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The Casimir Effect
HobbySpacer writes "A recent article in Physics World provides a lucid description of the the Casimir effect, which is an attractive force between two surfaces caused by electromagnetic fluctuations in the vacuum. The article discusses some practical application such as the nanotech machines mentioned here earlier."
isn't the force two objects excert on eachother called gravity? seriously though, I wonder how these forces are effected by non-vacumes - i.e. a virtual vacume with one lonely hydrogen moluecule. Is the H2 excerting forces on the two mirrors? are these forces the same magnitude as that the mirrors excert on eachother in pure vacume? more? less? 1/distance squared?
"A dictatorship would be a heck of a lot easier, there's no question about it." -George W. Bush
A while ago, I read Neal Stephenson's The Big U . The protagonist (well, one of them) was named Casimir, and, if I remember correctly, he built a rail gun.
;-)
Did Stephenson have a special reason for naming his protagonist after this strange force? Was it a metaphor for how he was mysteriously attracted to his female friend? Or am I just trying too hard to explain an author's choice of names?
all objects exert gravity.
The Casimir effect is something beyond that.
There's this other thing called a Casimir, when you have a Hamiltonian on an odd-dimensional space, you're guaranteed (by anti-symmetry) to have a null direction for the flow at any point, and this is called the "Casimir" for the flow. Does anyone know if this is the same thing?
Come on, give it up, that's
In simplistic terms this works because photons of certain wavelengths are excluded from the space between the plates. This doesn't happen on the outer faces of the plates, and the difference in the vacuum energy inside versus outside leads to an "attracting" force.
It only works on uncharged plates.
The forces between two plates in a non-vacuum are difficult to predict, at best. At that scale, the laws of thermodynamics begin to become inapplicable.
However, you can use the ideal gas equation to get an idea of what is happening:
PV = nRT
P is the Pressure, V is the Volume, n the number of molecules of gas, R the Rhydberg constant, and T the temperature. If you hold the temperature and the number of molecules constant and then decrease the volume (the case you mentioned above, where a single hydrogen atom has gotten in between the plates), the pressure will begin to grow linearly.
Because you are moving the plates together, the volume reduces in proportion to the distance between the plates. This means the pressure rises in proportion to the distance between the plates. I'll also make an assumption (a dangerous thing) that the temperature will remain constant because we'll give it time to cool off, and the number of particles remain the same. The last assumption is due to the plates being much larger than the distance between them, so only a very few number of particles on the edges will ever get to escape.
The force on the plates due to pressure is only the area of the plates times the pressure. As the pressure rises, the force rises proportionally.
Because the plates are attracted by the Casimir effect, and the casimir force grows quadratically as the plates draw nearer, eventually, even the pressure will be insignificant compared to the Casimir force. I think that's a pretty good conclusion using rough estimates.
In reality, you can't control the number of particles in the system unless you build some sort of box to hold stuff in between the plates. Also, the laws of thermodynamics depend on there being a large number (millions) of particles, so you can't use them with nay degree of reliability in these kind of situations. My conclusion is suspect, because it is really only an educational guess.
It is much easier to make a vacuum, thus making the problem a lot easier.
The radical sect of Islam would either see you dead or "reverted" to Islam.
Yes. That is exactly what is happening. However gathering energy from such a source is going to be almost impossible. Just like thermodynamics breaks down on a very small level, so does quantum mechanics. You get to a point where nothing can be predicted, things are being created and destroyed, conservation of energy is violated constantly, and all the laws of physics are turned upside down and become meaningless traffic laws. But if you scoot back and look at the larger picture, you'll see that there is a pattern to this madness. You see how a photon was created and destroyed, but how it really was "moving" from one localized area to the next, and it really was a "real" photon, transferring energy from one spot to the next. It has a life beyond the small localized areas. While at this level, things aren't as predictable as you hope (which hole did the photon travel through?), it is still predictable to a large degree. Then you scoot back some more, and the probablities begin to add up, and things begin to become predictable with high accuracy. The laser beam doesn't change course, the people around you don't vanish and reappear, and you can be sure that there is going to be a sunrise tomorrow. The point is, even in thermodynamics, you can get violations of energy conservation -- or so it seems. The problem is that you were only looking too close at what was happening, and by looking to close, things don't make "sense" anymore. Things are truly random. However, the rolling of those millions and billions of dice end up with predictable results. Gathering energy from these statistical anomolies is going to be as possible as predicting with high accuracy the roll of a die. Until you can sit on the throne of Einstein's God who doesn't roll dice, it will be impossible.
