Is Length Contraction in SR physical??
in [Relativity]
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From: PD on 6 Feb 2010 15:17 On Feb 5, 8:16 pm, Ste <ste_ro...(a)hotmail.com> wrote: > On 5 Feb, 16:02, PD <thedraperfam...(a)gmail.com> wrote: > > > > > On Feb 4, 8:16 pm, Ste <ste_ro...(a)hotmail.com> wrote: > > > > On 5 Feb, 00:49, kenseto <kens...(a)erinet.com> wrote: > > > > > On Feb 4, 6:04 pm, mpalenik <markpale...(a)gmail.com> wrote: > > > > > > On Feb 4, 5:59 pm, "kens...(a)erinet.com" <kens...(a)erinet.com> wrote: > > > > > > > It it does violate the PoR. You made the contradcictory claims that > > > > > > the pole can fit into the barn physically (materially) an at the same > > > > > > time you claim that the pole cannot fit into the barn physically > > > > > > (materially)......that a violation of the PoR. > > > > > > No. The doors are not closed simultaneously in the pole's frame, nor > > > > > are the two ends of the pole simultaneously in the barn in the pole's > > > > > reference frame. In the barn's frame, the two ends of the pole are in > > > > > the barn simultaneously and the doors shut simultaneously. In the > > > > > pole's frame, the two ends of the pole are in the barn at different > > > > > times and the doors shut at different times. > > > > > Sigh..You are making the contradictory claims: > > > > 1. The pole can fit into the barn with both doors close > > > > simultaneously. > > > > 2. The pole cannot fit into the barn with both doors close > > > > simultaneously. > > > > Take comfort Ken that at least there's someone here who understands > > > your simple questions. > > > So far it appears that there are at least two people confused and > > incredulous. > > Ken has been confused about this for 15 years. We'll soon see whether > > you can be unconfused at the rate that most freshman students become > > unconfused about it. > > I don't know Ken's past history, but certainly he seems to be asking a > fairly reasonable questions this time - and judging by the responses, > it's a question that children get taught not to ask! When Ken started asking these questions 15 years ago, they were reasonable questions. When after a couple of years it was clear he was not listening to the answers given to his questions, the tone of the responses became a little different.
From: mpalenik on 6 Feb 2010 18:40 On Feb 6, 4:43 am, Ste <ste_ro...(a)hotmail.com> wrote: > On 6 Feb, 08:10, mpalenik <markpale...(a)gmail.com> wrote: > > > On Feb 5, 11:15 pm, Ste <ste_ro...(a)hotmail.com> wrote: > > > > > Length contraction must follow for logical consitancy based on other > > > > measurements. > > > > "Logical consistency" is a far cry from "experimental evidence". > > > If you don't think the universe has to be logically consistant, then > > the entire framework of physics, and science in general, falls apart. > > I agree the universe has to be logically consistent - I'm a > determinist, after all. The point is that most theories have some > element of unspoken assumptions, and so there is a lot of room for > "logical conclusion" that is neither central to the theory, nor > consistent with reality. > > I think the most spectacular unspoken assumption is that SR describes > "physical reality", as opposed to merely describing the behaviour of > EMR. Don't ignore my other replies since this one is a few pages later in the thread, but this is where you are confused. The behavior of electromagnetic radiation was already described by Maxwell's equations *before* relativity. What Einstein did was to combine these two postulates: 1) The speed of light is constant in every reference frame. 2) Maxwell's equations (which describe E&M) are true in every reference frame. From there he derived the effects that this must have on "physical reality" (to use your term). It is explicitly stated in Einstein's original paper that this is what he is doing.
From: Peter Webb on 6 Feb 2010 19:35 "Ste" <ste_rose0(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". Nor do you seem to understand Minkowski' s geometric arguments. 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. (Unlike GR which generalises this concept of space-time but needs quite advanced mathematics).
From: Ste on 6 Feb 2010 21:30 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? > > > 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*. > 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*. > 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?
From: Ste on 6 Feb 2010 21:35
On 6 Feb, 10:55, mpalenik <markpale...(a)gmail.com> wrote: > On Feb 6, 5:32 am, 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: > > > > > On Feb 6, 3:43 am, Ste <ste_ro...(a)hotmail.com> wrote: > > > > > > Yes, with a bit of jiggerypokery, I think I have drawn it correctly, > > > > > and indeed, it does become shorter in the x' orientation as against > > > > > the x axis. > > > > > Just to be sure we're on the same page, you should have something like > > > > this (I added the circle, which represents the proper length of the > > > > ladder):http://s424.photobucket.com/albums/pp327/mpalenik/?action=view¤... > > > > Yes, that's basically what I had but without the circle (I was just > > > using a line on the x-axis to represent the ladder). > > > The ladder lies along the x' axis. The x' axis is the rest frame of > > the ladder. > > > > > Keep in mind this is in *non-Minkowski* spacetime, which means it will > > > > produce the oppose results that relativity produces (length expansions > > > > instead of contractions, reversed breaking of simultanaity). > > > > Ah right, because the way I looked at it, if you were using the x-axis > > > of the diagram to measure, then the "width" of anything on the x'-axis > > > had actually reduced when viewed from the x-axis. > > > That's because you're doing it wrong. You can only measure the parts > > of the ladder that are intersecting with the regular x axis. The end > > points of the ladder are marked by dots in my picture. You'll notice > > that the ladder intersects the x axis but at different values of t'. > > Let me try to clarify--different parts of the ladder intersect the x > axis at different values of t'. It traces out a solid rectangle in > spacetime as it moves. Indeed. > You can only measure along the x axis at a given t the parts of the > ladder that intersect the x axis at that given t. Of course. Because t=0 represents what you're visually observing in the present. > The two ends of the > ladder intersect the x axis at *different* values of t'. This > corresponds to different *times* in the ladder's frame. Look at where > the t' lines extended from the endpoints of the ladder intersect the x > axis. You'll see the line they intersect to make a line that is > *longer* than the length of the ladder. This has nothing to do with > optical illusions. This has to do with the amount of space the ladder > traces out along the x axis as it moves through spacetime. I'm afraid I disagree with this interpretation. I'm reminded of Einstein's quip that the "only thing that gets in the way of thinking, is education". Trust me, the interpretation you are putting on this is *not warranted* by the observational evidence. |