Is Length Contraction in SR physical??
in [Relativity]
|
Prev: Simultaneous events and Einstein's absolute time
Next: New Theory --- The Theory of Quantum Wave Sources
From: kenseto on 5 Feb 2010 10:26 On Feb 5, 3:42 am, mpalenik <markpale...(a)gmail.com> wrote: > On Feb 5, 3:24 am, Ste <ste_ro...(a)hotmail.com> wrote: > > > > > > > On 5 Feb, 07:08, mpalenik <markpale...(a)gmail.com> wrote: > > > > On Feb 5, 1:55 am, Ste <ste_ro...(a)hotmail.com> wrote: > > > > > > All it demonstrates is that you are not familiar with the > > > > > theory of relativity. > > > > > Then why is it that I seem to be able to understand it so well, even > > > > though I have no idea how to apply it mathematically? > > > > You have repeatedly expressed an incorrect understanding of the theory > > > and refuse to acknowledge it, despite the fact that multiple people, > > > including myself, have explained that your interpretation is flawed. > > > Why you think you understand it "so well" is beyond me. > > > I think you mean you've insisted that my interpretation is flawed - > > you haven't explained that argument at all. I'm perfectly willing to > > explain my arguments if you don't understand mine, but you can't > > seriously expect me to agree with you just because you *say* I'm > > wrong? > > Well, lets go through the points below where you disagree with me. > > > > > > > > > > > > > Of course, I understand what you're getting at, although I understand > > > > > > the concept differently. What you're getting at is the effect of > > > > > > propagation delays, > > > > > > No, this has nothing to do with propagation delays. > > > > > What *does* it have to do with then? Bear in mind that a propagation > > > > delay is a *physical* concept. A "rotation in time" is a purely > > > > geometric concept. > > > > > And incidentally, you're not the first person to have said "it has > > > > nothing to do with propagation delay", and yet no one who has said > > > > that has yet described *any* effect (in SR) that is not adequately > > > > explained by propagation delays. > > > > If you work through the math, you'll see that the effects I'm > > > describing are *after* propagation delay has been accounted for. It > > > is *not* adequately accounted for by propagation delays. Those must > > > be accounted for *separately*. > > > Then give me a concrete example of the difference between what would > > be predicted with 'mere' propagation delay, and the actual predictions > > of SR, and then we can discuss it. > > In this particular thought experiment with the barn and the ladder, > I've tried to explain the different to you but you refuse to believe. > In the full relativistic framework, an observer at rest in the center > of the barn can see both doors shut at the same time while the ladder > is entirely inside of the barn. This cannot be accounted for with > mere propagation delay. This requires the ladder to be contracted physically (materially)....not just a geometric projection effect. Ken Seto > > There are other effects of relativity that cannot be accounted for > with propagation delay, such as increased half lives of particles > moving at high speeds (which have been measured), but they're not > related to this thought experiment. > > > > > > > > > > > > > whereby both doors can appear to close > > > > > > simultaneously when, in physical reality, the distant door has already > > > > > > started to open before the near door closed. > > > > > > No, the doors close simultaneously in the frame of the barn but NOT in > > > > > the frame of the moving ladder. This is *after* correcting for any > > > > > "propagation delays" in the observation of the two doors. > > > > > I'm afraid I don't accept this. If it is necessary to make the analogy > > > > more complex, then consider this. The ladder has an observer sitting > > > > on each end of the ladder (in addition to the person stood in the > > > > middle of the barn watching the ladder go by). > > > > > The observer at the fore of the ladder naturally sees the front door > > > > close before the back door, and the front door will start to open > > > > again before the back door has even shut. The observer astern of the > > > > ladder sees the back door close before the front. The observer stood > > > > still in the middle of the barn equidistant from each door sees both > > > > doors close simultaneously. > > > > No, this is not how special relativity works. You must *first* > > > account for the propagation delays. The observers at the front and > > > rear of the latter, after accounting for propagation delays, will each > > > see the door open and shut at the same time. > > > > The relativistic effects have to do with differences measured due to > > > VELOCITY, NOT POSITION. > > > I accept that there are effects due to velocity. But in this context, > > what of them? > > The fact that the discrepancy in simultaneity between the closing and > opening of the two doors only occurs for observers at different > velocities. It does NOT occur for observers at the same velocity in > different locations. Once you account for propagation delay, there is > no descrepancy in simultanaity for observers at the same speed. But > the discrepancy REMAINS