A common metaphor for a brain is that of a digital computer, with inputs and outputs and computations happening in between. The metaphor has its problems but there is no doubt about this: brains (neurons) perform computation. When reading a recent Science Advances paper about the computational capacity of life (all of life), I learned that the computational capacity of neurons has been assumed to account for the full computational capacity of life. This assumption excludes nearly all of the biosphere from participation in computation (information processing), which seems unfair even to a neuroscientist like me. The new paper addresses this apparently narrow view by adding a new computational unit to the resources of life: “single-photon superradiance in cytoskeletal protein fibers.” In so doing, the author provides a revised estimate of the computational capacity of life. It’s delightfully vast.
The paper relies on extensive mathematics, which are largely outside my computational range (heh), but the author nicely explains the background and advance in the Abstract:
As physical systems, all life in the universe processes information according to physical laws. Estimates for the computational capacity of living systems generally assume that the fundamental information-processing unit is the Hodgkin-Huxley neuron, thereby excluding aneural organisms. Assuming the laws of quantum mechanics, the relativistic speed limit set by light, a universe at critical mass-energy density, and a recent experimental demonstration of single-photon superradiance in cytoskeletal protein fibers at thermal equilibrium, it is conjectured that the number of elementary logical operations that can have been performed by all eukaryotic life in the history of Earth, which is shown to be approximately equal to the ratio of the age of the universe to the Planck time, is about the square root of the number by the entire observable universe from the beginning. The existence of ultraviolet-excited states in these protein fibers, operating within two orders of magnitude of the Margolus-Levitin speed limit, motivates state-of-the-art performance comparisons with contemporary quantum computers.
But why just eukaryotic life? Don’t bacteria get to play? Yes, but only sometimes: the new elements in the model, cytoskeletal polymers, are rare in prokaryotes.
Computational capacity of life in relation to the universe
In Science Advances, 28 March 2025
From the group of Philip Kurian in the Quantum Biology Laboratory at Howard University.
Snippet by Stephen Matheson