# Thread: Is Negative energy real?

1. To explain why energy exist, scientists propose that there is negative energy in space, enough negative energy to make sure the positive and negative energy in space end up to zero. So anyone did the experiment to prove negative energy's existence, or it is just a theories ?

2. Originally Posted by johnzxcv
To explain why energy exist, scientists propose that there is negative energy in space, enough negative energy to make sure the positive and negative energy in space end up to zero. So anyone did the experiment to prove negative energy's existence, or it is just a theories ?
Energy isn't something that has a physical existence like an electron or an EM field. It's basically a bookkeeping system. It's a mathematical construct which describes a constant associated with systems. For example; If the force on a particle is F and it has the property that there exists a mathematical function V such that F = -grad V (which grad = gradient) then V is called the potential energy function. When a amount of work W is done on a body and that work changes the bodies speed then there is a function K such that amount of work W = change in K. K has the value K = mv^2/2 and is called the kinetic energy of the particle. If V is not a function of time then it can be shown that V + K is a constant during the motion of the particle. We give that constant a name and call it the mechanical energy of the particle. V and K are defined only up to a constant which means you can change the value of each without changing the physical results. The constant related to K is chosen such when v = 0 then K = 0. The constant related to V is chosen for convenience. For the gravitational potential energy that constant is set such that V(r) is zero at infinity so that the potential energy in the absence of gravity is zero.

If F is the force on the particle is a gravitational force then the potential energy is zero. If the particle is at rest then the total mechanical energy is zero. To measure that all you do is measure the location of the particle and plug that value into V to get E and you'll get a negative result. The same is true with a negatively charged particle. So the energy of a positively charged particle at rest in an electrostatic field is negative too.

It should be noted that the energy in both cases is always negative regardless of what those constants are set equal to.

So yes. There negative energy is very real. This is a universally known fact in physics. Any physicist will tell you the same thing.

3. So Negative energy is a theories . And nobody did the experiment to prove it's existence?

Just about anything in physics is "just a theory". There is very little "concrete proof" of any theory being ABSOLUTELY correct. "Physics theory" is so difficult because of the nature of

what is being examined...the majority of the time, experiments show results that posit a "thing or factor MAY be true.

......

"Negative energy" represents a "possibility" factor that deals with QM and would be difficult to prove as a genuine factor...a "real" thing. It may last as a theory, or may be gone in 6 months.

5. Originally Posted by Gerry Nightingale

Just about anything in physics is "just a theory". There is very little "concrete proof" of any theory being ABSOLUTELY correct. "Physics theory" is so difficult because of the nature of

what is being examined...the majority of the time, experiments show results that posit a "thing or factor MAY be true.

......

"Negative energy" represents a "possibility" factor that deals with QM and would be difficult to prove as a genuine factor...a "real" thing. It may last as a theory, or may be gone in 6 months.

Man if we can build a machine that fire negative energy . It will be so cool.
I mean we can make other object immediately cold and gain positive energy .

6. Originally Posted by johnzxcv
So Negative energy is a theories . And nobody did the experiment to prove it's existence?
Recall that I explained above that To measure that all you do is measure the location of the particle and plug that value into V to get E and you'll get a negative result. This is not something an experiment can be created for to prove it's existence. Not everything in nature is like that. For example; let a two charges of the same magnitude but opposite charge be separated by a distance r. That is to say that the negatively charged particle has charge q1 = -e (where e > 0) and the positively charged particle has charge q1 = e.
The potential energy of the two charge system is defined to be

So you see? The potential energy is negative by definition. If you wanted to measure it then the way to do it is to measure the charge on each particle and measure the distance between them and then use the expression above to calculate it.

Do you see what I mean now that energy is not something that is really proved to be negative by measurement? There are of course situations in which the results of an experiment imply that the potential energy has a particular value but that depends on a particular example. I don't have a very illustrative example in mind right now. Perhaps someone else does. If not and its something you must have then I'll keep it in mind and when it comes to mind someday I'll let you know. Okay? That might be weeks, months or minutes.

7. Originally Posted by johnzxcv
To explain why energy exist, scientists propose that there is negative energy in space, enough negative energy to make sure the positive and negative energy in space end up to zero. So anyone did the experiment to prove negative energy's existence, or it is just a theories ?
It's misunderstanding. And there's a lot of misunderstanding in physics.

For example, some physicists will tell you that energy is just some bookkeeping system that has no physical existence. This is absolutely wrong. Matter is made of energy. That's what E=mc² is all about. See for example Compton scattering. That's where a light wave is used to move an electron. The light wave loses energy as a result. If you did another Compton scatter with that light wave, and another and another and another, then in the limit you have removed all of the energy from the wave, and you have no wave left. All of the wave energy has been converted into the motion of electrons. Now look at pair production. You can convert a photon into an electron and a positron. So in a way an electron is made out of something that can be converted into the motion of an electron. In a way the electron itself is "made out of motion". But what we actually say is that matter is made out of energy.

And it's always positive energy. When potential energy is "defined" to be negative, there isn't really any negative energy anywhere. There's just less positive energy. There are no negative energy photons or particles or fields. None. The notion that there's negative energy in space is a popscience myth.

8. Originally Posted by Farsight
It's misunderstanding. And there's a lot of misunderstanding in physics.

For example, some physicists will tell you that energy is just some bookkeeping system that has no physical existence. This is absolutely wrong. Matter is made of energy. That's what E=mc² is all about. See for example Compton scattering. That's where a light wave is used to move an electron. The light wave loses energy as a result. If you did another Compton scatter with that light wave, and another and another and another, then in the limit you have removed all of the energy from the wave, and you have no wave left. All of the wave energy has been converted into the motion of electrons. Now look at pair production. You can convert a photon into an electron and a positron. So in a way an electron is made out of something that can be converted into the motion of an electron. In a way the electron itself is "made out of motion". But what we actually say is that matter is made out of energy.

And it's always positive energy. When potential energy is "defined" to be negative, there isn't really any negative energy anywhere. There's just less positive energy. There are no negative energy photons or particles or fields. None. The notion that there's negative energy in space is a popscience myth.
So you say that negative energy doesn't exist. Is that your point?

An excellent reply! I may not agree with some things (or a lot of things...my take on "light" is extremely wacky) but a proper analysis is a proper analysis, always.

......

10. Originally Posted by Gerry Nightingale

An excellent reply! I may not agree with some things (or a lot of things...my take on "light" is extremely wacky) but a proper analysis is a proper analysis, always.

......

Thanks Gerry!

11. Originally Posted by johnzxcv
So you say that negative energy doesn't exist. Is that your point?
Yes. There is no such thing as negative energy, just as there's no such thing as negative length. One length can be shorter than another, and you can say the difference between two lengths is "minus five metres", but there is no actual thing that exists that has a length of minus five metres.

12. Originally Posted by Farsight
Yes. There is no such thing as negative energy, just as there's no such thing as negative length. One length can be shorter than another, and you can say the difference between two lengths is "minus five metres", but there is no actual thing that exists that has a length of minus five metres.
If so how do we answer the question: Where does energy come from?

13. We can't. Conservation of energy is one of the most important tenets in physics. Energy can be neither created no destroyed. You will find people talking about "creation ex-nihilo", but I find it very unconvincing myself. So for this one it's hands up, and it's dunno guv.

