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In any complex community, whether an orchestra or a colony of microbes, you can notice a rhythm. In the mouse gut, bacteria change their abundance every day, and for a long time it seemed they were syncing their internal clocks with the host's. But when researchers looked closely at hourly measurements, the familiar picture fell apart.

They found no persistent trace of a 24-hour rhythm — what specialists would call a 'ridge' on a time-frequency map. Instead of a clear beat, the graphs showed something else: an enhancement of slow waves, a dip at intermediate frequencies, and a strange asymmetry in time. If the rhythm were real, the past and future of the oscillations would look similar. Here, the peak of correlation occurred at tens of hours, as if the echo decays unevenly.

Two types of bacteria turned out to be the main characters in this temporal drama. One group, degraders of complex sugars from the phylum Bacteroidota, amplified any disturbances, like a resonator. The other, producers of fatty acids from Bacillota A, served as the source of these disturbances. Their roles were determined not by the phase of oscillations but by how they respond to random jolts. Together, they create what the authors call 'pseudocoherence': the geometry of their interaction is such that random fluctuations (disorderly deviations) briefly align into a semblance of rhythm. This breaks time symmetry and creates the illusion of a clock where there is none.

This regime the authors call a stable but highly non-normal stochastic regime. And they propose a way to test it: if you knock out the genes responsible for internal clocks in mice, but 'pseudocoherence' persists — then the source of the rhythm is indeed not the ticking of biological clocks, but the very structure of the community.