I already wrote this somewhere else. If the curvature of space around a gravity source is proportional to the square root of distance, like the gravitational time dilation formula, then negative distance (internal space) becomes a complex number and gets an extra dimension - the real number and the imaginary. Is there any truth to that?
Gravity doesn't work like that. If it did, weird things would happen just by going underground.
Negative distance makes absolutely no sense, and even if it did, center of mass is a point which by definition has no volume meaning you can't be inside it.