# Are photons energy? What is energy, anyway?

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And after considering this pedantic argument further, instead of either calling a photon a " packet of energy" or a "carrier of energy" we could also consider a photon as simply an " energetic photon" but that's being pedantic.

I'm waiting to see if James R or exchemist can explain how the power output of a radio antenna is calculated, given that electromagnetic radiation isn't a form of energy.

I'd also like an explanation of what both of them think a "form" of energy actually is.

What colour is an Orange in the dark?
While this is fun, it's all pedantry.
Pedantic - not so

Colour of orange in the dark or under a blazing sun - it is the colour it is

What colour is it PERCEIVED to be - depends on how it is lit up

Pedantic - not so

Colour of orange in the dark or under a blazing sun - it is the colour it is

What colour is it PERCEIVED to be - depends on how it is lit up

Actually an Orange in the dark has no colour.
Colour in the first instant is determined by what part of the EMS is falling on that object, and what part of the EMS it actually reflects.
This was part of a very lengthy long debate on a now defunct forum.
https://www.scienceabc.com/nature/what-color-is-an-orange-in-the-dark.html

What Color Is An Orange In The Dark?

If you keep a ripe orange in one corner of your room that gets variable amounts of light as the day passes, you will see different intensities of the color orange on the piece of fruit. Perhaps the difference isn’t too evident for you, since you won’t be staring at the orange all day, but another exercise you can try is holding an orange in front of a bright torch. Believe it or not, but it will turn a bright flaming red!

Put that same orange under a purple light and it will appear scarlet, but under blue light, it will appear brown. Has your orange turned into a chameleon? No, of course not, but why is it changing color? The orange will change color in all these situations because, as vision scientists put it, color is not a property of an object. Color exists in our head!

PS, my apologies as this may seem to be off topic....

What Color Is An Orange In The Dark?

If you keep a ripe orange in one corner of your room that gets variable amounts of light as the day passes, you will see different intensities of the color orange on the piece of fruit. Perhaps the difference isn’t too evident for you, since you won’t be staring at the orange all day, but another exercise you can try is holding an orange in front of a bright torch. Believe it or not, but it will turn a bright flaming red!

Put that same orange under a purple light and it will appear scarlet, but under blue light, it will appear brown. Has your orange turned into a chameleon? No, of course not, but why is it changing color? The orange will change color in all these situations because, as vision scientists put it, color is not a property of an object. Color exists in our head!
Is, the above, not what I expressed in far fewer words?
Colour of orange in the dark or under a blazing sun - it is the colour it is

What colour is it PERCEIVED to be - depends on how it is lit up

What colour is it PERCEIVED to be - depends on how it is lit up
Would it be more correct to say "it depends on how the brain translates the perceived wavelengths into colors"?

Is, the above, not what I expressed in far fewer words?
The above says that in the first instant, the "perceived" colour of anything depends on the EMS falling on it.

Would it be more correct to say "it depends on how the brain translates the perceived wavelengths into colors"?
Seriously?

Please explain the difference in concept behind the words expression (apart from spelling)

The above says that in the first instant, the "perceived" colour of anything depends on the EMS falling on it.

And my post
Colour of orange in the dark or under a blazing sun - it is the colour it is

What colour is it PERCEIVED to be - depends on how it is lit up

????

please explain how the below is different

Actually an Orange in the dark has no colour.
Colour in the first instant is determined by what part of the EMS is falling on that object, and what part of the EMS it actually reflects.

Found this dozzy worth a look

The Longstanding Mystery of How Big a Proton Is May Finally Have Been Solved

BY MIKE MCRAE

SEPTEMBER 09, 2019

........the proton's radius at around 0.833 femtometres; a smidgeon off the 0.842 femtometres calculated by a landmark 2010 experiment.

PLUS

Unlike the convenient models of atoms in our text books, protons aren't like smooth little spheres. Lacking a distinct surface, the proton is instead a cloud defined by a threshold in its positive charge.

Method number two is a little less aggressive, relying instead on detecting changes in an electron's energy levels as it orbits a proton

Seriously?