for observers at different speeds. > > > > > > > > > > > Now *of physical necessity*, the observer in the barn who sees the > > > > doors close with the ladder inside, *must* be able to answer our > > > > question. If the ladder is inside the barn, then this observer cannot > > > > *possibly* observe both doors to be shut, unless the ladder is > > > > *wholly* and *physically* inside the barn. > > > > > The question that remains outstanding, is whether the ladder *actually > > > > fits* inside the barn, or whether it crashes before it even gets all > > > > the way into the barn. > > > > It fits in the barn in the barn frame, where both ends are in the barn > > > simultaneously. > > > So what you're saying is that the stationary observer in the middle of > > the barn could see that the ladder was in the barn and the doors are > > both closed, even though the ladder has a "proper length" that is > > longer than the distance between the two doors? > > Yes. > > > > > And if you say it does, then I'm going to ask you, are you *sure* it > > does? Have you done the calculations? > > Yes. Proper length (squared) is dx^2 + dy^2 + dz^2 - cdt^2. The fact > that the proper length is greater than that of the barn is accounted > for by the fact that some of the ladder is rotated in time, which is > what I've been trying to explain to you. > > > > > > > > > > > > > But that's why Ken wants a simple answer to the *physical reality*, > > > > > > which is why I devised a setup where the doors are equidistant from an > > > > > > observer (and therefore both must truly close simultaneously), > > > > > > This is what you don't understand, in this scenario, they are ONLY > > > > > closing simultaneously in the barn frame. > > > > > Yes, and the observer is *in* the barn frame. > > > > > > To a moving observer (at > > > > > ANY location, even a moving observer located at the center of the > > > > > barn) they do not close simultaneously. *THIS* is what the theory of > > > > > relativity states. > > > > > Bollocks! The doors cannot possibly close simultaneously "for the > > > > barn", unless they also *appear* to close simultaneously for the > > > > stationary observer positioned inside the barn and equidistant from > > > > each door. > > > > They DO appear to close simultaneously for the stationary observer at > > > the center of the barn. I have never said otherwise. > > > I had not mentioned a "moving observer" at the centre of the barn, > > although you are wrong in any event - see next. > > No, I'm not. > > > > > > > Also, even though this has nothing to do with the analogy as I > > > > presented it, an observer moving along an axis that is always > > > > equidistant from both doors *can* be moving and also observe the doors > > > > to be closing simultaneously. > > > > Only if you fail to take into account relativity. Under Newtonian > > > physics, you are correct. Under relativistic physics, you are not. > > > I don't believe you. Are you sure you have done the calculations and > > verified this for yourself? > > Did you read my second post where I corrected this? I misread your > original statement as "a moving observer equidistant between the two > doors," in which case, it is in general false. But yes, if the axis > of motion is perpendicular to the line between the two doors, then you > are correct. > > > > > How can the doors possibly not shut simultaneously with each other if > > you are, by definition, always maintaining equidistance from both, and > > you are moving with the same velocity relative to both? > > This is the difference between Newtonian mechanics and relativity. In > relativity, when you move, as I've tried to explain before, some of > your "space" axis gets rotated into your "time" axis, and so events in > front of you are slighty in the FUTURE of the stationary frame, which > events behind you are slightly in the PAST of the stationary frame.- Hide quoted text - > > - Show quoted text -- 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: paparios on 5 Feb 2010 10:44 On 5 feb, 01:29, Ste <ste_ro...(a)hotmail.com> wrote: > On 5 Feb, 02:37, "papar...(a)gmail.com" <papar...(a)gmail.com> wrote: > > > In the "real world" there are some that say that the source of the Big > > Bang could bechosen as an absolute reference, but it is the same case > > of you aboard the space ship, that is we don't know if the Big Bang > > was sitting still or moving with respect to something else. At the end > > it does not matter at all!!! An absolute frame of reference is not > > needed nor an abosulte time is needed. > > It doesn't matter mathematically, but it does matter physically. > > As I've said, if an absolute reference frame can be discerned that > would allow us to discern the movement of the universe itself, then > good. Otherwise, the absolute reference frame can simply encompass the > whole universe (which rules out any question of what the big bang - > and the universe - is moving relative to). What it is known is that no absolutes are needed, in order to predict what the results will be on a given physical experiment. Take GPS, for instance, where clock corrections on satellites, one based on SR and the other based on GR, are enough to ensure the necessary precision of the satellites clocks, by which the entire GPS system can perform as predicted. Those corrections do not need or care of some absolute reference frame located somewhere, far in the deep universe. Local frames of reference do quite well and work like a charm. Miguel Rios
