Let’s start by thinking about your brain. Among its other qualities, your brain is hot. It continually takes in energy, which you supply by eating and drinking and breathing; it undertakes a host of physiochemical processes that modify its detailed configuration (chemical reactions, molecular rearrangements, particle movements, and so on); and it releases waste heat to the environment. As your brain thinks (and does everything else brains do), it thus recapitulates a sequence we first encountered in chapter 2 when analyzing steam engines.
