Talk:Mass in special relativity: Difference between revisions
Count Iblis (talk | contribs) |
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So, Edgerck is saying: I ignored the kinetic energy because the kinetic energ due to recoil is small. Fair enough, but then he claimes that m is less than M. He didn't say by how much. As you can see it is less than M by an amount 1/2 e^2/M. Now e is the momentum of the photon (in c = 1 units), so this is just the kinetic energy of the atom he ignored. :) [[User:Count Iblis|Count Iblis]] 23:18, 1 June 2007 (UTC) |
So, Edgerck is saying: I ignored the kinetic energy because the kinetic energ due to recoil is small. Fair enough, but then he claimes that m is less than M. He didn't say by how much. As you can see it is less than M by an amount 1/2 e^2/M. Now e is the momentum of the photon (in c = 1 units), so this is just the kinetic energy of the atom he ignored. :) [[User:Count Iblis|Count Iblis]] 23:18, 1 June 2007 (UTC) |
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== Force carriers and mass == |
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This article is linked from the article on the [[Graviton]], which states: <blockquote>''"If it exists, the graviton must be [[Mass in special relativity|massless]] (because the gravitational force has unlimited range)[...]"''</blockquote> Note that '''massless''' links here. It might be valuable to provide some form of explanation of this property, and relate this concept to other physical forces (weak, strong, EM). --[[User:Tsuji|Tsuji]] 03:19, 2 June 2007 (UTC) |
Revision as of 03:19, 2 June 2007
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Rest mass VS relativistic mass
From the "Some reasons for abandoning the notion relativistic mass" we have:
One is forced to make statements like "The rest mass of a photon is zero", which sounds slightly odd because a photon can never be at rest, it always travels at the speed of light.
1) the statement isnt clear. I assume the author means "travels at c". But, this is also just not true as a photon going through any material like fiber optics or water or a bose-einstein condensate slows down dramatically in the last instance to within human walking speed. . Differences in the speed of light are the reason behind refraction.... delete, yes ?
Hfastedge 22:26, 27 Jun 2004 (UTC)
True, but irrelevant to the issue at hand. If you prefer change the statement to include "in a vacuum" (where the speed is indeed c). -- Fropuff 02:40, 2004 Jun 28 (UTC)
Relative mass is an example of trying to think of a concept (mass) in one paradigm (relativity) in terms of the old paradigm (classical Newtonian mechanics). It's an indication that the person isn't fully thinking relativistically but is still using a mishmash of nonrelativistic and relativistic concepts. Phys 21:23, 12 Nov 2004 (UTC)
- Relativistic mass is an outdated term - see the "editing POV" comment below. Also, photons always travel at c, however in mateials - the photons get absorbed, reemitted and bounce around between atoms in irregular (but predictable macroscopically) patterns. However, during their travel - they are always going the same speed - c. Think of a car along a twisty road vs an airplane taking the straight path - even if the car had the same speed as the airplane, the airplane would always get to the destination faster. Fresheneesz 06:38, 22 November 2005 (UTC)
Force equation question.
F=ma is OK, but when using relativistic force(F) and relativistic mass(m), there should also be relativistic acceleration(a), which has lorentz factor hidden inside. Using newtonian acceleration in a relativistic equation and then stating that the incorrect result is proof against relativistic mass is incompetence. I suggest to re-write the "F=ma" paragraph to be supporting for relativistic mass or to delete it.
Shouldn't the equation read as ?
After all, m is constant and is an implicit function of t. Alfred Centauri 04:01, 28 May 2005 (UTC)
- No, we're assuming that the velocity is constant. For the velocity to vary (i.e., acceleration), we require general relativity, not special. - mako 22:38, 17 July 2005 (UTC)
- If v is constant, mv is constant too, and therefore d mv is zero, and so is F. Something wrong?--Army1987 07:35, 24 August 2005 (UTC)
- Yeah, that crossed my mind after I submitted the last comment. I forget how this stuff works, and I'm not exactly yearning to review. (I don't think I've had to use this force equation, though it may apply in some sort of "relativistic rocket" problem.) Things don't make much sense when you try to formulate relativity in terms of Newtonian mechanics, but that's the equation given in books -- the book I have at hand doesn't explain much, but it does note that you have to use the chain rule when differentiating:
- If v is constant, mv is constant too, and therefore d mv is zero, and so is F. Something wrong?--Army1987 07:35, 24 August 2005 (UTC)
- - mako 18:45, 24 August 2005 (UTC)
The correct equation is of course F=dp/dt. Since p=mγt, the γ goes inside the derivative. -lethe talk 22:24, 25 November 2005 (UTC)
NPOV?
It seems to me the article is making an argument, rather than merely reporting usage. One can make an opposing argument, but that side is not being presented. I think it would be more NPOV if it was less strident about the advantages of the more modern usage. As the article does make clear, the older usage is still sometimes used, even by physicists, and one can argue in its favor also. Gene Ward Smith 22:19, 21 Jun 2005 (UTC)
- The goal was to report modern usage. However, it seemed appropriate to put the modern usage in a historical context and explain why this usage developed. I wasn't trying to present a POV although I certainly see how it could be intrepretted that way. -- Fropuff 23:29, 21 Jun 2005 (UTC)
The reasons for abandoning the notion relativistic mass are not convincing:
1. Pro-View: One is forced to make statements like "A photon has no rest mass", which sounds slightly odd because a photon can never be at rest.
Anti-View: Lene Vestergaard Hau of Harvard University and Ronald L. Walsworth and Mikhail D. Lukin of the Harvard-Smithsonian Institute have managed to brought light particles to a halt and then sped them back up to their usual speed.
2. Pro-view: The idea of mass increasing with velocity leads many to believe that the internal structure of a quickly moving object is somehow altered. However, the standard view of relativity is that the internal structure of an object is always unchanged, and that the different quantities measured by different observers for energy and velocity are simply the same reality seen from different points of view.
Anti-View: The quantum vacuum may in certain circumstances be regarded as a type of fluid medium, or aether, exhibiting energy density, pressure, stress and friction. This may alter the internal structure of an object.
3. Pro-View: The idea of relativistic mass combined with the notion of Lorentz contractions leads some people to the incorrect conclusion that an object traveling fast enough will form a black hole. However, by the very principle of relativity, if an object is not a black hole in one frame (its rest frame) it cannot be a black hole in any other frame either.
Anti-View: Some suggested that black holes were created during Big Bang and were tiny, some as light as 0.0000001kg. The density of matter as it crosses the event horizon varies inversely to the mass of the black hole, the miniscule nature of which had enormous pressures applied to create them. There is no evidence of their existence, but Hawking believes that these black holes could have evaporated.
4. Pro-View: If one wishes to retain the notion that mass measures the "resistance" to acceleration, then mass can no longer be treated as a scalar quantity. This is because it is easier to accelerate something perpendicular to the direction of motion than parallel to the direction of motion. In effect, an object would have more mass in one direction than other.
Anti-View: This is a misconception on the transverse and longitudinal stress in special relativity or fluid dynamics.
5. Pro-View: The primary reason that most physicists chose to abandon relativistic mass in favor of the rest mass is that rest mass is a Lorentz invariant quantity — it is the same in every reference frame. Strictly speaking, it is the time-like component of a four-vector (the energy-momentum four-vector). A four-vector is a Lorentz invariant quantity, but its individual components are not.
Anti-View: This is only one of the possible mathematical approaches. Richard Feynman was surprised that this was common though useful. (Feynman Lectures Vol 1 Section 16-1 Relativistic Mass)
I don't see a need for this pro- and anti-view stuff. Relativity is such a strange thing that there exist a wide variety of approaches to understanding it, some which work better in some situations than others. That said...
1. "A photon has no rest mass." That's just a terminology issue. As long as the concept is clear, it's okay. As Feynman says (v1 17-7), "If it is a particle of zero rest mass, what happens when it stops? It never stops!" The note about slowing light is a completely different kettle of fish: Bose-Einstein Condensate and quantum interference. Special relativity for the beginner stays in the classical realm.
2. This "internal structure" stuff is just not understood enough to say anything about it. And what about something like the electron? Scattering tests have established the point charge property of the electron down to a very small radius. Just how does this "quantum vacuum" change a point particle anyhow?
3. I can't say I remember the exact discussion from A Brief History of Time, but I do not see what primordial black holes have to do with relativistic mass.
4. Fluid dynamics? Eh?
5. Well, that's the most important aspect of the invariant mass: it's invariant. Note that the four-vector itself is not invariant. Only the scalar product of two four-vectors produces an invariant quantity. And I looked through the Feynman lectures 16 (and 17) and didn't see anything like you mentioned.
- mako 06:41, 10 July 2005 (UTC)
It is because there exist a wide variety of approaches to understanding, as you mention it, we should be more open-minded to new development instead of suppressing other views.
- But some approaches are more valid than others, and these "anti-views" are just plain nonsense. You can tell kids that babies are delivered to doorsteps by storks, and they'll believe that—until they know better.
- We can mention the various modes of interpretation, but only if we note their caveats. Science does not cleanly delineate into pairs of opposing viewpoints; particularly for something as old and established (it's the World Year of Physics 2005 for a reason) as relativity. - mako
"Plain nonsense" from Richard Feynman, Albert Einstein, Stephen Hawking, Paul Davies, Lene Vestergaard Hau...!? Wow, you'll be a great, revolutionary physicist!
- I'm afraid you're missing the point here. I appreciate the sarcasm, but I'm saying that those numbered points are nonsensical. But anyway:
- Feynman - Feynman uses the relativistic mass, and in the Lectures he does say "surprisingly enough", but that was probably in the context of the lecture, which used a Newtonian-relativity approach to a 2-body problem. He hasn't introduced four-vectors yet.
- Einstein - He rarely used the relativistic mass himself.
- Hawking - A Brief History of Time is a popular work, with very little math.
- Davies - He's a popular science author.
- Hau - As I already said, that's getting into quantum effects, which are outside the scope of this article.
- Anyway, I'm working on a rewrite which I hope will clear this subject up. The one main point (that is not as heavily emphasized in the article as it should be) is that popular and other math-simple approaches to relativity, or relativistic "extensions" to Newtonian mechanics, tend to use the relativistic mass as a conceptual aid. The full-blown four-vector approach tends to use matrix notation, which a popular audience is not so likely to be familiar with. - mako 22:21, 17 July 2005 (UTC)
Many have been so passionate on this debate, it could be more political than you could imagine... Don't underestimate Richard Feynman...
Usage examples
I don't think the usage examples are helpful at all. To illustrate what I mean, suppose I list every single paper from the past 5 years from arxiv.org:hep-ex -- I would bet none of them use the relativistic mass. Sure it would show current usage, but it wouldn't be very useful. The article already says enough about usage; a bit about the (almost nonexistent) controversy could be added, but isn't really necessary. - mako 02:29, 27 July 2005 (UTC)
In a recent survey by Gary Oas (arXiv:physics/0504110), 477 out of 637 textbooks and various other works still rely on the concept of relativistic mass. You should not meddle around here as you're a mathematician instead of physicist, or at least do more homework first!
- And what, may I ask, are you?
- As for me, I'm neither a mathematician nor a physicist: I'm an electrical engineering major. I am however working with the people who wrote hep-ex/0502040, so I am doing physics at a particle accelerator site.
- If you would read the paper you cite, it argues that the usage of the relativistic mass should be dropped. This doesn't support your argument. Perhaps you should solidify your position and actually defend it, instead of resorting to ad hominem attacks. - mako 23:57, 27 July 2005 (UTC)
We should not cover the truth, just like Gary Oas, who revealed that 477 out of 637 textbooks etc adopted RM, including Nobel Laureates like Leon Lederman, Richard Feynman, Martinus J.G. Veltman, Julian Schwinger, Robert Laughlin and so on. On the contrary, it is a shame that many physicists employed tactics like "Relativistic Mass is unfashionable, or outdated" as arguments. BTW, I am a physicist, reading more than 400 books and papers, and published a paper on this before. No, I'm not a promoter or destroyer of relativistic mass, afterall this concept is not created by me, and this is why I provide you Gary Oas's paper, which does not support RM. So, don't cover up the references to the public! Gosh, I'm not going to look at this website anymore...
- Buh bye. -- CYD
Relativistic mass and mass in rest OK
With the formulation of the theory of the special relativity of Albert Einstein the concepts of relativistic mass were introduced, m, that depends on the speed of a frame of reference in rectilinear movement uniform and mass in rest, m0 that talks about to a frame of reference taken in rest. These two states, for the inertial marks, that is to say, nonsubject to forces, are symmetrical due to the relative character of the movement. Of such form, that of its equivalence origin the equivalence between kinetic energy and mass, that was extended by heuristic route to all class of energy. For example, in a frame, the mass of a body, that in opposite directions absorbs the same amount and frequency of electromagnetic energy, increases its mass. The called modern relativity, that constitutes a revision of special relativity rejects the concepts of relativistic mass and mass in rest that it replaces and it unifies by invariant mass, that is, of a mass whose magnitude is independent of all frame of reference and result of transformation of the Lorentz. This revision is controversial, to see: Chapter 3 The energy has mass:
Editing POV
None of the information on this page is opinion. It is a current fact that relativisitc mass is a term that is rarely used in physics anymore - for the reason that it leads to confusion - but mostly because rest mass is used in so many equations - while relativistic mass is a much less useful (and less measureable) quantity. WAS, not to be inflammatory, but you really shouldn't edit a page giving me support just when we're having an argument about this issue. Since you like sources so much, heres a couple (look for the word outdated):
- http://math.ucr.edu/home/baez/physics/Relativity/SR/light_mass.html
- http://www.answers.com/topic/relativistic-mass
- http://relativistic-mass.borgfind.com/
- http://www.tardyon.de/mass.htm
If you look up similar things about relativistic mass you'll find numerous references to the "outdated", "antiquated", and "obselete" term. I hope the sources help. Thanks. Fresheneesz 06:31, 22 November 2005 (UTC)
Rest mass is more convienient in particle physics in general. Relativistic mass is more convienient some of the time especially in nonparticle physics. The fact that equations are equivelent whether one uses one or the other and that computers do most of the actual number crunching mean there is NO debate among physicists about which term to use. Whatever is most convienient is used. When invarience is needed, rest mass is used. When actual behavior is being discussed, the relativistic mass is what is actually MEASURED.
- http://math.ucr.edu/home/baez/physics/Relativity/SR/light_mass.html is the point of view of Philip Gibbs in 1997. It says "By convention relativistic mass is not usually called the mass of a particle in contemporary physics so it is wrong to say the photon has mass in this way. But you can say that the photon has relativistic mass if you really want to. In modern terminology the mass of an object is its invariant mass which is zero for a photon." He is right about convention and the use of "mass" for PARTICLES. But it is also true that by convention in contemporary physics, the "m" in E=mc squared refers to relativistic mass. Which mass to assume is all about convenience (and convention).
- http://www.answers.com/topic/relativistic-mass quotes wikipedia.
- http://relativistic-mass.borgfind.com/ says "However, the fact that some relativity courses continue to use relativistic mass demonstrates that this is a matter of opinion." Wikipedia doesn't take sides, making arguments. We do present encyclopedic arguments made by others. Physicists do NOT argue over this.
- http://www.tardyon.de/mass.htm says "In this document, the word "mass" will refer to the thought of "inertial mass", as initially intended by Newton when he first included it as a component of a classical mathematical equation. In that form, "mass" is simply a natural resistance to any change in the current state of motion of any specific part of existence." The author is wrong in thinking "inertial mass" = "rest mass". WAS 4.250 17:37, 22 November 2005 (UTC)
- Please refer to the article's external links. - mako 18:58, 23 November 2005 (UTC)
- WAS, your last post seems to confirm that "mass" means conventionally "rest mass". In arguing that it is an opinion, a convention at one point *was* the best way to do something according to some people - an opinion. But when it becomes a convention, it is no longer an opinion, but a tool used to make communicating easier. Perhaps in thinking the convention is the best way is an opinion - but the convention is *not* opinion.
- Also, when you meanioned that the author writing this is wrong in thinking "inertial mass" = "rest mass", he never said that. He said inertial mass *is* the inertia of an object - which is what relativistic mass is. Not like that is relavent to the argument or anything...
- In conclusion, can we now decide how to use this convention - and how to edit this page so that it makes sense? I think that it would be good to say that E is rest energy, and *then* note that in history, the m in that expression was relativistic mass. What do you think WAS, and anyone else? Fresheneesz 00:50, 25 November 2005 (UTC)
- Please refer to the article's external links. - mako 18:58, 23 November 2005 (UTC)
I'd like to see the page reverted to its original state (meaning -- no offense -- before you guys came along). If you look at the rest of Talk, you'll see that I've been "custodian" of this page for a while. I also wrote much of what WAS considered POV; I consider it a telling of straight facts. A lot of what I do on WP involves cleanup, POV included, and I feel that I have a pretty good sense of what constitutes POV. I am willing to argue about presentation here on Talk, but wholesale blanking is a reactionary thing to do. And regarding the arguments above, the rest mass and the rel. mass are both used in particle physics, as they are merely concepts in relativity. The rest mass is important because it is an intrinsic property of a particle. The rel. mass (people call it "energy" instead of mass nowadays) is what you measure in certain kinds of detectors. - mako 00:53, 27 November 2005 (UTC)
- I agree, all of my edits were compromises between the "original" and new edits. Fresheneesz 05:27, 28 November 2005 (UTC)
- I notice that a few remarks in the article are not facts but POV or worse. I'll make a few small improvements in the coming days. Harald88 22:15, 6 May 2006 (UTC)
Newton's laws
I want to remove the comment about Newton's laws remaining unchanged when you use relativisitc mass. Newton's first law remains unchanged whether you use relativistic mass or not, while Newton's third law becomes very difficult to keep and is usually thrown out due to the relativity of simultaneity, whether you use relativistic mass or not. The only place relativistic mass is relevant is
and
The first equation is Newton's second law, the second is simply the definition of momentum. There seems to have been some confusion earlier about whether the γ should be inside the derivative. It certainly should go inside, as I think is clear from this equation. -lethe talk 22:33, November 25, 2005 (UTC)
"concept" example
I'd like to keep the exposition of the "concept" section simple, without reference to relativistic mass before we've even defined it. Any good way to set up the observer and mass without bringing in too much complexity? - mako 09:45, 30 November 2005 (UTC)
"Mass* and energy in this theory also depend on velocity."
"*Modern physics teachers prefer to redefine mass such that it is velocity independent."
Gerard't Hooft. In search of the ultimate building blocks, (Cambridge University Press, Cambridge, 1997), p.17 He received 1999 Nobel Prize in physics for work in electroweak interactions.
Gerard't Hooft is wrong! Modern physics teachers and Wikipedia's contributors on relativistic mass, who are experts in other fields, prefer to redefine mass such that it is velocity independent.
And the subject is ...
What is the subject of this article??
Is it the relativistic mass in itself?
Is it a comparaison of the relativistic mass with others acceptions of mass?
Is it a nomenclature of every concepts of mass that exist from the begining of physics till today?
Is it an argumentation of what is good and what is no good between the different concepts?
Something else?
More I read the article and the talk page, more I'm confuse! Please help the poor reader that i am!
24.202.163.194 03:21, 27 December 2005 (UTC)
- You're right, I've always felt that this page lacks a clear topic. I propose a move to the title Mass in Special Relativity, as that is what the page is really about; more tellingly, rest mass redirects to this page. The current title seems to make this article a lightning rod for controversy. - mako 07:59, 28 December 2005 (UTC)
I agree with you. This new title is more in the heart of the problem than the actual one, which is not bad in itself, but the subject is larger than just the relativistic mass who should be a section of the new article. Perhaps the new article should be even larger and have the title 'Mass in physics'. But, being more a collaborative style than a contributor style, I prefer to wait for the opinions of others contributors to make a final decision. 24.202.163.194 16:23, 28 December 2005 (UTC)
- The page will be moved shortly if there are no further objections. - mako 00:02, 5 January 2006 (UTC)
- Mass in special relativity would be fine. Note the naming conventions with respect to capitalization. -- Fropuff 00:28, 5 January 2006 (UTC)
- Aye. - mako 09:06, 5 January 2006 (UTC)
Kinetic energy section of the article
E = Mc² being a special case where v = 0, then = 0 also, and E = Mc² reduce to E = mc². So, the following demonstration is not valid. That's why it has to be removed and replaced by a valid one.
What do you think of that?
24.202.163.194 04:23, 28 December 2005 (UTC)
- E = Mc² is valid for v not equal to zero; that's the whole point of the relativistic mass. I guess the page still needs some rewriting to make the concept clearer. - mako 07:59, 28 December 2005 (UTC)
For the validity of this demonstration, I have to make a further investigation into this subject. And, as much as possible, have the point of view of others contributors. 24.202.163.194 16:21, 28 December 2005 (UTC)
I'd just made a quick check up, and I am happy to tell you that you are right for E = Mc², M being the relativistic mass and not the rest mass. So, it is not a special case: that's was my mistake. Wrong reading! Thank you to have pointing it to me, and sorry for the perturbation! 24.202.163.194 17:09, 28 December 2005 (UTC)
Regarding the demonstration itself, my first investigations show me that it is not appear to be a stricly rigorous one, because they (physicists) do it with E and Eo at first, after they define m and m0 (or M and m here) base on their previous equations, and they finish by E = ym0c² ( E = yMc²). In the article, we begin by their end. But, even so, we can keep the one we have, for the moment, because their demonstration is very long and it would take an article by itself! 24.202.163.194 17:52, 28 December 2005 (UTC)
Gravity & Relativistic Mass
Sidestepping the pros and cons of whether the notion of relativistic mass is useful or not, and accepting that one could just talk about relativistic momentum and avoid the whole mess ...
