Scale Models Can "Compute" Casimir Forces

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."

Comments

Casimir Force

[manekineko2]

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:

The Casimir effect can be understood by the idea that the presence of conducting metals and dielectrics alter the vacuum expectation value of the energy of the second quantized electromagnetic field. Since the value of this energy depends on the shapes and positions of the conductors and dielectrics, the Casimir effect makes itself manifest as a force between such objects.

It's intro is similar:

In physics, the Casimir effect and the Casimir-Polder force are physical forces arising from a quantized field. The typical example is of two uncharged metallic plates in a vacuum, placed a few micrometers apart, without any external electromagnetic field. In a classical description, the lack of an external field also means that there is no field between the plates, and no force would be measured between them. When this field is instead studied using quantum electrodynamics, it is seen that the plates do affect the virtual photons which constitute the field, and generate a net force[1]â"either an attraction or a repulsion depending on the specific arrangement of the two plates. This force has been measured, and is a striking example of an effect purely due to second quantization.

Re:Casimir Force

[Anonymous Coward]

the casimir effect is an attraction of objects where none should exist

Re:Casimir Force

[Anonymous Coward]

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.

Re:Casimir Force

[MoellerPlesset2]

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 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), inducing an equally tiny opposite charge in the other one, in the area where they're close. The electrical field (capacitance) keeps and reinforces this. So you end up with a slight attractive force between the things, seemingly out of 'nowhere'.

Re:Casimir Force

[Joehonkie]

That is a great explanation, because I was wondering the same as the original comment. Thanks!

Re:Casimir Force

[Anonymous Coward]

You mean like Cathy Raymond?

Re:Casimir Force

[Hordeking]

<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.

Re:Casimir Force

[JustinOpinion]

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.

Re:Casimir Force

[Eternauta3k]

That contradicts other explanations in this discussion, where did you read that?

Re:Casimir Force

[MoellerPlesset2]

It's a different way of looking at it, but it doesn't contradict the other explanations.

Re:Casimir Force

[Wyrd01]

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's the catch with this one? Is the amount of pull so small it would take ages to build up enough energy to be usable?

Re:Casimir Force

[Cup-of-Tea]

If the plates don't move, no work is done and you get no energy.

Re:Casimir Force

[Alinabi]

Except that it is somewhat inaccurate. The correct explanation is that only photons of certain frequencies can exist in the space between the plates, while elsewhere you can have photons of any frequency.

Re:Casimir Force

[gardyloo]

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).

Re:Casimir Force

[Joehonkie]

That helps even further, as does the "boat" analogy below. I was hoping for the car analogy, but I will take what I can get.

Re:Casimir Force

[miquels]

>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

Mike.

Re:Casimir Force

[eric-x]

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.

Re:Casimir Force

[eric-x]

then=than

Re:Casimir Force

[fifedrum]

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

Re:Casimir Force

[curmudgeous]

...caused by pairs of virtual photons which spring into existence and annihilate constantly

For deity's sake, man, think of the photons! I propose we introduce a bill immediately to address this photonic annihilation!

Re:Casimir Force

[PsyciatricHelp]

Thats what she said

Re:Casimir Force

[orclevegam]

Someone else already gave a pretty good explanation of why this wouldn't work, but I'll see if I can give a slightly better explanation. Consider this, anytime you have unequal forces objects move, and we can in most cases convert that movement (which is simply excess energy) into power. When however forces are balanced no movement occurs, and no excess energy is released that can be harnessed. As a related example things are constantly attracted to the Earth via gravity, which is a force (rather well understood and easily quantified at that), however there is an opposing force in the collision of two solid masses, that is the force of gravity attracting an object towards the center of the Earth is opposed by the force of the ground pushing back at the object and preventing it from moving closer to the center of the Earth. In the example you give even though there is a force attempting to bring the plates together it is being canceled out by your supposed "something", thus resulting in a net zero for the forces involved, and therefore no way to harvest any energy out of the configuration. 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.