14. Originally Posted by Farsight
We can't. Conservation of energy is one of the most important tenets in physics. Energy can be neither created no destroyed. You will find people talking about "creation ex-nihilo", but I find it very unconvincing myself. So for this one it's hands up, and it's dunno guv.
Thanks

15. So you say that negative energy doesn't exist. Is that your point?
It really very much depends what type of "energy" you are talking about.
In most instances, energy is not a directly measurable quantity; furthermore, where you choose the zero point of energy to be is completely arbitrary. For example, in classical mechanics it is convention to set the zero point of gravitational potential energy at infinity, so every point within a gravitational field has negative potential energy. There is no problem with this whatsoever, because the only quantity that is directly measurable is not potential energy, but the gradient of the potential field, in other words differences in energy - and these are always positive. The same is true for kinetic energy, which is just the integral of momentum with respect to velocity :

In classical mechanics we usually set the integration constant C=0, but that choice is arbitrary, because again you cannot directly measure kinetic energy, only the work that you can perform as a result of it.

So in summary, there is no problem with the concept of negative energy at all; it works just fine, under some circumstances at least. The really interesting question is whether or not there is such a thing as negative energy density, which is a different matter altogether. In classical physics, the answer to this has to be a clear no, because such a concept would violate a number of energy conditions; in quantum physics however the situation is not so clear cut, because there are issues of regularisation and choice of gauge to consider. For example, in the Casimir effect the energy density between the plates is lower than in the surrounding vacuum region - if you take the vacuum energy density to be zero, then your Casimir region has a negative energy density. However, this is again an arbitrary choice, and when you compute the expectation value of your energy-momentum tensor, it is regular and well behaved.

It really all boils down to this - energy in and of itself is not observable or measurable, it is just a mathematical bookkeeping device, and as such the concept of negative energy is well defined and quite ordinary in some circumstances. What is observable are the effects this has, and once again we find that these are well within the laws of physics as we know and understand them.

16. Originally Posted by Markus Hanke
...energy in and of itself is not observable or measurable, it is just a mathematical bookkeeping device...
Markus, where did you learn this? Have a read of Einstein's E=mc² paper. The mass of a body is a measure of its energy-content. If a body gives off the energy L in the form of radiation, its mass diminishes by L/c². According to Einstein, energy isn't just some mathematical book-keeping thing, it's something real. Matter is made of it.

17. Markus, where did you learn this? Have a read of Einstein's E=mc² paper. The mass of a body is a measure of its energy-content. If a body gives off the energy L in the form of radiation, its mass diminishes by L/c². According to Einstein, energy isn't just some mathematical book-keeping thing, it's something real. Matter is made of it.
Sorry, I should have qualified this in the same way as I did in the first sentence - in most instances, energy is not directly observable. In the case of mass it clearly is, of course, but in other cases - such as gravitational potential energy - it is not.

18. That's muddied the waters. Because when you throw a brick up into the air and give it gravitational potential energy, you increase its mass!

Strictly speaking we should talk about the Earth-brick system, but the Earth's motion isn't measureable, and whilst momentum is p=mv is equal and opposite, KE=½mv² means the brick gets virtually all the energy. And at the top of its arc the kinetic energy has been converted into gravitational potential energy, and it's in the brick. Not in the Earth, not in the intervening space, not in the gravitational field, but in the brick. You can work this out by giving the brick 11km/s worth of kinetic energy. Then it and the energy you gave it leaves the system. Or you know it already, because you know about the mass deficit. Start with a brick drifting in free space that happens to come across the Earth. The brick falls, some of its mass-energy is converted into kinetic energy, and it hits the ground at 11km/s. The kinetic energy is dissipated and radiated away, and the cooled-down brick has lost a little mass. It has a mass deficit or defect. We say binding energy is negative, and we say gravitational potential energy is negative, but it's just less mass-energy, not actual negative energy.

19. That's muddied the waters. Because when you throw a brick up into the air and give it gravitational potential energy, you increase its mass!
Whatever it is you are trying to say, you still don't observe gravitational potential energy directly, only the effects of its gradient. You can only ever measure a difference in gravitational potential, not the potential itself.

20. Who wrote this?

Markus: I'd like to as a favor of you. I enjoy reading your posts. You have a keen mind and I don't want to miss out on what you have to say in threads I have an interest in. However if I don't know who you're referring to when you quote someone then things can get confusing. Therefore in the future please make it clear who you're quoting. It makes things hard if you don't because quite often some of the people you're quoting are in my ignore list and I can't see who's saying what.
Markus, where did you learn this? Have a read of Einstein's E=mc² paper. The mass of a body is a measure of its energy-content. If a body gives off the energy L in the form of radiation, its mass diminishes by L/c².
That part is very true.

According to Einstein, energy isn't just some mathematical book-keeping thing, it's something real. Matter is made of it.
This part is quite untrue. Mass truly is a bookkeeping system and Einstein knew this very well. Einstein said that the relationship E = mc2 only means that mass is equivalent to energy whereby equivalent he meant what Baierleina described in Does nature convert mass into energy? by Ralph Baierleina, Am. J. Phys. 75 4, April 2007, which is online at http://www.uaz.edu.mx/neutron/fm/lit...w/AJP75320.pdf
Originally Posted by Ralph Baierleina in American Journal of Physics
Just what did Einstein mean by “equivalence”? The Appendix gives my historical evidence; here I state only my conclusion. All things considered, I think it fair to say that, for Einstein in 1907, the “equivalence of mass and energy” meant a numerical proportionality between the two quantities. Inertia and energy remained distinct—though profoundly related—concepts. No subtle intrinsic identity of the
two notions was proposed or intended.
There has never been and there never will be a physical basis for asserting that energy is a physical entity. It has never be defined that way, it has never been used that way and those physicists who know what they're talking about don't think of it that way.

Mass
Mass in special relativity - Wikipedia, the free encyclopedia
Energy - Wikipedia, the free encyclopedia (caution - this page has errors in it)

21. Farsight, I've had this argument before on Physics Forums and got 3 penalty points for even suggesting it. These points took 6 months to expire, lol. I was trying to make the point that the energy resides in the mass by virtue of it's position but I kept getting back that was stored in the field. What field? I said GR doesn't have fields. Then I got reported, haha. The points expired at the end of July, but I am mightily encouraged by the three new ones I got today for suggesting that QM is a result of time actually having 2 dimensions. Well thankfully this is not just my speculation so I am hopeful my appeal will be successful. Sorry for the diversion folks, just wants to share!
This forum is so much more interesting and a much nicer place to hang out.

Cheers!

Why would want to join such an insipid forum? Where if you speak your thoughts on a "touchy" you get "points" (demerits?)

Not casting aspersions on your age...but aren't you a tiny bit old for nonsense? (site sounds like a "load" to me!)

Thanks for the excellent post!!! I have had the same thoughts for twenty-plus years and STILL NO ONE "SEES"...why? (I have been excoriated on TWO SITES for basically stating the

same thing!!! Why?)

.....

