Is Length Contraction in SR physical??
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From: mpalenik on 4 Feb 2010 19:17 On Feb 4, 6:47 pm, Ste <ste_ro...(a)hotmail.com> wrote: > On 4 Feb, 22:24, mpalenik <markpale...(a)gmail.com> wrote: > > > 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. > > And I ridicule this interpretation. Well, unfortunately for you, it's the correct interpretation. > > > 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. > > There is certainly an absolute time (I do not recognise it as a "real" > dimension in any event, but a device we use to express change and make > predictions). You have not presented any evidence for absolute time and in fact, experimental evidence exists to the contrary. As for space, it is difficult to say, but at the very > least I would refer to the "absolute reference frame" as that frame > which encompasses the whole universe within one frame. You can make multiple coordinate systems that encompass the whole universe, all equally valid. > > > 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. > > So in other words, you're describing exactly the same thing with > different maths? > > > 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? > > Both, within their own terms. Exactly, it's the same with velocities. An object has a 4 dimensional trajectory through spacetime. What velocity you choose to call that through three dimensional space depends on your orientation in 4 dimensional spacetime (i.e. your coordinate system). > > > Saying that an object has a velocity with respect to you is no > > different than defining your own set of coordinates in the universe. > > Indeed. The question still remains whether there is "absolute > velocity". Certainly this defining of coordinates relative to one's > self doesn't explain why an accelerometer on a rocket measures 10g (or > whatever), while the Earth registers no change. Because you can't define an inertial coordinate system in flat spacetime where you have acceleration. In the above example with the ant on the sphere, it's like trying to describe the location of the ant on a spinning sphere with a coordinate fixed system. The rocket is accelerating in its own frame and has to continually change coordinate systems. You cannot say which coordinate system is correct, but you can certainly tell if two coordinate systems are different.
From: artful on 4 Feb 2010 19:19 On Feb 5, 10:47 am, Ste <ste_ro...(a)hotmail.com> wrote: > On 4 Feb, 22:24, mpalenik <markpale...(a)gmail.com> wrote: > > > 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. > > And I ridicule this interpretation. Poking your tongue out and teasing isn't terribly productive. You would need to either a) show why it is invliad b) provide some 'better' interpretation that is equally as valid > > 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. > > There is certainly an absolute time (I do not recognise it as a "real" > dimension in any event, but a device we use to express change and make > predictions). your assertion that it exist even thou one cannot detect it (which means it has no effect on reality) is rather pointless. > As for space, it is difficult to say, but at the very > least I would refer to the "absolute reference frame" as that frame > which encompasses the whole universe within one frame. Oh dear .. so you don't even know what a reference frame is. Don't you realize that EVERY reference frame encompasses the whole universe? > > 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. > > So in other words, you're describing exactly the same thing with > different maths? Which shows there are multiple ways to describe a location which depend on frame of reference. There isn't one single absolute one. > > 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? > > Both, within their own terms. So which one is the absolute? > > Saying that an object has a velocity with respect to you is no > > different than defining your own set of coordinates in the universe. > > Indeed. The question still remains whether there is "absolute > velocity". velocity only makes sense when it is wrt something .. so you would need something that is absolutely at rest. What do you have in mind? And WHY must it be considered as absolutely at rest? > Certainly this defining of coordinates relative to one's > self doesn't explain why an accelerometer on a rocket measures 10g (or > whatever), while the Earth registers no change. Are you trying to make a point with that comments .. because you haven't
From: mpalenik on 4 Feb 2010 19:26 On Feb 4, 6:33 pm, Ste <ste_ro...(a)hotmail.com> wrote: > On 4 Feb, 22:09, mpalenik <markpale...(a)gmail.com> wrote: > > > On Feb 4, 5:00 pm, Ste <ste_ro...