# Are photons energy? What is energy, anyway?

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

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1. ### arfa branecall me arfValued Senior Member

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So this whole "is a wave energy, or is it a form of energy", I think depends on the following:

Is a "wave" what the wave is made out of; water waves are "made out of water", right?
Is a "wave" what propagates in a medium, in which case it's not the medium but a state of the medium? I think that argument was settled way back in this thread.
(but, this is sciforums)

Water waves depend on water as they propagate, but the waves aren't the medium; in some sense they map a medium to itself, something like how a purely mathematical function can map a domain to itself.

And I really think the claim "energy is not stuff", should be amended to "energy is not measurable stuff, but it is physical".

3. ### James RJust this guy, you know?Staff Member

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arfa brane:

I notice that, as time goes on, you respond to less and less of the content of my posts. Why is that? Why do you ignore so much of the content, and a lot of the questions I have put to you?

You still haven't explained how it can be that a form of energy is not energy.

But now I'm interested in the mechanics of this "conversion" you speak of. For instance, you say this:

It's great to hear that you're pretty sure you understand how electrical energy is converted into heat energy.

Is there a magical flow of a glowing substance in a wire that causes it to heat up? Or what?

Your talk about gauges strikes me as a bluff, because my understanding of what a gauge is has nothing to do with assuming that the proton in hydrogen is stationary. I think it's probably safe if I assume at this point that you have no idea what a gauge is in physics. It doesn't matter for this discussion, anyway.

Force and displacement are vectors, and when you take their scalar product you get a number, which is the work (energy). This is what the scalar product between two vectors does.

But you're right. Forces and distances (displacement) are no more "stuff" that energy is. You can't bottle a force. You can't collect a distance and put it in your pocket. There's no glowing "force" substance. etc.

You think that argument was settled? What do you think we agreed about that, then? My position is that a wave is a propagating disturbance of a medium of some kind (where "medium" is defined widely enough to include things like the electromagnetic field).

Do you agree with me?

And if you do, does this not imply that waves are not energy?

The sense in which they map, as I have been trying to get you to understand, is the same sense in which a ripple maps to a pond.

Now you're moving the goalposts with the weasel word "physical". One possible interpretation of that word is that everything described by physics is "physical". But that does not imply that everything described by physics is a substance (stuff).

Are you going to respond fully to my previous posts to you, including the questions, or are you going to ignore the parts you didn't like and pretend I didn't post them?

5. ### James RJust this guy, you know?Staff Member

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P.S. Oh, and arfa brane: how are you getting on with those 20 questions? You got as far as question 4, then you stopped. What happened?

7. ### Magical RealistValued Senior Member

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You know why. I already told you why in the ufo thread. Limit yourself to one or two paragraphs per post like everybody else does.

Last edited: Sep 30, 2019
8. ### James RJust this guy, you know?Staff Member

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Your answer is that people have short attention spans and are unable to cope with more than a paragraph or two at a time? That's far too superficial. You need to consider motives.

You ought to read this thread to find out the real reason. You might find it instructive. Seeing this kind of troll-like behaviour in somebody else might help you to reflect on your own typical behaviour.

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10. ### exchemistValued Senior Member

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Read your sources more carefully. A photon is a quantisation of a field. It does not itself constitute the field. In the QFT picture, I mean.

Yes, a field has energy in it. No need to tell me to read Einstein's papers as this is what I have been saying throughout. However, saying it has energy in it does not mean it "is" energy. After all, a moving cricket ball has energy, too.

And yes, waves in a field can transmit energy: since they possess energy, move, and can be absorbed, this obviously follows.

Last edited: Sep 30, 2019
11. ### exchemistValued Senior Member

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Energy is just as "physical" as momentum, no more, no less.

That is to say, a quantity that cannot be directly measured but can be calculated from measurements, which is very useful in analysing the behaviour of physical systems.

Oh, and pass us that jug of momentum, would you, when you have a moment?

Last edited: Sep 30, 2019
12. ### James RJust this guy, you know?Staff Member

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Magical Realist:

I agree with you that certain people don't like having their ill-thought-out opinions challenged, especially when those opinions have become articles of faith for them. Therefore, they ignore and distract and engage in other diversionary tactics, rather than addressing content. Often, they get personal. They start acting like petulant children, itching for a fight. Which is exactly what you are doing, following me around the forum to have little personal digs.

Last edited: Sep 30, 2019
13. ### Magical RealistValued Senior Member

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I'm just offering you some helpful advice. It's all on you if that somehow offends you.

14. ### Write4UValued Senior Member

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This may be of interest;

Light behaves as both particles and waves at the same time, and scientists have been able to observe this duality in action using an ultrafast electron microscope. The wave nature is demonstrated in the wavy upper portion, while the particle behavior is revealed below, in the outlines showing energy quantization.
Paul M. Sutter is an astrophysicist at The Ohio State University, host of Ask a Spaceman and Space Radio, and author of "Your Place in the Universe." Sutter contributed this article to Space.com's Expert Voices: Op-Ed & Insights.

15. ### Write4UValued Senior Member

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Are solids compressed waves?

16. ### arfa branecall me arfValued Senior Member

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Just this, informs me that you don't have any real idea what I actually said about the Coulomb gauge. I said nothing about "pretending the proton isn't there", where do you get this stuff?
The Coulomb gauge you wrote down, is a way to represent the nuclear energy in the equation without redundant degrees of freedom. It isn't really an approximation, either, and that's another thing I want to ask: where do you get that from?

Last edited: Oct 1, 2019
17. ### arfa branecall me arfValued Senior Member

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• This post is confirmation that arfa brane has been trolling throughout this thread. He is officially warned, and this thread is closed.
Because it's rubbish, mostly. Ok?

18. ### arfa branecall me arfValued Senior Member

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Oh, "physical" is a weasel word? I see.
But you seem to struggle with its meaning, repeatedly.

Physical need not be a thing which is "stuff you can put in a bottle". I can put a vacuum in a bottle, the bottle has "nothing" in it, is nothing a physical thing? It has a volume, maybe that's the physical thing. Or maybe nothing isn't really empty, or something equally vague.

19. ### arfa branecall me arfValued Senior Member

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Not until you show it fixes the charge of the proton at the origin, then its quite a reasonable assumption, James.

20. ### arfa branecall me arfValued Senior Member

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But there's a professor emeritus saying the particle is its field. An electron is its field, why isn't a photon its field?
This guy apparently does know a bit of QFT . . .

21. ### James RJust this guy, you know?Staff Member

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Don't be silly.

Also, if you have no interest in the thread topic, you shouldn't be posting in it. Leave the adults to discuss the topic.

Last edited: Oct 1, 2019
22. ### James RJust this guy, you know?Staff Member

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Right. We're done here.

You are clearly trolling.

You are officially warned, and this thread closed.

The pattern of behaviour you have displayed throughout this thread is unacceptable. Please review our site posting guidelines before posting to sciforums again - especially the section on trolling.

Last edited: Oct 1, 2019
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