[Paper Review] Status of Cosmology

Joel R. Primack|arXiv (Cornell University)|Dec 6, 1999

Cosmology and Gravitation Theories1 references3 citations

TL;DR

This 1999 paper by Joel R. Primack reviews the status of cosmological parameters using observational evidence from the late 1990s, emphasizing the Hubble parameter, age of the universe, matter density, baryonic and neutrino densities, and the cosmological constant. It concludes that current data favor a universe with h ≈ 0.65, t₀ ≈ 13 Gyr, Ωₘ ≈ 0.3, and Ω_Λ ≈ 0.7, pointing to a dark energy-dominated, flat cosmological model.

ABSTRACT

The cosmological parameters that I will emphasize are the Hubble parameter $H_0 \equiv 100 h$ km s$^{-1}$ Mpc$^{-1}$, the age of the universe $t_0$, 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, $h \approx 0.65$, $Ω_m \approx 0.3$, $Ω_Λ\approx 0.7$.

Motivation & Objective

• To assess the state of cosmological parameters based on observational data available in late 1999.
• To evaluate the consistency of measurements of H₀, t₀, Ωₘ, Ω_b, Ω_ν, and Ω_Λ with emerging cosmological models.
• To synthesize evidence from cosmic microwave background, large-scale structure, and supernova observations to constrain key cosmological parameters.
• To provide a coherent picture of the universe’s age, composition, and expansion rate consistent with current data.

Proposed method

• Analysis of observational data from cosmic microwave background anisotropies, large-scale structure surveys, and Type Ia supernovae.
• Use of the Hubble parameter H₀ = 100h km s⁻¹ Mpc⁻¹ as a central cosmological parameter.
• Application of the Friedmann equation to relate expansion rate, matter density, and dark energy density.
• Comparison of theoretical predictions with observational constraints on Ωₘ and Ω_Λ.
• Incorporation of baryonic and neutrino density estimates from Big Bang nucleosynthesis and structure formation.
• Use of the ASP Conference Series format to present a synthesized review for the cosmological community.

Experimental results

Research questions

• RQ1 What is the best-fit value of the Hubble parameter H₀ based on late 1990s data?
• RQ2 What is the estimated age of the universe consistent with current cosmological observations?
• RQ3 What is the measured matter density Ωₘ, and how does it compare to the critical density?
• RQ4 What evidence supports a non-zero cosmological constant Ω_Λ ≈ 0.7?
• RQ5 How do baryonic and neutrino densities align with predictions from Big Bang nucleosynthesis and structure formation?

Key findings

• The age of the universe is estimated at approximately 13 billion years, consistent with high-precision measurements of the Hubble parameter and cosmic microwave background.
• The Hubble parameter is constrained to h ≈ 0.65, implying H₀ ≈ 65 km s⁻¹ Mpc⁻¹.
• The matter density Ωₘ is found to be approximately 0.3, indicating a universe dominated by non-baryonic dark matter.
• The cosmological constant Ω_Λ is estimated at 0.7, indicating that dark energy dominates the energy budget of the universe.
• The combination of Ωₘ ≈ 0.3 and Ω_Λ ≈ 0.7 implies a flat universe with total density close to the critical density.
• The baryonic matter density Ω_b is consistent with predictions from Big Bang nucleosynthesis, supporting the standard model of cosmology.