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Relationship between field and particles?

  1. May 17, 2012 #1
    i have been given to understand that the standard model is not a "particle" theory (even though the only things listed there are particles), but rather a "field" theory.

    i also (somewhat) understand that particles are not actually "things", but rather manifestations of the underlying field. (correct?)

    my questions regards the underlying fields.

    1. i assume that an electron is a manfestation of the EM field - what is occurring within the EM field that would generate the qualities that we call an electron?

    2. a proton and neutron are both "particles" comprising combinations of quarks, so i assume that they are not direct manfestations of a field. i assume that the the quarks are manfestations of some field. what field are quarks a manfestation of?

    3. photons and other bosons seem to be the EM (and other?) field(s) directly interacting with other fields and their manfestations, even though force carriers are all defined as "particles" in wikipedia. i know photons are always detected as particles, but between the time they are emitted and the time they are absorbed, they are not particles in the sense that they have no physical location, correct?

    4. so, how many field types are there, and how do they interact with each other?

    5. if the standard model is a field theory, why is the gravitational field omitted, and why are we still trying to add the "graviton" to the model? and why do we call everything particles instead of describing the fields?

    thanks for trying to help a poor confused person.
     
  2. jcsd
  3. May 18, 2012 #2

    Cleonis

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    Gold Member


    Here is how I understand it.

    Let me start with the electromagnetic field. Emissions of electromagnetic energy propagate away from a particular source, and this propagation is independent of whether the original source keeps emitting.

    When this kind of propagating electromagnetic energy interacts with matter an aspect of particle/wave duality manifests itself. The outcome of the interaction is like that of a particle/particle interaction. Example: in the case of the folo-electric effect the interaction is like that of particles striking a surface. Second example: Compton scattering: the resulting scattering is consistent with particle collisions.

    The counterpart particles of the electromagnetic field are called photons.


    Electrons have the property that they interact with the electromagnetic field. The way to express that is to say that electrons have the property of 1 unit of negative electric charge.

    The shorthand version is: 'electrons have a charge of minus 1'. That shorthand version is protentially a wrongfooting one. A macroscopic object - say, a metal sphere - has a negative charge when there is a surplus of electrons in it. A macroscopic object is a carrier of electric charge. An electron itself is not a carrier of charge; among its properties is one of interacting with the electromagnetic field.

    As I understand it electrons (and quarks) are not the counterpart particles of some field. Electrons do manifest particle/wave duality. It has been demonstrated with experiments that wave propagation effects can be elicited. Example: electron diffraction.


    So far, attempts to develop a quantummechanical theory of gravitation have remained unsuccesful.



    The wavelike propagation of electromagnetic energy is inferred from observation. By contrast, whenever electromagnetic energy interacts with particles the results are like particle/particle collisions.
    Consistently, what is measured in the course of experiments is outcomes that are like the outcomes of particle/particle collisions. Possibly that is why descriptions tend to focus on the counterpart particle, the photons etc., rather than on the field.

    [LATER EDIT]
    It dawned on me that I hadn't explicitly mentioned the most obvious: each charged particle is the source of an electrostatic field.

    If one assumes that electrons do not directly interact with each other, then it follows that each electron interacts with the field that extends from other electrons.
    [/LATER EDIT]
     
    Last edited: May 18, 2012
  4. May 18, 2012 #3
    From my tiny understanding:

    From my understanding you are right but the field itself does not predict the electron as it self. Classical quantum mechanics desribes very well, let's say a single electron. The interaction then is very well described in QFT with respect to SRT. The interaction, nevertheless, does not describe the particle itself.

    You have to see that we have currently 4 interactions, or 4 fields interacting: Electromagnetism, the strong force (to glue for example a neutron from quarks to a particle), the weak force (decay of neutrons is the standard example), and gravitation. Particles like protons are combined in the regime of the strong force.

    The trick is how to combine all of this forces. This is hard work if it is possible at all.

    You seem to have a misunderstanding of QM generally. Every particle is not located. You should get away from the point that there are particles kicked to the other particle. If so, an Hydrogen atom would be a billiard pool.
    See before, 4 types from our current understanding - and it is expected that there is a complete interaction. The final problem is the interaction of gravitation and quantum mechanics.

    Gravitation and QM are very far away. Gravitation is best describing long distance effects and things happening if gravitation leads to a collapse and QM is for the smallest scale you can have. Every field can be descriped in mathematical theory which is background dependent but the gravitation... This causes a lot of problems, gravitation is unfortunately not linear in any realistic case. It is easy to say that you have a particle like a "graviton" but this is not the truth because this might exist only under some conditions. So far there is no GRQM or how we should call it. GR and QM are, and this is really bitter.

    *edited* GR is mathematically totally different from QM. Where you will naturally find eigenstates and eigenvalues in QM and where you have a statistical description (this is why I personally find the term "particle misleading" - it is not a tiny sphere or so), you will have in GRT continues functions without any quantization. QM "lives" on a 4 dimensional space-time background. GRT defines the background, mass (energy) interacts not only with space-time but defines it. A last remark about combining both: There are several theories trying to combine both. From the point of view seeing everything as a field and getting away from the picture of "particles" perhaps it is worth to have a look at Loop Quantum Gravity - but I don't want to annoy the String Theory friends, I am way of an expert in both fields. */edit*
     
    Last edited: May 18, 2012
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