Sweet-Parker model

The Sweet-Parker model is the foundational theory of resistive magnetic reconnection, developed independently by Peter Sweet and Eugene Parker in the late 1950s. It describes reconnection as a steady, laminar process occurring in a long, thin current sheet where oppositely directed magnetic fields diffuse together and annihilate, releasing magnetic energy as heat and plasma flow. The model predicts a reconnection rate that scales inversely with the square root of the Lundquist number — far too slow to explain explosive solar flares or the rapid energy release observed in coronal mass ejections. Its principal legacy is not as a final theory but as a baseline that revealed the necessity of fast reconnection mechanisms.

The Sweet-Parker model is the Newtonian mechanics of reconnection: it works beautifully until it doesn't, and its failures taught us more than its successes.