... I have a question: does the gravitational force exerted by an object increase as it approaches the speed of light? I would suspect not -- but I have no good clue one way or another.
If not, that would be a very solid argument in favor of the anti-mass faction.
MrG (Greg Goebel) / 27 february 2006
Here are some references:
1. the theory had to combine the following things: (i) From general considerations of special relativity theory it was clear that the inert mass of a physical system increases with the total energy (therefore, e.g., with the kinetic energy). (ii) From the very accurate experiments, it was empirically known with very high accuracy that the gravitational mass of a body is exactly equal to its inert mass.” “ Autobiographical notes by Einstein published in 1949
2. A moving body with rest mass M gravitationally may attract nearby objects with an increase mass, (gamma)M or 2(gamma)M depending on the direction of velocity or approach. (Olson, D. W. & Guarino, R. C. (1985). Measuring the active gravitational mass of a moving object. Am. J. Phys., (53) 661
CL / 28 february 2006
- Here's an abstract for the Olson paper. The authors note that it's only valid for a special case. (This question may be more general relativity than special.)
- Food for thought: If you go too fast do you become a black hole?. - mako 10:09, 28 February 2006 (UTC)
Nice response -- very often the reply to "I ask this question out of ignorance" tends to focus on "ignorance" instead of "question".
Einstein's comment is a bit confusing because I would think "inert mass" would mean "rest mass", but when he says that it "increases with total energy" ... well, that throws a spanner in the works. The second comment is straightforward: yes "relativistic mass" does imply greater gravitational force.
However, suggesting that this may be more a GR question than an SR question makes me want to back up a bit. Not being a physicist getting seriously into GR is not a step I am inclined to take. If Einstein complained about the math ...
Reminds me of the time I was thinking about SR paradoxes and started wondering about what would happen if two remote starships began to accelerate in the same direction in step. I quickly realized I was out of my depth; when I found out I was reinventing Bell's Paradox I didn't feel so bad.
I would like to leave this thread in place for a while to see if it attracts further comment.
MrG (Greg Goebel) 01 mar 06
Everybody: I've had to fix the "relativistic mass" concept section because it was trying to say that faster objects increase gravitational field due to their "relativistic mass". This is the way that lies toward the idea that objects become so massive with speed that they might form a black hole. Wrong. In the rest frame an object is not a black hole, so it can't be a black hole for anybody else, either. That would be a paradox, so it's obviously wrong.
http://math.ucr.edu/home/baez/physics/Relativity/BlackHoles/black_fast.html
The only time kinetic energy shows up as increased gravitational field is when it's the kinetic energy in a SYSTEM where the sum of momenta is zero. Otherwise, kinetic energy shows up as relatistic mass and as increased momentum, but not as gravity.
As for inertia, inertia is a tricky concept depending on how you define it. The only inertia of a body connected with its gravitation is the inertia it presents in its rest frame, which is to say, its center of momentum frame inertia. Inertias in other frames (and in different directions even in the same frame, when it's a moving one) don't agree with each other, as shown in this section. So which of these different inertias would be connected with gravity? Another paradox. The answer is "none." Only invarients (like invarient mass) are connected with gravity, because an object can't be, and not be, a black hole at the same time.
I might add that it's quite possible for two different inertial observers to see different gravitational pulls from the same mass in relativity, but this is a strictly directional thing caused by the overall shape of the gravity field being "squashed" in the sideways direction, as seen by moving observers. The same thing happens with electric fields and moving charges. However, just as the total charge in relativity is conserved and invarient to different observers, so is the mass and the gravitational field. An increased field in the transverse direction is compensated for by a decreased field in the direction of motion, and so the integrated total comes out the same for all observers. Still no black hole! Sbharris 01:38, 9 April 2006 (UTC)
- Just noticed this old discussion. What is really needed here is a page on "mass in GR". I'm working on one, actually :-). Much of it will be considerably more technical, with a long discussion of Komar mass and a short discussion of Noether's theorem, but I plan to include a section with questions like this in it as well.
- The situation is not as simple as the above remark makes it.
- Consider a pressure vessel containing a gas. If we add energy to the system by heating up the gas, the system gains energy, does not gain momentum, and hence gains mass. The only difference between the pressure vessel containing a hot gas and a cold gas is due to the motion of the molecules. See also http://arxiv.org/abs/gr-qc/9909014. Thus motion can affect the gravitational field, this makes it different than charge.
- There are some technical issues here too. The standard interconversion of curvature into forces requires a static metric, something that's lacking with a moving mass.
Pervect 20:21, 9 August 2006 (UTC)
Erroneous claim?
"the rest mass is an intrinsic property of an object" appears to be erroneous: according to SRT the rest mass increases with temperature, because the speed of the parts increases. Note: it might be that the article uses a different definition of "intrinsic", but its meaning should be both clear and consistent in one and the same article. Harald88 14:01, 6 May 2006 (UTC)
- Maybe better to say "invariant". Mass is never intrinsic, rather density is intrinsic, and mass is extrinsic. Temperature is instrinsic, by the way, so the fact that mass depends on temperature doesn't contradict anything. -lethe talk + 14:09, 6 May 2006 (UTC)
- That sounds better - but if that new phrasing is correct (and likely it is), then the Wikipedia definition of that term, Invariant (physics), is also erroneous. How should invariance be formulated so that it fits with a body that is increasing in temperature? Harald88 17:47, 6 May 2006 (UTC)
- We're always talking about closed systems here, and I've fixed up the Invariant (physics) section to make that clear. If you let energy or momentum in or out of your system, they're obviously not conserved!
- I'm afraid that that doesn't help: "relativistic mass" is in that sense also invariant. The way I understand it - and I propose to reformulate it accordingly - is that "invariant mass" is invariant under changes of coordinate systems. Harald88 19:17, 6 May 2006 (UTC)
- Noooo! See the Wiki on mass in special relativity. When we say relativistic mass we generally mean the total relativistic energy/c^2. It varies with inertial frame/inertial observer. Only the invariant mass (which is not the same thing, and is the relativistic mass only in the COM frame) is invariant (ie, Lorentz-invariant, ie, the same in all inertial frames).Sbharris 23:11, 6 May 2006 (UTC)
- I'm afraid that that doesn't help: "relativistic mass" is in that sense also invariant. The way I understand it - and I propose to reformulate it accordingly - is that "invariant mass" is invariant under changes of coordinate systems. Harald88 19:17, 6 May 2006 (UTC)
- mass in special relativity happens to be what we are editing. And apparently you misread what I wrote, for I fully agree with your last statements... Harald88 18:47, 9 May 2006 (UTC)
- Both density and mass are intrinsic quantities of objects, so long as the system is closed and we're not adding or subtracting stuff (like heat energy and therefore rest-mass) surreptitiously. If you don't close the system, mass changes and usually density does also. You can't just talk about an "object" in a loosey-goosey fashion. For any of this to make any sense, it has to be an isolated "well-defined object", with nothing spalling or flaking or boiling or radiating off it. Sbharris 19:06, 6 May 2006 (UTC)
- Hmmm, it occurs to me that density is not intrinsic, even to closed-system objects. They can always expand and contract spontaneously, due to phase changes and what-not. Mean density is intrinsic to closed systems, but only because mass is invariant, and if you define your system/object volume, so that it also is invariant. Sbharris 19:11, 6 May 2006 (UTC)
- A property of an object is intrinsic if it doesn't change when you have two objects. Density and temperature are intrinsic, mass is not. A property is extrinsic if it doubles when you have two of them. Mass and volume are extrinsic. A property is invariant if it doesn't depend on your reference frame. Mass and temperature are both invariant, density and volume are not. -lethe talk + 20:50, 6 May 2006 (UTC)
- Um, you're confusing your terms with the technical thermodynamic meanings of the terms intensive quantity and extensive quantity. Intrinsic and extrinsic are somewhat loosely defined terms of ordinary language. Don't use them when you really mean intensive and extensive. My revenge for your spelling pettiness :). Sbharris 22:48, 6 May 2006 (UTC)
- Wow, you're right. I stand corrected. I'm sorry. -lethe talk + 02:42, 7 May 2006 (UTC)
- Um, you're confusing your terms with the technical thermodynamic meanings of the terms intensive quantity and extensive quantity. Intrinsic and extrinsic are somewhat loosely defined terms of ordinary language. Don't use them when you really mean intensive and extensive. My revenge for your spelling pettiness :). Sbharris 22:48, 6 May 2006 (UTC)
- A property of an object is intrinsic if it doesn't change when you have two objects. Density and temperature are intrinsic, mass is not. A property is extrinsic if it doubles when you have two of them. Mass and volume are extrinsic. A property is invariant if it doesn't depend on your reference frame. Mass and temperature are both invariant, density and volume are not. -lethe talk + 20:50, 6 May 2006 (UTC)
- Wow, the article invariant (physics) is pretty confused about invariants versus conserved quantities. It claims that acceleration is invariant under Galilean transformations. Whoa! -lethe talk + 20:56, 6 May 2006 (UTC)
- Ok it looks like we're getting somewhere, thanks for the comments! I'll now correct "intrinsic" to "invariant" but will not yet link it until invariant (physics) has a compatible definition (I hope that Lethe agrees to do a little effort there). Harald88 22:03, 6 May 2006 (UTC)
- I'd certainly be happy to take an axe to that article, but first we have to decide what's to be done with it. My point is, I'm not sure we have a need for an article called invariant (physics). This article is about invariance and its relationship to conserved currents. It might be best merged with Noether's theorem or covariance and contravariance. What do you think? -lethe talk + 02:42, 7 May 2006 (UTC)
- I think Invariant (physics) should be merged into Covariance and contravariance. —Keenan Pepper 07:31, 7 May 2006 (UTC)
- That makes sense as there are too many small articles around. As invariance is used independently of covariance, that article could be renamed "Invariance, covariance and contravariance" (or simply "Invariance and covariance"). Harald88 08:38, 7 May 2006 (UTC)
- I was planning a rewrite of covariance and contravariance at some point. Maybe it's time I got back to that. -lethe talk + 07:55, 7 May 2006 (UTC)
- I think Invariant (physics) should remain separate, since: 1) invariance is an important principle in physics (conservation laws, symmetries etc.) and this article could be expanded alot, and 2) covariance and contravariance appears to be mainly a mathematical discussion, not physics. Rotiro 07:27, 25 May 2006 (UTC)
gravitational field?
"invariant mass is the only type of mass which is connected with a gravitational field".
Apart of the fact that GRT doesn't really belong in this article, I think to have seen otherwise; and it's ambiguous if active or passive gravitation is meant. Please provide the source and the corresponding equation, thanks! Harald88 22:44, 6 May 2006 (UTC)
- Well, the statement really should have read something like "invariant mass" is the source of the total gravitational field. There are "gravitomagnetic" effects for masses moving past at high velocities, just as there are magnetic effects from charges moving past at high velocities (this effect makes a charge look like a bigger charge, but only to the transverse observer--- other observers see a SMALLER charge). But total space-integrated charge is an invariant in relativity, and so is mass. But the mass that is invariant (frame invariant) is the invariant mass, which is the mass you see in the COM frame of your system. There's a discussion in chap 22 of MTW. The short argument is that you can't make something into a black hole by going past it really, really fast. You can't even make it LOOK like a black hole, because the effective gravitomagnetic increase in "mass" is proportional to gamma, so the field can't get infinite. Sbharris 23:23, 6 May 2006 (UTC)
- Your statement that "the effective gravitomagnetic increase in "mass" is proportional to gamma" corresponds to what I meant: that happens to correspond to "relativistic mass", not "invariant mass". Thus it remains obscure what argument there would be for preferring the use of either m or M=γm in GRT equations. Harald88 23:51, 6 May 2006 (UTC)
Thus I now take out the corresponding paragraph:
- For example, invariant mass is the only type of mass which is connected with a gravitational field (thus, no matter how fast an object goes, it cannot become a black hole because of relativistic mass).
If someone knows a way to rephrase it so that it is correct (either as Wikipedia statement or quote), please go ahead - but don't forget to indicate its relevance for this article about SRT. Harald88 18:38, 8 May 2006 (UTC)
- Well, how about invariant mass as the "source" of a total gravitational field? It's clear you can go by an electron very fast and see a larger electric field in your direction, but that's more or less an effect of your squished spacial coords. The source of the field is the (dressed) charge of the electron, and that doesn't change from frame to frame, because you correct for it. There's an invariant there.
- The source of a g field far out from an object is the integrated S-E tensor, and by the time you get far away from an object (low field limit-- linearized approximation to GR), that total flux through spacial boundary doesn't change, either. There's a sort of Poisson's equation for gravity-charge just as there is with electric charge. And the gravity charge is the rest mass or invariant mass that you're far away from.Sbharris 19:58, 8 May 2006 (UTC)
- It's still not clear what prevents M=gamma*m (or E=M*c^2) from being the source of the gravitational field (which equation can't you write in that form?), nor what that has to do with Special relativity.
- Note also that mass is not invariant like charge: an electron cloud of N electrons has a total charge of N*q_e, but total mass > N*m_e due to their kinetic energies. What will its total gravitational field be? Harald88 20:21, 8 May 2006 (UTC)
strange remark
"A more crucial flaw is that γ is undefined for v = c; in other words, these equations are not valid for photons."
-> It's a flaw of what exactly? Or, to put it differently: Is it also a "crucial flaw" of invariant mass that F=ma is not valid for photons?! Harald88 23:18, 6 May 2006 (UTC)
- photons don't have invariant mass unless in pairs, or confined. And if confined, they would be expected to show mass m = E/c^2 (see the end talk section in mass) and no doubt the same inertial mass F/a. In this case, the acceleration just induces the same Dopper shift that the g field does in my example. The photons hit the end of an accelerated box a little harder, and it feels just like mass. Sbharris 23:56, 6 May 2006 (UTC)
- Photons do indeed have an invariant mass. It is zero. I once again urge you to stop peppering Wikipedia with this nonstandard notion that mass includes kinetic energy. -lethe talk + 07:23, 7 May 2006 (UTC)
- Just wanted you to remind you of the state of our conversation as of May. See the remark above. Do you still agree with it? Or have you learned something since? Sbharris 15:51, 17 June 2006 (UTC)
- I concede that the concept of invariant mass of a system of particles is indeed used. I was wrong when I said it wasn't. -lethe talk + 16:44, 17 June 2006 (UTC)
- Thank you for that, but usage is by far the least of the problem. Read the paragraphs above. I'm reminding you that systems of photons have mass, and you're flatly denying it, and telling me I'm peppering Wikipedia with the nonstandard notation that mass includes kinetic energy (which by now I hope you'll see is a yawner of an idea). You removed my example in which a pair of photons become a pair of leptons, without change in mass of the system, because you apparently believed it was just wrong physics. Well, it's not wrong. It's correct, and it's illustrative of an important point about the invariance and conservation of MASS, which is the subject here in this article on MASS. I'm not trying to publicly bust your chops here, but I am trying to get you to see the reason for my frustration in dealing with you on this topic. Please try to be a little more flexible when next you revert an example of mine, because you personally find the physics or conclusion surprising. Consider instead that the problem may be that you haven't had contact with the ideas being explained. Use this Wiki as a chance to learn something about physics, rather than a chance to be obstructive. Sbharris 17:38, 17 June 2006 (UTC)
- Can you provide me with a diff of the particular reversion you're referring to now? I'm finding your remarks a little hard to follow out of context. -lethe talk + 18:20, 17 June 2006 (UTC)
- You reverted a number of my edits on April 14 in mass. See the long discussion the Mass: Talk section (Mass of compound systems) which follows that, on that date. Most of your claims there are just wrong. If you'll go back and read them, and then again read the edits you reverted me with, in the light of our following discussion, it may refresh your memory. Briefly, you kept saying that colliding objects which stick increase in mass, and I pointed out that this is not true of you consider the system mass (including the kinetic energy of the particles) before the collision. You said system mass was a nonstandard concept and reverted me. But you're wrong-- it is a standard concept. You left on the MASS page an "example" where massive particles are made of massless photons, which is a reversion of my example pointing out that a system of two photons which makes such particles, DOES have a mass. You denied this (you also deny it just above on THIS page on 7 May, even though it's perfectly clear what I mean). And so on. Sbharris 19:05, 17 June 2006 (UTC)
- So you mean for example this edit? Well nothing that stayed in the article was wrong, which is what you were claiming at the time, but I do recognize that there are two ways of talking about mass, and your way is indeed standard (and, yes, I was wrong when I said it was not), so it should have a place in the article. I do understand your frustration, and I sympathize. But please understand this: you "corrected" the article which you said contained mistakes. It is not a mistake to refer to mass the way I do. So I saw you "correcting" something which I knew to be correct, called it "confused" in your edit summary. I still know that there is nothing wrong with that description. Invariant system mass is not the only way of speaking. -lethe talk + 20:28, 17 June 2006 (UTC)
- You reverted a number of my edits on April 14 in mass. See the long discussion the Mass: Talk section (Mass of compound systems) which follows that, on that date. Most of your claims there are just wrong. If you'll go back and read them, and then again read the edits you reverted me with, in the light of our following discussion, it may refresh your memory. Briefly, you kept saying that colliding objects which stick increase in mass, and I pointed out that this is not true of you consider the system mass (including the kinetic energy of the particles) before the collision. You said system mass was a nonstandard concept and reverted me. But you're wrong-- it is a standard concept. You left on the MASS page an "example" where massive particles are made of massless photons, which is a reversion of my example pointing out that a system of two photons which makes such particles, DOES have a mass. You denied this (you also deny it just above on THIS page on 7 May, even though it's perfectly clear what I mean). And so on. Sbharris 19:05, 17 June 2006 (UTC)
- There's nothing nonstandard about it. I've referred you to MTW's gravitation, where there are many discussions of the T00 term in the stress-energy of "stuff." Mass (here I mean invariant mass) does include kinetic energy most of the time (by which I mean, for most of the things in our normal experience, and for most of the objects and particles and in physics, too). The ONLY cases where this isn't certainly true (though it still might be true) is in the case of the massless particles (photons and gravitons if there is such a thing as a graviton) and (presumably) for the leptons as well, since they have mass but no sub-particle structure (or at least, none so far found at the energy scales we have been able to explore). But a large fraction of the mass of hadrons including the familiar baryons like neutrons and protons, is kinetic energy. And yes, that's in their rest frames. So some large fraction (though perhaps not all) of ordinary atoms and objects is kinetic energy of quarks. And that would still be true at absolute zero. You're weighing pure energy of motion because these things are systems in motion, even at "rest." And by the way, the invariant mass of photons is generally non-zero, since we rarely examine them one at at a time. So long as there are more than one, and they not moving in the same direction, photons have mass. The sun radiates 4 million tons of photons a second, and even the Earth radiates a couple of kilos of them per second. That's all invariant mass. The sun gets less massive by that amount. Presumably its G field decreases happens for near observers as this happens (for example, the Earth no doubt gravitationally feels the pull of (4.4 million tons x 500 seconds) of photons inside its orbit, but loses the pull of anything outside that)Sbharris 18:25, 8 May 2006 (UTC)
- What is that about? It's well known and even explained here that the kinetic energy of the parts is included in both m and M. It's even possible that all mass is kinetic in origin (wave theories of matter). Harald88 08:49, 7 May 2006 (UTC)
- If it's in the article that rest mass can come from kinetic energy, then the article is wrong. This may be true for composite systems with nonzero temperature, but it is completely false for fundamental particles.
- Give it up! If it's true for neutrons and protons and atoms and paperweights, what does it MATTER if it might not be true for your last "fundamental particle" holdouts, like electrons?? "Rest mass" is NOT just a concept we ONLY apply to photons and leptons, and that's all. "Rest mass" is a concept which we apply to hadrons and atoms and ordinary objects. So let's just get on with it, and note that it includes kinetic energy much of the time (indeed, most of the time). Saying it CAN doesn't mean it ALWAYS MUST. But if it usually does, I think the article should certainly discuss it! Sbharris 18:25, 8 May 2006 (UTC)
- If it's in the article that rest mass can come from kinetic energy, then the article is wrong. This may be true for composite systems with nonzero temperature, but it is completely false for fundamental particles.
As for your suggestion that all rest mass comes from kinetic energy, well that is in contradiction to the fact that some particles have nonzero rest mass when their kinetic energy is zero. -lethe talk + 09:41, 7 May 2006 (UTC)
- It is correct (and not "may be true") that rest mass includes kinetic energy from parts in composite systems, and at first sight the article explains this very well. Note that the concept of mass is not limited to fundamental particles, just as the concept of length isn't limited to such either. But apparently you know the structure of fundamental particles, while I thought that nobody knows! What causes their mass (according to which publication)? Harald88 13:40, 7 May 2006 (UTC)
- For a single particle, there is a distinct difference between the rest mass and the total energy/relativistic mass. The former includes only the energy content of the particle in its rest frame, while the latter includes its kinetic energy. Thus, here is an example of a system where the rest mass does not include kinetic energy (and this explains the use of the word "rest" in the phrase "rest mass"). So at least for systems which are not composite, it's simply not true, what you're saying.
