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From: Koobee Wublee on 6 Aug 2010 02:57 On Aug 5, 12:31 pm, Tom Roberts < wrote: > PD wrote: > > Lots of important physical properties in physics are > > "merely observer-dependent quantities". Kinetic energy and momentum, > > for instance, both of which play a key role in conservation laws that > > are considered central to physics. > > I disagree. Kinetic energy and (3-)momentum are not involved in any important > conservation laws. Both are merely related to parts of the actual law: > conservation of 4-momentum. Note that this law is not observer dependent; nor is > it frame or coordinate dependent. Note also that the context here is SR (not GR). > > For instance, to get conservation of 3-momentum one must project > the conservation law for 4-momentum onto an inertial frame. I think Professor Roberts was somewhat intoxicated writing this post that yours truly is replying to. <shrug> > Nature uses no observers, so valid models of physics must not use observers, or > at least be independent of observer. Although nature care no observers, it is sentient beings like ourselves that are interested in observing the nature from our very point of view. That is why it is impossible to describe a geometry without specifying a set of coordinate system first. <shrug> Perhaps, these mysticisms in physics in the past 100 years were started by intoxicated self-styled physicists with the daunting tasks of educating the next generation of self-styled physicists who cannot think for themselves anymore. <shrug>
From: harald on 6 Aug 2010 08:08 On Aug 6, 5:12 am, glird <gl...(a)aol.com> wrote: > On Aug 4, 11:27 pm, Tom Roberts wrote: [..] > >< When you rotate a ladder to get through a narrow doorway, you do not affect the ladder itself, but the rotation has physical consequences. Similarly in SR, relative velocity is an analogous rotation that does not affect the object itself, but has physical consequences. > > > In SR, Einstein assumed that the axes of differently moving systems do NOT rotate. Right - but besides the point. Obviously, *relative* velocity cannot tell us which, if any, is physically affected by velocity. However, the claim that a ladder *is not affected* by rotation (a change of state) is already wrong, the physical effects are merely invisibly small for us; an elaboration about the *physics* shows just the contrary of its intended *geometrical* purpose. For example, rotation has in theory an extremely small effect on the radioactivity of C14 isotopes at the ladder's ends. Langevin gave a better example with the space traveler in order to illustrate that, as he put it, 'only a uniform speed relative to [the ether] cannot be detected, but any change of speed [..] has an absolute sense'. [..] > ><You did not read his paper carefully enough. He EXPLICITLY said that he was using the term "stationary system" as a LABEL, to distinguish it from other inertial systems. It is a label that can apply to ANY inertial frame (see the first paragraph of I.1 of Einstein's 1905 paper "Zur Elektrodynamik bewegter Körper"). In SR there is no need for any stationary system in YOUR sense -- you applied a PUN and read more into his word choice than is actually there. > > > True. It was, however, implicit that clocks set by his method would > be synchronous if and BECAUSE the given system (K) was physically at > rest in his empty space. No, not at all: K in that paper is an arbitrary inertial system. > I ask you again, Tom: Please discuss with me, in a non- > confrontational way, the meaning of each consecutive step and equation > in Einsteins paper. The following citation may be helpful: "We [...] assume that the clocks can be adjusted in such a way that the propagation velocity of every light ray in vacuum - measured by means of these clocks - becomes everywhere equal to a universal constant c, provided that the coordinate system is not accelerated. [..] "the principle of the constancy of the velocity of light," is at least for a coordinate system in a certain state of motion [..] made plausible by the confirmation of the Lorentz theory [1895], which is based on the assumption of an ether that is absolutely at rest, through experiment" - Einstein, 1907 [..] > Tom!! The purpose of that long harangue was to gain your attention > wrt the following questions: > 1. How do rotations and projections explain the length contractions > found by using Esynched=esynched clocks to plot the positions of the > ends of a relatively moving rod? > 2. How does Minkowski-rotations and projections explain the esynching > per se? I'll leave that for Tom. ;-) Cheers, Harald
