A recent paper tests a way to do macroeconomics without building detailed models of every person or firm. The authors use a theory called thermal macroeconomics (TM) that says a few macroscopic quantities — like an economy’s total money and amounts of goods — can be described by a single function called entropy. Where it is hard or impossible to derive that function from the behaviour of many individuals, the paper shows it can be measured instead, by an economic analogue of calorimetry (the way physicists measure heat and entropy).

The team ran agent‑based computer simulations of simple exchange economies. In these simulations agents meet and trade pairwise according to rules that conserve total money and goods. For testing the measurement method they attach a small, well‑understood “meter” economy to the system. The meter they use is a Cobb–Douglas type economy (a standard form in economics), and it exchanges money and goods with the simulated economy until the two settle into equilibrium. From the meter’s average holdings the researchers read off quantities that play the role of the value of money and the value of each good.

At a high level the measurement rests on a thermodynamic identity: small changes in an economy’s entropy equal a weighted sum of changes in money and goods, where the weights are the values read from the meter. In physics this is like using a thermometer and a calorimeter to measure temperature and heat capacity and so infer entropy. The authors show how to pick a reference state, measure the relevant values by letting the economies equilibrate with the meter, and thereby build up the entropy function for a range of simulated systems.