Are photons energy? What is energy, anyway?

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

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  1. Michael 345 New year. PRESENT is 72 years oldl Valued Senior Member

    Really??? I never would have guessed

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  3. Write4U Valued Senior Member

    I always thought that phrase meant the medium through which the energy propagates.

    Waves are a perfect carrier of all sorts of energy, as well as matter?
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  5. James R Just this guy, you know? Staff Member


    I see. Rather than admit you're wrong, you're planning on jumping ship out of the conversation. Already, you're ignoring most of the substance of my posts, while repeating your earlier errors.

    Oh, I'm being dishonest now, am I? About what, exactly?

    Look, I'll make it easier for you. Just answer yes or no to the following questions:

    1. Do you think photons are energy?
    2. If photons are energy, does that mean that energy can be photons?
    3. Do you think all mass is energy?
    4. If all mass is energy, does that mean you think everything is energy?
    5. If you don't think everything is energy, please name something physical that isn't energy (note: you've already excluded photons and matter from that list).
    6. Does energy have all the properties that photons are said to have, such as wavelength, frequency, a wavefunction, and so on?

    If you say that energy does not have all those photon properties, you need to explain how can photons can possibly be energy.

    So does all energy have a wavelength and a frequency that defines it? Does all energy have a polarisation? Does all energy have momentum?

    Again, I note that I responded explicitly to what you are re-posting. It is troll-like behaviour to pretend there was no response, and to ignore the response and then simply re-post the incorrect material. You need to stop that.

    Are you going to dispute that the Doppler effect is real, too, or put it down as an effect of gravity? Note that we observe the red-shift or blue-shift of light in contexts other than a cosmological one.

    You're still reifying energy. You can't put energy in a container. It isn't stuff that can be put in something. You can't put it in a photon. Asking "where is the energy in a photon?" is exactly like asking "where is the frequency in a water wave?" or "where's the carton that carries the electric charge of an electron?"

    I know what you said. What you said implies that all matter (all stuff with mass) is energy, along with all photons. What I'm wondering is: what is left that isn't energy, then, according to you? Is there any physical thing that isn't energy?

    If I'm not understanding what you're saying, you need to make it clear what you're saying.

    What is abundantly clear is that you keep claiming that photons are energy, and that's incorrect. Now you've also added the claim that just about everything else is energy too. Electrons are energy. Protons are energy. paddoboy is energy. That pot plant is energy. Everything is just a bundle of energy!
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  7. James R Just this guy, you know? Staff Member

    arfa brane:

    Yes, let's.

    Heat is a particular designated partition of energy, as I previously defined it. A photon is not energy, so it can't be heat.

    In the 19th century, for a long time, there was much debate as to what "heat" was. A lot of people thought it was a substance. They even had a name for it: "caloric". All those people were wrong, and now here we are in the 21st century, where some people still apparently hold the same view - a view that was well and truly proven incorrect during the 19th century.

    When people talk about a "flow" of heat, they are really talking about an energy transfer, which is nothing like the flow of a substance. Moving a number from column A to column B isn't the same as the flow of a substance.

    No it isn't. It's a flow of particles of one sort or another: photons, alpha particles, electrons, or whatever.

    Only the ones who aren't careful, or who are just wrong.

    You might need to quote him. Pardon me if I don't take your word for it.

    You're saying nothing will convince you? Then we're done here, I think. Pointless trying to argue against dogmatic views.

    No. You're confusing heat with temperature. They aren't the same thing. Like I said earlier, words have technical, precise meanings in physics. Non-physicists often conflate concepts that are distinct in physics. Case in point: confusing photons with energy.


    You need to realise that the physicist saying that is using a metaphor, whether he realises it or not. Numbers are not really absorbed.

    What happens to the photon when it is absorbed is: it disappears. What happens to its energy is that its energy is moved from column A to column B in somebody's table of energies.

    Because all of those things, like energy, are concepts. They are not "things". They are not substances.

    On the other hand, if somebody is keeping a Table of Momenta somewhere, then we inevitably find that when a photon is absorbed, the momentum associated with that photon appears as a contribution to the momentum of whatever it was that absorbed the photon. So, in that sense the momentum "persists" somewhere.