Time an again it has been shown there is no free energy no matter how you slice it. We had our peak during the big bang, and its all been going down hill since then. The most we can hope for is to harness as much of the already existing energy as we can.

Re:Casimir Force

[Anonymous Coward]

Yes, they do.
That's all that sucking is, creating a low-pressure area for everything else to flow into.
By your implication, nothing sucks, at all.

Re:Casimir Force

[Chih]

She's went from suck to blow!

Re:Casimir Force

[Anonymous Coward]

Yes, they do. That's all that sucking is, creating a low-pressure area for everything else to flow into. By your implication, nothing sucks, at all.

Most definitely not your girlfriend.

Re:Casimir Force

[divisionbyzero]

++

Nice explanation. It's already rated a 5, but I figured I'd mention it.

Re:Casimir Force

[electrosoccertux]

In these experiments, they ground the plates to account for this.

Re:Casimir Force

[aynoknman]

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.

Re:Casimir Force

[Anonymous Coward]

And actually, this explanation breaks down when you move to non-planar geometry. For conducting spherical shells, the Casimir force actually pushes outwards. It's more about density of modes--you can get Bessel functions inside spheres, but not between plates. :)

--aphyr

Re:Casimir Force

[Anonymous Coward]

It's a different way of looking at it, all right. But it is wrong none the less. Casimir has to do with "virtual photons" and not van der waals forces.

Re:Casimir Force

[Remus Shepherd]

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. Again, it's unlikely to pan out, but it's worth a try.

Re:Casimir Force

[Profane MuthaFucka]

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.

Re:Casimir Force

[Profane MuthaFucka]

No, they don't.

Re:Casimir Force

[Khashishi]

I'll try...

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 the inner pressure is less than the outer, and you get attraction.

I don't have a good explanation of what virtual particles are, but usually people say they are particles without enough energy to exist permanently, but they can exist for a short time due to Heisenburg energy uncertainty. That sounds like mumbo-jumbo to me. A particle needs positive kinetic energy to be a propagating wave, it could still exist as a decaying wave with less than positive kinetic energy. So you could have zero energy particles in vacuum which aren't propagating, but exist as an exponentially decaying wave (for a massive particle).

Re:Casimir Force

[Khashishi]

That's not quite right. The forces between the Moon and Earth aren't balanced, so the Moon continually falls toward the Earth. It's not a matter of canceling the force which causes no energy to be released. It's just that the direction of the force is perpendicular to the direction of movement.

Re:Casimir Force

[orclevegam]

Nope, still not possible. By the very nature of it it would take more energy to move the plate out of the way than would ever be generated by it moving in the first place. Essentially all the Casimiar force is is the quantum version of a pressure differential. It's a very interesting phenomenon and has some possible uses in the design of nano scale generators and parts, but it will never be a energy source on its own. To be clear what I mean is that the effective could be incorporated into the design of a generator for extra gains on efficiency or as part of a large principle, but the force itself is not enough to build a generator around and it will never be a primary motive force.

Re:Casimir Force

[Khashishi]

It's not exciting to anyone who knows any physics. A paddlewheel takes energy from moving water (or similar). It doesn't produce energy from nothing.

Re:Casimir Force

[orclevegam]

Nope sorry, it's still balanced, you just forgot to factor in the momentum of the moon. Once all the forces are factored in properly it still amounts to a net 0 (more or less, the moon is slowly de-orbiting, but it's going to take a very long time).

Re:Casimir Force

[Wyrd01]

Ah, that's a good point... whether you're using fancy casimir forces, or "just" gravity, in the end all I've described is something pulling on something else, but nothing is actually moving anywhere.

Another idea I've always thought would be cool is finding something that produces energy when it's crushed, and then build a layer of it under every house, so each household generates it's own small energy supply simply by virtue of being heavy.

I suppose the same limitations apply there too in that the crushing would have to result in some compression of the material to generate the energy, and the resulting energy would be a function of how far the material is compressed per unit of time.

