1. The problem statement, all variables and given/known data In the book "In searcg of life in the Universe" A.D. Ursula gave the following formula R1/C1 = R2/C2 (A) when the contact between two civilizations happens, where R - result from a contact and C - cost to make a contact for those civilizations. 2. Relevant equations The key equation is R1/C1 = R2/C2 3. The attempt at a solution Let R1 and C1 be result and cost for Earth. There is great silence because R1/C1 < R2/C2 (B) If it were otherwise it would mean that the contact already happened but there is a great silence. Hence equation (B) is fulfilled.