  The Casimir forces between two plates moving parallel to each other are found
by calculating the vacuum electromagnetic stress tensor. The perpendicular
force between the plates is modified by the motion but there is no lateral
force on the plates. Electromagnetic vacuum fluctuations do not therefore give
rise to "quantum friction" in this case, contrary to previous assertions. The
result shows that the Casimir-Polder force on a particle moving at constant
speed parallel to a plate also has no lateral component.
