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Is the quantum field an aether?

  1. Mar 12, 2006 #1
    Hi,

    I don't understand: On the one hand with special relativity Einstein
    got rid of the aether - the medium which electromagnetic waves use to
    travel and which can be used as an absolute reference system. On the
    other hand in quantum field theory quantum fields are invented which
    fill all space and which are the "medium" for particle waves. Isn't
    this reinventing the aether? In what way is this 'aether' bettern than
    the one Einstein got rid?

    Thanks for help,
    Pedro
     
  2. jcsd
  3. Mar 13, 2006 #2
    On Sat, 11 Mar 2006 ptamirez@yahoo.co.uk wrote:

    > Hi,
    >
    > I don't understand: On the one hand with special relativity Einstein
    > got rid of the aether - the medium which electromagnetic waves use to
    > travel and which can be used as an absolute reference system. On the
    > other hand in quantum field theory quantum fields are invented which
    > fill all space and which are the "medium" for particle waves. Isn't
    > this reinventing the aether? In what way is this 'aether' bettern than
    > the one Einstein got rid?


    Why bring quantum field theory into it? Even in classical field theory,
    the electromagnetic field fills all space and time, and is the "medium"
    for electromagnetic waves. Now, recall that the electromagnetic field is
    simply a function of time and space that tells you the field at a given
    point at a given time, and _can be equal to zero_ over some space and
    time. Can you really call something that can be equal to zero somewhere a
    "medium"? Recall that electromagnetic waves are essentially perturbations
    of this field from zero. When there is no wave (or static field) there,
    there is noting there except for a mathematical entity. No energy, no
    momentum, basically nothing. Hardly a medium in the sense that
    aether/ether was intended.

    That said, Pauli and other writers have used "ether" as a synonym for
    electromagnetic field.

    The advantage that such an entity has over the earlier material medium
    ether is that (a) it doesn't result in the various difficulties that came
    out of material medium ether theories and (b) it doesn't leave a material
    medium that we have to explain the properties of.

    --
    Timo Nieminen - Home page: http://www.physics.uq.edu.au/people/nieminen/
    E-prints: http://eprint.uq.edu.au/view/person/Nieminen,_Timo_A..html
    Shrine to Spirits: http://www.users.bigpond.com/timo_nieminen/spirits.html
     
  4. Mar 13, 2006 #3
    No, it's not. Quantum field is just a mathematical way of describing
    reality. It has the same status as the wavefunction, or probability
    distribution in statistical mechanics.
     
  5. Mar 13, 2006 #4
    ptamirez@yahoo.co.uk wrote:
    > Hi,
    >
    > I don't understand: On the one hand with special relativity Einstein
    > got rid of the aether - the medium which electromagnetic waves use to
    > travel and which can be used as an absolute reference system. On the
    > other hand in quantum field theory quantum fields are invented which
    > fill all space and which are the "medium" for particle waves. Isn't
    > this reinventing the aether? In what way is this 'aether' bettern than
    > the one Einstein got rid?


    It is just better defined. In a way, the classical background field
    (also termed the 'vacuum', or more neutral a 'coherent state' or -
    in quantum gravity - a 'Hadamard state') around which the quantum
    field is expanded into excitation modes (photons, gravitons, etc.)
    is the modern equivalent of the aether.

    However nobody uses the term since it it fraught with misleading
    connotations, and not really needed.

    See the entry ''What happened to the aether?'' in my theoretical physics
    FAQ at
    http://www.mat.univie.ac.at/~neum/physics-faq.txt

    Arnold Neumaier
     
  6. Mar 13, 2006 #5
    Hi Arnold,

    great, your FAQ answered my question fully. Congratulations for this
    very nice web page!

    Thanks.
    Pedro



    Arnold Neumaier wrote:
    > ptamirez@yahoo.co.uk wrote:
    > > Hi,
    > >
    > > I don't understand: On the one hand with special relativity Einstein
    > > got rid of the aether - the medium which electromagnetic waves use to
    > > travel and which can be used as an absolute reference system. On the
    > > other hand in quantum field theory quantum fields are invented which
    > > fill all space and which are the "medium" for particle waves. Isn't
    > > this reinventing the aether? In what way is this 'aether' bettern than
    > > the one Einstein got rid?

    >
    > It is just better defined. In a way, the classical background field
    > (also termed the 'vacuum', or more neutral a 'coherent state' or -
    > in quantum gravity - a 'Hadamard state') around which the quantum
    > field is expanded into excitation modes (photons, gravitons, etc.)
    > is the modern equivalent of the aether.
    >
    > However nobody uses the term since it it fraught with misleading
    > connotations, and not really needed.
    >
    > See the entry ''What happened to the aether?'' in my theoretical physics
    > FAQ at
    > http://www.mat.univie.ac.at/~neum/physics-faq.txt
    >
    > Arnold Neumaier
     
  7. Mar 17, 2006 #6
    ptamirez@yahoo.co.uk wrote:
    > Hi,
    >
    > I don't understand: On the one hand with special relativity Einstein
    > got rid of the aether - the medium which electromagnetic waves use to
    > travel and which can be used as an absolute reference system. On the
    > other hand in quantum field theory quantum fields are invented which
    > fill all space and which are the "medium" for particle waves. Isn't
    > this reinventing the aether? In what way is this 'aether' bettern than
    > the one Einstein got rid?


