Not a geophysicist so I'm just spitballing: the earth's magnetic field is mainly generated by the motion of the liquid outer core. I think the hypothesis here i

Not a geophysicist so I'm just spitballing: the earth's magnetic field is mainly generated by the motion of the liquid outer core. I think the hypothesis here is that the magnetic field is exerting some force on the inner core causing it to slow or speed up. But yes, there is an absolutely absurd amount of energy in this scenario. On the scale of "let's stop the moon spinning" big. Even at the scale of slowing from one degree of rotation per year to zero degrees over a few decades, it's a lot of energy. And that's not even counting all of the other energy drains in this system, like turbulence between the outer and inner cores from rotating at different rates, or the magnetic field of the inner core fighting the outer core. The amount of energy involved is just absolutely bonkers.