Slashdot Mirror
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."
Magnetism does possess a gyrative effect in low helic-effect vacuums while still possessing hertz-charged particles.
;) )
(If you can understand the above, you're very smart
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?
That is, if you wear a cashmere sweater, many women will want to touch you.
Try it out, you'll be amazed.
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.
Getting sick from a radioactive sweater
Not noteable, IMO a rubbish article.
Does this mean that there are extra forces inside my vacuum cleaner that will shorten its life?
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?
Novel theory: Modern Man evolved from psychopath
One of the open questions not addressed in that article is that the Casimir effect might be usable as a source of virtually unlimited energy. A brief non-technical introduction to this can be found here.
At this time the plausibility of constructing actual devices that extract this energy is unknown. As are the potential energy densities. For instance as far as I know, nobody has ruled out achieving controllable extraction of more energy than even Einstein's famous equation E=MC^2 allows! (Starting with non-reactive substances that are stable and don't give off any inconvenient radiation.)
Note that more than a few cranks have convinced themselves that they have the secret to unlimited energy here. However there is also serious research on the same, some of which is mentioned here. It may turn out to be nothing. It may make splitting the atom look like a firecracker.
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
At a distance of 0, wouldn't the force be undefined? Atleast, from the equation that's what I gather. 1/0 = undefined. Also, perhaps I do not understand your scenario, but wouldn't the perpindicular side, |-(where - is the perindicular side), on its end have a surface area, if mirrored, would react with the plate it's perpindicular to? That sounds awkward; let me try again: the very end of the - would be attracted to the |, causing Casimir forces between the two. I don't think that it would swing into a V-shape, since the article stressed that the surfaces had to be basically perfect for it to result correctly.
Another famous story used the effect:
Arthur C. Clarke's - Songs of Distant Earth
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.
Back when I was studying physics, I remember our quantum field theory lecturer talk about the Casimir effect. I forget the details of it now, but I remember that it is a consequence of the fact that the vacuum contains infinite energy. The maths made sense, but the lecturer went on to say that people had proposed practical methods of using the effect to extract limitless energy - and then referred to these people as crazies.
I get theory, but I'm not so hot on the practical. I never got to ask him why this couldn't be done. If the energy is there, why can't we get it?! Anyone care to enlighten me?
These guys seem to keep forgetting that matter is energy. Energy is energy. Energy seems to oddly exhibit much the same behaviors gravametrically and electromagnetically (assuming they arent subsets of each other) as energy in the form of matter. Photons are energy, and just like every other known form of energy "discovered" have mass - even at rest (covered here and a dozen other places over the last few decades, but no one wants to change a billion wrong formulae for the miniscule variances it would create - which in turn limits MANY other more significant "discoveries").
Thus, what all these people forget is, you cannot have a vacuum with any form of electromagnetic radiation in it. Or any form of energy. One seems the component of the other, but nonetheless (or because of that), each thusly exhibit mass, energy and such.
As for the absolute zero crap... you do NOT neeed absolute zero to create a vacuum. You CREATE absolute zero by CREATING a vacuum. Empty it of all energy, there is no heat. Add a photon, it is no longer absolute zero now is it? And nothing you can do can change that short of negating the energy of that photon - which so far we believe would require removing it, since we cannot destroy it (by current belief - right or wrong).
These endless misconceptions seem to permeate these scientific fields truly limiting research.
Worse yet, they are surprised, that energy, due to electromagnetic, gravametric and/or other similar "waves" attract each other in a vacuum - something we have know it does for a long time? Of course objects that would not normally do that elsewhere would do so in a vacuum. Put a cinderblock on a rough piece of wood and push it with 1/2 pound of force. Not gonna move... get rid of friction and try...
Now, in reality, there are a lot more forces involved than in that simple example in non-vacuum conditions... the attractive force needs to be able to overcome not just friction (of moving matter or energy in other forms out of the way), but gravity and other attractive fields that are interfering... too little attractive force to overcome all else that is "holding" or "blocking" the object.
This, and the story are 9th grade physics stuff... and they find it so amazing? We were taught this - properly no less (unlike the article) - back in 1979... in Junior High.
- Rob
WebMaster:
BinFeeds
XXX Thumbnailed Image Newsgroups but
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.
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.
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.
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.
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
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.
Fuck! It's like H.P. Lovecraft, jr!
(Yes, I know that's just silly. I guess someone could write a story about why there isn't a HP jr!)
my theory (and im a pre-undergraduate physics student - doing it next year) is that its just gravity. everything ive read suggests a minute force attracting the two plates, and that just screams out gravity to me. can someone point out where im wrong? ive been wondering about this for a while now..
Dont ask me...Im just the bass player.
If one were to position plates at radio frequncies, and then attach a radio to the plates, would it be possible to hear the radio waves generated in the cavity?
:)
And then of course, could you inject radio waves into the quantum sea using the same apparatus?
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?
Blaze a trail to the New World