Entities and attributes in science

[billvon]

It sounds like you think a laser beam is "made of energy".

No. It IS energy. You can say it is made of energy. That is less precide.

Energy is not a substance.

Correct! It is energy.

In fact, a laser beam is "made of" light. Light is not energy.

Light is, in fact, a form of energy. Specifically, light is electromagnetic radiation.

You're still vacillating between "light is energy" and "light carries energy".

For the fourth time now, light is energy. You can say light carries energy. That is less precise.

If you think that light is a "form of energy", doesn't it strike you as at all strange that so many other "forms of energy" seem so radically different from light?

Not at all.

Do you think you can put energy in a bottle by itself and detect its presence? Note, for example, that putting some light in a bottle with mirrored walls won't do the trick, because in that case light is in the bottle, not just energy.

Light is energy.

Focussing on what energy is, then ... Does the "non-material" nature of energy strike you as at all problematic?

No. There are things that exist that are non-material - like energy.

Previously, I asked you if it was possible to directly detect energy. You claimed that you could build an "energy detector". You have not responded to what I wrote to you about photocells. How do you respond to that? Do you still think you can detect energy, even though it is "non-material"?

Of course. You could do so as well.

Consider gravitational potential energy, to take another "form of energy". Can you build a gravitational energy detector, do you think?

There is no such thing as gravitational energy. There is gravitational POTENTIAL energy. And yes, you can detect it - but since gravitational potential energy is measured by both mass and distance (over short distances) then measuring that potential energy has two parts. First you measure the mass, then you measure the distance. You need both.

You're still flip-flopping between "energy is carried by things" and "energy is a non-material entity". Which is it? (Hint: it is neither.)

I have answered this five times now. I have to conclude either you are trolling or are simply incapable of understanding this discussion.

Have a good day!

 

[origin]

No. It IS energy. You can say it is made of energy. That is less precide.
...Light is, in fact, a form of energy.

That is not correct, light is composed of photons and photons are not energy. Photons carry energy.

 

[Guestfornow]

That is not correct, light is composed of photons and photons are not energy. Photons carry energy.

Maybe whoever wrote the following has misinterpreted Einstein's paper on the photoelectric effect.
Perhaps you can point out the errors for us all

About six weeks before he submitted his doctoral thesis at the University of Zürich in 1905, Einstein on March 18th submitted the paper ‘Über einen die Erzeugung und Verwandlung des Lichtes betreffenden heuristischen Gesichttspunkt’ (“On a Heuristic Viewpoint Concerning the Production and Transformation of Light”) to Annalen der Physik, the world’s premier physics journal at the time. In the paper, Einstein proposes the existence of energy quanta, light particles now called photons, motivated by Max Planck’s earlier derivation of Planck’s law of black body radiation.

--https://www.privatdozent.co/p/einsteins-1905-paper-on-the-photoelectric-8e3

What you propose is that, after a photon loses energy it's still a particle. That isn't what we observe, though.
Not when photons interact with charged particles, at least.
Photons get redshifted and appear to lose energy, but there's a different kind of explanation for that phenomenon.

 

[Guestfornow]

Focussing on what energy is, then ... Does the "non-material" nature of energy strike you as at all problematic?

If you asked me that question I would say it bothers me about the same as the non-material nature of time.
I would add that I understand time fairly well, but I can't tell you what it is.

Why are you trying to define energy beyond a conserved physical quantity? There are plenty of material and non-material things in physics, we don't know what a lot of them are but we understand what they do, or, what relevance they have if they don't do anything. Time doesn't do anything, it doesn't interact with particles.

 

[billvon]

That is not correct, light is composed of photons and photons are not energy. Photons carry energy.

Light is a form of energy. Again, you can say that light carries energy. That is not quite correct, though, although it's a common (minor) error. Everyone knows what you mean when you say it.

If something carries something else then the two are separable. If, for example, a train carries coal, you can remove the coal and you still have the train. If you remove the energy from a photon, you have nothing. You have removed the energy (which is what photons are) and there is nothing left.

 

[origin]

What you propose is that, after a photon loses energy it's still a particle. That isn't what we observe, though.

No, I didn't imply that or say that.

