Talk:Mass/Archive4

Higgs boson?
Do you think there be some mention of the hypothesis that mass arises as a result of interactions with (currently hypothetical) Higgs bosons? I know there's a see also at the bottom of the article, but the concept merits at least a mention, I think. I understand little of this so I would hesitate to add it myself; I hope someone more knowledgeable than I could discuss this. If not, I'll research it a bit myself. Thanks! &mdash; Knowledge Seeker &#2470; 03:08, 20 November 2005 (UTC)


 * We could add a section called "Origin of mass", but we know very little about it. Higgs fields are hypothetically at the origin of masses of elementary particles but do not account for all observed masses (for example, the mass of a proton is not the sum of its quark constituent masses, but a large part of it is generated by the strong field). Actually, mass is nothing else than energy "at rest", which is generated by fields, which arise from fundamental interactions... we can also view it dynamically, as something moving around in a trap, or vibrating.


 * I believe there are theories or a theory that states that mass is nothing more than the momentum of the particles that make up the larger particle, or in the case of elementary particles, just the momentum of the particle. The point of the idea is that the mass is simply momentum, and is the result of the speed of particles. Fresheneesz 22:03, 7 December 2005 (UTC)


 * Thanks for your reply. I think that an "Origin of mass" section is a great idea&mdash;I think it's fascinating. I realize that little is known, but even if you or anyone who's willing just explain what you've written here, I think the article would benefit. &mdash; Knowledge Seeker &#2470; 04:18, 8 December 2005 (UTC)

Alright, maybe i'll put in a small section about that. But since I don't know much about it, some help would be very appreciated. Fresheneesz 03:50, 9 December 2005 (UTC)


 * I thought momentum was just mass times velocity, so how can mass be caused by momentum? That seems circular to me. Also, it does not explain the mass of particles like the electron, which are believed to be fundamental (not made of smaller parts). —Keenan Pepper 05:45, 9 December 2005 (UTC)


 * Momentum is mass times velocity in classical mechanics, which offers no explanation of the origin of mass. In relativity momentum is not as simple, for example massless particles such as photons have momentum. The confusion probably originates in the different definition of mass used. Gravity acts on the energy (which results from rest mass and momentum). The vast majority of gravitational mass that makes up the everyday world is from protons and neutrons, and originates from the binding energy holding together their constituent quarks. This is well established. The origin of the mass of the fundamental particles (electrons, quarks etc) is not proven and is provided in the Standard Model of particle physics by the Higgs mechanism mentioned above. This is yet to be experimentally verified.Jameskeates 09:04, 17 August 2006 (UTC)

Intertial, graviational, active ??
It seems to me that these three "types" of mass are simply different measurements for mass. The concept of mass stays the same throughout every "type" but the equation used to derive the mass changes. Is there some reason that these are considered to be "types" of mass? Perhaps I just don't understand, but I think a definition of each should be kept, but that other references to it should be clarified as different places mass appears, rather than considering them fundementally different (which the article explictely states that noone has found). Fresheneesz 04:12, 9 December 2005 (UTC)


 * There is no reason to suppose that the force on a body due to gravity should depend on the same quantity that determines it's rate of acceleration. That is why it is interesting that these two prove to be the same. The active/passive distinction is less interesting as Newton's third law regarding equal and opposite reactions can be used to explain these.Jameskeates 09:07, 17 August 2006 (UTC)

Okay, time to put up or shut up, on the matter of system energy and mass
See discussion immediately above. Okay, lethe, you've had a month to provide your references, and haven't done it. My reference is to Taylor and Wheeler's Spacetime Physics (now referenced in the Mass article itself), which is as close at it gets to being the standard undergrad text on relativistic mechanics. The authors were professors of physics at MIT and Princeton and leaders in their field (relativistic physics) and so forth and I hope I don't have to go into it. Suffice to say, they're authorities on this subject, if anybody is.

Now, here's what they say about mass of systems, and I'd like you to read it carefully, because there really isn't space to repeat it every time we get into an argument about the mass of systems of unbound or bound particles. I am going to quote it here. I'm going to make use of it when I make a bunch of the changes I tried to make months ago to the mass and energy articles, particularly in the system sections. If you don't like these, then this here is your reference, and my challenge to you to find a better or more authoritative one, still stands. In the meanwhile, leave my edits alone, please.

From Taylor and Wheeler, page 224-5 section 8.3 (part of a much larger discussion):

''[discussion of life as a system property of atoms in a living animal, not to be found in any specific place]. Life is remarkable but in one respect the two-object system we are talking about is even more remarkable. Life requires organization, but the two-object system of figure 8.3 totally lacks organization. Neither mass interacts with the other. Yet the total energy of the two-object system, and it's total momentum, regarded from first one frame of reference, then another, then another, take on values identical in every respect to the values they would have had were we dealing throughout with a single object of mass 20 units [N.B.: being considered is a system of two masses each with 8 units of rest mass, and 4 units of kinetic energy distributed between them]. Totally unlinked, the two objects, viewed as a system, possess the dynamic attributes -- energy, momentum, and mass-- of a single object.''

