Mass density of the universe
Pro Research Analysisby 
Searched over 200M research papers
Mass Density of the Universe: Current Understanding and Measurements
Mean Mass Density and Galaxy Clustering
Observations of galaxy clustering have revealed that the mean mass density of the universe is significantly lower than what the Einstein–de Sitter cosmological model predicts. Specifically, the mean mass density is about one-third of the expected value from this model, suggesting either a need to revise our understanding of galaxy formation or to consider alternative cosmological models .
Vector Model and Experimental Observations
In the framework of the vector model for the gravitational field, the total mass density of the universe aligns closely with experimental observations. The total mass density is approximately (1.0 \times 10^{-29}) g/cm³, and the mass of the universe is around (10^{53}) kg . This model provides a theoretical basis that matches observed data.
Density Parameter Omega and Redshift Measurements
Recent measurements of the density parameter Omega ((\Omega)), which represents the mass density relative to the critical density, have been conducted using redshifts and fluxes of field galaxies. These measurements indicate that (\Omega) is approximately 0.9, with a range of +0.7 to -0.5, which is consistent with the Einstein-de Sitter model where (\Omega = 1) .
Mass-Energy Density and Cosmological Redshifts
The mass-energy density of the universe can also be determined through cosmological redshifts, their time drifts, and angular-diameter distances. This method provides an indirect measurement and can be used to construct models of the universe in observational coordinates .
Low Mass Density and Dark Energy
Several independent measures, including those utilizing clusters of galaxies, suggest that the mass density of the universe is low, approximately 20% of the critical density. Recent observations, including the mass-to-light function and high redshift supernovae, indicate a low-density universe ((\Omega_m \approx 0.2)) that is flat and dominated by dark energy .
Mass Distribution and Dark Matter
The distribution of mass in the universe, as determined from weak lensing observations and starlight, shows that stars trace mass well, even though they represent only a small fraction of the total mass. The mass-to-light ratio on large scales suggests a mass density of (\Omega_m = 0.26 \pm 0.02) . This indicates that most dark matter is located in large halos of individual galaxies.
Challenges in Measuring Mass Density
Despite extensive research, the average mass density parameterized by Omega remains uncertain by a factor of five. Most of the mass is in the form of dark matter, and its precise relationship with observable galaxies is still not fully understood. Advanced numerical simulations and new methods, such as redshift-space distortions, are being developed to improve these measurements .
Rotating Universe and Equilibrium Density
The theory of a rotating universe proposes an equilibrium density different from that of an expanding universe. This model suggests a denser universe with a radius much smaller than that of an expanding universe, with light traveling in a spiral due to gravitational forces .
Luminous and Nonluminous Matter
Dynamical evidence indicates that luminous matter constitutes only a small fraction of the total mass in galaxies, with the majority being dark matter. Observations of neutral hydrogen disks and complex stellar and gas motions in ellipticals support the presence of massive dark halos in spiral galaxies. These findings are consistent with a low-density universe where dark matter could be baryonic .
Median Density and Dark Matter Nature
While the mean matter density of the universe is well-measured, its median density remains less understood. The distribution of dark matter in low-density regions is sensitive to the initial power spectrum and the nature of dark matter. Different dark matter models, such as WIMPs and axions, predict varying median densities, but these properties are challenging to observe directly .
Conclusion
The mass density of the universe is a complex and multifaceted topic, with various models and measurements providing different insights. While the mean mass density is lower than some traditional models predict, new methods and observations continue to refine our understanding. The interplay between luminous and dark matter, as well as the role of dark energy, remains a critical area of research in cosmology.
Sources and full results
Most relevant research papers on this topic
Using time drift of cosmological redshifts to find the mass-energy density of the Universe
The mass-energy density of the Universe can be determined using cosmological redshifts, their time drifts, and angular-diameter distance, providing an indirect measurement for the Lemaitre-Tolman-Bondi model.
Tracing mass and light in the Universe: where is the dark matter?
Most of the dark matter in the Universe is likely in large halos of individual galaxies, with the entire mass-to-light ratio profile being accounted for by the aggregate masses of individual galaxies and gas.
DETERMINING THE MASS OF THE UNIVERSE
This research has developed tools that may significantly improve the measurement of the universe's mass, revealing that the usual treatment of galaxies as point masses is unjustified and proposing a method to determine cosmic mass density from redshift-space distortions.
DOI