Talk:Invariant mass

message: Shouldn't this be a redirect to rest mass? Keenan Pepper 06:26, 24 Mar 2005 (UTC)
replies: text: Yes, yes it should.  -lethe talk [ +] 03:03, 16 April 2006 (UTC)
replies: text: No, no it shouldn't.  "Rest mass" is used to refer to a single particle or system at rest.  "Invariant mass" is used to refer to a system of particles in motion, usually decay products.  The rest mass of a single particle is also its invariant mass, but the two terms deserve their own discussions. Strait 18:56, 16 May 2006 (UTC)
replies: text: Rest Mass currently directs to well click rest mass and see. This article discusses invariant mass and relativistic mass and describes rest mass as the same as invariant mass. I think this is the page you should be looking at. Jameskeates 13:12, 23 August 2006 (UTC)

text: One basic question is: "what is restmass of an electron?" To answer this question we need to solve the differential equation "of a non-point-like mass with (only hypothetically) its center point at rest". So we have to assume a space-curve oscillation r(t) (in unit meter. I would not call it string) revealing the restmass as an effective value. The basic principle theory is General Relativity combined with the Principles of Thermodynamics. 84.140.74.32 (talk) 11:20, 20 August 2023 (UTC)
replies: text: No, it should not. I am an undergraduate researcher at Rutgers University currently analyzing data from the Large Hadron Collider, and the Invariant Mass page has proven invaluable to me as I receive  my "crash course" in high energy physics to begin working (no pun intended). Ordinarily I would not learn this material for another year or two, so this article is incredibly valuable to me. Furthermore, the article addresses invariant mass within the scope of particle physics, whereas the special relativity page encompasses too much information for this topic. Don't fix what isn't broken.  15:38, 19 July 2010
—Preceding unsigned comment added by 128.6.27.165 (talk) 19:57, 19 July 2010 (UTC)
replies: text: You say "the special relativity page encompasses too much information", but I don't think people are suggesting merging this with mass in special relativity or any other page, just suggesting that "rest mass" may be a more common term in which case the title of the article should be changed from "Invariant mass" to "Rest mass". I think Strait's comment that "rest mass" and "invariant mass" have different meanings, and that rest mass refers only to a system at rest, is incorrect--relativity textbooks routinely talk about the rest mass of objects which are moving relative to the frame in which the analysis is being performed. The sentence in the current opening paragraph (which I am going to edit out), saying "If the system is one particle, the invariant mass may also be called the rest mass", also seems to introduce a false distinction, since both "invariant mass" and "rest mass" can be used to describe bound systems of multiple particles. If anyone thinks there is ever a context where rest mass and invariant mass could not be used interchangeably according to the accepted definitions, please point it out. Hypnosifl (talk) 19:11, 23 July 2010 (UTC)
replies: text: Well, the obvious one is the one for which "invariant mass" is most often used in particle physics, which is systems of UNBOUND particles. In that case, "invariant mass" is perfectly well-defined and often used. However, "rest mass" is undefined and meaningless. SBHarris 00:08, 24 July 2010 (UTC)
replies: text: Wouldn't even an unbound system have a center of mass, which would have its own well-defined rest frame? (the frame where the total momentum was zero) Even so, it may be that in practice physicists never actually use "rest mass" to describe the total energy (divided by c^2) of unbound systems in the center-of-mass frame, in which case the two terms do have a distinct meaning in practice even if it would be perfectly logical to define "rest mass" in this way. Hypnosifl (talk) 01:35, 24 July 2010 (UTC)
replies: text:  Yes, it would be perfectly logical, by extension. But in practice, nobody uses the term to refer to unbound systems. So, we have a sort of oddity of language, but not THAT odd. After all, the "rest frame" (and thus also COM frame) of bound systems is easier than finding the COM frame, which may not be obvious at all. Consider an assymetically expanding gas cloud: it has a COM frame and an invariant mass, but it's not at all obvious by inspection where that frame is. In most bound systems, by contrast, you just look at the motion of the center of mass, which is (usually) obvious by inspection. In solid objects it's the rest frame of the whole extended collection, and even in rotating objects it's the rest frame of the center of mass, around which it rotates. In a bottle of gas it's the frame of the bottle, and so on. Thus, rest mass and invariant mass are the same for single particles and extended objects and bound systems, but not for unbound systems, where the "rest mass" isn't defined. This is in part because the COM frame isn't obvious. But also it is in part because "invariant" mass can be used for systems involving photons which are never at rest. Physicists are comfortable talking about the invariant mass of a system of decay photons from the decay of a pi-zero (neutral pion) for example, but the "rest mass" of such a system sounds funny, since no part of it can be brought to rest, by any shift in reference frame. SBHarris 02:42, 24 July 2010 (UTC)
thread_title: Top

message: Someone proposed that Bare mass be merged into this article. However, as far as I can gather from a quick perusal, the two concepts are quite different. RockMagnetist (talk) 21:57, 24 January 2012 (UTC)
replies: text: Someone? Where namely, and what to merge? Incnis Mrsi (talk) 21:01, 4 February 2012 (UTC)
thread_title:  Merge proposal 

