

A327854


Value of the critical density of the Universe in g/cm^3 multiplied by dimensionless scale factor h^(2).


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OFFSET

28,2


COMMENTS

The critical density is defined as p_c = 3*H^2/8*Pi*G, where H is the Hubble constant and G is the gravitational constant (A070058) (cf. ESA, Critical density).
The critical density is the value of matter density that ensures the expansion of the Universe eventually halts, but the Universe does not recollapse in a "Big Crunch". This is often expressed via a density parameter Omega, defined as Omega = p/p_c, where p is the actual matter density of the Universe. Thus the Universe is "open", "flat" or "closed", depending on whether Omega < 1, Omega = 1 or Omega > 1. Observations suggest that the dark energy density Omega_Lambda and matter density Omega_m add to a value close to 1 (cf. Planck Collaboration, 2013).


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EXAMPLE

1.87840(9) * 10^(29) h^2 g cm^(3), where h = 0.678(9) is a dimensionless scale factor (cf. Aldrovandi et al., 2002, p. 4) for the present day Hubble expansion rate H_0, which equals 100*h km s^(1) Mpc^(1) and where the digit in parentheses denotes the standard uncertainty (cf. Tanabashi et al., 2018, table 2.1).


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STATUS

approved