The radical sect of Islam would either see you dead or "reverted" to Islam.
It only depends on how "opaque" the plates are to the light at those frequencies, and has nothing to do with charge. Photons are unaffected by charge.
Besides, having a charge on the plates means you are going to get a force between the plates -- attractive or repulsive, depending on the charge -- that is inversely proportional to the distance squared.
The Casimir force is inversely proportional to the distance to the fourth power, and so the electric force will become insignificant as the distance becomes very small.
The radical sect of Islam would either see you dead or "reverted" to Islam.
Maybe something based on this force could help out with this.
just to add more confusion to the story... one can show that the casimir force between two objects can also be viewed as a van der waals force. imagine two dielectrics separated by vacuum. in the casimir picture, the two dielectrics will attract because of vacuum zero-point energy fluctuations. as someone else pointed out earlier, this is, in very simple terms, because certain frequencies are not allowed in the vacuum creating a pressure. on the other hand, one can also generate the same force by having the particles in the dielectricum fluctuate, i.e. generate van der waals forces due to "dipoles".
from a physics point of view one has a hamiltonian (function which describes the whole system) for which one can integrate out the degrees of freedom of the dielectric or the degrees of freedom of the electromagnetic vacuum. if you remove the dielectric degrees of freedom, you get equations for the EM field which will give you a casimir force when you look at the cero point energies of the system with and without the dielectricum. if you integrate out the field, you will get an effective interaction term for the dielectrica and hence a vdW force.
note also, that both, van der waals and casimir forces depend with a power law on the distance between the objects, usually at a high power and are therefore extremely short-ranged. there are some nice papers and experiments measuring both at the usual archive xxx.lanl.gov. just search for casimir...
Here is another article from John G. Cramer's Alternate View Articles in Analog Sci-Fi Magazine.
Professor Cramer is the real deal. A physics professor at Washington University who is also a sci-fi fan and writer. He is also an excellent pop-science writer who can get his point across without dumbing things down. Enjoy.
is it just me or does this sound like something that would tie into ZPF energy theories?
p r m t h s
It would seem to me that both surfaces would want to become the leg on the T on the other (if both sides of the leg are mirrored). Would the absence of protons cause collapse into the shape of a V on the connected (or close to connected) side? I would think not since the 90 degree would be broken as soon as the force was observed, I'm assuming it would not be the only force because if so wouldn't momentum eventually make the plates paralell and the effect would complete the movement. Sounds like nanites will look like modern art or sports cars, composed of paralellagrams and curves.
Perhaps structures could use several atom mirrors like velcro in construction? Does the force disappear when the distance is 0?
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If matter and energy are different aspects of the same thing how can a true vacuum have energy in it?
hmm... is "importances" a word?
at any rate... I think one of the "very important" aspect of this has to do with multi (>3) dimentional physics. I can't remember where I read it, but physicists are theorizing that at millimeter (or less) distances, we will see gravity suddenly becomes disobedient of the inverse square law (which would prove the "we live in half dozen dimentions) theory. Now -- measuring gravity on a millimetre scale is hard enough, but when you throw in all these "fluctuation forces" (Van der Waal, Casmir, whatever), you will seriously screw up any chance you have on the Nobel prize... so people are trying to get all these things sorted out and verify some gravity, etc.
My life in the land of the rising sun.
Many years ago, I read a book co-authored by Buzz Aldrin (i forget what it's called) about some aliens from the Alpha Centauri system who come to Earth using a spacecraft powered by millions of tiny plates that extracted energy using the casimir effect. Apparently, a paper proposing this has been published somewhere.... Has anyone read this paper, and has anyone read this book - I'd love to know what it was called...
