Will a spinning magnet slow down or lose its magnetism? In an otherwise empty universe, a bar magnet spins pole-over-pole, emiting a magnetic wave (and also an electric wave (electromagnetism)?).
Since emitting an electromagnetic wave requires energy, it needs to come from somewhere. Will the energy needed come from the magnets's movement or its magnetism?
Or am I completely misunderstanding something?
EDIT: I somehow didn't notice this question when writing this one.
 A: According to the laws of electromagnetism, the spinning (or accelerating towards the fulcrum) magnet will loss its kinetic energy not its magnetism. So, it will slow down. Because the magnetism comes indirectly from the symmetrically arranged charged particles in a magnet, it will radiate its kinetic energy (assuming the symmetry of the particles is unchanged).
Hope this helps.
A: Electromagnetic waves emitted by the magnet carry away momentum and energy, as per Planck's relations
$$E=\hbar\omega, \mathbf{p}=\hbar\mathbf{k},$$
which means that there is a radiative back-action force on the magnetic moments emitting the radiation. Under the action of this force the magnetic moment might either

*

*flip (or otherwise change its direction - depending on the type of magnetism and whether we discuss these moments classically or in quantum language)

*transfer force/moment to the crystal (i.e., the bulk of the magnet)

The first effect would mean the randomization of the direction of magnetic moments, i.e., gradual loss of magnetization. The second effect would mean slowing the rotation of the magnet as a whole. Which of the two dominates depends obviously on how well the moments are anchored in their positions. For typical ferromagnets slowing is more likely, but there are probably "borderline" materials where interesting effects could be observed. Note also that the magnitude of the effect depends on many factors: how fast the magnet rotates, the geometry of the system, the size of the magnet (since flipping a few moments among billions would produce very insignificant changes), etc.
A: Permanent magnets do not require an energy input and do not emit radiation - rather, the magnetic effect is produced by the atoms making up the magnet all facing the same direction. The only time an electric or other type of field would be produced would be if a conductive object was moving inside of the magnetic field around the magnet, which would induce an electric current in the moving conductor. Going on this, your magnet would spin forever, as your theoretical universe is devoid of any and all matter meaning there is no gravity, friction or other objects for it to interact with in any fashion and no way for it to lose momentum.