"Matter is not energy of itself...rather, matter is the potential to manifest energy"<(by me, not my cousin the other Nightingale)

24. Originally Posted by Gerry Nightingale
Thanks for the excellent post!!! I have had the same thoughts for twenty-plus years and STILL NO ONE "SEES"...why?
Thanks Gerry. You’re very kind and most generous! Thank you for the kind remarks.
Originally Posted by Gerry Nightingale
I have been excoriated on TWO SITES for basically stating the same thing!!! Why?
Shear arrogance and ignorance I’d say. The next time it comes up refer them to
[b]The Feynman Lectures on Physics, Vol I[/i] by Feynman, Leighton, and Sands, Addison Wesley, (1963)(1989). Section 4-1 What is energy? page 4-1
Originally Posted by Richard Feynman
It is important to realize that in physics today, we have no knowledge of what energy is. We do not have a picture that energy comes in little blobs of a definite amount. It is not that way. However, there are formulas for calculating some numerical quantity, and we add it all together it gives “28” - always the same number. It is an abstract thing in that it does not tell us the mechanism or the reasons for the various formulas.
Originally Posted by Gerry Nightingale
"Matter is not energy of itself...rather, matter is the potential to manifest energy"<(by me, not my cousin the other Nightingale)
People like to see these things come from “the man” himself. From The Foundation of the General Theory of Relativity by Albert Einstein, Annalen der Physik, 49, 1916 (See - Deep questions)
Originally Posted by Albert Einstein
We make a distinction hereafter between “gravitational field” and “matter” in this way, that we denote everything but the gravitational field as “matter.” Our use of the word therefore includes not only matter in the ordinary sense, but the electromagnetic as well.
That might shut some of them up.

Actually you should read the entire paragraph
Is an electromagnetic field or an electromagnetic wave, such as a radio wave, a form of matter?

Electromagnetic fields and waves have energy, and hence have mass. They therefore must be regarded as a form of matter. This view was first introduced by Einstein when he formulated his theory of gravitation: “We make a distinction hereafter between ‘gravitational field’ and ‘matter’ in this way, that we denote everything but the gravitational field as ‘matter.’ Our use of the word therefore includes not only matter in the ordinary sense, but the electromagnetic field as well.” If we think of solids, liquids, gases, and plasmas as the first four states of matter, then electromagnetic fields and waves are the fifth state of matter.

Thanks for the affirmation, or rather....thanks from Albert (he did this first and best, devoid of personal ego.

(You are "preaching to choir" referencing Einstein to me...I regard his masterworks first and last before anything else, and then "pro-rate" it to any "new" hypothesis in theory.) This would

include my own junk as well. Many in QM feel Relativity is "old hat" and inappropriate for modern theory, that calculus "rules all" w/ regard to "new conditions".

I cannot subscribe to these opinions...and when I read of "new" findings I cringe. (my mind is too old to "accept magic as real", no matter how many say it is true)

.....

All I really want is the "truth of things"...and I have yet to find anything modern that "sticks"

26. Originally Posted by Gerry Nightingale
Thanks for the affirmation, ...
You're welcome

...or rather....thanks from Albert (he did this first and best, devoid of personal ego.
Or rather you're welcome for finding the quote for you.

Originally Posted by Gerry Nightingale
Many in QM feel Relativity is "old hat" and inappropriate for modern theory, that calculus "rules all" w/ regard to "new conditions".
I don't understand. They address nature from two different points of view. Relativity is mechanics for the macroscopic and very fast while QM is mechanics for the subatomic level with speeds v << c. Relativistic quantum mechanics is for the microscopic and very fast.

Originally Posted by Gerry Nightingale
(my mind is too old to "accept magic as real", no matter how many say it is true
Magic? What magic?

27. Interesting thread, so I hope it's okay for me to jump in and share my mind.

Negative energy and positive energy comes down to ground potential, we observe the world from our own frame of reference. As we live in a gravitational field the arrow of time and therefore the arrow of decreasing potential points from the past to the future which is radially inwards to the centre of gravity. We know this because an apple falling from a tree, never fails to arrive in it's own future, so all we have to do is draw the line.

We already know that looking out into the Universe is looking into the past, so it is not such a stretch of the imagination to see that the future is down. So we could say that all energy lower than ground potential is negative energy with respect to the observer.

Steven

28. Originally Posted by StevenS
Negative energy and positive energy comes down to ground potential, ....
What do you mean when you speak of ground potential? I.e. what exactly is ground potential?

Originally Posted by StevenS
...we observe the world from our own frame of reference.
Who is "we"? Different people live at different distances from the center of the earth and therefore at different gravitational potentials. For example, people in Denver CO, the mile high city, live at a much higher potential than people in Miami FL.

Originally Posted by StevenS
As we live in a gravitational field the arrow of time ...
I don't know whether you're aware of it or not but the proverbial "arrow of time" does not point in directions in spatial dimensions but in different directions in the time dimension.

Originally Posted by StevenS
...and therefore the arrow of decreasing potential points from the past to the future which is radially inwards to the centre of gravity.
If is the gravitational potential then the "arrow" of decreasing potential points in the direction . If you know your vector calculus then you know that this is the gravitational force Fg, i.e. .

Originally Posted by StevenS
We know this because an apple falling from a tree, never fails to arrive in it's own future, so all we have to do is draw the line.
Yes, but you're neglecting to take into consideration the case where the apple starts out with a non-zero velocity. If the velocity is large enough, i.e. larger than what's called escape velocity then it keeps going and doesn't stop.

Originally Posted by StevenS
We already know that looking out into the Universe is looking into the past, so it is not such a stretch of the imagination to see that the future is down. So we could say that all energy lower than ground potential is negative energy with respect to the observer.
Sorry, Steven, but not only is that bad argument but it's an incorrect one as well.
That onl

29. So are you saying that the arrow of time does not point in the direction of lower potential?

Steven

30. Originally Posted by StevenS
So are you saying that the arrow of time does not point in the direction of lower potential?

Steven
That's correct. Please keep in mind that you might be using the term differently than I am. I'm using it as defined here under Sean Carroll's website at Arrow of Time FAQ
What is the arrow of time?

The past is different from the future. One of the most obvious features of the macroscopic world is irreversibility: heat doesn't flow spontaneously from cold objects to hot ones, we can turn eggs into omelets but not omelets into eggs, ice cubes melt in warm water but glasses of water don't spontaneously give rise to ice cubes. We remember the past, but not the future; we can take actions that affect the future, but not the past (we can't unto our mistakes). We are all born, then age, then die; never the other way around. The distinction between past and future seems to be consistent throughout the observable universe. The arrow of time is simply that distinction, pointing from past to future.
You have it all mixed up with space and causality. I don't know why you're doing that.

31. Originally Posted by Jilan
Farsight, I've had this argument before on Physics Forums and got 3 penalty points for even suggesting it.
You shouldn't have. On page 185 of the Doc 30 Foundation of the General Theory of Relativity Einstein says "the energy of the gravitational field shall act gravitatively in the same way as any other kind of energy". It's quite clear that Einstein thought of energy as something real.

Originally Posted by Jilan
I was trying to make the point that the energy resides in the mass by virtue of it's position but I kept getting back that was stored in the field.
It isn't. You do work on the brick. You add energy to the brick. What's rather strange is how some people penalise people for saying something that's right.

Originally Posted by Jilan
I said GR doesn't have fields. Then I got reported, haha. The points expired at the end of July, but I am mightily encouraged by the three new ones I got today for suggesting that QM is a result of time actually having 2 dimensions.
Ummm. Time doesn't have two dimensions.

Originally Posted by Markus Hanke
Whatever it is you are trying to say, you still don't observe gravitational potential energy directly, only the effects of its gradient. You can only ever measure a difference in gravitational potential, not the potential itself.
Clocks rates relate to potential. You can plot the gravitational potential by placing clocks in an equatorial slice of space around the Earth.