From: PD on 5 Feb 2010 10:47 On Feb 4, 3:21 pm, Ste <ste_ro...(a)hotmail.com> wrote: > On 4 Feb, 15:19, PD <thedraperfam...(a)gmail.com> wrote: > > > > > On Feb 3, 9:32 pm, Ste <ste_ro...(a)hotmail.com> wrote: > > > > If it is presumed that the two events are an equal amount of distance > > > away from the observer, and that the information propagates along that > > > distance at an equal speed, then yes I would say simultaneity can be > > > determined this way in the absence of gravity considerations. What I > > > would make the point though that I recognise a distinction between > > > "proper distance" (i.e. that of a straight line) and the extended path > > > that real light might need to take in the presence of a gravity field.. > > > We can certainly arrange things such that the effect of gravity is > > much less than the size of the effects being examined, or that gravity > > is numerically accounted for, or that the set-up is configured so that > > gravity does not bend the path of the light. Let's take it as a > > presumption that in a *real* experiment, one of these three strategems > > is employed, and thus we'll dispense with gravitational curvature as a > > consideration, for simplicity. > > Ok. Obviously with everyone vigorously anticipating a slip-up and > their opportunity to go "aha!", I'm having to be more conscious of > covering all eventualities, lest any omission be interpreted as "a > lack of understanding". > > > > > > > Note here that we have accounted for propagation delay here, and the > > > > conclusions are not masked by that. > > > > > OK so far? > > > > Yep. > > > OK, good. Then here's the plan for the next string of posts, just so > > you know where we're going: > > 1. A simple note about experimental observations regarding this > > situation. > > 2. The idealized "thought experiment" by Einstein that distills these > > experimental observations. I may follow this up with a more elaborate > > example that makes the symmetry more apparent. > > 3. Explaining why the observations in (1) and (2) are completely > > consistent with known laws of physics *other* than relativity. > > 4. Understanding why these results are due to the frame-independence > > of the speed of light. > > 5. Review of the experimental data on the frame-independence of the > > speed of light. > > > So then, now that we have an unambiguous way of determining true > > simultaneity of a pair of events, an approach that we can agree on, > > then we'll make an interesting observation in nature. > > > We can set up an experiment that looks at a single pair of spatially > > separated events (events A and B) with two detectors in two different > > reference frames X and Y, which are moving relative to each other. > > Experiments of this type have actually been performed. I've already > > pointed you to a list of references that includes such experiments > > (among others). I want to emphasize that there is only ONE pair of > > events that is looked at from two perspectives at the same time, not > > an experiment that is repeated first with one detector and then with > > the other. > > I just want to be clear that I don't really have a mental picture of > this setup (starting distances and velocities remain unspecified), so > I might need more information. > > > And here is the result: > > 1. The detector in X is midway between the events and so the distance > > traveled by the signals are equal, as confirmed by an independent > > measurement. > > 2. The speed of the signals is equal, as confirmed by an independent > > measurement. > > 3. The signals arrive at the detector in X at the same time. > > > Therefore the original events are simultaneous. > > Ok, I think I can agree so far. > > > 1'. The detector in Y is midway between the events and so the distance > > traveled by the signals are equal, as confirmed by an independent > > measurement. > > 2'. The speed of the signals is equal, as confirmed by an independent > > measurement. > > 3'. The signals arrive at the detector in Y at different times. > > Therefore the original events are not simultaneous. > > I can conceive of a situation where this will be true, but I need you > to specify the velocities. The visualization will come with Einstein's distillation, but I'll toss in some numbers here so that you can make a sketch. 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? > > > 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. 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. > > > Before you splutter, "But... how can this BE?" let me remind you that > > these are the real observations -- that is, as nature ACTUALLY > > exhibits itself -- and we've already decided the conclusions that > > would necessarily be drawn from those observations. > > > With me so far? > > No. I want more clarification. I think I know what the issue is, but > first I'll let you be more concrete about the *velocities* of the two > detectors.