-- Fuck Beta
My favorite part of the article contained this sentence. "Consider the gap between two plane mirrors as a cavity (figure 1)." You look directly over to the right at figure 1, and all you see is a picture of some droopy, slow-witted looking scientist. Poor guy, the sentence describing his head uses the words "gap" and "cavity". Chalk that one up for one of the worst editorial mistakes ever.
they always what?
Watching Cowboy Bebop in my jammies, eating a bowl of Shreddies.
- You have mistaken the half-digested watered-down absolutes that you got in highschool from a teacher who didn't understand the words being mumbled with The Truth.
Nope - that's where you are wrong. There were no absolutes... that was one of the first things we were taught. My point is, the definition of a vacuum is the existence of nothing in an area - but many scientists (or those this particular writer is writing about) seem to forget the definition when writing. He was basically explaining as if they were different things that "a cup full of water then needs to have Hydrogen and oxygen added to it in the right combination" and then tried to define it as such without the H2O.... you'll misunderstand this one too probably. You create a vacuum and then you take out what? oh wait, there isnt anything, heat, energy or otherwise to take out. And this, by the way isnt some "Gee we dont understand physics" theory. It is the definition of a vacuum. Whether one exists or not is something else entirely, and probably does not, because even the process of creating a "vacuum" creates an almost vacuum - at least by using current technology.Obviously there are no absolutes. The first thing our teachers taught us was this... we have 5 limited senses, and even with the best machinery we have, they are still limited tremendously - and even above that, everything we build to augment their abilities is BASED OFF OF their abilities... IE: we build tools to allow us to "see" what we already know of in a better way... while we perceive so little because those senses are so limited. And all this based off imagination fueled by those limited senses.
My point was the article is contradictory in its own statements by a vacuum being redefined 3? 4? times, and so on and so on as I was trying to indicate.
- All of our knowledge is provisional. And contrary to the fairy-tales that you may have heard, scientists don't have a real picture of how anything actually works. They have detailed guesses. The guesses allow them to predict things. They spend their time testing those predictions because they don't have a clue when they will fall to pieces.
They (and we) know less than nothing. You know that, I know that, and hopefully THEY do. I thought I made that clear too... that their blatant disregard for what they learned because of the "absolutes" they determined was detrimental to our continued "learning" of anything real. I even said as much.I am beginning to think you just felt like griping instead of really reading and trying to understand what I wrote.
- Oh, and the biggest barrier to learning is in putting aside our mistaken preconceptions. You seem to have an unusually strong case of this affliction. Don't let it hobble you too much.
Or no such affliction whatsoever. My point was the writer had confliciting definitions of the subject matter thus making the article near nonsensicle in a scientific sort of way. To learn more about science, you need to have an open mind and realize that we know so little. To discuss a topic that has been theorized, you need to stick to consistency. The author was writing about the theories of others, using various differing definitions of the same things and trying to link them together in a "well, because the world is flat, you can fall of the edge, but if you go around it you will end up where you started because it is a sphere" which was my biggest complaint. You cant use different conflicting theories - in some cases in the same sentence - to explain others theories that are in all probability based on one of those theories and not the whole slew of them he used. And if the scientists involved actually were using each of those conflicting theories of vacuums, energy, matter, photons, space, et al to come up with their one theory, then how credible does it make their theory?Next time, dont be so grumpy and read what others write before you fire off an attack... heck, you wont even need to post anonymously when you can then post an intelligent response!
- Rob
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I dunno whether it was because the author of the article doesnt understand physics and such, or was talking for the layperson, but a vacuum has no energy, no matter, no vacuum fluctuations, etc.
Your opening sentence is incorrect, and that makes hash of the rest of your post. You seem to be discussing classical vacuum, and in fact seem to be stuck on classical physics in general. For instace, a complete absense of everything would not have a temperature of zero, it would have no temperature.
I'm not a big physicist myself, but you are criticizing things that you don't even have the faintest conception of. Vacuum fluctations result from virtual particles, which is a concept that some view of is necessary to rationalize certain other quantum effects that occur in particle interaction. You need to learn more.
- Your opening sentence is incorrect, and that makes hash of the rest of your post. You seem to be discussing classical vacuum, and in fact seem to be stuck on classical physics in general. For instace, a complete absense of everything would not have a temperature of zero, it would have no temperature.
