  For more than 35 years theorists have studied quantum or Casimir friction,
which occurs when two smooth bodies move transversely to each other,
experiencing a frictional dissipative force due to quantum electromagnetic
fluctuations, which break time-reversal symmetry. These forces are typically
very small, unless the bodies are nearly touching, and consequently such
effects have never been observed, although lateral Casimir forces have been
seen for corrugated surfaces. Partly because of the lack of contact with
phenomena, theoretical predictions for the frictional force between parallel
plates, or between a polarizable atom and a metallic plate, have varied widely.
Here we review the history of these calculations, show that theoretical
consensus is emerging, and offer some hope that it might be possible to
experimentally confirm this phenomenon of dissipative quantum electrodynamics.
