A (simple) theory for cause of Earth radial expansion

The surface on the inside diameter of a hollow sphere has opposite polarity to the outside surface. That means that a ball magnet placed inside a hollow ball magnet, will orient itself with the same polarity as the outer magnet, with attraction at the poles.

Per the closed loops rule, the interior magnet will have magnetic field lines around it along the sides that flow in direction opposite to the magnetic field inside the shell. The two magnets will repel at the sides and the equator, and attract at the poles. That can be illustrated with an iron bar inside a solenoid, repelling along the sides of the iron bar while there is attraction at the poles. An analogy could be that of water flowing through a pipe, the magnetic flux on the inside of the solenoid squeezes its way past opposite flux from the iron rod, compressing it from all directions at once, repelling the iron rod with a vector towards center of the radial axis

The combination of attraction and repulsion is the reason the iron bar in the GIF below levitates at the center of the coil, both along the longitudinal axis and also the radial axis.

The image below is a model where Birkeland current enters planets at poles along rotational axis, and plasmoid on Birkeland current in center of hollow shell repels at equator and attracts at poles, causing hollow shell structure as well as radial increase and/or decrease of shell, and also forms polar openings.

And, data showing Birkeland currents entering at poles of planets, on Jupiter (CHANDRA, 2000), Titan (Cassini, 2009) and Saturn (Keck Observatory, 2004).