- As for where mass comes from, if you like, I can point you to some papers about the Higgs mechanism. If I do that, will you point me to some papers about this "mass comes from kinetic energy" theory? -lethe talk + 16:25, 7 May 2006 (UTC)
- I don't have such theories at hand, but I can search for them. And we seem to speak different languages: I know of no evidence that the energy content of particles is composed of some kind of "rest energy" instead of some kind of "kinetic energy" - insofar such terms have meaning at that scale. Note also that IMO your use of the word "rest" does not correspond to the common use: I'd say that "rest" means that the centre of mass has a speed equal to zero in the chosen reference system. Harald88 22:48, 7 May 2006 (UTC)
- I would also agree with you and say that "rest" means that the centre of mass has speed equal to zero. An electron has energy .511 MeV in its rest frame. This provides evidence that the energy content of particles is composed of rest energy instead of kinetic energy. Now, shall I give you some references for the Higgs mechanism? I'm eager to read about your "all mass is kinetic" theory. -lethe talk + 23:01, 7 May 2006 (UTC)
- As I told you, don't have such a theory and don't have one at hand (perhaps Sbharris does), but I expect that one day there will be a satisfying wave theory of matter. That is perhaps incompatible with the Higgs theory, but perhaps not (think of the wrongly posed question of "particle or wave" nature of matter). If you have a better reference at hand for the Higgs mechanism, please add it to Higgs boson. Harald88 07:10, 8 May 2006 (UTC)
- The wave theory of matter has been well-known for about 100 years, it's known as quantum mechanics. It is not at all incompatible with the Higgs mechanism, which admits a quantum formulation. I wonder what you meant when you said "It's even possible that all mass is kinetic in origin (wave theories of matter)"? I guess you were just speculating about some hypothetical models that have not been published yet, which you expect to be published soon? Since we're only allowed to talk about established physics here in these articles, I'm not sure what relevance your putative theory has to this discussion. To sum up: rest mass is not kinetic energy content. As for better references for the Higgs mechanism, better than what? It's in every QFT textbook. -lethe talk + 08:01, 8 May 2006 (UTC)
- To the contrary: I reject speculation presented as fact - WP:NOR, nor do I propose to include any speculation. Let's stick to the subject matter. You claim that no kinetic (dynamic) energy is contained in particles. However, this is obviously controversial, as waves are kinetic by definition. Of course, your claim may be quoted as opinion, if it's notable and a good source is provided. Apart of that, that the rest mass of a body includes its kinetic energy is widely acknowledged and also explained in this article. If you think something is wrong, please discuss it.
- And about Higgs, once more: we're editing an encyclopdia. If you have some improvement to make, please add it in Higgs boson.
- That's all. Regards, Harald88 18:24, 8 May 2006 (UTC)
- Nothing I have said in this thread should be regarded as controversial. It's standard material in any physics curriculum.
- Firstly, let me say that I'm glad we agree on the utility of the WP:NOR policy. Therefore, let us no longer speak of your theory that "all rest mass comes from kinetic energy".
- Second, as for your comment about waves: you haven't got it quite right. A field excitation can be wavelike and still be at rest. Therefore to say "waves are kinetic by definition" is incorrect. Modern physics understands all matter as having wavelike properties, but some of those properties are more subtle than waves in the ocean. Welcome to quantum mechanics. I assure you once again that my claim that matter has energy content even when it is at rest is not controversial, rather it is your claim "waves are kinetic by definition" that is not only controversial, but actually wrong.
- Thirdly, that the rest mass of an object includes its kinetic energy is a controversial claim, at least that is my contention, which I was trying to discuss with Sbharris before you interjected with you "all mass is kinetic energy" theory. Then I went off into a sidetrack with you about whether all mass is kinetic. But I haven't forgotten the original point. So I agree with you, if something is wrong, it should be discussed here on this talk page, and that's exactly my intention. That original point was this: is kinetic energy always included in rest mass (nevermind that there is also always a non-kinetic component). I claim that the answer is obviously "no", as can be seen by considering fundamental particles. Sbharris may disagree. I'd like to get this issue hammered out with him.
- No, only that part of the total kinetic energy which remains in the COM frame of the system is included in "rest mass." That works for composite particles (hadrons) and composite systems (like atoms and bottles of gas and paperweights). For massive "fundamental particles" (electrons, neutrinos), if they prove to be fundamental, that component is obviously zero. But the kinetic energy of stuff and its radiation can be a big thing, if it's a very energetic reaction. There's one point in the Feynman lectures where he talks about the mass of an atomic bomb, where he notes that if you take all the residua of an atomic blast, cool it down, and weigh it, it will weigh less, by about a gram. But he didn't put in that part about collecting and cooling for nothing. He was actually being precise without seeming to be. He had a way of being offhand and informal, without being wrong. Because he knew what he was doing. Let's see if we can repeat this on Wikipedia. Sbharris 19:41, 8 May 2006 (UTC)
- I am pleased to discover that reading the first sentence of the above comment, I think you understand exactly what the issue is. I wonder now what the point of that long digression about "kinetic waves" was, but nevermind. Yes! The point is, Sbharris, and apparently you agree, contend that mass should be defined to include the kinetic energy in the COM frame. I contend that this definition is non-standard and should not be used on wikipedia. Now all we need to do is choose a talk page and start a new section and figure it out. -lethe talk + 19:52, 8 May 2006 (UTC)
- Fourthly, as for your invitation to me to improve the article on the Higgs mechanism, well, once I'm finished defending this article, and the hundred other tasks I have on my todo list, I will be sure to take you up on it. In the mean time, I only brought up the Higgs mechanism because you challenged me with " But apparently you know the structure of fundamental particles, while I thought that nobody knows! What causes their mass (according to which publication)?". I assure you that there is a well-regarded theory about what causes mass, and it has been published in literally thousands of papers since Peter Higgs came up with it in the 60s. And it has nothing to do with "all waves are kinetic". -lethe talk + 19:02, 8 May 2006 (UTC)
- Nothing I have said in this thread should be regarded as controversial. It's standard material in any physics curriculum.
- I did not propose a theory, but instead tried to explain to you in different ways that your Higgs-based theory isn't to be proposed as the only and absolute truth in Wikipedia - but I'm repeating myself. Of course the source of your "mass is fundamentally static" theory is appreciated. According to the Higgs article, "The Higgs boson mass has not been measured experimentally." Thus please don't present your inferences from that theory as a fact in a Wikipedia article. At the moment it's just an opinion or belief.
- You didn't propose a theory? Then what exactly were you referring to when you said "It's even possible that all mass is kinetic in origin (wave theories of matter)."? I'm quite curious. It sounded to me like you knew of a theory which explained the origin of mass as a form of kinetic energy. Now you say you never proposed any theory. What gives? Also, please don't put words in my mouth. I never said that the Higgs mechanism was the "absolute truth", nor did I propose to put the Higgs mechanism in wikipedia (it's actually already here). The Higgs mechanism is part of the Standard model, which is the most accurately verified scientific theory in the history of Man. Nevertheless, you are correct: the Higgs boson itself has not been directly observed. There are plenty of other mechanisms for breaking symmetry (technicolor, little higgs, etc). None of them have been experimentally verified, and so none of those models should be sold as "the absolute truth". In fact, that phrase may not have much meaning. The only scientific consideration is whether the model agrees with experiment. I'll let you know which of the Higgs mechanism and its competitors is the closest next year after the LHC goes online. -lethe talk + 21:19, 8 May 2006 (UTC)
- Again, I contrasted your speculation with alternative speculation, in a fruitless attempt to make you aware of it... and indeed I did put words in your mouth to make you aware of the similar words you had put in my mouth - again, to no avail.
- Happily we seem to agree on what statements to make in the article and what not - and that's the only thing that matters here. :-) Harald88 18:56, 9 May 2006 (UTC)
- Of course we all agree that "matter has energy content even when it is at rest" since here we're talking about the object as a whole - it's also true for a gyroscope in a box. But I'm surprised to find that, according to you, "mass should be defined to include the kinetic energy in the COM frame" is not generally agreed on. All books and articles I have seen about it either just state it as a fact or explain why, for example [1] reminds the reader of the fact that "When a stationary body is heated its mass increases, and yet this increase is clearly relativistic — a consequence of the increased motion of molecules". It will be interesting to see counter claims. Harald88 20:52, 8 May 2006 (UTC)
- In relativity, force and acceleration are not necessarily parallel. How can you divide F/a then? —Keenan Pepper 07:28, 7 May 2006 (UTC)
- That complication is independent of the choice between m or M. And obviously, as Newton's equations apply to matter only, they are unsuited for photons. OK I'll rephrase that sentence. Harald88 08:49, 7 May 2006 (UTC)
Newtonian energy?
"the Newtonian energy which consists uniquely of the kinetic energy".
I only know classical energy equations and they include potential energy. Thus:
- 1. Is the above sentence correct? (reference?)
- 2. Is the above sentence relevant for this article on mass?
Thanks, Harald88 09:13, 7 May 2006 (UTC)
- The discussion in which that text is found is about free particles. For a free particle, the only energy is kinetic energy. This is not at all clear from the text though. -lethe talk + 09:39, 7 May 2006 (UTC)
- If I rememeber well, I was taught that in classical physics for example chemical energy may also be included, thus I doubt that it is generally accepted as correct; and its relevance escapes me. Thus I propose to simply delete that phrase. Harald88 13:43, 7 May 2006 (UTC)
Mass of an empty box with reflecting walls
It should be noted in the discussion about photons that even if there are no photons in a box with reflecting walls, there is still a contribution to the mass from the zero point energy (related to the Casimir effect). Count Iblis 21:36, 8 May 2006 (UTC)
- Probably it's up to you to write that sentence, and please include a reference (is zero point energy to be included in mass?). Harald88 18:59, 9 May 2006 (UTC)
Invariant mass
Moved to Talk:Mass#Invariant_mass. Please, let's keep the dispute in one place.
- Why should we keep the dispute in one place when you're making changes to multiple articles? Just hold off doing one till we get to the other, since the same issues of physics are being discussed.
- From the revised article:
- When discussing the mass of composite systems such as a pair of interacting particles, a little care must be taken. If the constituents can be distantly separated, then one can define the mass of the system to be the sum of the rest masses of the constituents. Using this definition, one finds that the mass of the system will generally not be conserved. Over the course of a reaction, the mass of the system can increase or decrease, as the mass of the particles is converted to energy or vice versa.
- As you know, I'm strongly opposed to this entire idea, which is confusing. "If the constituents are distantly separated??" How distantly does that have to be? What a bizarre notion. How low does the pressure in a bottle of gas have to go before the kinetic energy of the molecules no longer contributes to its mass?
- Second, although before relativity people naively assumed that the mass of a system was the sum of the rest masses of particles which compose it, relativity itself shows this to be flatly wrong, so let's just note that it's wrong, and get on with it. It's so much easier to say that the old notion of summed rest masses was wrong, and relativity is the reason.
- Third, "over the course of a reaction the mass of the system can increase or decrease as the mass is converted to energy or vice versa". That's true only if you let the energy out, and the system isn't closed. The increase or decrease has nothing to do with mass-energy conversion. It's due to opening the system. If you close the system, mass is conserved, and invariant and end of story. So neat, so true, so useful to the working physicist, and something you won't now find in the Wiki, because you removed it. How about you put this back? Sbharris 20:31, 16 June 2006 (UTC)
Would you stop reverting edits without consideration?
When the mass of a system is not the sum of the rest masses of particles which make it up (for example a helium atom has less mass than 2 protons, 2 neutrons, 2 electrons) the reason is because energy has been lost from the system when it was assembled. No energy is "converted to mass". It's simply lost and not weighed. If it wasn't lost, it could be weighed, and then mass of the system would not change.
Similarly, when radium decays, the mass of the cooled decay products (ie, decay products at rest), is less than the mass of the radium. The difference represents energy lost to the system. If the energy were retained, no mass loss of the system would occur.
People have known that the mass of systems is not the same as the rest mass of their constituents (classical conservation of mass), since Einstein pointed out that they should different slightly according to E/C^2 where E is energy LOST FROM THE SYSTEM. That is why this notion is still used in calculation, but it's merely the historical understanding. So point that out. It's not a present "theory". It's the historical theory. It's the theory that relativity overturned. Sbharris 21:46, 16 June 2006 (UTC)
- The energy is not lost. If a particle decays into two moving particles, and you measure the two moving particles' rest masses, you will find a lesser mass. The two particles still have all their energy in the form of kinetic energy. No energy is lost. -lethe talk + 22:19, 16 June 2006 (UTC)
- Yes, indeed. But in that case, no mass is lost from the system, either. The kinetic energy counts, and contributes to system mass. See the point? Sbharris 11:01, 17 June 2006 (UTC)
sum of rest mass is not historical
Sbharris, please consider that perhaps there may be two usages; both current. One is the sum of the rest mass, which goes along with the mass defect and the nonconservation of mass; the other goes with the invariant mass and conservation is maintained. Also, why do you keep adding the phrase "in relativity theory"? What information is that supposed to convey? What other theory would we be considering in this article? -lethe talk + 22:15, 16 June 2006 (UTC)
- The article, being about SR, should presumably talk about the new results which SR brings to physics, which a check of the rest of the article, finds that indeed it does! So why stop here, in this section on systems? Before 1900, it was expected that the mass of a system would be the sum of masses of the pieces of the system, and that was called the conservation of mass (or matter). That should be labeled as the old conservation of mass theory. It's not used any more, except as a classical reference, which is what the mass "defect" is-- really a classical reference. It's a defect which would be expected on the basis of the old pre-relativistic theory, but which is explained perfectly well in relativity as the mass of the energy which leaked out of the open system, when we made the thing whose mass is "defective."
Here are some references:
- Griffiths, Introduction to Elementary Particles, 1987:
Except in elastic collisions, mass is not conserved. In the old terminology we would say that relativistic mass is conserved, but rest mass is not.
- Streater and Wightman, PCT, Spin and Statistics, and All That, 1964:
the interaction may produce new bound states whose mass would ordinarily be expected to be less than m1 + m2, but which in principle could also be greater.
- Sexl and Urbantke, Special Relativity and Relativistic Symmetry in Field and Particle Physics, 1992:
the relativistic version of the conservation laws has shown that only the sum of kinetic energy and rest energy is required to be conserved. If there are no further conservation laws implying further restrictions, then the conservation of rest mass to energy (or the other way around) will have to be expected in collisions. [...] conversion between mass and energy may be observed and tested in many kinds of experiments in the domain of elementary particles."
These three references all use the concept of mass defect, of mass in a collision defined to be the sum of the rest masses of the reactants. I also found a book that dealt in the invariant mass of the collision, thought you'd like to know. -lethe talk + 22:40, 16 June 2006 (UTC)
- The references are okay as far as they go, but they don't say what needs to be said, which is that the defect we're talking about results from our sloppy handling. We let mass escape from our system, and lo we find that we have a mass "defect." It's sort of like poor bank security resulting in a "cash reserve defect" because the cash went out the door in your teller's pockets. It doesn't imply nonconservation of dollars.Sbharris 23:22, 16 June 2006 (UTC)
- That's not true. Mass defect is not about closed systems and energy escaping. It's simply a different convention. -lethe talk + 06:54, 17 June 2006 (UTC)
- It's a bad convention that produces wrong numbers (which are the defect). The error turns out to be due to mass escaping. Since the origin of the defect is so simply to explain (the escaped energy carries away the mass of the mass defect) why not note it? —The preceding unsigned comment was added by Sbharris (talk • contribs) .
- That's not true. Mass defect is not about closed systems and energy escaping. It's simply a different convention. -lethe talk + 06:54, 17 June 2006 (UTC)
- Sure, they merely mean that the new terminology uses mass always to mean "rest mass". And rest mass is not conserved. But that's new-new. In the really old terminology (pre-relativity) mass IS conserved. You even label is "surprising" that it isn't. And indeed it was to the people of 1907 or whatever. But emphasize that this is the result of SR. —The preceding unsigned comment was added by Sbharris (talk • contribs) .
- On this point we seem to have perfect agreement. The first reference defines the word "mass" to mean rest mass, and rest mass is not conserved. The amount of nonconservation is called mass defect, and is what I've written about in the article. Now, since this is an article about SR, every statement in the entire article is about SR. What's relevant to the sentence under debate is not whether we're talking about SR or Newtonian physics, but rather whether we define mass to be the rest mass of the constituents or the invariant mass of the system (or, god forbid, the relativistic mass). -lethe talk+ 09:39, 17 June 2006 (UTC)
- Define it as you like, but note it's a bad definition, an old definition, and SR gives a better one where mass defect is seen as merely mass which has absconded. —The preceding unsigned comment was added by Sbharris (talk • contribs) .
- On this matter I disagree. I think it is neither bad, nor old (at least no less current than other defs). -lethe talk + 11:23, 17 June 2006 (UTC)
- Define it as you like, but note it's a bad definition, an old definition, and SR gives a better one where mass defect is seen as merely mass which has absconded. —The preceding unsigned comment was added by Sbharris (talk • contribs) .
- On this point we seem to have perfect agreement. The first reference defines the word "mass" to mean rest mass, and rest mass is not conserved. The amount of nonconservation is called mass defect, and is what I've written about in the article. Now, since this is an article about SR, every statement in the entire article is about SR. What's relevant to the sentence under debate is not whether we're talking about SR or Newtonian physics, but rather whether we define mass to be the rest mass of the constituents or the invariant mass of the system (or, god forbid, the relativistic mass). -lethe talk+ 09:39, 17 June 2006 (UTC)
- Yeah, but again (as in all other examples) the differences here are all due to having open systems. Mass is conserved even in SR, if systems are closed. So note HOW and WHY mass is not conserved in SR-- it sneakily leaks out as heat and energy. —The preceding unsigned comment was added by Sbharris (talk • contribs) .
- Mass is not conserved in a closed system, if you define mass to be the rest mass of the constituents. -lethe talk +
- Actually it is conserved in closed systems, EVEN if you just sum rest masses and don't add or subtract anything else. Take a bunch of rest masses at rest, stick them in a system, don't add or subtract energy or mass, close it, and let any reaction you want happen in there, and the final mass of the system WILL actually be the sum of the rest masses you put in. Including nuclear reactions. "Mass defects" result from summed rest mass being converted to other types of mass in systems (like kinetic energy, heat, radiation, whatever) and then allowed to escape. —The preceding unsigned comment was added by Sbharris (talk • contribs) .
- The mass in the system is, according to one definition, the sum of the rest masses. It's not that the other forms are allowed to escape, it's simply that they are not counted in this definition. -lethe talk + 11:23, 17 June 2006 (UTC)
- Actually it is conserved in closed systems, EVEN if you just sum rest masses and don't add or subtract anything else. Take a bunch of rest masses at rest, stick them in a system, don't add or subtract energy or mass, close it, and let any reaction you want happen in there, and the final mass of the system WILL actually be the sum of the rest masses you put in. Including nuclear reactions. "Mass defects" result from summed rest mass being converted to other types of mass in systems (like kinetic energy, heat, radiation, whatever) and then allowed to escape. —The preceding unsigned comment was added by Sbharris (talk • contribs) .
- Mass is not conserved in a closed system, if you define mass to be the rest mass of the constituents. -lethe talk +
- This definition is used currently. It has nothing to do with escaping heat energy. Streater and Wightman are talking about a closed system of interacting particles. -lethe talk + 09:33, 17 June 2006 (UTC)
- Well, here's a shock, but actually they aren't. You haven't quoted them saying specifically they are, and if they do, they're wrong. When particles interact, the system does not gain or lose mass in the COM frame, which is the frame you measure mass, usually. Gains or losses there are due to leakage. Two particles with kinetic energy can stick and become a particle with more rest mass than either of the inputs. The very best example is two photons which have NO rest mass and turn into and electron and positron. But the SYSTEM of photons DOES have rest mass (or as we call it, invariant mass) and that turns out to be just enough to equal the total mass of the of the leptons. —The preceding unsigned comment was added by Sbharris (talk • contribs) .
- Streater and Wightman are not wrong. The mass of a system may be measured in the COM frame, but the mass of a particle is measured in the particle's rest frame, irrespective of what system it may be a part of, what other particles and interactions may be present. The sum of these numbers may change, while the invariant mass of the system does not. -lethe talk + 11:23, 17 June 2006 (UTC)
- But what's the point? If you're lax about what energy you let in and out, you can make a particle or bound system of any rest mass you like. And name it Bill.Sbharris
- Streater and Wightman are not wrong. The mass of a system may be measured in the COM frame, but the mass of a particle is measured in the particle's rest frame, irrespective of what system it may be a part of, what other particles and interactions may be present. The sum of these numbers may change, while the invariant mass of the system does not. -lethe talk + 11:23, 17 June 2006 (UTC)
- Well, here's a shock, but actually they aren't. You haven't quoted them saying specifically they are, and if they do, they're wrong. When particles interact, the system does not gain or lose mass in the COM frame, which is the frame you measure mass, usually. Gains or losses there are due to leakage. Two particles with kinetic energy can stick and become a particle with more rest mass than either of the inputs. The very best example is two photons which have NO rest mass and turn into and electron and positron. But the SYSTEM of photons DOES have rest mass (or as we call it, invariant mass) and that turns out to be just enough to equal the total mass of the of the leptons. —The preceding unsigned comment was added by Sbharris (talk • contribs) .
