What ⧠ means
It combines spatial curvature with changes in the rate over time.
The spatial Laplacian sums curvature in each direction; a second time derivative tracks how the rate of change itself changes. Signs depend on the spacetime convention.
d’Alembert’s equation came before box notation
Poincaré used a box for the operator in 1901; d’Alembert’s one-dimensional wave equation dates to 1747. The STIX project, run by scientific and technical publishers, proposed extra math symbols in 1998 for accurate Web publishing; its 1999 list includes the d’Alembertian.
Don't confuse it with
1
Related characters
2
Questions people ask
1Why does ⧠ show as a box on some devices?
Because that device's fonts have no glyph for it. The character is still correct and still copies correctly — the box is a missing glyph, not a broken character.
More like this
10
How to type or find ⧠
- Search it as
- d’Alembertian · wave operator · wave equation
- Shows up in
- Anything that takes text · its shape is whatever your font draws
⧠\29E0Codes and encoding1 code points
A visible symbol can contain several code points. JS .length counts UTF-16 units; UTF-8 counts bytes.