Signal in the noise: temporal variation in exponentially growing populations

In exponential population growth, intrinsic variability in the timing of individual division events compounds to produce variable macroscopic outcomes. For a stochastic model of exponential growth, we derive a power-law relationship that relates noise in the macroscopic outcomes to growth rate and inoculum size. Population-growth experiments in E. coli and S. aureus with inoculum sizes ranging between 1 and 100 are consistent with this relationship. Noise encodes (and can be used to deduce) information about the early growth rate of a population.