  We study the effect of correlations in generation times on the dynamics of
population growth of microorganisms. We show that any non-zero correlation that
is due to cell-size regulation, no matter how small, induces long-term
oscillations in the population growth rate. The population only reaches its
steady state when we include the often-neglected variability in the growth
rates of individual cells. We discover that the relaxation time scale of the
population to its steady state is determined by the distribution of single-cell
growth rates and is surprisingly independent of details of the division process
such as the noise in the timing of division and the mechanism of cell-size
regulation. We validate the predictions of our model using existing
experimental data and propose an experimental method to measure single-cell
growth variability by observing how long it takes for the population to reach
its steady state or balanced growth.
