Every warm-blooded animal gets a 'budget' of about a billion heartbeats before their time is up.
March 30, 2026
Original Paper
Biological Time Equivalence in Vertebrates: Thermodynamic Framework, Comparative Tests, and Clade-Specific Deviations
arXiv · 2603.26377
The Takeaway
This paper provides a thermodynamic explanation for why the product of heart rate and lifespan is nearly constant across species. It suggests that biological time is a physical 'proper time' that flows faster or slower depending on an organism's metabolism.
From the abstract
The product of resting heart rate and maximum lifespan is approximately constant across adult warm-blooded vertebrates, $N^\star = f_H L \approx 10^9$ cardiac cycles, a regularity documented since Rubner (1908) but lacking a thermodynamic derivation. We derive $N^\star$ from the non-equilibrium second law by treating the adult organism as a metabolic non-equilibrium steady state (NESS) and introducing the closure $\dot{e}_p = \sigma_0 f$, linking entropy production rate to heart rate via a mass-