Are photons energy? What is energy, anyway?

Discussion in 'Physics & Math' started by origin, Aug 19, 2019.

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  1. BdS

    BdS Registered Senior Member

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    When an electron generates a photon by a change of motion, does that mean the electron is solely responsible for generating the photon? Or, is the electron part of a system of particles and fields so when it changes its momentum the photon could be generated by the systems field interactions rather than by the single electron. Eg. The electron is interacting with the atomic system field that binds it to the system nucleus and when the electron changes momentum it affects the interaction by the electron changing its speed relative to the systems nucleus field motion/spin. A de-synchronized moving electric charge in a moving magnetic field generates? If the electron is in synchronized motion with the systems field then nothing is generated?
     
    Last edited: Sep 24, 2019
    BdS, Sep 24, 2019
    #321

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  3. exchemist

    exchemist Valued Senior Member

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    Oh absolutely.

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    exchemist, Sep 24, 2019
    #322

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  5. arfa brane

    arfa brane call me arf Valued Senior Member

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    Actually that's not a bad question. The electron's change in motion is due to an interaction with a field.
    But the electron might be a free or a bound particle; you could say that complicates things.

    Perhaps the remainder of your post is some kind of attempt at un-complicating those things?
     
    arfa brane, Sep 24, 2019
    #323

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  7. BdS

    BdS Registered Senior Member

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    For an atomically bound electron a photon transfers momentum to it and its orbital momentum changes in the system. The electron moves to an excited state? In the excited state the electrons motion becomes desyncronised from its natural orbital in the system. Because the electron is out of sync motion with the system, can the system speed the electron up or slow it down with field interaction to return it to its ground state?

    Yes a bad attempt, sorry.
     
    BdS, Sep 25, 2019
    #324
  8. Write4U

    Write4U Valued Senior Member

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    Question:
    When an atom gets excited one or more electrons jump orbit (quantum) and break atomic symmetry? Then return to ground state and the electron returns to its original orbit, creating a wave forming pulsating effect?
     
    Write4U, Sep 25, 2019
    #325
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  9. arfa brane

    arfa brane call me arf Valued Senior Member

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    Bear in mind, electrons and other "particles" of the standard model have wavelengths, they have properties like waves; so do photons.

    An electron is sometimes called a matter-field--a single electron is a field and fields "have" energy. A single photon is a field too (ignore what James R or exchemist have to say about underlying fields or what photons are, they don't seem to really understand what a field theory is).

    Electrons in orbitals are bound, they aren't free to propagate like particles. When a bound electron absorbs a photon it means the electron moves to a higher energy level (yes, that's what it's called). Synchronisation doesn't have a lot to do with this. But make lots of electrons oscillate synchronously and they emit radiation with the same frequency, somehow all the discrete packets of radiation align in a classical electromagnetic wave
    .
    Also bear in mind that a lot of the ideas are theoretical; we don't really know what field quanta "look like" because looking at them means having them interact with fields.

    One way to make electrons emit photons is by aligning them with a magnetic field; as the field strength increases, each electron gains angular momentum and eventually emits a photon. The effect here is usually called spin precession.
     
    Last edited: Sep 25, 2019
    arfa brane, Sep 25, 2019
    #326
  10. QuarkHead

    QuarkHead Remedial Math Student Valued Senior Member

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    No, it most decidedly is not
    Again no. Electrons are as far as is known fundamental particles, and photons are so by construction
    Among your many foolish comments on this site, this surely takes the biscuit. Anyway, let them speak for themselves - they may surprise me and admit you are correct(!!)
    Ah, I see I made an error above - this is your most foolish statement ever
     
    QuarkHead, Sep 25, 2019
    #327
  11. Write4U

    Write4U Valued Senior Member

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    Is this in context?

