Among the Noguchi sculptures that are variations on a single theme, the most dramatic works employ the image of the void. Noguchi began the void series in Italy in 1970 with In Silence Walking, but it was in Japan that he created the largest work of this kind, Energy Void. In his voids Noguchi brought together a number of his theoretical interests, including physics (envisioning a circular flow of energy at the heart of matter), the concept of emptiness from Zen Buddhism, and the use of empty space as a positive formal element.