The missing billions in hard sphere nucleation.

The crystallisation of a metastable liquid is an everyday phenomenon, yet it still presents a number of puzzles. One such puzzle is the discrepancy between the crystallisation rate observed in experiments and that predicted by theory: the experimental and simulated rate densities for hard spheres - the "simplest" system showing a first-order freezing transition - disagree by up to 22 orders of magnitude. Nevertheless, it is precisely the utilisation of elementary model systems that facilitates the resolution of these enigmas. We present a comprehensive experimental investigation into the crystallisation of colloidal hard spheres at the particle level. Our ground breaking findings challenge the prevailing conceptualisation of crystal nucleation, elucidate the discrepancy between experiment and theory, and propose an alternative description.