  Mathematics demonstrates that an ideally evolving magnetic field has an
exponentially increasing sensitivity to non-ideal effects for all but truly
exceptional evolutions. On a time scale that depends only logarithmically on
the magnitude of non-ideality, an evolving magnetic field will generally reach
a state of fast magnetic reconnection. The effects of fast magnetic
reconnection proceed at a rate determined by Alfv\'enic, not resistive,
physics. The best known of these effects are associated with the transfer of
magnetic field energy to the plasma and the conservation of magnetic helicity,
which limits the energy transfer. As will be shown, weak non-ideality implies
helicity conservation in regions bounded by magnetic surfaces or rigid perfect
conductors. But, weak non-ideality makes the rapid transfer of energy subtle.
This transfer can be understood by the drive for Alfv\'en waves and two other
effects, which are present even in an ideal evolution, an effective parallel
electric field $\mathcal{E}_{||}$, which can accelerate particles despite the
particle acceleration due to the true parallel electric field $E_{||}$ being
negligible, and a coefficient $\nu_K$, which gives a rate for exponentiation of
the kinetic energy of particle motion along the magnetic field. Classical
theories of reconnection are two-dimensional and exclude the exponentially
increasing sensitivity that is robustly present for magnetic fields in
three-dimensional space.
