Scale Models Can "Compute" Casimir Forces 136
KentuckyFC writes "Place two conducting parallel plates a few nanometres apart and the well-known but difficult-to-measure Casimir force will push them together. The force depends crucially on the shape of the plates but nobody is exactly sure how. That's because calculations with anything other than flat plates are fiendishly difficult and measurements are even harder. Now a group at MIT has come up with an ingenious new way to investigate Casimir forces. What the team has noticed is a mathematical analogy between the Casimir force acting on microscopic bodies in a vacuum and the electromagnetic behavior of macroscopic bodies floating in a conducting fluid. Their idea is to build a centimeter-scale metal model of the system they want to investigate, place it in salt water, and bombard it with microwaves and see what happens. The team says the experiment does not measure the force on the scale model but instead a quantity that is mathematically related to the force. So the experiment is not a simulator but actually an analog computer that calculates the force (abstract). What's exciting is that the method should for the first time give researchers a way of testing nano-machines designed to exploit the Casimir force."
Casimir Force (Score:3, Interesting)
Could someone provide a comprehensible description for non-physicists of what the Casimir Force is? I looked it up on Wikipedia (and like all math and physics related articles there) came up with a borderline unintelligible "summary".
It's overview is:
It's intro is similar:
Re:Casimir Force (Score:5, Informative)
The way the Casimir force works is that when you put smooth plates very very close together, they are pulled closer.
This is posited to be caused by pairs of virtual photons which spring into existence and annihilate constantly.
When you put the plates close enough together, there's not enough room for photons to appear between them. Therefore there is theoretically more of a vacuum between the plates than outside. As we all know, vacuum's suck so we get a force pulling the plates together.
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Re:Casimir Force (Score:5, Informative)
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Re:Casimir Force (Score:5, Informative)
No car analogy here, sorry to say, but I can provide a somewhat more visual description than any I have seen on this thread so far. And I would very much appreciate any critiques by those who know QM (I know of it, and use it in my fiction, but I certainly don't know it. Dammit, I'm a writer, not a quantum mechanic).
First, visualize "quantum foam": virtual particles are constantly springing into existence in "empty" space, mostly to disappear again in very short intervals of time. When working at very small distances and units of time, space is full of these virtual particles, winking in and out. Some are more common than others, but all are present. The total population of these over an interval of time will exhibit QM statistical properties: that is virtual neutrinos will be much more common than virtual electron - positron pairs, which in turn will be very much more common than virtual protons and antiprotons. The sum of all this activity has been called quantum foam [wikipedia.org] [John Wheeler gets credit for this, back in 1955].
Particles are waves, and waves have wavelengths. If you can put a constraint on a location in space so that a particular wavelength cannot exist at that location, then the particle associated with that wavelength cannot exist. The quantum foam in that location is less rich than in other locations. There is now a kind of "pressure gradient" between the quantum foam in the constrained region and the unconstrained regions around it.
Placing two sheets of metal closer together than the longer wavelengths of light prevent some of those virtual photons from manifesting. (My understanding is that this would only block the ones whose wavelengths are constrained by the plates, which suggests a kind of polarizing effect, but for now we can ignore that.) The Casimir effect is the force exerted on each of these plates by the pressure gradient of the quantum foam from one side of the plate to the other.
I'm thinking that we are going to have an increased need to develop effective ways of visualizing this as we start doing more with nanomaterials. For instance, I'm guessing that some of the transmission properties of buckytubes are related to constraints on the quantum foam in the inside of the tube. That a tube of the right diameter would prevent any real electron or real photon introduced at one end from doing anything other than exiting at the other end; that the geometry would force the wave to propagate only down the center of the tube.
I'm also thinking that Casimir effects might explain the attachment and release of neurotransmitters in the synaptic gap (not that the gap is necessarily involved: the synaptic cleft [wikipedia.org] is around 20 nm across and that is an order of magnitude too large I think). However the surface geometries of the binding proteins are definitely in the range of Casimir effects, and it is possible that these are changing shapes in ways that release or attach the neurotransmitters. Also, I just now came across some stuff on electrical synapses [wikipedia.org] where the gap is less than 4 nm and there are transmission structures with lumens of 1.2 nm diameter, which I think does mean that Casimir effects are going to be present. (But that does not mean that they are being used. Then again, as a rule, life takes advantage of every condition and edge case it can.)
