The article lists three examples
of quantities that are scalars in Relativity: electric charge, spacetime interval, invariant mass, but where is the definition
of scalar in Relativity?
The article has three examples of scalars, but no clear examples of what are NOT scalars.
It lists several quantities:
- charge density
- current density
- momentum density
- stress-energy tensor
but does not specify whether these things are considered to be scalars or not.