Critical Waves and the Length Problem of Biology

TL;DR

This paper proposes that biological systems measure lengths using critical chemical waves similar to sound waves, which can be generated through reaction-diffusion systems tuned to criticality, offering a physical principle for biological measurement.

Contribution

It introduces the idea that biological length measurement can be explained by critical chemical potential waves, a novel application of physical principles to biological systems.

Findings

Chemical potential waves can be generated by tuning reaction-diffusion systems to criticality.

Oscillations are essential for stable and adaptable length measurement.

Biological structures like Min oscillations and mitotic structures may utilize these waves.

Abstract

It is pointed out that the mystery of how biological systems measure their lengths vanishes away if one premises that they have discovered a way to generate linear waves analogous to compressional sound. These can be used to detect length at either large or small scales using echo timing and fringe counting. It is shown that suitable linear chemical potential waves can, in fact, be manufactured by tuning to criticality conventional reaction-diffusion with a small number substances. Min oscillations in E. coli are cited as precedent resonant length measurement using chemical potential waves analogous to laser detection. Mitotic structures in eucaryotes are identified as candidates for such an effect at higher frequency. The engineering principle is shown to be very general and functionally the same as that used by hearing organs. PNAS Significance Statement: This paper invokes physical principles to address the question of how living things might use reaction-diffusion to measure out and regulate the many thousands of lengths required to make their body parts and internal organs. It argues that two ideas have been missing. One is that oscillation is necessary to achieve the necessary design stability and plasticity. The other is that the system must be tuned to criticality to stabilize the propagation velocity, thus enabling clocks to function as meter sticks. The broader significance is twofold: First, a fundamental piece of the machinery of life is probably invisible to present-day biochemical methods because they are too slow. Second, the simplicity of growth and form identified a century ago by D'Arcy Thompson is probably a symptom of biological engineering strategies, not primitive law.