Northeastern University experimental particle physicists Stephen Reucroft and John Swain put their heads together to write the following answer.
To understand the Casimir Effect, one first has to understand something about a vacuum in space as it is viewed in quantum field theory. Far from being empty, modern physics assumes that a vacuum is full of fluctuating electromagnetic waves that can never be completely eliminated, like an ocean with waves that are always present and can never be stopped. These waves come in all possible wavelengths, and their presence implies that empty space contains a certain amount of energy--an energy that we can't tap, but that is always there.
Now, if mirrors are placed facing each other in a vacuum, some of the waves will fit between them, bouncing back and forth, while others will not. As the two mirrors move closer to each other, the longer waves will no longer fit--the result being that the total amount of energy in the vacuum between the plates will be a bit less than the amount elsewhere in the vacuum. Thus, the mirrors will attract each other, just as two objects held together by a stretched spring will move together as the energy stored in the spring decreases.
 Image: Scientific
American CASIMIR EFFECT |
This effect, that two mirrors in a vacuum will be attracted to each other, is the Casimir Effect. It was first predicted in 1948 by Dutch physicist Hendrick Casimir. Steve K. Lamoreaux, now at Los Alamos National Laboratory, initially measured the tiny force in 1996.
It is generally true that the amount of energy in a piece of vacuum can be altered by material around it, and the term "Casimir Effect" is also used in this broader context. If the mirrors move rapidly, some of the vacuum waves can become real waves. Julian Schwinger and many others have suggested that this "dynamical Casimir effect" may be responsible for the mysterious phenomenon known as sonoluminescence.
One of the most interesting aspects of vacuum energy (with or without mirrors) is that, calculated in quantum field theory, it is infinite! To some, this finding implies that the vacuum of space could be an enormous source of energy--called "zero point energy."
But the finding also raises a physical problem: there's nothing to stop arbitrarily small waves from fitting between two mirrors, and there is an infinite number of these wavelengths. The mathematical solution is to temporarily do the calculation for a finite number of waves for two different separations of the mirrors, find the associated difference in vacuum energies and then argue that the difference remains finite as one allows the number of wavelengths to go to infinity.
Although this trick works, and gives answers in agreement with experiment, the problem of an infinite vacuum energy is a serious one. Einstein's theory of gravitation implies that this energy must produce an infinite gravitational curvature of spacetime--something we most definitely do not observe. The resolution of this problem is still an open research question.
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16 Comments
Add CommentI would suppose that this effect is responsible for part of the energy released in a lightning bolt as the discharge creates a vacuum that collapses violently creating another flash of light and heat. Similar to cavitation decay on propellor blades and the observed sonoluminescence.
Reply | Report Abuse | Link to thisIf the vacuum energy is composed of EM waves, it would be interesting to see a histogram of the energy in each frequency band, and then try find ways to alter that distribution. If we broadcast very low frequency waves into a space would be see a longer range 'artifically created' casimir effect?. Also if the assumption that the vacuum energy is infinite is based on it including all frequencies, then surely there is a lowere limit to wave length (/energy) at some point, probably the Planck length of something like that, or is the energy limited to the Planck energy, how does that fit? I'm not a Physicist, sorry. Of if the energy distribution mentioned above tails off at higher frequencies with an appropriate distribution function, the sum total could still be finite.
Reply | Report Abuse | Link to thisI could imagine someone building something to the right specs then see it burst apart from the vibrations created...that would be a momentous occasion! I mean, if it's truly infinite then it seems possible. I'm guessing the plates would resist the pressures and a wave would develop...then they'd just have to come up with a material that could withstand the forces but it would also be something that could be tuned.
Reply | Report Abuse | Link to thisthe problem of an infinite vacuum energy is a serious one. Einstein's theory of gravitation implies that this energy must produce an infinite gravitational curvature of spacetime--something we most definitely do not observe. The resolution of this problem is still an open research question.
Reply | Report Abuse | Link to thisif the energy is equally distributed all over the universe wouldn't this nullify the effect and cause no bending at all
thinking the curvature would be caused is because of seeing just that point instead of all of the surroundings
work is done because of the differental between 2 energy states.
JohnBosler, that is the conclusion I came to as well. The the gravitational curvature would be the same everywhere and therefore undetectable. However, the idea of everything being in an infinity deep gravity well... sounds undesirable. Using Occam's Razor I would say that it is false. Unless it can actually be observed and/or utilized somehow.
Reply | Report Abuse | Link to thisFirstly there's a problem with the notion of conductive plate: The velocity of the electric field is finitely less than the speed of light,-- so there's adjustment needed in the calculation for the 'quantumistic' spacing, (cf a wave against a shore).
Reply | Report Abuse | Link to thisThat's the wave view, Now the particle view--
Conductive plates consist of electric charges in balance but mobile ... so, like atoms align their charges s/p/d/f-shaped, such plates paired will align their charges across the gap ... And-need-we-say-it, attract, cumulative mutual opposites.
Thirdly, it would seem that as the speed of light in a plate is significantly less than C (maybe about 0.6 C for copper), the photon passing between two plates should pull toward each as its fringe drags toward refraction, but ripping the photon apart would take energy, so the plates, instead, co-attract....
That's the opposite of some proposed Casmir FTL effect. (But there's also another Russian experiment for induced-FTL....)
Ray.
Interesting
Reply | Report Abuse | Link to thisI have been a physicist for the past 10years and yet vacuum energy always intrigues me. I will always accept the following:
Reply | Report Abuse | Link to this1.) The vacuum is filled with vacuum fluctuations of all frequencies.
