The Boltzmann brain hypothesis dissolves on two independent grounds. First, the standard count NBB = rBB · T is a hybrid. It takes a constant fluctuation rate from one description of de Sitter cosmology (the 8D covariant phase space, in which time is a coordinate) and multiplies it by the unbounded integration time of another, the (6+1) D non-comoving picture, in which time is external. Neither description supports the product internally. The divergence is a coordinate artifact. Performed honestly within one frame, the phase-space integration over the de Sitter horizon yields P ~ 10^ (−8. 7 × 10¹2). Second, a Boltzmann brain is not a single particle. It is a joint configuration of order 10¹4 informationally distinct cells. In a closed box of side N, the per-step probability that k cells form a brain-shape connected cluster is bounded by the Klarner–Rivest lattice-animal count combined with Gibbs indistinguishability, P₀ ≤ k! (2eD) ᵏ / N^ ( (k−1) D), exponentially small in k. The closed-box ideal is recurrent: Kac's lemma gives a mean recurrence time ≳ 10^ (2. 22 × 10¹3) interaction steps: extremely long but finite. Any single physical departure from the closed-box-static idealization (slow thermal leakage at one missed step per universe lifetime, or cosmological expansion at one site added per universe lifetime) collapses the cumulative probability to ≲ 10^ (−2. 22 × 10¹3) even at T → ∞. Either route suffices to block the standard divergence. Together they show that Boltzmann-brain dominance is not a consequence of recurrence alone, but of combining recurrence with an unlicensed temporal or observer-moment multiplier.
Ira Wolfson (2026) studied this question.