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There is no thing there

  1. Feb 24, 2009 #1
    There is no "thing" there...

    I want to get myself clear on sometihng fundamental, so please correct any of my thinking.

    As I understand it, an electron is a "point particle", and has no volume, ie, it occupies no space. there is no "thing" there - the "particle" is really nothing more than an expression of the EM(?) field. is that correct?

    Further, protons and neutrons are made up of quarks, which are also point particles. thus, ultimately, even for protons and neutrons, there is really no thing there either. quarks are some manifestation of some other field - is that correct?

    Photons are pure energy, they are an expression of the EM field. there is no "thing" there either.

    I assume that the remainder of bosons and leptons which make up the standard model are also entities made from point particles or pur energy of some type, such that there is no "thing" there either. is that correct?

    so, based on those comments, should every "thing" in the universe actually be thought of only as expressions of fields or the interaction of fields, rather than as actual physical objects ("things")?

    thanks.
     
  2. jcsd
  3. Feb 24, 2009 #2
    Re: There is no "thing" there...

    As you correctly stated, all particles are point-like (at least in Standard Model) and all 'things' are made of such particles.

    So when you say "rather than as actual physical objects ("things")" you are definitely saying about something, that does not exists, and you know it. Then why you call that abstraction "physical"?
     
  4. Feb 24, 2009 #3

    marcus

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    Re: There is no "thing" there...

    That seems reasonable, and you could take the quotes off and just say everything physical, like this----how would this be?:

    I would say yes. How about you? I took out the word only because it didn't seem needed.

    Physics is a mathematical science, which means you use whatever model fits best and predicts best. How you think of it is somewhat a practical matter or matter of convenience.
     
  5. Feb 24, 2009 #4
    Re: There is no "thing" there...

    It may also be emphasized that Marcus is a mathematician :tongue2:
     
  6. Feb 24, 2009 #5
    Re: There is no "thing" there...

    Thank you for the responses. Now, would one of you please explain to me what a "field" is? :-)
     
  7. Feb 24, 2009 #6

    marcus

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    Re: There is no "thing" there...

    I'd love to hear what humanino (or any of several other people) would say to this question.
    I think it is a really interesting question. What kind of mathematical object do you use to represent a field? There are several ideas.

    Think of iron filings on a piece of cardboard and holding a strong magnet underneath.
    You get a picture, the fingers of filings point in the field direction and they are longer where the field is stronger. It is like a field of grass when the wind blows. The grass shows the direction, and to some extent the strength, of the wind.

    A field is a picture (on a piece of cardboard, or in 3D space, or on some other space or spacetime) of some physically measurable quantity, like charge or force or windspeed or the probability of detecting an electron at that point, or whatever. It is a picture.

    Fields ripple. Bumps in fields can travel. Fields can interact with other fields if they share the same pair of pants, called a Lagrangian.

    Now comes something very surprising: we are used to any field being defined on a background space (the cardboard). General Relativity gives a way of representing fields without a background space. The underlying continuum is factored out and ultimately rendered nonessential. Only its geometry remains! How can the field expressing the geometry of space or space time be represented without any underlay or background? How can there be a painting without any canvas?
    This strange idea got in the door around 1915 and a lot of physicists are still working on cardboard---still using backgrounds in representing their fields. Probably it is better not to think about this. Just think of pre-GR fields----iron filings, blades of grass etc.
    The pre-GR-style field theories are very beautiful and useful. So don't think about backgroundless GR-style fields.

    But anyway what you asked is a nontrivial (almost a deep) question. What is a field? How shall we represent fields mathematically? We think that physical reality is comprised of fields ("woven" of them if that is not too definite an image) and that they are more basic than particles (particles are a way of keeping track of fields that is appropriate and works in certain contexts, but not others). So the field is absolutely basic, but what is it? How one thinks of it is somewhat a matter of personal taste. We're human, with limited understanding of what reality is made of.

    Let's see if humanino agrees. :biggrin:
     
    Last edited: Feb 24, 2009
  8. Feb 25, 2009 #7
    Re: There is no "thing" there...

    Very nice explanation Marcus, I pretty much agree with everything. Not that I really want to, but since you seem to (legitimately) press for a reaction on my part, I will add one mathematical aspect.

    If we are to answer what a field is from a physicist's point of view, although I would stress Faraday's influence in putting forward the concept, then I would have nothing more to say. But if we are to begin a reflection on the directions in which the concept of field suggests us to move, then I would point out what non-commutative geometry provides us, and this it seems to me has direct relevance to the issue of background independance.

    Although we do not have a full (non-perturbative) quantum theory of gravity, we already know that at large distances or small energies a smooth manifold describing our space-time should emerge. The concept of field we are used to is simply a (smooth, possibly generalized) function on this manifold, a scalar like a temperature, a vector like the electromagnetic potential, or the equivalent operators in the quantum versions of the theories. Indeed one challenge in formulating quantum gravity is how to get those functions without the manifold to start with, in particular how do you separate positive and negative frequencies, or how do you get the right Lorentz structures. What non-commutative geometry provides us is to be able to reconstruct all the manifold geometric properties from only the algebra of the fields defined on it. So one can start with a manifold, define the procedure to reconstruct it from the algebra of functions, make sure nothing in this procedure relies on the commutativity of the algrebra, and finally get abstract constructs which give us (for instance) non-trivial topologies in manifolds that we do not know how to obtain otherwise. The classical version of the standard model coupled to gravity has already been shown to emerge in this scheme. Please do not tell me Fermilab has falsified this approach : we also know that at the classical level, the standard model would be several hundreds of sigma away from precision electroweak measurements.

    Of course, non-commutative geometry is only another (minor, far from the most popular) approaches to those issues, and I am not qualified at all to discuss about it, but I felt, if I had something to add here, this deserved to be included. :smile:
     
  9. Feb 26, 2009 #8
    Re: There is no "thing" there...

    Just to highlight - there is no such thing as 'pure' energy. When talking of energy it has some context, namely being a property of a particle or object. Other than that - I'd stick with the above helpers ideas of fields; exceptionally helpful!
     
  10. Feb 28, 2009 #9
    Re: There is no "thing" there...

    They are MODELED as point particles, quanta, in the standard model, but as one dimensional extensions (strings) in string theory....In quantum theory, an electromagnetic wave (field) is pictured as a quanta, a particle; same idea for the Higgs boson and higgs ocean (field)...
    If you consider the double slit experiment, for example, a photon or an electron can be seen to have properties of BOTH a wave and a (point) particle.....
     
  11. Mar 13, 2009 #10
    Re: There is no "thing" there...

    doesn't everything behave as a particle and a wave , like matter waves,
    can someone explain Quantum tunneling to me in a basic way . and i was just wondering
    does time have a field.
     
  12. Mar 13, 2009 #11
    Re: There is no "thing" there...

    Having dropped a lead shielding brick on my toe (2 x 4 x 8 inches, 26 pounds), if a lead brick is purely mathematical, that is heavy math.
     
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