From: Tom Roberts on 6 Aug 2010 19:21 glird wrote: > On Aug 4, 11:27 pm, Tom Roberts wrote: >> < In SR, "time dilation" and "mass variance" do not affect the object >> ITSELF, they are artifacts of measuring a moving object. > > > In SR they do. In Minkowski's mathematics (Minky-math) they don't. Not true. You attempt to make a distinction without a difference. >> < And we no longer say "mass variance", we call the quantity that varies >> "energy", not "mass". > > > Given that the equation e = mc^2 (energy equals mass times {the speed of > light in vacuo} squared) has been experimentally verified, explain how the > quantity of energy can vary if the m and c do not. You do not understand what E=mc^2 means. It means the REST ENERGY of an object is proportional to its mass. For moving objects, their mass remains fixed but their energy is increased. >> < When you rotate a ladder to get through a narrow doorway, you do not >> affect the ladder itself, but the rotation has physical consequences. >> Similarly in SR, relative velocity is an analogous rotation that does not >> affect the object itself, but has physical consequences. > > > In SR, Einstein assumed that the axes of differently moving systems do NOT > rotate. You don't understand. In SR, relative velocity is ANALOGOUS to a spatial rotation, but is not the same. It is a rotation in a space-time plane, not in a space-space plane like the ladder. >> You did not read his paper carefully enough. He EXPLICITLY said that he >> was using the term "stationary system" as a LABEL, to distinguish it from >> other inertial systems. It is a label that can apply to ANY inertial frame >> (see the first paragraph of I.1 of Einstein's 1905 paper "Zur >> Elektrodynamik bewegter Körper"). In SR there is no need for any stationary >> system in YOUR sense -- you applied a PUN and read more into his word >> choice than is actually there. > > True. It was, however, implicit that clocks set by his method would be > synchronous if and BECAUSE the given system (K) was physically at rest in his > “empty space”. That is just plain not true. Einstein never mentioned "at rest in empty space", and in SR there is no way to define it. > [... too much nonsense for me to deal with] Tom Roberts
From: glird on 6 Aug 2010 20:56 On Aug 6, 7:21 pm, Tom Roberts wrote: > glird wrote: > >>< Given that the equation e = mc^2 (energy equals mass times {the speed of light in vacuo} squared) has been experimentally verified, explain how the quantity of energy can vary if the m and c do not.> > >< You do not understand what E=mc^2 means. It means the REST ENERGY of an object is proportional to its mass. For moving objects, their mass remains fixed but their energy is increased. > You're talking about the wrong equation, Tom. The ones you refer to seem to be Longitudinal mass = m/q, Transverse mass = m/Q, in which Q = q^2 = c^2 - v^2, mass is the weight-is-a-form-of-energy of moving objects, and m is your "REST ENERGY" of a body, i.e. its energy when at rest on Earth. glird
From: artful on 6 Aug 2010 23:14
On Aug 7, 10:56 am, glird <gl...(a)aol.com> wrote: > On Aug 6, 7:21 pm, Tom Roberts wrote: > > > glird wrote: > > >>< Given that the equation e = mc^2 (energy equals mass times {the speed of light in vacuo} squared) has been experimentally verified, explain how the quantity of energy can vary if the m and c do not.> > > >< You do not understand what E=mc^2 means. It means the REST ENERGY of an object is proportional to its mass. For moving objects, their mass remains fixed but their energy is increased. > > > You're talking about the wrong equation, Tom. No .. hes not > The ones you refer to seem to be > Longitudinal mass = m/q, > Transverse mass = m/Q, I'm well aware of them. That is not what Tom was talking about. He is talking about proper/rest/invariant mass. Not the two frame- dependent masses. > in which Q = q^2 = c^2 - v^2, mass is the weight-is-a-form-of-energy > of moving objects, and m is your "REST ENERGY" of a body, i.e. its > energy when at rest on Earth. It has nothing to do with earth. |