A repulsive quantum force, opposite of casimir force, has been verified and measured. This is the cover story, [Measured long-range repulsive Casimir-Lifshitz forces], of the Jan 8, 2009 Nature journal and is from Harvard researchers: J. N. Munday, Federico Capasso & V. Adrian Parsegian.
Controlling the casimir forces is potentially a huge capability and DARPA has been funding work on it.
Last year creating a small scale comb allowed the casimir force to be reduced by 30 to 40%
Sufficient control of the casimir force could enable a breakthrough in space propulsion and energy extraction from the vacuum and highly efficient energy conversion. It could also make nanoscale machines work better with less or more friction as needed. Ultra-low friction bearing are also very high potential.
"When two surfaces of the same material, such as gold, are separated by vacuum, air, or a fluid, the resulting force is always attractive," explained Capasso.
The scientists replaced one of the two metallic surfaces immersed in a fluid with one made of silica, the force between them switched from attractive to repulsive.
Note: it is theorized that metamaterials can reverse and control the amount of casimir force.
The experimental verification that a bizarre quantum effect — the Casimir force — can manifest itself in its repulsive form is pivotal not only for fundamental physics but also for nanotechnology.
In 1948, Hendrik Casimir predicted that two uncharged, perfectly conducting plates in a vacuum would be attracted to each other because of quantum fluctuations in the vacuum's electromagnetic field between the plates. Generalized for real materials by Evgeny Lifshitz2 in 1956, Casimir's prediction has been verified many times and is now known as the Casimir–Lifshitz (C–L) force.
The Nature editors have summarized this Quantum levitation effect
Space is not completely empty; the vacuum teems with quantum mechanical energy fluctuations able to generate an attractive force between objects that are very close to each other. This 'Casimir–Lifshitz' force can cause static friction or 'stiction' in nanomachines, which must be strongly reduced. Until now only attractive interactions have been reported but in theory, if vacuum is replaced by certain media, Casimir–Lifshitz forces should become repulsive. This has now been confirmed experimentally. Repulsion, weaker than the attractive force, was measured in a carefully chosen system of interacting materials immersed in fluid. The magnitude of both forces increases as separation decreases. The repulsive forces could conceivably allow quantum levitation of objects in a fluid and lead to new types of switchable nanoscale devices with ultra-low static friction. Levitation depends only on the dielectric properties of the various materials.
6 pages of supplemental information on the experiments is here
Interstellartech Corp: Trying to use Casimir force to extract power
Fabrizio Pinto published in the Journal of Physics A: Mathematical and Theoretical on Membrane actuation by Casimir force manipulation.
Fabrizio Pinto is part of Interstellar Tech corp has been looking into trying to trying to create an engine by making use of the Casimir force. No Casimir force-based engine cycle could be devised if one assumed a constant Casimir force.
Areas of emphasis are:
1. Casimir force modulation; [now demonstrated by the University of Florida]
2. Repulsive Casimir force; [Prof Ulf Leonhardt and Dr Thomas Philbin 2007 report on theory and now this experimental work]
3. Lateral Casimir force;
4. Casimir force amplification
5. Energy issues in relation to the quantum vacuum.
One can implement a Casimir system engine cycle to transform thermal or optical energy into mechanical or electrical energy.
The Interstellar Tech corp proposal for the Transvacer device. They describe a casimir force-based engine where zero-point energy is transformed into mechanical energy.
Nasa study from 2004 on Casimir force Space Propulsion
A 57 page study of using "Study of Vacuum Energy Physics for Breakthrough Propulsion"
G. Jordan Maclay, Quantum Fields LLC, Wisconsin
Jay Hammer and Rod Clark, MEMS Optical, Inc. Alabama
Michael George, Yeong Kim, and Asit Kir, University of Alabama
4. Gedanken Vacuum Powered Spacecraft (on page 30)
A Gedanken spacecraft is described that is propelled by means of the dynamic Casimir effect, which describes the emission of real photons when a conducting surface is moved in the vacuum with a high acceleration. The maintenance of the required boundary conditions at the moving surface requires the emission of real photons, sometimes described as the excitation of the vacuum. The recoil momentum from the photon exerts a force on the surface, causing an acceleration. If one imagines the moving surface is attached to a spacecraft, then the spacecraft will experience a net acceleration. Thus we have a propellantless spacecraft. However, we do have to provide the energy to operate the vibrating mirror. In principle, it is possible to obtain this power from the quantum vacuum, and this possibility is explored. Unfortunately with the current understanding and materials, the acceleration due to the dynamic Casimir effect is very small, on the edge of measurability. One of the objectives in this paper is to demonstrate that some of the unique properties of the quantum vacuum may be utilized in a gedanken spacecraft. We have demonstrated that it is possible, in principal, to cause a spacecraft to accelerate due to the dissipative force an accelerated mirror experiences when photons are generated from the quantum vacuum.
Further we have shown that one could in principal utilize energy from the vacuum fluctuations to operate such a vibrating mirror assembly. The application of the dynamic Casimir effect and the static Casimir effect may be regarded as a proof of principal, with the hope that the proven feasibility will stimulate more practical approaches exploiting known or as yet unknown features of the quantum vacuum. A model gedanken spacecraft with a single vibrating mirror was proposed which showed a very unimpressive acceleration due to the dynamic Casimir effect of about 3x10−20m/ s2 with a very inefficient conversion of total energy expended into spacecraft kinetic energy. Employing a set of vibrating mirrors to form a parallel plate cavity increases the output by a factor of the finesse of the cavity, 10**10, yielding an acceleration per meter squared of plate area of about 3x10−10m/s**2 and a conversion efficiency of about 10**−16. After 10 years at this acceleration, a one square meter spacecraft would be traveling at 0.1m/s. Although these results are rather unimpressive, it is important to remember this is a proof of the principal, and to not take our conclusions regarding the final velocity in our simplified models too seriously. The choice of numerical parameters is a best guess based on current knowledge and can easily affect the final result by 5 orders of magnitude.