Originally Posted by StevenS
So are you saying that the arrow of time does not point in the direction of lower potential?
There isn't any arrow of time. It's just an abstract concept. Our is a world where things move and change. Have a look at the gif on the Wikipedia temperature page. Gaze at it for a while. The red dots are moving fast. Collisions occur, they give some of their kinetic energy to the slower blue dots. The temperature of the gas molecules equalizes, entropy increases, the system evolves, and people assign a "direction" to this. But it's just stuff moving and changing, that's all.

Considering how much I have advocated that energy and gravity exist as actual "metrics of potential", i.e., they exist of themselves independent of matter...it's remarkable how much time

everyone spends in engaging in discourse of "field theory" and then turn round and say "particles are all things!"

.....

If "QM" has it's way (and it does, never dare to question it) then surely, at some point, the idea of "fields" must be denied.

(Thanks for reading!) psssst, Jilan...never "rock the boat". It's been sinking for years, and no one will like you pointing that fact out to them!

33. Originally Posted by Gerry Nightingale

Considering how much I have advocated that energy and gravity exist as actual "metrics of potential", i.e., they exist of themselves independent of matter...it's remarkable how much time

everyone spends in engaging in discourse of "field theory" and then turn round and say "particles are all things!"

.....

If "QM" has it's way (and it does, never dare to question it) then surely, at some point, the idea of "fields" must be denied.

(Thanks for reading!) psssst, Jilan...never "rock the boat". It's been sinking for years, and no one will like you pointing that fact out to them!
You mean gravity and particles are not the same thing.

34. Originally Posted by Jilan
Farsight, I've had this argument before on Physics Forums and got 3 penalty points for even suggesting it. These points took 6 months to expire, lol. I was trying to make the point that the energy resides in the mass by virtue of it's position but I kept getting back that was stored in the field. What field? I said GR doesn't have fields. Then I got reported, haha. The points expired at the end of July, but I am mightily encouraged by the three new ones I got today for suggesting that QM is a result of time actually having 2 dimensions. Well thankfully this is not just my speculation so I am hopeful my appeal will be successful. Sorry for the diversion folks, just wants to share!
This forum is so much more interesting and a much nicer place to hang out.

Yes...that is exactly "what I mean". Energy and gravity exists as potentials that become manifest by the actions of matter and mass.

36. Originally Posted by Jilan
QM is a result of time actually having 2 dimensions
I would be somewhat sceptical of this ( what happens to a system of differential equations with more than one time coordinate ?? ), but at the same time I think it is interesting and certainly worth a closer examination.

37. The guy I know of working on two-timephysics is is Itzach Bars.
http://www.telegraph.co.uk/science/l...n-of-time.html
There are too many papers to link them all, but can be found on arxiv.

38. Negative energy? Consider the Penrose process (Wikipedia).
Inside this ergosphere, the time and one of the angular coordinates swap meaning (time becomes angle and angle becomes time) because timelike coordinates have only a single direction (and remember the particle is necessarily rotating with the black hole in a single direction only). Because of this weird and unusual coordinate swap, the energy of the particle can assume both positive and negative values as measured by an observer at infinity.
So a particle traveling in a Kerr black hole's ergosphere can have negative energy as viewed from infinity.

That's an extreme case of something very common: negative potential energy. Gravitational potential energy is always negative, and electromagnetic potential energy is often negative.

Then there is the question of the total energy of the Universe. There is a big problem with that, because in general relativity, one cannot localize gravitational energy. One cannot find any gravitational energy-momentum tensor. One can find the total gravitational potential energy of some object, because one can observe its total mass from a distance. (Observed mass) - (constituents' mass) = (gravitational potential energy). One can help out by finding a gravitational energy-momentum pseudotensor and integrating it over volume. It's called a pseudotensor, because while it is indexed like a tensor, it does not have the appropriate coordinate-transformation properties. It's thus something like the connection coefficients.

The usual belief about the total energy of the Universe is that it is zero, that its constituents' mass and its gravitational-potential energy mass cancel out.

I think that the problem that some people have is that they think of energy as some sort of stuff, meaning that there cannot be a negative amount of it. But if energy is some quantitative attribute, like electric charge, then it can indeed be negative.

39. I think that the problem that some people have is that they think of energy as some sort of stuff, meaning that there cannot be a negative amount of it. But if energy is some quantitative attribute, like electric charge, then it can indeed be negative.
Yes, that's exactly it. Energy is a property of a system, and many aspects of it are observer dependent and hence merely "bookkeeping devices".

40. Originally Posted by lpetrich
Negative energy? Consider the Penrose process (Wikipedia).

So a particle traveling in a Kerr black hole's ergosphere can have negative energy as viewed from infinity.

That's an extreme case of something very common: negative potential energy. Gravitational potential energy is always negative, and electromagnetic potential energy is often negative.

Then there is the question of the total energy of the Universe. There is a big problem with that, because in general relativity, one cannot localize gravitational energy. One cannot find any gravitational energy-momentum tensor. One can find the total gravitational potential energy of some object, because one can observe its total mass from a distance. (Observed mass) - (constituents' mass) = (gravitational potential energy). One can help out by finding a gravitational energy-momentum pseudotensor and integrating it over volume. It's called a pseudotensor, because while it is indexed like a tensor, it does not have the appropriate coordinate-transformation properties. It's thus something like the connection coefficients.

The usual belief about the total energy of the Universe is that it is zero, that its constituents' mass and its gravitational-potential energy mass cancel out.

I think that the problem that some people have is that they think of energy as some sort of stuff, meaning that there cannot be a negative amount of it. But if energy is some quantitative attribute, like electric charge, then it can indeed be negative.
I don't get it.Photon often negative.Can you explain that?

41. Originally Posted by Markus Hanke
Yes, that's exactly it. Energy is a property of a system, and many aspects of it are observer dependent and hence merely "bookkeeping devices".
What do you mean when you said "many aspects"? I.e. which aspects of energy are not bookkeeping devices?

42. Originally Posted by Physicist
What do you mean when you said "many aspects"? I.e. which aspects of energy are not bookkeeping devices?
I was thinking about quantities that are not observer dependent, e.g. invariant rest mass, or the energy-momentum tensor. I'm not sure if we should consider those merely "bookkeeping devices". What's your opinion on this ?

43. Originally Posted by Markus Hanke
I was thinking about quantities that are not observer dependent, e.g. invariant rest mass, or the energy-momentum tensor. I'm not sure if we should consider those merely "bookkeeping devices". What's your opinion on this ?
I contend that this is no different. stating that energy is a bookkeeping device is merely a statement saying that the sum of the different forms of energy that we define is constant in time. That holds for invariant mass as well. For example; if a photon slams into an atom the invariant mass if the atom increases as does its momentum. The sum of the kinetic energy of the photon and the atom becomes the sum of the kinetic energy of the atom and its invariant mass. That's the bookkeeping device in action.

There are numerous physicists who adhere to this notion. It's a shame that physics students are told that energy is the ability to do work because it's not true. However they never come across the correct understanding unless they read the Feynman lectures on this point. However there are articles and other texts which state this too. I have a thermal physics text in which the author states that he doesn't know what energy is. It's not because of his ignorance and he knows that. It's because its a quantity which is intentionally remain undefined. It's just like the term "set" in differential geometry. Have you ever read Schutz's book on geometry? He states that in that book. I can go on with other analogies if you'd like?

