The geometric properties of critical fluctuations in the three-dimensional (3D)
XY model are analyzed. The 3D
XY model is a lattice model describing superfluids. We present a direct evaluation of the Hausdorff dimension
DH of the vortex loops which are the critical fluctuations of the 3D
XY model. We also present analytical arguments for why $\ensuremath{\vartheta}$ in the scaling relation ${\ensuremath{\eta}}_{\ensuremath{\phi}}+{D}_{H}=2+\ensuremath{\vartheta}$ between
DH and the anomalous scaling dimension of the corresponding field theory must be zero.
We study the evolution of 3d weakly interacting bosons at finite chemical potential with the stochastic Gross-Pitaevskii equation. We fully characterise the vortex network in an out of equilibrium. At high temperature the filament statistics are the ones of fully-packed loop models. The vortex tangle undergoes a geometric percolation transition within the thermodynamically ordered phase. After infinitely fast quenches across the thermodynamic critical point deep into the ordered phase, we identify a first approach towards the critical percolation state, a later coarsening process that does not alter the fractal properties of the long vortex loops, and a final approach to equilibrium. Our results are also relevant to the statistics of linear defects in type II superconductors, magnetic materials and cosmological models.