What changes when electrical resistance reaches zero?
A different state of matter
Below a critical temperature, some materials become superconducting. Their electrical resistance vanishes, and sufficiently weak magnetic fields are expelled through the Meissner effect. Persistent currents and magnetic field expulsion are distinct features of this state.
Powerful magnets, real limits
Superconductors help produce the strong magnetic fields used in particle accelerators. Excessive temperature or magnetic field can destroy superconductivity. Type-II materials can admit magnetic flux in localized regions while remaining superconducting elsewhere, enabling operation in stronger fields.
Zero resistance is not zero energy
Maintaining the required low temperatures takes substantial engineering. CERN uses large cryogenic systems to cool its accelerator magnets. Eliminating resistance in a material does not eliminate the energy needed to run the surrounding machine.
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