A local distance-ladder measurement gives

PHYSICS · Multi-part · Fermi University Physics · Relativity & Gravitation · Astrophysics & Cosmology · Einstein's field equations

The Geometry of Gravity, Ch FRW cosmology as an exact solution

Problem

H_0 = 73.0\ \text{km s}^{-1}\text{Mpc}^{-1}

. Hubble's law

\dot d = Hd

holds exactly for the proper distance

d

to a comoving galaxy, whatever the spatial curvature. ((a)) Compute the Hubble radius

c/H_0

, in gigaparsecs. ((b)) A galaxy sits at proper distance

d = 5.0\ \text{Gpc}

today. Compute the ratio

\dot d/c

for this galaxy. Use

c = 2.998\times10^8\ \text{m s}^{-1}

and

1\ \text{Mpc} = 3.086\times10^{22}\ \text{m}