In another thread, the concept of Gravitomagnetism came up; apparently, this is the force responsible for frame dragging, the result of the fabric of space-time to twist in the direction of a massive rotating body.
My question is: is this “force” strictly a manifestation of the Force of Gravity, the Electromagnetic Force, or is this some kind of “bridge”, unifying G and EM at least
at the perhiphery of the G and EM fields?
Or is it like centrifugal force?
It’s a purely gravitational effect.
The reason it’s called gravitomagnetism is that there are analogies with the role of magnetism within electromagnetism. For instance, in EM you only get magnetic fields if the charged sources are moving and in GR you only get gravitomagnetic effects if the mass is moving (the usual textbook case is a spinning sphere).
Of course, the fact that there are formal analogies between EM and GR has always been a major starting point in attempts to unify them, but gravitomagnetism is only part of the deeper similarities between the theories. So it’s not usually terribly interesting in its own right when arguing about such attempts.