Question
(a) Use the distance and velocity data in Figure 3.62 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. Figure 3.62 Five galaxies on a straight line, showing their distances and velocities relative to the Milky Way (MW) Galaxy. The distances are in millions of light years (Mly), where a light year is the distance light travels in one year. The velocities are nearly proportional to the distances. The sizes of the galaxies are greatly exaggerated; an average galaxy is about 0.1 Mly across.
1. The recession velocity is directly proportional to distance from the Milky Way Galaxy. The constant of proportionality, called the Hubble Constant, is on average $1.57 \times 10^{-18}\textrm{ /s}$
2. 20 billion years.

# OpenStax College Physics, Chapter 3, Problem 64 (Problems & Exercises)  In order to watch this solution you need to have a subscription.

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