ABSTRACT
I discuss the physical meaning of the Drake equation and I analyze it in a way revealing the implications of its last term, namely the lifetime of technologically evolved civilizations, the importance of which is often overlooked. The analysis allows one to define a region in the parameter space of the Drake equation, where the so-called “great silence” may be easily understood. The adopted framework is also applied to the analysis of the Fermi paradox, under the assumption of a simplified scheme for the colonization of the galaxy. From the joint analysis of the Drake equation and the Fermi paradox, it appears that for sufficiently long-lived civilizations, colonization of the galaxy appears to be the only reasonable option to gain knowledge about other life-forms. The analysis allows one to define a corresponding region in the parameter space of the Drake equation, where the Fermi paradox strongly holds.
