  Reconnection plays a significant role in the dynamics of plasmas, polymers
and macromolecules, as well as in numerous laminar and turbulent flow phenomena
in both classical and quantum fluids. Extensive studies in quantum vortex
reconnection show that the minimum separation distance {\delta} between
interacting vortices follows a 1/2 scaling. Due to the complex nature of the
dynamics (e.g., the formation of bridges and threads as well as successive
reconnections and avalanche), such scaling has never been reported for
(classical) viscous vortex reconnection. Using the direct numerical simulation
of the Navier-Stokes equations, we study viscous reconnection of slender
vortices, whose core size is much smaller than the radius of the vortex
curvature. For separations that are large compared to the vortex core size, we
discover that {\delta}(t) between the two interacting viscous vortices
surprisingly also follows the 1/2 power scaling for both pre- and
post-reconnection events. The prefactors in this 1/2-power law are found to
depend not only on the initial configuration but also on the vortex Reynolds
number (or viscosity). Our finding in the viscous reconnection, complementing
numerous works on quantum vortex reconnection, suggests that there is indeed a
universal route for reconnection -- an essential result for understanding the
various facets of the viscous vortex reconnection phenomena and their potential
modeling, as well as possibly explaining turbulence cascade physics.
