Is Length Contraction in SR physical??
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From: kenseto on 10 Feb 2010 09:06 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.....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. > > > > 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....this is not the same as in the barn and the pole paradox where you claimed that the pole is physically contracted.
From: PD on 10 Feb 2010 09:09 On Feb 10, 7:56 am, kenseto <kens...(a)erinet.com> wrote: > On Feb 9, 5:54 pm, PD <thedraperfam...(a)gmail.com> wrote: > > > > > On Feb 9, 4:25 pm, kenseto <kens...(a)erinet.com> wrote: > > > > On Feb 9, 11:30 am, PD <thedraperfam...(a)gmail.com> wrote: > > > > > On Feb 8, 3:09 pm, kenseto <kens...(a)erinet.com> wrote: > > > > > > On Feb 8, 3:09 pm, PD <thedraperfam...(a)gmail.com> wrote: > > > > > > > On Feb 8, 12:38 pm, kenseto <kens...(a)erinet.com> wrote: > > > > > > > > On Feb 8, 11:42 am, PD <thedraperfam...(a)gmail.com> wrote: > > > > > > > > > On Feb 7, 7:34 am, kenseto <kens...(a)erinet.com> wrote: > > > > > > > > > > On Feb 6, 10:57 pm, PD <thedraperfam...(a)gmail.com> wrote: > > > > > > > > > > > On Feb 6, 9:02 pm, Ste <ste_ro...(a)hotmail.com> wrote: > > > > > > > > > > > > On 6 Feb, 17:16, PD <thedraperfam...(a)gmail.com> wrote: > > > > > > > > > > > > > On Feb 5, 8:14 pm, Ste <ste_ro...(a)hotmail.com> wrote: > > > > > > > > > > > > > > On 5 Feb, 16:00, PD <thedraperfam...(a)gmail.com> wrote: > > > > > > > > > > > > > > > On Feb 4, 9:57 pm, Ste <ste_ro...(a)hotmail.com> wrote: > > > > > > > > > > > > > > > > On 5 Feb, 02:48, "Peter Webb" <webbfam...(a)DIESPAMDIEoptusnet.com.au> > > > > > > > > > > > > > > > wrote: > > > > > > > > > > > > > > > > > "Ste" <ste_ro...(a)hotmail.com> wrote in message > > > > > > > > > > > > > > > > >news:3979bca1-a35e-4399-bc71-75d2fc680757(a)21g2000yqj.googlegroups.com... > > > > > > > > > > > > > > > > On 5 Feb, 01:12, artful <artful...(a)hotmail.com> wrote: > > > > > > > > > > > > > > > > > > On Feb 5, 11:49 am, 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. > > > > > > > > > > > > > > > > > > In the frame of the barn > > > > > > > > > > > > > > > > > > > 2. The pole cannot fit into the barn with both doors close > > > > > > > > > > > > > > > > > > simultaneously. > > > > > > > > > > > > > > > > > > In the frame of the pole > > > > > > > > > > > > > > > > > > Two different meanings for 'simultaneously'. So they are not > > > > > > > > > > > > > > > > > contradictory > > > > > > > > > > > > > > > > > > You really are not very good at thinking or arguing logically. > > > > > > > > > > > > > > > > > He seems perfectly reasonable to me. > > > > > > > > > > > > > > > > > He's saying that, if one stands in the middle of the barn equidistant > > > > > > > > > > > > > > > > from the doors on each side, and one closes the doors simultaneously > > > > > > > > > > > > > > > > (i.e. what I would call "absolutely simultaneously", but which for > > > > > > > > > > > > > > > > conveience we'll say "simultaneous according to an observer standing > > > > > > > > > > > > > > > > equidistant from each door), then is it possible that both doors can > > > > > > > > > > > > > > > > appear closed while the ladder is observed to be inside the barn. > > > > > > > > > > > > > > > > > It's a simple question, and the answer is "no!". > > > > > > > > > > > > > > > > > ______________________________ > > > > > > > > > > > > > > > > Its a simple question, and the answer is "yes". It is quite easy to devise > > > > > > > > > > > > > > > > an inertial frame in which the doors both appear closed and the ladder is > > > > > > > > > > > > > > > > fully contained in the barn. > > > > > > > > > > > > > > > > The question wasn't whether "an inertial frame can be devised...". > > > > > > > > > > > > > > > Even I can think of situations where it would *appear* that the ladder > > > > > > > > > > > > > > > was inside and both doors closed. The question is whether this is an > > > > > > > > > > > > > > > artefact of observation, or whether the ladder is actually inside with > > > > > > > > > > > > > > > both doors closed. The answer remains "no, the ladder does not fit > > > > > > > > > > > > > > > inside with both doors closed". > > > > > > > > > > > > > > > There is a simple test. > > > > > > > > > > > > > > We can determine whether the doors closed simultaneously. We do this > > > > > > > > > > > > > > using the test of simultaneity I indicated to you above: > > > > > > > > > > > > > > 1. Have the door-closings generate signals that travel at identical > > > > > > > > > > > > > > speeds from either event. > > > > > > > > > > > > > > 2. Have a detector positioned at equal distance from the barn doors. > > > > > > > > > > > > > > 3. If the detector receives the signals from the barn door-closings at > > > > > > > > > > > > > > the same time, then the two doors closed simultaneously unambiguously. > > > > > > > > > > > > > > You and I have agreed on this procedure. > > > > > > > > > > > > > > If the detector is stationary, then yes we agree that this determines > > > > > > > > > > > > > simultaneity. > > > > > > > > > > > > > > > Secondly, we can determine whether any part of the pole was outside > > > > > > > > > > > > > > the barn when those doors were closed by looking for the marks the > > > > > > > > > > > > > > ends of the pole would have made on the door. In the absence of those > > > > > > > > > > > > > > marks, we can safely conclude that the entire