Casimir and van der Waals forces

5 problems

• Casimir torque between two solid birefringent plates across vacuum

  Partially resolved

  Two crystals whose optical properties depend on direction should twist toward alignment because of quantum fluctuations, the Casimir torque. It has been measured with a liquid crystal on a solid crystal, but not between two solid plates across empty space.

• Why thermal Casimir data favor the dissipationless plasma model

  Contested

  The Casimir force between metals at room temperature depends on how electrons in the metal lose energy. Calculations using the standard description of a real, resistive metal disagree with most precision measurements, which instead match a description that ignores resistance.

• Dynamical Casimir photon creation by a moving massive mirror

  Open

  A mirror shaken fast enough should turn vacuum fluctuations into real photon pairs, the dynamical Casimir effect. It has been seen with electrical circuits that act like a moving mirror, but never with a real massive object.

• Speed and distance dependence of non-contact quantum friction

  Contested

  Two smooth surfaces sliding past each other without touching might still feel a drag from quantum fluctuations of the field between them, even at zero temperature. Most theories predict a tiny nonzero drag, but they disagree on how it depends on speed and distance, and no experiment has detected it.

• Casimir repulsion between solid bodies separated by vacuum

  Open

  Casimir forces are almost always attractive, and they have been made repulsive only with a liquid between the objects. Predicted repulsion across empty space, using magnetic, chiral or topological materials, has never been seen.