> Imagine for a moment that we were able to ‘switch off’ the earth’s magnetic fi eld. Navigation
would be made much harder since all compasses would be useless, with their needles pointing
randomly in any direction. However, as soon as we switched the magnetic fi eld back on, they
would all point north—their lowest energy state. Now if we wanted to force a needle to point
south we would have to use up energy and, of course, as soon as we let go, the needle would
return to its lowest energy state, pointing north.