I'm hoping to see some useful comments from the QM guys. Also materials engineers, anesthesiologists, and neurologists.
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I wonder what would happen if the surfaces are fractal, or as close an approximation as physical matter can achieve.
With fractals, the shape of the surface depends on the scale of the observer. So, in this case, the gap between the surfaces would also depend on the scale of the observer (in this case the wave). Since the relationship between shape and scale is non-linear, it should be possible to construct a fractal in which a given wavelength is allowed but some shorter wavelength is not.
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And in the process of fine-tuning the explanation, you've managed to completely lose everyone. For your misjudgement, I sentence you to a year of hard labor, teaching kindergartners why you cannot pound a square Bessel function through a round hole.
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Give kindergartners large enough hammers and they will.
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Re:Casimir Force (Score:5, Informative)
<pedantic>Vacuums do not suck! They are areas of lower potential, and everything has a tendency to move from a higher potential to a lower potential. Things in the non-vacuum area are blown into the vacuum area.>/pedantic<
FYI: Black holes do not suck, either. They're pretty cool.
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I think pushing is more appropriate then blowing. My guess is that suction and blowing should be used to describe the effects of the under/over pressure on other objects.
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<pedantic>XML parsing error.</pedantic>
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FYI: Black holes do not suck, either. They're pretty cool.
While temperature measurement of a black hole is bound to be a bit difficult, I'm willing to bet that by almost any measure they are hot rather than cool.
Depends on your definition of hot and cold. [pbs.org]
Of course, if you have things falling in, this stuff emits radiation like crazy, but only until it hits the event horizon. In other words, It gets really toasty outside the event horizon, but falls outside our discussion, by virtue of not being the black hole itself.
The event horizon is another story. It's a bit of a discontinuity in a lot of ways. If you assume the "trivial" solution of a nice, non-rotating black hole (the Schwarzschild solution), with nothing fa
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Suction is just a "perceived" effect in that there is no real "pulling force" involved, but rather an outside pushing force.
(I've also heard of a hypothesis that claims gravity works the same way, but I dunno about that.)
I suppose it's similar to the notion that centrifugal force is only a perceived force, it's really centripetal force - or a form of it (equal/opposite reaction).
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http://xkcd.com/123/ [xkcd.com]
Re:Casimir Force (Score:5, Interesting)
Good explanation.
An oft-used classical analogy is of boats on a wavy sea. It's been reported that two ships sitting on a wavy sea (but windless day) will slowly move closer together, as if they are 'attracted' to one another. The origin of the force is the waves of various wavelengths that form on the water surface. The sea surface has waves of all different sizes. In between the two ships, however, some wavelengths can't 'fit' and so those modes are suppressed. The end result is that there are fewer wave between the ships, so the greater pressure from the (more) waves on the other sides of the ships pushes them closer together. (I'm glossing over the details, e.g. that you have to take into account how the waves on the surface of the sea reflect off the ship's hulls... but hopefully you get the idea.)
The Casimir force is like the quantum version of this. According to quantum mechanics, the vacuum is constantly churning with the creation and annihilation of virtual particles. Thus there are quantum waves of all kinds of different wavelengths. In between two plates, some quantized modes can't exist, and are suppressed. The end result is that there is more pressure from the vacuum on the outside of the plates than in the gap between them. Hence the plates are pushed together by the vacuum pressure.
Note that in both cases the magnitude of the force is quite small, and so you have to be quite careful to observe the force and measure it properly.
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++
Nice explanation. It's already rated a 5, but I figured I'd mention it.
Dimensional explanation?? (Score:2)
Just wondering if Casimir forces are in line at all with string theory prediction of gravity acting over a bunch of small dimensions and then when distances are small enough gravity to take the small dimensions into account the force is stronger. By "in line" I guess I mean is the given explanation fairly definitive or is the extra dimension explanation within the realm of possibility. IINAP so apologies if I'm way off.
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No, but because Casmir dimensions are much bigger than the wrapped dimensions of string theory.
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The way the Casimir force works is that when you put smooth plates very very close together, they are pulled closer... we get a force pulling the plates together.
