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Why the Photon?

  1. May 16, 2007 #1
    A simple question but one I personnaly find difficult.

    Why do we need a photon to mediate the electromagnetic force?
     
  2. jcsd
  3. May 16, 2007 #2

    chroot

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    Because mediating it with pasta would seem awkward?

    - Warren
     
  4. May 16, 2007 #3
    :rofl: :rofl:
    That was a good one! :biggrin:
     
  5. May 16, 2007 #4
    I thought frogs might have been more appropriate. At least they make quantum leaps.
     
  6. May 16, 2007 #5
    My reason for asking this question was that four fold manifolds seem to come in two varieties.

    Riemann and Pseudo-Riemann

    The observed properties of light gives contradictory characteristics for Riemann geometry.

    And the photon seems an unnecessary requirement in pseudo-Riemann geometry.

    It just seems an idea founded historical convenience?

    Pasta would do the job equally well and a least spaghetti is consistent with string theory.
     
  7. May 16, 2007 #6
    Welcome to the forums
    Now i dont know whether you are talking about topological manifold or a smooth manifold. But see photon is an elementary particle now the definition itself says that it is elementary.
    Now if we put your logic in physics than there would be various discrepancies.for eg graviton is a virtual paritcle than whats the use of having it and so on...
    I hope that i have not misunderstood your queation.:smile:
     
  8. May 16, 2007 #7
    I’m particular interested in the Pseudo-Riemann manifold where the contracted Riemann-Christoffel tensor vanishes. This is the event arena of general relativity where the geometry is locally modelled on the Minkowski metric.

    Accepting the validity of relativity then a four-fold Riemann space-time must be rejected as the event arena for the physical world. We are left with the Pseudo-Riemannian Space-time.

    My question is how does the photon (and the graviton) fit into such an event arena.

    My feeling is, historically, these particles were initially invented to explain action at distance at a time when the geometry world was falsely thought to be Riemannian in nature. Riemannian Geometry being locally modelled on Euclid.
     
  9. May 16, 2007 #8

    Mentz114

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    Only if you quantise the EM field do you need a mediating boson. The photon is not a requirement in classical electrodynamics.

    In which case spaghetti hoops are probably most appropriate.
     
  10. May 17, 2007 #9
    I don’t think you have any choice in the matter; classical electrodynamics cannot describe the behaviour of the atom.

    You are not addressing my question of; why the mediator of electromagnetism should have an existence independent of other quantum mechanical systems?
     
    Last edited: May 17, 2007
  11. May 17, 2007 #10

    Mentz114

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    I don't understand. There is a debate about whether photons exist in the way other fundemental particles do. Some people will say they don't exist at all. It is a somewhat fuzzy area.

    Nobody really knows 'why' anything is the way it is.
     
  12. May 17, 2007 #11

    ZapperZ

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    This is a very strange question. It's like asking "why does an object needs a force to make it move or accelerate?".

    In QFT, you START with such field, the same way you make those 3 Newton Laws of motion. From there, you verify that they are correct based on observation.

    Now as for having "an existence independent of other quantum mechanical systems", I have no idea what you mean by this considering that the quantum field is a "quantum mechanical system".

    Zz.
     
  13. May 18, 2007 #12
    In general relativity there is no gravitational force, objects just follow geodesic paths through pseudo Riemannian space-time.

    Newton’s laws of motion are a set of rules used as the basis of a methodology which we use to make predictions about the motion of objects relative to a given reference system.(Given the ability to measure the location of objects relative to the reference grid). What underlies the nature of a force is unknown.

    In quantum mechanics the methodology is modified by the Born rule so that the probable outcomes (observable macroscopic effects) of experimental set-ups involving quantum entities can be predicted.


    Again the concept of a quantum field is an object used in our methodology, whether or not it has any physical reality is unknown and the assumption that it is a quantum mechanical system is perhaps premature.
     
    Last edited: May 18, 2007
  14. May 18, 2007 #13
    I don’t know whether LorentzR is theorist but he is mentally prepared to work in QG or to discuss interpretations.

    Regards, Dany.
     
    Last edited: May 18, 2007
  15. May 18, 2007 #14

    ZapperZ

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    So? Isn't it the same thing with QFT? You replace the classical "field" with a quantum "field". Same thing! Now you no longer have "forces", but rather an interaction via the exchange of a carrier.

    You are not making your case any better here. It seems that you are equating the two, which then begs the question on why you haven't started another thread titled "Why the Force?".

    It HAS a physical reality - the experimental observations (and there's tons of them) indicate that to be so. Why are people ignoring that fact? Is empirical observation THAT despised and irrelevant?

    Zz.
     
  16. May 18, 2007 #15
    Zz, come on! Not everyone that visits PF is a physicist.
     
  17. May 18, 2007 #16

    ZapperZ

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    What? Not being a physicist gives one the permission to ignore experimental observations? Can you dumb down the rules a little bit more here so that we can move this over to the philosophy forum?

    Zz.
     
  18. May 18, 2007 #17
    No. I think the rules are fine, just what they are supposed to be. It should be some kind of the dynamical equilibrium, otherwise or we move over to the philosophy forum or will remain alone.

    I think peoples are not in general ignoring the experiment, they don’t know that it exists and substitute the objective knowledge by subjective imagination. In addition, we have the moderators which are the control feedback loop to maintain the system alive.

    Regards, Dany.
     
  19. May 18, 2007 #18

    ZapperZ

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    But was exactly what I was doing, as a Moderator - pointing out experimental evidence that has been ignored in all of this. You somehow think that not being a physicist is a valid excuse for not considering it. I don't buy that.

    The whole existence of PF that distinguishes it from the gazillion other physics forums IS the higher standards and quality that we asked for in these discussions. Pointing out the obvious omission of experimental observations, in my book, is crucial because it is what distinguishes physics from philosophy. For some odd reason, you are allowing and even excusing such an omission

    Zz.
     
  20. May 18, 2007 #19
    I agree with everything you wrote (here).

    I also accept the existing reality.

    Regards, Dany.
     
  21. May 21, 2007 #20
    Pardon my scepticism but I find it difficult to visualise any experiment that can prove the existence of the photon. My understanding is that to gain any empirical information regarding the nature of the quantum world , you must first have any experimental set up which has some form of detector that will macroscopically respond (to be observable) to microscopic events in some meaningful way that will tell us something about the state of a quantum system (observables). Exactly what is happening at a microscopic level is open to conjecture, but no one can say for certain what determines the outcome of any experimental procedure.

    Quantum mechanics will predict with “100%” accuracy the probable outcomes of an experimental setup but tells us nothing about what is happening within the experimental set-up prior to the macroscopic response.

    Empirical observation, is vitally important since it informs us of the macroscopic behaviour of the physical world and gives us the information to confidently make predictions that will help us control our environment and ultimately improve the lot of humanity.

    It is the misinterpretation of the observations or the assumption of certainty about unproven theory that is despised and irrelevant!
     
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