Pete

I don't believe that is the case here. The dictionary defines open minded as receptive to arguments or ideas which seems quite accurate to me. What sense is that?

That mass-shelll condition refers to the fact that no matter what energy a particle has its energy and momentum will always satisfy the condition wherein E^2 - p^2 = m^2 where E = inertial energy, p = momentum and m = particles proper mass.

You're right. That is a very confusing question to me. I'm not sure what it is that you have in mind. Let's take it one step at a time. First lets use a solid example and walk through the measuring process. We'll use the double-silt experiment since it is prefect for clarification purposes, especially for the question that you asked. The term quanta is an adjective which tells you that the quantity that it is referring to comes in discrete quantities. Thus you can say that an electron is a quanta. Now consider something that isn't a quanta such as time(I hear that there is some suspicion that this may not be the case but I'm ignoring that). Time is not quantized in that it doesn't come in lumps so one can't use the term quanta to describe it. Nobody knows. QM is a theory of matter. It exists because some people invented it. QM describes nature. Why nature behaves as it does is a mystery.

Use a dictionary

Huh? Who said that there was? I sure didn't. I was referring to what Martin indicated would be the case in the future regarding the definition of mass. Recall Martin's comment I consider things like deleting those links (which are URLs to references, derivations and "textbook" definitions) as being censorship. I've already decided what to do in the future so there is no longer a problem. Let's let this die shall we?

I've been curious about this lately so I wanted to ask a question for the folks here. Who among you consider themselves to be open-minded physicists? For those who consider themselves to be open-minded can you think of a concrete example? Please explain what it means to you for a physicists to be open minded? Thank you all in advance. Pete

Comcast just stopped providing access to a newsgroup server. Does anyone know of a newsgroups server that can be used by the general public? Thanks.

I've changed my mind for the moment. I've decided to PM people when I want to mention this subject. Otherwise I'll avoid the subject. I have to say that this cencorship is a poor way to run a forum though. You're very welcome. Due to the censorship mentioned above I've decided that is how I will be handling things like that in the future, i.e. not in open forum but in PM Please let me know. Its probably a problem with the font. I had struggled with what symbols to use. I wanted the reader to focus on the subject and not be worried about notation and whether they symbols used were "pretty" or not. There were even times when I chose to use [math]\mu[/math] for [math]m_0[/math]. There is a general tendancy to replace write proper quantities with the associated Greek letter. Thus [math]\tau[/math] is used for t and [math]\sigma[/math] is used for s. [math]\mu[/math] is theGreek letter for m. I dislike that notaton myself. Mass is not a vector quantity. The complete definition of mass requires a second rank tesor to fully describe it, i.e. the stress-energy-momentum tensor. From that tensor one can see that pressure is also a source of inertia. If you have Schutz's book on GR then you can see how it is derived. Schutz has a nice GR book. Have you read it? iNow - In case you forgot I placed you on my ignore list. You should keep that in mind in case you were expecting me to either read your post or post a response.

Yes. It is. Please do more than merely say "No its not." since merely objecting helps nobody. My guess is that you're used to seeing people define the mass of an object according to the magnitude of the object's 4-momentum. That doesn't work in general since such a 4-vector doesn't aways exist, as I already indicated. When are you restricting the definition to a the very specific case of elementary particles rather than being as general as possible? Especially in those cases when a body is under stress as in the example I gave. Its good to do so especially since that has even appeared in a problem sections in a relativity text I had. Its good to learn relativity in a way such that one can solve any problem that could ever be posed to them. That is incorrect as I already indicated in the example I gave of a body under stress, i.e. (E,p) does not form a 4-vector. Is there a reason you ignored that portion of my response? The example I gave is quite valid. In fact you didn't even post a proof otherwise. All you did was to claim it was wrong. That kind of response is of no use to anybody. Merely claiming something is wrong can never be considered a proof. Martin - Since you ignored my question then I'll have to assume that you intend on censoring what I post on this topid from herein. As such I will will simply PM the person rather than post in the thread.

I disagree. I doubt that such heating would be significant. Consider how small the variation in pressure would be due to keeping the gas at a particular pressure. The pressure would depend a great deal more simply by firing it which would loose gas and decrease the pressure. I doubt that all air guns have the same amount of gas in the cartridges when they are being fired.

I'm merely trying to figure out what you were referring to when you said you were the one who added in that limit from who knows where. since I never brought up anything other than intrinsic spin. But you claimed here that I added something. Please show me what I said which led you to this conclusion. Thanks.

Mass is defined according to momentum. In the case of proper mass m0' date=' its defined in the limit where v -> 0 as in m[sub']0[/sub] = limit (v->0) p/v. This assumes that the limit exists and is independant of the state and orientation of the body. When the body has stress in it then the limit will depend on the orientation of the body. In such case there is no unique value that can be assigned to the limit since it would depend on the orientation of the body. I derived an example in this page http://www.geocities.com/physics_world/sr/inertial_energy_vs_mass.htm See equation 4. What I'm saying here isn't anything new. Its just not a well known fact. But it can be found in treatments such as Rindler's SR text or perhaps Mollers. One might attempt to define proper mass according to the magnitude of the stressed bodies 4-momentum but when a body is not isolated it will not have a 4-momentum (i.e. the quantity (E,p) will not be a 4-vector).