2.)Energy is infinite (perhaps this could help explain the expanding universe).
3.) Thirdly ,this might sound crazy but it is open to debate...Our physical universe is immersed in complex space (a space with reference frames for which V >> C.
Remember the math of complex analysis. your coordinates now change from X > iX ,Y > iY and Z > iZ. if V >> C using the lorentz transformation equations.
4.) so if we have a complex space for which a point iR is defined by iX + iY +iZ ,then energy in such a space will have the complex quantity "i" attached to it ..iE. This would mean that energy will be infinite (a consequence of lorentz transformation as soon as V >> C.
Strangely, the mathematics Complex analysis describes infinite spaces and infinite energies as imaginary entities i . Remember also in the lorentz transformation when ever V >> C ,all quantities become imaginary i.e dimensions and energy.
5.) But how does this energy get into our physical space? . Simple ..via electrons . Electrons are like portals. I believe that there is transformation of virtual energy(iE (infinite energy)) from complex side of the electron to real energy on the real side of the electron which is what we can measure.
6.) Electrons i believe are strange structures(portals) that bridge real-space and complex space and they continue to spew out energy into real space from complex space. This perhaps could be why there should be no such thing as a cosmological constant. And probably why the universe is expanding.
It is also possible that this energy transformation from complex-space to real-space takes place in a time interval defined by the value of planck's constant.
Casimir effect and coanda effect are versions of the same principle but for different forms of matter and energy. Gravity is another (if viewed as repulsive not attractive). It also dispenses for the need for "dark matter" to explain "local" gravitational law inconsistencies with the generally accepted universal model.
Reply | Report Abuse | Link to thisGreat article, much better description to the wiki page.
Reply | Report Abuse | Link to thisCame across the casimir effect watching the movie atlas shrugged, thought it was an interesing topic, didn't think it would be so complex.
I'm a physics and mechanical engineering student. Although I've been in school for about 6 years due to lack of direction, its given me reasoning to understand some things.
First off, Einstien was wrong to say that gravity was an infinite curvature in space time. It's something I don't get since he discovered planks constant was a quantum effect, how he could consider gravity a continuum. I had long sought a reasoning for how gravity functioned without outside information, and my reasoning was strikingly similar to Higgs field theory.
It is my understanding that there are force which result in the presence of a vacuum in order to create an equilibrium. I believe this is what spawned the creation of the universe. These force particles disobey the conservation of energy, yet form clusters which give rise to larger particles which do conserve energy. Once these forces are discovered then research will be taken to find how they cluster to form larger particles. Until we get to this point we will never truly understand such things as the casimir effect.
Your explanation doesn't really make sense. If the mirrors are moved slightly closer together, any standing wave shortens and has HIGHER energy. There's no wave that can't fit in without shortening.
Reply | Report Abuse | Link to thisYou're right, Clearwater 304! The current Wiki derivation uses a seemingly legerdemain analytical continuation that turns an originally infinite and positive sum into a negative finite number.
Reply | Report Abuse | Link to thisAn attractive force would come from damping of the excitations for frequency larger than a cut-off value. As the plates move together, the energy of each excitation increases (with the between-plate wavelength shortening). But the total energy decrease from losing the higher energy excitations to damping dominates. Energy decrease with separation decrease then means attraction. How much attraction would depend on the details of the damping.
Reply | Report Abuse | Link to thisWell, #13 does not really explain the Casimir effect. Here is a simple way to understand the attractive force, focusing on the 1-dimensional situation. Suppose a moveable conductive plate is positioned at a short distance l from one of two widely separated plates (distance L apart). With l << L, the states within the slot of width l are REALLY constrained so that the energy E of any one mode is widely separated from that of the next. This is not the case in open region L, where there are many more (in fact, about L/l) states, with energy evenly spaced between E and the next mode in the narrow slot---in other words, all slightly larger than E. Now on shortening l by dl (< 0), the mode in the slot shrinks in wavelength and therefore increases in energy proportional to -dl/l, whereas all the above L/l states lengthen and LOWER energy proportional to dl/L. The net change is slightly negative, because all the L/l modes' energies are slightly larger than the single mode in the slot.
Reply | Report Abuse | Link to thisthis is agreed with what I proposed in my modified special relativity theory in order to interpret Quantum tunneling, quantum entanglement , OPERA, Icarus, and SN 1987s. according to my research I define the vacuum energy with the equivalence principle, and I found it is possible to a negativity of the vacuum energy to be -infinity. I was disturbed about that, and I see this agreed with quantum field theory. Review my research in this site http://rxiv.org/pdf/1205.0091v1.pdf
Reply | Report Abuse | Link to thisAccording to this research everything is solved and interpreted in physics and no contradictions
I'm not exactly a scientist (yet) and I'm just riffing here, so chances are I may be wrong.
Reply | Report Abuse | Link to thisBut wouldn't an infinite curvature of spacetime be spherical? If so, wouldn't we be unable to observe it just as we are unable to observe the totality of a sphere from any point on its surface?
If this is the case, couldn't we calculate this infinite curve using Euler's equation and perhaps factor the infinite energy into Fourier transforms to convert the frequencies into something we can use?
From a mathematical point, zero, infinity and the imaginary number are paramount to the understanding of the universe. And they have a close relation to one another. At this point I am not qualified enough to validate my own hypotheses, but I really want to study these things in depth as they interest me immensely. Until then my best opinion would be that brilliant physicists the world over perhaps allow the mathematics to take precedence over the physical observations, as a lack of observed results does not always constitute a failed theory.