Are photons energy? What is energy, anyway?

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

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  1. arfa brane call me arf Valued Senior Member

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    Can we at least agree that quantum harmonic oscillators emit and absorb quanta that correspond to the difference between eigenvalues of the momentum operator?
     
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  3. exchemist Valued Senior Member

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    You are now, seemingly arbitrarily, returning to post 8 (eight) of this interminable thread, which I made on 20th August, almost a month ago. We are now at post 283.

    And now you introduce yet another red herring, in the form of Unruh radiation, a highly esoteric phenomenon for which there is so far no clear observational evidence. I suggest you get a grip of your mind.

    Energy is an attribute of a physical system, which can includes fields as well as matter. Energy is not an entity.
     
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  5. exchemist Valued Senior Member

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    Fuck off.

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  7. arfa brane call me arf Valued Senior Member

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    That you and James continue with this crap is a bit ironic.
    James R introduces a quote from Richard Feynman, from one of his lectures on physics.
    Feynman says (in the quote) nobody really understands what energy is; that's a little controversial, but he was that kind of guy, and I'm prepared to give him the benefit of the doubt. Nonetheless I want to know what he really means.

    Nobody understands what work is? maybe he didn't really mean that or something. But yeah, esoteric stuff appears on my Rindler horizon, right there. If nobody knows what the Unruh effect really is, or if we can ever test for it, does that present a problem for Einstein's field equations?

    But, we have James R to explain that James R does understand what energy is, that it "isn't stuff", although things called photons carry it around (its a property of photons, after all).
    So which is it, does nobody really know, or do James and exchemist belong to an exclusive, obviously privileged, group? Are they really human. . . ?
     
  8. arfa brane call me arf Valued Senior Member

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    So for all the dicks who don't know why in electronics, the magnetic field can be "ignored", or why, perhaps more pedantically the equations can be written in terms of electric fields only, is this I believe.

    Maxwell's equations describe a rank-2 tensor field; for an electromagnetic field to be present at a point in space, a charge must experience a force at that point in the field, there is no way around this.
    Moreover since the electric field is dual to the magnetic one, we only need consider that component of the field anywhere in a particular circuit (in which charge is conserved). So that's the one we measure (with voltmeters and ammeters) although we can also measure the magnetic potential we don't because we don't need to in general. That's less true as the energies scale, but is pretty much true for most electronics. Most electronics don't have multipoles in them either.
     
  9. James R Just this guy, you know? Staff Member

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    Maybe, but I don't see how that's in the least bit relevant to the debate, such that it is, about whether photons are energy. If a harmonic oscillator emits and absorbs photons (which it might), and those photons are the "quanta" you're referring to, then we're still no closer to settling the question about whether those "quanta" are energy or not.

    We can agree that the energy of a quantum harmonic oscillator is quantised - i.e. only certain numerical values are possible. But, again, that's beside the point.

    Why didn't you just give me a straight answer to the question I asked you, which was: do you still believe, 290 posts into this thread, that photons are energy? Well, do you?
     
    Last edited: Sep 19, 2019
  10. James R Just this guy, you know? Staff Member

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    That's a bit precious of you. You keep dancing around, going off on tangent after tangent while ignoring the central point of disagreement. Worse, you fail to even address any of the arguments against your initial claim, which I and exchemist have put to you. Your posts are starting to look like you're just stringing out the conversation because you like the attention, or something.

    It's interesting that you focus on that part of the quote. In context - and the reason why I referred to this in the first place - it is clear that Feynman is making the point that energy is merely (and I use that word ironically) a very useful conceptual, calculational concept. When he says nobody really understands what it is, I think what he means is that there's no a priori reason we'd expect this concept to be quite so useful as it turns out to be. After all, the starting point - say the definition of work - seems like an arbitrary human construct. And yet, to a large extent, nature appears to respect the concept.

    In case there's still confusion, Feynman nowhere says that energy is "stuff". You can't bottle it. You can't isolate it. There's no "pure energy". And so on and so forth, as explained over and over in the past 290 posts of this thread.

    You can't ignore magnetic fields in electronics. For example, inductors are used in electrical circuits, and they wouldn't work without magnetic fields. You can, to some extent, submerge the magnetism and talk about it in other ways, but you can't ignore it.

    When it comes to electromagnetic waves, they always come with both electric and magnetic components, and we have consistent relationships, such as: the magnitude of the magnetic field in an EM wave is always the magnitude of the electric field divided by the speed of light. We also know that light is a transverse EM wave. So, in other words, if we know what the electric field part is doing, it's always easy to deduce what the magnetic field part is doing, if we need to know that.

    More fundamentally, electricity and magnetism are two aspects of a single fundamental interaction: the electromagnetic force or field.

    But none of this has anything to do with the topic of this thread.
     