pole was inside the barn > > > > > > > > > > > > > > at the time the doors were closed. > > > > > > > > > > > > > > Agreed. I would expect this test is definitive, were it possible to > > > > > > > > > > > > > carry out. > > > > > > > > > > > > > And this has been tested in equivalent experiment. Documented. > > > > > > > > > > > > Has it really? Which experiment was that, because my sources say that > > > > > > > > > > > length contraction has *never* been experimentally observed. > > > > > > > > > > > I already told you the answer to that. Please look again. > > > > > > > > > > > > > Seto does not read experimental papers, because he finds them > > > > > > > > > > > > confusing. So instead he believes what makes sense to him, rather than > > > > > > > > > > > > letting experimental results tell him something different. > > > > > > > > > > > > You have to concede at least the possibility Paul that the reason Ken > > > > > > > > > > > finds them confusing, and so do I, is because *we* can see that they > > > > > > > > > > > rest on certain assumptions. That is, assumptions that you've > > > > > > > > > > > internalised, and assumptions which me and Ken reject.. > > > > > > > > > > > In Seto's case, it has more to do with thinking that SR says something > > > > > > > > > > it does not. I haven't yet figured out whether you are in the same > > > > > > > > > > boat. > > > > > > > > > > The only assumptions I make are those that have testable consequences. > > > > > > > > > > Which ones of those do you think I have that you reject? > > > > > > > > > > So are you saying that SR doesn't say that the pole can be completely > > > > > > > > > inside the barn with both doors close simultaneously? > > > > > > > > > SR *certainly* does not say that this statement holds true in both > > > > > > > > barn frame and pole frame. > > > > > > > > If you thought it did, then you never understood what SR says. > > > > > > > > I didn't say that that statement hold true in both barn and pole > > > > > > > frame. > > > > > > > Yes, you did. Two days ago you said just this: "The pole observer have > > > > > > to agree with the barn observer that the pole > > > > > > is completely inside the barn with both door close simultnaeously." > > > > > You said: "The pole observer have to agree with the barn observer that > > > > the pole is completely inside the barn with both door close > > > > simultnaeously." > > > > > You THEN said "So are you saying that SR doesn't say that the pole can > > > > be completely inside the barn with both doors close simultaneously? I > > > > ask this question because that's what I think SR says. > > > > > I told you No, SR does NOT say this, and neither does the PoR. > > > > > You THEN said, "I didn't say that that statement hold true in both > > > > barn and pole frame." > > > > I was referring to the obsolete SR interpretation. I disagree with > > > this old SR interprestion. I agree with Tom Roberts interpretation > > > that length contraction is not physical. It is the geometric > > > projection of the physical length of the pole is shorter and this > > > projection is able to fit into the length of the barn. > > > SR has not changed, Ken. What Tom is telling you is how SR has > > described the events for decades. > > This does not account for your misunderstanding what you've read.- Hide quoted text - > > Yes SR has changed. You and most of your SR brothers insisted that > there is physical length contraction It IS a physical length contraction. You mistakenly believe that "physical" means "material" when it has NEVER meant that. Thus you believe it leads to a contradiction, because material contraction can't happen and not happen in different frames. But "physical" does NOT mean "material" and so there is no contradiction. There is no contradiction in the same falling object tracing a straight line path AND a parabolic path in different frames, and there is no contradiction here. > which gives rise to the paradoxes > of SR....whereas Tom Roberts said that there is no physical length > contraction and that there is geometric projection shortening of the > pole. Geometric shortening is not physical....it is like I see you to > be shorter from a distant but you are not shorter physically. > > Ken Seto
From: mpc755 on 10 Feb 2010 09:13 On Feb 1, 9:55 am, "kens...(a)erinet.com" <kens...(a)erinet.com> wrote: > Is Length Contraction in SR physical?? Yes. The faster an object moves with respect to the aether the greater the aether pressure exerted on the object. If two observers are both moving relative to one another the rate at which their clocks tick is not relative. The observer moving faster with respect to the aether will have the slower ticking clock because they, and their clock, are under the greater aether pressure. Think of a clock dropped off the side of a boat with a paddle for the second hand. As the clock gets deeper and deeper into the ocean it will continually tick slower, as determined by a clock on the boat, because of the increase in the hydrostatic pressure. The increase in the hydrostatic pressure should actually cause length contraction on the clock itself. Now, drop an atomic clock off the side of a mountain. The atomic clock will continually 'tick' slower the deeper it falls into the valley, as determined by a clock on the summit. The increase in the aether pressure the deeper the clock is dropped into the valley should cause physical length contraction on the atomic clock itself.
