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Author Topic: What do you think energy is and why do you believe that?  (Read 3689 times)

Offline PmbPhy

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In many discussions over the years its come to my attention that most physics enthusiasts, and even some professional physicists, don't know what energy is. That's why I'm asking the question What do you think energy is and why do you believe that?

My goal is that we all come to have the same understanding of what is meant by the term energy as its correctly used in physics so that when we discuss something dealing with it we won't have to worry about its meaning. Thanks for your contribution.
« Last Edit: 12/06/2016 09:34:34 by PmbPhy »


 

Offline Thebox

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Re: What do you think energy is and why do you believe that?
« Reply #1 on: 12/06/2016 07:43:59 »
In many discussions over the years its come to my attention that most physics enthusiasts, and even some professional physicists, don't know what energy is. That's why I'm asking the question What do you think energy is and why do you believe that? I'm asking so that I can learn what people here think it is so that we can come to understand the correct meaning of the term energy. By the correct meaning I'm talking about how I describe it on my website. Please understand that I'm not being arrogant by any means. I say this because I've studied the subject in depth, read several articles from physics texts and journals and from prominent physicists such as Richard Feynman, Sheldon Glashow, A.P. French, John Stachel, Alan Guth, etc. A solid study of the subject shows exactly what is meant by the term energy. That's how I came to write my webpage on the subject. All I did was take what has been described and explained by these brilliant well-experienced first rate physicists and put it in my own words.

My goal is that we all come to have the same understanding of energy so that when we discuss something dealing with it we won't have to worry about its meaning like what happened recently. Thanks for your contribution. Please take note of whose posts I can't see.

I think energy is just a word, a word we use because we don't actually understand what energy is, so we give it this group name of energy. Energy is a group name that contains sub groups.

 

Offline PmbPhy

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Re: What do you think energy is and why do you believe that?
« Reply #2 on: 12/06/2016 09:50:56 »
Quote from: Thebox
I think energy is just a word, a word we use because we don't actually understand what energy is, so we give it this group name of energy. Energy is a group name that contains sub groups.
Thanks for answering half the question. However, it's not at all helpful to me if you only say what you think energy is. It's more important to me to explain why you think its that way. In fact that's what I really want to know, i.e. why people think energy is what they believe it to be. Many people have very different beliefs about what energy is. My goal is to learn why. Therefore stating only what you think it means is totally useless to me.

Note: I modified the question so as to extract unhelpful and irrelevant comments. Also, I found a wonderful book online all about energy for those who are interested: Energy: A Beginner's Guide by Vaclav Smil. It can be downloaded for free at: http://book4you.org/book/697501/3fd733
All you have to do is register with the site. Registration is free and does not require a credit card.
 

Offline JohnDuffield

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Re: What do you think energy is and why do you believe that?
« Reply #3 on: 12/06/2016 11:08:17 »
What do you think energy is and why do you believe that?

I think energy is the fundamental thing from which matter is made.

I believe that because in his E=mc² paper Einstein said "If a body gives off the energy L in the form of radiation" and "The mass of a body is a measure of its energy-content".

Light is a form of energy, and energy is something that exists inside a body. For example the Poynting vector "means that there is a flow of energy going around the electron". Energy is something real rather than some bookkeeping abstraction.     
 

Offline acsinuk

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Re: What do you think energy is and why do you believe that?
« Reply #4 on: 12/06/2016 13:14:39 »
Light is fundamental magnetic energy represented by a vibration of an area of flux/current that can move through space effortlessly. If it interacts with neutron matter it can transfer the vibration energy by increasing the matters temperature.
 

Offline PmbPhy

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Re: What do you think energy is and why do you believe that?
« Reply #5 on: 12/06/2016 16:53:06 »
Note: I'd like to remind people who chose to respond to the question in the subject line that it's a two part question. The second part, i.e. why you believe what energy is, is actually the more important question. It's actually the reason I created this thread, i.e. I'm trying to understand where folks obtain their beliefs. Of course I'd be glad to state my own reasons if anybody really wants to know. However in my experience that's never been the case.

Light is fundamental magnetic energy represented by a vibration of an area of flux/current that can move through space effortlessly. If it interacts with neutron matter it can transfer the vibration energy by increasing the matters temperature.
I don't know why this came up but I'm guessing that JD posted something having to do with light. He's on my ignore list so I'm unable to see his posts.

Light is an electromagnetic (EM) wave whose wavelength lies in the range 390 to 700 nm. Most of the energy in an EM wave is in the electric field component. An EM wave cannot interact with neutrons because their charge is zero and are therefore unable to interact via the electromagnetic interaction. I.e. neutrons cannot couple to an EM field.

