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MEMS Researchers Hope To Exploit Casimir Effect
smartalix writes "Researchers at Purdue University's School of Science are examining the Casimir effect (a phenomenon that explains Max Planck's and Werner Heisenberg's quantum vacuum fluctuation theory) and its impact on nanostructures in MEMS devices. At the distances these structures such as gear teeth, actuators, and such) will be operating from one another, the Casimir force may become something to reckon with, potentially forcing a limit to the level of miniaturization possible. The Purdue team is not only confirming Casimir's original theory, it is exploring possible ways to harness the effect in micromachines."
Well, someone had to say it!
Did anyone else go back throught the story description and read it like John Moshitta used to do in the Micro Machines commercials?
MicroMachinesMicroMachinesMicroMachines!!!
--"The perfect example of the man of action is the suicide." - William Carlos Williams
the Casimir effect (a phenomenon that explains Max Planck's and Werner Heisenberg's quantum vacuum fluctuation theory)
:) Quantum theory is full of such unhelpful infinities -- it was working out how to get rid of them ("renormalisation") that won Feynman his Nobel prize.
Whoa there, you've got it all backwards. The Casimir effect is EXPLAINED BY quantum vacuum fluctuations, though the description of the effect in the original article is so bad that I can forgive your misunderstanding.
First, let's get the names right. It was Heisenberg and Schrodinger (not Planck) who came up with the first quantum theory to predict vacuum energy. However the idea of this energy coming from virtual particles (or "spontaneously appearing and disappearing particles and photons" as the article puts it) comes from Dirac's theory of quantum electrodynamics, as perfected by Feynman, Tomonaga and Schwinger. There's no independent "quantum vacuum fluctuation theory".
Second, let's have a closer look at the physics. The article gets the basic idea right: two parallel plates close together are pushed together because there are less virtual particles between the plates than outside them. The detail, though, is wrong - photons do not "pile up" outside the plates. It's much simpler than that. In an (infinite) vacuum, photons can exist with any wavelength. But between two plates, photons can only exist with wavelengths that are simple multiples of the distance between the plates -- just like vibrations on a finite string. (So it's not simply a case of only longer wavelenths being excluded--shorter ones are too, unless they're the right length) Both inside and outside, each permitted wavelength will on average be occupied by the same number of "virtual" photons caused by vacuum fluctuations. Because there are less wavelengths permissible between the plates than outside them, there's overall a greater energy density outside, which translates into a higher pressure.
The more perspicacious reader will have noted that there's an infinite number of possible wavelengths outside, and a (smaller) infinity of permitted wavelengths inside, with the difference between the two being infinite. Since each wavelength carries the same (finite) amount of vacuum energy, doesn't this mean that the energy density of the vacuum is infinite and that the force between the two plates is infinite... Well, yes and no. It depends what you mean by infinity
One interested but little-known point about the Casimir effect is that it's not always attractive -- depending on the geometry of the components involved it can also be repulsive. However working out the result except in the most simple geometries is a VERY difficult problem...
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No mere gigawatts can power a delorian to the future!
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Zettabyte Storage
This talk of "virtual" photons is pretty fictitious. The Casimir effect is computed from the zero-point field ie. the lowest energy state for each wavelength. Ie. it's computed assuming no real photons. But I don't see where "virtual" photons come in either. You don't need to do any Feynman diagram computations to get the result. "Virtual" photons are just labels given to edges in Feynman graphs. No perturbation, no need to talk of "virtual" photons.
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IANAPhysicist. Got that out of the way.
Do you happen to know whether these people measuring the forces factored gravity into their measurements?
I know it is not normally a problem but the plates were very close together and so the force of gravity might be measurable. This has been niggling at me since I first heard about the casmir affect. Can anyone point me to a paper that explains the set up and the calculations.
AFAIK The forces measured are of the correct order of magnitude to fit the Casimir effect. I believe there has been significant error in the experiments but getting the computation exactly right is not easy. But they're way off for gravity.
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Computer chips don't use electrons to carry data; they use photons.
Yes they do use electrons you dork.
If Mr. Edison had thought smarter he wouldn't sweat as much. --Nikola Tesla
The only Casimir effect i've heard of nearly lobotomized a whole generation of french kids 25 years ago !
There are some nice write ups on it at everything2. Just take a look there.
-><- no
You are correct, but I doubt many people will realize it unless you explain it (or they think long and hard). For the non-physics majors out there:
Electrons have mass, and thus move very slowly compared to photons, which don't have mass and thus move at the speed of light. Among their other duties, photons carry the replusive and attractive forces we associate with charged objects such as ellections (as most of us had to memorize at some point, opposites attract and like-charges repel).
So how does this move data? To grossly oversimplify, when an electron moves down a wire (or through a semiconductor, or whatever) it emits a photon that goes rushing on ahead, and eventually encounters an other electron, which (because of the repulsive force of the electron coming towards it) starts moving in the same direction. The process continues all the way down the wire, with almost all of the distance being covered by the travel of photons. Thus we see the signal moving (via the photons) at a significant fraction of the speed of light even though the electrons themselves are poking along much more slowly.
-- MarkusQ
A cool picture of one of the earlier experiments can be found here.
I would still like to know the weight of the substrate and the ball to put my mind at rest. For example if the ball weighed 1*10^-20 kg and the plate 1 g then the force would be in the order of 6.6*10-15 N at the distance of 100nM they measured at which is detectable with the AFM referenced in the article. So either the ball is a lot lighter than my uniformed guess or the gravity between a ball and plate is vastly different between two point sources. OR I have mucked up my calculations somewhere.Probably all of the above
It's worth noting that many problems can be solved perturbatively in different ways leading to completely different sets of Feynman diagrams and hence different virtual particles. A good example is the use of ghost particles in gauge theory.
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Isn't the Casimir Effect supposed to be unexploitable for useful work (or net work)? Because if you could exploit it, you'd violate Carnot's Law, and create a perpetual motion machine... violating the laws of thermodynamics.
Unlike that lightsail argument before, this really would be a heat engine, exploiting ambient energy / zero point energy.
This lets them easily factor gravity out of the measurements by measuring the differences in attractive force as the distances are changed.
Incidentally, if 1/x^2 is inverse-square, and 1/x^3 is inverse-cube, is 1/x^4 inverse-hypercube?
-T
...who modded that down to -1, Interesting.
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Interestingly, the Casimir effect also occurs in biological systems. Proteins embedded in a lipid membrane restrict the fluctuations of the membrane and therefore decrease the entropy in the region between the proteins. Since thermal systems evolve toward maximum entropy, the proteins move toward each other. Here the fluctations are thermal instead of quantum mechanical, and the medium is the membrane instead of the vacuum, but the principle is the same.
If you google for "casimir membrane" you'll find a lot of papers on the subject.
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Could this be seen as evidence of string theory? Extra dimensions, etc.
Or, to follow up my thought, doesn't string theory predict that gravity will behave at something other than inverse-square at small distances?
16 times is 4-fold, if I'm not mistaken.
</nitpick>
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Physics: Making the universe open source.
If the distance is x then the frequencies that will fit in have to have wavelengths of x or even divisors of x (x/2, x/3, x/4, etc.) As x gets smaller, the frequences have to get higher and higher, and fewer of them can fit... and correspondingly, more are hitting against the outside of the plates. Each of them is imparting a force with an x^2 component, and the number of them is increasing at x^2 as the plates get closer, so you end up with a term like x^2^2, or x^4 for the energy increase.
-T