Matter density crude estimates

[Floyd_13]

TL;DR Summary

Resources on crude estimates of matter density before 1990

Liddle (2015, p.67) writes: "From the crude estimates that a typical galaxy weighs about $10^{11}M\odot$ and that galaxies are typically about a megaparsec apart, we know that the Universe cannot be a long way from the critical density."

Was this fact (i.e. that the actual density is likely close to the critical density) known from these crude counting estimates in the 1980s before the CMB precision measurements in the 2000s confirming flat geometry? If yes, does anyone have specific references to papers providing such crude estimates **before 1990**?

Reference: Liddle, A. (2015). An introduction to modern cosmology. John Wiley & Sons.

Thank you!

 

[renormalize]

Was this fact (i.e. that the actual density is likely close to the critical density) known from these crude counting estimates in the 1980s before the CMB precision measurements in the 2000s confirming flat geometry? If yes, does anyone have specific references to papers providing such crude estimates **before 1990**?

Absolutely! Here's a relevant 1972 quotation from Steven Weinberg, Gravitation and Cosmology, pg. 476:

"...and (15.2.1) gives the ratio of the present density to the critical density (15.2.3) as $$\frac{\rho_{0}}{\rho_{c}}=2q_{0}\tag{15.2.6}$$For $q_0>\frac{1}{2}$ the universe is positively curved, with $\rho_0>\rho_c$ , whereas for $q_0<\frac{1}{2}$ the universe in negatively curved, with $\rho_0<\rho_c$ . If we give credence to the values $q_{0}\simeq1$ and $H_{0}\simeq75\text{ km/sec/Mpc}$ deduced from the red shift versus luminosity relation (see Section 14.6), then we must conclude that the density of the universe is about $2\rho_c$ , or about $2\times10^{-29}\text{ g/cm}^{3}$."

Weinberg then goes on to say "Unfortunately, this result does not agree with the observed density of galactic mass." and offers on pg. 478 the galactic-density estimate $\frac{\rho_{G}}{\rho_{c}}=\text{0.028}$. Presciently, he then writes "However, if one tentatively accepts the result that $q_0$ is of order unity, then one is forced to the conclusion that the mass density of about $2\times10^{-29}\text{ g/cm}^{3}$ must be found somewhere outside the normal galaxies. But where?"

So an inkling of the need for dark matter was recognized over 50 years ago!

 

[Orodruin]

So an inkling of the need for dark matter was recognized over 50 years ago!

Well … Zwicky’s paper was published in 1933. Rubin’s in 1970 …

Some 70ish % of the energy density is also not matter at all. This was definitely not known when Weinberg wrote that and changes the entire evolution due to different equation of state.