Is Length Contraction in SR physical??
in [Relativity]
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From: PD on 11 Feb 2010 10:21 On Feb 11, 1:04 am, Paul Stowe <theaether...(a)gmail.com> wrote: > On Feb 10, 11:36 am, Ste <ste_ro...(a)hotmail.com> wrote: > > {Snip...} > > > The question therefore remains, how can the speed of propagation > > possibly be measured to be constant in all frames. > > The answer to your question is actually simple and 'intuitive' if you > think > about what must happen in a medium. The propagation of any type of > disturbance travels by 'conduction' from one entity to the next. Well, that's how disturbances travel *in a medium*. But it certainly isn't the only way that disturbances can travel. And in fact, the *reason* way disturbances travel in a medium is that the physical laws that govern the dynamical behavior of the medium take a particular form. This form occurs frequently in nature and so is given a particular name so that it can be recognized when it occurs again: it's called the wave equation and is recognized by its mathematical form. Whenever the physical laws of a medium can be algebraically manipulated to be in this form, then you can be sure the mathematical solutions of that equation will also embody themselves physically as a traveling wave in the substance. Note that this is not a given. Sometimes the physical laws of a substance are not of the form that can be manipulated into this form. And so even though it may seem intuitively plausible that there is conduction from one element of the substance to the next, no waves are expected, and in fact in such substances (though they are rare) no waves are observed. (And it simply isn't true that you can algebraically manipulate *anything* to make it look like a wave equation.) But on the other hand, there are other instances where the laws of physics governing the behavior of a system that totally LACKS a medium *still* can be placed in this mathematical form. In that event, you would expect that wave solutions to that equation would manifest themselves as physical waves, even in the absence of a medium. And this is precisely what happens in several cases -- the laws of electrodynamics and the laws of the propagation of fermions among the most famous. In summary, it is certainly true that waves occur in a lot of material media, and that it can be described as the successive interactions between adjacent elements of the medium. However, the presence of successive interactions between adjacent elements of a material medium does not guarantee wave propagation, nor is the presence of a material medium *required* for waves to be present. > This > is > set by the mean speed and spacing. If the medium is 'incompressible' > the > entities are all touching (spacing is zero) and the entities > 'infinitely > hard' In that case, the speed of propagation is infinite, and no > delta > 'pressures' are possible 'within the medium. OTOH, in any > compressible > medium there is spacing, and the entities have momentum and energy. > This > results a distinctive independent set speed by which any disturbances > (like wave propagation) will occur. This is designated as c for ANY! > medium > > Now it should be obvious that in the case of a medium it is this > process > that always dominates... The speed of sources must, by that > constraint, > alter there emission/field profiles to conform to this limitation. > > So now, start with a source of a omni-directional wave generator 'at > rest' > with respect to the medium. The resulting waves propagate outward 'at > c' > in all directions, resulting in a perfectly spherical field form. > Next, > give this source some speed v, obviously c hasn't changed so, in the > direction of motion the source is displacing forward at v so each > wave > front must be separating 'from the source' at c - v. In the > perpendicular > (transverse) direction the wave fronts are still separating from the > source at c. Thus, for the hemisphere in front of the moving source > the > wave field form is no longer spherical, but flatten into an > ellipsoid. > Now what happens to the back half??? Intuitively you would think > that > the wave front would be separating 'from the source' at c + v. > > However, remember that a wave is an oscillation (a back & forth > motion) so, > one cycle is c - v and c + v.. It turn, the