Please explain the difference in concept behind the words expression (apart from spelling)

I don't believe we perceive colors at all. We perceive wavelengths which are translated into electro-chemical signals and when processing the information, the brain makes a best guess of what color these wavelengths represent.
It's not always right .

Remember the chess board with the two squares which are identical in color, but the brain is unable to see them as the same color.
A and B are identical in color!
It is impossible for the brain to see these two squares as being the same color. The brain always tries to correct for shadow and cannot override this internal adjustment process.
(Its a survival tool)

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I don't believe we perceive colors at all. We perceive wavelengths which are translated into electro-chemical signals and when processing the information, the brain makes a best guess of what color these wavelengths represent.
It's not always right .

Remember the chess board with the two squares which are identical in color, but the brain is unable to see them as the same color.
A and B are identical in color!
It is impossible for the brain to see these two squares as being the same color. The brain always tries to correct for shadow and cannot override this internal adjustment process.
(Its a survival tool)

Intriguing

Slightly different answer to a slightly different question

However as for not seeing colour (the check board is designed to deliberately trick the brain) not sure I would agree with the not seeing colour statement

Not sure if experiments have been undertaken (to lazy to check) but I would design a test along the lines of using a known wavelength (say for discussion - green) - presenting said wavelength to the eye of the subject and document the response

Now it has been said that your green might not be my green ie if I saw your green I would call it red (ieie different brains different perceptions but same response to NAME of colour) because of what I/you have been taught that (name green) is the correct response to the brains interpretation of that wavelength

Again different to NOT SEEING COLOUR

it's nearly 4:30 so have to go

Thought of something I can try. Let you know how it turns out

Holiday Bali in two days so how long it takes to check my idea depends on how holiday turns out

However as for not seeing colour (the check board is designed to deliberately trick the brain) not sure I would agree with the not seeing colour statement
The board is designed to demonstrate the effect of shadow in our perception. It's our brain that tricks us.....

Now that you KNOW the colors are the same, you will still not be able to perceive these two as being the SAME color.

This is why I really love the lecture by Anil Seth, explaining this phenomenon.

Interestingly, the brain can very readily adapt to sound recognition and what may at first sound as garbled noise, can become clear with just a few audible clues. It's truly amazing!

I'm posting another Anil Seth Lecture where he answers some of the same questions raised here on occasion.
Can't do it here , so entered it in the Human Science forum under title; Anil Seth - Brainstorming

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Colour of orange in the dark or under a blazing sun - it is the colour it is
The thing is, that we always see things on Earth under the same conditions in general with our star being a yellow dwarf G2V star.
If we for example lived on a blue super giant star, the colour of an Orange would appear different.

My idea was to cut out the A and the B and check

Result above

Busy now

Cheers

Sydney Opera House under normal lighting conditions....

Sydney Opera House under other lighting conditions....

Not really. I disagree with the guy on quora about all particles being "pure energy". Particles are excitations in quantum fields, yes, but that's not the same as "pure energy". The guy sounds reasonable enough that I think I could probably convince him of that with a brief conversation about it. It's not that he's exactly wrong, but he's using a metaphor without realising it. Like I said, it's a common mistake, and even physicists are prone to making it. To some extent, it doesn't matter if we're a little loose with the language, but when the question is this one it is actually important to get it right.

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James, I'm not really interested in your deliberate act of confusion.
What I'm hearing is that you're not interested in whether you're right or wrong. As long as you walk away with your ego intact, you're content to be wrong. For you, this discussion ceased being about what is true some time ago. Now it's just about you trying to save face, at least as far as you're concerned.

Here are some interesting answers which again validates the main point I have been making since the start of this...Pedant/Pedantic/Pedantry

http://scienceline.ucsb.edu/getkey.php?key=3971
That's a really great question. In fact this question caused a great debate among physicists during the time of Isaac Newton. Newton thought that light was a stream of little particles and other physicists such as Christian Huygens thought that the universe was filled with tiny particles called aether particles and that light was just a wave moving through the aether.

To make a long story short, it turns out they're both kind of wrong... and they're both kind of right. In some situations light sort of acts like a stream of particles and in others it acts sort of like a wave. Today many physicists (myself included) like to say that light is neither a particle or a wave... it's just light.