From: kenseto on 5 Feb 2010 10:50 On Feb 4, 6:15 pm, mpalenik <markpale...(a)gmail.com> wrote: > On Feb 4, 6:12 pm, "kens...(a)erinet.com" <kens...(a)erinet.com> wrote: > > > > > > > On Feb 4, 11:54 am, mpalenik <markpale...(a)gmail.com> wrote: > > > > On Feb 4, 10:04 am, kenseto <kens...(a)erinet.com> wrote: > > > > > On Feb 3, 8:12 pm, PD <thedraperfam...(a)gmail.com> wrote: > > > > > > On Feb 3, 3:58 pm, kenseto <kens...(a)erinet.com> wrote: > > > > > > > On Feb 3, 3:36 pm, PD <thedraperfam...(a)gmail.com> wrote: > > > > > > > > On Feb 3, 12:19 pm, kenseto <kens...(a)erinet.com> wrote: > > > > > > > > > On Feb 3, 12:11 pm, PD <thedraperfam...(a)gmail.com> wrote: > > > > > > > > > > On Feb 3, 10:04 am, kenseto <kens...(a)erinet.com> wrote: > > > > > > > > > > > On Feb 3, 4:41 am, artful <artful...(a)hotmail.com> wrote: > > > > > > > > > > > > On Feb 3, 4:18 pm, Tom Roberts <tjroberts...(a)sbcglobal.net> wrote: > > > > > > > > > > > > > Uncle Ben wrote: > > > > > > > > > > > > > On Feb 1, 11:36 pm, Tom Roberts <tjroberts...(a)sbcglobal.net> wrote: > > > > > > > > > > > > >> [...] > > > > > > > > > > > > > > Tom Robrts takes the conservative position on what is "physical." > > > > > > > > > > > > > Hmmm. I tried not to make any statement about what is or is not "physical", > > > > > > > > > > > > because that word is too ambiguous. > > > > > > > > > > > > > To me it is irrelevant whether one considers this or that quantity to be > > > > > > > > > > > > "physical". What is important is whether or not a given quantity can be an > > > > > > > > > > > > appropriate model for some physical phenomenon. For that, it's QUITE CLEAR that > > > > > > > > > > > > no coordinate-dependent quantity can be a valid model of any physical > > > > > > > > > > > > phenomenon, as arbitrary human choices cannot possibly affect physical > > > > > > > > > > > > phenomena. Nor can the perspective from which one looks at an object affect the > > > > > > > > > > > > object itself. Coordinates are, of course, arbitrary human choices that define > > > > > > > > > > > > the perspective one uses to look at and describe objects and situations. > > > > > > > > > > > > > > To > > > > > > > > > > > > > be consistent, he would have to deny physicality to kinetic energy and > > > > > > > > > > > > > to the magnetic field of a moving charge. Or even motion itself. > > > > > > > > > > > > > I deny that any of those can be valid models for physical phenomena. I make no > > > > > > > > > > > > statement about their "physicality" -- arguments over word meanings are > > > > > > > > > > > > uninteresting (but inappropriate word meanings must be dealt with before the > > > > > > > > > > > > real discussion can even begin). > > > > > > > > > > > > > In every case I know of, if you analyze the physical situation sufficiently > > > > > > > > > > > > well, you will find an appropriate quantity that is a valid model for the > > > > > > > > > > > > physical phenomena in question. For instance, when considering a collision > > > > > > > > > > > > between two particles, don't use kinetic energy, use the Mandelstamm s (total > > > > > > > > > > > > energy squared in their center-of-momentum frame); instead of magnetic field, > > > > > > > > > > > > use the Maxwell 2-form; instead of motion, use the particles' individual > > > > > > > > > > > > trajectories. Tensor and geometric analysis provide methods to analyze all > > > > > > > > > > > > situations of interest in a coordinate-free manner. This is one of the major > > > > > > > > > > > > lessons of GR (but it took about a half-century to sink in). > > > > > > > > > > > > > > Or do > > > > > > > > > > > > > I not understand? > > > > > > > > > > > > > The issue is more subtle than you seem to think. It is not merely about the > > > > > > > > > > > > meanings of words, or about what is or is not "physical", it is about what types > > > > > > > > > > > > of quantities can be used to model physical phenomena. > > > > > > > > > > > > > Tom Roberts > > > > > > > > > > > > At first reading you seem to be equating 'physical' with 'frame > > > > > > > > > > > invariant'. ie. Only things that are not dependent on the observer > > > > > > > > > > > are physical. > > > > > > > > > > > > But am I right in my assessment that you are really saying that it is > > > > > > > > > > > only