44. stating that energy is a bookkeeping device is merely a statement saying that the sum of the different forms of energy that we define is constant in time
Ok, that makes sense, and I agree. But maybe then it is better to let go of the notion of energy being a property of a system altogether, and understand it as a continuous symmetry of that system instead - after all, Noether's theorem tells us that energy-momentum is just the conserved current of space-time translation invariance. This then covers all its various forms of it.

45. In fact, here is what is matched with what:

Symmetry Conserved Quantity
Time Translation Energy
Space Translation Momentum
Rotation Angular Momentum
Boosts Center-of-Mass Position

Space-time also has some discrete symmetries, space reflection and time reflection, but discrete symmetries are not associated with conserved quantities.

46. Originally Posted by Markus Hanke
But maybe then it is better to let go of the notion of energy being a property of a system altogether, and understand it as a continuous symmetry of that system instead ...
If I knew what you meant by that then I might agree with you.

47. Originally Posted by lpetrich
In fact, here is what is matched with what:

Symmetry Conserved Quantity
Time Translation Energy
Space Translation Momentum
Rotation Angular Momentum
Boosts Center-of-Mass Position

Space-time also has some discrete symmetries, space reflection and time reflection, but discrete symmetries are not associated with conserved quantities.
I don't understand what you mean when you say that Boosts are a symmetry. Will you please clarify that for me? Thanks.

48. Boosts: Lorentz transformations and their Galilean counterparts in the Newtonian limit.

"Continuous symmetry of a system...." I like this!

But tell me...does this concept imply a "tensor state" of what is considered "radiant energy?" In that the potential is in a "rest state?"

50. Originally Posted by lpetrich
Boosts: Lorentz transformations and their Galilean counterparts in the Newtonian limit.
I know what a boost is. I don't know what the symmetry is that you are referring to when you put it into the table. What is the relevant symmetry?

51. I probably should have clarified this a little more - basically what I mean is that the energy-momentum tensor is the conserved Noether current associated with space-time translation invariance of a given Lagrangian density :

http://www.physics.indiana.edu/~derm...ft-I-11-1p.pdf

As such energy-momentum arises from the symmetries of a system, rather than "just" being an ad-hoc property, if that makes more sense.

52. Originally Posted by Physicist
I know what a boost is. I don't know what the symmetry is that you are referring to when you put it into the table. What is the relevant symmetry?
Boost symmetry is like translational symmetry and rotational symmetry. Apply a boost and the laws of physics don't change, as with translations and rotations. All in the flat-spacetime limit, of course.

53. Originally Posted by lpetrich
Boost symmetry is like translational symmetry and rotational symmetry. Apply a boost and the laws of physics don't change, as with translations and rotations. All in the flat-spacetime limit, of course.
While that's true it doesn't give the symmetry that you say that it does. If you change frames from one inertial frame to one that's boosted then the center-of-mass does change and is therefore not conserved.

54. The "conservation" here is the fixity of the center of mass when extrapolated to some fixed time:
x = x0 + v*(t - t0)

Though center-of-mass location x changes as a function of time, x0 stays fixed.

55. Originally Posted by lpetrich
The "conservation" here is the fixity of the center of mass when extrapolated to some fixed time:
x = x0 + v*(t - t0)

Though center-of-mass location x changes as a function of time, x0 stays fixed.
That doesn't make any sense whatsoever because the conservation of a quantity is defined as being independent of time. But here you have it as actually being dependant of time and therefore it cannot be considered to be a conserved quantity. Your justification when extrapolated to some fixed time has no meaning.

56. I've seen the term "centre of momentum" used to describe the conserved quantity associated with Lorentz boost symmetry.

57. Is negative energy real..?
My five cents worth...

In Ground Potential theory, energy is converted to raw potential and when you do that you discover that the upper limit to our potential is 938 million volts, which is the surface potential of a proton.
This describes the total potential between the proton and the electron, not the observers actual potential, remember there are two halves to the proton-electron pair (in my theory), so the actual potential is (938 MV/2) which means 469 MV each particle.

Put differently, the particle pair are actually an electromagnetic wave, with a trough -469 MV and a crest +469 MV, and the space between them is irrelevant, as space is subjective. This also describes a quantized particle, because the wave oscillates between being a trough and a crest, so both protons and electrons ought to pop in and out of existence at wery short time scales.

So in my book, any particle on the negative side of the equation is composed of negative energy.

Steven

58. Originally Posted by KJW
I've seen the term "centre of momentum" used to describe the conserved quantity associated with Lorentz boost symmetry.
An assertion of having seen it is insufficient as justification and meaning of it. I'd like to see proof if you can find it. However I think that you're on the right track. I think he was confusing conservation of mass with conservation of momentum.

It's a sad thing when particle physicists use the term "center of mass" and "center of momentum" to mean the exact same thing.

However I still don't see that as being a legitimate conservation law. That's like saying that energy is conserved when you changed inertial frames because the energy in the rest frame never changes. The same thing holds here. There is one and only one center of momentum frame. When you boost to another inertial frame you are no longer in the zero momentum frame.

59. Originally Posted by Physicist
Originally Posted by KJW
I've seen the term "centre of momentum" used to describe the conserved quantity associated with Lorentz boost symmetry.
An assertion of having seen it is insufficient as justification and meaning of it. I'd like to see proof if you can find it.
Insufficient or not, "an assertion of having seen it" might be all that I have.

However, the nature of the conserved quantity does follow from the symmetry. Thus, the conserved quantity is analogous to angular momentum, but with hyperbolic rotation in a plane containing the temporal direction. The conserved quantity relates to angular momentum in the same way that the electric field relates to the magnetic field.

60. Originally Posted by KJW
However, the nature of the conserved quantity does follow from the symmetry.
That's okay. I'll do a search using Google.

Originally Posted by KJW
Thus, the conserved quantity is analogous to angular momentum, ..
The symmetry involved is the isotropy of space. So if space is isotropic then L = constant.

Originally Posted by KJW
..but with hyperbolic rotation in a plane containing the temporal direction. The conserved quantity relates to angular momentum in the same way that the electric field relates to the magnetic field.
I've always hated the phrase "hyperbolic rotation"! Blech!

I don't see what you mean by The conserved quantity relates to angular momentum in the same way that the electric field relates to the magnetic field. Where did you get this from? I.e. is it some sort of analogy? What are you saying is conserved here?

61. Originally Posted by Physicist
I don't see what you mean by The conserved quantity relates to angular momentum in the same way that the electric field relates to the magnetic field. Where did you get this from? I.e. is it some sort of analogy? What are you saying is conserved here?
From what I can figure, the conserved quantity isn't one of the familiar quantities like momentum, energy, or angular momentum. When I asked the question some time ago on another forum, the answer I received was "centre of momentum". But whatever that means, it is the temporal components of angular momentum in the same way that Lorentz boosts are the temporal components of rotation.

62. Originally Posted by KJW
From what I can figure, the conserved quantity isn't one of the familiar quantities like momentum, energy, or angular momentum. When I asked the question some time ago on another forum, the answer I received was "centre of momentum". But whatever that means, it is the temporal components of angular momentum in the same way that Lorentz boosts are the temporal components of rotation.
I have a friend who can tell me the answer for certain. He's the best relativist that I know of anywhere. Unfortunately he's been under the weather lately and the response won't come anytime soon. Thanks for your patience KJW. I find that to be a highly admirable trait in a physics discussion forum such as this.

