# Are photons energy? What is energy, anyway?

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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".

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?

Let's start with the assumption that if A is a form of energy, it can be converted into B which is a different form of energy.
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:

The motion or flow of heat has long been understood as the individual motions of molecules, atoms, ions, etc. Why does a wire heat up when electric current flows through it? It's called the conversion of electrical energy into heat energy, but what actually happens, how do electrons heat metal atoms? I'm pretty sure I understand what happens.
It's great to hear that you're pretty sure you understand how electrical energy is converted into heat energy.

Please give me your brief explanation of how that happens, exactly.

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

And I explained to you before that it's necessary to fix the Coulomb potential, because you "work in" the Coulomb gauge, and fix the proton's charge (at an origin).
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.

I still see no advantage in adapting the philosophy "energy isn't stuff, energy is a number". It has physical units. Work energy is force times distance. Forces and distances are not numbers; why does their product suddenly become "just a number"?
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.

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.
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?

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.
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.

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

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?

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

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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.
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.

A photon is a quantised field. A field has energy in it--see Einstein's papers. Waves in a field carry field energy from place to place.
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.

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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".

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?

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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.

Please grow up soon.

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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.

Please grow up soon.

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

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.
(Image: © Fabrizio Carbone/EPFL)
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.

Are solids compressed waves?

Also, see that r in there? That is the distance between the proton and the electron. The fact that there is an r there tells you that this energy term is a configuration energy that has something to do with the interaction between the proton and the electron.

If you pretend the proton isn't there, you can't write down that term, and if you can't write it down then you're no longer solving the SE for hydrogen.
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?

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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.
I notice that, as time goes on, you respond to less and less of the content of my posts. Why is that?
Because it's rubbish, mostly. Ok?

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).
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.

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

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.
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 . . .

I'm just offering you some helpful advice.
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.

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Because it's rubbish, mostly. Ok?
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.

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