Researchers see exotic force for first time

Quantum Levitation
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. Courtesy of the lab of Federico Capasso, Harvard School of Engineering and Applied Sciences

( -- For the first time, researchers have measured a long-theorized force that operates at distances so tiny they’re measured in billionths of a meter, which may have important applications in nanotechnology as scientists and engineers seek new ways to create devices far too small for the eye to see.

The advance, by researchers by Harvard and National Institutes of Health (NIH) researchers, used a novel combination of materials to create a repulsive Casimir force, which pushes apart certain materials when separated by distances so tiny — between 20 nanometers and 100 nanometers — that they’re nearly touching.

The force, which decreases in strength as the distance between the two materials increases, may provide a new means to build ultra-low friction and other nanoscale devices, such as new types of compasses, accelerometers, and gyroscopes.

“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,” said Federico Capasso, Robert L. Wallace Professor of Applied Physics at Harvard's School of Engineering and Applied Sciences (SEAS), who led the study. “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.”

The results from Capasso’s and his colleagues’ work will be published in tomorrow's edition of the journal Nature. Capasso's co-authors are Jeremy Munday, formerly a graduate student in Harvard's Department of Physics and presently a postdoctoral researcher at the California Institute of Technology, and V. Adrian Parsegian, senior investigator at the NIH in Bethesda, Md.

The discovery builds on previous work related to the Casimir force, which was theorized by Hendrick Casimir in 1948 as both attractive and repulsive, pulling materials together under some circumstances and pushing them apart under others.

Until now, however, researchers have only been able to measure the attractive Casimir force, which, in some cases, has created headaches for nano-engineers because it can cause the components of tiny devices to stick together. Discovery of the repulsive version of the Casimir force can potentially help researchers overcome this problem.

“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.

Instead of using gold-coated materials, Capasso and colleagues swapped out one of the gold surfaces for one made of silica, then immersed them both in a liquid, bromobenzene. That combination did the trick, switching the attractive Casimir force to repulsive. The Harvard researchers have filed for a U.S. patent covering nanodevices based on quantum levitation.

Yale University Physics Professor Steve Lamoreaux, in an accompanying article in Nature, called the advance “pivotal for both fundamental physics and nanodevice engineering.” Though applications of the repulsive Casimir force in nanoscale devices have yet to be explored, Lamoreau said that “the prospects look exciting.”

Provided by Harvard University

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Citation: Researchers see exotic force for first time (2009, January 7) retrieved 16 September 2019 from
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Jan 07, 2009
Who here can envision a nano-belt in a toroidal loop - similar to an escalator - made up of alternating gold and silicon patches? Now, take a gold nanoball, attach a small carbon-nanotube or other 'stick-like' object coming off the top of the gold nanoball. At the top of the stick make a crankshaft.

Now you're extracting useful energy from the Casimir effect. The only question is: can you extract MORE energy than it takes to spin the nano-belt?

How many people are going to scream "NO!" and reply with "conservation of energy violation"? But is it REALLY a conservation of energy violation when the entire universe is the system, we have no idea how much energy is in the system, and we have no idea whether localized fluctuations could be used even assuming universal conservation of energy?

Jan 07, 2009
I can, I've been thinking of ways of extracting energy from casimir forces for some time. The newly discovered repulsive force makes this more plausible.

Another possibility is a nano-oscillator. Use a gold rod on a pivot between two plates half silicon and half gold.

You would probably need to add something in the way of nano-springs as well to prevent a steady state being reached. In principle though, since the casimir effect does produce a measurable force, I can't see why you can't extract energy from it.

Jan 07, 2009
I have been told that the attractive Casimir force is created because the region between the objects was to small for certain "virtual particles" to form so there was what would be analogous to a lower pressure created between the objects compared to the rest of the sea of quantum fluctuations on the other sides. Is this description accurate and if so, in what way does the change in materials alter the phenomenon to create a repulsive force?

Jan 07, 2009
And out of curiosity, with the discussions of extracting energy from the Casimir force, isn't it just a force? A magnet provides a force (or field or whatever) but unless it is moving (i.e. has energy of motion relative to something else) it can't be used to provide energy. How is the Casimir force different? I am not a physicist so if the explanation involves calculus forget that I asked. ;-)

Jan 07, 2009
erm, Sean_W, as far as I'm aware repulsion due to the casimir effect can only take place when submerged in a fluid (rather than a vacuum) and using special materials. Furthermore the source of the repulsion is actually electromagnetic (I think). In summary this exotic set-up exploits the casimir effect to produce a repulsive electromagnetic force but for the life of me, I don't know how or why ;-)

Jan 07, 2009
Has anyone found a way of concentrating the casimir force to amplify its effects? What results if the casimir force measurement apparatus is enclosed in a high temperature furnace that surrounds the objects with high temperature black body radiation? Has that been figured out?

Jan 08, 2009
Lets see, to DUH, or to NO DUH?

Jan 08, 2009
Does the Casimir effect play any role at the atomic level? Does it work on all things with mass, or just things with a mass at or above a threshold level. I'm more curios about how it works than how it could be used. Something tells me you'll get more electricity from spinning tiny magnets in the nanodevices than with the Casimir effect.

Jan 08, 2009
I am off to patent gravity.

Jan 08, 2009
Nahhhh Glen anti-gravity is where's it's at...gravity's been done :P

Jan 08, 2009

for a better explanation of the Casimir force,

for a different way to get a repulsive force.

At maynard, you could build the same machine with a chain of magnets poled alternately and another magnet on the stick.

Jan 09, 2009
One can make a Casimir laser if we could pump the vacuum.

Jan 14, 2009
Both attractive and repulsive Casimir forces do not exist

Casimir extended the microscopic van der Waals force between atoms in a gas to the attraction between macroscopic structures in a vacuum.

However, recent experiments at Harvard have suggested that the Casimir force can be changed from attraction to repulsion by immersing gold spheres and silicon plates in liquid bromobenzene.

But the Harvard experiment not only falsely presupposes the attractive Casimir force exists, but then extends that falsity to conclude the attractive Casimir force can be changed to repulsion.

In fact, both attractive and repulsive Casimir forces do not exist.

Casimir did not conserve the EM radiation in the gap between structures, for if he would have, Casimir would have found the frequency of the EM radiation increases by QED as the gap decreases to maintain the necessary constant EM energy. Since the gradient of the constant EM energy with respect to the gap vanishes, there is no Casimir force.

However, at gaps less than 200 nm, the EM radiation reaches VUV levels and the structures charge oppositely by the photoelectric effect. Hence, the attractive force measured in Casimir experiments is electrostatic from QED induced VUV radiation.

In the Harvard experiment, the attractive QED induced electrostatic force of oppositely charged gold and silicon structures is changed to repulsion upon immersion in bromobenzene because the latter is an electron scavenger that alters charge distribution.

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