Is Length Contraction in SR physical??
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From: mpalenik on 4 Feb 2010 17:09 On Feb 4, 5:00 pm, Ste <ste_ro...(a)hotmail.com> wrote: > On 4 Feb, 15:37, PD <thedraperfam...(a)gmail.com> wrote: > > > On Feb 3, 9:23 pm, Ste <ste_ro...(a)hotmail.com> wrote: > > > > > Science is in the business of testing propositions by confronting the > > > > consequences of those propositions against *observable* measurement.. > > > > This is the spine of the scientific method. > > > > Indeed. But what if I have axioms that are not testable, but from > > > which testable hypotheses can be drawn? If the hypotheses that are > > > drawn from the axioms appear to be true, then is it reasonable to say > > > that the axioms are true? > > > Yes. > > Ok, but now you've cut your own throat, because if the axiom was some > unobservable phenomena, then you've just said it's reasonable to infer > its existence from the conclusions/predictions that are drawn from it. > Or have I misunderstood? The axiom is not unobservable if it has observable consequences. I think you're misunderstanding the definition of "observable". > > I disagree. Scientists are concerned with the unobservable only > > insofar as those have necessary, distinctive, and accessibly > > observable consequences. > > But then you've subtly contradicted your earlier statement. Now > scientists are concerned with the unobservable in certain > circumstances. No. Science is concerned with making observations and then basing a theory off of those observations. If it is not observable, you cannot base a theory off of it. If an axiom is indirectly observable, it is still observable--that is, if it is the only explanation for a given observation, then making that observation is the same as observing the axiom. > > > If those do not, then science is simply not > > concerned with them at all. This is why science has NO SAY on matters > > of spirits, souls, and deities. > > I dare say any self-respecting scientist is in competition with those > concepts. Not at all. It doesn't come up in science ever. There's no reason to talk about it. If you're talking about spirits and dieties, you're not doing science. > > > > > So your notion of "real" variables that > > > > cannot be measured has the same objective reality as, say, heaven. > > > > My "real" variables *are* objective reality, > > > You don't KNOW they are objective reality, until you can devise a test > > that shows their distinctive footprints. You have FAITH that they are > > objective reality. > > Yes, just as I have faith that there *is* an objective, naturalistic, > reality. But observation cannot discern between this and any other > axiomatic belief. > That's why science doesn't try to comment on reality beyond the way reality can be observed. > > > > Your inference of "real" properties independent of observed properties > > > > has the same scientific verifiability as God, which is to say none. > > > > But the scientific method itself has the same verifiability as God. > > > You've just never thought about the philosophy of science enough to > > > see the arbitrary assumptions that underpin it. > > > The scientific method does not have a priori validity, nor does it > > claim it. What it is is an *operational* convention that is adopted > > because it has demonstrated success. > > So in what way could it be falsified? For example, if the laws of physics were to completely change tomorrow morning, that would indicate that the scientific method is not good because it relies on past behavior being a predictor of future behavior.
From: Ste on 4 Feb 2010 17:14 On 4 Feb, 20:59, "papar...(a)gmail.com" <papar...(a)gmail.com> wrote: > On 4 feb, 00:53, Ste <ste_ro...(a)hotmail.com> wrote: > > > On 4 Feb, 02:35, YBM <ybm...(a)nooos.fr.invalid> wrote: > > > > Come on Ste, don't be stupid. Next time you'll choose a frame of > > > reference which is different only by the origin and will play the > > > same silly game. > > > How was it a silly game? I was told simultaneity can never apply to > > more than one frame, and I've just given you two frames where that is > > clearly untrue. I suppose if anything, this proves that I *do* > > understand. > > After reading your numerous posts, you seem to be certain that a given > reality is always present, which is independent of what is being > measured. > > I propose you the following thought experiment regarding that: > > a) You are in a space ship A in deep space. Your surroundings are such > that you experience no gravity at all In other words, "let us imagine that we are not in the real world...". > and, if you look through a > window, no stars or galaxies are seen. Basically you are in the middle > of nowhere. Of course, you don't know if your space ship is moving and > the ship engines appear to be dead. > b) Suddenly, you observe another space ship B on your window, which to > you appears to be approaching your location (it is becoming larger and > larger in size as time goes by). > > Now, which of the following conclusions describe the reality of the > gedanken: > > 1) Space ship B is sitting still and space ship A is moving at speed v > towards the location of B. > 2) Space ship B is approaching at speed v to your space ship A > location, where A sits still. > 3) Both space ships are moving in such a way their closing speed is v. > 4) It is impossible to determine if (1), (2) or (3) reflects reality > or, in other words, all alternatives (1), (2) and (3) can be true at > the same time. Indeed, on the information available, (4) is the only conclusion that one can reach. The question is whether this accurately describes reality (i.e. whether there really is no way to discern absolute velocity), and whether, indeed, there is no way of discerning absolute motion. It is a question that I am not yet able to answer. Of course, none of this detracts from the reality that, even if it is indiscernible, I still hold that there is an absolute background against which either (1), (2), or (3) are true. It is simply that we don't know which.
From: mpalenik on 4 Feb 2010 17:24 On Feb 4, 5:14 pm, Ste <ste_ro...(a)hotmail.com> wrote: > > Indeed, on the information available, (4) is the only conclusion that > one can reach. The question is whether this accurately describes > reality (i.e. whether there really is no way to discern absolute > velocity), and whether, indeed, there is no way of discerning absolute > motion. It is a question that I am not yet able to answer. > > Of course, none of this detracts from the reality that, even if it is > indiscernible, I still hold that there is an absolute background > against which either (1), (2), or (3) are true. It is simply that we > don't know which.- Hide quoted text - > In relativity, velocity is simply a choice of coordinates. In other words, what we call "time" and "space" are only defined for a given observer in a given frame of reference. Another observer who calls slightly different directions through the universe "time" and "space" will see your forward motion through what you call "time" as forward motion partly through "time" and partly through "space", which is why you appear to have a velocity to him, and vice versa. Since you seem to believe there is an absolute set of coordinates in the universe that define time and space (thereby defining velocity), maybe the question could be posed a slightly different way. Lets say that I have a spherical ball with no markings on it whatsoever and there's an ant sitting on the surface. To define the location of the ant, I draw a system of coordinates on the ball. I choose a point for the north pole and use spherical coordinates (like those you see on a globe). I describe the location of the ant in these coordinates. Now, you decide to do the same thing, except you choose a different point as the north pole and draw your spherical coordinates that way. You describe the location of the ant in your coordinates. We both give different numbers to describe the location of the ant, although we are both referring to the same point. Which of our sets of numbers is correct? Saying that an object has a velocity with respect to you is no different than defining your own set of coordinates in the universe.
From: kenseto on 4 Feb 2010 17:59 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....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. > > > > > > > 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. > > > > 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. > > > > > > > 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 -
From: mpalenik on 4 Feb 2010 18:04
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. |