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Pondering the Casimir Effect

Place two parallel plates close to each other in vacuum and a strange thing happens, as Dutch physicist Hendrik Casimir learned. The Casimir effect that he described draws the plates together, an effect that was successfully measured first in 1958 and, with greater precision, by Steve Lamoreaux in 1996. The effect becomes important at distances less than 100 nanometers. And if it seems like little more than a curiosity, be aware that Robert Forward looked at the possibilities of engineering to put this energy to use in an intriguing 1984 paper.

That paper (“Extracting Electrical Energy from the Vacuum by Cohesion of Charged Foliated Conductors” — see reference below) looks at the attraction between two parallel plates in a vacuum as the result of vacuum fluctuations of the electromagnetic field. As the two plates close on each other, longer electromagnetic waves no longer fit between them. The result: The total energy between the plates is less than the amount pushing them together from the vacuum that surrounds them. The Casimir effect increases as distance decreases, and if you get to atomic-scale distances, it has been measured at tons per square meter.


From a propulsion perspective, the idea that empty space contains energy in the form of these fluctuations of electric and magnetic fields is quite interesting, but we are in the earliest stages of understanding how the effect works. Interesting news, however, has just come out of Harvard University, where researchers have experimented with replacing the vacuum with a fluid. They were then able to measure a repulsive form of the Casimir effect. Working with a gold-coated microsphere attached to a mechanical cantilever in a liquid, the team measured its deflection as they varied the distance from a nearby silica plate.

Image: This is an artist’s rendition of how the repulsive Casimir-Lifshitz force between suitable materials in a fluid can be used to quantum mechanically levitate a small object of density greater than the liquid. Figures are not drawn to scale. In the foreground a gold sphere, immersed in Bromobenzene, levitates above a silica plate. Background: when the plate is replaced by one of gold levitation is impossible because the Casimir-Lifshitz force is always attractive between identical materials. Image courtesy of the Capasso lab. Credit: Harvard University.

A repulsive Casimir effect gets us into some practical uses for these strange phenomena, as Federico Capasso (Harvard School of Engineering and Applied Science) points out:

“Repulsive Casimir forces are of great interest since they can be used in new ultra-sensitive force and torque sensors to levitate an object immersed in a fluid at nanometric distances above a surface. Further, these objects are free to rotate or translate relative to each other with minimal static friction because their surfaces never come into direct contact.”

By contrast, attractive Casimir forces could obviously hamper extreme miniaturization. At the nanoscale, then, developing bearings that use this ‘quantum levitation’ is helpful in reducing friction among tiny components. Nanotechnology itself is a major interstellar driver — if we can reduce payload sizes down to nanotechnological scales, the propulsion problem becomes much more tractable. We can envision sending, for example, tiny probes that can use assembler technology upon arrival to build a robotic research station in a new planetary system, needing to accelerate far less mass than that of a conventional probe.

To the extent, then, that this work takes us deeper into a workable nanotechnology, it becomes useful for interstellar purposes. But it is also notable in that it suggests possible (though highly problematic) long-range uses of Casimir forces in propulsion, as Brian Wang notes in NextBigFuture. Brian flags Jordan Maclay’s “Study of Vacuum Energy Physics for Breakthrough Propulsion,” available here, which grew out of work for the Breakthrough Propulsion Physics project, and which takes a detailed look at ways this energy might be exploited.

The paper is Munday et al., “Measured long-range repulsive Casimir–Lifshitz forces,” Nature 457 (8 January 2009), pp. 170-173 (abstract). A Harvard news release is available. The reference for the Robert Forward paper is “Extracting Electrical Energy from the Vacuum by Cohesion of Charged Foliated Conductors,” Physical Review B 30, no. 4 (August 1984), pp. 1770–73.

Comments on this entry are closed.

  • James M. Essig January 12, 2009, 22:55

    Hi Paul;

    This is a most excellent topic.

    If the Casimar force is on the order of micronewtons per square meter for plates seperated by 100s of nanometers but tons per meter for seperations of atomic distances, one can imagine that some sort of stabilized neutronium could be fashioned into plates seperated by distances on the scale of the atomic nucleus. Since some forms of neutronium are theoretically superconducting, using stabilized forms of neutronium might permit titanic attractive Casimar forces between plates constructed of such materials. The ability to somehow reverse the direction of such titanic forces and cause them to interact over large distances would do a great service for we human space heads, and infact, for all of humanity as we plan to journey to the Moon, to Mars, and then to worlds beyond.

    Regarding sending out nanoprobes, such probes could perhaps include human embyos that would be stored on the distant worlds until the infrastructure was assembled to support the growing embryos in artifical wombs wherein the children upon birth would be raised to maturity by robots.



  • James M. Essig January 14, 2009, 11:46

    Hi Paul and Dad2059;

    I wonder if we will ever measure a laboratory induced force imbalance for the strong nuclear force mediating bosons (the 8 types of gluons), the weak force mediating bosons (the W-, W+, and Z0 bosons), and the still theoretical graviton, as well as the still hypothetical supersymmetric bosonic counterparts to the normal matter fermions.

    Perhaps nuclear force Casimir Apparatus plates seperated by femtometer scales composed of stabilized neutronium or Casimir Apparatus seperated by 0.01 to 0.001 femtometer scales made of very smooth quarkonium could do the job.

    Alternatively, ultrasmooth Casimir plates composed of material that is reactive to the weak force bosons which have a range on the order of 0.01 to 0.001 femtometers that are seperated by the same distance range might produce a weak force imbalance.

    Detection of the imbalance effects of zero point normal matter fermions such as the quarks, charged leptons and the neutrinos as well as the still hypothetical supersymmetric fermionic counterparts to the known normal mattergy force mediating bosons would be fantastic.

    Add the the above, the still theoretical standard model Higgs field and the stil hypotheticall fermionic Higgsino and one obtains a potentially marvelously complex overall vacumm zeropoint mattergy field with potentially many resources to draw energy from.