''This wider idea of mass-- the mass of an isolated system composed of disconnected objects: what right have we to give it the name of "mass"? Nature, for whatever reason, demands conservation of total momenergy [EM-4-vector] in every collision. Each collision, no matter how much it changes the momenergy of each participant, leaves unchanged the sum of their momenergies, regarded as a directed arrow in spacetime-- a 4-vector. Encounter or no encounter, and however complex any encounter, system momenergy does not alter. Neither in space direction orin magnitude does it ever change. But the magnitude-- the length of the arrow of total momenergy, figured as we figure any spacetime interval, is system mass. Whether the system consists of a single object or of many objects, and whether these objects do or do not collide or otherwise interact with each other, this system mass never changes. That is why the concept of system mass makes sense!'' [end of quote]

There's a great deal more discussion on this point, which I mercifully won't quote (unless you force me to). It would be better if you'd find the book and read it yourself, as I suggested many moons ago. Sbharris 20:10, 15 June 2006 (UTC)


 * Yeah, the wider idea of mass. --Pjacobi 20:20, 15 June 2006 (UTC)


 * OK. One, I wasn't aware that I was supposed to be looking for references, so sorry for making you wait months.  Two, just because you have posted a paragraph from Taylor and Wheeler does not give you the right to demand I leave your edits alone.  I continue to think your edits are misguided, and will continue to do violence to them.  Three, I've read the text you posted above very carefully.  It refers to a "wider idea of mass", a concept of "system mass".  This language very carefully implies that this is not the standard idea of mass.  Rightly so; this is not the standard idea of mass.  I will also note that just because Taylor and Wheeler said it does not make it gospel; they also invented the horrible term momenergy, and no one in his right mind uses that term.  Just because it's in their book doesn't give us the right to flout all physics convention and change Wikipedia accordingly.  I ask you to abandon your crusade to change all mass articles at Wikipedia.  -lethe talk [ +] 23:03, 15 June 2006 (UTC)


 * Taylor and Wheeler have hundreds of published papers in relativistic physics and several texts, including the number relativity text for 25 years: Gravitation. You dismiss them because of a neologism you don't like? Wheeler coined the term "black hole"-- maybe you don't like that, either? So? Neither did the Russians. In any case, you can find out physics convention and invariant mass for systems by googling the term in the titles of physics papers in physics journals. Try it.
 * The term "black hole" is used all the time, the term "momenergy" is not. If Taylor's term becomes widespread, good for him.  If it doesn't, then so be it.  Just because Taylor said "momenergy" does not mean Wikipedia has to say "momenergy".  Just because Taylor says "wider concept of system mass" does not mean that Wikipedia has to take this vague wider concept as our definition.  Moreover, I suggest that Taylor and Wheeler never intended that vague "wider concept" to be an operating definition of mass.  -lethe talk [ +] 03:19, 16 June 2006 (UTC)


 * Do you really want to debate this? Seriously? There are over a million hits for "invariant mass measurement physics" in google. A sampling shows mostly calculation of invariant mass of particle showers (a disconnected system if ever there was one) from momenta and energy, which allows instant knowledge of invariant mass (i.e. rest mass) for the particle which gave rise to the decay products. It's an enormously useful concept. For systems it's usually called invariant mass. For single particles which give rise to these systems, it's usually called rest mass. But it's the same thing. And yes, not only did Taylor and Wheeler intend the wider concept to be the opperating definition of mass, it has been the opperating definition of mass for the last half century of particle physics, ever since Mandelstam started to point out the usefulness of s^2. Sbharris 03:50, 16 June 2006 (UTC)


 * I never disputed that "invariant mass" was a common concept. Indeed, invariant mass is quite common.  What I dispute is that the rest energy of distant particles is referred to as the mass.  The Mandelstam variable you cite is exactly this quantity: the rest energy of the total system.  My point in a nutshell: despite what Taylor and Wheeler say, s^2 has never been called mass. -lethe talk [ +] 04:01, 16 June 2006 (UTC)


 * PS. So do you still want references from me?  I will give you a list of nuclear physics texts which deal with the mass defect, if that will please you.  I am hoping that you will concede it will that the concept of mass defect is standard and well-known, found in every nuclear physics textbook, and implies that mass is not conserved. -lethe talk [ +] 23:07, 15 June 2006 (UTC)


 * Mass defect has nothing to do with this argument, any more more than weight defect in a burned log has anything to do with the conservation of mass in chemistry. Mass is invariant in closed systems, and no nucleus when formed is a closed system. The energy is tapped off, and then its mass is less. Big deal. What many people don't realize is that if the system was kept closed, there would be no mass defect. Taylor and Wheeler point this out. You won't be able to find me a reference to the contrary, because you'd basically be asserting an exception to the conservation of invariant mass in closed systems. Sbharris 02:56, 16 June 2006 (UTC)


