Magnetic reconnection in space

Models of magnetic reconnection in space plasmas generally consider only a segment of the magnetic field lines. The consideration of only a segment of the lines is shown to lead to paradoxical results in which reconnection can be impossible even in a magnetic field constrained to be curl free or can be at an Alfv\'{e}n rate even when the plasma is a perfect conductor though pressureless. A model of reconnecting magnetic fields is developed that shows the smallness of the interdiffusion distance d$_{d}$ of magnetic field lines does not limit the speed of reconnection but does provide a reconnection trigger. When the reconnection region has a natural length $L_{r}$, the spatial scale of the gradient of magnetic field across the magnetic field lines must reach $L_{g }\sim $ $L_{r}$ / ln($L_{r}$ /d$_{d})^{3}$ for fast reconnection to be triggered, which implies a current density \textit{j $\sim $ B/}$\mu _{0}L_{g}$. The relation between magnetic reconnection in space and in toroidal laboratory plasmas is also discussed.