Re:Casimir Force

[Hordeking]

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.

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 falling in, and nothing escaping, then this black hole would be perfectly black, in the literal zero black body radiation sense.

Now, inside the event horizon is a completely different matter. Let me dumbly apply some theory here, and let's assume ideal gas law applies. Since all of the matter is infinitely densely packed in the singularity (even if we assume it actually has some dimension, it would be Planck or smaller, most likely), then if we consider volume to be infinitely close to 0 (lim V->0) with a invariant amount of mass m (the mass of the black hole), then the pressure rises to infinity (lim p->infinity). Temperature is directly proportional to pressure, ergo, the temperature also goes to infinity (lim t->infinity).

Again, I've made some really silly assumptions that don't reflect the real world at all (probably all black holes rotate, ideal gas law isn't relativistic, infinite temperature implies infinite kinetic energy, doesn't consider the possibility of hawking radiation, etc). I did this to simplify the explanation, more than to be correct.

So, depending on how you look at it, a black hole is really both pretty hot shit and really cool!

Re:Casimir Force

[Khashishi]

Force equals time rate of change in momentum. The momentum of the moon is oscillating. Hence, force is non-zero.

Re:Casimir Force

[rrohbeck]

<pedantic>XML parsing error.</pedantic>

Re:Casimir Force

[Anonymous Coward]

Yes, they do suck. What you just said is the very definition of "sucking," movement from higher potential to lower. I would love for you to try to show my one example of suction that doesn't involve that.

Re:Casimir Force

[adonoman]

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.

Re:Casimir Force

[mysticgoat]

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 [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 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 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.

Re:Casimir Force

[Stratocastr]

Let me answer your question and ONLY your question. The Casimir effect is when 2 smooth conducting metal surfaces are very close together but not touching (nanometers apart) then they exhibit attraction to each other. That's the effect. We DONT know why this occurs. Among popular unproven theories are the "too close for photon to fit, therefore vacuum" theory. I agree that this makes most sense but it is not an accepted rational explanation why the law of inertia is being violated. One thing is for sure , there are week nuclear forces involved at that infinitely small distance that become more powerful than large forces like gravity and friction. What the researchers are trying to do is measure the forces at play that are prominent at the nuclear level. A device to measure these forces would revolutionize the field of nuclear forces..

Re:Casimir Force

[mysticgoat]

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 without seeming to give back anything in return, other than gravity waves, which don't seem like a fair exchange. You know?

Re:Casimir Force

[Stratocastr]

Why do u need to cultivate the pulling force of the two plates in the first place? One, there is no known way of doing this. And two, if there were then we wouldn't need plates and stuff. Just hang an apple by a thread and use the force applied by gravity on the apple in your machine. Infact the only known way to make use of pulling forces is action-reaction. if u push a surface, it pushes u back. Hence we have space rockets.

Re:Casimir Force

[DrVomact]

Quantum foam of "virtual" wavicles, eh? And here I used to think that the concept of aether was silly. Turns out that the aether has been updated a bit with quantum theory...but there's once again stuff that fills the universe, and explains certain otherwise inexplicable phenomena. Not that I have an objection to this, mind you. I just think it's interesting.

Re:Casimir Force

[cyberchondriac]

IANA physics expert, but that sounds about right to me.
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).

Re:Casimir Force

[Kagura]

We have measured the Casimir effect, and we know why it occurs. Your post is very uninformed. I would link like I always do, but it's simply too easy for your to google the wiki page so you can learn about all sorts of things. For example, the Casimir effect doesn't happen at "infinitely small distances", but rather at many times the radius of a typical atom. At 10nm (100 times the radius of a typical atom), the Casimir force is so unmicroscopic as to be equal to one atmosphere of pressure.

Re:Casimir Force

[Kagura]

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. 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?

