  Whether intentionally introduced to exert control over particles and
macroscopic objects, such as for trapping or cooling, or whether arising from
the quantum and thermal fluctuations of charges in otherwise neutral bodies,
leading to unwanted stiction between nearby mechanical parts, electromagnetic
interactions play a fundamental role in many naturally occurring processes and
technologies. In this review, we survey recent progress in the understanding
and experimental observation of optomechanical and quantum-fluctuation forces.
Although both of these effects arise from exchange of electromagnetic momentum,
their dramatically different origins, involving either real or virtual photons,
lead to different physical manifestations and design principles. Specifically,
we describe recent predictions and measurements of attractive and repulsive
optomechanical forces, based on the bonding and antibonding interactions of
evanescent waves, as well as predictions of modified and even repulsive Casimir
forces between nanostructured bodies. Finally, we discuss the potential impact
and interplay of these forces in emerging experimental regimes of
micromechanical devices.

Optics