deletions | additions       diff --git a/Now_we_have_some_constraints__.tex b/Now_we_have_some_constraints__.tex  index 50bd007..cfc78a1 100644  --- a/Now_we_have_some_constraints__.tex  +++ b/Now_we_have_some_constraints__.tex 
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Now we have some constraints that come from the observations: We do not see alien's spaceship landing on Earth or have detected any E.T. signal coming from space. In \href{http://www.scientificamerican.com/article/alien-supercivilizations-absent-from-100-000-nearby-galaxies/}{recent news} a space survey of 100,000 galaxies didn't find any clear sign of advanced alien civilizations. The observations could only rule out the presence of massive galactic colonization, with aliens using an amount of energy comparable to the total output of their galaxy. Advanced aliens might be more energy savvy, but 100,000 it's also  a lot of galaxies. 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}.