Talk:Mass/Archive4

message: 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)
replies: text: 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)
thread_title: Intertial, graviational, active ??

message: 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)
replies: text: 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. SBHarris 21:19, 13 November 2006 (UTC)

text: 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. SBHarris 03:21, 21 November 2006 (UTC)
replies: text: 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.  SBHarris 03:36, 13 December 2006 (UTC)
thread_title: Relativistic mass is a better definition of mass than invariant mass

message: 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)
thread_title: Nobel laureates