Recent lattice calculations performed at zero temperature and in the maximal
center gauge indicate that quark confinement can be understood in this gauge as
due to fluctuations in the number of magnetic vortices piercing a given Wilson
loop. This development has led to a revival of the vortex condensation theory
of confinement. For a SU(2) gauge group, we show that also at finite
temperatures, center vortices are the relevant collective infrared degrees of
freedom determining the long-range static quark potential; in particular, their
dynamics reflect the transition to the deconfining phase.Comment: 14 pages, 6 figures, numerics completely overhauled w.r.t. original
version, physical conclusions unchange