I assume there is some reason this wouldn't work, but could we harness this "force" and convert it into useable energy?
Just attach something to the back of both these plates that will be pulled on by the plates as they try to move together. The "something" would not allow the plates to get together, but as far as my understanding goes, the plates would "perpetually" try to move together and you'd have a constant generation of energy.
But current physics laws don't allow endless energy for free, so what'
Re:Casimir Force (Score:4, Informative)
Re:Casimir Force (Score:5, Informative)
Just attach something to the back of both these plates that will be pulled on by the plates as they try to move together. The "something" would not allow the plates to get together, but as far as my understanding goes, the plates would "perpetually" try to move together and you'd have a constant generation of energy.
All you'd have in that case is a constant (and very, _very_ small, even for large plates) force. To actually do useful work, that force has to move something through a distance (which itself would have to be very small, because the plates have to be close together). Even if that were done, you'd then have to pull the plates apart to repeat the process, and to pull them apart takes just as much work as you'd get from letting them be pulled together.
Also note that people have predicted (I'll go to a talk next week on this) that the Casimir force might be able to be reversed (that is, there's a repellent force between the plates) if the plates have certain materials properties (in this case, probably a "left-handed" electromagnetic coupling -- that is, their permeability should be negative).
pulling apart could be made to use less energy (Score:2)
What if there were a way to shrink the effective size of the plates before pulling them back?
This would be similar to the way ducks paddle--the feet fold up for the forward stroke, then open up for the back stroke.
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Interesting idea. Unfortunately, the situations are quite different: the Casimir effect occurs in a field which can be roughly described by a potential gradient (which means, among other things, that the field is _conservative_ over most conditions of non-relativistic movemen
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Just hang an apple by a thread and use the force applied by gravity on the apple
I replied to a previous post of yours, but it looks like you need basic Physics help. Here's a starter [wikipedia.org]. Haven't you ever wondered why we can't design a hydroelectric dam that doesn't have to have water leave the lower altitude end?
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>could we harness this "force" and convert it into useable energy
Well, the Jovion corporation apparently has a method do do this- http://peswiki.com/index.php/Directory:Jovion_Corporation_and_Zero_Point_Energy [peswiki.com]
Mike.
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No, they don't.
Re:Casimir Force (Score:4, Insightful)
same reason you can't harvest energy when you hang a bowling ball on a string. Like Earth and the bowling ball, they attract each other, but potential energy is just potential energy
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how about those new shock absorbers intended for use in electric vehicles, instead of using them on motorcycles and cars/trucks, add them to your home so every step you take generates 1mW of power...
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You could of course attach those "somethings" to some kind of generator that generates electricity when they move and allow the Casimir force to bring the plates together thereby harvesting that energy (a very very tiny amount of energy), but in order to generate more energy from that effect you would need to separate the plates again which would take as much or more energy than was harvested from the effect in the first place.
*Unless* there is a plate configuration that will allow for repetitive movement. Think of a paddlewheel, with each paddle experiencing a Casimir force on an outside plate, then rotating or sliding out of the way so the wheel can move. There's a lot of challenges to overcome, so such a device is unlikely, but it may be possible.
That's why this research is so exciting -- it offers the promise of tapping into Zero Point Energy [wikipedia.org]. Again, it's unlikely to pan out, but it's worth a try.
Re:Casimir Force (Score:4, Informative)
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Just replace the Casimir force with gravity to get an idea of what you're proposing:
The way the gravitational force works is that when you put massive objects close together, they are pulled closer... we get a force pulling the masses together.
This much is true, but you can't generate energy by hanging a rock from a tree. You can store up energy for later use by lifting a rock up off the ground and harnessing that potential, but it's a one time deal.
Likewise with the Casimir force, you can use the energy of two plates attracted to each other, but then they'll hit each other and you'll be done.
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But current physics laws don't allow endless energy for free, so what's the catch with this one?
You would have us rob black holes of their virtual energies? Oh, man, that would be so unkewl.
OTOH, using buckytubes for lossless transmission of electrons or photons is going right down this path. That will be effectively cheating entropy. So, yeah, we prolly are going to be exploiting zero point energy, in some ways. Depending on how you look at it. It is certainly being considered.
