Nonequilibrium pervades nature, from the expanding universe to climate dynamics, living cells and molecular machines. Key to nonequilibrium states is the entropy production rate σ  at which energy is dissipated to the environment. Despite its importance, σ  remains challenging to measure, especially in nanoscale systems with limited access to microscopic variables. Here I present a recently introduced variance sum rule for displacement and force variances that permits to measure σ  by constraining energetics through modelling [1,2]. We apply it to measure the first heat map of human red blood cells in experiments with laser optical tweezers and ultrafast life-imaging microscopy. We find a spatially heterogeneous σ  with finite-correlation length of half a micron ξ~0.5μm and global σ~ 10⁶ k_BT/s per single cell, in agreement with calorimetry estimates. The variance sum rule sets a new resource for measuring entropy production rates in active and living matter [3].

References

[1]  Di Terlizzi, I., Gironella, M., Herráez-Aguilar, D., Betz, T., Monroy, F., Baiesi, M., & Ritort, F. (2024). Variance sum rule for entropy production. Science, 383(6686), 971-976.

[2] Di Terlizzi, I., Baiesi, M., & Ritort, F. (2024). Variance sum rule: proofs and solvable models. New Journal of Physics, DOI: 10.1088/1367-2630/ad4fb9.

[3] Roldán, É. (2024). Thermodynamic probes of life. Science, 383(6686), 952-953.

If you would like to attend this seminar, please register here.