 * The mass defect measures how much the mass changes in a reaction. You are correct that in a closed system, the total mass of the system is constant.  So of course I won't find a reference which claims that mass is not conserved in a closed system.  Unfortunately, not all systems are closed.  In fact, most reactions in particle physics involve decays into free particles, and for this reason, we need mass defect. -lethe talk [ +] 03:10, 16 June 2006 (UTC)


 * "Closed" doesn't mean you have a physical box around it! (Though that can be used in thought experiments). It simply means you don't have big losses from your system, before you can measure them. Very typically, high energy decay products (as free as can be) are measured with a calorimeter and path detectors, and that's all still a "closed system" because no significant energy has escaped from the decays which are counted. "Closed" is not an idea related to walls-- it's a concept. I will venture that most applications of the term "invariant mass" in physics involve unbound relativistic systems of many particles. Do you want me to give you the first 10 references to such everyday physics work, off the web? Do I really have to do that for you?  You can certainly do it yourself, so why are you pretending, or in active denial, or what? Start being a little less skeptical of what I'm saying. Because I'll be glad to post 10 or 20 in the next message, and certain will, if you keep on like this. (I'm curious as to what you'll say first). Sbharris 03:50, 16 June 2006 (UTC)
 * I would like to see 10 references which refer to the invariant total mass of a system of unbound relativistic particles. This is exactly the concept which I claim is nonstandard, and if you have 10 such references, I will eat my hat.  By the way, what do you mean "off the web"?  A lot of stuff on the web isn't real physics. -lethe talk [ +] 04:01, 16 June 2006 (UTC)


 * Dear Sbharris, I appreciate your efforts but I think that overall Lethe is right. I don't think it would be reasonable to change the terminology according to the suggestion of Sbharris, except maybe writing a separate small section discussing this approach. Yevgeny Kats 23:15, 15 June 2006 (UTC)

Invariant mass

 * Moved from talk:mass in special relativity, this section is in response to this edit. -lethe talk [ +] 05:04, 16 June 2006 (UTC)

This term is immensely common in particle physics, and if you google it you'll find at least 10 pages of references to physics papers where it's calculated for relativistic particle systems. Don't say it's "nonstandard" in the face of that. You're just being ridiculous.Sbharris 02:48, 16 June 2006 (UTC)


 * The standard terminology in physics is to define mass to be the sum of the rest masses of the particles. Taylor and Wheeler use the term "system mass" for the rest energy of the system, but this is nonstandard. -lethe talk [ +] 03:13, 16 June 2006 (UTC)


 * You are pulling my leg, yes? Here's a random quote from a working physicist studying electroweak symmetry breaking from WW scattering at the Tevatron



''::Invariant mass is often referred to just as mass. The unit of mass used when is that of energy, the electron volt: this can be seen from the equation. The mass of the proton is 938 MeV, and those of the W and Z, and, are 80.4 GeV and 91.2 GeV respectively...."''

And so on. You want more of this? It's just working physicist stuff; the langauge they use in their publications, which by definition is the standard usage. Sbharris 04:33, 16 June 2006 (UTC)


 * I want an example of the total mass of distant particles. You've given me several examples of single fundamental particles. -lethe talk [ +] 04:46, 16 June 2006 (UTC)


 * See above. The "decay products" of a W boson are particles distant from each other when measured. How distant do you require them to be? In calorimeters in high energy physics the decay product particles may be meters away from each other when their energy and momenta are measured. How do you think we know the rest mass of W? Find one at rest and weigh it really quickly? In practice, most of these short lived particles are never seen intact. Sbharris 04:55, 16 June 2006 (UTC)


 * The quote is about the mass of the W boson, not the mass of the decay particles. The mass of the decay particles is different from the mass of the W particle, which is exactly the issue we're arguing over.  To support your side of the argument, you need a reference about the mass of distant decay particles being the same as the mass of the single W boson.  -lethe talk [ +] 04:59, 16 June 2006 (UTC)


 * Yes, the mass of the distant particle system is what we call the invariant mass of the system, as the quote notes. YOU are the one claiming that "[t]he standard terminology in physics is to define mass to be the sum of the rest masses of the particles." It is not. The invariant mass of a system of decay particles is in general NOT not be the sum of their rest masses. It is, however, the REST MASS (also the invariant mass) of the particle which gave rise to them, since this quantity is conserved when a particle changes to a shower of particles. Once you know it, it's the same in all reference frames. Simple enough?


