An artist’s conception of the measurement scale of the universe. Baryon acoustic oscillations are the tendency of galaxies and other matter to cluster in spheres, which originated as density waves traveling through the plasma of the early universe. The clustering is greatly exaggerated in this illustration. The radius of the spheres (white line) is the scale of a “standard ruler” allowing astronomers to determine, within one percent accuracy, the large-scale structure of the universe and how it has evolved. (Credit: Image by Zosia Rostomian, Lawrence Berkeley National Laboratory)