cycle must remain in- > phase > with the rest of the field (it's one contiguous field). Thus the > actual > distance of the wave form must contracted by Sqrt(1 - [v/c]^2) on the > axis > of motion. The end result, the field flattens (distorts) into an > ellipsoid who's radius is defined as a function v multiplied by the > cosine > of angle (w) relative to the axis of motion. > > R(w) = R[Sqrt(1 - [vCos w/c]^2)] > > Now, look at a situation where we have two interacting fields in > equilibrium. > If at rest the centerline distances are, say, x. Then, if both are > in > uniform motion each field so x -> x' = xSqrt(1 [v/c]^2). Now, > consider > the QM interpretation of matter. If matter consists of waves it makes > no difference what particular type, all wave must behave this way. > > Now, let's thake the classic MMX and evaluate it in the context of a > QM > wavicle system. The time it take a photon to to complete a complete > transit is L/c and, because the system is moving, in axis > perpendicular > axis L = 2d/Sqrt(1 - [v/c]^2)... Along the axis of motion the matter > contracts and d -> d' = dSqrt(1 - [v/c]^2). The round trip time is > L = 2d'/(1 - [v/c]^2) = 2d/Sqrt(1 - [v/c]^2). > > The result is obvious, the reason is likewise obvious. > > Last I checked any number divided by itself is unity, thus, > > Sqrt(1 - [v/c]^2) / Sqrt(1 - [v/c]^2) = 1 > > making all inertial measurements of wave speed invariant. But!, there > are real physical consequences. These are, real field distortions, > and > a measureable alteration of rate in physical processes. However, > since > all physical processes are affected equally it is also clear that the > actual perception/observations/measurements in moving systems are all > equally affected, making the perception in all such systems appear > the > same. However, it is physically noticable by relative motion. > > Paul Stowe
From: PD on 11 Feb 2010 10:23 On Feb 11, 1:08 am, Ste <ste_ro...(a)hotmail.com> wrote: > On 11 Feb, 02:07, PD <thedraperfam...(a)gmail.com> wrote: > > > > > > > > I definitely can't make this aether theory work. For what I lack in > > > mathematical skill, I've made up for with programming skill, and it is > > > clear that propagation speed cannot be constant with reference to an > > > absolute frame - its effects would be immediately obvious. > > > > The question therefore remains, how can the speed of propagation > > > possibly be measured to be constant in all frames. > > > Indeed, as this appears to be wholly unintuitive. We'll get to how > > this can be. > > > What we will now do is imagine that at some point after the observers > > on trains A and B made their observations, they compared notes. > > Although it might have seemed surprising to both of them that they did > > not agree whether the original strikes were simultaneous or not, a > > moment's thought by both of them makes them feel better. > > A's conclusion that the strikes were simultaneous is sound and > > consistent with the laws of physics (as we will show), but it also > > makes sense to him WHY those same laws of physics would have produced > > the observation that B made. > > Likewise, B's conclusion that the strikes were NOT simultaneous and > > consistent with the laws of physics, but it also makes sense to him > > WHY those same laws of physics would have produced the observation > > that A made. > > > We'll go through that in a bit. > > > But first it's helpful to recap, A and B both agree that not only are > > their own observations consistent with the laws of physics, but EACH > > OTHER'S observations are also consistent with the laws of physics. And > > that's really all we can hope for. > > > Sadly, this does not answer the question whether the original strikes > > really were simultaneous or not. And in fact, because there is no > > physical priority given to either reference frame, the conclusion must > > be that they are both right -- or better said, that the answer is > > different, depending on the reference frame. > > Indeed. It is easy to reconcile the notion of perspective with the > laws of physics. But the question still remains of how to reconcile > this with material reality. I suppose that depends on whether what you call "material reality" is the set of axioms that you maintain nature OUGHT to respect, or whether "material reality" is the reality that we can observe.