- This definition is used currently. It has nothing to do with escaping heat energy. Streater and Wightman are talking about a closed system of interacting particles. -lethe talk + 09:33, 17 June 2006 (UTC)
- Loose language in the last sentence. The first sentence has it right. Sum of kinetic and rest energy (and some other stuff) is conserved. And that's mass. And mass is conserved unless you let your kinetic and other energy leak out of your system. And that's the mass "defect." But as I said before, it's a mass defect like the weight defect in a burned log with ashes that weigh less. It doesn't imply nonconservation of mass. It just means you didn't keep track of your mass and it went up the chimney. —The preceding unsigned comment was added by Sbharris (talk • contribs) .
- Sum of kinetic energy and rest energy is not mass, unless you want to talk relativistic mass mγ. -lethe talk +
- It is both in the COM frame. Sum of kinetic energy and rest energy and potential energy and all other kinds of energy in a compound object ARE what you weigh as the mass, since you weigh in the COM frame. Yes, they are also the relativistic mass (total E/c^2), which is agreed a bad concept, but in this special case the relativistic mass is also the rest mass of the compound object (not the sum of the rest masses of its parts, but the mass of the whole thing, as you'd weigh on a scale). Like the mass of a nucleus or atom or box of gas. That's because relativistic mass (and energy) IS ordinary mass (and "rest energy" for the compound system) in the COM frame, which is (again) the frame you're in if you're weighing something. It is the minimal mass (or if you like, energy) you can get by choosing reference frame. All other frames give you more energy. —The preceding unsigned comment was added by Sbharris (talk • contribs) .
- Right, but the cited sentence never mentioned COM frame. -lethe talk + 11:28, 17 June 2006 (UTC)
- Well, it missed an opportunity, then. Total energy is conserved (with regard to reactions), but it is not invariant. Neither is sum of rest masses (usually). But the total mass of closed systems is both conserved and invariant. Since this is an article about mass, wouldn't it be nice to point out that, instead of insisting on using outdated definitions of mass which are constructed peicemeal, and which do change. Focus on conserved quantities where you find them. —The preceding unsigned comment was added by Sbharris (talk • contribs) .
- OK, well we're not arguing about whose definition of mass is the best, we're arguing about whose definition is used. It's nice that invariant mass is conserved and invariant, but it can't tell you much about constituent particles, so not everyone uses it. Thus there are two definitions presently in the article. I claim that this definition, in terms of rest mass, is not some historical relic, but rather is in current usage. Furthermore, it has nothing to do with closed vs. open systems. -lethe talk + 12:34, 17 June 2006 (UTC)
- Well, it missed an opportunity, then. Total energy is conserved (with regard to reactions), but it is not invariant. Neither is sum of rest masses (usually). But the total mass of closed systems is both conserved and invariant. Since this is an article about mass, wouldn't it be nice to point out that, instead of insisting on using outdated definitions of mass which are constructed peicemeal, and which do change. Focus on conserved quantities where you find them. —The preceding unsigned comment was added by Sbharris (talk • contribs) .
- Right, but the cited sentence never mentioned COM frame. -lethe talk + 11:28, 17 June 2006 (UTC)
- It is both in the COM frame. Sum of kinetic energy and rest energy and potential energy and all other kinds of energy in a compound object ARE what you weigh as the mass, since you weigh in the COM frame. Yes, they are also the relativistic mass (total E/c^2), which is agreed a bad concept, but in this special case the relativistic mass is also the rest mass of the compound object (not the sum of the rest masses of its parts, but the mass of the whole thing, as you'd weigh on a scale). Like the mass of a nucleus or atom or box of gas. That's because relativistic mass (and energy) IS ordinary mass (and "rest energy" for the compound system) in the COM frame, which is (again) the frame you're in if you're weighing something. It is the minimal mass (or if you like, energy) you can get by choosing reference frame. All other frames give you more energy. —The preceding unsigned comment was added by Sbharris (talk • contribs) .
- Sum of kinetic energy and rest energy is not mass, unless you want to talk relativistic mass mγ. -lethe talk +
- The sum of rest energy and kinetic energy as measured in the COM frame is the invariant mass, but that's not quite the same as what's mentioned in the cited sentence. -lethe talk +
- Which cited sentence?? Since the mass in the COM frame is the invariant mass, it's the mass calculated for every frame, and which can be weighed directly in the COM frame, which is the rest frame of the object. It's what we ordinarily MEAN by mass of objects. It happens also to be total relativisitic energy/c^2 (which makes you think at first we're going down that ugly road), but that's only a special a trick of the COM frame, and isn't true of any other frame. —The preceding unsigned comment was added by Sbharris (talk • contribs) .
- The sentence I'm referring to is Sexl and Urbantke's "only the sum of kinetic energy and rest energy is required to be conserved". This sum is conserved in all reference frames, and that's what Sexl and Urbantke refer to. You respond that this sum is mass, but that's not true. This sum is mass when measured in the COM frame, but in all other frames it is not, even though it is still a conserved quantity in other frames. This conserved sum, in arbitrary frame, is what Sexl and Urbantke are referring to. -lethe talk + 11:28, 17 June 2006 (UTC)
- Which cited sentence?? Since the mass in the COM frame is the invariant mass, it's the mass calculated for every frame, and which can be weighed directly in the COM frame, which is the rest frame of the object. It's what we ordinarily MEAN by mass of objects. It happens also to be total relativisitic energy/c^2 (which makes you think at first we're going down that ugly road), but that's only a special a trick of the COM frame, and isn't true of any other frame. —The preceding unsigned comment was added by Sbharris (talk • contribs) .
- Finally, mass defect is not due to nonclosed systems, rather it's due to which quantities you choose to define as your mass. -lethe talk + 09:42, 17 June 2006 (UTC)
- Well, yes, if you define your composite mass as something which is wrong, there will be a "defect" between that, and what turns out to be reality. The difference turns out to be escaped mass. I can "define" the mass of the ash of a fire as the mass of the wood and kindling I put into it, and then talk about a "mass defect" when my ash doesn't come out to what I think it should be, and what went into it. But that's just a silly way to go about reality. Make your definitions fit the facts, not the other way around. Note that the old definitions were slightly wrong and didn't fit facts (rest masses weren't quite additive when heat/radiation/energy was allowed to escape), and the new definitions from SR give the right numbers.Sbharris 10:58, 17 June 2006 (UTC)
- The question of "right" and "wrong" does not apply to terminology, which is determined solely by convention. It is, in my opinion, not silly to talk about wood losing mass while it burns. I don't want to debate whether this definition is right or wrong. The only debate left to have is whether it is found in the literature. My claim is that the three references support it. -lethe talk + 11:33, 17 June 2006 (UTC)
- Well, yes, if you define your composite mass as something which is wrong, there will be a "defect" between that, and what turns out to be reality. The difference turns out to be escaped mass. I can "define" the mass of the ash of a fire as the mass of the wood and kindling I put into it, and then talk about a "mass defect" when my ash doesn't come out to what I think it should be, and what went into it. But that's just a silly way to go about reality. Make your definitions fit the facts, not the other way around. Note that the old definitions were slightly wrong and didn't fit facts (rest masses weren't quite additive when heat/radiation/energy was allowed to escape), and the new definitions from SR give the right numbers.Sbharris 10:58, 17 June 2006 (UTC)
- The sum of rest energy and kinetic energy as measured in the COM frame is the invariant mass, but that's not quite the same as what's mentioned in the cited sentence. -lethe talk +
mass is converted into energy
Harald, when a reaction causes a change in mass of the participating particles, it is because some of their mass is converted to energy. This energy need not be radiation, it can be potential energy. The entire point of the segment is that mass can be converted into energy. This is a common way of describing things, and I don't understand why you don't like it. -lethe talk + 08:12, 17 June 2006 (UTC)
- But in an article about systems, we need to take note of the fact that when "rest mass" of a system of particles (at rest to each other as well) is "converted" to "energy" (here we mean something other than the rest energy of the particles), that energy does not stop contributing to the mass of the system until it is allowed to escape it. That's true if it's kinetic energy, radiation, potential energy, whatever you like. Again, put a nuke in a box and blow it up on a scale, and according to SR the scale won't budge, so long as the box holds. Sum of rest masses is now very different, but the particles are no longer at rest, and everything else in the box counts as rest mass OF THE SYSTEM (aka invariant mass).Sbharris 11:11, 17 June 2006 (UTC)
- Lethe, I agree that some people use that poor formulation, but see below. Harald88 08:19, 17 June 2006 (UTC)
mass is not identical to energy
One editor here doesn't understand that energy isn't mass, and so he keeps on reverting to the poor statement that mass can be "converted" into other forms of energy. As most of us know, energy can be converted from one form into another and it can also escape a system, but energy can't be "converted" from mass, just as it can't be "converted" from electricity. Harald88 08:16, 17 June 2006 (UTC) In particular, mass is a measure of energy content, as Einstein so strikingly explained in 1905. Pretending that mass is a measure of energy content and is itself a form of energy, leads to the contradiction that a form of energy is a measure of its energy content. That kind of confusion is unhelpful. Harald88 08:26, 17 June 2006 (UTC)
- It's not a contradiction if you make a distinction between the mass of systems and the mass of particles. The mass of systems in their COM frame is its total energy/c^2, aka the relativistic mass AND the invariant mass (for that one frame only). That's because this is the frame where the m(rel) is minimized, and becomes m(rest) or m(invariant). Only part of that is the rest masses of the particles in the system. —The preceding unsigned comment was added by Sbharris (talk • contribs) .
- Although I roughly agree with your argument (with the exception that we don't really know if the same is also valid for particles, eventhough you claim it isn't so), that was not really the issue here. This was more subtle: how to formulate the relationships between matter, mass, energy and radiation in a clear and consistent way. However, when only writing that "rest energy can change", the argument is incomplete in the way that you state; and the more precise phrasing of "rest energy" highlights the incompleteness of the statement. Harald88 00:05, 18 June 2006 (UTC)
- Look, I have no problems with the way the article treats the mass of particles. The problems with m(rel) and m(rest) are well laid out. The problems come when we get to mass of systems, where basically m(rest) corresponds to m(invariant)-- that COM frame m(rel) which is also m(invariant) is the lowest m(rel) for that system you're ever going to see, from any inertial frame. Since it's E(rel)/c^2 it includes rest masses, kinetic energy, potentials, heat, radiation in the system, whatever. But E(rel) for that system in any OTHER frame is larger! This is the minimal E(rel)-- the best you can get. And because it's the COM frame mass, it's what you weigh.
- Now if we want to go through all the problems of giving two conventions for masses of systems, we can do that. But I think the one with the addition of rest masses is a waste of time, because it's not the one we ever measure. The only mass of any system we ever measure is the one we CAN measure for enclosed systems in the COM frame, and that includes everything-- heat, kinetic energy, potential, the whole enchilada. It may be less or more than the rest masses of identifiable particle consituents, but at least it can be measured. It's what we've historically CALLED the mass of systems, because it's what we WEIGH when we weigh a system. As for sytems of unbound particles, we can calculate the system mass by adding up rest masses, but that's going to give us a wrong answer for what we'd weigh if we could weight it (and also for what we'd weigh if the system sprang from some single particle of indentifiable rest mass). So again, when we calculate this, we want to calculate the invariant mass of the system, not add up rest masses of components.
- Finally, invariant mass of closed systems is both invariant and conserved, and that's more than you can say about most physical properties. So it deserves to be given top billing. It's the mass associated with all the energy inside a sphere, E = mc^2, if only the sphere is at rest in front of you. That's pretty easy to understand for the lay person, so it should be put that way. In fact, if you do, the reader will probably begin to wonder how many "fundamental particles" are just that kind of thing. They're at "rest" but how much of their mass is the rest mass of their constituents, such as quarks. And the answer is we don't know, but probably not much. Sbharris 00:52, 18 June 2006 (UTC)
- OK, I see that we essentially agree. Harald88 10:16, 18 June 2006 (UTC)
- Your suggestion that invariant mass is the only one we can measure is not very accurate. How will you measure the system invariant mass of a scattering of a tau particle off of a positron, for example? In such an experiment, there is no bound state, and the only masses that can be measured are the rest masses of the constituent particles. -lethe talk + 11:59, 18 June 2006 (UTC)
- This whole mess is why I put in a substantial addition about the mass of systems. Deleting it didn't help, because it explained all the questions we're arguing over, and now we're arguing over them again. If you'd all read the examples I gave again, you'd quite asking the same questions, I think. Invariant mass of a system is a measure of the minimal energy content of a system (the minimized one you see in the COM frame). But it may contain more or less mass than the sum of the rest masses of the paticles used to construct the system. —The preceding unsigned comment was added by Sbharris (talk • contribs) .
- What if I say rest energy instead? -lethe talk + 08:33, 17 June 2006 (UTC)
- That's perhaps unusual... but certainly better. However, now that we have increased clarity, it's also easier to see that the argument is incomplete, see above.
- But sorry for interrupting (and my lack of tact); I'm sure that the two of you can complete it (for example you may give as additional example a temperature increase). Harald88 00:05, 18 June 2006 (UTC)
proposed edits
Current:
In popular science and basic relativity courses, however, the observer-dependent kind of relativistic mass is usually still presented, due to its conceptual simplicity and the fact that certain equations from nonrelativistic mechanics retain their form (namely, Newton's second law). Einstein's famous equation E = mc^2 \,\! remains generally true for all observers only if the m\,\! in the equation is considered to be relativistic mass. It is true for invariant mass, only in specific circumstances to be discussed.
Proposed:
In popular science and basic relativity courses, however, the observer-dependent kind of relativistic mass is usually still presented. Einstein's famous equation, E=mc^2, is generally true as written only if the m in the equation is considered to be the relativistic mass. A slightly different and more complicated form of this equation, E^2 - p^2 c^2 = m^2 c^4 is required when invariant mass is used.
Arguments:
Newton's second law, F=ma, does NOT work when invariant mass is replaced with relativistic mass. This is pointed out later in the article.
The "conceptual simplicity" of relativistic mass is highly debatable. We can objectively agree that it relativistic mass is commonly used in popular science, and that Einstein's famous equation E=mc^2 uses relativistic mass.
Current:
The main benefit of using the relativistic mass is that the formulas
and
from nonrelativistic mechanics retain their form, and are valid for relativistic situations when used with M in place of m. The first equation is Newton's second law, the second is simply the definition of momentum.
Proposed:
The main benefit of using relativistic mass is that the formula
p = mv
does not need to be modified.
Argument: F = dp/dt is always true, regardless of whether one uses relativistic or invariant mass. It's the basic defintion of force. Thefore F=dp/dt is not an argument for using relativistic mass.
I am also looking for a way to improve the discussion on "conservation of mass". The way I would
describe the situation is that energy and momentum are conserved, and that the mass of a system is re-computed from its energy and momentum via the relationship m = sqrt(E^2 - (pc)^2) / c^2.
Most specifically, the mass of a system is not the sum of the masses of its parts. Energy and momentum do have the property that the total energy of a system is the sum of the system-component energies. Momentum behaves similarly. Mass does not behave in this manner.
- Invariant mass (including that of systems) is separately conserved as well, in any frame, so long as the system is closed (but that also is a caveat for energy and momentum). While it is true that the mass of system is not the sum of rest masses of system parts, the mass of the system (or object, simple or compound) is its total energy/c^2 in the COM frame, which is useful, and in any case can be computed according to the invariant formula, and doesn't change. That's the main reason to use it as the definition of "mass," rather than relativistic mass.
- It's certainly true the F = dp/dt remains true under all definitions of mass. Relativistic mass is used to try to make p = mv remain true (as you point out), and also to try to make E=mc^2 remain true in all frames. But as noted in the article, p=mv isn't all that useful and in any case is true only in the direction of v. Having E = mc^2 defined true for all frames simply redefines "mass" as total relativistic energy/c^2, and that's not very useful because we already have total relativistic energy to do that job. With m = invariant mass, E = mc^2 remains true in the COM frame only, but since that's the frame we usually work in with compound objects (it's the only frame in which they can be weighed on a scale, for example), invariant mass actually does most of what we want, and keeps E=mc^2 for most situations, too. That's confusing, because people are told that E=mc^2 is not true in general, except for simple single resting masses. But it has much wider application. Heat an object or a can of gas on a scale, and E = mc^2 still remains perfectly correct. Both E and m simply increase. The same happens in a chemical reaction or even for a nuclear bomb which liberates heat. E and m would remain constant if you didn't allow the heat and radiation to escape. SBHarris 19:46, 30 July 2006 (UTC)
- I've made the edits I proposed - I think that by snipping a lot of material, I've improved the flow of the article.
- Please sign your entries by adding four tildes in a row: "SBHarris 18:24, 5 August 2006 (UTC)". I would probably agree that your edits have improved the flow, but at the cost of decreasing the knowledge content (as is ever the case, truth and clarity are conjugate variables). The reader needs to clearly undertand that E = mc^2 is also perfectly true for systems in the COM frame, which is most things. Most people actually believe that when you blow up a nuke, the mass decreases. They teach this is school. Strickly speaking, this is wrong. Mass doesn't decrease until you let the energy of the explosion "out". The mass you weigh for the bomb is invariant and constant and conserved. It's the same AFTER the explosion. It doesn't decrease until you remove the heat and light, THEN the heat and light has the mass you're "missing." So you can't get rid of mass in the COM frame. It's conserved. Since this is an article on mass in relativity, this needs to be highlighted so the reader understands it completely. Anyway, I've added some bits which I hope do the job. SBHarris 18:24, 5 August 2006 (UTC)
- Similarly, the purpose of the force equation was to stress that Newton's force law remains valid with relativistic mass. That is worth stressing because of some common misconceptions that have appeared in recent literature (don't people read old literature nowadays?). Thus I'll reinsert a remark about that. Harald88 11:26, 6 August 2006 (UTC)
- I like the final result - I think the article is considerably more focused now. Meanwhile I've made a very minor edit to add a hyperlink, and a slightly less minor edit to explain that the relativistic energy momentum equation is a generalization of E=mc^2 (as was promised earlier). Pervect 20:23, 6 August 2006 (UTC)
- I'm okay with the result, which gets in the necessary info. I originally put the section on mass of systems in after the E-m-p equation, because it's a little easier to introduce, as a sumation of this. But it can be done as it's done here. SBHarris 20:37, 6 August 2006 (UTC)
contradiction
The article now states an apparent contradiction (and it's for sure an inconsistency in presentation of facts) about the current use of relativistic mass. Now I don't have an oversight of all modern books and courses, so I don't know which statement is more correct:
"In [...] basic relativity courses [...] the observer-dependent kind of relativistic mass is usually still presented"
or,
"The concept has been eliminated from all modern physics textbooks as confusing and inappropriate."
At least these two POV's should be combined, insofar as they are verifiably correct; probably the best place is in the section of the first statement. Thus I now remove both from the article space, until it has been sorted out. Harald88 19:16, 7 August 2006 (UTC)
- FYI, the user who made the changes about elimination of "relativistic mass" in modern textbooks is the same one who yesterday derided the discussion of photons in a box in the photon wiki, as being a "college textbook exercise." IOW, he's really concerned with textbooks when it suits him to be, but otherwise not. My question: Do we really care about pedgogics here, or should be move it all to an isolated section ("Stuff they teach or used to teach, which was confusing and no longer used by professionals")? SBHarris 21:05, 7 August 2006 (UTC)
- The point is that you are using an obsolote notion (relativistic mass/ rest mass) in order to support your POV on the calculation of the "photon in a box" which in turn is something that you picked up off a FAQ for beginners. Do you have any references, other than the FAQ, that what you are writing about the photon "mass" in general is verifiable? A reference to an experiment published in a peer refereed journal on the "photon in the box", the "photn mass" being non-zero, the photon having "relativistic mass" please. Ati3414 00:24, 8 August 2006 (UTC)
- This is pretty basic physics. Here's the standard equation for the invariant mass of two photons of energy E1 and E2 [2] (units of c=1 are used). Note that for angles of 180 degress, the mass is simply m^2 = 2E1*E2. If the photon energies are equal, the invariant mass of the pair is 2E. SBHarris 00:41, 8 August 2006 (UTC)
What I'd like to see, but it's too much work!
I'd like to see the explanaton of invariant mass given first. We tell people that it is modern practice to use invariant mass, and then the article spends a lot of time explaning relativistic mass, which while not wrong is a bit dated.
This strikes me as being too much work for the amount of gain, though. Pervect 05:57, 10 August 2006 (UTC)
- Historically the article started out with a long discussion by somebody who loved the concept of relativistic mass, and was distrustful of invariant mass. After much arguing, we finally got it to the state you see, but it was a long haul. Personally, I'd also like to present invariant mass first as well, then move to invariant mass of systems. SBHarris 22:16, 10 August 2006 (UTC)
photon-like particles that aren't photons?
I find "other particle moving at the speed of light" puzzling: what particles other than photons move at the speed of light? Harald88 21:46, 10 August 2006 (UTC)
- Gravity waves move at the speed of light. So if gravitons exist, they are massless and move at the speed of light. Neutrinos were thought until recently to be massless. They are very nearly so and move so close to the speed of light that the neutrinos from a supernova explosion arrived at Earth before the light did. Some theories say that all particles are massless in their "bare" condition and only gain mass as a result of interactions, especially with the Higgs boson. JRSpriggs 03:12, 11 August 2006 (UTC)
- Thus hypothetical particles... OK why not! Harald88 12:23, 11 August 2006 (UTC)
Proper number of links per article per tech term ??
