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No anti-photons

  1. Feb 19, 2009 #1
    I need some help in appreciating this consensus.

    We are told the following things:
    - that we have anti-electrons, anti-protons but no anti-photons.
    - that photons - or more specifically emr - have an electrical component and a magnetic component.
    - the the magnetic component of emr runs 90 degrees to the electrical component.

    So more specifically if you have an emr traveling towards you then if the electrical component is upwards at some point then the magnetic component will be 90 degrees to this.

    Now, technically 90 degrees can be either in a clockwise direction or an anti-clockwise direction.
    If it were 180 degrees - ie magnetic aspect 180 degrees to electric aspect - then there would be no question on my part.
    But it is 90 degrees - which implies in a clockwise or anticlockwise direction.

    That's fine.
    So say we have one emr with its electro moment up and its magnetic aspect 90 degrees clockwise then its magnetic effect will also be clockwise to the electric orientation.
    And if we have another emr with its electro moment up and its magnetic aspect instead 90 degrees anti-clockwise then its magnetic effect will be anti-clockwise to the electric orientation.

    So my query is that if you can have a clockwise emr effect and an anti-clockwise emr effect then why is not the clockwise emr considered to be the anti-particle of the anti-clockwise emr? Why are these two particles, which behave oppositely, considered to be the same particle?
  2. jcsd
  3. Feb 19, 2009 #2
    These are basically differences in the polarisation of the light. When anti particles were theorised you basically had a situation where you were getting particles predicted going backwards in time which is not allowed, so feynmann said well what if theyre going forward in time but with opposite charge. This turns out to be correct. So why charge? Well if you just consider conservation laws and stuff and current flow if you have a negatively charged particle going one way and you want it to go the other and say theyre the same thing, charge conservation says they have to have positive charge. Mass stays the same because it doesnt care. Changing the charge takes care of most of it, i think spin is changed too although im not sure because magnetic moment would be taken account of with the change of charge (i think).

    Anyway given that photons have no charge this doesnt come into it. A photon moving backwards in time conserves the same quantities as a photon going forwards in time, except for spin (again, im not 100% sure).

    Hope this helps
  4. Feb 19, 2009 #3
    Thanks Funky. About spin, I think the spin is opposite when the particle and anti-particle are the same way up (ie particles have up-down as well as spin) but the spin is the same when particle and anti-particle are head-to-toe; though they still remain oppositely charged. Not sure on all this but I'm sure someone else can comment and correct this for me?

    I'm not sure how polarisation would play in this as the orientations of the magneto parts would be the same in both cases; just pointing the opposite way to each other.

    I see that you're answer is that photons that are left or right are the same because they aren't localised charge particles. (Correct me if I'm taking liberties). But are you happy that clockwise and anti-clockwise photons would have an opposite magnetic effect (due to the opposite spin that you mentioned)? ie One would magnetically effect things clockwise on the electro up-rise; and the other would magnetically effect things anti-clockwise on the electro up-rise?

    And they would have this behaviour throughout their entire length.
    So doesn't that make them opposites to each other?

    Is it acceptable to say that there are leftwise photons and rightwise photons?
  5. Feb 19, 2009 #4
    Photons as light can be circularly polarized - given a twist to the left or right that propagates in time as a rotating polarized direction.
    In fact, any photon or part of this original light, is equivalently polarized in both circular (and linear) directions, time-wise, unless we measure one.

    In classical-speak, any photon is like a pendulum that can swing like a weight on a string, around a circular path, or like a pendulum that can swing linearly, in some direction, or like a pendulum that's = two pendulums swinging around each other circularly, and across and through each other linearly, until you look at its string.
    Last edited: Feb 19, 2009
  6. Feb 19, 2009 #5
    To push this analogy (which actually fits the picture except for a little thing called mass), light can be polarized along its direction of travel. The pendulum picture as far as direction, is the string; so how do you make a string pendulum move along its string? do you shorten it and tie a loop somewhere? can you make it rotate torsionally and consistently one way or the other - which is I guess what a photon polarized in the z direction is.

    The model still looks ok then; a string with a weight on it can move in 3 ways = 3 polarizations of its motion in space.
    Does light have other ways it can be, or what?
  7. Feb 19, 2009 #6
    Just to clarify things. This question is not about polarization.

    For all electromagnetic radiation, irregardless of polarization

    [tex]\overline{S}=\frac{1}{\mu} \overline{E} \times \overline{B}[/tex]

    S is the Poynting vector and defines the direction and magnitude of the momentum; or the direction of propagation.

    This is equivalent to asking, "Why is there not a complimentary,

    [tex]\overline{S}=-\frac{1}{\mu} \overline{E} \times \overline{B}[/tex]

    I think that this version of an antiphoton is an artifact of the definition of the cross product--the defined chirality of the coordinate system (x cross y = z). If spacetime were a nonorientable manifold, (like a Klein bottle) it might work.

    But this is in the particle physics folder, and the above is classical, so I guess all bets are off.
    Last edited: Feb 19, 2009
  8. Feb 19, 2009 #7
    If the photons we "see" are those formed in the sub-space matrix by cheirality in the rod structure, then any instrument we employ to detect particles of another cheirality will not register their presence.

    One might term the differences as electronic-photon and positronic-photon.

    A corresponding reversal in matter forming particles may be the basis for the dark matter that everyone is so eager to discover.

    It may be possible to detect the effects that such structures may have on observable photons via a search for the gravitational lensing that would occur but without the corresponding visible galaxies that cause the phenomenon.
  9. Feb 21, 2009 #8
    But we don't have to work with the electric and magnetic fields. The 4-vector potential of an electromagnetic field is a longitudinal wave. The physical spatial phase of the electric and magnetic fields vanishes as only a geometric convention. Though, all is not lost, if the 4-potential is found to be elements of a psuedotensor, and spacetime can turn itself inside out...but this runs off into the weeds of wild speculation.
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