Is Length Contraction in SR physical??
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From: Ste on 4 Feb 2010 20:56 On 5 Feb, 00:19, artful <artful...(a)hotmail.com> wrote: > 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 That is what I'm trying to do. That's why I want to discuss specific examples, so that I can show you that the physical reality is not nearly as complex as the maths would lead you to believe. > > > 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. That's the point, it *doesn't exist*. Time is an abstract concept. > > 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? No, an reference frame only encompasses that which is in the reference frame. By definition, if there is more than one reference frame, then you can't be using all of them at once. As I say, in my "universal reference frame", an observer does not undergo a change in reference frame when accelerating. > > > 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. No, if you're describing the same thing with different numbers (or words), then it means that you're arguing over language. > > > 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? Neither. I can give you a model-sized globe and an ant glued to it. It doesn't matter where you draw the lines onto the globe, nothing about where you draw the lines changes the physical nature of where the ant is in relation to the globe - it remains in the same place, no matter where you draw the lines. When you learn to look at the physical world in the mind's eye as God would, you'll understand the inconsequential nature of where the lines are drawn on the globe - much more important, if you are an ant, is to develop a concept of the globe in the first place. > > > 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? There are two solutions to this really. I genuinely don't know whether it is possible to discern some sort of absolute background against which one can be at rest, but if not then the 'entirety of the universe' is the absolute reference frame. Of course, your guess is as good as mine as to where the edges of the universe are. > > 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 The point is that acceleration is a physical change, and has physical effects - you know, the sort of effects that physics is supposed to explain. When someone says "why did the astronaut twin come back younger, you're not supposed to say 'because he changed his reference frame', you're supposed to say because...", and obviously that answer remains outstanding. Of course, the jig would be up for these mathematicians if, after all, time didn't slow down, only the clock did (because of a mechanical effect).
From: Ste on 4 Feb 2010 21:15 On 5 Feb, 00:26, mpalenik <markpale...(a)gmail.com> wrote: > 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. Then by this argument, God is a valid scientific explanation, because he can be inferred from his effects. > > > 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. I never said I could disprove it. That was precisely my point. I asked what happens in science when observations cannot discern between two theories? > > > > > 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 if science is not just "what scientists do" (as Paul Draper has contended), then what is it? And please, don't come back and say "it's what scientists do when they do 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), If they don't consider the question beyond applying the maths, then you confirm my contention elsewhere that too many "physicists" have no theoretical understanding of the physical world, beyond the crude application of maths that they've learned by rote. > 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). Ah, so it is the "existing theory that decides what they can observe"! You know I can see Paul slapping his forehead in dread. > > > 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. Yes, I'd been led to believe that falsifiability defined a "scientific theory", and that anything that wasn't falsifiable wasn't scientific. > 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. Indeed. I'm still interested to hear your views on what defines the "scientific method". > > 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. Aha! You beat me to it. So what did you mean by: "[science] relies on past behavior being a predictor of future behavior."? If the universe is indeterministic, then how can past behaviour *possibly* be a predictor of future behaviour?
From: Ste on 4 Feb 2010 21:16 On 5 Feb, 00:49, 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. > 2. The pole cannot fit into the barn with both doors close > simultaneously. Take comfort Ken that at least there's someone here who understands your simple questions.
From: mpalenik on 4 Feb 2010 21:16 On Feb 4, 8:56 pm, Ste <ste_ro...(a)hotmail.com> wrote: > On 5 Feb, 00:19, artful <artful...(a)hotmail.com> wrote: > > > > Don't you realize that EVERY reference frame encompasses the whole > > universe? > > No, an reference frame only encompasses that which is in the reference > frame. By definition, if there is more than one reference frame, then > you can't be using all of them at once. As I say, in my "universal > reference frame", an observer does not undergo a change in reference > frame when accelerating. > This is wrong on so many levels. First of all, in the framework of GR, you actually can describe an accelerating observer with a single reference frame in the geometry of curved space time. But we don't need to get into that right now, we can have a meaningful discussion simply within the framework of SR. Second of all, replace the term "reference frame" with "point of view"--meaning your viewpoint of the velocities and distances to objects around you. You're essentially saying that an observer does not undergo a change of "point of view" when accelerating. Third of all, a single reference frame DOES encompass all objects in the universe. From your reference frame, you can assign 6 coordinates to every object in the universe--3 for position and 3 for velocity. This is how every object is encompassed by a single reference frame. Every object has coordinates within every reference frame. It is simply a matter of different reference frames assigning different coordinates to each object. But all frames are equally valid.
From: J. Clarke on 4 Feb 2010 21:24
artful 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. Uh, logic says that either the pole fits in the barn or it does not fit in the barn. It can't do both in relativity. |