Please note that the content of this book primarily consists of articles available from Wikipedia or other free sources online. In special relativity, electromagnetism and wave theory, the d''Alembert operator Box, also called the d''Alembertian or the wave operator, is the Laplace operator of Minkowski space. The operator is named for French mathematician and physicist Jean le Rond d''Alembert.There are a variety of notations for the d''Alembertian. The most common is the symbol Box the four sides of the box representing the four dimensions of space-time and the Box which emphasizes the scalar property through the squared term (much like the Laplacian). In keeping with the triangular notation for the Laplacian sometimes Delta is used.