I noticed that you chose not to address the subject of this thread. Care to take a shot at it?
 

Offline Thebox

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Re: What do you think energy is and why do you believe that?
« Reply #6 on: 12/06/2016 17:23:50 »
Quote from: Thebox
I think energy is just a word, a word we use because we don't actually understand what energy is, so we give it this group name of energy. Energy is a group name that contains sub groups.
Thanks for answering half the question. However, it's not at all helpful to me if you only say what you think energy is. It's more important to me to explain why you think its that way. In fact that's what I really want to know, i.e. why people think energy is what they believe it to be. Many people have very different beliefs about what energy is. My goal is to learn why. Therefore stating only what you think it means is totally useless to me.

Note: I modified the question so as to extract unhelpful and irrelevant comments. Also, I found a wonderful book online all about energy for those who are interested: Energy: A Beginner's Guide by Vaclav Smil. It can be downloaded for free at: http://book4you.org/book/697501/3fd733
All you have to do is register with the site. Registration is free and does not require a credit card.

I never explained what I thought energy was, I explained what the word energy means, energy being a generalised group term with subgroups rather than something specific.
Elastic ''energy'', kinetic ''energy'', nuclear ''energy'' etc.

If I was to define energy as an entity ,  I would define energy as the  positive nature of positive work and expansion. My reason would be because:

+E=>4/3 pi³   because ''things'' expand when ''energy'' is gained in a ''things'' independent entropy (S).
 

Offline Bill S

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Re: What do you think energy is and why do you believe that?
« Reply #7 on: 12/06/2016 20:10:27 »
Thanks for this thread, Pete, especially for the second part of the question; it is always easier to say what you think than why you think it. Writing down the answer to the “why” is a good learning experience.

I’m with The Box in saying that energy is in some ways a blanket term, but I’m not sure his examples are of the best.  I would go for: Mass Energy, Kinetic Energy and Potential Energy.
 
Why? Because they manifest clear differences.  That said; I think it could be argued that there is only kinetic energy.

Why? Because, as JD quoted from Einstein: "The mass of a body is a measure of its energy-content".  This energy reflects atomic movement, so is, arguably, kinetic energy.

In the case of potential energy; the word “potential” implies that it is not actually energy, until it moves.  Thus, it is potential kinetic energy.

Acsinuk says: “Light is fundamental magnetic energy…”  This sounds like saying that a photon is pure energy, but perhaps that is my misinterpretation. In any event; experts seem to disagree on this point.
 
Matt Strassler; https://profmattstrassler.com/articles-and-posts/particle-physics-basics/mass-energy-matter-etc/matter-and-energy-a-false-dichotomy/  says:

“Energy is something that photons have; it is not what photons are.”

“ Photons are particles just as electrons are particles; they both are ripples in a corresponding field, and they both have energy.”

On the other hand, Sascha Vongehr http://www.science20.com/alpha_meme/quantum_perspective_nonexistence_light-76047

 argues that the energy of a photon = ħ, and that this is exhausted in a single reaction, after which the photon no longer exists.  This could be interpreted as saying that the photon is “pure energy”.

So, what do I think energy is?

I think it is a manifestation of the interaction between massive objects. 

I equate that with the statement that "The mass of a body is a measure of its energy-content" by suggesting that the interaction involved is that between atoms within the mass. 
 

Offline Thebox

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Re: What do you think energy is and why do you believe that?
« Reply #8 on: 12/06/2016 20:22:24 »


 
Matt Strassler; https://profmattstrassler.com/articles-and-posts/particle-physics-basics/mass-energy-matter-etc/matter-and-energy-a-false-dichotomy/  says:

“Energy is something that photons have; it is not what photons are.”



I personally would not agree with this, I do not think photons have ''energy'', I think they have potential energy and the ''energy'' is made/released when a photon interacts with ''matter'' or a medium.
I do not think energy exists unless there is a minimum of two components ''interacting''. 

 

Offline PmbPhy

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Re: What do you think energy is and why do you believe that?
« Reply #9 on: 13/06/2016 01:28:26 »
Regarding what energy is I was hoping that I'd see something that gives you enough information to be able to calculate it, it's properties, from those a way to determine how to calculate it, etc. When I asked "why" it was to seek out the source of your belief, i.e. where exactly did you learn it from.
 

