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 generations passed in history. The general assumptions are:

  • There are 1011 seconds in 1 history
  • In 1 generation, there is 1/3 of a lifetime.
  • In half a lifetime, there are 109 seconds

Therefore, the number of generations passed is

\displaystyle 1history=1\:history\times \frac{10^{11}\:sec}{1\:history}\times \frac{1\:generation}{\frac{1}{3}\:lifetime}\times \frac{0.5\:lifetime}{10^9\:sec}

\displaystyle 1history=150\:generations          ☚