    The ether was sidestepped, because the geometry went from rotationally
    invariant, to Lorentz invariant. The Laplace operator went over to the
    wave operator, and so propagation was built into the geometry, and did
    not require a factitious cause. The ether is thus an artifact of
    contracting the Lorentz group by letting c->infinity. The lost symmetry
    is assigned to the "stiffness" of the vacuum. See here:

    http://www.physics.gatech.edu/people/faculty/finkelstein/Emptiness031215.pdf

    http://arxiv.org/abs/hep-th/0106273

    -drl

    -drl
     
  8. Mar 17, 2006 #7
    Roman Werpachowski wrote:
    > No, it's not. Quantum field is just a mathematical way of describing
    > reality. It has the same status as the wavefunction, or probability
    > distribution in statistical mechanics.
    >

    All of modern theoretical physics is just a mathematical way of
    describing reality. However, assigning some mathematical features 'more
    reality' than others can only be done on either experimental or
    philosophical grounds neither of which have their grounding in the
    formalism itself.

    Dirk
     
  9. Mar 26, 2006 #8
    ptamirez@yahoo.co.uk wrote:
    >I don't understand: On the one hand with special relativity Einstein
    >got rid of the aether - the medium which electromagnetic waves use to
    >travel and which can be used as an absolute reference system. On the
    >other hand in quantum field theory quantum fields are invented which
    >fill all space and which are the "medium" for particle waves. Isn't
    >this reinventing the aether? In what way is this 'aether' bettern than
    >the one Einstein got rid?


    This reply, in full (below), originally intended for someone else, is
    eminently suitable here.
    Some of what follows is discussed in greater depth in the "Yang-Mills
    Equations in Maxwell Form" article in http://federation.g3z.com/Physics
    where more detailed cited from Maxwell's treatise are provided.

    The reply to follow:
    > Bilge said: The causal structure of spacetime is determined by the
    > geometry.
    >
    > I'm getting confused. What really is an ether?


    Aether.

    The causal structure of spacetime is determined by the constitutive
    relations of the electromagnetic field. For Minkowski spacetime they
    are:
    D = epsilon_0 E; B = mu_0 H.
    For Galilean spacetime they would be (to use Maxwell's "G"):
    D = epsilon_0 (E + G x B); B = mu_0 (H - G x D)
    where "G" would indicate the velocity relative to a certain
    distinguished frame where wave propagation is of equal velocity in all
    directions.

    > What is your understanding of ether?


    A lot of it is historical revisionism and mythology built up by people
    who never read the originals (much less, transcribed and copy-edited
    them, as I have done).

    Maxwell never talked about any "aether". Instead, the central premise
    of his theory was that the vacuum was a dielectric capable of
    charge-screening, vacuum polarization, with a non-trivial relation
    between (D,H) and (B,E) holding, particularly, in the close vicinity of
    point-like and line-like sources. He believed that infinities in the
    classical field theory are avoided because the vacuum polarizes near
    such sources, thus leading to a distinction between "bare" and
    "dressed" charges (which, in turn, he briefly discussed in Chapter 1).
    All of this eventually came to be adopted as the central features
    (after the 1940'/s) of what came to be known as renormalization theory.

    His relations were the Galilean invariant ones above (as far as any
    relations were set out explicitly); not the Lorentz relations.

    It's because Lorentz relations were found to hold in all frames, that
    you no longer see the "G" in the alphabet soup comprising Maxwell's
    nomenclature (A, B, C = total current = J + dD/dt, D, E, F = force
    density, (G), H, I = magnetization, J).

    The biggest misconception cast, in the way of historical revisionism,
    was that relativity did away with an *otherwise equivalent* "aether"
    theory. What it did away with is NOT equivalent -- it did away with the
    "G" and the Galilean invariant relations posed above, which Maxwell
    originally surmised. The difference between the Lorentz and Galilean
    relations *is* the difference between Minkowski and Galilean spacetime.
    And the instant you write down (D = epsilon_0 E; B = mu_0 H), you're in
    Relativity, not Galilean physics.
    So, Relativity began (whether its participants realized it or not) as
    soon as the G was dropped and (what are today known as) Maxwell's
    equations were first written down .. after Maxwell died.

    ... which gets back to the original point: the constitutive relations
    determine the causal structure of spacetime; in particular,
    distinguishing causal structure of Galilean spacetime from that of the
    Minkowski spacetime; distinguishing Galilean relativity from Poincare
    relativity.

    The punchline comes at the very end ... in the presence of point-like
    sources, *no* linear relations can hold between the (D,H) and (B,E)
    fields. For a singularity in the sources (rho, J) mean a singularity in
    (D,H) via the relations (div D = rho; curl H - dD/dt = J). In the
    presence of a linear relation that would entail a singularity in (E,B),
    which would make the force law (F = rho E + ...) ill-defined --
    contradiction. Therefore, a linear (D,H) vs. (E,B) breaks down near
    point sources.

    Given the foregoing, about constitutive relations reflecting the causal
    structure that nature already puts there, this is then a clear
    indication that the causal structure, itself, breaks down near
    point-like sources and is being reflected as such by the break down of
    the linear relations between (D,H) and (B,E).
     
  10. Mar 31, 2006 #9
    Given that the classical doesn't really define or accept aether, it's like giving a mathematical equation to the existence of a cat.


    :wink:


    Before saying if there is or is not an aether, science must first understand what, if any, particles and/or mechanisms are appearing as "the aether". Only then, can you deny or accept its possibility. The classical knowledge base with the experiments, so far, are based on not knowing what light really is, not knowing what magnetism really is, and not knowing what gravity really is. Absolute defining, by equations and by tests of something that is still unknown, is still only speculation or theory.



    So, "Is the quantum field an aether? "-----, if you want a 'true' answer---

    ---it is presently unknown
     
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