 * The quote doesn't say what you're claiming here. It never says "the mass of the distant particle system is what we call the invariant mass of the system".  It only refers to the mass of a W boson.  -lethe talk [ +] 05:41, 16 June 2006 (UTC)


 * If you want a formula for the invariant mass of system of two photons (which can be any distance apart physically that your heart desires), it's in the first paragraph of the article below. It's a stndard formula in physics and doesn't even need a reference. It tells how much of the energy of the photons is available for the reaction of pairs of new particles which have rest mass, such as electrons and positrons. Sbharris 05:23, 16 June 2006 (UTC)


 * You're right. That website uses the phrase "invariant mass" to mean the rest energy of the reaction.  Find me a couple of more references like that one, and I'll be eating my hat.  I will mention however that I have in my hands a book by Griffiths in which he calls the book Spacetime physics by Wheeler and Taylor "unorthodox". -lethe talk [ +] 05:41, 16 June 2006 (UTC)


 * Here's an offhand comment on the invariant mass of two photons, and why it's a good thing it exists, from a prof of physics at Cal Poly Pomona. I'll just keep chucking these things at you until you read one that somehow penetrates your prejudice. But it is indeed the standard way physicists think. Even in Pomona. Sbharris 05:45, 16 June 2006 (UTC)
 * Alright, I see that physicists do indeed refer to this concept. I still have doubts about the prevalence of the phrase, but it doesn't really matter, I guess.  If the phrase is used, then it's used.  I have rewritten that section again.  Do you have objections to the current version?  (even if I concede that the term is used, I'm loathe to revert to your version, which was, if you'll pardon the offense, extremely long (much longer than necessary) and badly formatted). -lethe talk [ +] 06:28, 16 June 2006 (UTC)

Wait till you see my proof of E = Δmc^2 with no calculus. Formatting and how long is necessary to get the point across, depends on the reader. Look at how badly I did with you. And taste for math is strictly an acquired one. Sbharris 07:42, 16 June 2006 (UTC)


 * I'll add that I was working on a π0 calorimeter last summer, and the phrase "invariant mass" is indeed used in this manner. - mako 08:15, 16 June 2006 (UTC)


 * Heavens, yes. Thanks for the note. It irks me no end for somebody who's apparently never been there (have you BEEN to SLAC or Fermilab, oh, omniscient editor? I have), to tell me how people in a profession think and behave. And then rejects textbooks by such professionals to boot. Insufferable. Somebody's latex needs breaking: it's the membrane that keeps one editor in particular (and you know who you are) from getting out into the real world to see how high energy physics is actually done. Sbharris 18:25, 16 June 2006 (UTC)
 * Are you talking about me? -lethe talk [ +] 19:00, 16 June 2006 (UTC)


 * Yes invariant mass is a wide spread concept in particle physics. I couldn't be bothered reading long winded arguments before so I;ll summarise my understanding and hope this clears some things up. Invariant mass is useful because it is invariant under Lorentz transforms. In the rest frame of a particle it is equal to the rest mass. When you are in a frame where the particle is moving, the invariant mass is still equal to the rest mass (it is invariant!). 4-momentum conservation can be used to show that the invariant mass of the decay products is equal to the invariant mass of the decaying particle and therefore its rest mass. The invariant mass of a system of particles is not equal to the sum of the rest masses of the individual particles. I think you are probably arguing more over a misunderstanding of different concepts than over actual physics.Jameskeates 09:28, 17 August 2006 (UTC)

Definition of Mass depends on the Vague Defn of Matter
The Wiki article on Matter defines matter as follows: "Matter is commonly defined as the substance of which physical objects are composed. It constitutes the observable Universe. According to the theory of relativity there is no distinction between matter and energy, because matter can be converted to energy (see annihilation), and vice versa (see matter creation)."

The pivotal term of this definition is substance, for which Wiki does not have a definition. There is a definition for Chemical Substance, but it does not address the needs of this particular definition.

Suggestions? Volunteers? Bvcrist 21:09, 11 August 2006 (UTC)


 * You need to read past the lead paragraph. Unfortunately the overview is much more specific, defining "matter" as elementary fermions, making it a subset of "mass" but not all of it (since bosonic fields and such also contribute to energy, and it is total energy which is essentially what links to gravity, as mass). For example, a static electric field around a charged object, or the magnetic field around a magnet, both have energy and thus mass. But generally neither one are considered matter. I'll see if I can fix up the intro paragraph a bit so it reflects the distinction. S  B Harris 21:53, 11 August 2006 (UTC)


 * Guess I'm confused. My understanding is that "matter" is the base material from which all particles are made.  Is that correct, wrong or a state of confusion on my part?


 * In older literature, mass was often considered to be identical with "electromagnetic mass".  Does the current day concept of mass mean that mass always entails (includes) either or both electric and magnetic fields?