Isnt that the definition of absolute zero? I'd go to google and post a dozen links confirming that, but it would be wasting space. And besides, my point was the article's author was referencing various definitions for a vacuum, in his article making his interpretation of the theory quite... I'm not even sure what to call it... other than probably not a very accurate interpretation of the theory.- I'm not a big physicist myself, but you are criticizing things that you don't even have the faintest conception of. Vacuum fluctations result from virtual particles, which is a concept that some view of is necessary to rationalize certain other quantum effects that occur in particle interaction. You need to learn more.
Oh, I'm sorry... so, you are saying "vacuum fluctuations result from scientists being unable to explain unnaccountable for instances of energy, mass, gravity and/or electromagnetism where they theorized there was supposed to be none - this is possibly due to the fact that these scientists were wrong in their initial theory of what a vacuum was and didnt even bother to account for simple things such as the energy or mass of a photon - that simply because until recently photons were erroneously thought to have no mass, so now instead, we'll create these virtual instances of something probably photon or photon like that explain the errors in our equations due to not understanding enough about the principles of a vacuum under any of our own definitions so that our results are at least a little more accurate until we have to make up some more bullshit so that 3+2=7". Right? Ooops, maybe I do understand the concepts very well. Again, my point was the author of the article used conflicting theories generally held separate in the basis of larger ones as explanations for the theories known as the Casimir Effect. Get it now?"virtual particles"... How neat! It's based off the same stupid principle that particles even exist, which is also believed to be untrue - it just makes it easier to work with because we can quantify "amounts" of energy easier when measured thus (also because "we" cannot seem to grasp measuring energy as an n-dimensional field as opposed to as a grouping of particles.).
I am far more well versed in the field than you would be had you dedicated your college career to it - my current occupation not withstanding (which was chosen because I thought it time to work for myself in something I found more fun).
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I tell ya, man, this quatum physics stuff is almost as hard to comprehand as women.
Table-ized A.I.
HAH!
(-1, Raw and Uncut is the only way to read)
Confusion would be an excellent description. What in Heisenberg's name are you driving at here? The London force or dipole dispersion force varies as 1/r^6, where r is the separation radius.
The Casimir effect between two parallel uncharged plates in a vacuum at zero kelvin is given by:
pi^2 h-bar c
F = ----------- A
240 r^4
A = area of the plates and r is the separation distance.
The Van der Waals interaction can be considered and computed as a semi-classical electrostatic effect. The Casimir effect, although sometimes referred to as a "long-range Van der Waals effect" is fundamentally a quantum concept as shown by the appearance of h-bar in the equation above.
As you indicate, both forces follow a power law, but the Casimir effect will appear, again, between "neutral, conducting" plates at absolute zero, i.e. in a configuration where electrostatic forces due to charge distribution are not present, and the power relationship differs by an order of magnitude.
So the two forces are fundamentally different conceptually and similar in that they both describe attractive forces between objects. However the latter similarity would also allow you to say that casimir == ferromagnetism if that is the only metric.
I also know that last year they determined that a photon at rest DOES have mass, finally "proving" correct other theorists who also claimed it was a big flaw in einstein's theories. Heck, it even finally made slashdot a few months ago.
Ooops... if you dont want to do the research, then at least pay better attention to slashdot and you'd know you were wrong. Including numerous non-related articles where photons, that supposedly travel one speed, exhibitted far slower speeds.
Ah well... the truth is it is all probably wrong. We see one thing, and we apply the theory we create for it to everything... which is the reason why a number of theorized quantum particles cant exist either... but alas... I am done with this debate. Universities and researches half the globe around claim photons at rest have mass, there are quantum particles that travel faster than light, blah, blah, blah... while others claim them frauds.
My only reason for believing those who seem to see things as not so simple is the quite simple "rule" that humankind has more often than not (or more accurately "virtually always") learned some "short" time in the future, that (s)he is totally wrong about every theory.
Then again, that's why they are theories.
