Length Contraction is WRONG

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1 "ripzone23" Length Contraction is WRONG vrijdag 12 april 2002 21:06
2 "Eric Prebys" Re: Length Contraction is WRONG zaterdag 13 april 2002 0:55
3 "Russell Blackadar" Re: Length Contraction is WRONG zaterdag 13 april 2002 1:33
4 "Stephen Speicher" Re: Length Contraction is WRONG zaterdag 13 april 2002 7:57
5 "John" Re: Length Contraction is WRONG zaterdag 13 april 2002 13:10
6 "Oriel36" Re: Length Contraction is WRONG zaterdag 13 april 2002 21:11
7 "David Hartley" Re: Length Contraction is WRONG zaterdag 13 april 2002 23:09
8 "Bilge" Re: Length Contraction is WRONG zondag 14 april 2002 11:25
9 "Oriel36" Re: Length Contraction is WRONG zondag 14 april 2002 19:43
10 "Bilge" Re: Length Contraction is WRONG zondag 14 april 2002 23:52
11 "Nicolaas Vroom" Re: Length Contraction is WRONG maandag 15 april 2002 17:59
12 "ripzone23" Re: Length Contraction is WRONG dinsdag 16 april 2002 22:16


1 Length Contraction is WRONG

Van: "ripzone23"
Onderwerp: Length Contraction is WRONG
Datum: vrijdag 12 april 2002 21:06

WRONG? No, just wanted someone's attention. My other post on the subject was ignored, rightly so, since the FAQ explains this "paradox" somewhat.

I still had one question concerning the barn & pole "paradox". What would happen if the runner took a "snapshot" of the barn and pole when he was at the exact center of the barn (no closing doors involved) and the barn viewer did the same? Now, regardless of whether or not they take their respective pictures at the same time, what will the pictures show? Will the runners picture show a pole much longer than the barn? Will the barn-viewer's picture show a pole much shorter and able to fit inside the barn?

The difficulty I have is that it seems to me that the center of the barn is THE center of the barn regardless of viewer.

Also, if this question is answered by the simultaneity clause, let me put a twist in. What if the barn viewer is standing at the center of the barn and the runner crashes into him, and at that exact moment of impact, a picture is taken by barn viewer and runner, what will the picture show? Will the runners pole be sticking out past the barn door, or will the pole fit exactly in the barn? How would you be able to tell who was moving and who was standing still?

Obviously, the impact will create a simultaneous event. But is seems like it would be important to define who was moving because the energy from the moving person will push on the stationary person, right? Would this fact not disallow the moving person from calling his frame of reference as being at rest?


2 Length Contraction is WRONG

Van: "Eric Prebys"
Onderwerp: Re: Length Contraction is WRONG
Datum: zaterdag 13 april 2002 0:55

ripzone23 wrote:
>

WRONG? No, just wanted someone's attention. My other post on the subject was ignored, rightly so, since the FAQ explains this "paradox" somewhat.

I still had one question concerning the barn & pole "paradox". What would happen if the runner took a "snapshot" of the barn and pole when he was at the exact center of the barn (no closing doors involved) and the barn viewer did the same? Now, regardless of whether or not they take their respective pictures at the same time, what will the pictures show? Will the runners picture show a pole much longer than the barn? Will the barn-viewer's picture show a pole much shorter and able to fit inside the barn?

The difficulty I have is that it seems to me that the center of the barn is THE center of the barn regardless of viewer.

Also, if this question is answered by the simultaneity clause, let me put a twist in. What if the barn viewer is standing at the center of the barn and the runner crashes into him, and at that exact moment of impact, a picture is taken by barn viewer and runner, what will the picture show? Will the runners pole be sticking out past the barn door, or will the pole fit exactly in the barn? How would you be able to tell who was moving and who was standing still?

Obviously, the impact will create a simultaneous event. But is seems like it would be important to define who was moving because the energy from the moving person will push on the stationary person, right? Would this fact not disallow the moving person from calling his frame of reference as being at rest?

You're implicitly assuming that a camera would correctly show the instantaneous state of the barn and the pole in *either* frame. In fact, it shows the state of things when the light left the source, and while both observers would have to agree on what the camera image showed, they would *disagree* on what that meant in terms of when the light left the source. Try the problem again, only this time factor in the propagation time of the light, and you'll find there's no "paradox".