63. If a star made up of exotic matter produces negative energy,then it would to absorb radiations from near by objects and will become hotter and hotter. Such a star would turn into a white hole eventually.
A very funny thought indeed

64. If a star made up of exotic matter produces negative energy,then it would to absorb radiations from near by objects and will become hotter and hotter.
I think the exact opposite is the case. An exotic matter star would be gravitationally repulsive, so photons would be deflected away from it. It would receive less radiation than ordinary matter stars.

65. So an Exotic star would get colder and colder, so does it's negative energy also increase?

66. So an Exotic star would get colder and colder, so does it's negative energy also increase?
I couldn't tell you the answer to this, since I don't know what kind of processes would be taking place in the interior of such an object. The very first problem I have is that I don't see how such a star could even exist, given that exotic matter also repulses itself, so the way I see it is that no such stars could ever form in the first place.

67. johnzxcv: To explain why energy exist, scientists propose that there is negative energy in space, enough negative energy to make sure the positive and negative energy in space end up to zero. So anyone did the experiment to prove negative energy's existence, or it is just a theories ?

cinci: I read once that if you consider the gravitational forces between all the bodies in the universe as negative and compare it to all the kinetic and energy equivalent of mass, they add up to zero. Could this be what you're referring to?

68. Originally Posted by cincirob
johnzxcv: To explain why energy exist, scientists propose that there is negative energy in space, enough negative energy to make sure the positive and negative energy in space end up to zero. So anyone did the experiment to prove negative energy's existence, or it is just a theories ?

cinci: I read once that if you consider the gravitational forces between all the bodies in the universe as negative and compare it to all the kinetic and energy equivalent of mass, they add up to zero. Could this be what you're referring to?
No , that is not what I mean, even if gravitational forces is negative , it still won't be enough to add to zero because gravitational forces is very weak. There was negative energy in space.

69. johnzxcv No , that is not what I mean, even if gravitational forces is negative , it still won't be enough to add to zero because gravitational forces is very weak. There was negative energy in space.

cinci: Gravity is the weakest of the know forces, but the energy in question here is the energy that accrues if all the mass in the universe falls back together. The force involved is proportional to the mass so it is not small for something like a galaxy. And, it is applied over long times.

70. Originally Posted by johnzxcv
No , that is not what I mean, even if gravitational forces is negative , it still won't be enough to add to zero because gravitational forces is very weak. There was negative energy in space.
That's not true. See Zero-energy universe - Wikipedia, the free encyclopedia

The amount of gravitational energy per unit volume might be small but its enormous compared to how much there is.

71. Originally Posted by Physicist
That's not true. See Zero-energy universe - Wikipedia, the free encyclopedia

The amount of gravitational energy per unit volume might be small but its enormous compared to how much there is.
If you said so , how about the force between charge? Are they negative energy too? Since they also follow the square law. If so then visual photon is negative?

72. johncxcv: If you said so , how about the force between charge? Are they negative energy too? Since they also follow the square law. If so then visual photon is negative?

cinci: I suppose you could look at it that way, but it doesn't lead to any startling conclusions that I can think of. The negative energy astrophysicists are concerned with, dark energy, is their only explanation for the accelerating expansion of the universe. I don't think anybody is clear on what it is.

73. Originally Posted by johnzxcv
If you said so , how about the force between charge? Are they negative energy too? Since they also follow the square law. If so then visual photon is negative?
The potential energy of a positive charge in the field of a negative charge is negative. However the energy in the field itself is positive.

74. Originally Posted by Physicist
The potential energy of a positive charge in the field of a negative charge is negative. However the energy in the field itself is positive.
Do fields really have energy or do particles have energy by virtue of their position in them? Fields certainly have the ability to transfer energy but that is not the same thing as having it if you see what I mean. ....
Would you say that a gravitational field "has energy" for example? This question has concerned me for some time....

75. Jilan: Do fields really have energy or do particles have energy by virtue of their position in them? Fields certainly have the ability to transfer energy but that is not the same thing as having it if you see what I mean. ....
Would you say that a gravitational field "has energy" for example? This question has concerned me for some time....

cinci: One definition of energy is the ability to do work. Since fields can and do move things, they are doing work and therefore must have energy.

76. Originally Posted by Physicist
The potential energy of a positive charge in the field of a negative charge is negative. However the energy in the field itself is positive.
If you said so then why the energy in gravity field is negative not positive, what make it differ from charge field?

77. Originally Posted by johnzxcv
If you said so then why the energy in gravity field is negative not positive, what make it differ from charge field?
It's a rather complicated thing. The point objects in gravity are always attractive making the potential always negative. So when all the objects are the same and attract the total potential is negative. When all the objects are the same but repel (as in electrodynamics) then the total energy is negative.

That applies to continuous systems. When you have a system of point charges then it gets complicated when you take the limit from point charges to a continuous charge distribution.

78. Originally Posted by Physicist
It's a rather complicated thing. The point objects in gravity are always attractive making the potential always negative. So when all the objects are the same and attract the total potential is negative. When all the objects are the same but repel (as in electrodynamics) then the total energy is negative.

That applies to continuous systems. When you have a system of point charges then it gets complicated when you take the limit from point charges to a continuous charge distribution.
You can get a better idea it you follow the derivations, even if you don't know the math you might be able to get a sense of the symmetry involved if you pay close enough attention.

See

Electrostatic energy
http://www.physics.uci.edu/~sasha/co...TM_Gravity.pdf

There's a very interesting point that even the physics community doesn't have a full understanding of and that's self energy. What is the energy of a point object? This results in a perplexing situation when you derive the expression for electrostatic energy. Even though you can have negative energy with point charges you'll always have positive energy with a continuous distribution of charges.

Introduction to Electrodynamics (3rd Edition) | David J. Griffiths; Reed College | digital library BookOS

Turn to section 2.4.4 Comments on Electrostatic Energy and read the part which is entitled (i) A perplexing "inconsistency."

I think you'll find it fascinating!

79. In the Newtonian limit, gravitational potential energy is negative. In general relativity, I don't know if it has been possible to settle the question one way or another. It must be pointed out that in GR, gravitational energy cannot be localized, something that adds to the difficulty. But one can do so in the spherically-symmetric static case by analyzing the Tolman-Oppenheimer-Volkoff stellar-structure equation (general relativity - Solving the Tolman–Oppenheimer–Volkoff (TOV) equation - Physics Stack Exchange, Wikipedia, etc.).

It starts with this metric (c = G = 1):

where V and M are functions of radial coordinate r. Pressure P is a function of density ρ, which is in turn a function of r.

M matches onto the Schwarzschild solution's mass, so it measures the total mass inside radius r.

Let us now consider what the mass unaffected by gravity is. We do this by integrating ρ over a 3-space hypersurface for constant t:

Thus,

So M < Mnogr by an amount that's equal in the Newtonian limit to the Newtonian-gravity self-energy.

Thus, in the spherically-symmetric static case, GR gravitational potential energy is negative.

In general, the TOV equation is very difficult to solve without doing a lot of number crunching, but there is a solution for constant ρ, and that Physics Stack Exchange page mentions it.