Re:Casimir Force

[Anonymous Coward]

But if you were to wrap that string around an axle, and then meter the rate at which the bowling ball descended due to gravity with an escapement mechanism... And then with the right gearing you could put some dials in place that measure this metered descent. And since it's rate is fairly consistent, you could keep time by it give or take a second per month. So in essence, you'd have a clock. And since my grandfather liked bowling and being punctual, I think I'd call such a device a grandfather clock in his honor. Why not?

Sure, it's not free energy since you have to wind it up every now and then. But it's not a completely useless way in which to store energy. (Not sure how the principle would translate with the scale of casimir forces though.)

Re:Casimir Force

[Anonymous Coward]

He needs basic English help, as well.

Re:Casimir Force

[newcastlejon]

Your sarcasm detector appears to be out of alignment. (I hope; parent does use 'u' and actually bothers to type 'and stuff')

Re:Casimir Force

[jd]

Give kindergartners large enough hammers and they will.

Re:Casimir Force

[Khashishi]

What is your definition of sucking, if a vacuum doesn't suck?

Re:Casimir Force

[jd]

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.

Re:Casimir Force

[petermgreen]

http://xkcd.com/123/

Re:Casimir Force

[Anonymous Coward]

Sorry, the AC is not informative, he's wrong. How do you think van der Waals forces are transmitted? FedEx? vdW and Casimir are very much the same thing.

Re:Casimir Force

[MoellerPlesset2]

In these experiments, they ground the plates to account for this.

No, that's to account for residual static charges, which are something else.
Similarly, grounding doesn't stop the vdW force either.

Re:Casimir Force

[MoellerPlesset2]

But it is wrong none the less. Casimir has to do with "virtual photons" and not van der waals forces.

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 why it does not contradict the other explanation given.

Besides which, it's a well-known fact that the Casimir effect and van der Waals forces are closely related. You only need to visit the Wikipedia article linked at the top of this page to find that out.

Re:Casimir Force

[fractoid]

Where are my mod points? The distance between two physical objects which approximate fractals ('fractoids', which by a strange noncoincidence is my nick ;) is also fractal-esque. Very interesting, I'd be interested to hear the opinion of someone more versed in the mathematics of all this. I'm afraid to say I've wasted my time on women, wine and song (well ok cars and computers) and this kind of deep stuff is a bit beyond me. :P

Re:Casimir Force

[fractoid]

Actually, if I understand him right, Bessel functions fit into round holes OK but have problems with square holes. And, I presume, meeting women.

Re:Casimir Force

[fractoid]

"Suck, Irma, suck! 'Blow' is merely a manner of speech!!"

Re:Casimir Force

[fractoid]

That's all very... um, sorry, I'm stuck for adjectives and all I can come up with is "groovy (but probably not), baby!"

Re:Casimir Force

[fifedrum]

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...

Cool jobs

[zappepcs]

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...

Re:Cool jobs

[JustinOpinion]

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

[clonan]

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 more dramatic....I just wonder how accurate the predictions will be.

Re:Makes Sense

[AndrewNeo]

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?

[DriedClexler]

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!

Re:A computer?

[MoellerPlesset2]

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!

I don't have a problem with that definition. But it also means 'quantum computers' shouldn't be called 'computers' either.

Re:A computer?

[sunking2]

Bet you can't even play Crysis on it.

Re:A computer?

[Pope]

You can; the problem lies in the fact that the player is simultaneously dead and alive, so the score counter can never increment.

Re:A computer?

[Ungrounded Lightning]

Yep.

Just like more typical "analog computers" where a voltage or current represents a value in the computation.

Re:A computer?

[ceoyoyo]

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?

Contained lightening

[cbiltcliffe]

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.

Re:Contained lightening

[Soul-Burn666]

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 turn creates a reverse electric field. This is the field that can destroy your microwave emitter and is the danger with placing metals inside the microwave oven.

Same goes for the little metal strips that are used to close bags of sliced bread.

Re:Contained lightening

[ceoyoyo]

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

[Theoboley]

Does this have anything to do with the Led Zeppelin Song?