Bvcrist 16:51, 16 August 2006 (UTC)


 * Mass (the best definition of which is invariant mass) includes all the energies that are present in a closed system which has no net momentum. So it includes fermionic particles, fields, stresses, kinetic energies, photons, the whole enchilada. But historicallyn we have not tended to include things like light and kinetic energy in with our idea of "matter." When asked, "what is matter?" the answer would be "Oh, you know, that solid stuff" The only problem is that modern physics shows that a lot of solid "stuff" is made of static fields and kinetic energy. A nucleon, for example, is 99% made up of the kinetic energy of quarks, and the energy of massless gluons (the glons, like photons, have no mass, but their ENERGY contributes mass to the system). And yet nucleons (protons and neutrons) are considered the building blocks of matter, making up all but about 1/4000th of the weight of ordinary objects. So the whole thing is very badly defined. We've done the best we can in this article, but as it is, the article defines matter as electrons and quarks, and that means (although the article doesn't say it specificially) that 99% of any ordinary object is not fermionic matter particles at all, but rather trapped energy, exhibiting mass. The old literature used to posit that perhaps all matter is that kind of thing, with trapped electromagnetic energy filling the entire role of mass. Today we know that most of the trapped energy is kinetic energy, plus potentials related to other deeper forces (the color force of QCD). Still, the concept is the same. And also, we can't QUITE get down to the idea of all mass being "energy" in the pure sense. That would require the decay of the proton so that all matter would be convertible to photons. That's been theorized, but so far not proven. I hope you're not even more confused that before.  S  B Harris 18:52, 16 August 2006 (UTC)


 * Thanks for the explanation on "mass" SBHarris. Very succint and truthful.


 * A couple of questions and comments, if I may. Since nothing in the universe is ever truly at absolute rest and since mass does not fade in and out of our "dimension", the universe and all its particles should have a net momentum since closed systems are just a convenience for discussing or analyzing an event.  So I am at odds with the idea (concept) that mass (invariant mass) has no net momentum.  Suggestions?


 * I am very intrigued by the remaining 1% (or any amount >0%) of any particle that is not due to fields, stresses, KE and such because that minute piece of any particle seems like it should be considered as "true matter". That piece of "true matter", if it exists, might be or have "true mechanical or physical mass", which might not be invariant, but that sort of invariance is for another discussion.  In the same vein, Max Born speculated that the electron might, at its core, be composed of a "mechanical mass" just like Malcolm MacGregor (LLNL) has also proposed (The Engimatic Electron 1993).  The size of this so-called "mechanical or physical mass" of the electron seems (by various collider expts) to be smaller than 10(-18) cm.  If we then also look at the so-called "relativistic mass" or "rest mass" of a photon and keep in mind the radiation pressure of photons, then photons just might also have a "true mechanical mass" albeit one that is less than 10(-48) kg.  Bottom line from one point of view is that particles and bosons may at their cores have a piece of true mechanical or physical matter that has a true mechanical or physical mass. Plausible?


 * As you can see, I have strayed from my main concern, the definition of matter. Since, if I understand correctly, some sort of "non-mass" based matter is at heart of any particle and that matter, by its current definition, has mass (fields etc.) as one of its attributes or properties, then the question is "Excluding mass, what are the measurable characteristics of matter?"  Therein is the challenge since matter is the group or set that encompasses mass, elementary particles, composite particles etc.  Suggestions? Bvcrist 17:40, 17 August 2006 (UTC)


 * Sorry for the long delay. Obviously, I don't know the answer. However, if you subtract the masses of particles which are due to their EM fields or charge, and their "color-charge" as well, then presumably you'd be down to the "mechanical mass" you're talking about. That might well be zero for photons, but maybe not zero for charged leptons. Consider the fascinating decay of the muon. Almost all of its mass turns out to be "peeloff-able" in terms of two neutrinos, so that you wind up with a 1/206th mass "pit" (the electron) with the same charge. And that extra mass disappears into a pair of neutrinos. But different flavors of neutrinos. On carries "muonness" and the other "electronness," and you begin to wonder where is the partner of the electron neutrino that goes off. Maybe it's another electron neutrino in the electron itself? You get the feeling that the electron would like to decay also, and one of the products is that electron neutrino, but it can't happen because there's no place to put the charge. But neutrinos, which we now know have a tiny rest mass, look just like electrons with no charge-- same spin, same flavor, just different mass. Perhaps that's exactly what they ARE. Maybe electron neutrinos are electron "pits," or naked mechanical mass, as it were. With a tiny radius and only a few eV in mass. So there's an electron neutrino in every electron, but you never see it naked, because it's always cloaked in the mass of the electron's charge. Speculation. There's not much we can do here, tho. Clearly, most of "matter" and "mass" are bosonic fields, not neutrinos (if that's what the pits of all fermions turn out to be). We just need a better definition of matter as we use the term. This mechanical core is something entirely different. S  B Harris 00:45, 11 October 2006 (UTC)

The idea that there is an electron neutrino "inside" the electron is like that old chestnut that a neutron is made up of an electron and a proton. Today you could add the neutrino as well, but none of it works. If you try to confine an electron in the proton or neutron radius, the uncertainty principle makes it jiggle so it has a huge energy. If you tried to put an electron neutrino in each electron, you would have a similar problem. Carrionluggage 06:02, 11 October 2006 (UTC)