From: kenseto on 10 Feb 2010 09:13 On Feb 9, 8:00 pm, Edward Green <spamspamsp...(a)netzero.com> wrote: > On Feb 1, 9:55 am, "kens...(a)erinet.com" <kens...(a)erinet.com> wrote: > > > Is Length Contraction in SR physical?? > > According the most informed SRian, Tom Roberts, the answer to this > > question is NO. His answer is that length contraction is the geometric > > projection effect of the length of a moving meter stick onto the SR > > observer's frame. When a moving meter stick rejoins the stay at home > > meter stick they will have the same physical length. Furthermore if > > length contraction is physically real how come SR does not predict > > length expansion? Is that becasue SR assumes that the observer is in a > > state of absolute rest? > > Regarding the ever-popular reality of length contraction, I prefer > that annoying point of view that it's certainly real, however much it > depends on perspective, because effects involving perspective are real > too! He who doubts this should try to move the two meter stick > through the one meter wide door without a suitable rotation. He will > find that this purely "artificial matter of perspective" reflected in > the apparent length of the stick will mean the difference between > walking through easily, and bending or breaking the stick. > <...> Qestion: can you pass a 2" diameter metal ball through a 1" diameter opening? > > > Reply to author Forward > > > You must Sign in before you can post messages. > > To post a message you must first join this group. > > Please update your nickname on the subscription settings page before > > posting. > > You do not have the permission required to post. > > What are you on about!? This is the open net. I don't need no > stinkin' permission to post. ;-)
From: PD on 10 Feb 2010 09:20
On Feb 10, 8:05 am, PD <thedraperfam...(a)gmail.com> wrote: > On Feb 10, 12:21 am, Ste <ste_ro...(a)hotmail.com> wrote: > > > > > On 9 Feb, 21:02, PD <thedraperfam...(a)gmail.com> wrote: > > > > On Feb 9, 12:26 pm, Ste <ste_ro...(a)hotmail.com> wrote: > > > > > > Two trains are on adjacent tracks, going in opposite directions, > > > > > though I say that only to deliberately reinforce an ambiguity here. It > > > > > doesn't matter whether the trains are going at different speeds, and > > > > > in fact it isn't even important if one of the trains is stopped, or in > > > > > fact whether they are going in the same direction but one faster than > > > > > the other. All that matters is that there is a relative velocity > > > > > between them. > > > > > > Two lightning strikes occur, drawn to the trains because of the > > > > > friction of the air between the trains. In fact, one lightning strike > > > > > leaves a scorch mark (a 1 cm spot, if you want to be precise) on > > > > > *both* trains as it hits. The other strike leaves a scorch mark > > > > > somewhere else on *both* trains. > > > > > > The question now is, were the strikes simultaneous or not? > > > > > > There is an observer on train A, and an observer on train B, and they > > > > > are both looking out the window when the strikes occur. > > > > > > They make the following observations: > > > > > 1. The observer on train A sees the two lightning flashes > > > > > simultaneously. > > > > > 2. The observer on train B sees the flash from the front of his train > > > > > before he sees the flash from the rear of his train. > > > > > > Now, it is not yet possible to determine whether the strikes were > > > > > simultaneous originally. We have more work to do. But I want to see if > > > > > you have a picture in your head of what has transpired. > > > > > I have a basic picture, yes. > > > > OK, then. > > > Let's now follow up these two observations above and couple them with > > > more observations. > > > 3. After the strikes, the observer on train A runs a tape measure from > > > his location to the scorch mark of one strike and makes note of the > > > number. Then he runs a tape measure from his location to the scorch > > > mark of the other strike and makes note of the number. These numbers > > > are equal. Note the scorch marks are on his train, but that's an > > > undeniable marker of where the event WAS when the signal propagation > > > began. > > > Not really. If his train is moving, then the scorch marks will have > > actually moved from the location of the event. > > With respect to what is the train moving? In this reference frame, the > train is not moving at all, though the other one is. I remind you that > it is not stated, nor is it clear, whether both trains are moving or > only one is. Nor does it matter, because even if the train is moving > relative to the track doesn't guarantee that the train is moving in > any absolute sense. For example, if the track itself were moving (say > because the surface of the earth is moving) and the train is moving in > the opposite direction, one could easily visualize that the train is > not moving at all, even if the train is moving relative to the track. > > This is a crucial point about reference frames. We are making > statements about observations made IN THIS