nature / reality itself that is physical. The measurements and > > > > > > > > > > > calculations we make are parts of our models of reality .. and so are > > > > > > > > > > > never really 'physical' themselves. The best models (and > > > > > > > > > > > measurements) for reality are those that are not observer dependent, > > > > > > > > > > > because physical reality is not observer dependent (ignoring some > > > > > > > > > > > interpretations of QM :)). > > > > > > > > > > > > In the case of length contraction, what we define as length (roughly > > > > > > > > > > > speaking: the spatial distance between two simultaneous events in a > > > > > > > > > > > given time) is contracted .. even though the proper interval is > > > > > > > > > > > invariant. In both cases they are valid (but different) measurements > > > > > > > > > > > of the same pair of events. > > > > > > > > > > > > Ken's claim that contraction not being 'physical' means a pole doesn't > > > > > > > > > > > physically fit between the barn doors at the same time in the barn > > > > > > > > > > > frame of reference (in the well-known 'paradox'). I guess the issue > > > > > > > > > > > there is really whether 'between the barn doors at the same time in > > > > > > > > > > > the barn frame of reference' itself is physical .. as it is observer / > > > > > > > > > > > frame dependent. > > > > > > > > > > > No it was specified that, in the barn frame, the barn doors close > > > > > > > > > > simultaneously for a very brief period while the pole is completely > > > > > > > > > > inside the barn. This requires real physical contraction and not > > > > > > > > > > observer dependent. > > > > > > > > > > No, it doesn't. You obviously don't understand the pole and barn > > > > > > > > > puzzle at all. > > > > > > > > > No it is you who don't understand the pole and the barn paradox. > > > > > > > > Ken, look again. It is stated explicitly in the pole and barn paradox > > > > > > > that in the pole frame, the pole is LONGER than the barn. This means > > > > > > > the physical shortening of the rod obviously is not frame-independent. > > > > > > > If it required the rod to be physically shorter to all observers, then > > > > > > > it would be claimed to be shorter than the barn in the pole frame, > > > > > > > too. Since this is not claimed, then it is not required to be observer > > > > > > > independent. > > > > > > > You get a clue....in the barn frame you claimed that the doors are > > > > > > closed simultaneously while the pole is completely inside the barn. > > > > > > In the barn frame, yes. Only in the barn frame. > > > > > No....once it is physically contracted it is contracted to all > > > > observers. > > > > > > > This means that the pole is physically shortened and physically > > > > > > shortened pole is not observer dependent. > > > > > > No it certainly does not mean that. > > > > > Sure it means that. > > > > > > Because if it did mean that, then > > > > > the pole would also have to be shorter than the barn in the pole > > > > > frame. > > > > > The point is: the pole is not physically contracted in the barn frame > > > > or the pole frame. In the barn frame the geometric porjection of the > > > > pole unto the barn frame is contracted and this projected length is > > > > able to fit into the barn with both doors close simultaneously. > > > > This is correct so far. > > > > > In the > > > > pole frame the geometric projection of the length of the barn is > > > > expanded and this expanded length is able to encase the pole > > > > completely with both doors close simultaneously. > > > > This is incorrect. In the pole frame, the length of the barn is > > > *also* contracted but the closing of the doors is no longer > > > simultaneous. *Time* as well as distance gets "geometrically > > > projected" in the pole frame. > > > No. What I said is correct. What the pole observer sees must agree > > with what the barn observer sees. The pole observer does not see the > > barn is contracted....he must see the projected length of the barn is > > expanded in order to agree with what the barn observer sees. > > No, it isn't, and even a cursory glance at the most elementary texts > discussing relativity will tell you so. > > > > > > In the barn frame, closing the doors simultaneously just long