# Are photons energy? What is energy, anyway?

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

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

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I certainly poked fun at certain attitudes you display in some of your posts, and I guess you could regard that as a personal attack of sorts. I'm sorry if I hurt your feelings, but I make no apology for pointing out certain truths such as: the mere fact that somebody does not agree with you doesn't mean they have evil ulterior motives driving an "agenda" to tell lies.

You are prone to playing the man rather than the ball at times. It's a bit rich to get all upset when somebody like me merely highlights your tactics.

Well, as you know, I have, on several occasions, moderated you for making personal attacks on other posters. As a general rule, I do not moderate people who make personal attacks on me while I am in a vigorous disagreement with them in a thread, because to do so would look at best churlish and at worst like an abuse of power.

Is this where I'm supposed to congratulate you?

Always good to get feedback on how I'm progressing.

Repeating yourself doesn't actually strengthen your argument, such as it is. I've written quite a lot more in my posts subsequent to where I first commented on that quote.

3. ### arfa branecall me arfValued Senior Member

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--https://chem.libretexts.org/Bookshe...re_of_Atoms/6.2:_Quantized_Energy_and_Photons
See what I quoted there? A photon is the gauge quantum (particle) of the EM field. It's a packet (a wavepacket) of quantized energy. That's commonly used language, sorry, but it just is.

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Again at the risk of repeating myself [which I'll continue to do as long as necessary] this whole shemozel was simply some "cock waving" exercise by one or two, or three, to inflate there own egos when obviously as has been shown, this is nothing more then an application of pedant.
"Electromagnetic radiation, in classical physics, the flow of energyat the universal speed of light through free space or through a material medium in the form of the electric and magnetic fields that make up electromagnetic waves such as radio waves, visible light, and gamma rays."
And supplementary, a photon can take the guise of any part of the EMS/EMR, and the energy associated with any guise of that photon, depends entirely on the frequency and/or wavelength.
:::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::
https://en.wikipedia.org/wiki/Photon_energy
"Photon energy is the energy carried by a single photon."
So what part of the photon is not actually part of this energy that it is said to carry? Or to use James' childish analogy, what part of the photon is the bucket and what part is not the bucket?

And to continue the definition from that link on what a photon is.....
"The amount of energy is directly proportional to the photon's electromagnetic frequency and thus, equivalently, is inversely proportional to the wavelength. The higher the photon's frequency, the higher its energy. Equivalently, the longer the photon's wavelength, the lower its energy."
So again [yeah yeah I'm repeating myself, sorry James] what part of the wavelength is not a part of what constitutes the photon, and/or what part of that wavelength constitutes the energy that it carries?

Last edited: Aug 31, 2019

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As I keep saying, this is simply an exercise in pedantry by would be's if they could be's, and some support for troubled mates.
"The amount of energy is directly proportional to the photon's electromagnetic frequency and thus, equivalently, is inversely proportional to the wavelength. The higher the photon's frequency, the higher its energy. Equivalently, the longer the photon's wavelength, the lower its energy."
The photon, the wavelength, the frequency are all part and parcel of what makes up the photon and the energy that is...while certainly a photon can be said to carry energy, so to can it be said that a photon is energy.
Those that continue to stringently disagree, are effectively saying that the magnetic field isn't what's responsible for magnetism.
"Photon energy is the energy carried by a single photon." [WIKI]
So what part of the photon is not actually part of this energy that it is said to carry? ..... what part of the photon is the bucket and what part is not the bucket?

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

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arfa brane:

Still flogging that horse?

"As the frequency of electromagnetic radiation increases, the magnitude of the associated quantum of radiant energy increases."​

Now, that's a careful statement, but it doesn't say what you think it says. Here's how you interpret it:
First thing to notice is that the quote you're referring to doesn't say the photon is a "packet of energy". That's your interpretation, not what it says.

Second, there's no such thing as "a wavepacket of energy" (quantised or otherwise). That's another thing you've inserted in there that isn't any part of what you quoted.

Third, I note again your appeal to "common usage", as if that determines what is correct or true. Like I said before, it's not my fault if lots of people get it wrong, including some textbook writers. It doesn't make them any more correct just because there are other wrong people keeping company with them.

So, how about we look at what that quote actually says, now?

It talks about "the magnitude of the ... quantum of radiant energy". "Magnitude" is a fancy word for size, so it's talking about the size of the "quantum of radiant energy". The word "quantum" in this context means something like "fixed amount" or "discrete amount". To give another context, lawyers often refer to the "quantum of damages" or similar, to refer to the discrete amount of money that somebody is liable for.

