Understanding fluids requires mathematical tools that operate at different scalesKARL GAFF / SCIENCE PHOTO LIBRARYMathematicians have finally succeeded in unifying the laws of physics that govern the motions of particles at different scales. Their efforts resolve a question set by mathematician David Hilbert in 1900 as part of an ambitious programme for all mathematicians of the 20th century and could deepen our understanding of the complex behaviour of fluids in the atmosphere and oceans.This is a major result in my view. I thought it was completely beyond reach, says Benjamin Texier at the University of Lyon