So, some might say that because light can carry energy from the sun to the earth it must be matter. Others might say that because you can't hold a lump of light in your hand light isn't matter. It all depends on what you mean by the word 'matter.' But the important thing to remember is that light doesn't care what you call it, it will still act the same way no matter what. That's why in physics we try not to worry too much about what things are called and focus on understanding how things actually behave.

None of that addresses the question of whether photons are energy (they are not). There's no problem with anything in this quote, but it's irrelevant to our discussion.

"Both your class, and the entirety of science is having this debate. First, some precision. Photons are not in light, they are light. Light is made up of photons, so one photon is like one unit of light. Additionally, photons aren't really matter, although this depends on how you define things. Traditionally people say that for something to be called matter, it has to have mass and photons don't really have mass... although this also depends on how you define it.
Okay so far. I wrote the same thing, above.

I'll cut to then end, and then explain the controversy. Light is a form of electromagnetic radiation, which is a form of energy.
Nup. Wrong! Back to school with you!

This energy always comes in distinct units, which we call photons.
Sloppy. Yes, the energy in light comes in discrete amounts. Those amounts are associated with individual photons. The mistake comes when you say that the photons are the energy, or vice versa.

In this way, light is like a particle, but it still doesn't have mass, so it's not really matter. The way these particles behave though, is very strange. Sometimes they behave more like a wave, like a ripple moving across a pond. Sometimes they behave more like actual solid objects, like bullets being shot from a gun. And the craziest thing is that whether they behave one way or the other depends largely on whether or not anyone is watching them at the time. I cannot explain this behavior... actually no one can. All we can do as scientists is observe that it is the case and describe it using mathematical laws. If you want to know more about how we know this to be true, there is a famous physicist by the name of Richard Feynman who explains it quite nicely....
All fine, but irrelevant.

Now I said that whether light has a mass or not depends on your definition, let me explain that. As I said, photons, and thus light, is energy. But there is a famous equation E=mc2 that tells us that the mass and energy are perfectly equivalent. E is energy, m is mass and c is the speed of light in a vacuum.
Another error, even though it's a very common mistake. Energy and mass are not "perfectly equivalent". A certain amount of energy can be associated with a certain quantity of mass, but it is an error to think that mass is energy. If it was, we wouldn't need two different symbols with two different units, for starters. And besides, at this point the guy has forgotten about how he careful distinguished matter from light, earlier. He's muddled. He says light is energy. He says light is not matter. But then he says matter is energy, which would make matter and light the same thing. See? Muddled.

You can convert mass into energy and energy into mass.
Nup. More sloppy thinking. You can, for instance, convert mass into photons, but that's not the same thing at all, since neither mass nor photons are energy.

As a matter of fact, that's what the sun does every day, it converts some of its mass into energy, which we see as light.
From here on, it's just error compounding error.

The sun turns some of its matter into photons, and there's energy associated with both the matter and the photons, but no matter is turned into energy. How could it? Energy isn't stuff that real physical things can turn into.

As my time is short and precious, let's add some more while I have the time.....
QUESTION:
I'm reading an excellent book by Kauffmann, Discovering The Universe, in which he describes when electron jump to a higher level or a lower level. If they go to a higher level they emit a photon. If they go to a lower level they absorb a photon.

It causes me to ask if photons exist as a seperate entity within all atoms or are they created at certain energy levels for the purpose of absorption, or emission, or do they exist omnipresently in the fabric of the universe? Anyway, where does the photon for absorbtion come from?

Hope this isn't too stupid a question.
It certainly isn't a stupid question, and really cuts to the heart of the question of interpreting quantum mechanics.

The simplest answer is that when a photon is absorbed by an electron, it is completely destroyed. All its energy is imparted to the electron, which instantly jumps to a new energy level. The photon itself ceases to be. In the equations which govern this interaction, one side of the equation (for the initial state) has terms for both the electron and the photon, while the other side (representing the final state) has only one term: for the electron.