So, the quote is talking about the size of the fixed amount of radiant energy associated with a photon of a particular frequency.

But the really important word in that quote - the smoking gun - is the word "associated". This "quantum of radiant energy" is associated with the photon. That implies that the "quantum of energy" is not the photon itself, but is a property of the photon (i.e. associated with it).

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

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No. It's an exercise in refusing to change your mind even when you've convincingly been shown to be wrong, in many different ways.

This is muddled.

Energy cannot take the "form of electric and magnetic fields". Energy is a number. Electric and magnetic fields are fields. You can't turn a number into a field, or vice versa, no matter what you do. Similarly, electromagnetic waves are waves, not numbers. You can make a wave in electromagnetic fields (or a wave "of" EM fields, if you prefer), but you can't make a wave in energy. There's no such thing as a wave of energy.

EM waves have an associated energy, and it can be useful to think of them transferring energy from one place to another, but we must be wary of falling into the trap of thinking that the energy is like a substance (or "stuff") carried by the wave. It is nothing of the sort.

"Carried by". Which implies that the photon carries the energy, not that it is energy.

The spin, the frequency, the polarisation, the particle-like nature, the wave-like behaviour, the wave-packet, ... and so on and so forth. Basically, any of the other properties that photons have apart from energy.

Note the wording. In reference to the photon, there is talk of "its energy". In other words, energy is something the photon possesses, not something the photon is. It really can't get any clearer than this.

The wavelength, like the energy, is a property of the photon. It would be just as nonsensical to say "photons are wavelength" as it is to say "photons are energy". Do you think photons are wavelength, paddoboy? Or do you think they have or possess a wavelength?

As to your second question, no part of the wavelength constitutes the energy, because wavelength is not energy and energy is not wavelength. A wavelength is the length of something; we might measure it in metres, for instance. Energy, on the other hand, is measured in Joules. 1 metre is not the same as 1 Joule. If they were the same, we wouldn't need two different units.

As I have shown over and over again, you two are wrong and I am correct. Call me pedantic as much as you like. If I'm pedantic, at least I'm also right. I'd rather be pedantic and right than where you are, stuck in the Land of Wrong with your heads in the sand.

I can be said to carry a sandwich, so it can also be said that I am a sandwich. Er... no.

Last edited: Sep 3, 2019
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I could very well say the same about you, and a familiar agenda re-enforcing that. I have given links, showing at best you are wrong, and at worst it is pedant [or is that pedantry.
Yes, you need to do better.
So what part of the photon is not energy? That question has been asked at least three times now.

The wavelength and frequency are part and parcel of what makes up the photon. Nice pedantry again James.
You have as far as I can see deliberately misinterpreted that or just failed to understand.
Take it easy....calm down, the excitement may not be good for you!

Yeah another invalid analogy James. But I'll humour you and ask again, if the photon is strictly said to be the carrier of energy [like lollies in a bag] what part of the photon is not energy?

Last edited: Sep 3, 2019

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https://energyeducation.ca/encyclopedia/Photon
"A photon is a particle of light which essentially is a packet of electromagnetic radiation"
https://www.livescience.com/38169-electromagnetism.html
"Electromagnetic (EM) radiation is a form of energy that is all around us and takes many forms, such as radio waves, microwaves, X-rays and gamma rays. Sunlight is also a form of EM energy, but visible light is only a small portion of the EM spectrum, which contains a broad range of electromagnetic wavelengths"

So much for the smart arse pedants!!

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Let me help to lighten the load for you somewhat James.....
If I was a teacher in a science class, and a student answered that a photon is a carrier of energy....I would mark him correct. If another student answered that a photon is a packet of energy, I would also mark him correct. You see? That's what is meant by pedantry James. Both are correct, both are often answered that way, and to say one is wrong is pedantry [did I get that pedantry right?

]

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

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*sigh*

And answered, explicitly, in my post #81. You just ignored my answer, for some reason.

They are properties of the photon, like its energy. We talk about "the wavelength of the photon", "the photon's frequency", "the energy of the photon" an so on.

We could make a list of different "types" of energy, for example: heat, kinetic energy and potential energy. The word "photon" will not appear in the list of types of energy, at least not if the list is compiled by somebody who knows her physics. The photon will, on the other hand, appear in a list of particles in the Standard model, which also includes things like electrons.

If you think the photon is energy, then tell me: do you also think electrons are energy? Do you think everything is energy, perhaps?

This is muddled, just like the Encyclopedia Britannica's description. I see what the author is trying to get across there, but the result is that he or she is misleading the reader into a common misconception - the very one that has you and arfa trapped.