enough > > > for the man with the pole to run from one end of the barn to the other > > > corresponds to the front door being open, while the back door is > > > closed just long enough for the man with the pole to run to it, then > > > the back door opening and the front door closing after the back end of > > > the pole enters the barn. > > > The problem with what you said is that you claim both possibilities: > > 1. The pole can fit into the barn physically with both doors close > > simultaneously. > > From the barn's frame it can. Do you realize that this requires that the pole is physically (materially) contracted? IOW it is a geometric projection effect. > > > 2. The pole cannot fit into the barn physically with both doors close > > simultaneously. > > In the pole's frame, it cannot. Simultanaity is frame dependant in > relativity. What is simultaneous in one frame is not in the other. > The two ends of the pole are never simultaneously within the barn in > the pole's frame. This is a geometric projection effect. So in the barn frame you choose real physical contraction and in the pole frame you choose geometric contraction....Right? Ken Seto > > > > > That's not physics when you claim all possibilities. > > I'm not claiming all possibilities. I am claiming a very specific > thing happens. You can even calculate the times during which the ends > of the pole are within the barn in the two reference frames. You get > a different answer in each frame. Time, space, and simultanaity are > frame dependant quantities in relativity.- Hide quoted text - > > - Show quoted text -
From: PD on 5 Feb 2010 10:53
On Feb 4, 4:59 pm, "kens...(a)erinet.com" <kens...(a)erinet.com> wrote: > On Feb 4, 10:47 am, PD <thedraperfam...(a)gmail.com> wrote: > > > On Feb 4, 9:04 am, kenseto <kens...(a)erinet.com> wrote: > > > > On Feb 3, 8:12 pm, PD <thedraperfam...(a)gmail.com> wrote: > > > > > On Feb 3, 3:58 pm, kenseto <kens...(a)erinet.com> wrote: > > > > > > On Feb 3, 3:36 pm, PD <thedraperfam...(a)gmail.com> wrote: > > > > > > > On Feb 3, 12:19 pm, kenseto <kens...(a)erinet.com> wrote: > > > > > > > > On Feb 3, 12:11 pm, PD <thedraperfam...(a)gmail.com> wrote: > > > > > > > > > On Feb 3, 10:04 am, kenseto <kens...(a)erinet.com> wrote: > > > > > > > > > > On Feb 3, 4:41 am, artful <artful...(a)hotmail.com> wrote: > > > > > > > > > > > On Feb 3, 4:18 pm, Tom Roberts <tjroberts...(a)sbcglobal.net> wrote: > > > > > > > > > > > > Uncle Ben wrote: > > > > > > > > > > > > On Feb 1, 11:36 pm, Tom Roberts <tjroberts...(a)sbcglobal.net> wrote: > > > > > > > > > > > >> [...] > > > > > > > > > > > > > Tom Robrts takes the conservative position on what is "physical." > > > > > > > > > > > > Hmmm. I tried not to make any statement about what is or is not "physical", > > > > > > > > > > > because that word is too ambiguous. > > > > > > > > > > > > To me it is irrelevant whether one considers this or that quantity to be > > > > > > > > > > > "physical". What is important is whether or not a given quantity can be an > > > > > > > > > > > appropriate model for some physical phenomenon. For that, it's QUITE CLEAR that > > > > > > > > > > > no coordinate-dependent quantity can be a valid model of any physical > > > > > > > > > > > phenomenon, as arbitrary human choices cannot possibly affect physical > > > > > > > > > > > phenomena. Nor can the perspective from which one looks at an object affect the > > > > > > > > > > > object itself. Coordinates are, of course, arbitrary human choices that define > > > > > > > > > > > the perspective one uses to look at and describe objects and situations. > > > > > > > > > > > > > To > > > > > > > > > > > > be consistent, he would have to deny physicality to kinetic energy and > > > > > > > > > > > > to the magnetic field of a moving charge. Or even motion itself. > > > > > > > > > > > > I deny that any of those can be valid models for physical phenomena. I make no > > > > > > > > > > > statement about their "physicality" -- arguments over word meanings are > > > > > > > > > > > uninteresting (but inappropriate word meanings must be dealt with before the > > > > > > > > > > > real discussion can even begin). > > > > > > > > > > > > In every case I know of, if you analyze the physical situation sufficiently > > > > > > > > > > > well, you will find an appropriate