Is Length Contraction in SR physical??
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From: Ste on 6 Feb 2010 22:26 On 6 Feb, 20:32, PD <thedraperfam...(a)gmail.com> wrote: > On Feb 5, 8:40 pm, Ste <ste_ro...(a)hotmail.com> wrote: > > > On 5 Feb, 18:43, PD <thedraperfam...(a)gmail.com> wrote: > > > > On Feb 5, 12:59 am, Ste <ste_ro...(a)hotmail.com> wrote: > > > > > It's laughable that two people who already claim to understand are > > > > patting themselves on the back for coming up with an allegedly > > > > "impressive" explantion, and yet the people to whom the concept was to > > > > be explained are still not convinced. > > > > I continue to be mystified by your expectation that it is the > > > objective of physicists to compellingly explain physics to > > > nonphysicists. > > > If they are *purporting* to explain, then it should be explanatory. > > That depends. It may be completely explanatory to someone with a bit > more background, while still a mystery to those missing a few key > concepts. > I disagree that for something to be explanatory, it must be > explanatory to *anyone*. I'm not saying it needs to be explanatory to anyone Paul. I'm saying that if you are *purporting* to explain something to a particular individual, then it is utterly risible for two people who already understand to be patting themselves on the back for conceiving an "impressive" explanation which actually left no impression at all on the person who needed an explanation, and to whom the explanaton was *purportedly* being given.
From: Ste on 6 Feb 2010 22:37 On 7 Feb, 00:35, "Peter Webb" <webbfam...(a)DIESPAMDIEoptusnet.com.au> wrote: > "Ste" <ste_ro...(a)hotmail.com> wrote in message > > news:12c2f6df-085e-4024-ad03-5bd5a7099bb3(a)d37g2000yqa.googlegroups.com... > > > > > > > On 6 Feb, 04:30, "Peter Webb" <webbfam...(a)DIESPAMDIEoptusnet.com.au> > > wrote: > >> "Ste" <ste_ro...(a)hotmail.com> wrote in message > > >> > Indeed. But understanding the physical nature of these theories is > >> > necessary for scientific advance. I mean, you can teach any fool to > >> > follow rules that are already laid down. But the people who are coming > >> > up with the rules need to have genuine understanding. > > >> Ohh, you mean insight into what is "really" happening. That is exactly > >> what > >> Minkowski did when he pointed out that the time and space transformations > >> of > >> Einstein were exactly the same as a rotation in spacetime of an invariant > >> vector, and that explained other stuff like Energy and Momentum. > > >> It also provided the basis for the General Theory of Relativity, which > >> uses > >> this concept as a base. It provides a link between the two theories which > >> does not rely on the mathemetics just happening to work out the same for > >> treating SR as a special case of GR. > > >> If you want "genuine understanding" of SR, Minkowski space-time is the > >> second thing you should learn, right after Einstein's algebraic approach > >> based on his two axioms. > > > I *do* have a genuine understanding already. > > I doubt it. If you genuinely understood SR you wouldn't have any problem > resolving the barn and ladder "paradox". I have resolved it, and I gave you your simple answer: *no*, the ladder does not fit. > Nor do you seem to understand Minkowski' s geometric arguments. Indeed, because I'm more interested in physical reality than geometry. > If you do > want a genuine understanding of SR, you will need to learn this. Its > actually not all that difficult at all; you don't need much maths beyond an > understanding of "imaginary" numbers, its very simple. I already do understand what SR describes, but *without* the maths. That's why I can give you an accurate description of what SR predicts when you give me examples that I can picture in my head.
From: Ste on 6 Feb 2010 22:40 On 7 Feb, 02:56, YBM <ybm...(a)nooos.fr.invalid> wrote: > Ste a écrit : > > > On 6 Feb, 10:29, mpalenik <markpale...(a)gmail.com> wrote: > ... > > Because *that* is what SR is all about - it is about describing the > > behaviour of *light*. > > No. So where is your *observational evidence* that SR describes something other than light? And I don't mean some Professor's opinion, I mean a documented *experiment* that proves that SR is not just about optical effects. > >> The differences in measurement are due to > >> the different coordinate systems. It has nothing to do with what you > >> *see* it has to do with how you make your measurements. > > > It has *everything* to do with what you *see*. > > No. Back to Reverend Ian Paisley mode. > >> When one > >> observer measures length, he measures along the x axis. When another > >> observer measures length, he measures along the x' axis. The proper > >> length of the object doesn't change, but the measured length has > >> nothing to do with optics, visibility, or propagation delays. > > > Of course the measured length has *everything* to do with optics. How > > do you think we usually carry out measurements? > > > And why do you think the ladder appears the correct size for an > > observer in the x' frame? > > Wrong again. > > Stop pretending talking abour SR when you're not, you are > talking about a fantasy out of you mind. No, *you're* taking about fantasy. I'm talking about the *physical reality* of these theories you claim to be expert about.