The center pressure becomes infinite if

80. if matter converts to energy, then why can't Dark matter be your "unobservable negative" gravitational potential energy? the up and the down anti-quark would hold your gravitational potential energy. With a combined mass of 7.2, times that by Dark energy, and it equals 4.9 . . . The sqrt. of 7.2 is 2.683. Divide 2.683 by normal matter= sqrt. of C .
And 100/.268 =373 also 7.2^3 = 373 and Dark Energy times the sqrt. of C= 373

81. Originally Posted by David Hawkins
if matter converts to energy, ..
It doesn't. Where did you get that idea from? See Does nature convert mass into energy? by Ralph Baierlein, Am. J. Phys. 75 , 320 (2007)
First I provide some history of how the equation E = mc2 arose, establish what “mass” means in the context of this relation, and present some aspects of how the relation can be understood. Then I address the question, Does E = mc2 mean that one can “convert mass into energy” and vice versa?
I think he addresses the matter into mass thing too. In any case he describes what E = mc2 means very clearly. It's only at http://home.comcast.net/~peter.m.bro.../baierlein.pdf

82. cinci: Most of what we call mass is a function of kinetic energy; for instance, the rest mass of three quarks is a small fraction of the mass of a proton or neutron. The bulk of the mass is the motion of the quarks within the proton/neutron. But I think Baierlein sort of slides over the electron-positron reaction in the statement below.

Baierlein from Does Nature Convert Mass Into Energy?" In a significant sense, the annihilation of the electron and positron in positronium is like a movie of pair creation run in reverse. For the topic of E=mc2, there is nothing intrinsically new. After noting that the annihilation does not “convert mass into energy,” we may go on.

I don't see anything in the statement that allows us to note that the annihilation does not “convert mass into energy.”

Further, if the big bang theory is to be believed, there was nothing but energy at the inception of the universe so if there is any non-kinetic mass at all today, it must be here as a conversion of energy into mass.

If his point is that most of what we recognize as mass is really kinetic energy I think he's right. But I don't think he can rule out mass-energy conversion completely.

83. Originally Posted by cincirob
I don't see anything in the statement that allows us to note [I]that the annihilation does not “convert mass into energy.”
Of course not. When someone posts a reference to an article,you're supposed to read the entire article. The person who posted doesn't always post it so that you can read a ready made and very handy sound bite. I posted it so that you can read and hopefully absorb what the author is teaching in that paper. The purpose of the paper is to show that nothing is converted into energy because energy was the same before the reaction as it was after it and therefore nothing was converted.

Einstein defined matter as follows:
We make the distinction hereafter between "gravitational field" and "matter" in this way, that we shall denote everything but the gravitational field as "matter." Our use of this word therefore includes not only matter in the ordinary sense, but the electromagnetic field as well.
Therefore when you have an electron and a positron moving towards each other there is a certain amount of mass and a certain amount of matter present. The energy is determine from the rest mass and the kinetic energy of both particles when they're far apart. When they annihilate each other the mass remains the same as it was before because mass is a conserved quantity. Since photons are produced in the process there is matter there as well. It didn't disappear. And even if it did then it didn't go into energy because the energy is completely determined by the energy of the moving particles as equaling their rest energy and kinetic energy.

It's unwise to think that you can read a paper and find what you want in one sentence. It's the entire paper that's important. That's why the author wrote and entire paper rather than a single sentence.

84. cincirob: I don't see anything in the statement that allows us to note [I]that the annihilation does not “convert mass into energy.”

Physicist: Of course not. When someone posts a reference to an article, you're supposed to read the entire article. The person who posted doesn't always post it so that you can read a ready made and very handy sound bite. I posted it so that you can read and hopefully absorb what the author is teaching in that paper. The purpose of the paper is to show that nothing is converted into energy because energy was the same before the reaction as it was after it and therefore nothing was converted.

[B]cinci: I absorbed a lot of things before I read the article and one of them is the First Law of Thermodynamics and converting mass to energy certainly has to be consistent with that law. If that's all the guy was trying to say, he could haves saved a lot of time. Nobody is implying that the energy comes from nowhere.

Einstein defined matter as follows: We make the distinction hereafter between "gravitational field" and "matter" in this way, that we shall denote everything but the gravitational field as "matter." Our use of this word therefore includes not only matter in the ordinary sense, but the electromagnetic field as well.

cinci: Yes, Einstein recognizes "matter in the ordinary sense." And sometimes "matter in the ordinary sense" is converted to "energy in the ordinary sense".

Physicist: Therefore when you have an electron and a positron moving towards each other there is a certain amount of mass and a certain amount of matter present. The energy is determined from the rest mass and the kinetic energy of both particles when they're far apart. When they annihilate each other the mass remains the same as it was before because mass is a conserved quantity. Since photons are produced in the process there is matter there as well. It didn't disappear. And even if it did then it didn't go into energy because the energy is completely determined by the energy of the moving particles as equaling their rest energy and kinetic energy.

It's unwise to think that you can read a paper and find what you want in one sentence. It's the entire paper that's important. That's why the author wrote and entire paper rather than a single sentence.

cinci: I didn't disagree with the entire paper, I disagreed with that particular sentence. After an annihilation, you say what remains is "their rest energy and kinetic energy". Annihilation produces only photons which have no rest energy since they don't exist at rest.

If all you're saying here is that energy has mass, I think the world is already comfortable with that notion. If this is just the semantics of saying mass instead of matter, then it's a waste of time.

85. cincirob - You're really wasting a great deal of your time with this "matter into energy" thing, especially if you're not willing to do the heavy work of reading all about it.

In physics matter is an ill defined term. That's why so many physicists don't even define it. It's too vague. And the expression E = mc2 talks about the equivalence between energy and mass, not energy and matter, because there is no equivalence relationship between the two.

It appears to me that you're confusing matter with mass and that's a no-no. See Matter - Wikipedia, the free encyclopedia
Matter should not be confused with mass, as the two are not quite the same in modern physics.
There are various interpretations of the mass-equivalence relationship when it comes to the annihilation process. Some physicists don't think of photons as having any matter while others, such as Einstein and, for example, Hans C. Ohanian, do. He's a friend of mine and the author of several physics texts including ones in GR and SR. But it has no meaning to say that because matter disappeared then it was converted into energy because the energy before and after was the same so the matter simply disappeared into oblivion.

I'm going to end this post with the most important thing that can be said about this subject. Even saying that matter will be converted into energy has no meaning at all. Energy is a book-keeping system and matter is merely "stuff" that, in a manner of speaking if you will, we can hold in our hands. Changing one into the other literally has no meaning whatsoever.

86. Physicist: cincirob - You're really wasting a great deal of your time with this "matter into energy" thing, especially if you're not willing to do the heavy work of reading all about it.

cinci: There's really not much heavy work associated with this.

Physicist: In physics matter is an ill defined term. That's why so many physicists don't even define it. It's too vague. And the expression E = mc2 talks about the equivalence between energy and mass, not energy and matter, because there is no equivalence relationship between the two.

It appears to me that you're confusing matter with mass and that's a no-no. See Matter - Wikipedia, the free encyclopedia

Matter should not be confused with mass, as the two are not quite the same in modern physics.

