Living Motors and Heat express
A cell is a city where tiny motors work nonstop. They carry cargo, move cilia, and make muscles contract. All this work generates heat, just like a car engine warms up. But measuring the heat from a single motor a few nanometers in size is no easy task.
Stochastic modeling helps us peek into this world. The scientists built simple models: one describes the motion of cilia (like rowers in a boat), the other the work of a molecular motor that takes steps along a filament, like a person walking on a tightrope. Then they calculated how the heat capacity of such a system changes with parameters.
Negative heat capacity is not a paradox but a consequence of the system spending energy on work rather than on heating. It's like a refrigerator that cools by consuming electricity. In living cells, such effects could be key to understanding how motors coordinate their actions.
This approach, calorimetry under non-equilibrium conditions, opens a new way to study biological machines. By measuring heat, we can understand how they work without interfering with their operation.
Original abstract
as written by the authors arXiv:2602.15127
Micro-calorimetry offers significant potential as a quantitative method for studying the structure and function of biological systems, for instance, by probing the excess heat released by cellular or sub-cellular structures, isothermal or not, when external parameters change. We present the conceptual framework of nonequilibrium calorimetry, and as illustrations, we compute the heat capacity of biophysical models with few degrees of freedom related to ciliar motion (rowing model) and molecular motor motion (flashing ratchets). Our quantitative predictions reveal intriguing dependencies of the (nonequilibrium) heat capacity as a function of relevant biophysical parameters, which can even take negative values as a result of biological activity.
Negative heat capacity appears in astrophysics: star clusters can cool down by giving off energy while their interiors heat up.
In Stanislaw Lem's novel 'Solaris', the planet's ocean exhibits activity that is hard to explain with ordinary physics. Negative heat capacity is an example of how living systems defy the usual laws of thermodynamics.