The black hole bit: IDKWTFITA, but it has always bothered me that black holes remove matter and energy from our universe
Question: Uncertainty Principle (Score:3, Interesting)
Years ago, I read "A Brief History of Time" and Stephen Hawking asserts that the reason that Particles randomly pop into existence and annihilate again is because of the uncertainty principle. You can never know the exact momentum and position of a particle with complete certainty, and the more you know of one, the less you know of the other. Then, he says, you can never have a true vacuum. The position and momentum of this "vacuum"
Hawking radiation (Score:3, Informative)
No, that is what Hawking, and a considerable number of other scientists believe. Essentially, nature is allowed to "borrow" energy from nowhere provided the product of the energy and time the energy exists does not exceed Planks constant. When it does so, a particle and its matching antiparticle (to keep all the charges, baryon numbers etc. matched) spring into existence for a very short time, then cancel out again, "repaying" the borrowed energy.
Except that if this happens really close to the event horizon
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Re:Question: Uncertainty Principle (Score:4, Informative)
Does the Uncertainty Principle play into this at all?
The uncertainty principle (or quantum indeterminacy, if you prefer) is fundamental to quantum mechanics, so it plays a role in ... well in just about everything.
Hawking's explanation is one way of looking at virtual particles [wikipedia.org], which are indeed the origin of vacuum fluctuations.
If his explanation seems wrong, it is because the uncertainty principle is usually misrepresented in mainstream media. It is usually described as an a measurement imprecision: as if a particle has a definite position and velocity, but there is some law that prevents us from measuring it properly. That's (if I may be so bold) a very antiquated interpretation. The more modern interpretation is that a particle is inherently fuzzy: wavelike and indeterminate in its properties. The wavefunction for a particle inherently is 'spread out': it specifies a spread in various variables (e.g. position or momentum).
The Heisenberg uncertainty principles (there are actually many such relations; there is one between position and momentum; one between time and energy; etc.) describe how these indeterminacies evolve. Certain kinds of interactions (which you can call 'measurements' if you like) will reduce one kind of indeterminacy, but there will be a corresponding 'spread out' in another quantity.
Now back to virtual particles. The time-energy Heisenberg uncertainty says that deviations in energy are allowed as long as they don't exist for 'too long' (I'm being loose with language, the actual equations of course set rigorous bounds on all these things). So a vacuum can suddenly have 'more energy' as long as that energy disappears in a short amount of time. This is what virtual particles are: particles that are created 'out of nowhere', exist for a short time, then disappear. The interesting thing is that though these short-lived particles cannot be directly measured, their effects are very real. In fact if you think about a charged particle that emits a static electric field which exerts a force on some other particle, it is in fact virtual particles which are being exchanged between the two particles which explains the origin of the force between them (and explains the seeming 'action at a distance'). A time-varying electric field would instead generate 'real' photons, which are the light and radio waves we are all familiar with.
Some people think that virtual particles sound 'silly and made up' or somesuch. But they are a natural prediction of modern quantum theory, and they happen to nicely explain a wide variety of experimental results.
So Hawking is right that vacuum fluctuations arise because of quantum indeterminacy (which you can call 'Heisenberg uncertainty' if you prefer). The vacuum has particles appearing and disappearing all the time, and they produce real, measurable effects (like the Casimir force), even if they cannot be directly measured. (Just like a static electric field.)
(Disclaimer: I'm not a quantum physicist, so I've probably made a few mistakes. Corrections and clarifications are welcome.)
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May the mod points be with you.
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I agree that Hawking might have jumped to his conclusion rather abruptly. However, it is valid.
Heisenberg Uncertainty Principle says that the error in your measurement of the momentum times the error in your measurement of the position must be greater than or equal to Planck's constant divided by two. The important thing to keep in mind (and what Heisenberg didn't realize when he first proposed it) is that it's not just your error in measurement, it's the very nature of the universe to not be a well-defined
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It's stranger than you think. Many speak about measurements of characteristics such as position and momentum, but experimental evidence suggests that it goes much deeper than that.
