A joule is a unit of energy.
This work shares a similar idea to my piano concerto "AMPERE". I imagined that the energy of the pianist goes through the pianists' fingers directly into the piano, coming out as an aura.......hence the big differences in dynamics and tempo changes. These changes are a result of the aura growing and then the energy of this aura being transmitted back into the piano.
Dai Fujikura (edited by Harry Ross)