quantity that is a valid model for the > > > > > > > > > > > physical phenomena in question. For instance, when considering a collision > > > > > > > > > > > between two particles, don't use kinetic energy, use the Mandelstamm s (total > > > > > > > > > > > energy squared in their center-of-momentum frame); instead of magnetic field, > > > > > > > > > > > use the Maxwell 2-form; instead of motion, use the particles' individual > > > > > > > > > > > trajectories. Tensor and geometric analysis provide methods to analyze all > > > > > > > > > > > situations of interest in a coordinate-free manner. This is one of the major > > > > > > > > > > > lessons of GR (but it took about a half-century to sink in). > > > > > > > > > > > > > Or do > > > > > > > > > > > > I not understand? > > > > > > > > > > > > The issue is more subtle than you seem to think. It is not merely about the > > > > > > > > > > > meanings of words, or about what is or is not "physical", it is about what types > > > > > > > > > > > of quantities can be used to model physical phenomena.. > > > > > > > > > > > > Tom Roberts > > > > > > > > > > > At first reading you seem to be equating 'physical' with 'frame > > > > > > > > > > invariant'. ie. Only things that are not dependent on the observer > > > > > > > > > > are physical. > > > > > > > > > > > But am I right in my assessment that you are really saying that it is > > > > > > > > > > only nature / reality itself that is physical. The measurements and > > > > > > > > > > calculations we make are parts of our models of reality .. and so are > > > > > > > > > > never really 'physical' themselves. The best models (and > > > > > > > > > > measurements) for reality are those that are not observer dependent, > > > > > > > > > > because physical reality is not observer dependent (ignoring some > > > > > > > > > > interpretations of QM :)). > > > > > > > > > > > In the case of length contraction, what we define as length (roughly > > > > > > > > > > speaking: the spatial distance between two simultaneous events in a > > > > > > > > > > given time) is contracted .. even though the proper interval is > > > > > > > > > > invariant. In both cases they are valid (but different) measurements > > > > > > > > > > of the same pair of events. > > > > > > > > > > > Ken's claim that contraction not being 'physical' means a pole doesn't > > > > > > > > > > physically fit between the barn doors at the same time in the barn > > > > > > > > > > frame of reference (in the well-known 'paradox'). I guess the issue > > > > > > > > > > there is really whether 'between the barn doors at the same time in > > > > > > > > > > the barn frame of reference' itself is physical .. as it is observer / > > > > > > > > > > frame dependent. > > > > > > > > > > No it was specified that, in the barn frame, the barn doors close > > > > > > > > > simultaneously for a very brief period while the pole is completely > > > > > > > > > inside the barn. This requires real physical contraction and not > > > > > > > > > observer dependent. > > > > > > > > > No, it doesn't. You obviously don't understand the pole and barn > > > > > > > > puzzle at all. > > > > > > > > No it is you who don't understand the pole and the barn paradox. > > > > > > > Ken, look again. It is stated explicitly in the pole and barn paradox > > > > > > that in the pole frame, the pole is LONGER than the barn. This means > > > > > > the physical shortening of the rod obviously is not frame-independent. > > > > > > If it required the rod to be physically shorter to all observers, then > > > > > > it would be claimed to be shorter than the barn in the pole frame, > > > > > > too. Since this is not claimed, then it is not required to be observer > > > > > > independent. > > > > > > You get a clue....in the barn frame you claimed that the doors are > > > > > closed simultaneously while the pole is completely inside the barn. > > > > > In the barn frame, yes. Only in the barn frame. > > > > No....once it is physically contracted it is contracted to all > > > observers. > > > That's YOUR claim. That is NOT the claim of relativity, and that is > > NOT what is observed in nature. > > > Remember that "physical" does not mean "material". > > Physical and material are the same.. No they are not. I've corrected this several times, but you