Is Length Contraction in SR physical??
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From: Ste on 4 Feb 2010 20:09 On 5 Feb, 00:17, mpalenik <markpale...(a)gmail.com> wrote: > 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. That is the issue to be tried, is it not? > > > 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. There is no experimental evidence that disproves this, because it is axiomatic. The challenge is, however, on me to keep this axiom consistent with what is observed, and so far I have heard nothing that disproves an absolute timeframe. > > 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. But then you're just describing the same thing with different numbers - the relationships should all be the same. The contention of relativity, surely, is that the "observer" is in a reference frame that does *not* encompass the entire universe (because otherwise it would be impossible to "change reference frames" without leaving the universe itself). > > > 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). See above. > > > 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. I don't really understand the maths of relativity, and I'm quite sure that these "reference frames" are required for mathematical purposes. What I reject is that these reference frames are necessary for understanding, or that they reflect any truth about the real world. > 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. This seems another way of saying "something physical is happening to the rocket, and nothing is happening to the Earth, and the reference frame is invalid once any physical changes occur".
From: artful on 4 Feb 2010 20:12 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.
From: artful on 4 Feb 2010 20:18 On Feb 5, 12:09 pm, Ste <ste_ro...(a)hotmail.com> wrote: > But then you're just describing the same thing with different numbers > - the relationships should all be the same. The contention of > relativity, surely, is that the "observer" is in a reference frame > that does *not* encompass the entire universe (because otherwise it > would be impossible to "change reference frames" without leaving the > universe itself). That is just completely laughable. Why do you bother having discussions on topics when you have no understanding of the basic terms. What is the point? Don't you know that EVERY reference frame encompasses the entire universe? Don't you know that changing reference frame is just a change of coordinate values for events? Don't you know that whenever you accelerate, you are changing your frame of reference (ie the frame(s) in which you are measured as being at rest) .. that there is no need to leave the universe to do that? Gees.
From: eric gisse on 4 Feb 2010 20:33 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. ....and now you have met Ken Seto. He's only been doing this for 15 years...
From: mpalenik on 4 Feb 2010 20:56
On Feb 4, 8:18 pm, artful <artful...(a)hotmail.com> wrote: > On Feb 5, 12:09 pm, Ste <ste_ro...(a)hotmail.com> wrote: > > > But then you're just describing the same thing with different numbers > > - the relationships should all be the same. The contention of > > relativity, surely, is that the "observer" is in a reference frame > > that does *not* encompass the entire universe (because otherwise it > > would be impossible to "change reference frames" without leaving the > > universe itself). > > That is just completely laughable. Why do you bother having > discussions on topics when you have no understanding of the basic > terms. What is the point? > > Don't you know that EVERY reference frame encompasses the entire > universe? > > Don't you know that changing reference frame is just a change of > coordinate values for events? > > Don't you know that whenever you accelerate, you are changing your > frame of reference (ie the frame(s) in which you are measured as being > at rest) .. that there is no need to leave the universe to do that? > > Gees. Thank you. Ste: exactly what he said. |