constant $Ω_Λ$. The evidence currently favors $t_0 \approx 13$ Gyr, $h \approx 0.65$, $Ω_m \approx 0.4\pm0.1$, $Ω_b = 0.02h^{-2}$, $0.001 < Ω_ν< 0.1$, and $Ω_Λ\approx 0.7$.

Cosmological Parameters 2000

TL;DR

This review addresses the problem of pinning down the fundamental cosmological parameters by synthesizing constraints from multiple observational probes within FRW and ΛCDM frameworks. It combines relative-distance indicators, fundamental-physics methods, CMB data, and large-scale structure to estimate , , , , , and , finding broad concordance on a nearly flat universe with Gyr, , –, –, and a nonzero hot dark matter component . The work highlights that SN Ia and CMB measurements are particularly powerful for constraining flatness and dark energy, while cluster baryon fractions and Lyman-α forest data inform ; it also notes model-dependent tensions in arc statistics and lensing results. The significance lies in demonstrating cross-method consistency and outlining a path for tighter constraints with upcoming CMB missions and improved distance calibrations, enabling sharper insights into dark matter and dark energy physics.

Abstract

The cosmological parameters that I emphasize are the age of the universe , the Hubble parameter km s Mpc, the average matter density , the baryonic matter density , the neutrino density , and the cosmological constant . The evidence currently favors Gyr, , , , , and .

Paper Structure

This paper contains 10 sections, 3 equations, 1 figure, 1 table.

Table of Contents

  1. Introduction
  2. Age of the Universe $t_0$
  3. Hubble Parameter $H_0$
  4. Relative Distance Methods
  5. Fundamental Physics Approaches
  6. Conclusions on $H_0$
  7. Hot Dark Matter Density $\Omega_\nu$
  8. Cosmological Constant $\Lambda$
  9. Measuring $\Omega_m$
  10. Conclusion

Figures (1)

  • Figure 1: The Great Seal of the United States, found on the back of the American dollar bill, includes a pyramid representing strength and duration, capped by the eye of Providence. Here we use this to represent the visible matter in the universe ($\Omega_{vis} \approx 0.005$), with the upper triangle containing the eye representing the metals (elements heavier than hydrogen and helium, with $\Omega_{metals}\approx 10^{-4}$) since most of the mass of our bodies is made up of these elements. The three-dimensional nature of the pyramid, which here continues below the part shown on the Great Seal, makes it useful for showing graphically the relative proportions of the dark baryons, cold dark matter, and cosmological constant (or dark energy).