message: An author has removed this statement: Only when the system as a whole is at rest (its total momentum is zero), will invariant mass be equivalent to the familiar concept of rest mass. I've corrected the misuse of the apostophe, but so far as I can tell, this statement is completely true. Since ordinary objects (like a tank of gas or a solid composed of vibrating atoms) are "systems", what we weigh as "mass" on a scale in the COM frame IS the "invariant mass" of the object-at-rest. The "rest mass" of a system, is the mass of the system when the system is at rest, and that's the mass of the system in its COM frame, where the scale is. It is indeed the invariant mass of bound systems that we're all familiar with, in everyday life, since we measure the mass of bound systems in their COM frame in everyday life, and that mass includes contributions from all energies that show up in that frame, in the system (like the energy of molecules in a hot gas, or the kinetic and potential energies of vibrating atoms). I think that deserves a mention, but it has been systematically removed. So, defend doing that, please, or I'll put it back. SBHarris 17:58, 25 June 2012 (UTC)
thread_title:  Invariant mass is usually what we weigh as "mass" 

message: I noticed there's a Japanese version of this page (http://ja.wikipedia.org/wiki/%E4%B8%8D%E5%A4%89%E8%B3%AA%E9%87%8F) which links to the English page, but the English page doesn't link to the Japanese page. Sorry, I don't know how to edit this as I'm just a Wikipedia reader..  — Preceding unsigned comment added by 58.7.92.17 (talk) 13:52, 14 January 2013 (UTC)
replies: text: Done. — Quondum 15:48, 14 January 2013 (UTC)
thread_title:  Japanese Version 

message: Shouldnt there be a link (or at least mention somewhere) the relation to s, the mandelstam variable?  — Preceding unsigned comment added by 146.50.70.176 (talk) 09:24, 18 April 2013 (UTC)
thread_title:  Mandelstam variable s 

message: Rest mass redirects here. Since they are NOT the same, they 
either need to be carefully differentiated here, or the article needs to be split.
This whole article needs a rewrite.  I am NOT familiar with the concept of invariant mass, or I would do it myself.
The article goes to great lengths to explain that the sum of the rest masses is not equal to the invariant mass.  I am not sure how useful that tidbit is, since it fails to discriminate between the two concepts.
There are a multitude of other problems with this article.  It seems to be claiming (I had to read it several times to understand it probably is not) that invariant mass changes with velocity.  It claims that the invariant mass IS the total energy of the system divided by c² as long as a certain frame of reference exists (note the only requirement is its EXISTENCE, not its use as the actual frame of reference).  Since total energy IS a function of velocity (relative to the f.o.r.), invariant mass is not invariant if we take the sentence as it is written.  Too many clauses, too many qualifications.
Why not say simply that for individual fundamental particles, invariant mass is identical to rest mass (if I understand the concept) but that in systems of particles, the center of momentum frame is not the rest frame, the individual particles have momentum in that frame and so the invariant mass is the sum of both the rest mass of each constituent and their momentum (or energy).  { I am not clear whether the invariant mass includes other sources of potential energy??} { I am also not aware of how the concept fits into General Relativity.  The article seems to dabble with GR, but avoids direct discussion - most likely a wise choice}
Seems this article agonizes over the existence of composite particles and systems.  And is tripped up by them.  Nowhere is it clear (if it is actually true, as I am assuming) that two observers of the same system (why does it have to be bound?  Isn't the only requirement that it be measurable?) will agree on the invariant mass, while the measured mass will be relative??  That is, the invariant mass does not change with a different choice of reference frame, while a particle's or system's measured mass may change.
I also take exception to the use of m₀ or M₀ to mean both rest mass and invariant mass in the same article.  At least, it sure confused me.72.172.11.228 (talk) 01:11, 31 May 2013 (UTC)
replies: text: Buddy the answer you need is here: Energy And Mass In Relativity Theory  2009 by Lev Okun . Read that and do not trust what you read on the internet. 89% wrong, 90% of the time. I am not really dead (talk) 20:58, 15 February 2016 (UTC)
thread_title:  Edit needed - rest mass is NOT invariant mass 

message: I can not do it, but someone should delete the material here, then restart. Okun is not as much fringe as the page suggests and the new work by Frank Wilczek "Origins of Mass"  is not even mentioned here. If a Noble prize winner's work is missed, guess what else is.... And amazingly it does not refer to Max Jammer Concepts of Mass in Classical and Modern Physics. Cambridge (Mass): Harvard U.P., 1961 New York: Harper, 1964 New York: Dover, 1997. . This article needs a  Requiem Mass then a restart. I am not really dead (talk) 21:35, 14 February 2016 (UTC)
replies: text: I agree that this page should be rewritten. What are your thoughts on Mass in special relativity? For the moment this article should cover what your students need. --EduardoW (talk) 16:23, 10 December 2017 (UTC)
thread_title: Rewrite this page

message: I have the following suggestion to avoid the redundant covering of material here and in Mass in special relativity, and fix this article:
* Turn Invariant mass into a disambiguation page listing Mass in special relativity#Terminology and a new page Invariant mass of multiple particle systems.
* Move all relevant content from here to Invariant mass of multiple particle systems, trim out all redundant content and fix some further issues.
* Remove Mass_in_special_relativity#The_mass_of_composite_systems and insert a link to Invariant mass of multiple particle systems.
Thoughts on this? --EduardoW (talk) 16:23, 10 December 2017 (UTC)
thread_title: Suggestions for a rewrite