How Can a Magnet Pull Forever Without Running Out of Energy?

How Can a Magnet Pull Forever Without Running Out of Energy? A fridge magnet holds a postcard for a decade and consumes nothing. The question of how it manages that has a hidden assumption inside it, and the assumption is wrong: force does not cost energy. Work costs energy, work requires movement, and nothing is moving. The table holding up a book is doing the same thing, and nobody asks what powers the table. That disposes of the puzzle in about two minutes. The rest of the video is the part nobody tells you. In 1911 Niels Bohr proved in his doctoral dissertation that classical physics cannot produce magnetism at all. Not weak magnetism. None. Hendrika van Leeuwen proved it independently in 1919. Every magnetic phenomenon you have encountered exists only because the world is quantum mechanical, and the theorem showing it predates Schrödinger's equation by fourteen years. What holds a ferromagnet together is not magnetism either. Work out the dipole interaction between neighbouring iron atoms and you get an alignment that thermal agitation should destroy at about one kelvin. Iron stays magnetic to one thousand and forty-three kelvin. The factor of a thousand means the mechanism is something else: the exchange interaction, which is electrostatic repulsion operating under the Pauli exclusion principle. The magnet on your fridge is held by the antisymmetry of fermion wave functions. Also covered: where the energy in a permanent magnet actually came from (one pulse of current in a factory, lasting milliseconds), why every magnetic perpetual motion machine fails for reasons of field geometry rather than engineering, why muscles make holding things feel expensive when it isn't, the Einstein-de Haas experiment of 1915 and the gyromagnetic ratio that came out wrong by a factor of two, Barkhausen's 1919 loudspeaker that let you hear domain walls jumping, superconducting magnets running in persistent mode for years with no power input, and the Earth's core, which genuinely does burn something like a terawatt to keep its field going, and reverses polarity because of it. The permanence is not quite permanent. The magnetised state is metastable, the barrier protecting it is finite, and the waiting time scales exponentially with volume. For anything you can hold, the exponent is large enough that the question stops mattering. #magnets #magnetism #permanentmagnet #neodymium #fridgemagnet