So who was talking about angular momentum? Not I. I was talking about intrinsic angular momentum, i.e. spin.

Just because ~60% of physicist disagree with me doesn't mean anything other than they disagree with me. I am merely stating my personal opinion and what I choose to do. My opinion is firmly based on physics and a thourough study of the concept of mass in relativity. I am not alone in this view as evidenced in various physics texts and journal articles (e.g. American Journal of Physics). And this is not merely a semantic issue either since there is no way to define proper mass in all possible cases (proof provided upon request). Frankly most physicists who object to the idea of relativistic mass do so because they don't fully understand relativity in regards to the inertia of stress and the stress-energy-momentum tensor. And the link had nothing to do with this point since the material on that page is a derivation/justification of the expression of the momentum of radiation.

Not according to Severian. I did what? Where?

I don't see why that would be true. When it was thought that the proper mass of a neutrino was zero it was still known that anti-neutrinos existed. A particle can have an antiparticle even when its proper mass is zero.

The answer to your question hinges on the definition of the term mass (the definition of which a controversial subject). The answer to your question is forthcoming once you have the definition of mass in place. Simply put, mass is defined so that momentum p is conserved, i.e. mass is defined as the m in p = mv. Note: I use the symbol m to represent inertial mass (often referred to as relativistic mass). This should not be confused with proper mass which is often represented using the same symbol as Severian has above. Strictly speaking one defines m so that mv is a conserved quantity in elastic collisions in an inertial frame of reference. One then defines this product as the momentum of the particle. That an em wave has momentum can be shown my demanding that the total momentum of a system be conserved in all processes, both mechanical and electromagnetic. I posted this derivation on my website at http://www.geocities.com/physics_world/em/momentum_of_radiation.htm That an electromagnetic field behaves as if it has mass dates back as far as 1885 and was due to J.J. Thomson who noted that a charged conductor in motion behaves as if its mass increases. You can glean from my comments above that I disagree with this assertion. To say that only rest mass is used in relativity is a bit misleading. Strictly speaking one cannot define mass in all generality as proper mass (aka rest mass) since it only works in special cases. As far as being out of date - That's a bit misleading too. In particle physics it is convenient to use the symbol m for proper mass and then symbol refer to it as “mass” just as one uses the symbol “T” for a particle’s lifetime and refer to it only as “lifetime” and not “proper lifetime.” There is basically a gentlemen’s agreement among practitioners that the “proper” is understood. Otherwise it’s a pain in the butt to have to keep adding the adjective “proper” before the terms. However when one is working in GR or cosmology one has to be a bit more careful. For example; if you were to look in Peeble’s cosmology text then one would see that inertial mass and gravitational mass are not the same as proper mass. In fact they are different. The former includes terms which take stress into account since stress has inertia and therefore mass. Sounds like a jerk to me. I agree with Martin. He was quite right when he said Mass isn't a completely simple concept. As Max Jammer wrote in Concepts of Mass in Contemporary Physics and Philosophy' date=' page 167

Are you saying that all particles must have a non-zero intrinsic spin?

Same here. I guess he means that in non-rel qm spin is added ad hoc where perhaps in rel qm it can be derived?

I find myself in agreement with big314mp to the extent that the question could have been stated a bit better. Something is said to be necessary when it is of an inevitable nature or when it is logically unavoidable, that cannot be denied without a contradiction or determined or compulsory, i.e. required. One must first refine more of what property of releaitivity one is speakling about before you can determine if it meets the requirement that is being sought after. For example: all scientific principles must be infallible, i.e. all reasonable compliance to a theory must be born out in experiments. One might as of a theory "Has it been proven to be valid under any and all possible circumstances. Since it would take an infinite amount of time, money and reseources to be completely tested then I believe there is a practical limit where the wise physicist would not demand that all possible experiments be carried out. Muff said.

Since there would be deformations due to the induced stress in body then different materials would deform in different, but similar, ways, I think that they'd al still be cylinders though. Isn't there anybody in the know who is in willing to take a shot at answering this question? I sent it to my old college physics advisor and he told me to recalculate it. I be;ieve that he means to tell me that I made a simple mistake (He rarely gives direct answers). I plan on redoing the work from scratch No takers though huh? Sorry I haven't posted recently. I've unexpectedly been in the hospital for a bit. Pete

I'm doing it only to see if I can solve it. No other reason.

That can't be used as a definition because there are quantum states for which there is no associated wave function.

I tried calculating the mass of a rotating cylinder but since I got the wrong answer I must have made a mistake somewhere. Can someone check my work and see if they can spot where I went wrong? The derivation is at http://www.geocities.com/physics_world/sr/rotating_cylinder.htm Thanks Pete

Up to now I've associated with either joking or sarcasm. I've only used it to denote joking. I see now that my association of it with sarcasm is invalid. Thank you for the clarification Phi.