From: Peter Webb on 6 Feb 2010 22:43 "Ste" <ste_rose0(a)hotmail.com> wrote in message news:86583d1c-3ce6-4d27-b43b-8463952c1d02(a)z41g2000yqz.googlegroups.com... On 6 Feb, 10:29, mpalenik <markpale...(a)gmail.com> wrote: > On Feb 6, 5:01 am, Ste <ste_ro...(a)hotmail.com> wrote: > > > On 6 Feb, 09:23, mpalenik <markpale...(a)gmail.com> wrote: > > > But as I'm saying to you, I think you're confusing an optical effect > > with a physical effect. That is, you're confusing *appearances* with > > concrete reality. > > What part of this picture do you think is optical? It's *geometrical* > it doesn't have anything to do with what you can visibly see. Don't you realise that SR is about the behaviour of *light* - that is, EMR? And SR describes how *observations* made by way of *light* change in response to physical circumstances? ___________________________ No. SR says the length is contracted. It is. Doesn't matter if you measure its length with light waves, neutrinos, or a metre ruler. > > > An important point, however, is that neither one of the sets of axes > > > (either x,t or x',t') is inherantly better than the other. Neither > > > set is more correct than the other. > > > Indeed. > > How can you agree with that and claim that the differences in > measurement are optical? Because *that* is what SR is all about - it is about describing the behaviour of *light*. _______________________ No. Its not. It describes the behaviour of any particle or object capable of carrying information (causality). The *only* thing that SR is *not* required for is light, as the length transforms for ligh waves were already known to be the Lorentz transformations from solving Maxwell's equations. > The differences in measurement are due to > the different coordinate systems. It has nothing to do with what you > *see* it has to do with how you make your measurements. It has *everything* to do with what you *see*. _______________________________ What is observed. You don't have to "see it" at all; Einstein's transforms work in the dark just as well. > When one > observer measures length, he measures along the x axis. When another > observer measures length, he measures along the x' axis. The proper > length of the object doesn't change, but the measured length has > nothing to do with optics, visibility, or propagation delays. Of course the measured length has *everything* to do with optics. How do you think we usually carry out measurements? _________________________________ Lots of ways. Normally I measure length by puting a ruler next to an object. You put a ruler next to the ladder, you will see it has contracted exactly per Einstein. And why do you think the ladder appears the correct size for an observer in the x' frame? ____________________________ Without knowing what the x' frame is, I would hazard a guess and say the ladder is stationary in that frame.
From: PD on 6 Feb 2010 22:54
On Feb 6, 8:52 pm, Ste <ste_ro...(a)hotmail.com> wrote: > On 6 Feb, 17:14, PD <thedraperfam...(a)gmail.com> wrote: > > > On Feb 5, 8:03 pm, Ste <ste_ro...(a)hotmail.com> wrote: > > > > > Suppose events A and B are 10,000 m apart. The detectors X and Y are > > > > obviously 5,000 m from each event. Detectors X and Y are in motion > > > > relative to each other at a constant speed of 100,000 km/sec, along > > > > the line that includes A, B, X, and Y. > > > > > Now that you have some numbers, are you ready to proceed with the > > > > discussion as I've outlined? > > > > So you have A, B, and X, all on a common axis, and Y moving along this > > > axis relative to X at 100,000km/s? > > > Yes. > > Ok. > > > > > > > > > Thus, depending on X or Y, the events are simultaneous or not > > > > > > simultaneous. And since the same procedure is used in both, there is > > > > > > no obvious way to determine which of these is "true" and why the other > > > > > > is not "true". > > > > > > The answer to this will have to turn on a specific discussion of the > > > > > evidence. > > > > > Actually it doesn't depend on the details of the evidence. We have > > > > already determined that the procedure determines simultaneity or > > > > nonsimultaneity unambiguously. > > > > No we haven't! > > > > If X and Y are moving in such a way as to be approaching one event and > > > receding from the other, and if they are moving in *opposite* > > > directions (relative to each other - they may in fact be both > > > approaching one event and both receding from the other), then there > > > will be no simultaneity at all, because there has to be a time > > > interval for the measurement to take place, > > > Please look at the procedure again. > > I have. I can picture the situation in my head. > > > The only thing that is required is to note at the detector X or the > > detector Y whether the signals from the events arrive