Re:NO, IT Doesnt

[Hordeking]

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

[circletimessquare]

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

Re:i am not happy with this story summary

[morgan_greywolf]

Here you go. You said you didn't mind joke form!

Re:i am not happy with this story summary

[circletimessquare]

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"

Re:i am not happy with this story summary

[GameMaster]

The artist/writer forgot that Mathematics (and, by extension, all the rest) are just an extension of Philosophy.

Re:i am not happy with this story summary

[Atmchicago]

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.

Re:i am not happy with this story summary

[NudeAvenger]

logic puzzle: "it was the bus' last stop - the bus driver got off"

Re:i am not happy with this story summary

[Anonymous Coward]

Where's the "whoosh" moderation when you need it?

Re:i am not happy with this story summary

[kennykb]

bus driver: "Where's the toilet?"

Re:i am not happy with this story summary

[steelfood]

Everybody else: "Where did the driver go?"

Re:i am not happy with this story summary

[morgan_greywolf]

computer scientist: "run the bus through the debugger and watch for fence post errors!"

Re:i am not happy with this story summary

[Anonymous Coward]

engineer: "there was already at least one person on the bus when the twelve passengers boarded"

Re:i am not happy with this story summary

[ColaMan]

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?"

Re:i am not happy with this story summary

[m50d]

Lies. Philosophy is just mathematics done without the rigour.

Re:Is this really the scientific method at work?

[jmv]

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.

Re:Is this really the scientific method at work?

[CTalkobt]

>> 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?

Re:Is this really the scientific method at work?

[u38cg]

No. They know the mathematics behind the system, however, they cannot solve the equations directly. What they have done is taken a system that works according to the same equations. Knowing how this system responds means that you can also work out how the first system responds. Easy.

Eureka!

[moteyalpha]

I like it as it reminds me of Archimedes. If you can't compute the volume , stick it in a tub of water and do an atomic integral of the volume.
Also I didn't see the meme so I have to do this,
But will it run Linux?

Re:Eureka!

[Anonymous Coward]

Yes, it will! There is a special distribution of linux currently being developed for all manner of analog computational machines, called Analix. Progress is slow, as right now development is limited by 2coders1compiler. Analog compilers are expensive, man.

to the contrary - important for nanotech

[peter303]

Nano-machines may not work as predicted unless you take into account the vacuum energy fluctuations. The sign of the force appears to be shape and material dependent.

ah, a true geek

[circletimessquare]

taking a silly throwaway joke and analyzing it in complete seriousness

Re:ah, a true geek

[poena.dare]

Everyone knows that empty buses are constantly creating and destroying virtual passengers. You obviously were asleep in class the day they covered Kramden diagrams.

Re:ah, a true geek

[Alzheimers]

The virtual passengers aren't destroyed, they're just sent to the moon. Bang-zoom, to the moon.

You guys are all idiots.

[Anonymous Coward]

Just ask Casimir. He invented the damn thing, didn't he?

Does this mean ...

[Dragged Down by the]

that if I put the nozzle of my vaccuum cleaner really close to the floor, I won't even have to turn it on?

Re:Does this mean ...

[denis-The-menace]

Yup. Just like the Shamwow(tm) can pick up spilled pop through a carpet. ;)

http://www.youtube.com/watch?v=oyjLx2rdNMA

Re:Does this mean ...

[gardyloo]

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 :)

Re:Does this mean ...

[Dragged Down by the]

Rats. Thought I'd invented something.

Re:Is this really the scientific method at work?

[Anonymous Coward]

Per Slashdot norms, I will tell you to just RTFA if you want to know how accurate the summary is. Then someone will tell me I must be new here.

Question: Uncertainty Principle

[A. B3ttik]

I have a question: Does the Uncertainty Principle play into this at all?

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" would _both_ be zero and since that simply can't be, there must be fluctuations.

WTF??!?!