 * No, bad analogy. Do the math. If the neutrino has a rest energy on the order of an eV you can stick it into a volume smaller than the minimal experimentally measured 10^-18 m radius for the electron, without going anywhere near the electron rest energy. An easy way to think of it is that the quantum limit for confining a particle in space is on the order of its Compton wavelength, h/mc. For an electron, the Compton wavelength is 2x10-12 m. So imagine if the neutrino had 10^-6 of the electron mass, or 0.5 eV instead of 0.5 MeV. That gives you a Compton wavelength and confinement/uncertainty position of 2x10-18 m. As I recall, that's about the experimental limit for the known bounds of the electron radius. We don't know they're point particles-- only that they're smaller than 10-18 m. So this would fit theory fine. And since we really don't know the lower limit of the possible neutrino mass very well, there's plenty of wiggle room here should we need it.  S  B Harris 01:22, 24 October 2006 (UTC)
 * Wups. Sorry, but just realized that Compton wavelength is INVERSELY proportional to mass. So for small-mass neutrinos we do indeed have a big problem with confining them. Duhhh. We all have off-days. S  B Harris 01:41, 7 November 2006 (UTC)

Also the spin is wrong. Both the electron and the neutrino are spin 1/2 particles. Carrionluggage 06:02, 11 October 2006 (UTC)
 * Yep. So? Perhaps the pure charge component of the electron (electron minus neutrino) has no intrinsic spin. All the spin of the electron is due to the neutrino. S  B Harris 01:22, 24 October 2006 (UTC)

In answer to the item about invariant mass having or not having net momentum, it certainly does. In its own rest-frame the momentum vector has length mc (m is the rest mass, c the speed of light) and it points directly into the future (positive time axis). You can get the momentum in any other reference frame (frames such that the particle is moving) with a Lorentz transformation from the original (mc,0,0,0). Carrionluggage 06:02, 11 October 2006 (UTC)

Gravitational mass is rest mass
This is just an opinion. You have a system of two masses with a spring between them away from the earth and other gravitational influences. The displacement of the spring measures the gravitational force between the two masses. The mass-spring-mass is aligned with the y-axis. Now bring them up to speed along the x-axis. Though the masses have been relatively increased the spring displacement is the same as the frame riding along with the masses. So it seems to me that gravitational attraction is determined by rest mass. I tried searching google for an answer to this question but have not found any. Scot.parker 21:37, 20 October 2006 (UTC)
 * I believe your thought-experiment is OK, but is too specialized to be a proof in general. You might take a look at: Nordtvedt_effect which is a little more complicated. I think if a non-zero Nordtvedt Effect were found, it would show an inequality of Gravitational mass and rest mass, but the chain of definitions is intricate, because there is active gravitational mass and also passive. Carrionluggage 23:00, 20 October 2006 (UTC)

Consider n-bodies being observed by a single observer outside that system of n-bodies. It seems to me that there are two possibilities. One is that all masses attract each other according their rest masses (rest mass is actually invariant of the observer). The other possibility is that a particular mass is attracted to all the other masses as it perceives their relativistic masses according to it's own rest frame. In other words the relative velocity of two bodies with equal velocity (vectors) would be attracted to each other due to the fact that they are at rest relative to each other. But if the two masses had different velocities relative to themselves and the observer then the observer would perceive their attraction in accordance with how each mass perceives the mass of the other body. Is the gravitational field of the earth greater because of the increase in relativistic mass due to it's rotation? Scot.parker 18:46, 21 October 2006 (UTC)


 * The idea of gravitational mass is essentially a Newtonian idea, applying mainly to Newtonian gravity. At least one author believes that there is no such concept as gravitational mass in General relativity.  see http://www.citebase.org/abstract?id=oai%3AarXiv.org%3Aphysics%2F0111134 or the arxiv version http://arxiv.org/abs/physics/0111134, which is a set of slides with the following quote:


 * According to General Relativity, the source and receptor of gravitational field is the density of energy-momentum tensor T which is coupled to gravitational field like density of electric current is coupled to electromagnetic field.


 * For a point-like particle 


 * For a particle at rest (v = 0) mass m is the source and receptor of gravity.


 * Thus, according to GR, there is no such notion as gravitational mass mg.


 * Once upon a time, I had actually edited the article to reflect this POV, but "Newtonian mechanics" got edited into "Classical mechanics" at some point by another editor. Probably the point needs to be discussed more fully.  I should add that Okun's views as quoted above are not necessarily universal, but I'm not sure what authors would represent an opposing view (to meet WP:NPOV).


 * I'm not sure how to fit this information into the article without derailing it. Right at the start doesn't seem like a good point to get into these issues.  I was hoping the "quick fix" of mentioning that gravitational mass was a Newtonian concept right at the lead would be enough, but this "quick fix" didn't hold up under editing by other editors.  Perhaps we can achieve some consensus on this point with this discussion.