Anyway, I am really done with this conversation... a simple web search on simply photon and mass will result in a dozen different conflicting theories nowadays, many held by our premeire universities and institutions (such as Brookhaven Labs, where I used to live...) We could argue till the end of time... and the only thing that would happen is the theories we were arguing about would be replaced by others (just like sections of Einsteins are being revised to incorporate other theories to explain away the variances he didnt account for).
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the energy cannot be extracted because i decreed that there would be no free lunches.
It's spelled "actually."
Well I guess so, but of course it wouldn't really be zero, just very very close. Atomic forces would insure that.
They weren't really clear on how a perpendicular casimir force works either. Does it twist like a right hand rule(the balls and plate), does fold at an angle, or is it held in place. The story said the force was observed, but what movement?
It's possible even likely I misunderstood, I was jsut wondering if anyone else gets it.
Novel theory: Modern Man evolved from psychopath
...I also know that last year they determined that a photon at rest DOES have mass,...
Nope. There's no such thing as a "photon at rest". A photon always travels at the speed of light.
However, you are correct that there is no such thing as an absolute vacuum. Since photons have mass (m=E/c^2), the only way to create an absolute vacuum is to take all particles and photons out, and that's not possible (microwave background radiation).
But! There is a quantum theory concept of zero-point energy. Like everything else in quantum physics, it's totally weird, and the Casimir effect is closely associated with it. There's more to it than your explanations, so maybe you should do a Google search on "zero-point energy".
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Rob, you seem to have a few misconceptions yourself. Quantum field theories can be slightly counterintuitive, to say the least! However, these theorist are quite correct and it is a little unfair to "jump on them" in such a hostile manner. Let me see if I can explain what the modern view of the vacuum is.
We model the existence of all particles as energy levels. As you pointed out, mass is just a form of energy - the lowest energy rung corrosponds to a particle at rest and the energy is just mc^2. Of course, this is only true for MASSIVE particles, massless particles only have kinetic energy. We have a vacuum state that has "no particles in it".
To make this notion precise, we define the vacuum state of a system to be any state such that trying to eliminate a particle (a photon, a massive particle etc) will give you zero. This way, any process that tries to remove a particle to go ahead (such as destroy a particle at point A and recreate it at point B - this is the way Quantum theories see particles as moving!) will contribute zero if it operates on the vacuum state.
However, operators such as the energy operator do not always have a "remove particle BLAH" in every term. Thus, when they operate on the vacuum state it is possible to have a non-zero mean. By the uncertainity principle, if there is a NON-COMMUTING observable then there also exists a (non-zero) fluctuation of this value - measured by physisicts and mathematicans as the square of the deviation from the average.
Some people choose to interpret these as virtual particles popping in and out of existence. The mathematics works the same, so this is a just a picture in ones head to help one think about these things. The mathematics gives us the option - we can take the "picture" interpretation or just do the maths.
Hope this helps!
Damien Martin
Imagine a "vacuum" with two metallic (reflecting) plates in it, sitting near each other. The vacuum isn't pure. Photons could exist in it, momentarily, as governed by Heisenberg's Uncertainty Principle, wherein the energy of the photon is inversely proportional to the time it exists. Gamma rays would exist for a short period of time, radio waves much longer. Eventually, the Universe checks its books and corrects the accounting error, the photons go back to non-existence - conservation of mass-energy is upheld.
Here's where it gets weird. The photons kinda-sorta existed (virtually), so they kinda sorta could exert an influence. Whoa. Strange.
Next, only certain frequencies are allowed. The frequencies allowed to "kinda sorta exist" are modal, that is, they have to terminate with a node on one of the plates. So, clearly, you can't have gigantic radio waves between these two plates - radio waves are meters in length, they're too big to fit between the plates. You can have some blue photons, and all the gammas you can handle.
Meanwhile, on the OTHER side of the plate, you get all of the radio waves you want - you have an entire universe to stuff them in! And the blue photons, and all the gammas you can handle. So ... there's just a few more potential electromagnetic waves (virtual photons) on the OUTSIDES of the plates than there are on the INSIDE of the two plates - this leads to a net push of the plates together.
But that's not all - the force experienced by those two plates depends on a lot of things. In the symposium in question, it was demonstrated that, with the right geometry (concentric shells, weird flower-like arrangements) that the Casimir effect can be repulsive.