EM radiation is not a "form of energy". Saying "EM radiation [is] ... radio waves, microwaves, X-ray and gamma rays" is okay, but notice that's saying EM radiation is waves, and waves are not energy, as I have explained previously.

"Sunlight is a form of EM energy" is also wrong. Sunlight is EM radiation, sure, but EM radiation is not energy.

Quoting other people who are also wrong does not make you right.

Fair enough. I probably would, too.

And that's where you'd both be wrong.

No. Both are not correct, for reasons I have explained in some detail. If they are popular answers, that still doesn't make them right. Popularity is not a guarantor of correctness.

Yes, you used the word "pedantry" correctly, there. Like I said before, you can call my correction of your error pedantic to your heart's content, but I'm still right and you're still wrong.

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*sigh* indeed, although not quite as dramatic as exchemist's *click*
You mean your childish sandwich analogy...that's one step below the ridiculous bucket analogy with both being invalid.
While I agree with that, your continued refusal to answer the question, " what part of the photon is not energy" invalidates your argument of correctness on your part and again validates unnecessary pedantry.
Sounds like more of your typical belittling exercise again James. That may work with river [as you recently did] but it won't with me. Electrons, and protons for that matter, have energy and mass. Photons have only energy. So we can conclude that protons and electrons are therefor matter. Photons are not.Which again raises the question what part of the photon is not energy, if it can only ever be inferred a a carrier as you stubbornly keep saying.
Likewise your continued refusal [after the links I have given] to deny this is just pedant, detracts from your impartiality and simply re-enforces a stone-walling persona. Perhaps because to admit you maybe in error [as a scientist of sorts] against a lay person like myself, maybe just too much to bare?

Both can certainly be seen to be correct, and both are correct disregarding your unnecessary pedant.
And its your right to continue to stone wall and cast aspersions on my reputable links to re-enforce your error of judgement. But it's still pedant.

15. ### arfa branecall me arfValued Senior Member

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Do either electric or magnetic fields carry energy? Is it physically meaningful to talk about the energy in or of a field?
Actually any wave can be said to have an energy wave "in it".

From a physics textbook: "Since $dE/dt$ depends on $kx - \omega t$, it also satisfies the wave equation and corresponds to an energy wave."
That's back to front. The properties aren't "apart from" the energy, they are measureable properties because of the energy.
No that's not true. You are right, but so am I. That is, a photon can be said to carry energy, and can be said to be a form of energy.

The physics textbook I quoted from does this several times. As mentioned, you can google "electromagnetic energy" and find the same language--a photon is a form of energy, electromagnetic energy and it carries the energy as it propagates.

That kind of follows if you also accept that energy and momentum are what propagates in wave motion.

Last edited: Sep 4, 2019
16. ### arfa branecall me arfValued Senior Member

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And here's something from a man called Erwin Schrödinger, who wrote an article in Scientific American in 1953.

"We must start with the well-established concept that matter is composed of corpuscles or atoms, whose existence has been quite tangibly established . . .
and with Max Planck's discovery that energy also comes in indivisible units, called quanta, which are supposed to be transferred abruptly from one atom to another.
. . . each small system, atom or molecule, can harbor only definite discrete energy quantities . . . In transition from a higher to a lower "energy level" it emits excess energy as a radiation quantum of definite frequency . . ."

As anyone who has looked at the "particle in a box" scenario, or the quantum oscillator, understands what the energy of such an oscillator is defined by. Quantum oscillators have discrete energies and energy is absorbed or emitted in discrete packets (wavepackets!), called photons . . .

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

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The mistake you're both making, which is no doubt also made by some textbook writers, is a mistake called reification.

Reification is treating something that is immaterial as if it was a real thing, like an object or a substance. People typically do it with things like love, or happiness or evil. Love is a concept, a feeling, lots of things, but it is not an object or substance. You can't bottle love. You can't touch it.

The same thing is true of energy. You can't bottle energy. It's not a substance. You can't catch it or touch it. Energy is a very useful concept and calculational device, but it is not stuff - not a thing or a substance.

Photons, or waves more generally, are made of something - some "stuff". They can be caught. They can exert forces on other things. They are not mere concepts.

To say that photons of light are energy is to make a fundamental category error, and to reify the idea of energy itself.

But I've already said essentially this many times, and I fully expect that this point will continue to fly over both your heads.

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

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No, I mean where I explicitly answered your precise question - the one you're saying I haven't answered, like this:

I have not refused to answer it. I have explicitly answered exactly that question. Go back and read my answer in post #81, then I will accept your apology.

