Inertial Frame Dragging and Relative Rotation of ZAMOs in Axistationary Asymptotically Flat Spacetimes

In axistationary, asymptotically flat spacetimes, zero angular momentum observers (ZAMOs) define an absolute standard of non-rotation locally, as can be verified by the absence any Sagnac effect for these observers. Nevertheless, we argue that on a global scale only physically meaningful concept is relative rotation. The argument substantiated solving Einstein’s equations approximate thin shell model, where maintain degree freedom, relaxing natural assumption vanishing rotation at asymptotic infinity, outset analysis. solution reveals determine differences in rate ZAMOs, thereby establishing globally. interpretation context inherently linked to freedom transform between coordinate systems rotating each other, implying arbitrary ZAMO located radius may claim one non-rotating scale, and notion Lorentz frame which measure devoid meaning. Kerr spacetime then briefly discussed this interpretation.