Are photons energy? What is energy, anyway?

paddoboy:

I see. Rather than admit you're wrong, you're planning on jumping ship out of the conversation. Already, you're ignoring most of the substance of my posts, while repeating your earlier errors.

Oh, I'm being dishonest now, am I? About what, exactly?

Look, I'll make it easier for you. Just answer yes or no to the following questions:

1. Do you think photons are energy?
2. If photons are energy, does that mean that energy can be photons?
3. Do you think all mass is energy?
4. If all mass is energy, does that mean you think everything is energy?
5. If you don't think everything is energy, please name something physical that isn't energy (note: you've already excluded photons and matter from that list).
6. Does energy have all the properties that photons are said to have, such as wavelength, frequency, a wavefunction, and so on?

If you say that energy does not have all those photon properties, you need to explain how can photons can possibly be energy.

So does all energy have a wavelength and a frequency that defines it? Does all energy have a polarisation? Does all energy have momentum?

Again, I note that I responded explicitly to what you are re-posting. It is troll-like behaviour to pretend there was no response, and to ignore the response and then simply re-post the incorrect material. You need to stop that.

Are you going to dispute that the Doppler effect is real, too, or put it down as an effect of gravity? Note that we observe the red-shift or blue-shift of light in contexts other than a cosmological one.

You're still reifying energy. You can't put energy in a container. It isn't stuff that can be put in something. You can't put it in a photon. Asking "where is the energy in a photon?" is exactly like asking "where is the frequency in a water wave?" or "where's the carton that carries the electric charge of an electron?"

I know what you said. What you said implies that all matter (all stuff with mass) is energy, along with all photons. What I'm wondering is: what is left that isn't energy, then, according to you? Is there any physical thing that isn't energy?

If I'm not understanding what you're saying, you need to make it clear what you're saying.

What is abundantly clear is that you keep claiming that photons are energy, and that's incorrect. Now you've also added the claim that just about everything else is energy too. Electrons are energy. Protons are energy. paddoboy is energy. That pot plant is energy. Everything is just a bundle of energy!

 

arfa brane:

Yes, let's.

Heat is a particular designated partition of energy, as I previously defined it. A photon is not energy, so it can't be heat.

In the 19th century, for a long time, there was much debate as to what "heat" was. A lot of people thought it was a substance. They even had a name for it: "caloric". All those people were wrong, and now here we are in the 21st century, where some people still apparently hold the same view - a view that was well and truly proven incorrect during the 19th century.

When people talk about a "flow" of heat, they are really talking about an energy transfer, which is nothing like the flow of a substance. Moving a number from column A to column B isn't the same as the flow of a substance.

No it isn't. It's a flow of particles of one sort or another: photons, alpha particles, electrons, or whatever.

Only the ones who aren't careful, or who are just wrong.

You might need to quote him. Pardon me if I don't take your word for it.

You're saying nothing will convince you? Then we're done here, I think. Pointless trying to argue against dogmatic views.

No. You're confusing heat with temperature. They aren't the same thing. Like I said earlier, words have technical, precise meanings in physics. Non-physicists often conflate concepts that are distinct in physics. Case in point: confusing photons with energy.

Yes.

You need to realise that the physicist saying that is using a metaphor, whether he realises it or not. Numbers are not really absorbed.

What happens to the photon when it is absorbed is: it disappears. What happens to its energy is that its energy is moved from column A to column B in somebody's table of energies.

Because all of those things, like energy, are concepts. They are not "things". They are not substances.

On the other hand, if somebody is keeping a Table of Momenta somewhere, then we inevitably find that when a photon is absorbed, the momentum associated with that photon appears as a contribution to the momentum of whatever it was that absorbed the photon. So, in that sense the momentum "persists" somewhere.

Fundamentally, it's due to the nature of the electromagnetic interaction. By the way, in beta decay - which involves the weak interaction - W bosons appear and disappear, too, and they have mass.

A photon's energy is related to its frequency and momentum, but if you want to invoke some kind of causation between those quantities you'll have a hard time of it. All of those things, though, are abstract quantities in the same sense. Momentum is no more a substance than energy or frequency is.

Energy is conserved in many situations; that's a major motivation for introducing the concept in the first place. It does not follow from the fact that energy is often conserved that therefore photons are energy. They are not.

What? I'm talking about some photons flying though space. Both the source and the photons themselves could be light years away from me. The only interaction I have is when one of those photons finally reaches me and is absorbed, at which point I notice that my motion somehow changed its energy.

I could say a lot of things. You haven't yet said why you think it helps your argument that photons are energy.
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The following is from your reply to exchemist. I hope you don't mind if I address your questions as well.

I know that when they say that they are glossing over the thing that is actually absorbed and emitted - usually photons.

I understand that people say that kind of thing, but it's a bit muddled. If they want to talk about energy, they really should probably just talk about energy, and if they want to talk about photons they should talk about photons. If they want to talk about both at the same time, it would be better to say that the oscillators emit photons which have energy E=hf, or whatever.

It comes from an electromagnetic interaction between the electron and something else - often the nucleus of an atom. For instance, an electron may change its quantum state in an atom, and one outcome of that change is the creation of a photon.

No. It's created via the electromagnetic interaction.

Tell us what you think electromagnetic radiation actually is.

One thing is clear: whatever it is, it can't be energy.

You care enough to stick to your guns, despite not being able to make any convincing argument that photons are energy.

Initially, I thought it might make sense to you that a photon "carries" energy in the same way it "carries" momentum, or polarisation, or frequency, or any of those other properties it has. Later, I realised that the word "carries" tends to reinforce the error of reification that you keep making, so now I'm trying to reduce my usage of that form of words in this discussion. A photon's energy is not in the photon. A photon is not a container for energy. Energy is not stuff that can be contained, and it is not stuff that can be carried in the literal sense.

I thought you were beginning to understand this new idea at one point in our discussion, but then you regressed back to your initial mistaken position. Now we seem to be at the point where stubbornness has taken over and you've stopped listening, like paddoboy did from the start.

 

On the subject of where photons come from when they are emitted and where they go to when they are absorbed, one way to look at it is from the point of view of quantum field theory. In QFT, photons are excitations of the electromagnetic field, which exists everywhere in space. The creation of a photon takes place when something "shakes" the field in the right way.

It's kind of like asking where a water wave "comes from" when it carries energy from one place to another. Suppose I throw a rock into a flat pond. By doing so, I created a disturbance in the water that then propagates outward as a water wave. If something absorbs the energy of that wave (by which I means the wave interacts with something that decreases its amplitude and therefore the associated energy value), then the wave "disappears" and we get our flat pond back again.

To "shake" an electromagnetic field so as to create an electromagnetic disturbance that travels as a wave through the field, you usually accelerate a charged particle of some kind. Such waves can pass on energy to other charged particles.