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From: Inertial on 4 Aug 2010 19:27 "Da Do Ron Ron" wrote in message news:2e052410-588c-4f0d-a9ac-a91cacf24dbe(a)j8g2000yqd.googlegroups.com... > >Earth to glird: > >Einstein's "stationary" system was not Newton's (absolutely) >stationary system, >but you are of course correct about the latter's clocks becoming truly >synch'd >via even Einstein's definition; however, how are we to find such a >truly at-rest >system in order to make us of its truly synchronous clocks??? We can't as there is no such thing as a truly (absolutely) at rest system, nor truly (absolutely) synchronous clocks (unless, trivially, they are at the same location).
From: harald on 4 Aug 2010 19:41 On Aug 4, 8:38 pm, Da Do Ron Ron <ron_ai...(a)hotmail.com> wrote: > Earth to glird: > > Einstein's "stationary" system was not Newton's (absolutely) > stationary system, > but you are of course correct about the latter's clocks becoming truly > synch'd > via even Einstein's definition; however, how are we to find such a > truly at-rest > system in order to make us of its truly synchronous clocks??? > > ~RA~ That was the main point of at first Newton, and later also Lorentz and Einstein: in theory at least, you CANNOT determine such a "truly at rest" system; you can only determine a class of "inertial frames". Newton and Lorentz found it still a useful concept to mention, while Einstein found indeterminable concepts completely useless. That is a philosophical dividing line. Harald
From: Tom Roberts on 4 Aug 2010 22:22 Da Do Ron Ron wrote: > On Jul 28, 2:10 pm, Tom Roberts <tjrob...(a)sbcglobal.net> wrote: >> Da Do Ron Ron wrote: >>> Can we now agree that a correct measurement of the length of a >>> passing rod requires absolute synchronization? >> No. In part because you have not defined "absolute synchronization", >> and in part because there is nothing "incorrect" about measuring the >> length of a passing rod by marking its endpoints simultaneously and >> then ascribing the distance between marks as the length of the rod. >> After all, that is what we mean by those words. > > It's odd that we can agree that special relativity does not have > absolute > simultaneity (or synchronization) without even mentioning a definition > of > absolute synchronization, much less being forced to supply such. Not so odd. For any sensible meaning of "absolute synchronization", SR does not have it. > This proves that in order to merely agree or to disagree about the > existence of absolute synchronization, there is no need to produce > an absolute synchronization procedure. In order to assert the need for it, it must be defined. In order to assert that SR does not have it, only the general meaning of "absolute" is needed. > As you shall soon see, not only is SR's passing-rod length measure- > ment incorrect, but even it's "stationary" measurement is bogus. > > The length of a "stationary" rod is euphemistically called "the > proper length." This is a meaningless appellation unless one can > prove that one's ruler was not physically contracted during the > measurement process. I see no such proof in SR. You are confused. Nobody has any intention of "proving" such assertions. This is the DEFINITION of "proper". We use rulers as measurement tools, and they measure what they measure. This ruler I hold in my hand is CLEARLY AND VISIBLY "not physically contracted" -- it measures 1 foot long, as it should. (More specifically, all the inter-atomic bonds of the ruler have their equilibrium lengths in their instantaneously comoving inertial frames.) This is what we mean by these words. You want to ascribe some sort of "absolute" meaning to "length" and "physically contracted". until you give detailed meanings of these phrases, they are meaningless when you attempt to use them. They have their usual meanings when I use them. > I notice that you unhesitatingly fell into the same euphemistic > mode in this case by saying "marking its endpoints simultaneously." > And this was just after you had agreed that SR does not have true > or absolute simultaneity! Hmmm. Simultaneity is determined by synchronized clocks at rest in an inertial frame. It is not "absolute" in any sense. > It's either simultaneous or not. And in SR, it's not. No. In SR whether or not a given pair of events are simultaneous depends on which frame one is using (and many pairs of events are not simultaneous in any frame). Again, you attempt to ascribe some "absolute" meaning to words that do not have such aspects. > You need to fully describe SR's procedure for measuring the length > of a passing rod. I did: mark the endpoints simultaneously in your frame and then measure the distance between marks -- that is the length you measure for a moving rod. Note it cannot be said that this is "the length of the rod", but only "this is the length measured in this frame for that rod" (saying "length of the rod" implicitly implies an attribute intrinsic to the rod, and this is not). > The entire burden of proof lies on your shoulders because you are > claiming to have a correct measurement system. I need do nothing > but beg for the proofs. I have no interest in "proving" anything to you. You need to learn something about modern physics before there is any point in continuing. If you want to discuss "absolute simultaneity", "absolute synchronization", or related quantities, you must define what you mean by them, and how they can be implemented in the world we inhabit. Tom Roberts