Another editor (AySz88\^-^) and I have been having a discussion about proper number of links to have per technical term (such as invariant mass) in an article such as this. We agree that the proper number is somewhere between EVERY one, and ONLY ONE per article (the first one). The other editor has a reasonable approach to this idea, so I'm going to paste his suggestions right here. This should keep us out of a link-delink war, at least for this article. [And I'm seriously thinking of going to the WP:PUMP or the vague Wikipedia:Manual of Style (links)#Overlinking to propose a better general guideline for hyperlinks in tech stuff, too, so that other physics pages get treated the same way].
Anyway, I'll agree not to link any more than one tech phrase per (my!) screen, and if anybody wants to delink stuff up to once per section, I won't object. Personally, it doesn't bother me if EVERY use of a tech term is hyperlinked, though I understand if some people find it annoying if it is, and others if isn't. I certainly find it annoying if anything OTHER than tech terms are linked (for example, day of month dates). But I know some people OCD about that also. Anyway, what say you all? SBHarris 01:03, 14 November 2006 (UTC)
- Overlinking. Hello; about the links, repeating the links is definitely okay if it has been a while since the last time the word was used, but repeating links every paragraph or so is not necessary especially if every paragraph is discussing those same subjects. There isn't a reason to repeat a link in, for example, the second and fifth paragraphs of a section, especially if one would need to read the second paragraph of the section anyway to understand paragraphs which follow (and if this isn't true, the section should probably be split into two). Personally, I think that there should be no repeats within a section, and no more than two per screen if the sections are very short. The section about this in the Manual of Style is Wikipedia:Manual of Style (links)#Overlinking, but it's somewhat vague.
Keep in mind that "a page" can be different depending on your display resolution - you might see only one link per page while I (working on 1280x1024) might see twenty on a screen. Most people seem to use something close to 1024x768.
Also, "relativistic mass" redirects back to the exact same article, so I removed all the links to it.—AySz88\^-^ 00:11, 14 November 2006 (UTC)
- Overlinking. Hello; about the links, repeating the links is definitely okay if it has been a while since the last time the word was used, but repeating links every paragraph or so is not necessary especially if every paragraph is discussing those same subjects. There isn't a reason to repeat a link in, for example, the second and fifth paragraphs of a section, especially if one would need to read the second paragraph of the section anyway to understand paragraphs which follow (and if this isn't true, the section should probably be split into two). Personally, I think that there should be no repeats within a section, and no more than two per screen if the sections are very short. The section about this in the Manual of Style is Wikipedia:Manual of Style (links)#Overlinking, but it's somewhat vague.
- Link everywhere: I say you can't link too much. --Michael C. Price talk 08:18, 14 November 2006 (UTC)
- At risk of violating WP:POINT, I've fixed your last statement to reflect your view. Is that helpful? You may be interested to know that WP:MOS does not agree with you, nor do most editors, nor do I. Most words don't need to be linked (though they could be, as you can see above), because we all know perfectly well what they mean in context. Second, even overlinking odd words too much detracts from the usefulness of linking other odd words, because it's like crying wolf (or simply crying) too many times. It's like too many italics. Good linking is like good swearing. Or like spice in cooking. Too much and you totally spoil the whole efffect, and the whole point. Which is of course a kind of emphasis. SBHarris 21:25, 12 May 2007 (UTC)
- Link everywhere: I say you can't link too much. --Michael C. Price talk 08:18, 14 November 2006 (UTC)
Erroneous statement "which change cannot be observed"
I have the impression that this article is so much affected by a one-sided POV that it even resulted in errors. The 1950 claim has been corrected to satisfaction (at least, it now looks fine to me), but more remains to be done. For example, the claim that relativistic mass change "cannot be observed". To the contrary: Feynman explained with a perfectly simple and straightforeward example how to observe relativistic mass increase, and I was similarly taught at college how to calculate the required increase of magnetic force in order to keep particles in their orbit because of mass increase - which boils down to accurately measuring relativistic mass. Of course this has to be done in motion, just as also time dilation is measured on moving clocks. Harald88 21:55, 9 May 2007 (UTC)
- The phrase segment you refer to seems to be this one: "...some change in internal structure of the object, which change cannot be observed". What it says is that one cannot observe changes in the internal structure of an object as a function of the speed of an observer relative to the object (to make it clearer, as it does not matter who is considered to be at rest).
- This corresponds to physical observation. If a deep-space proton flies by you at 0.999c, there will not be any change to your internal structure (or mass).
- You can also read it as saying that there is no actual increase of the mass of the body, even if an observer "sees" an increase of its relativistic mass. In fact, that different observers (in different inertial frames) will see different values of the relativistic mass of the same object.
- This also means that there is no change in the inertia or gravitational properties of the body, within special relativity, for different speeds of the body relative to an observer.
- Calculations done with "relativistic mass" can give the right results, as a 4-coordinate transformation method, but with considerable care and pain. However, interpreting the results as an actual change in mass of the object is not warranted. That's why the phrase says ...some change in internal structure of the object, which change cannot be observed".
- Hope this proves helpful. Thanks. Edgerck 22:17, 9 May 2007 (UTC)
- It was indeed helpfull to see such a clear display of prejudice. To start with, it would be a misconception to think that the relativistic mass concept suggests a change in internal structure (and even more, to think that the proper mass of a body perfectly corresponds to the amount of protons and neutrons). Such a misconception must of course not be conveyed by this article.
- But the sentence that follows the sentence we cite above seemed to suggest that relativistic mass can not be measured. Anyway, now I see that you have attempted to improve the text (but it's not really clear now, and it sounds more like a defence of an opinion using a circular argument than like an objective introduction of "mass").
- Also, a general claim that there is no change in the inertia of a body with speed is erroneous. It might be that such a claim can be correct with certain definions of inertia, but in the ones I know inertia is resistance against acceleration, just as Wikipedia now states. By the way, calculations with relativistic mass are quite painless. :-)
- Your last claim, "interpreting the results as an actual change in mass of the object is not warranted", may not be promoted in a Wikipedia article: it boils down to claiming that the opinion of Feynman and others was wrong because again other people have a different opinion about what should be meant with "mass". Instead, [WP:NPOV]] requires this article to represent the literature's different opinions fairly and accurately.
- I hope that this was helpful too! I'll check the article at a later time. Harald88 18:01, 12 May 2007 (UTC)
While everyone is entitled to their opinion, of course, the article clearly states the chronology and evolution of the concept of mass in special relativity, and does so with source citations anyone can verify, from 1912 to present mainstream use in physics.
The begriff "relativistic mass" was created by Tolman in 1912 (with one definition) and then redefined by Tolman and others in 1934. While Feynman, Max Born, Schwartz, and other physics Nobel Prize winners deserve our study, the concept of science is that it is in constant progress. So, rather than being undeserving of the work of such giants and continue looking at physics on the same level they stood, we need to stand on their shoulders and look farther, higher, till we reach present day knowledge. It is not whether their "opinion" was wrong -- physics is an exact science governed by observation. No one can, or ever will, observe "relativistic mass" as mass.
Regarding your physics question, according to relativity theory: inertia provides resistance against acceleration 'and there is no change in the inertia of a body with speed relative to an observer. So, you see once again that the theory directly contradicts the idea of a relativistic mass that changes with speed.
Present day, mainstream, and verifiable knowledge is clearly given in the article. There have been a couple revisions lately. Please read the article when you have time. Thanks! Edgerck 23:34, 12 May 2007 (UTC)
Mass of composite systems and conservation of mass in COM frame
On May 10 a number of changes were made:
<-- it is not true that mass is conserved for closed systems during chemical and nuclear reactions -->.
- : (Center of Momentum frame for systems) + If a rest frame (also called center of mass frame or COM frame) can be defined for the system (which is equivalent to say that the system is not massless), then in the rest frame p = 0 and E takes on a value such that the mass is defined by:
- Since the COM frame (also called center-of-momentum frame) is chosen as the frame to measure the mass of most compound objects, Einstein's mass-energy equivalence formula E = mc² continues to apply in these circumstances. For example, if the mass of a nuclear bomb were measured by weighing it, this system mass would be a conserved invariant mass and would not change, even after the bomb exploded. However, after the explosion, this total system mass would also include the heat and light from the explosion. Only after the heat and light was removed (resulting in a non-closed system) would the mass of the constituents of the bomb show a decreased mass (in this case, a mass decrease equal to the mass of the heat and light removed). + : (Center of Momentum frame for systems)
- Invariant mass is a concept widely used in particle physics, as the invariant mass of a particle's decay products is equal to its rest mass. It is this that is used to make measurements of the mass of particles such as the z particle or top quark. + This relation, which is valid only for the rest frame, is Einstein's famous mass-energy equivalence formula E = mc². <-- this relation cannot be applied to photons, so it cannot be applied to imply mass conservation in atomic explosions even if the system is considered large enough to be closed immediately after the explosion -->
The comments in the <--> bracketts are completely wrong, and I'm amazed that a physicist made them. The Einstein E = mc^2 CAN be applied to photons even if the m stands for invariant mass (all systems of photons have an invariant mass so long as not traveling in the same direction) so a nuclear or chemical reaction would NOT change total mass if confined on a scale, in a superstrong box. Blow up a nuke in such a box on a scale and the temp in the box would go up millions of degrees, but the mass of the box as seen by the scale, wouldn't budge. Only after you let the heat and radiation out, would the mass go down. And then, of course, the heat and radation carries away the missing mass, and in the COM frame, still HAS that mass, as part of a system in the old frame. Even a single photon has an invariant mass if it's part of a system in a COM frame, such as the box. In such a system the photon bouncing in the box will deliver downward momentum in any gravity field, and will contribute weight E/c^2, and thus (by the equivalence principle) also E/c^2 inertial mass. Thus, even a single photon's energy will contribute to invariant mass of that system. SBHarris 08:57, 24 May 2007 (UTC)
- I agree with your comments. I'll check the history of the article and revert to the latest correct version. Count Iblis 12:57, 24 May 2007 (UTC)
- I do not want to be overbearing and I feel I already discussed all clarifications on my edit and references. So, for right now, I just want to leave the matter in your hands and in the hands of the community. I'll be very happy to just watch and see how the system processes the correct information (see my talk page for definition) that I inserted, referenced according to the WP reliable sources policy, and clarified when contested. Thank you for your kind review. Edgerck 19:15, 24 May 2007 (UTC)
Richard Feynman in The Character of Physical Law wrote "The energy associated with motion appears as an extra mass, so things get heavier when they move." This POV and the associated name "relativistic mass" are outdated and not used in physics today. The opposite view, that ("things do not get heavy when they move") and that the only type of mass is invariant mass, is not the least controversial today (see WP:RS source below). This article is in violation of WP:NPOV and WP:RS. Historical references may mention the previous use of "relativistic mass", as done in the version of 03:09, 24 May 2007 (ref. below).
I am sourcing this comment under WP:NPOV and WP:RS, to (inter alia) Mass.
The last version that is not in violation is 03:09, 24 May 2007, as edited by 137.132.3.11.
I formally request the editor who reverted from 03:09, 24 May 2007 to reinstate that version in a timely manner, preventing other WP editors from working on the current version visible -- with the subsequent loss of work.
Thanks. 20:14, 25 May 2007 (UTC)Edgerck
- Hi Edgerck,
- The reason why I reverted your version was that you deleted a lot content, e.g. the example about the atomic bomb. The current version, like it or not, describes pretty accurately how professional physicists who use special relativity on a daily basis use this theory. Now, there are some physicists who hold minority opinions, like e.g. Okun. They prefer to define things in a slightly different way.
- Although these things can be mentioned in this article, it is wrong to then delete any mention of the relativistic mass of the photon by saying that gamma times m is undefined. That's just silly. Of course, you can define the relativistic mass by declaring it to be the zeroth component of the four momentum. So, this is i.m.o. just a straw man argument.
- Here on wikipedia, you have to be tolerant. I have my own POVs that go against the consensus on wikipedia which I can justify using reliable sources too. E.g. in modern physics one does not regard units and dimensions as fundamental quantities; you can use units in which h-bar = c = G = 1. This is regarded not just as a trick, but taken literally, i.e. h-bar, c and G are no more than conversion factors and the dimensions we have assigned to length time and mass are only there for historic reasons (Okun is a well known physicist who strongly disagrees with this view).
- But if I were to edit wiki articles on this subject, completely rewriting them from the (correct) POV giving all the sources, then you would get an article that most other editors would not be happy with. E.g. the explanation of why dimensional analysis works would now be very difficult to follow for most people.
- Now, in your edits of this article you didn't even address the examples that were given in the article, you just deleted them. Count Iblis 20:51, 25 May 2007 (UTC)
WP policy says that "Zero information is preferred to misleading or false information". Thus, what did not meet WP policy should be (as it was) deleted. Please provide a WP:NPOV and WP:RS compliant reference for every affirmation of article content that you make above (eg, example about the atomic bomb) or please do not use them in WP discussions or articles. Thanks.Edgerck 21:06, 25 May 2007 (UTC)
- Don't be silly. Generally, sum of 4-momentum is conserved for all observers (all frames) in systems of interacting particles. See for example [3]. Conservation of energy and momenta as separate quantities are derivative of this, and the split between time-like and space-like quanties for energy and momentum (which cannot be defined without a frame) is what makes conservation of each of them single-frame-dependent, through time, in an interaction. Conservation of 4-momentum is much more general, and its limitations are only for volumes so large that space-like intervals need to be considered-- but then we don't have interacting systems anymore, do we? In any case, what we're talking about as "mass", and what you weigh on a scale, is the square root of the norm of 4-momentum. So obviously, it's conserved as well for small systems like fissioning nuclei and atom bombs. As for needing an RS cite for this, if I have a cite for a general case, I hardly need one for a specific one, by logic. Example: If angular momentum is conserved for all bodies, cite given, I don't need WP:RS to say it's conserved for a figure skater named Alice as she pulls in her arms, now do I? SBHarris 05:14, 26 May 2007 (UTC)
SBharris, I kindly ask you to please keep a civil tone. I did not question conservation of 4-momentum or energy, so this is off-topic. Mass is not in general conserved in SR even for closed systems, and I source this affirmation to authoritative elementary texts, including Lev Davidovich Landau and Evgenii Mikhailovich Lifshits, (1987) Elsevier, ISBN 0750627689.
BTW, your logic fails when you consider that mass must be conserved because E and p are conserved and m² = E² - p² in c=1 units. Can you see the mistake? Anyway, whether you can see it or not is irrelevant for this talk-page and WP (this is not a usenet discussion group in physics), as all the WP:NPOV verifiable sources say that mass is not conserved in SR in general, even for an isolated (free) system. Thank you. Edgerck 20:54, 26 May 2007 (UTC)
I also kindly remark that I verifiably sourced my comment about the current WP:NPOV and WP:RS violations to (inter alia) Mass -- which is linked to http://math.ucr.edu/home/baez/physics/Relativity/SR/mass.html. Thanks. Edgerck 21:43, 25 May 2007 (UTC)
- Edgerck, please stop using these Straw Man arguments. This is all matter of definition. What matters is not what Okun has written or what you can find in the Landau&Lifshitz series (physics is not religion with Okun et al. the prophets). What matters is if given some definition of mass an assertion is correct. This article discusses several definitions of mass. One of these definitions is the invariant mass which is defined to be the energy in the zero-momentum frame. The fact that invariant mass is conserved (for an isolated system on which no external forces act) then follows from conservation of energy and momentum.
- You can edit this article by giving the perspective of Okun, e.g. by saying that: "according to Okun, the relativistic mass of the photon cannot be defined". But just saying that it cannot be defined because Okun says so, is not allowed under the Wikipedia rules (even if the citation to Okun's article is given). This is because you can define the relativistic mass as the zeroth component of the four momentum which also works in case of the photon. Only if you demand that it must be given by a relation m times gamma does it become undefined. But that is not the standard definition. Count Iblis 21:56, 26 May 2007 (UTC)
CI: Please be respectful to others and their points of view. This means: Do not simply revert changes in a dispute. A tag calling the dispute a dispute -- see WP:NPOV and references -- should not be reverted unless there is a resolution. I disagree with its removal.
I kindly ask you to please reinstate the tags and follow WP policy.
Wikipedia relies on what reliable sources have said about the matter. By relying what sources have reported about a subject, WP limits the influence of an editor's POV. The incorrect information in this page is not accepted in the mainstream, and it is easy to find numerous sources taking the "correct", or mainstream, position.
I have made all the proper requests according to WP policy. I have no need to repeat myself, as WP has all my comments and edited pages in the archives. I am now entering a disengage phase in the hope that this will be helpful. Edgerck 23:29, 26 May 2007 (UTC)
- Edgerck, there are many reliable sources that disagree with some of the points you have been making here. And you can't hold an article hostage by placing an POV tag on it, only to remove it when you get your way. Wikipedia has a very important rule that superseeds all other rules: Wikipedia:Ignore all rules. This rules says: "If the rules prevent you from improving or maintaining Wikipedia, ignore them." In this case you made edits that amounted to removal of a large amounts of content. You did not even address the issues raised in the removed content (you could have explained the removed examples differently...). Count Iblis 00:10, 27 May 2007 (UTC)
CI: WP policy says that "Zero information is preferred to misleading or false information". Thus, what did not meet WP policy should be (as it was) deleted. But (as you can see above) I said that before. You can "ignore all rules" at a price, and here the price was WP:NPOV, fairness, and maybe more.
Finally, no one can claim lack of my explanations. I used well-documented edit summary lines (that you called "chatty"), I left HTML tags in the text to call attention to incorrect text that was deleted, and I was available in multiple talk pages that you insist in revert. And, I summarized all the reasons in my user talk page, with a commented list of non-controversial answers in special relativity. Thank you.Edgerck 03:39, 27 May 2007 (UTC)
- My two cents worth: I think the longer version of the article is a better starting point. I recall that the book A Guide to Introductory Physics Teaching by Arnold B. Arons has some useful comments -- I will look them up when I am back in my office. For the record, I am a professional physicist and have been teaching Special Relativity in a university physics department for the last few years. Timb66 10:56, 27 May 2007 (UTC)
All hands, including Timb66: I do not know about Timb66 qualifications but while it is easy and has no consequences for anonymous expert users to claim that invariant mass is conserved in SR, or that it is conserved in nuclear fission or fusion, this is not so for those few who use their real identities and qualifications. That's why I myself would prefer anonymous participation here, but I decided not. I want people to understand that these edits are serious and not some willy-nilly change.
As I announced about a week ago, I am conducting a public experiment to verify the trustworthiness of information in WP. Since information in WP is dynamic, I think this question cannot be answered by simply sampling at specific times. Instead, I decided to measure the lifetime of correct information (defined as correct according to WP policy) that was seeded in WP edits of selected articles. To reduce error in defining what is correct information I used topics that are not the least controversial today, even though they are widely misunderstood (to motivate editing interest).
This is not a "trap". To make sure that my justification for the edits were visible to any editor, I used several channels. I used well-documented edit summary lines, I left HTML tags in the text to call attention to incorrect text that was deleted or changed, and I was available in multiple talk pages, in addition to my own and a special talk page for this experiment. I also answered questions in other editor's talk pages.
Some changes, notwithstanding all the above, were reverted without a WP valid justification. Applying WP policy, typically results in the following steps, after a revert:
1. my statement, in the talk page, that the reverted version was correct according to NPOV and RS, with current, authoritative, mainstream, supporting references (while the current version is not), with a call for that version to be reinstated.
2. back arguments, without understanding (or, perhaps even reading) the current references, that the changes do not make sense and contradict well-known (but outdated) authors.
3. Reaffirmation of #1, with more references and with a tag for NPOV dispute placed in the article.
4. The tag is deleted under a call to the "break all rules" WP policy, stating that the article cannot be held "hostage" to a clearly incorrect edit.
While this goes on, anyone reading WP or editing it will not see correct information, where correct information means information that is not the least controversial today.
Now, how many more hoops should a voluntary WP editor have to jump in order to assure that WP reflects a viewpoint that is not controversial? Escalating the edit difference to any form of litigation does not seem to be a pleasant or fun activity, or rewarding in time.
The WP idea of "anyone can edit" finds its limits in the observation that "ignorance is bliss". Those who ignore, by definition, ignore that they ignore. Many subjects, most (but not all) of them technical, have subtleties that are important. It may be easy to read a correct phrase but it is a lot harder to write one, as anyone taking a test knows.
So, requiring a WP editor to follow NPOV and RS when the editor simply does not understand the subject (eg, is not able to ascertain the falsity of his beliefs versus what the references say), seems to be nonsensical. No one can write what they do not understand. The emphasis in WP:Verifiability goes nowhere in such context, and we can see that in WP.
WP is an encyclopedia project but the bottom of the iceberg is currently dominated by an education project for editors, which is open ended.
Looking at this as a pyramid, at the top we have well-educated, scholar editors, numbering (say) one hundred. At the bottom, we have well-meaning but clueless editors who want to edit what looks to them to be an error or lack of an example that they heard somewhere, but which is not correct (according to WP:Verifiability references that they do not have and, even if they would read, would have the same "error").
I don't have the answers. The problem is not anonymity. Academic qualifications do not always mean fairness or even competence. But it seems to me that current WP rules are somewhat in contradiction with the WP goals.
The experiment I mentioned above, hopefully, asks some of the right questions that we need to see in order to improve the quality of information found in WP. The experiment page is at Reliance on Information. Thanks. Edgerck 15:51, 27 May 2007 (UTC)
Reply by Count Iblis
You are making a big issue out of a minor point. The source of the disagreement is not the physics, but a simple matter of definitions. You seem to insist on defining invariant mass for composite systems in a clumsy way. If photons escape you will automatically re-define the system by omitting the photons. Fine, you can write that Okun et al. do this, why they do this, and that if you do this then what you get is what you wrote. But you cannot write (or suggest) that it isn't possible to define a composite system by including photons.
