On burning a lump of coal

Abstract

Burning something, (e.g. the proverbial lump of coal, or an encyclopaedia for that matter), in a blackbody furnace leads to an approximately Planck emission spectrum with an average entropy/information transfer of approximately $3.9 \pm 2.5$ bits per emitted photon. This quantitative and qualitative result depends only on the underlying unitarity of the quantum physics of burning, combined with the statistical mechanics of blackbody radiation. The fact that the utterly standard and unitarity preserving process of burning something (in fact, burning anything) nevertheless *has* an associated entropy/information budget, and the quantitative *size* of that entropy/information budget, is a severely under-appreciated feature of standard quantum statistical physics.