How a clock is like a steam engine

Our new work on the thermodynamic cost of timekeeping has been published in Physical Review X.

Thermodynamics tells us that there are two fundamental types of machine than cannot operate without releasing heat. One is the mechanical engine, which releases heat to do work, and the other is the computer memory, which releases heat when it rewrites itself. Recent theoretical work has shown that some clocks also operate as thermal machines, whose useful output is accurate ticks. Just as thermodynamics limits the efficiency of a steam engine, it also limits the accuracy of at least some types of clock.

In this experiment, carried out in Oxford and with collaboration from Vienna, we have created a particularly simple clock in which the heat flow, and therefore the entropy production, can be directly measured. As expected, the accuracy improves as the entropy production rate increases.

Intriguingly, a similar relationship between entropy and accuracy was previously predicted to hold for two very different types of clock: one based on chemical reactions and one based on quantum mechanics. Does this mean that all clocks are thermodynamic machines? It is time to find out.

Our paper is:

Measuring the thermodynamic cost of timekeeping
A.N. Pearson, Y. Guryanova, P. Erker, E.A. Laird, G.A.D. Briggs, M. Huber, N. Ares
Physical Review X 11 021029 (2021)

and media coverage is here:

Artist's conception of a clock

Artist’s conception of a clock behaving a little bit like a steam engine.