"The factors f_lf_if_c should not depend strongly on the evolution of the Galaxy... and so can be regarded as constants. Since the Galaxy is between 11 and 18 billion years old, the number N of stars older than 5.3 billion years is about twice the number of stars formed after the Sun, and thus approximately equal to the number of stars in the Galaxy, 1011. Thus p \leqslant 10^{-11}. If we accept the usual values of f_p=0.1 to 1 and n_e = 1 found in most discussions... then f_lf_if_c \leqslant 10^{-10}. The number of communicating civilizations now existing in our Galaxy is less than or equal to p x (number of stars in galaxy) = 1; that is to say, us."