  Turbulent mixing of liquids and gasses is ubiquitous in nature. It is the
basis of all industrial fluid mixing processes, and it determines the spread of
pollutants or bioagents in the atmosphere and oceans. Biological organisms even
use it to survive in marine ecosystems. A fundamental component of turbulent
mixing is the separation of two nearby fluid elements, i.e., pair dispersion.
Despite almost eighty years of intense scientific inquiry, no clear
understanding of this fundamental aspect of turbulence has emerged. One
critical unresolved question is the extent to which the initial separation of
the fluid particles influences their subsequent motion. Surprisingly, our
measurements in a laboratory water flow at very high turbulence levels (Taylor
microscale Reynolds numbers up to R_lambda = 815) suggest that the initial
separation remains important for all but the most violent flows on Earth. This
observation has important consequences for such varied problems as pollution
control, combustion modelling, hazardous chemical control, and even the
understanding of how animals locate food, predators, and mates.