If, for example, a train carries coal, you can remove the coal and you still have the train. If you remove the energy from a photon, you have nothing. You have removed the energy (which is what photons are) and there is nothing left.

I guess the same could be said of an electron. You can't remove the charge from an electron but it is still a particle. An electron is not pure charge.
If photons are just pure energy, that would mean that energy has a spin of 1 and energy has momentum. That would not make sense.

 

[billvon]

I guess the same could be said of an electron. You can't remove the charge from an electron but it is still a particle.

Yep. And uncharged electrons are electron neutrinos - another form of lepton.

 

[Guestfornow]

If photons are just pure energy, that would mean that energy has a spin of 1 and energy has momentum. That would not make sense.

You're overthinking it.

The energy of a photon is frequency-dependent, Take away the frequency and there is no photon. The frequency is of an oscillating field.

So one takeaway is that oscillating fields are a form of energy. Pure energy doesn't make sense. Energy in a field does.
Physics is about meaningful descriptions; it's also about what kind of questions are meaningful. These tend to be about what can be measured or more generally, observed.

 

[origin]

Yep. And uncharged electrons are electron neutrinos - another form of lepton.

You're overthinking it.

I just agree with the physics community that clearly states that photons are not pure energy, which makes perfect sense to me.
You are not disagreeing with just me, you are disagreeing with the consensus of physicist, which is fine, but I am on the side the physicists with this one.

 

[Guestfornow]

I just agree with the physics community that clearly states that photons are not pure energy, which makes perfect sense to me.

Can you post a quote from that community to back up your argument?
I don't know what "pure energy" might be.

 

[billvon]

I just agree with the physics community that clearly states that photons are not pure energy

I've never heard them described as pure energy either, just as I have never heard matter described as pure matter. Photons are, however, a form of energy.

 

[origin]

Can you post a quote from that community to back up your argument?

Simply type into Google "is light energy?"

I don't know what "pure energy" might be.

Sorry for any confusion I caused by saying the word pure. What I was trying to say was that photons are not energy. A photon is a subatomic particle that has several properties and one of those properties is that it carries energy, it is not itself energy.

There is not much more I can add. Google the question "are photons energy" and check the results, I agree with the results from Google.

 

[Guestfornow]

There is not much more I can add. Google the question "are photons energy" and check the results, I agree with the results from Google.

Well I actually did try what you suggest. The results, or some of them, say that light is a form of energy.
You can check this yourself.
One of them says the energy of a photon depends on its frequency; that's what I said.
Do you still agree with the results from Google?

 

[Guestfornow]

A photon is a subatomic particle that has several properties and one of those properties is that it carries energy, it is not itself energy.

Ok. I agree that a photon has several properties.
It propagates or moves at the speed of light--no surprise there. It has spin or polarization, it has momentum.

What happens if a photon is absorbed? What properties remain that tell you a photon is not the momentum, not the polarization, not the energy from the oscillations of the field? What should I be able to observe after a photon is absorbed?

 

[billvon]

Simply type into Google "is light energy?"

I am not a fan of using popular media to define science. Nevertheless I tried your experiment:

Top results:
"In fact visible 'light' is a form of radiation, which can be defined as an energy that travels in the form of electromagnetic waves." (ESA)
"Light energy is a form of electromagnetic radiation." (scholarschools.com)
"Light energy is a kind of kinetic energy with the ability to make types of light visible to human eyes. Light is defined as a form of electromagnetic radiation ..." (byjus.com)

So all those hits agree that light is a form of energy. Two out of three say it explicitly.

Google the question "are photons energy"

OK I tried that too. Results:

"A photon (from Ancient Greek φῶς, φωτός (phôs, phōtós) 'light') is an elementary particle that is a quantum of the electromagnetic field, including electromagnetic radiation such as light and radio waves" (Wikipedia)
"As quanta of light, photons are the smallest possible packets of electromagnetic energy." (Symmetry magazine)
"A photon is a particle of light which essentially is a packet of electromagnetic radiation. The energy of the photon depends on its frequency" (energyeducation.ca)
"Photons are simply discrete packets of light energy." (study.com)

I agree with all the above. Light is made up of photons, and photons are quanta of EM energy.

