deletions | additions       diff --git a/Consider_trying_to_understand_Frank__.tex b/Consider_trying_to_understand_Frank__.tex  index 86429e7..2fb4cdf 100644  --- a/Consider_trying_to_understand_Frank__.tex  +++ b/Consider_trying_to_understand_Frank__.tex 
...
Consider trying to understand Frank Drake's \textbf{Fermi Paradox} which estimates the number of technological civilizations that might exist among the stars. ($R$ is the annual rate of star formation, $n_e$ is the average number of habitable planets, $f_p$ is the fraction of stars that have planets, $f_p$ is the fraction of stars that have planets, $f_l$ is the fraction of habitable planets, $f_i$ is the fraction of life-bearing planets that develop an intelligent life-form, and $f_c$ is the fraction of intelligent life-forms that decide to communicate)  \begin{equation}\nonumber  N =\underbrace{\overbrace{R}^{\approx10} \times \overbrace{f_p}^{\approx 1} \times \overbrace{n_e}^{\approx 0.2}}_{\sim 2} \times \underbrace{f_l \times f_i \times f_c \times L}_{?}  \end{equation}  \begin{itemize}  \item $R$ the rate of star formation, which tells how many stars are born every year in our Galaxy.  \item $n_e$ is the average number of habitable planets in any planetary system  \item $f_p$ is the fraction of stars that have planets   \item $f_l$ is the fraction of habitable planets that host life  \item $f_i$ is the fraction of life-bearing planets that develop an intelligent life-form  \item $f_c$ is the fraction of intelligent life-forms that decide to communicate  \end{itemize}  Kind of hard, right? Now use the figure below, which allows you to play with the number $N$ of communicative civilizations in the Galaxy as function of their average longevity $L$. Is it a bit easier?