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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: whoever on 6 Aug 2010 07:11 "glird" wrote in message news:f5b48cc3-fe58-4888-81c3-0ec9128a5747(a)l20g2000yqm.googlegroups.com... >“Mass” denotes a >quantity of matter, whether or not it has weight (in grams) in a g- > field. Weight in a g-field is not measured in grams. Mass is measured in grams. >< 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. No .. you are wrong. Time dilation and length contraction etc is the same in both .. a moving observer does not have any effect on the length, mass, rate of time for an object .. both in SR and the Minkowski geometry that models it >>< 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. It is total energy (including the energy-equivalence of mass) that is conserved >>< 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. Irrelevant. You clearly did no understand the analogy >>>< Einstein wrote, "It is essential to have time defined by means of >>>stationary clocks in the stationary system, and the time now >defined >>>being appropriate to the stationary system we call it `the time of the >>>stationary system'." > He was, as usual, rightly wrong. > (Though he was right in that only a stationary esynched system would >have synchronous clocks, he was wrong about it being "essential that >etc." Indeed, since there is no such thing in the universe as a >stationary system, his Special Theory, as he said in his general >theory, is restricted to a hypothetical point. > 'stationary' was just a label. Again, you don't understand ><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”. ALL systems are at rest in their own frames. > I ask you again, Tom: Please discuss with me, in a non- >confrontational way, the meaning of each consecutive step and equation >in Einstein's paper. > The purpose is to put to rest the myriad arguments on these >newsgroups, as to what “these words” or “that” equation mean; both to >Einstein and by themselves. > Here is an example: In E's SR paper he set forth the thesis that if >a moving system set its clocks to read the same times as those of “the >stationary system, K”, they would disagree with cs K as to the >simultaneity of two given events. In HIS mind, the reason for that was >because clocks of an Esynched system would NOT have identical settings >as each other, but would lag behind each other in their direction of >motion by –vx/c^2 seconds. (In Minkowski's theory, that doesn't >happen. Instead, he says that the axes of the moving system rotate in >spacetime, by exactly the amount required to let the projected results >fit the LTE's predictions.) SR and Minkowski are identical in what they describe > However!! Here is something copied from my 2007 book, “A Flower for >Einstein”. Who cares .. from what you've posted you don't understand SR enough to comment .. let alone write a book worth reading or quoting from [snip rest unread] --- news://freenews.netfront.net/ - complaints: news(a)netfront.net ---
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: Da Do Ron Ron on 6 Aug 2010 14:02 Harald generously listed *two* allegedly supporting experiments: > - exact deflection of electron beams (Lorentz 1904, Einstein 1905). > - the effect of speed on clocks (Einstein 1905; applied in the GPS > system). I will simply ignore the first because it is not even listed here: http://www.xs4all.nl/~johanw/PhysFAQ/Relativity/SR/experiments.html As for the second, can Harald define "speed"? (Is it a relative speed or an absolute speed?) ~RA~
From: PD on 6 Aug 2010 14:17
On Aug 6, 1:02 pm, Da Do Ron Ron <ron_ai...(a)hotmail.com> wrote: > Harald generously listed *two* allegedly supporting experiments: > > > - exact deflection of electron beams (Lorentz 1904, Einstein 1905). > > - the effect of speed on clocks (Einstein 1905; applied in the GPS > > system). > > I will simply ignore the first because it is not even listed here:http://www.xs4all.nl/~johanw/PhysFAQ/Relativity/SR/experiments.html Why would you do that? Predictions come in two sorts -- that which can be tested in a targeted experiment, and that which is essential to the design of a device or a process (e.g. a practical application). He listed two of the latter. You cited a partial compendium of the former. The point is, relativity is so established that it is routinely used in everyday applications. If relativity did not make reliable predictions, these applications would work at best by accident. > > As for the second, can Harald define "speed"? (Is it a relative speed > or an absolute speed?) I'm not Harald, but I'm sure you've been told that as far as we know, all speeds are relative, and that's the context of the prediction. |