(a) Use the distance and velocity data in Figure 3.59 to find the rate of expansion as a function of distance.
(b) If you extrapolate back in time, how long ago would all of the galaxies have been at approximately the same position? The two parts of this problem give you some idea of how the Hubble constant for universal expansion and the time back to the Big Bang are determined, respectively.

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Galaxy 1 300 Mly Galaxy 2 150 Mly Galaxy 3 Galaxy 4 MW 190 Mly v₁ = -4500 km/s v₂ = -2200 km/s Galaxy 5 450 Mly v₁ = 2830 km/s v₂ = 6700 km/s