This article makes it very clear that the invariant mass of nuclei that are involved in nuclear reactions is not conserved, so as far as the physics is concerned, there is no disagreement at all!Count Iblis 16:33, 27 May 2007 (UTC)
- This article makes it very clear that the invariant mass of nuclei that are involved in nuclear reactions is not conserved, so as far as the physics is concerned, there is no disagreement at all!Count Iblis 16:33, 27 May 2007 (UTC)
WP Policy for removing NPOV tags is resolution, not removal war. The technical content issues also affect Talk:Mass-energy_equivalence, and Talk:Introduction_to_special_relativity. The POV expressed by the editor above is not mainstream for more than 50 years in research and more than 30 years in textbooks, according to mainstream references (it is easy to find even more). [1], [2], [3],[4], [5], [6], [7], [8], [9], [10], [11]
References
- ^ Lev Davidovich Landau and Evgenii Mikhailovich Lifshits, (1987) Elsevier, ISBN 0750627689.
- ^ Lev Okun, The Concept of Mass, Physics Today, June 1989.
- ^ "Does mass change with velocity?" by Philip Gibbs et al., 2002, retrieved Aug 10 2006
- ^ Edwin Floriman Taylor, John Archibald Wheeler, Spacetime Physics: introduction to special relativity, W.H.Freeman & Co Ltd (1992), ISBN 0716723271.
- ^ Lev Borisovich Okunʹ, The Relations of Particles, (1991) World Scientific, ISBN 981020454X, p. 116-119, 127.
- ^ Usenet Physics FAQ
- ^ Gary Oas, On the Abuse and Use of the Relativistic Mass, 2005.
- ^ "Does light have mass?" by Philip Gibbs, 1997, retrieved Aug 10 2006
- ^ "What is the mass of a photon?" by Matt Austern et al., 1998, retrieved Aug 10 2006
- ^ William S. C. Williams, Introducing Special Relativity, CRC Press (2002), ISBN 0415277620
- ^ "Ouch! The concept of `relativistic mass' is subject to misunderstanding. That's why we don't use it. First, it applies the name mass--belonging to the magnitude of a four-vector--to a very different concept, the time component of a four-vector. Second, it makes increase of energy of an object with velocity or momentum appear to be connected with some change in internal structure of the object. In reality, the increase of energy with velocity originates not in the object but in the geometric properties of space-time itself.", in Edwin Floriman Taylor, John Archibald Wheeler, Spacetime Physics: introduction to special relativity, op.cit.
This dispute will never be resolved to your liking. The issue is not whether or not relativistic mass is an oudated concept. Of course, it is outdated and the current article says so. But that doesn't mean we can't write about relativistic mass in this article (or perhaps another) wiki article. Count Iblis 18:03, 27 May 2007 (UTC)
It's easy to do a diff between the current version and the version edited by 137.132.3.11 at 03:09, 24 May 2007, which is the last version I saw that complies with WP:Verifiability. Significant differences exist with the current version, for example:
CURRENT VERSION
- Reactions in this special inertial frame (so long as the system remains closed) do not produce changes in mass, relativistic mass, or energy.
which is incorrect per references cited; and this section (which is correct and cites mainstream reference using current POV) was deleted:
VERIFIED VERSION
- Today[1], following Einstein, instead of introducing the concept of relativistic mass when changing frames of reference, one uses the relativistic energy-momentum relation. In this relation, mass is always invariant. Scales and balances operate in the rest frame of objects being measured, measuring mass.
- <reference/>
and also this was deleted, even though is cited almost verbatim in current POV references):
VERIFIED VERSION
- This usage is less confusing because it does not appear to make the increase of energy of an object with velocity or momentum to be connected with some change in internal structure of the object that would increase its mass, which change cannot be observed. In other words, one cannot observe changes in the mass of an object as a function of the speed of an observer relative to the object (to make it clearer, as it does not matter who is considered to be at rest).
but this fringe view was added without reference (no mainstream author supports it):
CURRENT VERSION
- For example, this formula states that a photon (which moves at the speed of light) has relativistic mass.
This incorrect view (rejected since 1920, mass is not conserved in SR, not even in closed systems), was also added, also without WP:RS source :
CURRENT VERSION
- Note that the invariant mass of a closed system is also independent of observer or inertial frame, and is a constant, conserved quantity for closed systems and single observers, even during chemical and nuclear reactions.
And more. The differences (additions and deletions), are such that the current article should be immediately provided with the tags that I inserted, to prevent trusting users from trusting such content, and reversed as soon as possible to the last verified version.
This is not about one definition, or a historical note that became too large. It's about basic misleading and false information that was inserted while verified and correct by WP:RS information that contradicted it was simply deleted.
Thank you. Edgerck 18:29, 27 May 2007 (UTC)
- You wrote: "CURRENT VERSION
Reactions in this special inertial frame (so long as the system remains closed) do not produce changes in mass, relativistic mass, or energy.
- which is incorrect per references cited; and this section (which is correct and cites mainstream reference using current POV) was deleted:"
- Reply: This is not incorrect at all. Okun considers something else he does not consider the invariant mass of the entire' system after the reaction. If you consider the whole system which has some total four-momentum, then the invariant mass corresponding to that total four-momentum cannot change assuming that the system is completely isolated and insulated. If you think that his is oincorrect, then just give a counterexample instead of giving the same refs over and over again (which don't prove your point).
- Of course, if you just add up the (invariant, or rest) masses of the particles in the system, then that sum will decrease after the reaction. If that point is not clearly explained in this article, then that must be explained better in this article. No one is objecting to that. What we are objecting to is the notion that Okun can declare a "fatwa" on wikipedia, precluding us to consider the isolated system containing the particles as a system in its own right with its own invariant mass, which will then be conserved because the isolated system has, by asumption, no interactions with anything else. Count Iblis 20:24, 27 May 2007 (UTC)
Edgerck wrote:
"but this fringe view was added without reference (no mainstream author supports it):
CURRENT VERSION
- For example, this formula states that a photon (which moves at the speed of light) has relativistic mass."
You are confusing two issues. One is the fact that the use of "relativistic mass" is fringe. There is no dispute about that, and the article does say that in the scientific community no one uses "relativistic mass" (because it is the same as the total energy).
Another issue is that if we do consider this (fringe) concept of relativistic mass, then the photon has a relativistic mass equal to E/c^2. How on Earth can that be disputed (apart from a straw man-like argument that m times gamma is undefined)? Count Iblis 20:38, 27 May 2007 (UTC)
Hi. I am having trouble following this discussion because I can't see the boundaries of the postings. Can you please insert lines to mark the boundaries in this section? i could do it using the history but it would be quicker for one of you two. thanks! Timb66 21:18, 27 May 2007 (UTC)
CI: WP policy prohibits editing other people's postings in the talk-page. I just reverted what you did with this talk-list. What you are doing is not new. This is not a show of good faith. DO NOT EDIT MY POSTS, MARK OR MOVE THEM.
It also seems to be a good guess that you are using multiple user IDs to manipulate discussions.
Please act kindly, fairly and respect the community's rules. Thank you.Edgerck 00:15, 28 May 2007 (UTC)
Modified copy of the above section as requested by Timb66
Richard Feynman in The Character of Physical Law wrote "The energy associated with motion appears as an extra mass, so things get heavier when they move." This POV and the associated name "relativistic mass" are outdated and not used in physics today. The opposite view, that ("things do not get heavy when they move") and that the only type of mass is invariant mass, is not the least controversial today (see WP:RS source below). This article is in violation of WP:NPOV and WP:RS. Historical references may mention the previous use of "relativistic mass", as done in the version of 03:09, 24 May 2007 (ref. below).
I am sourcing this comment under WP:NPOV and WP:RS, to (inter alia) Mass.
The last version that is not in violation is 03:09, 24 May 2007, as edited by 137.132.3.11.
I formally request the editor who reverted from 03:09, 24 May 2007 to reinstate that version in a timely manner, preventing other WP editors from working on the current version visible -- with the subsequent loss of work.
Thanks. 20:14, 25 May 2007 (UTC)Edgerck
Reply by Count Iblis
Hi Edgerck,
The reason why I reverted your version was that you deleted a lot content, e.g. the example about the atomic bomb. The current version, like it or not, describes pretty accurately how professional physicists who use special relativity on a daily basis use this theory. Now, there are some physicists who hold minority opinions, like e.g. Okun. They prefer to define things in a slightly different way.
Although these things can be mentioned in this article, it is wrong to then delete any mention of the relativistic mass of the photon by saying that gamma times m is undefined. That's just silly. Of course, you can define the relativistic mass by declaring it to be the zeroth component of the four momentum. So, this is i.m.o. just a straw man argument.
Here on wikipedia, you have to be tolerant. I have my own POVs that go against the consensus on wikipedia which I can justify using reliable sources too. E.g. in modern physics one does not regard units and dimensions as fundamental quantities; you can use units in which h-bar = c = G = 1. This is regarded not just as a trick, but taken literally, i.e. h-bar, c and G are no more than conversion factors and the dimensions we have assigned to length time and mass are only there for historic reasons (Okun is a well known physicist who strongly disagrees with this view).
But if I were to edit wiki articles on this subject, completely rewriting them from the (correct) POV giving all the sources, then you would get an article that most other editors would not be happy with. E.g. the explanation of why dimensional analysis works would now be very difficult to follow for most people.
Now, in your edits of this article you didn't even address the examples that were given in the article, you just deleted them. Count Iblis 20:51, 25 May 2007 (UTC)
Reply by Edgerck
WP policy says that "Zero information is preferred to misleading or false information". Thus, what did not meet WP policy should be (as it was) deleted. Please provide a WP:NPOV and WP:RS compliant reference for every affirmation of article content that you make above (eg, example about the atomic bomb) or please do not use them in WP discussions or articles. Thanks.Edgerck 21:06, 25 May 2007 (UTC)
Reply by Sbharris
Don't be silly. Generally, sum of 4-momentum is conserved for all observers (all frames) in systems of interacting particles. See for example[4]. Conservation of energy and momenta as separate quantities are derivative of this, and the split between time-like and space-like quanties for energy and momentum (which cannot be defined without a frame) is what makes conservation of each of them single-frame-dependent, through time, in an interaction. Conservation of 4-momentum is much more general, and its limitations are only for volumes so large that space-like intervals need to be considered-- but then we don't have interacting systems anymore, do we? In any case, what we're talking about as "mass", and what you weigh on a scale, is the norm of system total vector 4-momentum. So obviously, it's conserved as well for small systems like fissioning nuclei and atom bombs. As for needing an RS cite for this, if I have a cite for a general case, I hardly need one for a specific one, by logic. Example: If angular momentum is conserved for all bodies, cite given, I don't need WP:RS to say it's conserved for a figure-skater named Alice as she pulls in her arms, now do I? SBHarris 05:14, 26 May 2007 (UTC)
Reply by Edgerck
SBharris, I kindly ask you to please keep a civil tone. I did not question conservation of 4-momentum or energy, so this is off-topic. Mass is not in general conserved in SR even for closed systems, and I source this affirmation to authoritative elementary texts, including Lev Davidovich Landau and Evgenii Mikhailovich Lifshits, (1987) Elsevier, ISBN 0750627689.
BTW, your logic fails when you consider that mass must be conserved because E and p are conserved and m² = E² - p² in c=1 units. Can you see the mistake? Anyway, whether you can see it or not is irrelevant for this talk-page and WP (this is not a usenet discussion group in physics), as all the WP:NPOV verifiable sources say that mass is not conserved in SR in general, even for an isolated (free) system. Thank you. Edgerck 20:54, 26 May 2007 (UTC)
I also kindly remark that I verifiably sourced my comment about the current WP:NPOV and WP:RS violations to (inter alia) Mass -- which is linked to http://math.ucr.edu/home/baez/physics/Relativity/SR/mass.html. Thanks. Edgerck 21:43, 25 May 2007 (UTC)
Rebuttal by SBHarris
SBharris, I kindly ask you to please keep a civil tone. I did not question conservation of 4-momentum or energy, so this is off-topic. Mass is not in general conserved in SR even for closed systems, and I source this affirmation to authoritative elementary texts, including Lev Davidovich Landau and Evgenii Mikhailovich Lifshits, (1987) Elsevier, ISBN 0750627689.
- Answer Since we're discussing what is partly a matter of controversy of modern notation in physics-- namely, how shall we define "mass" is SR-- the text you're referring to is not very useful, because it's based on lecture notes from the middle of the last century. Landau and Lifschitz are both dead. Landau died in 1968 and did no creative work after his skull fracture and coma in 1962. His lecture notes are not appropriate to the subject of modern notation in physics. If L&L say "mass" is not conserved in closed systems in SR, they must refer to some mass defined as some kind of sum of invariant masses, not the total system invariant or proper mass, which most modern relativists (included Thorne, see my own much more recent reference), and also originally and usually Einstein (see your own reference below) preferred as the definition for "msss". This quantity is directly the 4-momentum norm, so obviously it's conserved if total 4-momentum is, in systems. Which, in fact, is the case; are you really arguing otherwise? Discussion of 4-momentum of systems is hardly off topic, since most of the physics community now defines mass in SR as Mandelstam's s, a simple function of the length of the system total 4-momentum vector (the 4-momentum vector norm, in natural units). You do understand this, I hope. The Baez reference you give discusses the issue fully, and Taylor and Wheeler, as well as Thorne in the reference I gave you, all discuss it fully. Thorne is full professor of physics at Caltech, co-author of the most-used text in GR, and one of the most famous living relativists. His elementary text, which I referenced for you directly above, is available online, and is still being expanded by Thorne. If you want to know how the average modern physicist thinks of mass in SR, you must read Misner, Thorne, Taylor, Wheeler, etc. Who are all still alive. Not edited lecture notes of a man in his grave for close to half a century, now.
BTW, your logic fails when you consider that mass must be conserved because E and p are conserved and m² = E² - p² in c=1 units. Can you see the mistake? Anyway, whether you can see it or not is irrelevant for this talk-page and WP (this is not a usenet discussion group in physics), as all the WP:NPOV verifiable sources say that mass is not conserved in SR in general, even for an isolated (free) system. Thank you. Edgerck 20:54, 26 May 2007 (UTC)
- Answer I see no mistake in logic. If you pick a particular frame and stick to it, so that E and p are conserved for a system interaction, then obviously total E² - p² will be conserved also in that frame. It's just a matter of picking out the E and p vector components for each particle, adding them up, then doing the square and subtraction AFTER that, then taking square root to get length of your system vector. Those are vector rules: because these are all vector quantities, so you have to add the components separately before you consider their total 4-length to get the proper mass of the system.
For individual photons moving in opposite directions, that minus sign means the momenta can cancel when added, but the energies always simply add. So even though (for example) each photon has zero proper mass (this is always the case in any frame), the sum of their masses as calculated by summed 4-momenta, is NOT zero. Instead, the system of two photons where p's cancel (eash photon has the same E) has a 4 momenta of 2E, and the length of this in natural units is the same as its relativistic mass. This is true for any frame in which total p = 0 (proper mass is the same as relativistic mass wherever total system p = 0), so obviously mass of sytems in interactions is equally conserved in all such frames (ie, on scales where you can weigh a system, so p must be zero in the system) no matter which definition of mass you use.
What isn't so obvious, is that proper mass (invariant mass) of systems is conserved in interactions, even in frames where p is not zero, simply because 4-momentum of systems is Lorentz-invariant (pick any frame you like, and even change it before and after the interaction, and it still works!), whereas E and p are not Lorentz-invariant, so are not conserved if you change frames. Nor is relativistic mass, since it's a function of E (in natural units, it IS E). That's one reason why proper mass is a more useful definition of mass: for any given interaction you can switch frames from COM to lab frame, and back, and it makes no difference in the answer. The mass of a particle is easy to calculate in its own rest frame, if that's also the summed energy of its decay produts in the COM frame of the decay products, which is the same as the norm of summed 4-momenta for them in the lab frame. Thus, it's better to define mass that way, as the norm of summed 4-momenta, and simply say THAT mass (by that definition) is conserved in all interactions. But the case for interactions in systems which you can weigh on scales (like a bomb in an unbreakable box), where total p = 0, should be especially easy to see, and I cannot fathom why you argue with it when used as an example. The sum of rest masses is not conserved, but the summed mass of a p=0 system, before and after interaction, which is Lorentz-invariant, IS conserved. Simply because system 4-momentum is, using vector addition rules. You seem to want to define mass as something other than length of a vector for systems, then also refuse to use vector rules to add system masses. Sorry, but most modern physicists would prefer to do it the 4-momentum way, and that way works. Proper mass (system total 4-momentum norm) is conserved.
I also kindly remark that I verifiably sourced my comment about the current WP:NPOV and WP:RS violations to (inter alia) Mass -- which is linked to http://math.ucr.edu/home/baez/physics/Relativity/SR/mass.html. Thanks. Edgerck 21:43, 25 May 2007 (UTC)
- Answer And I kindly observe that there isn't a sentence in that essay to suggest that mass isn't conserved in an interacting system, unless (perhaps) it's some kind of sum of rest masses, or sum of proper masses, that you're talking about. But as discussed above, it's not kosher to sum proper masses-- to get system proper mass you don't sum proper masses, but rather you must sum E's and p's separately as vector quantities, and then calculate system proper mass AFTER, as the norm of the final vector. That quantity IS conserved.
For systems on scales, all types of system mass (either relativistic or proper/invariant) are conserved over time, so long as the system is closed. But change frames and now relativistic mass of the system is no longer conserved, because it's not Lorentz-invariant. However, total system invariant mass obviously still is conserved, because obviously total system summed 4-momentum still is invariant. I gave you a cite for conservation of 4-momenta in interactions in SR (see equation 1.3 in Thorne). If you go to Baez above to see that 4-momenta is the basis of the most commonly used definition of mass in SR today (no matter what Landau and Lifschitz thought 60 years ago), then there you are. It's nice that Einstein associated mass with "proper mass" (which is associated with the total 4-momentum) also. We have Baez to thank for finding those references. SBHarris 18:20, 28 May 2007 (UTC)
Reply by Count Iblis
Edgerck, please stop using these Straw Man arguments. This is all matter of definition. What matters is not what Okun has written or what you can find in the Landau&Lifshitz series (physics is not religion with Okun et al. the prophets). What matters is if given some definition of mass an assertion is correct. This article discusses several definitions of mass. One of these definitions is the invariant mass which is defined to be the energy in the zero-momentum frame. The fact that invariant mass is conserved (for an isolated system on which no external forces act) then follows from conservation of energy and momentum.
You can edit this article by giving the perspective of Okun, e.g. by saying that: "according to Okun, the relativistic mass of the photon cannot be defined". But just saying that it cannot be defined because Okun says so, is not allowed under the Wikipedia rules (even if the citation to Okun's article is given). This is because you can define the relativistic mass as the zeroth component of the four momentum which also works in case of the photon. Only if you demand that it must be given by a relation m times gamma does it become undefined. But that is not the standard definition. Count Iblis 21:56, 26 May 2007 (UTC)
Reply by Edgerck
CI: Please be respectful to others and their points of view. This means: Do not simply revert changes in a dispute. A tag calling the dispute a dispute -- see WP:NPOV and references -- should not be reverted unless there is a resolution. I disagree with its removal.
I kindly ask you to please reinstate the tags and follow WP policy.
Wikipedia relies on what reliable sources have said about the matter. By relying what sources have reported about a subject, WP limits the influence of an editor's POV. The incorrect information in this page is not accepted in the mainstream, and it is easy to find numerous sources taking the "correct", or mainstream, position.
I have made all the proper requests according to WP policy. I have no need to repeat myself, as WP has all my comments and edited pages in the archives. I am now entering a disengage phase in the hope that this will be helpful. Edgerck 23:29, 26 May 2007 (UTC)
Reply by Count Iblis
Edgerck, there are many reliable sources that disagree with some of the points you have been making here. And you can't hold an article hostage by placing an POV tag on it, only to remove it when you get your way. Wikipedia has a very important rule that superseeds all other rules: Wikipedia:Ignore all rules. This rules says: "If the rules prevent you from improving or maintaining Wikipedia, ignore them." In this case you made edits that amounted to removal of a large amounts of content. You did not even address the issues raised in the removed content (you could have explained the removed examples differently...). Count Iblis 00:10, 27 May 2007 (UTC)
Reply by Edgerck
CI: WP policy says that "Zero information is preferred to misleading or false information". Thus, what did not meet WP policy should be (as it was) deleted. But (as you can see above) I said that before. You can "ignore all rules" at a price, and here the price was WP:NPOV, fairness, and maybe more.
Finally, no one can claim lack of my explanations. I used well-documented edit summary lines (that you called "chatty"), I left HTML tags in the text to call attention to incorrect text that was deleted, and I was available in multiple talk pages that you insist in revert. And, I summarized all the reasons in my user talk page, with a commented list of non-controversial answers in special relativity. Thank you.Edgerck 03:39, 27 May 2007 (UTC)
Reply by Timb66
My two cents worth: I think the longer version of the article is a better starting point. I recall that the book A Guide to Introductory Physics Teaching by Arnold B. Arons has some useful comments -- I will look them up when I am back in my office. For the record, I am a professional physicist and have been teaching Special Relativity in a university physics department for the last few years. Timb66 10:56, 27 May 2007 (UTC)
Reply by Edgerck
All hands, including Timb66: I do not know about Timb66 qualifications but while it is easy and has no consequences for anonymous expert users to claim that invariant mass is conserved in SR, or that it is conserved in nuclear fission or fusion, this is not so for those few who use their real identities and qualifications. That's why I myself would prefer anonymous participation here, but I decided not. I want people to understand that these edits are serious and not some willy-nilly change.