(a)hotmail.com> wrote: > > > > > 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". > > No, I merely think you're confused. If it is tolerable to have an > axiom that is unobservable, but whose effects are not, then that > vindicates my "faith" in the existence of variables that may not be > directly observable, but whose existence is inferrered from > consequential effects. If it's existence can be inferred from consequential effects, then it is observable. Nobody is arguing that if there are measurable consequential effects that it's not within the realm of science. > > > > > 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. > > Which is really a non-sequitur in relation to my statement. > > > 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. > > But what if observations are unable to discern between two axioms that > both explain the same effects? Such as the pink elephants that I described? You still haven't proven that theory incorrect. You said you didn't *like* it, but that's not a disproof of a theory, and there are likely many truths that you don't like. > > > > > 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. > > But I've been told that "science" is "what scientists do". Are you > seriously telling me that a scientist has never contemplated spirits, > souls, and deities? And are you telling me that no scientist is > religious (in the traditional sense)? Not everything that scientists do is science. I play the piano and record music. That doesn't make it 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. > > But it *does* comment on reality beyond mere observation, *all the > time*. What is string theory but a comment on reality beyond what is > observed? What are the various interpretations of QM, but a comment on > reality beyond what is observed? > That's why 1) most of the time scientists don't worry about that question beyond "psi squared represents probability" (which is a measurable, testable effect), and 2) scientists when they do think about that try to find interpretations that allow observed quantum behavior to make sense in the context of known theory (which has been experimentally tested). > > > 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. > > That wouldn't falsify falsificationism, it would merely falsify the > existing laws of physics. Falsificationism? I thought we were talking about the scientific method. If the laws of physics change on a daily, hourly, or random basis, with no connection whatsoever to the previous laws of physics, then the scientific method is useless. > > What you mean is if *determinism* was falsified, that would falsify > the scientific method. That's not what I mean at all. Determinism is falsified through quantum mechanics.
From: artful on 4 Feb 2010 19:27 On Feb 5, 11:16 am, kenseto <kens...(a)erinet.com> wrote: > On Feb 4, 4:11 pm, artful <artful...(a)hotmail.com> wrote: > > > > > > > On Feb 5, 2:57 am, Tom Roberts <tjrob...(a)sbcglobal.net> wrote: > > [snip] > > > > I think "fictitious" covers it well. > > > Yeup .. that's the word that had eluded me :) Thanks. > > > > What's wrong with simply stating the truth: "length contraction" is purely > > > geometrical in the 4-D spacetime of relativity. As is common, geometrical > > > relationships can have physical consequences (e.g. the ladder does or does not > > > fit through the doorway). Physics can never be separated from geometry. > > > I think it better to say length contraction can be *modeled* by a > > geometrical projection. Pure geometry is a purely abstract notion .. > > and length contraction is more than just that because, as you say, it > > has physical consequences. Of course, one can then argue that if the > > consequences of length contraction (including measurement of it by > > whether things fit in barns) are physical, then doesn't that mean the > > length contraction is physical in the same sense. ie Can something > > non-physical have a physical consequent? Surely the geometry is > > modelling something physical .. that's pretty much the point of > > physics.. in which case is it misleading to call it *purely* > > geometrical? > > > Further .. I think perhaps the confusion would be relieved by changing > > your working somewhat: > > > Physical reality is modeled by the geometry of the 4-D spacetime of > > relativity. As is common, geometrical relationships can have physical > > consequences (e.g. the ladder does or does not fit through the > > doorway). "length contraction" is one such physical consequent > > Fitting a ladder through a narrow door way is not the same as fitting > a long pole into a shorter barn with both doors close simultaneously. That you cannot see the analgoy just shows you have NO idea what SR says Both have a longer length object fitting within a shorter spae Both have a geometrical rotation and projection The ladder fits thru the doorway just as 'physically' as a pole fits in the barn.
From: kenseto on 4 Feb 2010 19:49
On Feb 4, 6:04 pm, mpalenik <markpale...(a)gmail.com> wrote: > On Feb 4, 5:59 pm, "kens...(a)erinet.com" <kens...(a)erinet.com> wrote: > > > > > It it does violate the PoR. You made the contradcictory claims that > > the pole can fit into the barn physically (materially) an at the same > > time you claim that the pole cannot fit into the barn physically > > (materially)......that a violation of the PoR. > > No. The doors are not closed simultaneously in the pole's frame, nor > are the two ends of the pole simultaneously in the barn in the pole's > reference frame. In the barn's frame, the two ends of the pole are in > the barn simultaneously and the doors shut simultaneously. In the > pole's frame, the two ends of the pole are in the barn at different > times and the doors shut at different times. Sigh..You are making the contradictory claims: 1. The pole can fit into the barn with both doors close simultaneously. 2. The pole cannot fit into the barn with both doors close simultaneously. |