Offline agyejy

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Re: What do you think energy is and why do you believe that?
« Reply #10 on: 13/06/2016 02:57:35 »
Just for the sake of accuracy:

Light is an electromagnetic (EM) wave whose wavelength lies in the range 390 to 700 nm. Most of the energy in an EM wave is in the electric field component. An EM wave cannot interact with neutrons because their charge is zero and are therefore unable to interact via the electromagnetic interaction. I.e. neutrons cannot couple to an EM field.

The energy and the electric and magnetic field components of a photon in free space are equal. Here is a reference:

http://physics.bu.edu/~duffy/PY106/EMWaves.html <- Lecture notes on EM waves

Quote from: The notes
The energy in an electromagnetic wave is tied up in the electric and magnetic fields. In general, the energy per unit volume in an electric field is given by:



In a magnetic field, the energy per unit volume is:



An electromagnetic wave has both electric and magnetic fields, so the total energy density associated with an electromagnetic wave is:



It turns out that for an electromagnetic wave, the energy associated with the electric field is equal to the energy associated with the magnetic field, so the energy density can be written in terms of just one or the other:



http://physics.info/em-waves/ <- Here is another source

Quote from: Another Source
For an electromagnetic wave in free space, half the energy is in the electric field and half is in the magnetic field

η = f5c9c91a150d2cbacffaafe8ad6db883.gif
 
η = 2093f73e4e518f0612402fa286c81906.gif + 2093f73e4e518f0612402fa286c81906.gif

This gives us this very compact equation for the total energy density of an electromagnetic wave…

η = c6a92804d5e4f09b959a2415cc19d3b1.gif

or this one, if you prefer to state things in terms of the magnetic field instead…

η = 5f623f322443ba002d7cdce28a4c23f6.gif

This is an interesting and simple set of relations, but keep in mind that it only works for electromagnetic waves in free space. Things are different in a media and the electric and magnetic fields can have any values they want if they're static.

http://web.mit.edu/8.02t/www/materials/StudyGuide/guide13.pdf <- Here is an example from MIT

Quote from: The MIT link
To relate intensity to the energy density, we first note the equality between the electric
and the magnetic energy densities ...

So except from some pretty specific cases in fairly specific materials the energies of the electric component and magnetic component of an EM wave are either identical or nearly equal.

Additionally, while the neutron has no net electrical charge it does have a magnetic field which means it can interact with an EM wave.

http://adsabs.harvard.edu/full/1993ApJ...417...12G <- Neutron-Photon scattering in the early Universe

Now the cross section for neutron-photon scattering is much lower than for proton-photon or electron-photon scattering but it isn't zero.
 
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Offline JohnDuffield

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Re: What do you think energy is and why do you believe that?
« Reply #11 on: 13/06/2016 08:29:50 »
Good stuff agyejy.
 

Online jeffreyH

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Re: What do you think energy is and why do you believe that?
« Reply #12 on: 13/06/2016 08:42:34 »
agyejy posted some interesting observations. Now John tell me where in the post the supporting evidence for the assertion that the electron is a knotted photon was made. I can't see it. That is what you believe though. You stated it publicly.
 

Offline acsinuk

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Re: What do you think energy is and why do you believe that?
« Reply #13 on: 15/06/2016 17:55:37 »
Photons are vibrating magnetic energy and can move through space effortlessly providing there is no voltage drop across the area of flux-current.  If they interact with a charged field of matter which provides a voltage then vibration energy can be transferred as heat
 

Offline IAMREALITY

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Re: What do you think energy is and why do you believe that?
« Reply #14 on: 15/06/2016 20:32:23 »
I think energy is merely an attribute of mass, and not these globs that are found anywhere in nature; but rather an abstract concept that exists merely in individual calculations, and something we haven't yet been able to wrap our heads around.

Why do I believe this?  Cause the very wise physicist Feynman believes that, and trust me; that dude knows what he's talking about!  Have you read or watched his lectures?  I'd point you to chapter 4-1 if you haven't.  It'll give you a good sense of what I'm talking about!!!

 :P
 

Offline PmbPhy

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Re: What do you think energy is and why do you believe that?
« Reply #15 on: 16/06/2016 06:44:32 »
Quote from: IAMREALITY
Why do I believe this?  Cause the very wise physicist Feynman believes that, and trust me; that dude knows what he's talking about!
Thank you very much for directly answering that part of the question. I greatly appreciate it. And it's nice to see someone who has the same take on the subject that I do!  :)

Quote from: IAMREALITY
Have you read or watched his lectures?
Yep.