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    An illustration of the helium atom, depicting the nucleus (pink) and the electron cloud distribution (black). The nucleus (upper right) in helium-4 is in reality spherically symmetric and closely resembles the electron cloud, although for more complicated nuclei this is not always the case. The black bar is one angstrom
    (10−10 m or 100 pm).
    Classification
    Smallest recognized division of a chemical element
     
    Write4U, Sep 25, 2019
    #328
  12. arfa brane

    arfa brane call me arf Valued Senior Member

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    Who decided though, was it you?

    Actually an electron has been called a matter-field since at least the 1950s. By for example, Erwin Schrodinger. So I think you're wrong.
    But by all means provide some evidence that I'm wrong. That would also be evidence that a photon isn't a field.

    Otherwise please stop making yourself look silly.
     
    arfa brane, Sep 25, 2019
    #329
  13. arfa brane

    arfa brane call me arf Valued Senior Member

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    But what is a fundamental particle?

    I find it hard to believe that there are still people who don't know what the answer is. The answer as far as I've been able to figure, is that there are no particles, only fields.
    How else do you explain that almost any kind of "particle" including molecules, behaves identically in a 2-slit experiment?

    This supports the notion that quanta are in fact, continuous wavelike objects. Continuity at a boundary is important, but you possibly already know that too?

    And the 2-slit experiment, as an example of "looking at" field quanta, says that they have to interact with fields as I stated earlier. Unless, that is, one supposes the quanta don't interact with either slit?
     
    arfa brane, Sep 26, 2019
    #330
  14. Write4U

    Write4U Valued Senior Member

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    deleted for fear of "demerits"
     
    Last edited: Sep 26, 2019
    Write4U, Sep 26, 2019
    #331
  15. exchemist

    exchemist Valued Senior Member

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    Er, no, I am not going to surprise you in this regard.

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    Seems to me he is now confusing a field with a disturbance in a field. But I do not pretend to have studied QFT, so I am sitting this one out.
     
    exchemist, Sep 26, 2019
    #332
  16. arfa brane

    arfa brane call me arf Valued Senior Member

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    From an author who is also a professor emeritus (does it matter where?):

    --https://arxiv.org/ftp/arxiv/papers/1204/1204.4616.pdf

    I note this guy says the Schroedinger eqn is a field eqn. That makes sense if it defines a field.
     
    arfa brane, Sep 26, 2019
    #333
  17. James R

    James R Just this guy, you know? Staff Member

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    arfa brane:

    Yes. It's essentially just a convenient way of carving up energy into conceptual categories. It's like making a table titled "Energy" and then having columns labelled "kinetic energy", "gravitational potential energy", "chemical energy", "heat energy" etc. It helps with the accounting system if you categorise things.

    As an analogy, consider actual accounting, with money. There are "debits" and "credits", for instance, and "balance" and other things. But all of those are columns in somebody's ledger. They are all, conceptually, money. Or - better - they are all ways to keep a count of money. They are not the same as little green bank notes.

    I agree that heat is energy. In fact, I explicitly defined it as such, earlier in the thread.

    It depends on the context, I guess. I would suppose that the "zero point energy" of a field would be lowest possible value of the field's energy, or something like that.

    How does a field have energy? The same way anything has energy. We assign a value to the energy, and specify a method for calculating that value.

    No.

    Neither quantum oscillators, nor any photons they might emit or absorb, are energy. Energy isn't "stuff". Getting it yet?
     
    Last edited: Sep 26, 2019
    James R, Sep 26, 2019
    #334
  18. Write4U

    Write4U Valued Senior Member

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    This is strange. I have read several analyses like;
    OK so far?
    But then;
    https://physics.stackexchange.com/questions/496608/instantaneous-quantum-features

    (p.s. this was the basis for my original assumption that quantum is restricted to "c".)
     
    Write4U, Sep 26, 2019
    #335
  19. James R

    James R Just this guy, you know? Staff Member

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    Really? By whom?

    No. You're mistaking the ripple in the pond for the pond itself.

    For somebody who has not managed to grasp a simple point in over 300 posts, it definitely takes some chutzpah to start claiming that the people who have been patiently trying to educate you don't know what we're talking about. Apart from the arrogance, it's disrespectful, especially since you haven't shown that a single thing either of us has said is incorrect, so far.

