When work is performed solely by magnetism, is there an equivalent loss of energy from the magnetic field? When two magnets are placed within appropriate proximity and released, the attractive force will perform work and bring them together.  Work is performed overcoming friction.  Can we measure a reduction in the total energy of the magnetic field?
 A: Yes, if you can measure the energy stored in the magnetic field, you should find that it is reduced when two magnetic dipoles come together. By way of explanation: the potential energy of a pair of aligned, end-to-end, identical magnetic dipoles can be found using the equation in this Wikipedia article, plugging in $\vec{m}_j = \vec{m}_k = m\hat{z}$, $\vec{e}_{jk} = \hat{z}$, and $\vec{r}_{jk} = r\hat{z}$ to get
$$U = -\frac{\mu_0}{4\pi r^3}\bigl(3 (m)(m) - m^2\bigr) = -\frac{\mu_0 m^2}{2\pi r^3}$$
Here $r$ is the distance between the dipoles and $m$ is their dipole moment. This energy is stored in the dipoles' mutual magnetic field. As they get closer, the energy drops.
It's worth noting that the work done to bring these dipoles together is actually performed by the electric force, for real magnetic dipoles which consist of current loops.
A: From the statements offered I can only assume that we don't actually KNOW the answer.  If the magnetic field strength is reduced due to the work performed, either the magnet goes inert or the energy is replaced from somewhere else.  My original question was more of a conservation of energy thing and the answered must be "it must be magic".
