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Dissecting the photon (Again)

  1. Jan 12, 2015 #1
    When we dissect the photon we find an electric field and a magnetic field according to Maxwell. In order to determine the propagation mechanism of a single photon through the fabric of space-time, is there an experimental apparatus designed to determine which field may plow the path, in order that the other field may follow? I am thinking of a slit/filter system for isolating individual photons, and then a thin film detection system designed to capture angstrom level fluctuations in the presence of an oncoming photon. Is there any research going on in this field? Where?
  2. jcsd
  3. Jan 12, 2015 #2


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    Theoretically speaking, a photon is the weakest possible vibration of the electromagnetic field. By this I mean that if we describe the electromagnetic field quantum-mechanically, the smallest possible nonzero excitation is defined to be a photon. In that sense it's not the photons that are fundamental, but the fields that are fundamental.

    Also, the electric and magnetic fields are inseparable from one another in the sense that they depend on one's reference frame. Classically speaking, magnetism is a force coming from a moving reference frame and can be calculated using just special relativity and the coulomb (electrostatic) force.
  4. Jan 12, 2015 #3
    While recognizing the available theory, I was wondering if anyone had tested this experimentally. We can create a B field using a moving E-field, and we can create an E-field using a moving B field. Has anyone tried to detect a slight leading edge from either one using an angstrom scale sensor?
  5. Jan 12, 2015 #4


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    Not that I'm aware of, but I don't think the technology exists yet to do so.

    To measure the individual electric and magnetic field in a light wave at visible frequencies would require a detector sensitive enough in time to measure at sub femtosecond level. Light takes about 1.6 femtoseconds to travel 500 nanometers (a green wavelength in the visible spectrum), so you'd need a much faster detector to actually track the shape of a light wave. The best detectors we have nowadays are orders of magnitude shower than this, so we'd never be able to resolve anything clearly.

    It's also useful to consider the mechanism generating the electromagnetic fields.

    Ultimately, electromagnetic waves are generated by moving charge, and no charge at rest experiences or generates a magnetic force. So a charge will have a radially outward extending electric field until it's moved, at which point it starts to also generate a magnetic field.

    In that sense, one could say the electric field precedes the magnetic field.
  6. Jan 12, 2015 #5
    Very insightful Jfizzix. Thank you. The technology may exist. An experimental detector would necessarily need to include engineering for the crystal structure of the material used for each detector. I think it is possible to collimate a photon array using optics to strike a target to make replicate data points. Also, duplicate experiments with simultaneous electric and magnetic sensing materials embedded in thin deposited/lithography layers could be arranged. Perhaps a photomultiplier would be an experimental platform if it could be created in a thin film system to amplify the result. Some experimental tuning would be necessary. Regarding the movement of charge to create the magnetic field: I believe you are thinking of a charged particle, which is not relevant to this experiment. Folks who use AC induction motors know that the E-Field leads the B-Field by 90 deg. phase. esp. due to the initial acceleration of the electrons in a wire. The point here is to dissect a photon, to find out whether the E-Field component creates the B-field at light speed, or whether the B Field component creates the E-Field. The two fields are orthogonal in 3 dimensions, but it is my heartfelt opinion that one must slightly lead, or seed the other. As a photon is excited from the valence electron, electrical energy is converted to photon energy. This fact may provide clues as to which field leads. The answer to this question can shed light on how to build a photon. So, in that light, where is research being done to answer this question?
  7. Jan 12, 2015 #6


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    There is not, because you are misunderstanding what a photon is. A photon doesn't contain an electrical and magnetic field, it's not an object that be "dissected" to find what's inside it, and it doesn't follow a path through space in the sense that you''re thinking. Perhaps most important, despite the mental image created by that word "particle", you cannot think of a photon as a small object travelling along the path of a light beam.

    If you search this QM forum you will find a number of threads discussing what a photon is and is not - I would encourage you to pay particular attention to the posts made by our science advisors. You might also try Feynman's book "QED: The strange science of light and matter", which is written to avoid the (rather daunting) math of quantum field theory.
  8. Jan 12, 2015 #7


    Staff: Mentor

    I just want to re-emphasize what Nugatory correctly said with a few points.

    First at the most basic level there is no electric and magnetic fields - there is only an EM field - and the photon is the quantum of that field. This is seen most clearly by the assumption of relativity and Coulombs law alone you get Maxwell's equations:

    But in QM what a quantum of a field is, is handled by that advanced and somewhat intimating area of Quantum Field theory. The view it gives is far from the simple idea of a photon as a particle in the usual sense.

    Actually in QFT everything, electrons, quarks, everything is a field and the particles are excitations of that field.

    The following book, at the beginner level, explains that particular view:

    I like it first because the Kindle version is dirt cheap, but also because it avoids some of the misconceptions of other approaches.

    If your math is a bit more advanced then the following is simply superb:

    But as a build up you may need Susskinfs book:

    Last edited by a moderator: May 7, 2017
  9. Jan 12, 2015 #8


    Staff: Mentor

    That's not possible because magnetic fields are simply the result of the existence of electric fields and the space-time geometry of relativity. They are really one and the same thing - the EM field. This is seen in relativity - what is a magnetic field in one frame becomes an electric field in another and conversely:

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