at the same time > > or at different times. This is a point decision. It is a yes or no > > question. "Signal from A just arrived at X. Did signal from B arrive > > at X at the same time? Yes or no." > > If detection is instantaneous (i.e. if a photon is absorbed > instantaneously), then it is possible for A and B to be simultaneous > according to both X and Y. However, if detection is not instantaneous, > then it is *not* possible. I didn't say "according to both X and Y". What I said in fact was the opposite. Please reread. What I did say is that X is *right* in concluding that A and B are simultaneous, based on the procedure we established as reliable. Also, Y is *right* in concluding that A and B are not simultaneous, based on the same reliable procedure. But yes, photons are absorbed instantaneously, or at least MUCH faster than the propagation delay for the signals to arrive. > > I'm working on the assumption that detection in the real world is > *not* instantaneous, but is a process that requires a time interval. > > > If the answer is yes, and if we ALSO know that the distance from X to > > A is the same as the distance from X to B (which we can check later if > > we wish), and if we ALSO know that the signal speeds from A and B are > > the same (which we can check later if we wish), then we KNOW the > > events A and B were simultaneous, even though they happened some time > > ago. Likewise, if the answer is no, then we KNOW the events A and B > > were not simultaneous, even though they happened some time ago. > > As I say, there is a third way here: the answer is "no", and we know > that the events were indeed simultaneous. How would you derive from the procedure we agreed upon, where the answer to the relevant condition is "no", that the events were nevertheless simultaneous? On what basis would you come to that conclusion. Do you need the procedure re-explained to you? > > > Do you agree that those are the right conclusions, based on the yes or > > no question above, and given that the other conditions can be > > established? > > No. I think your mistake is in assuming that both the photon and > detector have an absolutely zero diameter (and therefore detection > occurs as soon as the surface of the zero-diameter objects touch). In > reality, nothing in space will have a diameter of zero. I don't know why you think diameter has anything to do with it. Note the size of the distance between A and X and between B and X. If a detector is 1.5 mm across, do you think this is going to be a dominant effect? > > > > and if they are moving in > > > opposite directions along an axis in common with A and B, then there > > > is *no way* they can maintain equidistance for the whole of that time > > > interval. > > > Nor do they have to. But if the events leave a mark, then it is > > certainly possible for anyone to go measure with a tape measure any > > time later the distance from the marks to the detector and DIRECTLY > > MEASURE that distance, right? > > Yes, and if you do that according to my assumptions above, you'll find > that the detection *process* takes place over a spatial distance, and > you'll find that those distances are *not* the same for both X and Y. The only distance that matters is the distance the signal has to travel, do you not agree? The signal starts at the location of the event, where it leaves a mark, and the signal stops at the location of the detector, where there is also a mark. Then we can certainly measure the distance between the marks at our leisure, no? > > > > The fault, therefore, lies in saying that X and Y are "midway between > > > the events", when in fact they are not. > > > Let's not jump ahead. I'll show how this works in Einstein's > > distillation of this kind of experiment in a bit. > > > I just want you to understand the conditions that we have to > > establish, and what consequences would necessarily follow from that. > > Ok. > > > > > If the procedure is trustworthy in > > > > frame X, then it is trustworthy in frame Y. If the two frames are > > > > otherwise equivalent, there is no reason to say, "But the answer > > > > arrived at in X is right and the answer in Y is wrong." We've already > > > > agreed this procedure works. > > > > The procedure is not trustworthy. The two frames are not equivalent, > > > because X and Y do *not* remain midway between the events for the > > > entirely of the time interval (and, more importantly, the deviations > > > from the midpoints are not symmetric). > > > If the events leave a mark, and we can later measure the distance from > > the marks to the detector and we find those distances are equal, would > > you then agree the conclusions are the necessary ones? > > Yes I would agree with that, although I would warn you that I already > have the picture drawn in my head. |