 * Standard GR textbooks, such as Wald "General Relativity" generally don't talk about "gravitational mass". Certain conditions must be met in order to define "mass" in General Relativity at all.  A standard textbook treatment, like the above mentioned Wald will usually talk about "ADM mass, Bondi Mass, and Komar mass", rather than "gravitational mass".   See the article Mass in General Relativity for more information.  This is already linked to the article, BTW.  Pervect 19:09, 23 October 2006 (UTC)

Gravitational mass is inertial mass so there is no need to make any distinctions in GR once the equivalence principal is assumed as a postulate. M does appear in the metric though so it is certainly relevant. However in SR there is the quantity E/C2 and there is also rest mass. I know I don't know everything. I am just expressing my opinion based upon what I know. Scot.parker 22:13, 23 October 2006 (UTC)

Relativistic mass is a better definition of mass than invariant mass
People seem to discard the notion of relativistic mass because it is not frame-independent. Why relativistic mass is not frame-independent? In relativity, there is no absolute inertial frame of reference such as ether. It states that every motion is relative. Can we find out that whether an object is moving or at rest without a reference object? Definitely not. This also means the kinetic energy of an object is relative but not absolute. Before the introducing of special theory of relativity, we assumed that energy can be neither created nor destroyed. It exists in many form. We could not deny that kinetic energy is a form of energy. An object would have different kinetic energy in different frame of reference. Not only kinetic energy, photon seems to have different energy too in different frame of reference. Relativistic doppler effect states that photon has different frequency in different frame of reference. The energy of photon depends on its frequency. Apparently, the energy in the universe is frame-dependent. From special theory of relativity, a new form of energy is introduced namely rest mass-energy. Rest mass-energy as other form of energy could be converted into other forms of energy. Photon could be converted into rest mass-energy through pair production. Is mass a form of energy? Invariant mass of a particle is its rest mass-energy. Relativistic mass however could be any form of energy. Why relativistic mass is useful concept? How could we know the mass of an object? Inertial mass and gravitational mass are equivalent. When we weigh an object, we definitely measure the force that applied on it by our gravitational field on it. According to Newton's Law of Universal Gravitation, gravitational force that applied on a body is proportional to gravitational mass of the body. Since inertial mass and gravitational mass are equivalent, gravitational mass of an object should increase if its inertial mass increases. From special theory of relativity, we know that inertial mass of macroscopic object should increase when it absorbs certain amount of electromagetic radiation. However, the increment is so tiny to measure. In case that electromagnetic energy is fully converted into thermal energy of the object, the invariant mass of the particles that constitutes the object do not change. This implies that energy actually can be observed as mass. Thermal energy is actually the sum of potential energy and kinetic energy of the particles that constitute the object. So, what do you think? In my opinion, relativistic mass is true mass. It is not frame-independent because the motion of an object is relative. Why does an object with non-zero rest mass could not reach the speed of light? Kinetic energy of an object can be observed as inertial mass too. Thljcl 13:10, 13 November 2006 (UTC)
 * Take a look at mass in special relativity. And the history of this talk page. We don't use relativistic mass for "mass" because we already have relativistic energy for the concept of relativistic mass (just divide by c^2). On the other hand, we have a new conserved quantity (besides momentum and energy) in special relatitivity which needs a name, particularly because it is frame invariant quantity (unlike momentum and energy). This is the norm of the E-M 4-vector, and it turns out to be more or less what Newtonians and everybody else have been talking about for years, when they used the term "mass." So in special relativity, it is this (invariant mass) which is identified with the old classical Newtonian and historical mass (it's certainly what we weigh when we weigh an object). And this actually works out closer to GR mass, for many purposes as well. You can look at mass in general relativity, but for long distances and flat space, the source of gravity is more or less the SR mass, which means the invariant mass. It certainly is NOT relativistic mass--- you can't make (or see) a black hole in some inertial frames and not others, by increasing KE and relativistic mass of a gravitating object.  S  B Harris 21:19, 13 November 2006 (UTC)

