The Power of Fluctuations in Life and Matter

In science, random fluctuations (e.g., noise) are typically regarded as a nuisance to be minimized or avoided if possible. Yet in many important scenarios, valuable information can be gleaned from their careful study. In this talk, I will discuss three such examples, from different disciplines.

First, I will discuss the “Problem of the Random Walk”, an abstract mathematical problem that was solved quite generally by Einstein, and paved the way to an elegant experiment by Perrin that proved – for the first time – that matter is made of atoms. Remarkably, the “smoking gun” relied on the fluctuating trajectories of small particles moving about randomly in a liquid.

Next, I will discuss a seminal biological experiment, in which bacteria were exposed to a virus, and the number of survivors counted. The experiment was not reproducible, with the survivor number fluctuating hugely between different runs. Rather than declare failure, Luria and Delbrück realized that these fluctuations are proof that random mutations drive evolution, opening a new field.

Finally, I will discuss recent work on the problem of cell size control – how individual cells can properly time their divisions to achieve a particular size. I will show that also here the study of fluctuations, in this case in cell size, can inform us about the underlying biological processes.