As I announced about a week ago, I am conducting a public experiment to verify the trustworthiness of information in WP. Since information in WP is dynamic, I think this question cannot be answered by simply sampling at specific times. Instead, I decided to measure the lifetime of correct information (defined as correct according to WP policy) that was seeded in WP edits of selected articles. To reduce error in defining what is correct information I used topics that are not the least controversial today, even though they are widely misunderstood (to motivate editing interest).
This is not a "trap". To make sure that my justification for the edits were visible to any editor, I used several channels. I used well-documented edit summary lines, I left HTML tags in the text to call attention to incorrect text that was deleted or changed, and I was available in multiple talk pages, in addition to my own and a special talk page for this experiment. I also answered questions in other editor's talk pages.
Some changes, notwithstanding all the above, were reverted without a WP valid justification. Applying WP policy, typically results in the following steps, after a revert:
1. my statement, in the talk page, that the reverted version was correct according to NPOV and RS, with current, authoritative, mainstream, supporting references (while the current version is not), with a call for that version to be reinstated.
2. back arguments, without understanding (or, perhaps even reading) the current references, that the changes do not make sense and contradict well-known (but outdated) authors.
3. Reaffirmation of #1, with more references and with a tag for NPOV dispute placed in the article.
4. The tag is deleted under a call to the "break all rules" WP policy, stating that the article cannot be held "hostage" to a clearly incorrect edit.
While this goes on, anyone reading WP or editing it will not see correct information, where correct information means information that is not the least controversial today.
Now, how many more hoops should a voluntary WP editor have to jump in order to assure that WP reflects a viewpoint that is not controversial? Escalating the edit difference to any form of litigation does not seem to be a pleasant or fun activity, or rewarding in time.
The WP idea of "anyone can edit" finds its limits in the observation that "ignorance is bliss". Those who ignore, by definition, ignore that they ignore. Many subjects, most (but not all) of them technical, have subtleties that are important. It may be easy to read a correct phrase but it is a lot harder to write one, as anyone taking a test knows.
So, requiring a WP editor to follow NPOV and RS when the editor simply does not understand the subject (eg, is not able to ascertain the falsity of his beliefs versus what the references say), seems to be nonsensical. No one can write what they do not understand. The emphasis in WP:Verifiability goes nowhere in such context, and we can see that in WP.
WP is an encyclopedia project but the bottom of the iceberg is currently dominated by an education project for editors, which is open ended.
Looking at this as a pyramid, at the top we have well-educated, scholar editors, numbering (say) one hundred. At the bottom, we have well-meaning but clueless editors who want to edit what looks to them to be an error or lack of an example that they heard somewhere, but which is not correct (according to WP:Verifiability references that they do not have and, even if they would read, would have the same "error").
I don't have the answers. The problem is not anonymity. Academic qualifications do not always mean fairness or even competence. But it seems to me that current WP rules are somewhat in contradiction with the WP goals.
The experiment I mentioned above, hopefully, asks some of the right questions that we need to see in order to improve the quality of information found in WP. The experiment page is at Reliance on Information. Thanks. Edgerck 15:51, 27 May 2007 (UTC)
Reply by Count Iblis
You are making a big issue out of a minor point. The source of the disagreement is not the physics, but a simple matter of definitions. You seem to insist on defining invariant mass for composite systems in a clumsy way. If photons escape you will automatically re-define the system by omitting the photons. Fine, you can write that Okun et al. do this, why they do this, and that if you do this then what you get is what you wrote. But you cannot write (or suggest) that it isn't possible to define a composite system by including photons.
This article makes it very clear that the invariant mass of nuclei that are involved in nuclear reactions is not conserved, so as far as the physics is concerned, there is no disagreement at all!Count Iblis 16:33, 27 May 2007 (UTC)
Reply by Edgerck
WP Policy for removing NPOV tags is resolution, not removal war. The technical content issues also affect Talk:Mass-energy_equivalence, and Talk:Introduction_to_special_relativity. The POV expressed by the editor above is not mainstream for more than 50 years in research and more than 30 years in textbooks, according to mainstream references (it is easy to find even more). [2], [1], [3],[4], [5], [6], [7], [8], [9], [10], [11]
References
- ^ a b Lev Okun, The Concept of Mass, Physics Today, June 1989.
- ^ Lev Davidovich Landau and Evgenii Mikhailovich Lifshits, (1987) Elsevier, ISBN 0750627689.
- ^ "Does mass change with velocity?" by Philip Gibbs et al., 2002, retrieved Aug 10 2006
- ^ Edwin Floriman Taylor, John Archibald Wheeler, Spacetime Physics: introduction to special relativity, W.H.Freeman & Co Ltd (1992), ISBN 0716723271.
- ^ Lev Borisovich Okunʹ, The Relations of Particles, (1991) World Scientific, ISBN 981020454X, p. 116-119, 127.
- ^ Usenet Physics FAQ
- ^ Gary Oas, On the Abuse and Use of the Relativistic Mass, 2005.
- ^ "Does light have mass?" by Philip Gibbs, 1997, retrieved Aug 10 2006
- ^ "What is the mass of a photon?" by Matt Austern et al., 1998, retrieved Aug 10 2006
- ^ William S. C. Williams, Introducing Special Relativity, CRC Press (2002), ISBN 0415277620
- ^ "Ouch! The concept of `relativistic mass' is subject to misunderstanding. That's why we don't use it. First, it applies the name mass--belonging to the magnitude of a four-vector--to a very different concept, the time component of a four-vector. Second, it makes increase of energy of an object with velocity or momentum appear to be connected with some change in internal structure of the object. In reality, the increase of energy with velocity originates not in the object but in the geometric properties of space-time itself.", in Edwin Floriman Taylor, John Archibald Wheeler, Spacetime Physics: introduction to special relativity, op.cit.
Reply by Count Iblis
This dispute will never be resolved to your liking. The issue is not whether or not relativistic mass is an oudated concept. Of course, it is outdated and the current article says so. But that doesn't mean we can't write about relativistic mass in this article (or perhaps another) wiki article. Count Iblis 18:03, 27 May 2007 (UTC)
Reply by Edgerck
It's easy to do a diff between the current version and the version edited by 137.132.3.11 at 03:09, 24 May 2007, which is the last version I saw that complies with WP:Verifiability. Significant differences exist with the current version, for example:
CURRENT VERSION
- Reactions in this special inertial frame (so long as the system remains closed) do not produce changes in mass, relativistic mass, or energy.
which is incorrect per references cited; and this section (which is correct and cites mainstream reference using current POV) was deleted:
VERIFIED VERSION
- Today[1], following Einstein, instead of introducing the concept of relativistic mass when changing frames of reference, one uses the relativistic energy-momentum relation. In this relation, mass is always invariant. Scales and balances operate in the rest frame of objects being measured, measuring mass.
- <reference/>
and also this was deleted, even though is cited almost verbatim in current POV references):
VERIFIED VERSION
- This usage is less confusing because it does not appear to make the increase of energy of an object with velocity or momentum to be connected with some change in internal structure of the object that would increase its mass, which change cannot be observed. In other words, one cannot observe changes in the mass of an object as a function of the speed of an observer relative to the object (to make it clearer, as it does not matter who is considered to be at rest).
but this fringe view was added without reference (no mainstream author supports it):
CURRENT VERSION
- For example, this formula states that a photon (which moves at the speed of light) has relativistic mass.
This incorrect view (rejected since 1920, mass is not conserved in SR, not even in closed systems), was also added, also without WP:RS source :
CURRENT VERSION
- Note that the invariant mass of a closed system is also independent of observer or inertial frame, and is a constant, conserved quantity for closed systems and single observers, even during chemical and nuclear reactions.
And more. The differences (additions and deletions), are such that the current article should be immediately provided with the tags that I inserted, to prevent trusting users from trusting such content, and reversed as soon as possible to the last verified version.
This is not about one definition, or a historical note that became too large. It's about basic misleading and false information that was inserted while verified and correct by WP:RS information that contradicted it was simply deleted.
Thank you. Edgerck 18:29, 27 May 2007 (UTC)
Reply by Count Iblis
You wrote: "CURRENT VERSION Reactions in this special inertial frame (so long as the system remains closed) do not produce changes in mass, relativistic mass, or energy.
which is incorrect per references cited; and this section (which is correct and cites mainstream reference using current POV) was deleted:"
Reply: This is not incorrect at all. Okun considers something else he does not consider the invariant mass of the entire' system after the reaction. If you consider the whole system which has some total four-momentum, then the invariant mass corresponding to that total four-momentum cannot change assuming that the system is completely isolated and insulated. If you think that his is oincorrect, then just give a counterexample instead of giving the same refs over and over again (which don't prove your point).
Of course, if you just add up the (invariant, or rest) masses of the particles in the system, then that sum will decrease after the reaction. If that point is not clearly explained in this article, then that must be explained better in this article. No one is objecting to that. What we are objecting to is the notion that Okun can declare a "fatwa" on wikipedia, precluding us to consider the isolated system containing the particles as a system in its own right with its own invariant mass, which will then be conserved because the isolated system has, by asumption, no interactions with anything else. Count Iblis 20:24, 27 May 2007 (UTC)
Additional reply by Count Iblis
Edgerck wrote:
"but this fringe view was added without reference (no mainstream author supports it):
CURRENT VERSION
- For example, this formula states that a photon (which moves at the speed of light) has relativistic mass."
You are confusing two issues. One is the fact that the use of "relativistic mass" is fringe. There is no dispute about that, and the article does say that in the scientific community no one uses "relativistic mass" (because it is the same as the total energy).
Another issue is that if we do consider this (fringe) concept of relativistic mass, then the photon has a relativistic mass equal to E/c^2. How on Earth can that be disputed (apart from a straw man-like argument that m times gamma is undefined)? Count Iblis 20:38, 27 May 2007 (UTC)
Reply by Timb66
Hi. I am having trouble following this discussion because I can't see the boundaries of the postings. Can you please insert lines to mark the boundaries in this section? i could do it using the history but it would be quicker for one of you two. thanks! Timb66 21:18, 27 May 2007 (UTC)
Reply by Count Iblis (to Timb66)
I've partitioned the discussion in sections for clarity :) Count Iblis 21:47, 27 May 2007 (UTC)
quote from Arons
Thanks for cleaning up the above discussion. By the way, I am not anonymous, my name and affiliation are on my user page.
As promised, here is the quote from A Guide to Introductory Physics Teaching by Arnold B. Arons (1990, page 263):
For many years it was conventional to enter the discussion of dynamics through derivation of the relativistic mass, that is the mass-velocity relation, and this is probably still the dominant mode in textbooks. More recently, however, it has been increasingly recognized that relativistic mass is a troublesome and dubious concept. [See, for example, Okun (1989).] Not only does it get one into the infelicities associated with longitudinal and transverse masses, but it also tempts one to associate relativistic mass (rather than just rest mass) with gravitational effects. The latter association is basically incorrect. The sound and rigorous approach to relativistic dynamics is though direct development of that expression for momentum that ensures conservation of momentum in all frames:
rather than through relativistic mass. Unfortunately, it is more difficult to derive the momentum expression in a simple way that it is to obtain the mass-velocity relation from the collision gedanken experiments prevalent in the literature. [See Peters (1986) for a recent effort to simplify this derivation.]
I suggest the above quote be included verbatim in the article. Timb66 01:44, 28 May 2007 (UTC)
Thanks! Count Iblis 22:07, 28 May 2007 (UTC)
Edgerck on massless photon
Nonetheless, in SR, a photon has no mass. So, if an atom emits a photon, the system atom+photon has less mass, even though it has the same energy. Hope this is useful. Edgerck 22:36, 28 May 2007 (UTC)
Thanks Edgerck! I guess we can now move on! :) Count Iblis 23:23, 28 May 2007 (UTC)
- You are copying my quote from my user page. I had a minor edit on it, changing "weight" to "mass", which I changed above as well. Barring vandalism, the quote above is correctly mine. Have fun with it! Edgerck 00:00, 29 May 2007 (UTC)
- BTW, I also edited the item's title, to keep it on the polite tone we should all enjoy in these discussions. Please feel free to add your opinion in your personal comment, also kindly. Thanks.Edgerck 00:05, 29 May 2007 (UTC)
- Eh, you have a problem here. What do you do with a system of electron plus positron (or for that mattter, a single neutral pi-meson), which annihilates/decomposes into a pair of photons? According to you, the system mass just disappears, since the leptons or mesons have mass, but the photons do not. What do you think happens to the system's gravitational field when the mass disappears? Do you think this results in an expanding gravity wave with a hole in the middle of it, like a bubble, and a sharp boundary? If so, I assure you that GR contains no equations for what happens to G fields when source mass just disappears like that. The reason is that it doesn't have to, because it does not happen. Anymore than Maxwell's equations contain prescriptions for what happens to the EM field when charge disappears, like an electron winking out of the universe with no positron to counterbalance. That's what you're saying happens to mass (which has only one sort of "charge"), and I'm here to tell you that it doesn't. SBHarris 00:18, 29 May 2007 (UTC)
Edgerck gravity gedanken
A perfectly-mirrored evacuated sphere contains an atom at its center. It sits on a scale, which weighs atom and container. Now the atom emits a photon. While it is in flight Edgerck maintains the atom has less mass and weight, since the photon is massless and carries away energy. Presumably the system has less mass and weight while the photon is in flight? Presumably it has less of a gravity field? Now the photon bounces from the mirror and is reabsorbed by the atom. Does it now go back to its original mass, weight, and total gravitational power? If the gravitational field the atom and sphere generates, jitters like the system weight and mass are said to, now we have a gravitational wave generator. But gravitational waves carry energy. Where does the energy come from? Does this system run down, and what is the mechanism for this, in GR? Where is the changing mass-quadrupole moment, when an atom emits a photon? The student wishes to know. SBHarris 00:58, 29 May 2007 (UTC)
- I will tell my opinion. I say my opinion because it may be right or wrong — you decide.
- First, it's important to distinguish mass from the gravitational force acting upon a particle or body. It is not necessary to have mass in order to suffer the influence of a gravitational force!
- A photon is massless; the gravitational attraction between a photon and a large mass (the Earth) is determined by their energy-momentum tensors, not just by their energies (that's why "relativistic mass" is not useful here either). The known result in GR is that the gravitational force attracting a horizontally moving photon to the Earth (ie, horizontal to the Earth's surface) is twice as large as that attracting a vertically moving photon.
- So, after the photon is emitted the atom loses mass given by E/c^2 and recoils. As the photon bounces back and forth in the box, vertically and horizontally, the photon may be subject to different gravitational forces as well. Nonetheless (and this is a grave error in SR!) the photon does not change its energy in the gravitational field, so that if and when it's absorbed by the atom, the atom increases its mass by the same amount E/c^2.
- Result: the photon should have lost energy, but does not in SR. In GR, the photon red-shifts and the atom (if absorption of the less energetic photon is possible) will have less mass after absorption of the red-shifted photon.
- Hope this is useful. Edgerck 01:42, 29 May 2007 (UTC)
- Not really. We don't really need to have an external G field for this problem to work--that's only necessary to weigh it. Let us dispense with the earth and put our atom in its mirrored sphere out in space, between stars. The problem that your system is supposed to change mass while the photon is in flight, means that this system will still radiate gravitational waves, even sitting out in space. Do you believe this? The system can also be made of two atoms trading a single photon. You believe this all has less mass while the photon is in transit. Does that mean it creates less gravity? Has a smaller gravitational field? Yes or no? The G field goes up and down as the photon is transferred back and forth? You can't escape this. SBHarris 04:48, 29 May 2007 (UTC)
- Addendum: About two weeks ago, foreseeing that some readers/editors of WP might fall into this trap, I pre-empted this question in my edit of this very page Mass in special relativity. My answer to this question survived several revisions until CI simply reverted the page to the current, incorrect page. Please see the last correct (LC) version, edited by 137.132.3.11 at 03:09, 24 May 2007 and look for section "Mass and gravitation". The LC version is here.
- It is interesting that the same person (Sbarris) who could not see the relevance of the reverted version, also does not know the answer that was given in the LC version.
- Huh? What answer? You still haven't come to the real basis for my question. If the mass of a thing changes as it undergoes a reversible "constant energy decrease in mass," of the sort which you claim is possible in closed systems emitting photons, then its gravitational field will change, along with its mass. (Unless you're positing a disconnect between a thing's mass and its gravitational field). But physics will not support such gravitational waves from things (closed systems) going up and down in mass, according to your ideas. Thus, you have a really big problem in your explanation. Address it, please. SBHarris 04:48, 29 May 2007 (UTC)
- This question and answer then exemplifies what I observed before, that WP editing rules are nonsensical. People get angry over an impossible proposition. Truth is subjective. An editor cannot write what he does not agree on. But anyone can edit.
- So, I find that WP's rules are putting us somewhat at odds, and that is not what I personally want. Thank you. Edgerck 04:01, 29 May 2007 (UTC)
- I follow SB's thought experiment but not your explanation; your addendum sounds more like resignation than explication. You don't answer any of SB's questions directly. Is it because you find them invalid? If so, in what way? Robert K S 04:17, 29 May 2007 (UTC)
- It's all given above. I did answer the question and I did it 2x. In case any of you lost the first answer: search for these words above: "Result: the photon should have lost energy, but does not in SR."
- For the second answer (which I actually gave two weeks ago), please click here (also given above) and read the section "Mass and gravitation".
- Hope this helps more. Edgerck 05:50, 29 May 2007 (UTC)
- Let's try it this way. Do you agree that an object's gravitational attraction is proportional to its mass? And that therefore if its mass is reduced, so too reduces its gravitational pull? Robert K S 06:04, 29 May 2007 (UTC)
- Short answers -- 1) In SR: no answer; 2) in GR: No and (by logical consequence) No. All said above. Edgerck 06:14, 29 May 2007 (UTC)
- Okay, but I have the feeling I didn't ask the right question. What's your answer if, instead of framing it in terms of "attraction", I ask if GR "spacetime curvatures" are the function of an object's mass? Robert K S 06:28, 29 May 2007 (UTC)
- I am sorry to have to ask this: why don't you get it that this is off-topic in SR? I sourced it according to WP:NPOV and WP:RS. Thanks. Edgerck 17:49, 29 May 2007 (UTC)
- We get that it's off-topic for an SR article, but since it's physics, it's not off-topic for an SR article TALK page, if it helps to clarify the problems and subject. You claim you answered this 2-weeks ago, but your pointer just points to an article which says the same thing you're saying now: that it's off-topic for SR. Which is a cop-out. SBHarris 18:12, 29 May 2007 (UTC)
I started a discussion on Talk:Invariant_mass on whether both that page and this page are needed. Editros of this page are welcome to comment there. Timb66 09:31, 29 May 2007 (UTC)
Comments on the definition of mass
Sbharris did a good job above by pointing out the flaw. But his argument involves gravity and that allowed Edgerck some opportunities to avoid checkmate.
To recapitulate, Edgerck is saying that the (invariant) mass of a closed box is not given by the total energy in the zero momentum frame.
- Be truthful: I never said that. Please do not say what I said anymore, because you don't seem to be able to do it well. Further, this is not a "I said, you said" discussion. This is a WP group that should follow WP policy in WP:verifiability. I am also editing the section title, to be more civil. Edgerck 18:12, 29 May 2007 (UTC)
- You are saying exactly that in case of the "atom+photon" system on this talk page and we discussed this issue further on your own talk page. Please forgive me for trying to understand your reasoning. Anyway, in the argument below, you can just take a box containing an atom and a photon instead of a box filled with radiation. The conclusion will be the same. Count Iblis 18:42, 29 May 2007 (UTC)
The mass, he says, is given by the contribution to the total energy of the "massive degrees of freedom".
- Be truthful: I never said that or used those terms within quotes.
- I am going to stop commenting here. This looks like manipulation of information but is not going to go very far, as any one can verify the archives. Edgerck 18:12, 29 May 2007 (UTC)
E.g., in a closed box filled with radiation, the energy of the radiation does not contribute to the invariant mass of the box.
In principle one could define mass this way. As long as your definitions are mathematically consistent, nothing will go wrong. The only way to point out that the definition is flawed is by showing that it is not related to what you measure when measuring properties that sould be directly related to mass.
This is what Sbharris did above by looking at gravitational effects. We could, of course, look at inertia instead, thus staying firmly within the realms of Special Relativity. This will deny Edgerck any option but to capitulate.
Consider a closed box filled with radiation (Edgerck does not dispute that the radiation contributes to the internal energy of the box). Let's now look at collisions. A mass collides with the box at some velocity and is reflected. How do we compute the velocity the box gains? Of course, that's pretty trivial. Momentum and energy are conserved. You write down that the total four-momentum stays the same. Some manipulations involving inner products with the four-vectors can be used to simplify the algebra.
In the end you obtain an answer that only depends on the intitial four-momenta of the systems involved. Never will you encounter an answer that involves the contribution of the four-momentum of the box from only massive particles. So, the mass as defined by Edgerck, is not what you measure when measuring inertia.