What if kinetic energy of a moving body converted into thermal energy or other kinds of energy such as electromagnetic radiation? When a body moves too fast, it definitely could not turn into a black hole. However, this does not make me to change my mind. How could we know or perceive the gravitational field of earth? At first, we assume the earth remains at rest. An object with a certain distance from earth would fall on the earth. This is true if the observer remains at rest on the surface of the earth. Actually, an object with a certain distance from earth fall on the earth could only be observed or perceived by the observer who remains at rest on the surface of earth. This is totally different story for an observer that is falling toward the earth by the force of gravity. He could not notice that object is falling or moving. Indeed, he finds that the earth is accelerating toward him while the object remains at rest. What I mentioned is actually Equivalence Principle. Equivalence Principle is an important postulate of General Relativity. Constant accelerated frame could produce the same effect as constant gravitational field does. That is why an object could never turn into a black hole by increasing its kinetic energy. One could notice the change in mass of the object only in a constant inertial frame of reference. He could not step over to another frame of reference. Actually, suppose you could make a rocket that can accelerate approach the speed of light, you could not find any differences of your own mass with a balance when you are in the rocket. It is because for your own frame of reference, the speed of rocket is different from other frame of reference. You could never find the change in your mass because of your motion. When you are moving, you actually could not find out the your motion without referring to other object. Indeed, what you see is others are moving while you are not. Just as what you see in a car. In another word, a freely falling object is weightless. That is why when we mention the gravitational field of an object, we should assume that object remain at rest or an observer is remain at rest relative to the object. For a freely falling object above the earth, it has no weight and earth is accelerating toward it.Thljcl 00:13, 14 November 2006 (UTC)
 * I am missing your point. The equivalence principle applies to accelerated frames, not inertial frames. Certain gravitational field components disappear or appear in accelerated frames, and this is why mass needs to be defined according to inertia, not weight, in such frames. In various inertial frames there is total energy, which is frame-dependent, and there is invariant mass x c^2, which is frame-independent. This "rest energy"/c^2 is a better candidate for "mass" simply because it doesn't change with the inertial observer. Yes, it changes if you heat an object. If you heat an object, its rest mass and weight increase. Yes, rest mass (invariant mass) of systems also increases if the kinetic energies of objects in the system increase in a way which cannot be taken care of, by a simple change of inertial frame. For every system of objects, there is a inertial frame which minimizes the total kinetic energy of the system, but which may not reduce it to zero. That is the COM frame, where the total momentum is zero. In that frame, kinetic energy is minimized, but it may not be zero, and what there is left, DOES contribute to invariant mass. And would contribute to making a black hole as well. It's only the minimal kinetic energy you can't get rid of by observing from different inertial frame, which contributes to an object (or system's) overall gravitational field, inertia, and weight (if you can weigh it). For example, *all* the heat in a sample of ideal monatomic gas is present as kinetic energy. But if the gas is confined, you can weigh that kinetic energy just as well as if it was all stored as potential. It contributes to invariant mass in just the same way, because all the momenta zero out, and total energy is the same as system "rest energy" for all of these systems, even if the parts aren't at rest. So you're getting what you're asking for. It's only system kinetic energy which is the result of some system total momentum which is non-zero, which doens't contribute to its invariant mass. But that's a GOOD thing. S  B Harris 03:21, 21 November 2006 (UTC)

Can equivalence principle apply to an inertial frame of reference? Suppose you are in a space which is away from any gravitational field, you are in a rocket which accelerates upward with the constant acceleration of 1g. Could you ever distinguish whether you are in a gravitational field or not? When you are on earth, is the earth accelerate upward with the constant acceleration of 1g? (Ignoring the earth is rotating and orbiting around the sun) The earth is apparently an inertial frame of reference. So, we could regard the earth as a constant accelerated frame as well. (In fact this is not true since the value of g varies with the distance from earth, however, in a sufficienlty small region, this remains true. We can replace the gravitational field with many different constant accelerated frames.) Or, in another word, constant gravitational field (which does not exist) can be regarded as a constant accelerated frame or vice versa. Thljcl 14:33, 21 November 2006 (UTC)
 * No. An intertial frame is one in which Newton's first law holds and things float around "weightless." Even objects falling in g-fields from astronomical objects suffer microgravity due to tidal effects, so seem to be in inertial frames only to first order. If you can detect those tides (and you can) you can always tell the difference. Thus, equivalence principle holds locally but not over large distances. Nature seems to always be giving you a way to tell the difference between flat space, and what you see as an inertial observer falling along a geodesic in curved space.  S  B Harris 03:36, 13 December 2006 (UTC)

Nobel laureates
Should Wiki explain that the following Nobel Laureates are wrong in teaching that mass is velocity-dependent? (Or mass can be defined differently as long as groups of physicists understand each other. It is not a matter of right and wrong?)

•Leon Lederman, (Nobel Laureate 1988) The God Particle: If the Universe Is the Answer, What Is the Question? (Houghton Mifflin, 1993) p. 205

•Robert Laughlin, (Nobel Laureate 1998) A Different Universe: Reinventing Physics from the Bottom Down (Basic Books, 2005) p. 125

•Martinus J.G. Veltman (Nobel Laureate 1999) Facts and Mysteries in Elementary Particle Physics (World Scientific Publishing Company, 2003) p. 137

•Gerard ‘t Hooft, (Nobel Laureate 1999) In search of the ultimate building block (Cambridge University Press, 1997) p.17

•Julian Schwinger (Nobel Laureate 1965) Einstein's Legacy: The unity of space and time (Dover, 2002) p. 84

•Richard Feynman (Nobel Laureate 1965) Perfectly Reasonable Deviations from the Beaten Track, (Basic Books, 2005) "It was successful, the necessary consequential phenomena (like mass changing with velocity) were ultimately observed experimentally." p. 283.

•George Smoot (Nobel Laureate 2006) Physics 139 Homework, url: http://aether.lbl.gov/www/classes/p139/welcome.html User:Feynman66, 13 December 2006 (UTC)


 * See mass in special relativity. - mako 03:23, 13 December 2006 (UTC)