I've read the passage over and over again, and I swear that _that_ is his line of reasoning, but it makes NO sense to me. I thought that the uncertainty principle was all about measurements, and altering things whenever you try and look at it... not about whether some random hypothetical area of space can exist as a vacuum or not.

Am I missing something, or did Stephen Hawking take some particularly potent Valium that day?

Re:Question: Uncertainty Principle

[JustinOpinion]

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, 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.)

Re:Question: Uncertainty Principle

[SBacks]

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 particle.

So, if you looked at a pure vacuum, you would know it's momentum is EXACTLY zero, so your error in position would have to be infinite. This makes no sense, so a pure vacuum is impossible.

Re:Question: Uncertainty Principle

[A. B3ttik]

Thanks a bunch for the response... that's a very clear answer, exactly what I was looking for.

May the mod points be with you.

Re:Question: Uncertainty Principle

[Latinhypercube]

Wow. Thank you for such a concise explanation of Virtual Particles (and Quantum physics). After reading 2 books on the subject your explanation is so much more intelligible. If you ever write any more descriptions of Quantum physics I'd love to read. Thanks.

Re:Question: Uncertainty Principle

[heironymous]

Well, quantum mechanics is weird. It defies the common sense our brains have acquired living in a macroscopic world. So please pardon me if what I write seems weird, or even more metaphysical than scientific.

You write that "the uncertainty principle was all about measurements, and altering things whenever you try to look at it." Well, almost but not quite. The measurement isn't altering the thing being looked at. The measurement is actually bringing the object's properties into existence.

I've often heard it explained that the uncertainty principle follows from the fact that to look at an object, you have to bounce a photon off of it, which alters it. So you can't measure it accurately. That's a classical analogy that doesn't really capture what we think is going on at the quantum level. To repeat, this analogy is bad. I know it's weird, but...

It's not that the object has an unmeasurable position and momentum that gets perturbed by the photon. It's more accurate to say that the object's position and momentum don't really exist until an attempt is made to measure them.

In other words, it not merely that you the observer can't know what the vacuum's position and momentum are, the vacuum itself can't. A constant zero for both momentum and position would allow nature to violate the uncertainty principle. So a true vacuum can't exist.

Re:Question: Uncertainty Principle

[sjames]

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 measurement because it's easier to wrap your head around not being able to know a particle's position than the particle not having a position to know.

One great experiment showing this is a setup in a vacuum where sodium atoms are very slowly streamed towards a grating where the slits are too small for a sodium atom to fit through. As it turns out, some of the sodium atoms show up on the other side anyway. That's becasue their momentum is well defined (but not perfectly), so they have no exact position. When they get to the point where they might be on one side or might be on the other, some of them end up being on the other side but never actually pass through the slit.

It turns out that a camel CAN pass through the eye of a needle, but only extremely slowly and only if no one is looking :-)

I for one...

[Justin Ames]

welcome our Casimir force powered nanobot overlords.

I don't get it...

[Anonymous Coward]

OK, we can't accurately model the Casimir effect 'cause it involves some weird quantum stuff that we just haven't grocked yet. No problem with that.

So we model it by putting 2 metal shapes in a conductive liquid. Does that mean we can't even mathematically model 2 pieces of metal in a conductive solution?

A. We can't -- What does that say about our understanding of simple (non-quantum) physics?

B. We can -- Why don't we just use those models (equations) to model the Casimir effect?

Re:I don't get it...

[Ungrounded Lightning]

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?

Hawking radiation

[AlecC]

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 of a black hole, one of the two particles can fall into the hole and the other doesn't, resulting in the net creation of a particle outside the event horizon. The energy needed to "balance the books" and create the particle comes from the black hole. This means that black holes are continuously emitting particles, which are called Hawking Radiation, and losing energy. However, to maximise the chance of one particle falling in and the other escaping, the gravitational field has to be very non-linear, which means that the hole has to be small. The smaller the hole, the faster it evaporates, so the faster it shrinks which eventually leads to a runaway; tiny black holes explode. However, stellar mass black holes evaporate so slowly that it takes a bucket load of exponents to measure the time until they explode.

