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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."
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...
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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!
Information theory is life. The rest is just the KL divergence.
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.
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.
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<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.
Disclaimer: The opinions and actions of the US Gov't are in no way representative of those held by this author or its ci
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"
intellectual property law is philosophically incoherent. it is your moral duty to ignore it or sabotage it
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.
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?
If the plates don't move, no work is done and you get no energy.
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.
"You can't allow somebody to commit the crime before you detain them." [Condoleezza Rice]
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).
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.