|MLA Citation:||Bloomfield, Louis A. "Question 1235"|
How Everything Works 20 Aug 2018. 20 Aug 2018 <http://howeverythingworks.org/print1.php?QNum=1235>.
Nonetheless, a large permanent magnet isn't really permanent. The random fluctuations of thermal energy and the influences of passing magnetic fields gradually demagnetize large permanent magnets. However, good permanent magnets demagnetize so slowly that the changes are completely undetectable. You might have to wait a billion years to detect any significant weakening in the magnetic field around such a magnet.