It's a common misunderstanding that a Lorentz transformation tells you what things "look" like to different observers (partly because of sloppy wording in textbooks). Lorentz transformations tell you the positions of things assuming you've already appropriately corrected for signal propagation delays. In general, the problem of what things really "look" like (to your eye, or to a camera) is more complicated.

--
-------------------------------------------------------------------
Eric Prebys, Fermi National Accelerator Laboratory
Office: 630-840-8369, Email: prebys@fnal.gov
WWW: http://home.fnal.gov/~prebys
-------------------------------------------------------------------


3 Length Contraction is WRONG

Van: "Russell Blackadar"
Onderwerp: Re: Length Contraction is WRONG
Datum: zaterdag 13 april 2002 1:33

ripzone23 wrote:
>

WRONG? No, just wanted someone's attention. My other post on the subject was ignored, rightly so, since the FAQ explains this "paradox" somewhat.

I still had one question concerning the barn & pole "paradox". What would happen if the runner took a "snapshot" of the barn and pole when he was at the exact center of the barn (no closing doors involved) and the barn viewer did the same?

Well, real pictures are tricky because they are always views of the *past* -- it takes finite time for light to travel to the film from the events being photographed. And the image on film does not even record a single (simultaneous) instant of time, since in general the events being photographed are not all at the same distance from the film and hence have different light-travel times before they are recorded.

Also, I am not sure how you'd propose to measure the length of the pole (or the barn) from a snapshot taken by someone at its center. The camera would have to shoot both directions simultaneously -- which could be arranged, I suppose -- but the orientation would be wrong. It would be like looking end-on at a 2x4 and trying to guess its length.

We can minimize these problems by placing the barn-frame's photographer not the at the center of the barn, but rather, at a distance of (say) 1000m away on a perpendicular line drawn through the barn's center. This photographer must click his shutter at time t=1000/c after the event which we want to record, namely the passing of the pole's center and the barn's center. At a distance of 1km, parallax is very small and so, at least in the vertical plane containing the pole, we can consider all the events in the image as essentially simultaneous. Also, we have the advantage of seeing the pole and barn side-on from this vantage point. (Perhaps we should put a big window in the barn so we can see the pole when it is inside.)

Similarly, we can have an accomplice of the runner, moving parallel to the runner and at the same speed, but separated by 1000m, take a picture, also along the perpendicular in his frame so that the barn and pole are imaged side-on. He too will click his shutter at t'=1000/c (in his frame; note the prime) after the event.

Now, regardless of whether or
> not they take their respective pictures at the same time, what will the pictures show?

In my changed statement of the problem, they don't actually get taken at the same time -- but they do both record the same event, namely, the event at which the center of the pole is at the center of the barn. However, the recorded events at the ends of the pole will not be the same in the two images, due to the relativity of simultaneity, and this accounts for the differences that I describe below.

Will the runners picture show a
> pole much longer than the barn?

Yes, or rather that's what his accomplice's picture will show.

(As an aside for more advanced readers, yes, I'm aware of Penrose-Terrell rotation. It's true that the image will present the illusion that the barn is rotated rather than contracted; however, in the present case it will be clear that the barn is not *really* rotated since the pole will manifestly be sticking out of both doors in the image.)

Will the
> barn-viewer's picture show a pole much shorter and able to fit inside the barn?

Yes.

>

The difficulty I have is that it seems to me that the center of the barn is THE center of the barn regardless of viewer.

Of course, but that's not the relevant issue here. The center of the pole being at the center of the barn is of course a single event and is perceived as such by both frames. But the interesting thing is when you consider the events that are simultaneous to this center event, but at the respective ends of the pole. Since the distance to the ends is nonzero, SR predicts that simultaneity will depend on frame. The simultaneous front and back events in the barn frame (which as we know happen to be inside the barn) will not be simultanous in the runner's frame, but rather, *different* events will be simultaneous in that frame. Ones that are outside the barn.

>

Also, if this question is answered by the simultaneity clause,

R of S is the answer, but as we've seen, *not* applied at the center of the pole but rather at its ends.

let me put a twist in.
> What if the barn viewer is standing at the center of the barn and the runner crashes into him, and at that exact moment of impact, a picture is taken by barn viewer and runner, what will the picture show?

