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mysearch
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Hi,
I am interested in how the component densities, as assumed by the LCDM model, have been determined. For example, it seems that the critical density can be determined by rearranging of the Friedmann equation as follows:
[1] [itex] \rho_C = \frac {3H^2}{8 \pi G} [/itex]
Therefore, it is assumed that the accuracy in determining the critical density is actually linked to the accuracy of the observational measurements underpinning the value of the Hubble’s parameter [H], i.e.
[2] [itex] H=71km/s/mpc[/itex] or [itex] 2.31*10^{-18} m/s/m [/itex]
[3] [itex] \Rightarrow \rho_C= 8.53*10^{-10} Joules/m^3[/itex] or [itex]9.54*10^{-27} kg/m^3[/itex]
However, the critical density is normally assumed to comprise of a number of distinct components, which all have a different % values in the present era, but which then change at different rates, as a function of time, due to their different ‘equations of state’. However, while the changes in the LCDM model can be examined via one of the many ‘cosmic calculators’ now available, these models all seem to be predicated on some general acceptance of the relative values of the densities components in the present era, e.g.
[4] [itex] \rho_C (100 \%) =\left[ \rho_M (4 \%) +\rho_{CDM} (23 \%) + \rho_R (0.008 \%) + \rho_k (~0 \%) +\rho_{DE} (73 \%) \right] [/itex]
In [4], we see the generally accepted % estimates, in the present era, of normal matter [M], cold dark matter [CDM], radiation [R], curvature [k] and dark energy [DE]. However, the requirement for CDM and DE appears to be based on the assumption that there is not enough normal matter in the universe, e.g. protons and electrons. So my basic question is:
How is/was the particle mass or density of the universe determined so accurately?
Would appreciate any insights. Thanks
I am interested in how the component densities, as assumed by the LCDM model, have been determined. For example, it seems that the critical density can be determined by rearranging of the Friedmann equation as follows:
[1] [itex] \rho_C = \frac {3H^2}{8 \pi G} [/itex]
Therefore, it is assumed that the accuracy in determining the critical density is actually linked to the accuracy of the observational measurements underpinning the value of the Hubble’s parameter [H], i.e.
[2] [itex] H=71km/s/mpc[/itex] or [itex] 2.31*10^{-18} m/s/m [/itex]
[3] [itex] \Rightarrow \rho_C= 8.53*10^{-10} Joules/m^3[/itex] or [itex]9.54*10^{-27} kg/m^3[/itex]
However, the critical density is normally assumed to comprise of a number of distinct components, which all have a different % values in the present era, but which then change at different rates, as a function of time, due to their different ‘equations of state’. However, while the changes in the LCDM model can be examined via one of the many ‘cosmic calculators’ now available, these models all seem to be predicated on some general acceptance of the relative values of the densities components in the present era, e.g.
[4] [itex] \rho_C (100 \%) =\left[ \rho_M (4 \%) +\rho_{CDM} (23 \%) + \rho_R (0.008 \%) + \rho_k (~0 \%) +\rho_{DE} (73 \%) \right] [/itex]
In [4], we see the generally accepted % estimates, in the present era, of normal matter [M], cold dark matter [CDM], radiation [R], curvature [k] and dark energy [DE]. However, the requirement for CDM and DE appears to be based on the assumption that there is not enough normal matter in the universe, e.g. protons and electrons. So my basic question is:
How is/was the particle mass or density of the universe determined so accurately?
Would appreciate any insights. Thanks