  The coupling of conduction electrons and magnetic textures leads to quantum
transport phenomena described by the language of emergent electromagnetic
fields [1-3]. For magnetic skyrmions, spin-swirling particle-like objects, an
emergent magnetic field is produced by their topological winding [4-6],
resulting in the conduction electrons exhibiting the topological Hall effect
(THE) [7]. When the skyrmion lattice (SkL) acquires a drift velocity under
conduction electron flow, an emergent electric field is also generated [8,9].
The resulting emergent electrodynamics dictate the magnitude of the THE via the
relative motion of SkL and conduction electrons. Here, we report the emergent
electrodynamics induced by SkL motion in Gd$_2$PdSi$_3$, facilitated by its
giant THE [10,11]. With increasing current excitation, we observe the dynamic
transition of the SkL motion from the pinned to creep regime and finally to the
flow regime, where the THE is totally suppressed. We argue that the Galilean
relativity required for the total cancellation of the THE can be generically
recovered in the flow regime, even in complex multiband systems such as the
present compound. Moreover, the observed THE voltages are large enough to
enable real-time measurement of the SkL velocity-current profile, which reveals
the inertial-like motion of the SkL in the creep regime, appearing as
current-hysteretic behavior of the skyrmion velocity.