From: PD on 11 Feb 2010 10:24 On Feb 11, 8:39 am, kenseto <kens...(a)erinet.com> wrote: > On Feb 10, 10:32 pm, "Inertial" <relativ...(a)rest.com> wrote: > > > "Tom Roberts" <tjroberts...(a)sbcglobal.net> wrote in message > > >news:kvSdnQR4g8u56O7W4p2dnAA(a)giganews.com... > > > > Nor does the rod get "physically shorter" by any measure we take in any > > > other frame, either. Making a measurement of its length does NOT affect > > > the length of the rod itself, regardless of how the measurement is made. > > > Just using 'length' is also a linguistic problem (similar to that of using > > 'physical'). > > > Does it mean 'proper length' / 'intrinsic length' / 'rest length' .... or > > does it mean the 'measured length' (ie the distance between the coordinates > > of two points at a given time in a given inertial frame) (or is there a > > better term for that 'length' that I can't think of atm :)) ??? > > There is no such thing as measured length of a moving rod. Of course there is, Ken. Even at horse races, horses are measured to win over second-place finishers by three and a half lengths. What makes you think it is impossible to measure the length of a moving rod? How to do it has been described to you dozens of times. > There is a > predicted length or geometric projected length of a moving rod. I > don't understand why you physicists keep on using the word *measured* > instead of *predicted*. Is it to give your SR theory more credence? > > Ken Seto > > > > > If we refer to its 'length' 'in some inertial frame', then that would seem > > to imply one means the 'measured length', because the 'proper' / 'intrinsic' > > / 'rest' length does not depend on the frame of reference/ So when we say > > 'the length of the rod is shorter in the frame of the barn', that would seem > > to imply that length as measured in that frame, and not the rest length.. > > > Though a tilted ladder doesn't get 'physically shorter' it is also not as > > 'tall' (it has a lower 'height'). Can one say it is 'physically' not as > > tall? A 6 foot ladder lying on the ground is still a 6 foot ladder, but it > > is no longer 6 foot tall. > > > It all comes down to the ambiguities of the English language (and I suspect > > the same or similar ambiguities in other spoken languages). That being one > > of the reasons why relationships and statements in physics are often made > > using the less ambiguous language of mathematics. > > > Now. . the question is .. does Ken understand the linguistic issues here ... > > and is he of the opinion that the measured length of a rod (((ie the > > distance between its endpoints at a given time in a given frame of > > reference))) is predicted to be shorter in a frame in which it is is motion > > in a direction parallel to the line between those endpoints (eg in the pole > > and barn paradox). Ie if it was possible to devise an experiment where one > > could accurately (enough) measure that length, would that measurement be > > shorter than the proper/intrinsic/rest length of the rod?
From: PD on 11 Feb 2010 10:32 On Feb 11, 9:07 am, kenseto <kens...(a)erinet.com> wrote: > On Feb 10, 8:49 pm, PD <thedraperfam...(a)gmail.com> wrote: > > > > > On Feb 10, 4:57 pm, kenseto <kens...(a)erinet.com> wrote: > > > > On Feb 10, 9:39 am, PD <thedraperfam...(a)gmail.com> wrote: > > > > > On Feb 10, 8:06 am, kenseto <kens...(a)erinet.com> wrote: > > > > > > On Feb 9, 5:56 pm, PD <thedraperfam...(a)gmail.com> wrote: > > > > > > > On Feb 9, 4:29 pm, kenseto <kens...(a)erinet.com> wrote: > > > > > > > > On Feb 9, 11:32 am, PD <thedraperfam...(a)gmail.com> wrote: > > > > > > > > > On Feb 8, 2:58 pm, kenseto <kens...(a)erinet.com> wrote: > > > > > > > > > > On Feb 8, 3:25 pm, PD <thedraperfam...(a)gmail.com> wrote: > > > > > > > > > > > On Feb 7, 8:39 am, kenseto <kens...(a)erinet.com> wrote: > > > > > > > > > > > > > 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. > > > > > > > > > > > > Why should I listen to what you said when you did made sense.?? > > > > > > > > > > > Ken, it isn't wise to stop listening to people if you do not > > > > > > > > > > understand what they are saying. It would be important in that case to > > > > > > > > > > say, "I don't understand what you are saying. Can you explain it > > > > > > > > > > differently so I can understand it?" > > > > > > > > > > I don't listen to you because you keep on making contradictory claims. > > > > > > > > > For example the pole is physically contracted to fit the barn and at > > > > > > > > > the same time the pole does not fit into the barn because it is not > > > > > > > > > physically contracted. > > > > > > > > > Those are not contradictory claims. > > > > > > > > Yes they are. > > > > > > > > >Those are different accounts made > > > > > > > > in different reference frames. There is no requirement that the > > > > > > > > accounts be identical in different reference frames, and therefore > > > > > > > > they are not contradictory. > > > > > > > > They have to agree whether the physical length of the pole can fit > > > > > > > into the shorter barn. > > > > > > > No, they do not. There is no such requirement. > > > > > > There is the requirement that if you claim physical contraction then > > > > > the pole is really contracted > > > > > I have no idea what you mean by "really contracted". It is physically > > > > contracted in one frame because it actually fits between the doors > > > > when the doors are closed. How can that be called anything other than > > > > physical? It does NOT mean *materially* contracted though -- as in > > > > squeezing or cooling. > > > > Contraction by cooling is "really physically contracted", or > > > "materially contracted", and it is NOT a geometrically contracted > > > effect. > > > Indeed, but you act as though this is the ONLY way something can be > > physically contracted. Not so at all. > > > > IOW, when a meter stick is "really physically contracted" or > > > "materially contracted" its physical length or material length is > > > "physically" or "materially" shorter than the observer's meter stick. > > > "Physically" does not mean "materially". Never has, Ken. Get that out > > of your head. It's wrong. > > > > I don't understand why you insist on hijacking the word "physical" and > > > give it a different meaning than the standard meaning. > > > The standard meaning is the meaning given by physicists, since that > > which is physical is what is studied by physics. > > Electric field is physical, but it is not material. This should be > > enough to tell you that what you think is the "standard meaning" has > > something wrong with it, Ken. > > > So much of your difficulty in understanding physics, Ken, is that you > > insist that words mean what you want them to mean and you never ask > > what they really do mean. If you only asked what some words meant in > > physics, so much of your misunderstandings would be quickly resolved. > > > > I don't > > > understand why you don't except the correct phrase that length > > > conraction in SR is a "geometric projection effect". > > > > BTW the physical length or material length of the pole DOES NOT > > > actually fits between the doors when the doors are closed. The > > > *geometric projection* of the pole can fit into the barn with both > > > doors are closed.....the reason is that geometric projection is not > > > physical or material. > > > Oh, Ken, Ken, Ken. The doors are both closed at the same time, and the > > ends of the pole do not touch the doors. The pole is completely inside > > the barn. > > Yet you want to insist that the pole is only geometrically inside the > > barn and not physically inside the barn? Is it physically sticking out > > of the barn? How does it physically do that without physically making > > marks on the barn doors where the pole physically hits them? > > Here's the problem: What you wrote here means that there is material > or physical contraction. Why? Because the only way that the material > pole can be completely inside the barn with both doors closed > simultaneously is that it is physically or materially contracted. That is not so, Ken. You see, that is the only way YOU can think of this happening, and so you assume it IS the only way it can happen. In this way, you prevent yourself from learning anything new. Things can be physically contracted without being materially contracted. However, YOU can only think of one way something can be physically contracted, and that's if it's materially contracted. That's YOUR limitation, and yours only. > If > this is true then why do you need the explanation that length > contraction in SR is a geomrtical projection effect? > > > > > Do you see what kind of nonsense your word games get you into? > > ROTFLOL....it is you who is playing word games. Tom Roberts said that > length contraction in SR is a geometric projection effect and you said > that length contraction in SR is a physical Yes, physical. > or material effect. No, not material. "Physical" does not mean "material". I've repeated this to you at least 10 times, and yet you continue to make the two words synonymous when they are not. > So who > should I trust? You or Tom Roberts? I trust Tom Roberts becasue he > seem to be more knowledgeable than you. Ken, Ken, Ken. You see, you are struggling because you're trying to learn relativity from a NEWSGROUP. And there you have all manner of people who will say all sorts of things, and many of those people are just plain whacko, and you are forced to choose who you should trust as the authority to believe. And then you have to make that decision on who to trust by who "seems" to be more knowledgeable about a subject that you know nothing about. It does not occur to you that the reason why you have struggled to learn ANYTHING consistently over 15 years is that you are using the WRONG venue to learn it. A newsgroup is NOT the right place to learn relativity. Anyone who tries it will spend 15 years learning practically NOTHING, and will still be confused about who to trust. Does it not occur to you that you have been wasting your time by choosing this venue to provide you with reliable material so that you can learn relativity? Has it not occurred to you that you would be better served by spending $40 every few months on a decent book on the subject? > > Ken Seto > > > > > > Ken Seto > > > > > You get so confused about terms like "physically contracted" and > > > > "materially