  11. arfa brane call me arf Valued Senior Member

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    I didn't say that. I said that roughly, you can write equations for say, a rotating pair of vectors, a voltage and a current. This is sufficient to calculate the response of a circuit to forced oscillations, a frequency response and a so-called power curve.

    There's nothing stopping you from using equations for the magnetic field; if you use say, a moving coil meter to measure voltages that means you aren't "ignoring" magnetic potential, right? It's just a way of saying you don't need to do both, or as you say, a circuit with inductance in it takes care of the phase say, between voltage and current for an AC input.

    And I still think the idea of energy not being "stuff" is hard to reconcile with photons that carry it around. They don't "use" energy carrying it around, right?
     
  12. James R Just this guy, you know? Staff Member

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    Do you find it equally hard to reconcile the idea that love is not stuff, despite the fact that people carry it around in their hearts?
     
  13. BdS Rattling cages since inception :) Registered Senior Member

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    Do photons have volume?
    Whats contained in that volume?
    Is a photons volume defined by its wavelength?
    Photons can be polarized so do they contain a magnetic field?
    Photons most distinct feature is their speed c, kinetic energy or motion. The motion of what though?
     
  14. James R Just this guy, you know? Staff Member

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    That's a difficult question to answer. I can't really think of any circumstance in which a consideration of the volume of a photon would be relevant. Being quantum objects, photons have inherent uncertainties in their position, momentum and energy. I guess the uncertainty in position could be interpreted as a kind of volume, in principle.

    Photons are "made" of electric and magnetic fields, or they are excitations of the electromagnetic field, if you prefer.

    That's one way you could look at it, I guess.

    Photons are light, and light is an electromagnetic phenomenon, so both electric and magnetic fields are involved. The polarisation direction, by convention, is the direction of the electric field oscillation in a light wave.

    The motion of the particle-like photon, or the motion of the excitation of the field, or the motion of the probability wave associated with the photon - whichever way you want to look at it.
     
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  15. arfa brane call me arf Valued Senior Member

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    Well I can say I find it quite hard to see what that has to do with photons. So what does it have to do with them?
     
  16. exchemist Valued Senior Member

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    I suppose one might say that the volume of a photon is defined by the spread in its wavelength: the greater the spread, the smaller the volume.

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  17. James R Just this guy, you know? Staff Member

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    Love is an idea - a concept. Energy is an idea - a concept. Ideas can be attached to objects. Love is attached to hearts; energy is attached to photons.

    Point is: love doesn't have to be a "thing" in order to be associated with something like a heart or a person who walks around the place. Similarly, energy doesn't have to be a "thing" in order to be associated with a photon that walks around the place.

    We're now almost at post #300 in this thread. The same point has been put to you over and over again in different ways. Why are you still struggling with the idea?
     
  18. Michael 345 New year. PRESENT is 69 years old Valued Senior Member

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    Really? love is not stuff - fact that people carry it around in their hearts

    love is not stuff - correct

    fact that people carry it around in their hearts - poetic but false

    Love - concept - more akin to a biochemical / electrical feeling not located to and body region

    But what would I know about reality?

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  19. Plazma Inferno! Ding Ding Ding Ding Administrator

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    ADMIN WARNING:

    Please, restrain from using inappropriate language when addressing other members.
     
  20. arfa brane call me arf Valued Senior Member

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    Ok, try this: when an electron emits or absorbs a photon, the electron's momentum changes. So for a charged particle, a photon represents a change in momentum.

    We can't see photons propagating, unlike waves on the surface of a liquid, all we can do is arrange for charged particles to absorb them. In the frame of propagating electromagnetic radiation then, we can talk about what the radiation is relative to what electrons are doing--oscillating back and forth in a broadcast antenna say.

    So this radiation represents electron momentum; without the electron matter-field, what can we say the radiation really is? How to reconcile electron momentum with a freely propagating wave, moreover, a wave that doesn't propagate in any kind of material? Or conversely, how do photons propagate like waves do and is there a displacement wave, in which case, what is displaced?
     
  21. arfa brane call me arf Valued Senior Member

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    Maybe what Feynman meant was nobody really understands why electrons can transmit and receive changes in momentum over a distance.
     
  22. exchemist Valued Senior Member

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    Incidentally, I think I know why paddo stopped posting in this thread. He got the same answer as you, Origin and I have been giving, on the dot net site: https://www.scienceforums.net/topic...ave-mass/page/3/?tab=comments#comment-1116708
     
  23. Write4U Valued Senior Member

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    Question; Do fields consist of particles or do particles emerge from disturbances in a pre-existing field?
    https://www.symmetrymagazine.org/article/july-2013/real-talk-everything-is-made-of-fields
     
    Last edited: Sep 23, 2019
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