If you mean at the first instant of the crash, before either photographer has accelerated due to the crash, then the answer is of course the same as above.

But if you mean after the crash, the answer is complicated and you really have to give us more information before an answer can be given. For one thing, since the runner cannot stop in zero time (infinite acceleration) he won't be at the middle of the barn at the end of the crash. And surely the "stationary" observer will no longer be stationary in the barn frame after the crash. Also the pole may well have been distorted physically by the huge forces generated by the crash. But if it survives without distortion, and if it comes to rest in the barn frame, it will be longer than the barn.

Will the runners
> pole be sticking out past the barn door, or will the pole fit exactly in the barn? How would you be able to tell who was moving and who was standing still?

You can't. That conjecture -- or perhaps we can say that fact since nobody yet has found a way to do what you propose -- is the very foundation of relativity.

>

Obviously, the impact will create a simultaneous event. But is seems like it would be important to define who was moving because the energy from the moving person will push on the stationary person, right?

And the "stationary" person will push on the moving person. It's precisely symmetrical; their roles are perfectly reversed when you change frames.

(Yes, the stationary person has zero kinetic energy in his own frame, but in the runner's frame he has an enormous KE. Energy is frame dependent, and so is momentum, which I think is even more relevant to your question. The upshot is that nobody can say which observer's point of view is the "right" one.)

Would this fact not disallow the
> moving person from calling his frame of reference as being at rest?

It would if it were a "fact". But it isn't.

I suppose you could force it to be true by fiat, but there would be no physical basis for doing so. Besides, a barn in the U.S. is not in the same frame as a barn in India, so one must ask which barn would you designate as "stationary"? Whichever you picked would be damned inconvenient, so physicists would probably just ignore your fiat and do things the easier way, which turns out to be SR.


4 Length Contraction is WRONG

Van: "Stephen Speicher"
Onderwerp: Re: Length Contraction is WRONG
Datum: zaterdag 13 april 2002 7:57

On Fri, 12 Apr 2002, Russell Blackadar wrote:

> ripzone23 wrote:
> >

I still had one question concerning the barn & pole "paradox".

>
[...]

That was a really great explanation, Russell.

Stephen
sjs@compbio.caltech.edu

Welcome to California. Bring your own batteries.

Printed using 100% recycled electrons.
--------------------------------------------------------


Mese Length Contraction is WRONG

Van: "John"
Onderwerp: Re: Length Contraction is WRONG
Datum: zaterdag 13 april 2002 13:10

Very cool, I'm going to save that one and go over it for a while.

Many thanks,

John


6 Length Contraction is WRONG

Van: "Oriel36"
Onderwerp: Re: Length Contraction is WRONG
Datum: zaterdag 13 april 2002 21:11

Russell Blackadar wrote in message news:<3CB76EB8.5C0BFDEF@mdli.com>...
> ripzone23 wrote:
> >

WRONG? No, just wanted someone's attention. My other post on the subject was ignored, rightly so, since the FAQ explains this "paradox" somewhat.

I still had one question concerning the barn & pole "paradox". What would happen if the runner took a "snapshot" of the barn and pole when he was at the exact center of the barn (no closing doors involved) and the barn viewer did the same?

>

Well, real pictures are tricky because they are always views of the *past* -- it takes finite time for light to travel to the film from the events being photographed. And the image on film does not even record a single (simultaneous) instant of time, since in general the events being photographed are not all at the same distance from the film and hence have different light-travel times before they are recorded.

Wonderful!,now take the next step and apply it to cosmic expansion in all directions and figure out why nature prohibits a true discernment of its actual structure and motion insofar as we are surrounded by 'past' observance in all directions.Reducing acceleration to 'distance covered' by light is exactly the same as distance covered at different locations on the planet either side of the Equitorial line,seconds of a clock being a proportion of varying distance rather than a measure of a seperate quantity that SR covered calls time.

Looking down from space at the axis of rotation (North or South pole) we notice that the distance covered is at the poles is at a min while at the greatest circumference (Equator) it is at a max.Nobody mistakes the notion of acceleration as anything but rotation in this instance,distance covered for a given interval changes but nothing else does, making SR concepts superfluous otherwise cosmic acceleration would be incorrectly misinterpreted.

