Are photons energy? What is energy, anyway?

arfa brane:

Look, this is ridiculous. Just above, I gave you a concise definition of the term "reification". Granted, it's probably a new idea for you, but to use that term in a way that would give it almost the exact opposite meaning to the one I just explained for your benefit, and to do so practically in your next post, is either arrogant wilful ignorance or else bullheaded stupidity. Either way, I'm coming to the view that further discussion with you on this topic is likely to be a huge waste of my time, since you're obviously not listening to anything I have to say.

Fundamentally, energy is a property of a system of one kind of another. It doesn't so much get transferred from place to place as it gets converted from one form to another. Fundamentally, it is an accounting system. Feynman's explanation of it in his famous Lecture on Physics is a good one.

I didn't say it doesn't exist. I said it isn't a substance. Love exists, but it's not a substance.

Yes. In other words, the concept of kinetic energy is a useful way to assign a quantitative measure to particle motion,

Substitute? Motion is not energy. Energy is not motion.

What happens is that we have a number, called the total energy of the system. That number is the sum of a partition of various "kinds" of energy that we assign to the system. For example, the total energy might be the sum of kinetic and potential energy. Then, when the system changes in some way, we take some energy out of the "kinetic" column and put it in the "potential energy" column, or vice versa. Often the total energy remains constant, which is one of the things that makes energy such a useful idea.

Point is: shuffling numbers from one column to another is quite unlike transferring a physical substance from one place to another.

 

Do you think physics professors are infallible, perfect human beings who never make mistakes?

Is it possible that there could be significant numbers of physics professors out there who have some screwy idea about energy?

Note, that it may be possible to have some wrong-headed ideas and not have it affect your daily work in the least, because getting the concept wrong doesn't actually affect the calculations you're performing using that concept, or the numbers you get out when you calculate.

Yes, photons propagate at c. No, photons are not a form of energy, for reasons I have clearly explained. Yes, photons have an energy associated with them that we can take from one column and put into another column when a photon interacts with something else.

A photon is not a field. You could say it is an excitation of a field, if you like.

And yes, I have already "admitted" that we can associate an energy density with electric and magnetic fields - make a new column in the "energy" table and write down some numbers associated with the fields in a particular region. When certain physical processes occur, we can move some numbers from one of those columns into a different column, so to speak.

They aren't equivalent. Not really. Not unless you regard "mass" as simply a number we associate with "stuff".

 

If this is you coming around just a little, then I'm glad you're getting there. We'll wait and see how paddoboy goes.

Energy, being an abstract concept, is hard to think about. The problem is, it's such a useful concept that the idea has percolated through so that every non-expert man-in-the-street believes he has an idea of what energy is. To an extent, that's true, but one problem is that it is very easy to start thinking of energy as a "thing" that can move around and to exist almost independently of other "stuff". Worse, this kind of thinking is actively promoted by people who know nothing about what energy actually is. People talk about "spiritual energy" and "crystal energy" and "energy auras" and all kinds of things like that. In sci-fi films we see glowing "creatures of pure energy" and things like that, despite the fact that such a notion makes no sense at all.

When you pay your electricity bill, you're not paying for some energy "stuff" to be shipped from the power station to your home via wires. Really, you're paying for the coal that is burned to drive electrons through your wires.

No textbook is perfect. There are many reasons that faculties choose one book rather than another. It may be that the content is good on some topics, not so great on others. It could be that the publisher gave the faculty a good deal to use the textbook and associated resources. It could also be the flaws are considered minor and unimportant in the context of what is being taught, or even that the flaws are not noticed.

 

paddoboy:

The debate is not about what is "real", but about what is a substance and what isn't. Time is not a substance. As for "space", it really depends on how you choose to define that word. I don't think "spacetime" is a substance, at least not in any way that I use that concept.

And so.... what?

You're hopelessly muddled. The form of your argument in this quote goes like this: M is E, but E is not M. You're contradicting yourself.

You only had to read though one post. I gave you the post number. Why are you so lazy? Here's the quote from post #81:

You: "So what part of the photon is not actually part of this energy that it is said to carry?"
Me: "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."
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You are very definite about that. Okay, please identify for me which fundamental particles in the Standard Model of Particle Physics are matter, and which are not. Are neutrinos matter? Are W bosons matter? Is the Higgs boson matter? Are electrons matter? Are quarks matter? Are gluons matter? What makes one particle matter and another not? Please tell me.

If you think that you have a rock solid definition of "matter", tell me what it is.

There is no wiggle room when you make a silly statement like "photons are energy". They aren't. There's no ambiguity in that. Energy is not "stuff". Energy is not a substance. Energy is not photons.

Either your ego is getting in the way to such an extent that you simply refuse to see the obvious, or else you're not intellectually equipped to follow the argument I have put to you. Those are really the only options at this point.

I think you're too entrenched in your position to do the honourable thing and back down on this. This discussion has evolved to the point where the most interesting question is the test of your character, or lack thereof. There's really nothing further to discuss on the matter of whether a photon is or isn't energy.

 

Quoting yourself as an authority now?

This: "while all mass is energy, not all energy is mass" is wrong.

Mass is not energy. Not if by "mass" you mean "matter". Just above, you were trying to distinguish photons from "matter", saying that photons can be energy because they are not "matter". But here you are saying that all "mass" is energy, just like all photons are energy.

So, it looks like I was right all along. You are actually making the mistake of assuming that every kind of particle is energy. Hence everything with mass is energy and photons, even though they have no mass, are energy as well.

Just to be clear then, you are saying that the only thing that exists in the universe is "energy". Would that be a fair summation of your position, given that all mass is energy as well as all the other energy that is not mass?