    Pull your head in.

    I can see why you're confused about such statements. An electron, of course, does not exist in some abstract world of energy levels. It is a physical particle. Saying that it "moves to a higher energy level" is just shorthand for saying that its energy increases, so that it ends up with a higher energy. It's a metaphor. Unfortunately, you've fallen into the trap of thinking the metaphor is a description of "stuff". (*)

    Hold that thought! Now, apply it to the idea of "energy".

    ----
    (*) We could, of course, go one more step and start talking about the ontological status of the electron itself. But, given the difficulties with energy, this is likely to be way above the current level you're operating at.
     
    James R, Sep 26, 2019
    #336
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  20. James R

    James R Just this guy, you know? Staff Member

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    Let's look in a bit more detail about what that guys says, shall we?

    A benefit of QFTs is that quanta of a given field must be identical because they are all excitations of the same field, somewhat as two ripples on the same pond are in many ways identical.​

    Note: quanta are like ripples in a pond. They are not the pond. They are the ripples.

    When a field changes its energy by a single quantum, it must do so instantaneously, because a non-instantaneous change would imply that, partway through the change, the field had gained or lost only a fraction of a quantum. Such fractions are not allowed because energy is quantized. Field quanta have an all-or-nothing quality.
    ​
    Unfortunately, for the uninitiated, it is possible to get the impression that the energy quanta he is talking about here are the same thing as the field quanta. They are not the same thing. The first two sentences talk about what happens to the energy associated with the field. The last sentence talks about the excitations of the field itself, which are a different thing.

    The QFT language of creation and annihilation of quanta expresses this nicely. A quantum is a unified entity even though its energy might be spread out over light years--a feature that raises issues of nonlocality intrinsic to the quantum puzzle.
    ​
    Here, he talks about the field quanta again, not energy quanta.

    "Fields are all there is" should be understood literally. For example, it's a common misconception to imagine a tiny particle imbedded somewhere in the Schroedinger field. There is no particle. An electron is its field.
    ​
    An electron is its field, in the sense that it is an excitation of a field. The electron is a ripple in the pond that is the electron field.

    ---
    The take-away message here, for the purposes of this thread, is that, once again, nothing here says that field quanta are energy, or that energy quanta are the same thing as field quanta, or that particles are energy, or any of that rubbish.
     
    James R, Sep 26, 2019
    #337
  21. exchemist

    exchemist Valued Senior Member

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    Absolutely.

    A footnote on the electron energy level business:-

    When an electron in an atom absorbs a photon, it moves to different atomic orbital. That orbital has (not is, has) a higher energy than the one it was in before. Energy levels are thus indeed not "things" but a way of representing graphically the energy of atomic orbitals. The entity is the electron in a particular orbital state, and the energy is one of its properties...along with angular momentum, phases, nodes etc. Rather like a photon, in fact.

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    exchemist, Sep 26, 2019
    #338
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  22. arfa brane

    arfa brane call me arf Valued Senior Member

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    --https://en.wikipedia.org › wiki › Matter
    --https://www.ribbonfarm.com › 2015/08/20 › qft
    --https://en.wikiquote.org › wiki › Unified_field_theory

    Just a handful. Don't please point out that none of the three links are from universities, or even google books. I have a university-approved textbook that uses the term too.
    A matter-field, and a matter-wave are (somewhat confusingly) synonymous in QFTs.
     
    arfa brane, Sep 26, 2019
    #339
  23. arfa brane

    arfa brane call me arf Valued Senior Member

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    And you appear to have fallen into the trap of thinking you understand QFT, and what energy means in that context. Energy is definitely not a metaphor.
    You're saying I pay a monthly power bill, but it's a metaphor?

    Plus, you seem very keen to leap to the conclusion that I'm confused (!?), whereas I think that's exactly what you are.
     
    arfa brane, Sep 26, 2019
    #340
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