 

[James R]

billvon,

I am not a fan of using popular media to define science. Nevertheless I tried your experiment:

Top results:
"In fact visible 'light' is a form of radiation, which can be defined as an energy that travels in the form of electromagnetic waves." (ESA)
"Light energy is a form of electromagnetic radiation." (scholarschools.com)
"Light energy is a kind of kinetic energy with the ability to make types of light visible to human eyes. Light is defined as a form of electromagnetic radiation ..." (byjus.com)

So all those hits agree that light is a form of energy. Two out of three say it explicitly.

Yikes!

With so many sources getting this fundamentally wrong, it's no wonder that you and others have picked up the wrong message somewhere along the line and are now struggling with a misconception.

Taking the quotes in turn:

• The ESA one starts by saying light is a "form of radiation", which is fine. Radiation consists of particles. Light consists of particles (photons). But then it goes off the rails, claiming that "radiation ... can be defined as an energy that travels in the form of electromagnetic waves". Well, I suppose it can be defined like that, but defining it that way just opens a can of worms which will be an ongoing source of confusion and inspecificity. Claiming that energy can take the "form of" electromagnetic waves is just hopelessly muddled. Energy just isn't stuff. It has no form. You can't turn energy into light, or light into energy.
• scholarschools.com makes the same mistake. If it just said "light is a form of electromagnetic radiation", everything would be fine, but instead it claims that light energy is electromagnetic radiation, which is just plain wrong. It's taking one property of electromagnetic radiation and pretending that's a complete description of the electromagnetic radiation. It ought to be obvious that it isn't anything like a complete description.
• byjus.com is probably the worst example of the three. First, it conflates the difference between "light energy" and "kinetic energy"; that is, it doesn't even appreciate that these are different "forms of energy". Then it claims that kinetic energy has the ability to make visible light, which it (obviously?) doesn't. The last sentence is fine, although it's not really a definition so much as a deduction.

Moving on...

OK I tried that too. Results:

"A photon (from Ancient Greek φῶς, φωτός (phôs, phōtós) 'light') is an elementary particle that is a quantum of the electromagnetic field, including electromagnetic radiation such as light and radio waves" (Wikipedia)

This is unproblematic.

"As quanta of light, photons are the smallest possible packets of electromagnetic energy." (Symmetry magazine)

Pop science getting it wrong.

A photon is not a packet of energy. You can't open the packet and see anything. You can't put energy in a packet, because energy is a concept.

"A photon is a particle of light which essentially is a packet of electromagnetic radiation. The energy of the photon depends on its frequency" (energyeducation.ca)

No problems here. Notice the form of words: "the energy of the photon". It doesn't claim the photon is the energy or the energy is the photon. It only says that it's possible to (conceptually)associate some energy with a photon. Of course, if doesn't say that explicitly.

"Photons are simply discrete packets of light energy." (study.com)

Just wrong, again. Pity any poor science students who rely on study.com.

I agree with all the above.

Logically, you can't, because they don't all agree with one another.

Light is made up of photons, and photons are quanta of EM energy.

Half right, but still half wrong, I'm afraid. Back to school with you!

 

[James R]

Guestfornow:

Welcome to sciforums. Did this discussion inspire you to sign up?

I can't see why they can't both be right.

Did you read through the whole thread? I have explained why several times, in some detail.

I'm happy to answer questions.

Is light a form of information and does light carry information?

Light is not a form of information. Information, like energy, is a concept. Light is made of physical particles.

Energy curves spacetime.

Hmmm.... spacetime. Are you sure that's not a concept? And what about that curvature thingy you mentioned? That sounds like maths.

How is it that energy isn't a thing?

It is a "thing". It's just not an entity, in the sense I have defined that term. It's a concept, an attribute.

Moreover, all the theories can say about what energy is, is that it's a conserved quantity.

Yes. All that means is that if you calculate a number at the start of some process, you'll get the same number when you recalculate at the end of the process.

When light is converted to, say, electrical energy, there isn't anything left over. How do you explain this?

The photons are absorbed in some way. As a result, some electrons move around a bit faster, or something along those lines. There is no "conversion" of photons to electrical energy. How could a particle possibly be "converted" into a number?

