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which states that at any given time the minimum value for the number of galactic communicative civilizations in order to achieve contact scales with the volume of the galaxy to the power 1/4. This is also the scaling for then minimum communicative phase lifetime required for contact. The absence of a message then allows to estimate that in our Galaxy $L  The galactic volume can be estimated as 10^{12}-10^{13} cubic light years: therefore in our Galaxy $L  It also means that at this time in our Galaxy there can should  be at max less than  $N\approx 350...625$ communicative civilizations. %and the lifetime of such civilizations is also usually shorter than 1000\...3000 years. This does not necessaril%y mean that the number of intelligent civilizations in the Galaxy is limited to this number, it just implies %that their communicative phase is limited to a short time. There could be different reasons for this, including %transition to more efficient forms of communication than electromagnetic signals, loss of interest, singularity %etc. (many of these possibilities have been extensively discussed in the context of the \href{http://en.wikipedi%a.org/wiki/Fermi_paradox}{Fermi paradox}). Nevertheless self-annhilation / destruction of natural resources is a %realistic possibility. Overall the absence of contact tells us that there should be an important transition in %the characteristic of human civilization occuring in a timescale shorter than about 1000\...2000 years.