You're the one claiming that I have "refused" to answer you question. I have given you a clear and unambiguous answer, but you're pretending that never happened. It's ill-mannered. I have taken time to carefully and patiently explain a point for your benefit, and in return you ignore the substance of my posts.

And wavelength, and frequency, and polarisation, and electric and magnetic field amplitudes, and wavepackets, and wavefunctions, and spin and momentum, and a whole bunch of other things, besides. Only energy. Ha!

If, by "matter", you mean things with rest mass, then I agree with you that photons are not matter. But the definition of "matter" is somewhat up for grabs.

Anyway, let us assume that we agree that photons are not matter. Do we also agree that energy is not matter? It does not follow, by the way, that because two things are not a third thing, those two things must be the same. A car and a house are not pieces of fruit, but neither is a car a house.

19. ### arfa branecall me arfValued Senior Member

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But that seems to be exactly what Schrödinger is saying: atoms emit discrete quanta of energy. What's he talking about??
No, and Schrödinger wouldn't be happy with "matter is not energy" if he was still alive.

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

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arfa brane:

Yes, electric magnetic fields have an associated energy density, and waves can be said to carry energy from one place to another. Neither of those facts make fields and energy the same, nor do they make waves and energy the same. But I've already told you that.

Without context, it's hard to comment on this. But the term "energy wave" strikes me as misguided.

No.

There are lots of kinds of energy that have nothing to do with the non-energy properties that photons have. For example, if I talk about the gravitational potential energy near the Earth's surface, that doesn't mean the gravitational field of the Earth suddenly has a polarisation, or a wavelength, or a wave function or any of the other properties commonly associated with photons.

The non-energy properties of photons do not follow from the fact that a photon has energy.

Just because it is possible to string words together that way doesn't mean that it's right. People can say and write all kinds of things that are wrong.

Well, that's interesting language, once again. A photon is a form of energy and it carries energy.

You seem to be saying two things at once? So which is it? Is the photon energy, or does it carry energy? Those two things are not the same.

What propagates in wave motion is some kind of disturbance in a substance or a field.

I explained this in an earlier post. A "quantum" is just a fixed amount of something. In this case, Schrodinger is talking about quanta of energy - discrete amounts of energy. He is merely saying that energy comes in discrete units, not in arbitrary amounts.

A quantum oscillator is not energy. Do we agree on that, or not?

We can agree that quantum oscillators can absorb and emit photons, but you're begging the question by assuming that those photons are energy.

21. ### arfa branecall me arfValued Senior Member

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That looks like you reifiying energy--as something that isn't physical.

But if that's true, how does energy get transferred from place to place? How do you increase or decrease energy if it doesn't exist?
At this point you might try to explain that an increase in energy in a system of particles means the particles move around more. So you substitute an increase in energy with an increase in movement (vibration, translation etc). Which still leaves the question unanswered: how does the energy increase? Is there a transfer of something real and physical, or as you say, of something that isn't a thing or substance?

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

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He's saying that what an atom emits something - like a photon, say - then the associated energy (of the photon, for instance) will always be a multiple of a certain number. In short, he is saying that atomic energies are quanitised - they come in multiples of a "quantum".

I really don't see much point in pursuing what Schrodinger may or may not hypothetically be happy with if he was still alive. Already, you're reaching back almost 100 years in physics to make your argument about Schrodinger - back to a time where a lot of ideas were still in flux and were up for debate. A lot of debates have been settled in physics in the past 100 years. Terminology that used to be used more loosely has firmed up to have well-accepted and well-defined meaning in the discipline.

At the risk of opening yet another can of worms, if I had to hazard a guess, I'd guess that both you and paddoboy will insist that Einstein's equation $E=mc^2$ tells us that mass and energy are the same thing. Well, I have news for you: they aren't the same, and it's the same mistake as with the photons if you claim that "mass is really just compressed/confined energy" or something like that.

This error is also widespread, and the root cause is the same: the reification of energy. Energy is not a substance. Nor can it turn into a substance. Therefore, energy can't turn into mass, or vice versa. (And don't start me on all the textbooks that talk in these terms about nuclear binding energy and the like. They are all wrong about that, too, no matter how useful a shortcut that kind of thinking may be.)

Last edited: Sep 4, 2019
23. ### arfa branecall me arfValued Senior Member

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So you're now saying a university recommended a physics textbook that has "misguided" ideas in it? I don't think that's very likely. Textbooks are peer-reviewed by professors before they recommend them.
I'm saying what that textbook says; photons propagate at c, photons are a form of energy so it follows that energy is carried from place to place. Carried by what? By "the" electromagnetic field. You can also say that "the photon" is "the electromagnetic field" in a discrete form. You've already admitted that the fields have an energy density.