College Physics Problem 1.30

A generation is about one-third of a lifetime. Approximately how many generations have passed since the year 0 AD?


We are looking for the generations passed in the history. The general assumptions are:

  • There are 10^{11} s in 1 history
  • In 1 generation, there is 1/3 of a lifetime.
  • In half a lifetime, there are 10^{9} s

Therefore, the number of generations passed is

history times frac{10^{11} s}{1 history} times frac{1 generation}{1/3 lifetime}times frac{0.5 lifetime}{10^{9} s}=150 generations