 

[James R]

billvon:

There is no such thing as gravitational energy. There is gravitational POTENTIAL energy.

I wrote "gravitational potential energy". Don't be petty.

And yes, you can detect it - but since gravitational potential energy is measured by both mass and distance (over short distances) then measuring that potential energy has two parts. First you measure the mass, then you measure the distance. You need both.

Why did you skip out on considering the matter of where the gravitational potential energy is?

I have answered this five times now. I have to conclude either you are trolling or are simply incapable of understanding this discussion.

How disappointing of you to try an ad hominem attack. I really expected you would be among the last of the people here who would express his frustration by resorting to that kind of nonsense.

If you're going to keep engaging with this, please do so in good faith. If you feel like you can't do that, it might be better to just walk away from it and take some deep breaths.

If you had fully considered all the points I put to you and come up with arguments to refute them, then you might be on more solid ground. But to claim that I am incapable of understanding this discussion - which, I might add, you jumped into very late in the piece - is just silly nonsense. Do better.

 

[James R]

Guestfornow:

Maybe whoever wrote the following has misinterpreted Einstein's paper on the photoelectric effect.
Perhaps you can point out the errors for us all

Okay.

The main error is in the part that says "In the paper, Einstein proposes the existence of energy quanta, light particles now called photons,..."

Yes, Einstein proposed the existence of energy quanta. I can't recall whether he introduced the word "photon" in his 1905 paper. But to confuse the energy quanta with photons is not something I think that Einstein did. That is a mistake made by whoever wrote that description of Einstein's paper.

What you propose is that, after a photon loses energy it's still a particle.

Typically, photons lose energy when they are absorbed, at which point they disappear. Also, don't misunderstand. All that happens to the energy when a photon disappears is that a number is moved from one column in somebody's energy ledger to a different column. The photon itself is not the energy. The energy was never the photon.

Photons get redshifted and appear to lose energy, but there's a different kind of explanation for that phenomenon.

Yes. You might like to consider the notion that photons have a frequency, too: a rather strange thing for a particle to have, you might say. Maybe this frequency thing is an attribute we use to describe the photon. Maybe the energy is somehow related to the frequency.... oh wait! E=hf for a photon. There's an equation, with some numbers! A number on the left called "energy", and two numbers on the right, called "Planck's constant" and "frequency".

If, as some have claimed, a photon is energy, we might ask: where is the photon in that equation I just wrote down? Is the "E" the photon, perhaps?

Why are you trying to define energy beyond a conserved physical quantity?

I'm not. I said energy is a number.

It seems that lots of people don't like the idea that energy is a number, for some reason. But that's what it is.

There are plenty of material and non-material things in physics, we don't know what a lot of them are but we understand what they do, or, what relevance they have if they don't do anything.

Okay. So what?

The energy of a photon is frequency-dependent, Take away the frequency and there is no photon. The frequency is of an oscillating field.

The frequency is of an oscillating field.

I take it that this frequency you mention can be described as an attribute of this oscillating field you mention? Something used to describe the oscillating field? Is it a number, by any chance?

So one takeaway is that oscillating fields are a form of energy.

Are oscillating fields numbers?

Pure energy doesn't make sense.

As a substance, it doesn't make sense. Because energy isn't a substance.

Energy in a field does.

Okay. So what?

Ok. I agree that a photon has several properties.
It propagates or moves at the speed of light--no surprise there. It has spin or polarization, it has momentum.

Right. And energy, generally speaking, lacks those properties - spin, polarisation, momentum.

This ought to suggest to people that a photon is not energy, and energy is not a photon. But for some reason, there's a disconnect in understanding.

 

[Guestfornow]

If, as some have claimed, a photon is energy, we might ask: where is the photon in that equation I just wrote down? Is the "E" the photon, perhaps?

Where does the equation say energy is a number?

The thing about qualitative statements, about saying you know what something is, is that it has to line up with what other people in the scientific community say. Suppose instead of energy and light, the subject is time. Is time a number, why does it move in the same direction, at an apparently (up to quantum measurements) linear pace? How do numbers flow?

Can you tell us, since you know energy is a number? I maintain this is not what physics says about energy.
It could be that it's an entirely human invention, but maybe time is too. Can you say?