REFERENCE FRAME, and in > this reference frame, the train is not moving, the scorch marks are > not moving, and we can measure the speed of light in this reference > frame. > > > > > > 4. After the strikes, the observer on train B runs a tape measure from > > > his location to the scorch mark of one strike and makes note of the > > > number. Then he runs a tape measure from his location to the scorch > > > mark of the other strike and makes note of the number. These numbers > > > are equal. Note the scorch marks are on his train, but that's an > > > undeniable marker of where the event WAS when the signal propagation > > > began. > > > I'm not sure I agree with this. > > It is exactly the symmetric situation with train A. Since the strikes > left marks on both trains, there is no reason to rule it out here if > it was permissible on A. > > > > > > 5. The observer on A runs some experiments to measure the speed of > > > light and the isotropy of the speed of light (that it is the same in > > > either direction), and finds that the signal speed is the same. (Note > > > this isotropy would NOT hold if the signal were sound, for example.) > > > And *how* does he measure this? > > A variety of ways. You could, for example, follow the procedures used > by experimenters as documented in the papers referenced on the first > Google search return on "experimental basis for relativity". > > > > > > 6. The observer on B runs some experiments to measure the speed of > > > light and the isotropy of the speed of light (that it is the same in > > > either direction), and finds that the signal speed is the same. (Note > > > this isotropy would NOT hold if the signal were sound, for example.) > > > > Given these *observations* 1, 3, and 5, what would the observer on > > > train A conclude about the simultaneity of the original strikes? > > > I must admit I don't have a clear enough picture of what is happening. > > This gedanken seems to presuppose the very thing in question, that is, > > relativity. > > No, it doesn't presuppose anything other than what is *actually > observed* in experiment. I cannot underscore this enough. For example, > the claims that both (5) and (6) are both true may seem > counterintuitive. How can both trains measure the speed of light to be > the same from both directions, if the trains are moving relative to > each other? Certainly an aether-based theory would not hold this is > true. Does this mean we are *assuming* relativity is true so that > these statements are both true? No. Statements (5) and (6) are the > results of *experimental observation*. Nature really does behave this > way, even if we find it counterintuitive. > > > > > Let's refine it a bit by stipulating that the Earth is stationary, the > > track is stationary, and the clouds are stationary, > > On what basis would you make such an arbitrary stipulation, when you > KNOW that this is not the case? > You may be tempted to say, "Because we have to have an absolute > reference for stationary *someplace*, and we might as well make it > Earth because we live here." A moment's thought will tell you this is > foolish. Physical laws don't care where we live. Then, in the search > for finding an absolute reference for rest, you may eventually ask > yourself why such an absolute reference would be needed at all, > especially if there is nothing you can clearly identify that would fit > the bill... > > > and we'll also > > stipulate that the lightning strike happens in an instant (even though > > it doesn't), and marks all locations at that instant. > > > Now, where are the trains on the tracks when the lightning strikes, > > and are they moving? > > You see? You are trying to establish an absolute reference frame, even > if it means doing so completely arbitrarily, JUST SO you can say > whether the trains are absolutely moving or not. As a side note, let me just offer the word of encouragement that you are asking all the right questions and wrestling with all the right issues. In other words, this is what students do when they actually learn something. You are on your way to really understanding what relativity is saying, and also on your way to learning how to check whether the claims that are made do in fact match experimental observation. But as a cautionary note, let me also remind you that we are ONLY trying to put together an understanding of where the frame-dependence of simultaneity comes from, which is only one small stepping stone in the exploration of special relativity, which in turn is itself a small stepping stone in the exploration of general relativity. As you can see, this takes work, and extended thinking, and asking lots of serious questions. This is why many of the basic ideas in physics cannot be explained compellingly in a few sentences to interested and intelligent hobbyists. Physics students would be expected to discuss this in class for about an hour, then think about it and work through issues for about four or five hours outside of class (with other students or with the teacher for some of that), before moving on to the next stepping stone. |