\(F_\rho=i\sqrt { 2{ mc^{ 2 } } }\,G.tanh\left( \cfrac { G }{ \sqrt { 2{ mc^{ 2 } } } } (x-x_z) \right)\)
where \(i\) in the expression for \(F_\rho\) of a wave travelling along \(t_T\) rotates \(c\) along \(t_T\) to \(t_c\) and a similar \(i\) rotates \(c\) along \(t_g\) to the \(-t_c\) direction in the equivalent expression for \(F_\rho\) of a wave travelling along \(t_g\).
The result is, the forces act opposite to each other, and \(-\psi\) appears if we consider \(t_c\) to be positive only. And we have like charges repel and unlike charges attract.
