In addition to relativity, Albert Einstein explained Brownian motion, the dance of minute particles when suspended in fluids, by showing that impacts with surrounding molecules could create this random jittering. Theorists have argued that Brownian motion may not be completely random, as Einstein predicted, and now experimentalists have confirmed it. They tracked micron-size plastic and glass spheres in water with lasers at microsecond intervals and nanometer-length scales. Their results validate a corrected form of the standard theory describing Brownian motion, wherein the inertia of the fluid makes the trajectories of the particles more predictable for much longer than previously expected. The findings, published October 11 online by Physical Review Letters, are fundamental to understanding the dynamics of a living cell and building structures at the nanoscale, says biophysicist Ernst-Ludwig Florin of the University of Texas at Austin.