In short, it isn't always 1/r^4, and it isn't always attractive.
Now, for those of you who would like a free lunch out of this effect, it's not going to happen. Why? 'cause you have to push the plates back apart to complete a full cycle for any "free energy" machine you would like to devise. It's like a waterfall - you only get that energy from something falling down ONCE.
No, it doesn't have anything to do with the Higgs boson. No, it doesn't come from some folded-up dimension. No, it doesn't have to do anything with gravity at small ranges. C.E. results entirely from QM + EM.
On an aside, correcting other bits of non-information in these posts: no, photons are not influenced by charge. No, photons do not constantly form electron-positron pairs - most photons do not have enough energy to form an electron-positron pair - do the math if you don't believe me. The refractivity of materials comes from something entirely different. Photons don't have a non-zero rest mass - they never "rest" (discussion of the Bose-Einstein condensate usually ignores that the information about the photon was stored) - and many experiments have placed upper limits on the proper mass of a photon as being no greater than 10^-50 grams.
I am far more well versed in the field than you would be had you dedicated your college career to it.
Uh-huh. I'm counting at least 20 points scored on the crackpot index, ten from that sentence alone. Unusually low score, perhaps, but in the absense of substance that's all I've got to go on.
The humourous part is that I'd lay money your theories, assuming you actually HAVE any as opposed to merely disagreeing with thousands of very smart people, have no coherent explanation for the casimir effect or other similar phenomena.
My response to the whole italisized bullshit paragraph is that once again, you make it clear that you do not have much understanding of any physics that I've ever seen, and persist in mixing classical and quantum physics without regards for the very carefully defined boundaries placed on those definitions. Your attacks would have much more substance if you weren't attacking strawman physics. (Basically, nobody claims the classical definition of vacuum is anything but an approximation useful in certain circumstances anymore.)
I won't be replying any further, so please take the crackpot's great joy of having the last word and milk it for all it's worth.
Just wondering, but are you perhaps a proponent of electromagnetic theories of cosmology and somewhat disappointed in the standard model?
------ The only greater hazard to your liberty than n politicians is n+1 politicians.
It's not wasting time, I'm educating myself.
I was wondering. As an archaeologist, I usually only pay attention to physics as entertainment. I have a friend however, who is a physicist, who has frequently expressed dissatisfaction with the standard model and what he refers as the "epicycle" problem of adding complexity in order to continue ironing out the contradictions that keep intruding. He recommended a book on electromagnetic cosmological theory.
I have been wondering how on one hand a Bose-Einstein condensate can be produced, thanks to the operation of the uncertainty principal, and yet IBM can still apparently herd individual atoms into patterns of smiley-faces and other interesting patterns, which seems to violate the uncertainty principal, since the location and momentum of the atoms employed must both be pretty well fixed in order to produce a readable image as claimed. Anyway, thanks for the reply.
------ The only greater hazard to your liberty than n politicians is n+1 politicians.
Sorry about the wierd characters. I had to do some strange things to get this through the lameness filter.
If two tiny mirrors were attracted to each other with both the forces of gravity and the casimir effect, the work done by their movement would generate energy that could be captured. Once they are together, they could be slid apart, moved back apart while not facing each other and moved to face each other again.
1)
_____________
|
v
Casimir effect + gravity
n
|
_____________
2)
=============
^
|--Capture the energy of collision.
3)
slide right____________
____________slide left
Slide mirrors apart using stored energy.
4)
___________
^
|---------------|
v
__________
Push mirrors apart using stored energy.
5)
slide right _________
_________ slide left
Push or rotate mirrors to face each other again.
6) Repeat
I think if all the energy is captured, steps 3, 4 and 5 should eat up all the energy that was gained by the work that gravity performed. The rest of the energy, the work that was done by the Casimir effect is yours to keep. Do this with a billion little mirrors in a space-based power plant and you're set.
I must be missing something cause perpetual motion let's all sorts of bad things happen like time travel, superluminal flight and entropy reversal. Sorry about being sloppy with my terminology. I'm probably misusing "work", "force" and "energy" in this context.
So am I wrong about something or is this scheme truly money for nothing and chicks for free?
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