The opposite happens when an electron emits a photon. The photon is not selected from a "well" of photons living in the atom; it is created instantaneously out of the vacuum. The electron in the high energy level is instantly converted into a lower energy-level electron and a photon. There is no in-between state where the photon is being constructed. It instantly pops into existance.

So the question is: where does the photon come from?

Strangely, it doesn't seem to come from anywhere. The universe must put the extra energy somewhere, and because electrons in atoms are electromagnetic phenomena, a photon is born with the required energy. In a weak-force interaction, say the decay of a neutron, that energy goes into a neutrino particle which is also instantaneously created. Each force has its own carrier particles, and knows how to make them.

That's really all we can say about it. There are many interpretations of what this and other phenomena in quantum mechanics mean on a deeper level, and whole libraries worth of books which argue points of view on the matter. But my personal philosophy is that of the famous physicist Richard Feynman, who said: "Shut up and calculate."
<<<<<<<<<<<<<<<<<<<>>>>>>>>>>>>>>>>>

Dave Kornreich
Dave was the founder of Ask an Astronomer. He got his PhD from Cornell in 2001 and is now an assistant professor in the Department of Physics and Physical Science at Humboldt State University in California. There he runs his own version of Ask the Astronomer. He also helps us out with the odd cosmology question.
I have no problem with anything there. Sounds like Dave is on the right track. Note that he nowhere says that photons are energy.

arfa brane:

I'm not a fucking idiot you condescending prick.
Some people just can't stand being corrected. I'm tempted, on the basis of this incivility, to just stop interacting with you. People aren't pricks just because they disagree with you. Grow up.

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.
No. You can't create "stuff" from numbers.

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?
A photon, as I and others have already explained many times, is an excitation of the electromagnetic field.

Your question is no different from asking where a water wave gets its properties from. It gets some of them from the nature of water itself. It gets others from the nature of whatever it is creating the disturbance that is the wave.

Oh bullshit. That is so NOT it.

The photon does not travel "in the EM field"; it IS the EM field, you dick.
Another error. A photon is an excitation of the field; it is not the field itself. Your statement is equivalent to claiming that a water wave in a pond is the pond.

What is wrong with these people--https://en.wikipedia.org/wiki/Electromagnetic_radiation
Infrared radiation in the spectral distribution of a black body is usually considered a form of heat, since it has an equivalent temperature and is associated with an entropy change per unit of thermal energy. However, "heat" is a technical term in physics and thermodynamics and is often confused with thermal energy. Any type of electromagnetic energy can be transformed into thermal energy in interaction with matter. Thus, any electromagnetic radiation can "heat" (in the sense of increase the thermal energy temperature of) a material, when it is absorbed.[38]
What is wrong is that whoever wrote that is hopelessly muddled about the difference between heat and radiation. Apart from that, the rest is sort of okay.

You realise that wikipedia is full of errors, don't you? It's a publicly editable encyclopedia. It is only as accurate as its contributors. Mind you, apparently even the Encylopaedia Britannica gets some of these things wrong - again, it's only as good as its contributors. People make mistakes.

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.
Oh well, indeed. Maybe somebody will help correct them, like I'm helping by correcting you. Maybe you can take what you learn here and spread the knowledge around. Maybe together we can correct the internet, bit by bit.

---
Regarding Schrodinger's Scientific American article, which you quoted, the first thing to realise is that he is writing for a popular audience, not that this excuses errors. Secondly, the article was apparently written in 1953, and Schrodinger did not have the benefit of today's understanding of quantum field theories and the like at that time.

With that in mind, let's take a look....

Within one tremendously fertile decade at the turn of the century came the discoveries of X-rays, of electrons, of the emission of streams of particles and other forms of energy from the atomic nucleus by radioactive decay . . .
This is ambiguous. On the one hand, it can be read as saying that particles are a form of energy and there are other forms. On the other hand, Schrodinger might just be saying that energy can be emitted from the nucleus by many different processes. It's not clear which meaning he meant. If it was the former, then he was wrong; if the latter, then no problem.

