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\section*{Counting Civilizations} We now know that there is on average \textbf{one planet orbiting every star in the Universe} \citep{2013ApJ...764..105S, 2012Natur.481..167C}. Just in our Galaxy this means we have 100 billions planets. Since we have about 100 billion galaxies in the Universe, there are about 10,000,000,000,000,000,000,000 = $10^{22}$ planets out there. But how many of these planets are hosting life? And in particular, how many host intelligent life we might be able to communicate with?  In order to estimate the number of technological civilizations that might exist among the stars, in 1961 Frank Drake proposed the following simple equation