Physicist: Matter should not be confused with mass, as the two are not quite the same in modern physics. There are various interpretations of the mass-equivalence relationship when it comes to the annihilation process. Some physicists don't think of photons as having any matter while others, such as Einstein and, for example, Hans C. Ohanian, do. He's a friend of mine and the author of several physics texts including ones in GR and SR. But it has no meaning to say that because matter disappeared then it was converted into energy because the energy before and after was the same so the matter simply disappeared into oblivion.

cinci: Yes, I agree. But your wiki article says: Still, special relativity shows that matter may disappear by conversion into energy, even inside closed systems, and it can also be created from energy, within such systems.

Nobody says that the matter disappeared into oblivion. Look what you did. First you say matter is an ill-defined term but you can't make your argument without using it. At anything above the quantum level, nobody is confused about the term "matter". And all of what people think of as matter has mass. And if you annihilate it you get energy.

Physicist: I'm going to end this post with the most important thing that can be said about this subject. Even saying that matter will be converted into energy has no meaning at all. Energy is a book-keeping system and matter is merely "stuff" that, in a manner of speaking if you will, we can hold in our hands. Changing one into the other literally has no meaning whatsoever.

cinci: You article is just some physicist trying to look like he understands something that nobody else gets. We all get it. It's the first law of thermodynamics.

And if you don't think E=mc^2 literally means anything, then you don't understand reactors (and I'm sure you do). Any physicist that doesn't understand what the article talking about needs to get out of the business. Is the world a better place if we stop saying "mass can be converted to energy"?

87. Originally Posted by cincirob
Physicist: cincirob - You're really wasting a great deal of your time with this "matter into energy" thing, especially if you're not willing to do the heavy work of reading all about it.

cinci: There's really not much heavy work associated with this.
That's why I said that you're wasting a great deal of time with this, not energy. The heavy work comes in the form of a proper study of physics and a very solid study of relativity, not from a book or two but years of intense study where both textbooks, journal articles and your own scientific work is done. Your comments in this thread tell me that you don't have that kind of knowledge and/or experience. In particular your use of matter when it comes to talking about mass-energy equivalence.

Originally Posted by cincirob
[B]cinci: Yes, I agree. But your wiki article says: Still, special relativity shows that matter may disappear by conversion into energy, even inside closed systems, and it can also be created from energy, within such systems.
That wiki page is wrong on that part. That can't be avoided since there's no text or journal which is error free. That's why I quoted that phrase and not didn't tell you to study and accept the entire page

Originally Posted by cincirob
Look what you did. First you say matter is an ill-defined term but you can't make your argument without using it. At anything above the quantum level, nobody is confused about the term "matter".
If you thought that was a problem then you are severely mistaken. A great number of concepts/terms in math and physics are ill defined but are well understood. For example; time, space and energy are such quantities. They too are not only ill-defined but they aren't even defined at all. But we know exactly what they are. The same is true with matter, especially when so many people disagree about its meaning.

Think of matter as another word for "stuff" in a very very loose way. On a macroscopic way it's something we can touch or hold in our hands. Mass, on the other hand, is that property of matter which describes its inertia. And its mass that's equivalent to energy, not matter.

Originally Posted by cincirob
cinci: You article is just some physicist trying to look like he understands something that nobody else gets. We all get it. It's the first law of thermodynamics.

Not at all. That's a totally unjustified claim. As such please provide some sort of proof or justification of it. That author is a highly respected astrophysicist. He got his PhD at Princeton and taught at Harvard in the 60's. He serves as the book review editor for the American Journal of Physics. To get something published in a journal not only the author has to agree with what's in the paper but so does the editor and all the peer reviewers who decide whether its right or wrong.

Besides he's certainly not the only one that explains this since there are several other authors over the last 60 years who've written similar articles. One is E = mc2 for the Chemist: When is mass conserved? by Richard S. Treptow, [i]Journal of Chemical Education, Vol. 82(11), Nov. (2005). Also its found in A Relativistic Misconception by C. Roland Eddy, Science, Vol 104, No. 2700, Sept. 27, 1946. It can also be found in Spacetime Physics by Edwin F. Taylor and John Archibald Wheeler. I assume you know who these particular authors are?

Originally Posted by cincirob
And if you don't think E=mc^2 literally means anything, ..
Now you're putting words into my mouth. I never said nor implied such a thing. What I mean is identical to what's worked out an example for nuclear fission at Nuclear Fission

Originally Posted by cincirob
then you don't understand reactors (and I'm sure you do). Any physicist that doesn't understand what the article talking about needs to get out of the business. Is the world a better place if we stop saying "mass can be converted to energy"?
This forum is a better place if we make sure what is said to be true is both accurate and true and consistent with that our experts wish to make certain that is taught by publishing articles in the journals to explain what's correct or not.

If you're not interested in what is true then why are you posting here?

88. cinci: And if you don't think E=mc^2 literally means anything, ..

Physicist: Now you're putting words into my mouth. I never said nor implied such a thing.

cinci: OK, this conversation is over.

You said exactly this: Even saying that matter will be converted into energy has no meaning at all. Energy is a book-keeping system and matter is merely "stuff" that, in a manner of speaking if you will, we can hold in our hands. Changing one into the other literally has no meaning whatsoever.

89. Originally Posted by cincirob
cinci: And if you don't think E=mc^2 literally means anything, ..

Physicist: Now you're putting words into my mouth. I never said nor implied such a thing.

cinci: OK, this conversation is over.
Wonderful! No more of you putting words into my mouth.

Originally Posted by cincirob
You said exactly this: Even saying that matter will be converted into energy has no meaning at all.

Yet once again you're confusing the difference between mass and matter. That's been the entire source of your problem in this entire thread. Since you don't seem unable to grasp the fact that they are very different things you keep making the same mistakes, even after all the times I've corrected you!

Originally Posted by cincirob
Energy is a book-keeping system and matter is merely "stuff" that, in a manner of speaking if you will, we can hold in our hands. Changing one into the other literally has no meaning whatsoever.
Originally Posted by cincirob
That's correct. It's meaningless to change matter into energy. I should also point out that since it's mass that represents the quantity of matter. Therefore without talking about mass it makes no sense to say how much matter is present.

Originally Posted by cincirob
You're very wrong again because, as I said, you insist on confusing mass with matter. Please stop doing that.

I showed you in my last post why mass and energy remain the change during nuclear reactions. However it appears that you didn't even take a look at the site I showed you, i.e. Nuclear Fission

90. Physicist: You're very wrong again because, as I said, you insist on confusing mass with matter. Please stop doing that.

I showed you in my last post why mass and energy remain the change during nuclear reactions. However it appears that you didn't even take a look at the site I showed you, i.e. Nuclear Fission

cinci: Nobody questions that in a closed system the energy remains the same, 1st law of thermodynamics. You're pretending that everybody is a dunce when it comes to this issue. As for your Nuclear Fission article, equation 5 of the article gives the mass difference before and after the fission. And they give it in terms of its energy equivalent in electron volts. Now if you don't want to say that that mass was converted to energy because it already was energy, bully for you. But going around and telling people that mass isn't converted to energy will breed more confusion than understanding.

I worked on the design of a fast fission nuclear reactor (710A) for four years in the 60s. I know how they work.

If you follow out your line of reasoning then the next thing you have to do is change all the "atomic masses" on a world full of periodic tables to say "atomic energy". I'm sure that won't confuse anybody.

91. Originally Posted by cincirob
Physicist: You're very wrong again because, as I said, you insist on confusing mass with matter. Please stop doing that.
When you stop confusing them I'll stop correcting you.

Don't worry about it though since I'm leaving for a while until and if a problem with the forum is resolved.

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