Elucidating the origin of anomalous diffusion in crowded fluids.

Anomalous diffusion in crowded fluids, e.g., in the cytoplasm of living cells, is a frequent phenomenon. So far, however, the associated stochastic process, i.e., the propagator of the random walk, has not been uncovered. Here we show by means of fluorescence correlation spectroscopy and simulations that the properties of crowding-induced subdiffusion are consistent with the predictions for fractional Brownian motion or obstructed (percolationlike) diffusion, both of which have stationary increments. In contrast, our experimental results cannot be explained by a continuous time random walk with its distinct non-Gaussian propagator.