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Empty space can set objects in motion

  1. Feb 5, 2004 #1

    Monique

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    http://www.nature.com/nsu/040126/040126-19.html

    I thought this was interesting:
     
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  3. Feb 5, 2004 #2

    Monique

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    What? Noone interested?
     
  4. Feb 6, 2004 #3
    I don't see what is so special or surprising in this. Seems quite normal/expected to me. Maybe I'm missing something?

    By the way: the Casimir-effect also gets "movement from nothing". And that's much nicer, because you won't have to apply large fields to obtain it.
     
  5. Feb 6, 2004 #4
    Would this qualify as an Ether test ?
     
  6. Feb 6, 2004 #5
    Here I go getting in over my head again... but I figure the more I post, the more people will have to rebut, and the more everyone will learn, right? That's the idea anyway.

    Why don't they give up and admit to zero point energy? Seriously folks, virtual particles popping in and out of existance in empty space so fast that they cannot be observed? Has this ever been truly proven? This relates to McQueen's statements in the 'wave-particle duality' thread. People seem to measure force exerted and assume there is matter presently exerting it, when in fact there need not be present matter, only energy. The source of energy can be anywhere. These 'virtual photons' are likely nothing more than an undiscovered medium to convey that energy. Does this make sense to anyone else?
     
  7. Feb 6, 2004 #6

    Monique

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    So how does the Casimir-effect work?
     
  8. Feb 6, 2004 #7
    I first came across the idea of an energy in vacuum in reading about the idea of false vacuum. Imagine a cup with a marble in it. The cup sits on a table. The marble stays nicely in the cup as long as the system is not disturbed. Does the marble have any potential energy? Well, not in relation to the cup. Yet if the cup and table were suddenly not there, the marble would fall to the floor.

    The idea seems to be that the marble in the cup is in a state of false zero energy. Our visible universe is said to be in a similar condition. If the marble could get out of the cup somehow, it would fall to the floor, expressing its potential energy as motion. If the universe is in a false vacuum state, then there is a certain potential even in the absense of matter for some energy to be present. If there is energy present, then mass energy equivalence suggests there must be some mass present. There it is, a virtual particle.

    The wave theory however does not restrict the location of the particle to the inside of the cup. Correct solution to the wave equation (I do not have the math to do this myself, but so I have heard it said) gives a small probability that the marble is actually on the table, or even on the floor. If a marble behaved as a quantum object, and you put it in a cup, you would not be suprized to find it on the floor, because of the phenomena called tunneling. Of course a marble is an absolutely huge statistical universe of quantum objects, and the probability that any one of them is outside the cup is low, so the probability that they would all suddenly appear together outside the cup is vanishingly small. But when we are talking about extremely small objects like electrons, quantum tunneling becomes a real and measurable effect that turns out to be useful. Extremely small objects may contain only a very few quantum parts, so it becomes more likely that you will see a very small object make a quantum leap, for example, between electron shells in an atom.

    Well I am just sketching from memory. Alan Guth has a book called The Inflationary Universe which has a good discussion of these ideas with nice illustrations throughout.

    I don't know if this has been helpful but I am very interested in these ideas and thought I'd throw in a few words.

    Thanks,

    Richard
     
  9. Feb 9, 2004 #8
    Basically like this: two (infinite) plates are placed close together in vacuum. Because the virtual photons generated between the plates are restricted in frequency (the very long-frequency ones 'do not fit' between the plates), the photon-distribution will be different between the plates as compared to the outside. This results in a nett-force, pushing the plates closer together.

    Nicer story
     
  10. Feb 9, 2004 #9
    World sheet plates?

    Hi Suyver, and all

    Good job on the Casimir effect explanation, I thought. Only I think the plates do not have to be infinite. The effect, if memory serves, has been measured even in the tenth of a millimeter range of separation between plates whose area I do not recall, except my mental image was that the plates were perhaps the diameter of a small coin. Anyway if it was measured, surely the plates were not infinite, since that would require a rather large apparatus.

    I wonder if there is a measurable Casimir effect between plates arranged in time dimensions? Lets see, a wire could be set up in a frame so that its world sheet would be like a plate. THen a second wire could be added to the frame so that the second wire is parallel in the frame to the first wire, and separated by a small distance. The frame could then be set in motion, creating a pair of world sheets. If there is a Casimir effect in time, would it be possible to detect an attraction between the two wires? Would it also work with glass fiber? I don't know.

    Anyway, thanks for being here.

    Richard
     
  11. Feb 20, 2004 #10

    TeV

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    I agree.Nothing surprising except requirement of 17 T and 100kV/m (?). Take for instance dielectric body or charged body placed in strong Elictrical field .It will move if nothing else stops it.Why is that value taken (17 T)?.I guess it has something to do with quantuum magnetic spin of watter molecules ? Using Cassimir effect energy of Vacuum can be stored and explored(smallish amount in practical range though.)
     
  12. Feb 20, 2004 #11

    TeV

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    I wrote:
    " Take for instance dielectric body or charged body placed in strong Elictrical field ."
    ________________________

    I just noticed this and must correct myself here.
    It was typo.
    Certainly,I was referring to movement of feromagnetic body in magnetic field or movement of charged body in strong electrical field.
    Neutral dielectric body wouldn't exhibit total net translational movement in electrical field.There will be distortion force present though.
    I apologise for confusion in my post.Today was madness at work.
     
  13. Feb 21, 2004 #12

    TeV

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    Wow !,received two private messages regarding last post.
    I see further clarification is needed.
    "Neutral dielectric" body is the term for the object which does not disturb surrounding E field by its' presence.
    In everydays experience something like that isn't usual but in nature is quite possible (example is body made of neutrons).
    Common dielectric will be polarised in E field and can exhibit rotational or translational movement as object in nonuniform E field configurations.
    The same holds for Magnetic fields and ferromagnetic materials but with one fundamental difference:dielectric material polarisation effect can be cancelled (in principle) by adequate amount of charge brought to the body surface of dielectric.Magnetic polarisation effect cancelling in the same fashion isn't viable since there are no magnetic charges.Elementary monopoles still wait to be detected.
     
  14. Feb 22, 2004 #13
  15. Feb 22, 2004 #14

    Nereid

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    Casimir effect

    This physicsweb article seems like a good, concise summary of the physics and its applications.

    It's actually difficult to measure the effect with parallel plates, and there are some subtleties - a.k.a. details - that are important for applied physics.
     
  16. Feb 23, 2004 #15
    Re: Casimir effect

    Cool! That's the exact same link that I provided a few posts up... :wink:
     
  17. Feb 23, 2004 #16

    Nereid

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    So we make a great team, right? Just gotta work on the communication and coordination (where's the smilie for red-faced-Nereid, seems I'll be using it quite a lot) :wink:
     
  18. Feb 27, 2004 #17
    Do you all see any connection to Brownian motion here?
     
  19. Feb 27, 2004 #18
    No, I don't see the connection.

    Brownian motion is an effect caused by real momentum-transfer when molecules (in solution / gas) interact with an object. The Casimir-effect is caused by "a localized change in the vacuum-pressure" (note quotes!) and this could be seen as interaction of virtual photons with an object.
     
  20. Feb 27, 2004 #19
    But isn't Brownian motion, like this Casimir application, a quantum-statistical effect that manifests overall virtual actions as real macroscopic dynamics?
     
  21. Feb 27, 2004 #20

    ahrkron

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    No, Brownian motion is a classical effect. QM is not needed for its description.
     
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