Original sentence: Except for this, the equations are symmetric under interchange of electric and magnetic field.Fully symmetric equations can also be written if one allows for the possibility of "magnetic charges" analogous to electric charges.If magnetic charges do not exist, or if they exist but where they are not present in a region, then the new variables are zero, and the symmetric equations reduce to the conventional equations of electromagnetism such as.In fact, symmetric equations can be written when all charges are zero, and this is how the wave equation is derived.The extended Maxwell's equations, simplified by nondimensionalization, are as follows:.The standard form of the equations provide for an electric charge, but posit no magnetic charge.With the inclusion of a variable for these magnetic charges, say , there will also be "magnetic current" variable in the equations,
Edited sentence: As shown here, Maxwell's equations can be expressed in terms of magnetic monopoles, as can other electrodynamic phenomena.But fully symmetric equations could be written if one allowed for the possibility of "magnetic charges" exactly analogous to the observed electric charges.Except for this, the equations are symmetric under interchange of electric and magnetic field; in fact symmetric equations can be written when all charges are zero, and this is how the wave equation is derived.However, it should be noted that the fact that we can write a mathematical expression for something presents no evidence of its existence in this universe.So, if magnetic monopoles exist, two of Maxwell's equations, simplified by nondimensionalization, would have to be changed as follows:.When no magnetic charges are present in a region, these symmetric equations reduce to the conventional equations of electromagnetism (that is, ).With that in mind, the standard form of the equations provide for an electric charge, but posit no magnetic charge.With the inclusion of these magnetic charges, say , there will also be "magnetic current",