To make the unphysical nature of Edgerck's definition even more clear, suppose that the photon does have a tiny mass of, say eV so that it is physically irrelevant. Note that the best limits are of the order of eV. Then, according to Edgerck's definition, the mass of the box would include the energy of the black body radiation. Count Iblis 13:30, 29 May 2007 (UTC)
Invitation to fair discussions
Folks, as I said before, I need to let the group digest the information I provided in my edits.
I regret if I have unsettled any views here, but WP photon agrees with WP:NPOV and WP:RS in saying that the photon is massless, so when an atom emits a photon (the photon momentum cancels with the atom's recoil momentum), the system atom+photon must have less mass .
I am going to stop commenting here, and just observe once in a while the evolution of the special relativity pages. I refer any editor and reader to the standard, authoritative, current textbooks that I cited according toWP:NPOV and WP:RS, for any such notions as discussed here. I fully agree with those sources and don't think these issues are the least controversial today.
Looking at this list's archives, I see evidence of information manipulation. I also see that competent editors left this group, dismayed. I invite this group to become more than just a raunchy usenet discussion group and follow the WP policy. You yourselves will have much to gain, not just WP.
Finally, I personally regret that I am not able to invite you over for a cup of coffee and have a chat. I think that I would like to meet each one of you personally. Thanks for giving me so much food for thought in regard to the education process in physics and the editing process in an open environment. Edgerck 18:12, 29 May 2007 (UTC)
- "so when an atom emits a photon, the system atom+photon must have less mass". This is false. You can't source this from the literature. The photon is massless? Of course! The atom has less mass in the ground state than in the excited state? Of course! But can you add up the (invariant) mass of the photon to the invariant mass of the atom in its ground state to obtain the invariant mass of the atom+photon system? No, this is contrary to the way mass is defined for composite systems. No reputable source agrees with your conclusion. Count Iblis 18:27, 29 May 2007 (UTC)
- You say:
I regret if I have unsettled any views here, but WP photon agrees with WP:NPOV and WP:RS in saying that the photon is massless, so when an atom emits a photon (the photon momentum cancels with the atom's recoil momentum), the system atom+photon must have less mass.
COMMENT: Wrong! As Count Iblis notes, that doesn't follow at all, inasmuch as photons contribute mass to systems even when free within the system, just as they contribute mass when absorbed into objects (yes, Einstein was right about that, and we have not overturned this idea in any way). And if you want a cite, see Taylor and Wheeler, Spacetime Physics, p 232: "A photon has no rest energy-- that is, no mass of its own. However, a photon can contribute energy and momentum to a system of objects [contributes 4-momentum or EM 4-vector magnitude]. Hence the presense of one [emphasis added] or more photons can increase the mass of that system. More: a system consisting entirely of zero-mass photons can itself have non-zero mass!" Following are some simple single photon-plus particle interactions which are just the sort that Ed Gerck is referring to-- except the answers given (that the system mass is invariant through them all) are not the ones that Ed wants us to accept. This is an authoritative text. I've given my cite specifically by page and even quote. Ed, let's see you do that with Landau and Lifschitz on this point. It would do you a lot of good to read the entire chapter 8 of this undergrad SR text, written by physicists who were full professors at (respectively) MIT and Princeton. Wheeler invented the term "black hole" and he does know relativistic physics historically. SBHarris 18:42, 29 May 2007 (UTC)
- You say:
Folks: It is clear that my quote above needs clarification, which I am letting the group process. I added the comment in parentheses, to help with the process: (the photon momentum cancels with the atom's recoil momentum). Regarding the excellent book Spacetime Physics, I cite it in one of my non-controversial points in physics, for their two-photon example with mass. I agree with Taylor and Wheeler -- please note that they rightly say "can", not that it always does. Thanks again for your verification and inquiring minds. Edgerck 19:06, 29 May 2007 (UTC)
- Taylor and Wheeler only say "can" because of the one special case of the 2-photon system where the photons are going in the same direction. THAT system has no mass. But an extra photon FROM THE OUTSIDE adds mass to any other kind of system, including any with a particle that has rest mass. A photon emitted from within a system does not change the system mass, if the system boundaries are drawn to continue to include the emitted photon. In your example, when an atom emits a photon, of course momenta cancel. If we start with an atom of rest energy E and a frame in which it is at rest, the atom's energy is E. If it emits a photon of energy e in this frame, then the atom now has energy E-e, and that includes not only its (new) rest mass, but also its kinetic energy of recoil (so the actual rest mass is a bit less than this, which is why the photon e comes out less if the atom emitting it is free to recoil, as directly confirmed by Mossbauer). The system energy is the sum of 4-momentum vectors (or EM-4-vectors if you like) and since the momenta cancel, that energy remains E. The invariant mass of the system remains E/c^2. When momenta in systems cancel, as they do here, Einstein's equation E = mc^2 remains true even when m is invariant mass.
And BTW, if you think Taylor and Wheeler is such an excellent book, why don't you read chapter 8? Particularly page 249 in which they point out that the .93 kg of mass converted to heat and light in a 20 megaton hydrogen bomb, does not appear as a mass deficit until the products cool; of such a bomb they say: "Thus, part of the constituents has been converted to energy, but the system mass has not changed!" Here, Taylor and Wheeler affirm in two examples what you explicitly deny. SBHarris 19:27, 29 May 2007 (UTC)
Folks and Sbharris in particular: It's easier to calculate the atom+photon mass (after the emission) in the atom's rest frame, where the atom is at rest and there is no kinetic energy for the atom or Doppler shift for the photon (even though a Doppler shift appears in the COM frame, where the emitter is not at rest). Since mass is invariant, the same result will apply to the COM frame and the lab frame.
Using m for the mass of the system atom+photon in the atom's rest frame, m² = [(M - e) + e]² - e², where M is the atom mass before the photon is emitted and e is the photon energy (also its momentum), in c=1 units. The result is m² = M² - e². The mass of the atom+photon system is less than the atom mass before emission. Mass is not conserved in a closed system.Edgerck 13:55, 30 May 2007 (UTC)
- You forgot to consider the change in kinetic energy of the atom. Whatever frame you chose, after the photon is emitted, the velocity of the atom will have to change in order to satisfy conservation of momentum. M is thus not the energy of the atom before the collision. If you "rewind the movie" of the atom emitting the photon, you'll see an atom at rest absorbing a photon and ending up in an excited state. The total energy of the atom is gamma M, which to a good approxmation will be given by M + p^2/(2M). P is the momentum of the atom, which in c = 1 units is just e. This explains the magnitude of the "missing mass error" in your calculation
- m = sqrt[M² - e² ] is approximately M[1-1/2 e^2/M^2] = M - e^2/(2M)
There's no kinetic energy in the atom's rest frame. There's no kinetic energy history component in the energy-momentum equation. An observer "waking up" on the atom can readily calculate the atom's 4-momentum and add it to the photon's 4-momentum, to calculate the system's 4-momentum, and then the resulting magnitude, which is the system's mass. The same observer can then compare that value for mass to the mass value in the atom's rest frame before the photon was emitted, resulting in a mass deficit for the system in the atom's rest frame. Since mass is an invariant, an observer in the lab frame will measure the same thing. Note that energy is conserved in the process -- the system energy does not change when the photon is emitted.
Let me give another example, this time using a result already provided in Spacetime Physics. Take a laser medium as a closed system including some photons. These photons will be copied by the stimulated emission process, resulting in a field of photons all with the same momenta and collinear (because of the stimulated emission process). According to "Spacetime Physics", these photons will have mass zero. However, they did take energy out of the laser medium, which energy resulted in a decrease in mass of each photon emitter (atom or molecule). So, at the end of the process, in the closed system, mass decreased.
You can also see that Spacetime Physics contradicts itself on the atomic bomb example, versus the 2-photon system example. Only in the case when the photons have opposing momenta they will have mass equivalent to their energy according to E=mc², but the opposing momenta case is the exception, not the rule. So, most photons will not add up to compensate the mass decrease.
Another problem with Spacetime Physics in the atomic bomb example is that it puts E=mc² in front stage, whereas E=mc² only plays second fiddle in the energy released (less than 10%). For a verifiable quote on this, please read below.
When Einstein's most famous formula E=mc2 is mentioned, the atomic bomb is usually not far behind. Indeed there is a connection between the two, but it is subtle, and sadly, some popular science texts get it wrong: they will tell you that a nuclear explosion is "caused by the transformation of matter and energy" according to Einstein's formula, and that the gigantic conversion factor c2 is responsible for the immense power of such weapons.
The strength of the nuclear bond depends on the number of neutrons and protons involved. It varies in such a way that binding energy is released both in splitting up a heavy nucleus into smaller parts and in fusing light nuclei into heavier ones. This, as well as the chain reaction phenomenon, explains the immense power of nuclear bombs.
Einstein's formula plays second fiddle in that derivation - it's all about different kinds of energy. Sure, there are some radioactive decay processes following nuclear fission, and, if so inclined, one can view the decay of a neutron decaying into a slightly lighter proton as a transformation of rest energy into other energy forms. But these additional processes contribute a mere 10 per cent of the total energy set free in nuclear fission. The main contribution is due to binding energy being converted to other forms of energy - a consequence not of Einstein's formula, but of the fact that nuclear forces are comparatively strong, and that certain lighter nuclei are much more strongly bound than certain more massive nuclei. in MPG - Atomic Bomb
This is, BTW, another point where WP needed the correction I edited in.
Thanks for your comments. Edgerck 18:17, 31 May 2007 (UTC)
- I have given a detailed calculation below which shows that you are completely wrong. Of course, you can choose the frame in which the atom is at rest, but you cannot just take the energy of the photon to be the difference of the rest masses of the atom in the ground state and excited state. The energy of the photon in any frame is given by the diference in the total energy of the atom before and after the emission of the photon. But in any given frame the velocity of the atom must have changed because momentum must be conserved.
- So, there is a difference in kinetic energy of the atom as well, which you did not take into account at all. And the only way to take this effect into account is by doing a fully fledged calculation, as I did below. But then the fact that the invariant mass stays the same is basically "build in" a priori. But anyway, I did also evaluate all the quantities of interest in the rest frame of the atom after emission explicitely below. Count Iblis 18:43, 31 May 2007 (UTC)
CI: In 1958 Mößbauer reported that all atoms in a solid lattice absorb the recoil energy when a single atom in the lattice emits a gamma ray. Therefore, the experiment (atom+photon) can be done in such a way that the emitting atom will move very little even in the lab frame, therefore there is not any need for us to argue about the recoil velocity. Otherwise -- when recoil is significant -- the emitted photon's energy is reduced by the kinetic energy expressed in the atom's recoil velocity in the lab frame, which is automatically taken into account when I consider the photon energy in the inertial frame on the atom. In the atom frame, the emitter is at rest.Edgerck 19:21, 1 June 2007 (UTC)
- Yes, and I've tried to tell Count Iblis that recoil velocity and energy isn't an issue in this system, because you can jigger it so they are so small as to make no difference in the physics. Alas, you can't do the same with recoil momentum, which remains. The basic reasons the photon adds mass to the Mößbauer while in flight (so mass never decreases so long as the system is closed to include the photon), is that the photon's momentum cancels its energy so it individually has no mass. However, the photon's momentum in the system is cancelled by the emitting system's recoil (even if that system is huge and gets almost no energy or velocity, it still gets the entire photon momentum), and thus when you're calculating system invariant mass, emitter and photon momenta cancel, their energies thus are free to add, and so total energy and total mass is conserved. Voila. SBHarris 19:39, 1 June 2007 (UTC)
Sbharris and all: For WP purposes, I have spoken my peace for my experiment's purposes and I am happy to let the information be processed within the community. Now, if you could help me find verifiable sources that say that mass is conserved in closed systems at all times in SR, that would be useful as well.
I note again that if any topic that I selected for correct information is not entirely clear, not sufficiently referenced, or even proves to be wrong, then that topic will be eliminated from the evaluation. You can read my experimental conditions for reducing my influence on the WP experiment on reliance on information. Thank you for your kind dialogue and help.Edgerck 19:50, 1 June 2007 (UTC)
The decay: excited atom ----> ground state atom + photon
Suppose that we know the (invariant) masses of the atom in the excited state and in the ground state. Let's denote the mass of the excited atom as and the mass of the ground state atom by . Consider the frame in which the excited atom is at rest. That frame is thus the center of mass (zero momentum) frame.
Now, let's calculate the energy of the photon and the velocity of the atom in terms of and . We assume that the photon will be emitted in the negative x-direction and we only write out the time and x-components of four-vectors. The four-momentum of the excited atom is , the four momentum of the atom in the ground state is and the four-momentum of the photon is , where is the energy of the photon.
Conservaton of four-momentum gives: . We can write this as: . Square both sides: . Insert in here: , and , and the inner product . This yields:
- (1)
The x-component of the equation yields:
- (2)
Eliminating from (1) and (2) gives:
where
All this has been derived rigorously from four-momentum conservation: , the invariant mass of the combined system is thus equal to . But what the above derivaton shows is that you don't need to make any ad hoc assumptions like Edgerck did to do these calculations. Edgerck obtained incorrect results because he did not rigorously stick to four-momentum conservation. From his incorrect reasoning he found that the invariant mass of the photon atom system was less than that of the excited atom. Count Iblis 18:27, 30 May 2007 (UTC)
Perhaps it is interesting to perform a Lorentz transformation to the rest frame of the atom after the photon has been emitted. The energy of the photon is this frame is given by:
Here we have used the above equations for and . We can now do what Edgerck attempted to do above: Write down the total four-momentum of the atom-photon system in te rest frame of the atom and square it to obtain the square of the invariant mass.
The four-momentum of the atom is:
The four-momentum of the photon is:
The four-momentum of the atom-photon system is:
And thus:
Insert in here which we derived above, and you get:
Edgerck's mistake was to assume that , or . This is clearly false, although it is approximately true:
If we define ΔM as the mass difference between exited and ground states of the atom: , then this becomes (exactly):
Edgerck's mistake amounts to ignoring the second term in this equation. The second term is much smaller than the first term, so to a good approximation it is the square of the photon energy divided by twice the mass of the atom. The photon's energy is also the momentum of the photon, which in turn must be the momentum of the atom before the photon was emitted, so it is just (to a good apprximation) the kinetic energy which Edgerck didn't take into account. Count Iblis 23:47, 30 May 2007 (UTC)
- Hmm, the last can't be right, and I'm confused by your new epsilon which you don't define. In any case, the kinetic energy of the recoil atom is generally WAY less than that of the photon. Here one problem is that Ed first claimed atoms changed mass in emitting a photon because the photon is massless, then blamed the disparity on the kinetic energy of the recoil atom, which is many orders of magnitude less. For example, consider Tc99m, which emits a photon of 142,683 eV, but recoils at only 0.11 eV kinetic energy, which is insignificant, and not even strong enough to break a bond (so called "hot atom chemistry" bond breaking generally requires beta and alpha emitters for this reason-- even a gamma photon usually doesn't carry enough momentum to give the parent nucleus enough recoil to do much chemically). The 0.11 eV energy of course comes out of the total available decay energy in the COM frame and results in a photon which has 0.11 eV less in that frame than it would if the atom were held still (for example in a crystal)-- the latter situation resulting in the photon getting all the energy (0.11 eV more), rather like an elastic collison between infinitely disparate masses.
It's interesting to calculate the velocity of recoil for this system (about 460 m/sec in the COM frame) and then to see what happens by Doppler shift to the photon energy from the frame of the recoil atom: for Newtonian v doppler shifts (as here) you get e' = e (v/c), so a 142 kev photon get shifted up in energy (as seen by the atom) by 142,000 eV (460 m/sec/3e8 m/sec) = 0.22 eV, which is exactly twice the atom recoil kinetic energy in the COM frame! Add energies of photon and atom, and there's more energy in the atom frame. Energy is not conserved over this process, but of course it's not expected to be, because you don't get energy conservation when you change frames. In this case to the recoil atom-- something else that Ed didn't note. That happens in Newtonian physics, too, of course. The whole system gains energy when you look at it from any frame but the COM frame (which is here the lab frame), and of course the frame of the recoil atom, which is going thataway at about the speed of sound, is not the COM frame or lab frame. So the whole system of atom+photon increases in energy when you change to the recoil atom frame, but that's just what you'd expect. What doesn't change is the invariant mass of the system, which is the same in either frame (or any frame), as you prove above. I'm trying to think of an elegant and obvious reason why for low velocities, the increase in total energy for the system works out as just twice the kinetic energy of the atom, if you change to the recoil atom frame. Hmmm. SBHarris 06:23, 31 May 2007 (UTC)
- is the difference of the two rest masses of the atom (Edgerck wrongly took this quantity to be the photon energy). But I'll check the algebra later today (you are welcome to make corrections if you spot errors) :) Count Iblis 18:46, 31 May 2007 (UTC)
- Okay, since I don't see it until it's introduced at the end, I've replaced it with a ΔM, if that's okay with you. And yes, I think you've got it. If you do the calculation for the recoil energy for Tc99m using your equation, you do indeed get (142,000 eV)^2/(2*9.2e10 eV) = 0.11 eV, so that checks with my result, doing it the old fashioned way by conservation of plain old 3-D momentum. Note again the odd fact that this recoil energy is same as the change in the system decay energy due to frame shifting to the recoil atom. It's not obvious that this should be so. But I don't think that was Ed's error, as noted. His was much worse, amounting to maintaining that subsystem rest mass's should be additive in systems, so that when M_2 does not equal M_1 because the photon has taken off energy which has no rest mass, that simply means rest mass is not conserved. But nobody ever said rest masses are additive in relativity. It's the system total rest mass which is conserved, and it's not the sum of the component rest masses. Ed seems to want it both ways: he wants mass to be some quantity which is additive in systems (which would make it relativistic mass, making photons massive), but at the same time he insists that photons should have zero mass, meaning he wants mass for them to be invariant mass. It has to be one way or the other. SBHarris 04:29, 1 June 2007 (UTC)
- is the difference of the two rest masses of the atom (Edgerck wrongly took this quantity to be the photon energy). But I'll check the algebra later today (you are welcome to make corrections if you spot errors) :) Count Iblis 18:46, 31 May 2007 (UTC)
- My comments are above. See Mößbauer (1958) to verify the experimental set up so that the recoil velocity can be neglected in the lab frame, allowing the same results that I report for the atom frame to be calculated in the lab frame as well. Edgerck 19:25, 1 June 2007 (UTC)
- Well, no, because although the Mößbauer systems allows you to neglect recoil energy and velocity in the lab frame, and consider them to be the same as the atom frame (you basically tack the atom down), you can't by this mechanism neglect atomic recoil momentum, which remains. This doesn't change the photon's energy (because recoil energy is now nil), but that momentum does change the system's energy, because it changes the emitter's momentum, and thus invariant mass of the system is the same as the sum of emitter relativistic energy change, and emitted photon relativistic energy. Which are both nonzero, and can be (in this case) simply added (they are equal, and of opposite sign). What energy the photon gets in Mößbauer systems, the emitter looses--- as is the case in all systems, of course. But because we remain in the COM frame (even if this is also now the atom frame, which essentially does not change), the energy of the Mößbauer photon with energy E adds E/c^2 to the system mass, because the photon's momentum remains cancelled by the emitter's momentum, no matter how well the emitter is tacked down-- and thus their energies are free to simply add, in a 4-vector calculation. In a way, this is much simpler system than if we had a recoil energy. The emitter, of course, loses E energy, and looses E/c^2 mass if we don't include the photon (but then the system is open). SBHarris 19:50, 1 June 2007 (UTC)
About the kinetic energy, note the Edgerck wrote above (in the invitation to fair discussion section) :
"Using m for the mass of the system atom+photon in the atom's rest frame, m² = [(M - e) + e]² - e², where M is the atom mass before the photon is emitted and e is the photon energy (also its momentum), in c=1 units. The result is m² = M² - e². The mass of the atom+photon system is less than the atom mass before emission. Mass is not conserved in a closed system.Edgerck 13:55, 30 May 2007 (UTC)"
So, Edgerck is reasoning like this. M is the (invariant) mass of the excited atom. He subtracts the photon energy e from M where e is measured in the rest frame of the ground state atom) to obtain the mass of the ground state atom. This is, of course, not correct. He then takes the four momentum of the atom after it has emitted the photon to be (M-e,0), because in the atom is at rest. The photon has a four-momentum of (e,e). The total four momentum is then (M-e+e,e)=(M,e). And this then leads to the false conclusion that m^2 = M^2 - e^2.
So, the source of this mistake was to take e to be the difference of the two rest masses, while it should be taken to be equal to the difference in total energy. So, the error is just the kinetic energy that he ignored. Now, this is indeed small, but so is the effect he claimes:
m^2 = M^2 - e^2 --->
m = sqrt[M^2 - e^2] = M sqrt[1-e^2/M^2] = approximately
M[1-1/2e^2/M^2] = M - 1/2 e^2/M
So, Edgerck is saying: I ignored the kinetic energy because the kinetic energ due to recoil is small. Fair enough, but then he claimes that m is less than M. He didn't say by how much. As you can see it is less than M by an amount 1/2 e^2/M. Now e is the momentum of the photon (in c = 1 units), so this is just the kinetic energy of the atom he ignored. :) Count Iblis 23:18, 1 June 2007 (UTC)
Force carriers and mass
This article is linked from the article on the Graviton, which states:
"If it exists, the graviton must be massless (because the gravitational force has unlimited range)[...]"
Note that massless links here. It might be valuable to provide some form of explanation of this property, and relate this concept to other physical forces (weak, strong, EM). --Tsuji 03:19, 2 June 2007 (UTC)