  The ability to steer light propagation inside scattering media has long been
sought-after due to its potential widespread applications. To form optical foci
inside scattering media, the only feasible strategy is to guide photons by
using either implanted or virtual guide stars. However, all of these guide
stars must be introduced extrinsically, either invasively or by physical
contact, limiting the scope of their application. Here, we focus light inside
scattering media by employing intrinsic dynamics as guide stars. By
time-reversing the perturbed component of the scattered light adaptively, we
concentrate light to the origin of the perturbation, where the permittivity
varied spontaneously. We demonstrate dynamic light focusing onto moving targets
and imaging of a time-variant object obscured by highly scattering media,
without invasiveness and physical contact. Anticipated applications include
all-weather optical communication with airplanes or satellites, tracking
vehicles in thick fogs, and imaging and photoablation of angiogenic vessels in
tumors.