Re:Hawking radiation

[rastos1]

Wow. I don't know if you are right, sir, but you have talent for explaining things. Thanks for that post.

Re:Is this really the scientific method at work?

[Anonymous Coward]

>> 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?

The sheer lack of reading comprehension in some of these threads boggles the mind...

They understand how the force appears, and how it manifests itself, but they do not understand how the material and/or shape/orientation of the plates affects the force.

This neither implies a bad summary, nor a lack of understanding that would throw scientific method out the window.

Dimensional explanation??

[Stripsurge]

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.

Re:Dimensional explanation??

[Kagura]

If it's not, then string theory is wrong.

Re:Dimensional explanation??

[JamesP]

No, but because Casmir dimensions are much bigger than the wrapped dimensions of string theory.

Patent to extract energy from Casimir effect?

[HansWurst]

http://nextbigfuture.com/2009/02/jovion-corporation-gets-patent-for-zero.html
Full patent (pdf) http://www.calphysics.org/Patent7379286.pdf

How is this supposed to work? I don't get it...

1. gas gets pushed through micro-cavities (small enough for the casimir effect to work)
2. ???
3. "free" energy from heated gas

CPU power?

[Twinbee]

I wonder what equations they'd otherwise have to solve, and what kind of CPU power would be needed.

pulling apart could be made to use less energy

[Chirs]

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.

Re:pulling apart could be made to use less energy

[gardyloo]

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.

      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 movements); each position/size/orientation of the plate is a state function, and there's no way to get from one state to another without doing the same amount of work.
      The ducks' feet case occurs in a flow regime (referring to the fluids through which they move) governed by high Reynold's numbers. This means that the motion is dissipative, and fluid turbulence carries fluid energy and entropy away from the duck's feet. The foot position and shape is *not* describable by a state function, and the motion is *not* conservative (it's analogous to a ratchet movement, which happens preferentially in one direction if heat can flow from the ratchet to the surroundings).
      A better fluid flow analogy for the Casimir plate effect is that of a bacterium swimming. At that size, the situation is in the low Reynold's number regime, and things are very nearly reversible (a human shrunk to the size of a bacterium, or even quite a bit larger, could not make headway in one complete stroke cycle when swimming -- you'd go backwards just as much as forwards). A good exposition on this is here: http://brodylab.eng.uci.edu/~jpbrody/reynolds/lowpurcell.html.

Could it work like a motor?

[Anonymous Coward]

Ok, so what I'm understanding here is that the Casimir effect can be observed to pull two metal plates together. However, if the plates are deformed, the effect is altered/disappears. So if there is a force which can be turned on/off, why can't we use it to power a motor? Surely there must be creative ways to change the shape (i.e. turn off the casimir effect) without expending all of the energy gained from the movement of the plates.

I'm picturing a rotary engine here, but instead of explosions in a cylinder pushing a rod, the Casimir effect would be pulling the rods.

"exploit"?

[v1]

...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?

[Chris Burke]

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 a college calculus class, and while it was too long ago to toss out any specific examples sometimes there simply wasn't a simple closed form solution. Does that mean the underlying flux equations weren't understood?

It's the same here, more or less. They know the equations. That doesn't mean they can solve the equations for any arbitrary surface with a simple F = a + b type answer. So instead they're performing experiments to find out the answers. Which is kinda what the scientific method is all about. Which is kinda why you sounded like a tool in your first post.

Possible virus?

[LeBleu]

Right around the time I downloaded the PDF linked from this article, my Windows XP machine decided that it needed to reboot. After rebooting I discovered that I had the twext.exe rootkit/trojan. (see description of what it does here)

I recommend you double check c:\windows\system32\ and see if you have a twext.exe, if you have the misfortune to be running windows. If it is there, you are infected.

Note: If you are infected, you will need to reboot to system recovery console and rename twext.exe. It still runs in safe mode and protects itself from removal.