Morphological computational capacity of Physarum polycephalum

Abstract: While computational capacity limits of the universe and carbon-based life have been estimated, a stricter bound for aneural organisms has not been established. Physarum polycephalum, a unicellular, multinucleated amoeba, is capable of complex problem-solving despite lacking neurons. By analyzing growth dynamics in two distinct Physarum strains under diverse biological conditions, we map morphological evolution to information processing. As the Margolus-Levitin theorem constrains maximum computation rates by accessible energies, we analyze high-throughput time-series data of Physarum's morphology--quantified through area, perimeter, circularity, and fractal dimension-to determine upper bounds on the number of logical operations achievable through its hydromechanical, chemical, kinetic, and quantum-optical degrees of freedom. Based on spatial distribution of ATP and explored areas, Physarum can perform up to ~$10^{36}$ logical operations in 24 hours, scaling linearly in the non-equilibrium steady state. This framework enables comparison of the computational capacities of life, exploiting either classical or quantum degrees of freedom.