Five years later Einstein told us that energy has mass and mass is energy; in other words they are one and the same
It's an understandable mistake he is making here - one that many physicists make. In practice, it doesn't make much difference if you pretend this is true. But, technically, it's wrong. Energy and mass are not one and the same. You can't make stuff from numbers.
Each small system--atom or molecule--can only harbor discrete energy quantities. . . .
Fine.

In transition from a higher to a lower "energy level" [the system] emits the excess energy as a radiation quantum of definite wavelength . . .
This is okay, but only if the word "radiation quantum" is understood to mean a discrete quantity of energy associated with a photon ("radiation"). An erroneous reading would be to interpret this as saying that energy (numbers) can somehow turn into photons (stuff).

arfa brane:

Ok, EM radiation can't be energy. So confusingly, this radiation carries energy.
What's confusing you?

A bucket can carry water. Are you confused as to why the bucket is not the water? (Note: this analogy is imperfect, because energy isn't "stuff" like water is, but hopefully you get the point.)

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.
What do you find problematic about any of that? You're dismissing it, but you're not saying why.

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 . . .
Are you telling me that you don't care how many good arguments I make, you're unwilling to believe me because I disagree with some "big name" authorities about certain subtle points?

You need to understand that Science isn't a dogma. There are no High Priests of Science. Ideas stand or fall on their merits in science, not according to how many Nobel prizes you've been given - at least in the ideal practice of science.

What you're telling me is that even though you can't put a coherent argument together to explain how a photon could possibly be energy, you're just going to go right on believing that's what it is, because it's some kind of article of faith for you, or because it will shake your faith in the Holy Men of Physics if you ever found out that they made a mistake or two.

This is also precisely paddoboy's attitude here. He doesn't realise that Science isn't based on dogma and authority, either.

What "something else"? . An electron spontaneously emits radiation (in discrete amounts), when it accelerates. Accelerating an electron means it has to interact with an electric field (or a magnetic field). In the first case the electron accelerates linearly; in the second case it follows a curve.

Electrons accelerating in a strong magnetic field generate synchrotron radiation.
LEDs emit radiation which is monochromatic, because electrons in the LED accelerate (not very far) in an applied (constant) electric field--the "something else" . . .
Okay. That's all good. What's the relevance?

A photon is energy, but when you see light you don't see energy. Seeing light means you interact with photons and they exchange momentum with electrons.

OK? That's a fairly standard explanation; energy can't be measured but it can be calculated.
Yes. I agree with all that.

But keep telling yourself that most modern textbooks are wrong, that a university education in physics won't be helpful.
I haven't talked about most modern textbooks. I believe that so far we have discussed what one textbook says - one that you happen to have at hand. Nor have I made any comments about a university education in physics.

No point in consulting any literature at all, really.
I don't know where you're getting this stuff from. Not from anything I've said. How can we hope to identify errors in the literature if we don't consult it?

Considering Einstein, Schrodinger, probably Maxwell too, were all confused about it and so managed to mislead a lot of people . . .
I wouldn't put all the blame on them. People manage to mislead themselves. Also, this stuff isn't necessarily taught. People (even teachers) aren't always as careful as they should be in how they use the language, and as a result their students sometimes take away the wrong ideas.

I'm waiting to see if James R or exchemist can explain how the power output of a radio antenna is calculated, given that electromagnetic radiation isn't a form of energy.
Electromagnetic energy doesn't have to be energy in order to have an energy associated with it. Energy is useful precisely because it's a good accounting system.

I'd also like an explanation of what both of them think a "form" of energy actually is.
I've already told you, but maybe I wasn't clear.

We can talk loosely about different forms of energy - kinetic energy, potential energy, heat, spring energy, etc. What is really going on when we do that is that we're partitioning or assigning categories to some abstract quantity called the "total energy" of some system or other. We're saying we can associate X amount of energy with the mass in the system, and Y amount of energy with the motions that are going on, and Z amount of energy due to the relative distances between separate objects in the system, and W amount of energy with the orientation of the system in space, and so on and so forth. The usefulness of this partitioning is that when physical changes to the system occur we can move some energy from column Z, say, to column Y, and yet the total Y + Z (or X + Y + Z + W + ...) will remain unchanged if we've set things up carefully.

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