contracted" and "really contracted", as though they all > > > > mean the same things. They do not. The sooner you learn the > > > > distinctions, the better. > > > > > >.....IOW, not just a geometric projection > > > > > effect. > > > > > > > > The physical length cannot fit into the barn is > > > > > > > an absolute concept and it is not observer dependent. > > > > > > > I'm sorry, Ken, that is just wrong. > > > > > > It is not wrong....also assertion is not a valid arguement. > > > > > Factual matters are decided by documented facts, not argument, Ken. > > > > The point is not to *convince* you that you are wrong. I'm only > > > > pointing out when you ARE wrong, and I'd be happy to direct you to > > > > where you can look up the documented facts. However, there is no point > > > > in trying to convince you that you are wrong by making a compelling > > > > argument. I might as well be arguing with a stone pig. > > > > > > > > > Nor is it contradictory to say that a falling ball has a straight-line > > > > > > > > trajectory AND a parabolic trajectory in the same fall. Galileo knew > > > > > > > > that. I don't see why you don't understand that. > > > > > > > Do you understand what I wrote in this paragraph? Do you see why this > > > > > > is also not a contradiction? > > > > > > What you are describing here is a geometric projection of a falling > > > > > ball in the ship from the shore observer's point of view > > > > > No, it is a PHYSICAL shape of a trajectory. That is the point. The > > > > straight line path is a PHYSICAL trajectory. The parabolic path is a > > > > PHYSICAL trajectory. The falling ball has BOTH a straight line > > > > physical trajectory AND a parabolic physical trajectory, as seen in > > > > different frames. What is *measured* is physical. > > > > > >....this is > > > > > not the same as in the barn and the pole paradox where you claimed > > > > > that the pole is physically contracted.- Hide quoted text - > > > > > - Show quoted text -- Hide quoted text - > > > > > - Show quoted text -- Hide quoted text - > > > - Show quoted text -- Hide quoted text - > > > - Show quoted text -
From: Paul Stowe on 11 Feb 2010 11:10
On Feb 10, 11:16 pm, "Inertial" <relativ...(a)rest.com> wrote: > "Paul Stowe" <theaether...(a)gmail.com> wrote in message > > news:0db4a675-2ae3-4b9d-af25-9b5f4fac9d55(a)a16g2000pre.googlegroups.com... > > > > > > > On Feb 10, 11:36 am, Ste <ste_ro...(a)hotmail.com> wrote: > > > {Snip...} > > >> The question therefore remains, how can the speed of propagation > >> possibly be measured to be constant in all frames. > > > The answer to your question is actually simple and 'intuitive' if you > > think > > about what must happen in a medium. The propagation of any type of > > disturbance travels by 'conduction' from one entity to the next. This > > is > > set by the mean speed and spacing. If the medium is 'incompressible' > > the > > entities are all touching (spacing is zero) and the entities > > 'infinitely > > hard' In that case, the speed of propagation is infinite, and no > > delta > > 'pressures' are possible 'within the medium. OTOH, in any > > compressible > > medium there is spacing, and the entities have momentum and energy. > > This > > results a distinctive independent set speed by which any disturbances > > (like wave propagation) will occur. This is designated as c for ANY! > > medium > > > Now it should be obvious that in the case of a medium it is this > > process > > that always dominates... The speed of sources must, by that > > constraint, > > alter there emission/field profiles to conform to this limitation. > > > So now, start with a source of a omni-directional wave generator 'at > > rest' > > with respect to the medium. The resulting waves propagate outward 'at > > c' > > in all directions, resulting in a perfectly spherical field form. > > Next, > > give this source some speed v, obviously c hasn't changed so, in the > > direction of motion the source is displacing forward at v so each > > wave > > front must be separating 'from the source' at c - v. In the > > perpendicular > > (transverse) direction the wave fronts are still separating from the > > source at c. Thus, for the hemisphere in front of the moving source > > the > > wave field form is no longer spherical, but flatten into an > > ellipsoid. > > Now what happens to the back half??? > > The opposite > > > Intuitively you would think > > that > > the wave front would be separating 'from the source' at c + v. > > It does > > > However, remember that a wave is an oscillation (a back & forth > > motion) so, > > Not for light. It is side-to-side > > > one cycle is c - v and c + v. > > Nonsense [snip rest] From the Handbook of Physics (Section 3, Chapter 8 - Acoustics, Rev 2 1967), The surfaces of constant sound pressure on the other hand are given by R = constant, which corresponds to the ellipsoid x'^2 + y^2 + z^2 = constant = R^2 as pictured in Fig. 8.2. It is interesting to note that the field is the same up and down wind and that the intensity is larger in the directions at right angles to the flow. Go check it out for yourself. As for using the words "back and forth" I guess I should of said cyclic... Paul Stowe |