## MEMS Researchers Hope To Exploit Casimir Effect 39

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."*
## three words: quantum flux capacitor (Score:1)

Well, someone had to say it!

## Re:The Casimir Effect? (Score:2, Interesting)

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.

## Re:The Casimir Effect? (Score:3, Informative)

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.

## Re:The Casimir Effect? (Score:1)

A cool picture of one of the earlier experiments can be found here [aps.org].

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

## Re:The Casimir Effect? (Score:2)

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

## Re:The Casimir Effect? (Score:2)

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 t

## Re:The Casimir Effect? (Score:1)

16 times is 4-fold, if I'm not mistaken.

</nitpick>

## Never mind... (Score:1)

## I wonder who the monkeys were... (Score:2)

## John Moschitta (Score:1)

MicroMachinesMicroMachinesMicroMachines!!!

## here's how it really works (Score:5, Informative)

the Casimir effect (a phenomenon that explains Max Planck's and Werner Heisenberg's quantum vacuum fluctuation theory)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...

## Fiction (Score:2)

## Re:Fiction (Score:3, Informative)

It's true that virtual particles used to be primarily considered to be a mathematical construct to aid calcul

## Re:Fiction (Score:3, Interesting)

No it isn't. Sounds like you're competent to do the calculations yourself. Pick up a book or paper on Hawking radiation. No need to use that nonsense about pair-production with one half falling past the event horizon. That's just a story made up for the popular science press. It comes from the fact that in curved spacetime there is no natural choice of time coordinate and so you can't distinguish betw

## Re:Fiction (Score:3, Insightful)

It comes from the fact that in curved spacetime there is no natural choice of time coordinate and so you can't distinguish between positive and negative energy modes meaning that you can't distinguish properly between creation and annihilation operators.The answer to that's not so clear: it's true the number operator in different (curved) reference frames is different, since the annihilation/creation operators are different. However, saying that has nothing to do with pair-production isn't exactly correc

## It's just a picture for the minds' eye (Score:2)

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.

## Re:It's just a picture for the minds' eye (Score:2)

Anyway, the whole situation isn't THAT different than the whole explanation for quark confinement (compressed flux tubes, and all that), the explanation for particle production by an inflating universe (relaxation of lowest-energy modes), or even Feynman diagrams as "particle graphs" - none of them are entirely correct, but they're all 'suggestive', and are easy to understand intuitively. I will agree that the Hawking radiation example is a little too specific for me.

## Re:It's just a picture for the minds' eye (Score:2)

I don't see it that way at all. But...

## What have you been smoking? (Score:1, Redundant)

Computer chips don't use electrons to carry data; they use photons.Yes they do use electrons you dork.

## Re:What have you been smoking? (Score:2)

I'm pretty sure there's actually a name for this bucket brigade type action.....

-psy

## Re:What have you been smoking? (Score:1)

## Correct (Score:5, Informative)

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

## Re:Correct (Score:1)

## No thanks ! (Score:3, Funny)

## Don't know what the casimir effect is? (Score:3, Informative)

## Re:Perpetual Motion Machines, Zero Point Energy (Score:2)

## Casimir effect in biological systems (Score:1)

If you google for "casimir membrane" you'll find a