    Fundamentally, it's due to the nature of the electromagnetic interaction. By the way, in beta decay - which involves the weak interaction - W bosons appear and disappear, too, and they have mass.

    A photon's energy is related to its frequency and momentum, but if you want to invoke some kind of causation between those quantities you'll have a hard time of it. All of those things, though, are abstract quantities in the same sense. Momentum is no more a substance than energy or frequency is.

    Energy is conserved in many situations; that's a major motivation for introducing the concept in the first place. It does not follow from the fact that energy is often conserved that therefore photons are energy. They are not.

    What? I'm talking about some photons flying though space. Both the source and the photons themselves could be light years away from me. The only interaction I have is when one of those photons finally reaches me and is absorbed, at which point I notice that my motion somehow changed its energy.

    I could say a lot of things. You haven't yet said why you think it helps your argument that photons are energy.

    The following is from your reply to exchemist. I hope you don't mind if I address your questions as well.
    I know that when they say that they are glossing over the thing that is actually absorbed and emitted - usually photons.

    I understand that people say that kind of thing, but it's a bit muddled. If they want to talk about energy, they really should probably just talk about energy, and if they want to talk about photons they should talk about photons. If they want to talk about both at the same time, it would be better to say that the oscillators emit photons which have energy E=hf, or whatever.

    It comes from an electromagnetic interaction between the electron and something else - often the nucleus of an atom. For instance, an electron may change its quantum state in an atom, and one outcome of that change is the creation of a photon.

    No. It's created via the electromagnetic interaction.

    Tell us what you think electromagnetic radiation actually is.

    One thing is clear: whatever it is, it can't be energy.

    You care enough to stick to your guns, despite not being able to make any convincing argument that photons are energy.

    Initially, I thought it might make sense to you that a photon "carries" energy in the same way it "carries" momentum, or polarisation, or frequency, or any of those other properties it has. Later, I realised that the word "carries" tends to reinforce the error of reification that you keep making, so now I'm trying to reduce my usage of that form of words in this discussion. A photon's energy is not in the photon. A photon is not a container for energy. Energy is not stuff that can be contained, and it is not stuff that can be carried in the literal sense.

    I thought you were beginning to understand this new idea at one point in our discussion, but then you regressed back to your initial mistaken position. Now we seem to be at the point where stubbornness has taken over and you've stopped listening, like paddoboy did from the start.
    Last edited: Sep 5, 2019
  8. James R Just this guy, you know? Staff Member

    On the subject of where photons come from when they are emitted and where they go to when they are absorbed, one way to look at it is from the point of view of quantum field theory. In QFT, photons are excitations of the electromagnetic field, which exists everywhere in space. The creation of a photon takes place when something "shakes" the field in the right way.

    It's kind of like asking where a water wave "comes from" when it carries energy from one place to another. Suppose I throw a rock into a flat pond. By doing so, I created a disturbance in the water that then propagates outward as a water wave. If something absorbs the energy of that wave (by which I means the wave interacts with something that decreases its amplitude and therefore the associated energy value), then the wave "disappears" and we get our flat pond back again.

    To "shake" an electromagnetic field so as to create an electromagnetic disturbance that travels as a wave through the field, you usually accelerate a charged particle of some kind. Such waves can pass on energy to other charged particles.
    exchemist likes this.
  9. exchemist Valued Senior Member

    Yes that's exactly what I've being trying to explain to him, too. A photon is a travelling, wavelike disturbance in the EM field and has properties in much the same way that a water wave does, though there are obviously differences, too. One of these properties is energy. And that's it, really.

    But as he is reverting to posts a fortnight old now, in order to keep the argument going, I'm beginning to lose interest -I don't think any new points will be made. We seem to have an idee fixe from him and the usual doglike barking of support from paddo, who has smelt an argument and duly turned up to piss on a few lamp posts and further his various vendettas.

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    origin likes this.
  10. exchemist Valued Senior Member

    It means a fixed (discrete, indivisible) amount. I explained the usage of the word quantum a few posts back, but I don't expect you can remember, it, even if you have read it. I'm bored with this now.
    Last edited: Sep 5, 2019
  11. arfa brane call me arf Valued Senior Member

    That wasn't the question.

    So you don't know what a quantum of linear momentum is, or maybe you pulled it out of your ass?
    Don't be a condescending prick.
    It does make sense to me. When I see that language or read it, I do understand it. I'm not a fucking idiot you condescending prick.

