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ChemicalRain5513 t1_jbsveml wrote

How can you prove anything is zero? Even for the photon mass the best we have is an upper limit of 10^-18 ev/c^2.


SwitchingtoUbuntu t1_jbtgdx4 wrote

Yeah I mean technically we can't say anything is actually zero but the lower bound is pretty low.


luckyluke193 t1_jbuu6ht wrote

The superconducting coils that generate the magnetic fields for MRI and NMR spectroscopy systems have zero DC resistance.

They usually operate in persistent mode, meaning that there is no power supply attached to them. As long as you keep them superconducting, you can have hundreds of amps circulating in the coils without any change in the current over several years.