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In the weak field, one can make an analogy between electromagnetism and gravity with a few other assumptions also necessary such as low velocities and others. This can be formalized as "gravitoelectromagnetism" or GEM for short. There's a wiki overview at https://en.wikipedia.org/w/index.php?title=Gravitoelectromagnetism&oldid=970487534
If we use this weak field analogy, we can regard gravity as a force, the coulomb force of electromagnetism between charges is, except for a necessary minus sign, is analogous to the gravitational force between masses. The sign issue comes into play because like charges repel, but "gravitational charge" is always positive, and two objects with positive masses, positive "gravitatioanl charge", attract each other, they do not repel each other.
If we have two moving charges, covariance demands that in the rest frame of said particles, there is only an electric force, while in a frame moving relative to the two charges, there is both an electric component and a magnetic component to the force.
Similar reasoning applies to gravity in the weak field using the GEM approximations.
So if we consider two stationary masses, we have only the "electric" GEM components betwen them. If we go to a frame in which the masses are moving, we find that there is both an "electric" force and a "magnetic" force. This is necessary for covariance, for our choice of frame not to matter to things we can observe.
In the strong field, where GEM doesn't work things are not so easy. There is an approach I like involving the Bel decomposition of the Riemann tensor, but I think what I'd write on that would not be helpful without a detailed knowledge of the Riemann tensor and tensor mathematics. I'm guessing that this is not a background you share, so it wouldn't be productive to go into it.
I would concentrate on understanding the origin of the magnetic force in special relativity first, and why it is needed for covariance. Then you can consider linear frame dragging to be a similar phenomenon - something that we need to make our theory covariant.
As far as experiment goes, though, we've directly confirmed frame-dragging from the rotating earth.
If we use this weak field analogy, we can regard gravity as a force, the coulomb force of electromagnetism between charges is, except for a necessary minus sign, is analogous to the gravitational force between masses. The sign issue comes into play because like charges repel, but "gravitational charge" is always positive, and two objects with positive masses, positive "gravitatioanl charge", attract each other, they do not repel each other.
If we have two moving charges, covariance demands that in the rest frame of said particles, there is only an electric force, while in a frame moving relative to the two charges, there is both an electric component and a magnetic component to the force.
Similar reasoning applies to gravity in the weak field using the GEM approximations.
So if we consider two stationary masses, we have only the "electric" GEM components betwen them. If we go to a frame in which the masses are moving, we find that there is both an "electric" force and a "magnetic" force. This is necessary for covariance, for our choice of frame not to matter to things we can observe.
In the strong field, where GEM doesn't work things are not so easy. There is an approach I like involving the Bel decomposition of the Riemann tensor, but I think what I'd write on that would not be helpful without a detailed knowledge of the Riemann tensor and tensor mathematics. I'm guessing that this is not a background you share, so it wouldn't be productive to go into it.
I would concentrate on understanding the origin of the magnetic force in special relativity first, and why it is needed for covariance. Then you can consider linear frame dragging to be a similar phenomenon - something that we need to make our theory covariant.
As far as experiment goes, though, we've directly confirmed frame-dragging from the rotating earth.