From: Tom Roberts on 4 Aug 2010 22:55 Da Do Ron Ron wrote: > On 7-30-2010, T Roberts wrote to Harald, in part: >> ...any effect that depends upon arbitrary human choices for description cannot >> possibly model a real physical phenomenon, and is "not real" in that sense. >> One instance of this is that any coordinate-dependent effect is "not real", >> and both "time dilation" and "length contraction" are coordinate dependent. > > Therefore, SR's "length contraction," "time dilation," and "mass > variance" > are all irrelevant to physics. (Because they do not, as you rightly > said, > pertain to physical phenomena.) This is not true. For instance, the "time dilation" of a high energy muon beam makes it possible to construct beamlines for muons that are hundreds of meters long. Just as rotating a ladder to get through a narrow doorway does not affect the ladder but has physical consequences, so too "time dilation" and "length contraction" do not affect the object ITSELF, but can have physical consequences. > [... further nonsense in the same vein as before...] > When the twins of the "Twin Paradox" are replaced with clocks, and a > third clock is added, then we have direct proof that clocks run at > different physical rates in different inertial frames. Not true. This only shows that the clock rate COMPARISONS depend on their relative motion. (They also depend on the method of comparison.) When at rest in any inertial frame, a standard clock ticks at its standard rate IN THAT FRAME. So clocks do NOT "run at different physical rates in different inertial frames" -- they run at their standard physical rate. The world is more complicated than your expectations. There are experiments that implement the twin scenario, and their results are consistent with the predictions of SR. Tom Roberts
From: Tom Roberts on 4 Aug 2010 23:12
harald wrote: > as you should know, SRT does NOT make any claims about > physical reality. SR is a MODEL of physical reality within a specified domain. Within that domain it is an accurate description of physical phenomena. Modern physics makes no "claims about physical reality", but instead MODELS it. That is, there is no expectation that the mechanisms in the model are "what nature actually uses"; it is only claimed that the model gives accurate results within its domain. > Most of our disagreements are about physical > reality, and now you pretend that you make no claims about it. You actually have no idea whatsoever about what "physical reality" is, either. All you have are mental MODELS you think are appropriate. We differ in the MODELS we use. Mine (SR) has the advantage of extensive experimental support in its domain; I have no idea what model(s) you are trying to use. >> One instance of this >> is that any coordinate-dependent effect is "not real", and both "time dilation" >> and "length contraction" are coordinate dependent. > > No, that is NOT an instance of that: here you confuse the effect of a > different point of view (no change of state, only a change of its > description) with the coordinate dependent observation of a physical > effect (a change of state that can be hidden by a simultaneous change > of perspective). > Kinetic energy for example is coordinate dependent, but the change of > state of an accelerated particle is certainly "real" in the sense that > something physical happens with it: the impact phenomenon is not > coordinate dependent. Similarly is the time dilation phenomenon in a > muon ring not coordinate dependent. You are confusing coordinate-dependent effects with coordinate-INdependent effects. Acceleration is complicated, so let me not attempt to discuss it. Instead, consider two identical bullets, one traveling at 100 m/s and one traveling at 1000 m/s relative to the target. The first will produce much less damage in the target than the second, even though in their respective rest frames the kinetic energy of each bullet is zero, and those velocity values are coordinate dependent. What you are missing is that there is also a coordinate-INdependent method of discussing such collisions, and they properly predict the difference in damage to the target. Look up "Mandelstam variables" -- "s" is what replaces kinetic energy in a coordinate-INdependent (frame-INdependent) way. The same sort of thing can be done for acceleration. By being careful about coordinate dependence and independence one can separate which aspects are modeling some physical phenomenon, and which aspects are merely coordinate issues. You are too sloppy above to do that. The "time dilation" of a muon is indeed coordinate dependent in the sense that the measured muon lifetime depends on what coordinates are used (i.e. in which inertial frame the measurement is made). Such measurements of course do not affect the intrinsic lifetime of the muon. Tom Roberts |