Unification: what does it mean for the forces to become equal?

Question

The Coulomb force constant $k_c$ has si-units of $Nm^2C^{-2}$. The gravitational force constant $G$ has si-units of $Nm^2kg^{-2}$. What does it mean that at very high energies these forces become equal? How can we compare different forces?

Answer 1

It means that at lower energies the electromagnetic force dominates, and the gravitational effects are barely noticeable if not negligible. If you want to actually test gravity on a microscopic scale in a system that is also subject to electromagnetism (eg charged particles) you have to reach high enough energies for the two forces to be roughly equal in magnitude.

The weak force at high energies becomes equal to the EM force. Physically, why? Because at high energies ($mc^2$ where $m$ the mass of the weak bosons) you can actually create $W$ and $Z$ bosons to carry the interaction.