    Why are you so convinced that it's wrong to say a photon is a form of energy, when clearly that's what electromagnetic energy "becomes", when as you say, an electron interacts with "the" electromagnetic field. So you might come to the conclusion that the photon is created out of the energy "in" the field.
    But you don't really know do you? That's why it's so much easier for your small brain to handle properties--a photon has properties.
    Where does it get them from, if photons are created and destroyed but energy isn't?

    Wait. Please don't bother trying to answer that.
  12. arfa brane call me arf Valued Senior Member

    Oh bullshit. That is so NOT it.

    The photon does not travel "in the EM field"; it IS the EM field, you dick.
  13. arfa brane call me arf Valued Senior Member

    Ok, EM radiation can't be energy. So confusingly, this radiation carries energy. But this energy depends on whether I'm moving towards or away from the source.

    So when an electron emits a photon, the photon isn't energy, but rather a thing that carries energy and momentum away from the electron. But this energy and momentum depends on the motion of the electron because it can be moving.

    Nah, that's not really it, sorry for trying to think like you.
    I'm still stuck on the idea that there are thousands of books and articles in the world, many of them saying something that James R informs me is wrong. Saying a photon is a form of energy like many physicists do (this includes Schrodinger and Einstein), is wrong; it's misleading . . .

    Much easier to understand the photon as a collection of properties which appear and disappear! Somehow or other.
    Last edited: Sep 5, 2019
  14. origin Heading towards oblivion Valued Senior Member

    Oh great, now a photon is not only energy it is also the EM field.
    Just when you think it can't get any worse.
  15. arfa brane call me arf Valued Senior Member

    What is wrong with these people

    Don't they realise James R and exchemist, here at sciforums, are sure that EM radiation can't be a form of heat? That would mean having to also accept the EM radiation is a form of energy (although that seems to depend on what is meant by "heat").

    Oh well.
    Last edited: Sep 5, 2019
  16. paddoboy Valued Senior Member

    James, I'm not really interested in your deliberate act of confusion. While I can't answer all your questions, that in no way somehow deems that you are are not, and remember what my only claim is...pedant, OK
    I have a busy period ahead of me so will be back in a day or two.
    You take it easy, OK and avoid that over excitement!
  17. paddoboy Valued Senior Member

    Problem is that it is condoned sadly, while others don't have the same right.
    But spot on Arfa!!!
  18. arfa brane call me arf Valued Senior Member

    Sorry about the delay.
    --Scientific American [Sep 1953].

    Alrighty then . . .
  19. arfa brane call me arf Valued Senior Member

    No, you're confusing my use of the phrase "average kinetic energy" with temperature.
    I'll see if quoting Erwin, once more, can shed some more light on what I actually meant to say:
    Temperature is a measurement of average energy (not necessarily all kinetic), distinct (because of the process of measurement) from the energy itself.
  20. paddoboy Valued Senior Member

    Two points that are adequately supported so far in this thread, according to the evidence.....
    [1] The photon definition is pedant at best, and [2] while all mass is energy, not all energy is mass.
    The rest is side tracking deliberate attempt at confusion.
  21. Magical Realist Valued Senior Member

    Last edited: Sep 5, 2019
  22. arfa brane call me arf Valued Senior Member

    My attempt at answering all 6 questions won't be limited to "yes" or "no". That would imply each question can be answered that way, which is a little presumptuous.

    Anyway: 1) Yes I do think photons are energy; that energy can be photons follows immediately if in fact 1) is describing an equivalence.

    2) Of course. Bring together equal amounts of matter and antimatter--result, lots of photons.

    3) Einstein was the first to say this. Hardly anyone believed him at the time. But yes, mass and energy are another equivalence.

    4) Well, it seems that is an inevitable conclusion; however I'm happy to exclude space and time from the "everything".

    5) What really is "something physical"? Is time physical? Do you mean something we can measure (so in some sense "proving" it's physical)? Otherwise see my answer to 5).

    6) A cricket ball has a deBroglie wavelength (hence a frequency if the ball is in motion). It has a wavefunction. That it can't be detected in large, "classical" objects is kind of beside the point.
  23. Write4U Valued Senior Member

    This is more fully explained :
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