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

[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

[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: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.

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.

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?

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?