  We study quantum friction and Casimir forces with a full-relativistic
formalism for atoms modelled as Unruh-DeWitt detectors in the presence of
arbitrary macroscopic objects. We consider the general case of atoms with
arbitrary relativistic trajectories in arbitrary quantum states (including
coherent superpositions) close to objects that impose arbitrary boundary
conditions. Particularizing for conducting plates, we show that, for relative
velocities close to the speed of light, the quantum friction diverges while the
Casimir force is almost independent of the velocity. Since we include the
effect of the finite size of the detector and the finite interaction time, we
also obtain quantum friction when the detector is isolated but follows a
non-inertial trajectory.