Quote from: IAMREALITY
I'd point you to chapter 4-1 if you haven't.  It'll give you a good sense of what I'm talking about!!!
No need. I actually used it as a reference in the webpage where I address the question What is Energy? If you'd like to read it then just go to http://www.newenglandphysics.org/physics_world/cm/what_is_energy.htm

The reference at the bottom of the page reads
Quote
[2] The Feynman Lectures on Physics, Vol I, Feynman, Leighton, and Sands, Addison Wesley, (1963)(1989). Section 4-1 What is energy? page 4-1.

The other references read as follows. From reference [1] by H.A. Kramers who was talking about some of the more difficult concepts which need to be defined, he wrote
Quote
My own pet notion is that in the world of human thought generally, and in physical science particularly, the most fruitful concepts are those to which it is impossible to attach a well-defined meaning.

From reference [3] Newtonian Mechanics by A.P. French,
Quote
Of all the physical concepts, that of energy is perhaps the most far-reaching. Everyone, whether a scientist or not, has an awareness of energy and what it means. Energy is what we have to pay for in order to get things done. The word itself may remain in the background, but we recognize that each gallon of gasoline, each Btu of heating gas, each kilowatt-hour of electricity, each car battery, the wherewithal for doing what we call work. We do not think in terms of paying for force, or acceleration, or momentum. Energy is the universal currency that exists in apparently countless denominations.
     The above remarks do not really define energy. No matter. It is worth recalling once more the opinion that H.A. Krammers expressed: “The most important and fruitful concepts are those to which it is impossible to attach a well-defined meaning.” The clue to the immense value of energy as a concept lies in its transformation. It is conserved – that is the point. Although we may not be able to define energy in general, that does not mean that it is only a vague, qualitative idea. We have set up quantitative measures of various specific kinds of energy: gravitational, electrical, magnetic, elastic, kinetic, and so on. And whenever a situation has arisen in which it seemed that energy disappeared, it has always been possible to recognize and define a new form of energy that permits us to save the conservation law. And conservation laws, as we remarked at the beginning of Chapter 9, represent one of the physicist’s most powerful tools for organizing his description of nature.

From reference [4],l i.e. Thermal Physics Daniel V. Schroeder wrote
Quote
To further clarify matters, I should really give you a precise definition of energy. Unfortunately, I can't do this. Energy is the most fundamental dynamical concept in all of physics, and for this reason, I can't tell you what it is in terms of something more fundamental. I can, however, list the various forms of energy - kinetic, electrostatic, gravitational, chemical, nuclear - and add the statement that, while energy can often be converted from one form to another, the total amount of energy in the universe never changes. This is the famous law of conservation of energy. I sometimes picture energy as a perfectly indestructible (and unmakable) fluid, which moves about from place to place but whose total never changes. (This image is convenient but wrong - there simply isn't any such fluid).

Since I wrote that I've been wrestling with the common definition where most physicists claim that energy is defined as the ability/capacity to do work.
 

Offline Colin2B

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Re: What do you think energy is and why do you believe that?
« Reply #16 on: 16/06/2016 12:37:47 »
Since I wrote that I've been wrestling with the common definition where most physicists claim that energy is defined as the ability/capacity to do work.
Just a few thoughts rather than a definitive reply:

I think there are 2 levels to energy. At the top level I agree with majority of physicists who describe it as a property of objects and systems. I also view it is an abstract, mathematical concept that allows us compare disparate properties in a consistent manner. In this way we can talk about forms of energy, transfer of energy, energy content, storage etc and convert between different forms, almost like transferring between bank accounts and undergoing a currency conversion. Why do I think this, because this is the way I was taught to think about it. Also, it makes sense when you do the experiments to establish the relationship between, say, work and heat - you put a paddle in water, do work with the paddle, measure the heat and effectively calculate the conversion factor. It also makes sense when you consider what I think of as the next layer down.

At the next level down we have to ask what is actually happening, because there is no substance or thing being transferred or stored. In most cases the mechanics appear to involve either activity or the potential for activity. Heat being activity of molecules, light the activity of the em fields, stored chemical energy the amount of activity necessary to separate compounds, etc. In each case there is a root cause, rather than a mystical component.




 

Offline JohnDuffield

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Re: What do you think energy is and why do you believe that?
« Reply #17 on: 16/06/2016 14:12:48 »
agyejy posted some interesting observations. Now John tell me where in the post the supporting evidence for the assertion that the electron is a knotted photon was made. I can't see it.
See Pete's website article: http://www.newenglandphysics.org/physics_world/cm/what_is_energy.htm

"An interesting example of energy flow is the energy flowing around an electron. An electron has a charge as well as a magnetic moment. It therefore has a magnetic field. The cross product of the electric field E and magnetic field H gives the Poynting vector S = ExH which is the energy flow per unit volume. See Figure 4 below:



This means that there is a flow of energy going around the electron. What is it that's actually flowing? All we can do at this point is give it a name. And the name we give it is energy."


