The choice of the concept of magnetic field lines or of electric current lines: Alfvén medal lecture
Magnetic fields other than those of permanent magnets must be produced by electric currents, which are produced by particle motions; changing magnetic fields are caused by changing electric currents. What Alfvén emphasized in reviewing the progress in cosmic electrodynamics was that even if current i is difficult to measure, and thus should be determined by curl B, the whole current system, including its generation, the transmission, and dissipation, should be considered together.
The success of the magnetic reconnection theory proposed by Dungey (1961) has become the prevailing view in magnetospheric physics, so that we tend to look at solar and magnetospheric phenomena through a filter that can recognize only magnetic field lines and their movements and try to understand magnetic reconnection as the only process for dissipating magnetic energy.
In a scientific field, it is dangerous to rely on only one concept. Alfvén’s point was that we should also use a filter that can see electric currents (Alfv´en, 1967, 1977, 1981, 1986).