insist on making the same error. An electric field is physical. It is not material. A radio wave in empty space is physical. It is not material. Please, Ken, you must correct your confusion of the language before you can correct your confusion about the concepts. >..you claimed that the longer > pole is able physically fit into the shorter barn with both doors > close simultaneously. The only way this can happen is that the pole > contracted physically or materially. That is not so. Material contraction is NOT the only way this can happen. This is precisely the point. Just because YOU can't think of any other way doesn't mean there ISN'T any other way. > > > > > > > > This means that the pole is physically shortened and physically > > > > > shortened pole is not observer dependent. > > > > > No it certainly does not mean that. > > > > Sure it means that. > > > No, Ken, it does not. It may mean that to YOU, but not to physics. > > ROTFLOL....Physics does not include making contradictory claims. They aren't contradictory. They only SEEM contradictory because you don't understand the meaning of the words being used. > > > > > > > Because if it did mean that, then > > > > the pole would also have to be shorter than the barn in the pole > > > > frame. > > > > The point is: the pole is not physically contracted in the barn frame > > > or the pole frame. In the barn frame the geometric porjection of the > > > pole unto the barn frame is contracted and this projected length is > > > able to fit into the barn with both doors close simultaneously. In the > > > pole frame the geometric projection of the length of the barn is > > > expanded and this expanded length is able to encase the pole > > > completely with both doors close simultaneously. > > > Notice that using the geometric concept both frames reach the same > > > conclusion that the projection of the pole is able to be encased by > > > the projection of the barn completely with the doors close > > > simultaneously. Also this approach satisfies the PoR and it is frame > > > dependent. > > > > >But this is explicitly said to be NOT the case in the barn and > > > > pole puzzle. In the pole frame, the pole is LONGER than the barn. So > > > > the shortening cannot possibly observer independent. > > > > What you said here violates the PoR.<sgrug> > > > No, it certainly does not. The PoR does NOT say that the same results > > will be seen in different reference frames. It says that the DIFFERENT > > results are all consistent with the SAME laws of physics in the > > different reference frames. > > It would help if you learned things like what the PoR actually says. > > 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. Sorry, Ken, that has NOTHING to do with the PoR. What do you think the PoR says? Quote it here:____________________________________ > > > > Ken Seto > > > > > > That's why your claim of > > > > > physical length contraction is bogus. > > > > > Physicists with clues (not you apparently)invented the alternate > > > > > explanation that length contraction is a geometric effect. This > > > > > explanation avoids the bogus assertion that the pole is physically > > > > > contracted and BTW geometric porjection is observer dependent. > > > > > > Ken Seto > > > > > > > Here's a quarter. Buy a clue. > > > > > > > > > > Ken Seto > > > > > > > > > > > Obviously there is *some* 'physical' relationship between the barn > > > > > > > > > > doors and pole that means an observer in that frame would measure the > > > > > > > > > > pole as being within the barn. How would you best describe that > > > > > > > > > > relationship? Is talking about 'between the barn doors at the same > > > > > > > > > > time in the barn frame of reference' something valid and meaningful to > > > > > > > > > > say?- Hide quoted text - > > > > > > > > > > > - Show quoted text -- Hide quoted text - > > > > > > > > > - Show quoted text -- Hide quoted text - > > > > > > > > > - Show quoted text -- Hide quoted text - > > > > > > > - Show quoted text -- Hide quoted text - > > > > > > > - Show quoted text -- Hide quoted text - > > > > > - Show quoted text -- Hide quoted text - > > > > > - Show quoted text -- Hide quoted text - > > > - Show quoted text -- Hide quoted text - > > > - Show quoted text -- Hide quoted text - > > > - Show quoted text - |