  The chiral magnetic effect is a novel quantum phenomenon proposed for
high-energy nuclear collisions but which has yet to be observed. We quantify
the axial charge relaxation time, due to sphalerons, which enters in
simulations of this effect. An extrapolation of weak coupling calculations of
the sphaleron rate yields rather different relaxation times than strong
coupling AdS/CFT calculations. The AdS/CFT relaxation time is the larger one of
the two by an order of magnitude, but the weak coupling relaxation time may not
be reliable because it is only marginally bigger than the microscopic
thermalization time. The role of quark masses has yet to be accurately
assessed.
