Edited sentence: Although the gauge transformation does change A, it does not change the relative phases of charged particles exposed to the field, so the results of experiments remain the same.In quantum mechanics, however, a charged particle's phase depends on the A to which it is exposed, and different experimental results can be obtained in cases where the B field to which the particle is exposed is identical, while only A changes.That is, Maxwell's equations have a gauge symmetry.The fields remain the same under the gauge transformation, and therefore Maxwell's equations are still satisfied.Until the advent of quantum mechanics, the significance of this gauge symmetry was not fully understood, because it was not clear whether it was the fields or the potentials that were the fundamental quantities