deletions | additions       diff --git a/Now_we_have_some_constraints__.tex b/Now_we_have_some_constraints__.tex  index cfc78a1..efd5f5e 100644  --- a/Now_we_have_some_constraints__.tex  +++ b/Now_we_have_some_constraints__.tex 
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In the words of italian Nobel prize Enrico Fermi: "Where is everybody?" What Fermi meant is that it's quite surprising we have seen no sign of extraterrestrial intelligent life, despite the fact the Universe is so vast and long-lived. This is the essence of the \textbf{Fermi Paradox}.  Ok I know I know, there is \href{http://en.wikipedia.org/wiki/Roswell_UFO_incident}{Roswell}... the \href{http://en.wikipedia.org/wiki/Wow!_signal}{WOW signal}... \href{http://en.wikipedia.org/wiki/List_of_reported_UFO_sightings}{UFO} sightings... Well, I am not going into that. I will just state that the most economical explanations for all the aforementioned cases stories  have nothing to do with E.T. and that at this time there is no clear evidence that prove we had contact with alien life. Let's use the \href{http://bit.ly/KDLFp6}{Occam's razor} and throw away the conspiracy spoon. Back to us. The Fermi Paradox suggests that the number of communicative civilizations $N$ in the Galaxy is small\footnote{There are some solutions to the Fermi Paradox that do not require $N$ to be small, for a nice review have a look at this \href{http://waitbutwhy.com/2014/05/fermi-paradox.html}{great post}}. Our revised version of the Drake Equation then implies two\footnote{Of course the third option is that both $f_i$ and $L$ are small} interesting alternatives: \begin{enumerate}  \item $f_i$ is a small number. That is\textbf{ life is common in the Universe, but intelligent life is not}.