This paper is also remarkable for the development of the idea of the scalar potential.
The magnetic field is not conservative in general, and hence cannot usually be written in terms of a scalar potential.
Similar results can be obtained by applying the first-order term, to the scalar potential.
With some care the scalar potential can be extended to include free currents as well.
With reasonable values for the scalar potential, the size of the extra dimension is large enough to solve the hierarchy problem.
We need something else besides the scalar potential for describing correctly a time-varying electric field.
The scalar potential is an example of a scalar field.
Further, the scalar potential is the fundamental quantity in quantum mechanics.
The functions assumed for the scalar potentials are not stated.
When the above equation holds, is called a scalar potential for .