If you know the momentum of a particle the the very last decimal place (for example, it is absolutely zero), it HAS no position AT ALL. It is everywhere and nowhere. However, the universe is not infinite. we know the particle must be within the universe, so it can't actually have no momentum at all, ever.
People talk about measurem
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For deity's sake, man, think of the photons! I propose we introduce a bill immediately to address this photonic annihilation!
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It's essentially the same thing as the plain old van der Waals force, which they teach in high school chemistry. Basically you have two uncharged things close together. Due to tiny fluctuations in their charge distribution, one becomes slightly positive (or negative), induci
Re:Casimir Force (Score:4, Informative)
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Well then you don't know what you're talking about.
All electromagnetic interactions occur through virtual photons, regardless of if it's the Casimir effect or just classical electrical charges. Saying 'virtual photons' are involved explains nothing in itself.
What is true is that it's the fluctuations of the quantum field that gives rise to the random charge fluctuations I mentioned. And that is also wh
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In these experiments, they ground the plates to account for this.
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Just like a gas exerts pressure on the walls of a vessel from real particles bouncing off the walls, a perfect vacuum also exerts some pressure on walls due to virtual particles bouncing off the walls. Usually you don't notice this pressure since it's balanced by an equal pressure on the other side of the wall, so you could just label this as zero pressure. But if you put the walls close enough together, there's not enough room for large wavelength virtual particles to be between the walls, so t
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Cool jobs (Score:5, Funny)
Don't you wish you had a job where some very important work you're doing can be described thus:
Their idea is to build a centimeter-scale metal model of the system they want to investigate, place it in salt water, and bombard it with microwaves and see what happens.
This sounds like a Saturday afternoon in the garage with just a couple too many beers, an old tube tv, a broken microwave, and a friend that is just a little too happy to be 'experimenting' with stuff at your place because of the garage fire he had last year.
Props to Myth Busters for making 'blowing shit up' cool again...
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This sounds like a Saturday afternoon in the garage with just a couple too many beers, an old tube tv, a broken microwave, and a friend that is just a little too happy to be 'experimenting' with stuff at your place because of the garage fire he had last year.
More likely this will be a multi-year research project that will use atomically-flat substrates, ultrapure reagents, $250,000 of precision electrical equipment, and an untold number of late nights for grad students agonizing over every last detail.
Physics: Doing simple-sounding things in fiendishly precise ways.
Makes Sense (Score:2)
This kinda makes sense.
My understaning of the Casmiri effect is that Zero-Point Energy is constantly creating and destroying particles of all sizes and frequencies. The two plates exclude some frequencies which creates a pressure imbalance which pushs the plates together.
So an electrolyte has charged particles everywhere. The microwaves energize them. The objects exclude some microwave energy creating an imbalance which pushes the plates together...
Since the forces are so much stronger the effect is much
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Zero-Point Energy
imbalance which pushes the plates together
So basically eventually this line of research will lead to the discovery of the Gravity Gun?!
A computer? (Score:5, Funny)
How does this setup possibly count as a "computer"? It's not. It's just a physical process whose input/output, under one interpretation, is isomorphic to that of a computation its user wants to know the result of ... oh, I see. Never mind!
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I don't have a problem with that definition. But it also means 'quantum computers' shouldn't be called 'computers' either.
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Take the computer you're typing on. At it's core is a bit of silicon and metal etched in particular patterns. When you perform a computation, you trickle some electricity through it, and measure the result. That computer is ALSO a "physical process whose input/output, under one interpretation, is isomorphic to that of a computation its user wants to know the result of."
Get the joke now?
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You can; the problem lies in the fact that the player is simultaneously dead and alive, so the score counter can never increment.
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Yep.
Just like more typical "analog computers" where a voltage or current represents a value in the computation.
Contained lightening (Score:2)
Their idea is to build a centimeter-scale metal model ........ and bombard it with microwaves and see what happens.
Anybody ever put a metal can in a microwave oven? I think it's pretty obvious what will happen.
Das Spitzensparken.
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The problem with placing metals inside a microwave are not inheritely because of materials made of metal. The main problem is closed circuits.
A friend of mine always places a metal spoon inside a cup of water before boiling it in the microwave, to remove the chance of super-heated water and it isn't at all dangerous.