The Poynting vector for the electron goes round and round, the Poynting vector for a photon is linear:

« Last Edit: 21/06/2016 14:51:00 by JohnDuffield »
 

Online jeffreyH

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Re: What do you think energy is and why do you believe that?
« Reply #18 on: 16/06/2016 16:57:50 »


Show me where in this article where the Poynting vector is spinning round and round an electron.
https://en.m.wikipedia.org/wiki/Poynting_vector

You try to make it look like you know what you are talking about by misrepresenting the work of others. This may be because you have no original work of your own to present.
 

Online jeffreyH

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Re: What do you think energy is and why do you believe that?
« Reply #19 on: 16/06/2016 17:34:51 »
Tellingly John what you neglected to post was the next paragraph from Pete's page.

"How seriously must we take the physical existence of this energy? No more and no less than any other bookkeeping practices. The physical quantities are those such as the EM field."

To neglect this paragraph is to misrepresent Pete's intention for your own ends. That is not an honest way to promote your case.
 

Offline PmbPhy

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Re: What do you think energy is and why do you believe that?
« Reply #20 on: 16/06/2016 18:27:12 »
Quote from: agyejy
The energy and the electric and magnetic field components of a photon in free space are equal. Here is a reference:
I'm a firm believer of admitting ones mistake as soon as possible and in this case I appear to be quite wrong. I must have remembered that wrong. So thank you for correcting my mistake. It's greatly appreciated.  :)
 

Offline Colin2B

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Re: What do you think energy is and why do you believe that?
« Reply #21 on: 17/06/2016 14:52:15 »
Tellingly John what you neglected to post was the next paragraph from Pete's page.

"How seriously must we take the physical existence of this energy? No more and no less than any other bookkeeping practices. The physical quantities are those such as the EM field."

To neglect this paragraph is to misrepresent Pete's intention for your own ends. That is not an honest way to promote your case.

An important paragraph which aligns with light not being energy, but the oscillation of the EM fields just like any other wave where a physical property oscillates.
 

Offline garth john greiner

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Re: What do you think energy is and why do you believe that?
« Reply #22 on: 21/06/2016 12:16:05 »
I believe that energy is a fundamental part of universal mechanics. The production of Energy in my opinion is a direct result of the behavior of  chemicals interacting with each other to form anything from star systems to intelligent life forms.
I feel that energy and purpose work together to deliberately form life. ( im a strong believer in the anthropic principle). The reason i feel this way about energy is i observe how my own body produces energy or indeed struggles to as the case maybe
and i spend alot of time observing nature. My answer to this question is limited to a post big bang understanding. A little look at pre-big bang energy production might be interesting ;-)
 

Offline JohnDuffield

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Re: What do you think energy is and why do you believe that?
« Reply #23 on: 21/06/2016 14:55:29 »
Show me where in this article where the Poynting vector is spinning round and round an electron.
It doesn't mention the electron, but see the static field section: "Although there are only static electric and magnetic fields, the calculation of the Poynting vector produces a clockwise circular flow of electromagnetic energy, with no beginning or end. While the circulating energy flow may seem nonsensical or paradoxical, it is necessary to maintain conservation of momentum".

You try to make it look like you know what you are talking about by misrepresenting the work of others. This may be because you have no original work of your own to present.
I'm not misrepresenting anything. The article on pmb's website says what it says, and so does the Wikipedia article.

Tellingly John what you neglected to post was the next paragraph from Pete's page.

"How seriously must we take the physical existence of this energy? No more and no less than any other bookkeeping practices. The physical quantities are those such as the EM field."
Don't blame me if the article says What is it that's actually flowing? All we can do at this point is give it a name. And the name we give it is energy" and then contradicts itself by claiming this thing flowing round and round is some book-keeping abstraction. 
« Last Edit: 21/06/2016 15:00:29 by JohnDuffield »
 

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Re: What do you think energy is and why do you believe that?
« Reply #24 on: 21/06/2016 15:15:13 »
Energy is just that. Book keeping. Since it deals with conservation it is a book balancing act. You cannot say that something mathematical in nature has to have a strictly physical existence. I don't ever see Mr pi walking down the high street. Or Mrs sigma either. Some people may see imaginary things and they may well be numbers but it doesn't make them real.
 

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Re: What do you think energy is and why do you believe that?
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