The problem is with stuff like a plate with a closed metal running around the circumference. When the microwaves hit the metal, it energizes it, creating current through the circuit, which in tu
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Yes. I've got a big, heavy metal mixing bowl. I frequently forget to soften the butter before putting it in the bowl, so I toss the whole thing in the microwave. So long as you're careful not to let the bowl touch the metal walls of the microwave, it's fine.
NO, IT Doesnt (Score:1)
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Does this have anything to do with the Led Zeppelin Song?
Yes. It will be played loudly in the lab as the experimentation is underway. They'll use the "Energy Waves" in the "Rock Bands" frequencies to rock our world with some new discoveries.
i am not happy with this story summary (Score:4, Funny)
until it can be rephrased in such a way that it asserts the ascendency of physicists over mathematicians. or the ascendency of mathematicians over physcists. i need to keep score. joke form is acceptable
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Re:i am not happy with this story summary (Score:5, Funny)
at a bus stop, twelve passengers get on a bus. at the next stop, thirteen get off
theologian: "a miracle! a miracle!"
biologist: "reproduction in action"
physicist: "measurement error. roughly nine percent statistical deviation is within acceptable tolerance ranges"
mathematician: "if one person gets in, the bus is empty again"
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I think you forgot to specify that the bus had 0 passengers before those twelve people entered it. Otherwise, there could simply have been a passenger sitting there beforehand.
ah, a true geek (Score:2)
taking a silly throwaway joke and analyzing it in complete seriousness
Re:ah, a true geek (Score:4, Funny)
Everyone knows that empty buses are constantly creating and destroying virtual passengers. You obviously were asleep in class the day they covered Kramden diagrams.
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The virtual passengers aren't destroyed, they're just sent to the moon. Bang-zoom, to the moon.
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Everybody else: "Where did the driver go?"
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Average person: "There were already passengers on the bus when these twelve got on."
(Looks at the theologian, biologist, physicist and mathematician)
"When you're holding a hammer, everything looks like a nail, right guys?"
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The artist/writer forgot that Mathematics (and, by extension, all the rest) are just an extension of Philosophy.
Eureka! (Score:5, Interesting)
Also I didn't see the meme so I have to do this,
But will it run Linux?
Does this mean ... (Score:1)
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Yup. Just like the Shamwow(tm) can pick up spilled pop through a carpet. ;)
http://www.youtube.com/watch?v=oyjLx2rdNMA [youtube.com]
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Yes. But the problem is that there's no force gradient in that case, and the floor will suck just as much as your vacuum nozzle :)
CPU power? (Score:2)
I wonder what equations they'd otherwise have to solve, and what kind of CPU power would be needed.
"exploit"? (Score:2)
...give researchers a way of testing nano-machines designed to exploit the Casimir force."
No, when dealing with nano-technology, you do not exploit the casmir force, you plan your entire design around it. It's a big deal when you're doing nano.
This is like saying you're going to "exploit" the feature of low pressure in your spacecraft design.
Re:Is this really the scientific method at work? (Score:5, Insightful)
They understand the Casimir effect and the related equations, they just can't solve them. So what they do is they find another problem that has the same equations and they measure on that system. If both systems behave using the same equations, then the result should be the same.
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>> The force depends crucially on the shape of the plates but nobody is exactly sure how.
The quote is from the summary text... should I assume this is false or that per Slashdot norms, it's a bad summary?
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The quote is from the summary text... should I assume this is false or that per Slashdot norms, it's a bad summary?
No, it's fine. Understanding the effects of the microscopic equations on macroscopic shapes requires solving the equations, which is very difficult and sometimes has no closed form solution. Every tried solving the electric field equations over something other than an infinite parallel plate capacitor? It's a biatch. I remember having to integrate flux equations over various 3D surfaces for
Re:Is this really the scientific method at work? (Score:4, Interesting)
to the contrary - important for nanotech (Score:3, Informative)
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It's not that "we can't". It's that "it's a REALLY hard computation to run". Like cracking some modern cyphers or computing the folding of proteins.
It's doable but hard for both for the Casimir force and for the forces in the model - because it's the same math.
So do you want to buy a LOT of supercomputer time and wait months (or whatever) for each answer? Or do you want to build a cheap apparatus and take some measurements?