'Every point is the valid center' is a really poor misinterpretation of the true structure of the cosmos insofar it takes our position as a 'center' at face value and works on from there,quite profound in its infantile perspective actually.At a fundamental level SR cannot distinguish acceleration from rotation for it locks in time with space whereas a more subtle approach would discern that seconds,minutes,hours of a clock relate to proportions of distance covered.

Where for the last 100 years,SRists may have thought that clocks,seconds, minutes,etc were measuring a seperate quantity (time) ,they were instead toying around with proportions and ratios of distance covered.It does'nt take a genius to figure out why you cannot translate acceleration into rotation through SR and especially with the ambiguous if poorly objective "Clocks measure time".


7 Length Contraction is WRONG

Van: "David Hartley"
Onderwerp: Re: Length Contraction is WRONG
Datum: zaterdag 13 april 2002 23:09

In article <3CB76EB8.5C0BFDEF@mdli.com>, Russell Blackadar writes
> ripzone23 wrote:
>>

WRONG? No, just wanted someone's attention. My other post on the subject was ignored, rightly so, since the FAQ explains this "paradox" somewhat.

I still had one question concerning the barn & pole "paradox". What would happen if the runner took a "snapshot" of the barn and pole when he was at the exact center of the barn (no closing doors involved) and the barn viewer did the same?

>
I partially answered this in my post on "Visual appearance of moving rod" which I sent before seeing this one. The time-lag distorts things considerably: "what you see is not what you observe".

The barn viewer - if he is next to the centre of the pole, at the centre of the barn - sees the front of the pole half way between him and the exit, and the back end still outside, well short of the entrance. But when he sees the doors close, a little while later, he sees the pole completely inside the barn.

The runner sees the same light as the barn observer, as he is at the same event, so he sees the same pattern: the front of the pole appears to be about half way to the exit door, the back of the pole has not yet reached the entrance. The actual distances are different but their ratios are the same. Using the figures in the FAQ (barn 40m, pole 80m, gamma 2), the exit door of the barn is 10m in front of the runner, but appears to be about 77m away. The door has already closed and opened again - the front end of the pole has already exited - but the runner hasn't seen the door shut yet and sees the front end as still within the barn. The entrance door is 10m behind but seems to be only a little over 5m away. The runner will have left the barn before he sees the back of the pole go through this door and then sees the door close.

> Well, real pictures are tricky because they are always views of the *past* -- it takes finite time for light to travel to the film from the events being photographed. And the image on film does not even record a single (simultaneous) instant of time, since in general the events being photographed are not all at the same distance from the film and hence have different light-travel times before they are recorded.

Also, I am not sure how you'd propose to measure the length of the pole (or the barn) from a snapshot taken by someone at its center. The camera would have to shoot both directions simultaneously -- which could be arranged, I suppose -- but the orientation would be wrong. It would be like looking end-on at a 2x4 and trying to guess its length.

We can minimize these problems by placing the barn-frame's photographer not the at the center of the barn, but rather, at a distance of (say) 1000m away on a perpendicular line drawn through the barn's center. This photographer must click his shutter at time t=1000/c after the event which we want to record, namely the passing of the pole's center and the barn's center. At a distance of 1km, parallax is very small and so, at least in the vertical plane containing the pole, we can consider all the events in the image as essentially simultaneous. Also, we have the advantage of seeing the pole and barn side-on from this vantage point. (Perhaps we should put a big window in the barn so we can see the pole when it is inside.)

Similarly, we can have an accomplice of the runner, moving parallel to the runner and at the same speed, but separated by 1000m, take a picture, also along the perpendicular in his frame so that the barn and pole are imaged side-on. He too will click his shutter at t'=1000/c (in his frame; note the prime) after the event.

It is interesting to consider another accomplice, also moving parallel to the runner and 1000m to the side, but lagging behind so that he takes his photo when he coincides with the barn-frame photographer. He sees the same light as the barn photographer, so his photo will show the pole inside the barn. But the pole is fixed in his frame, ahead and to the side, so he has to angle his camera forward. This shows the Penrose-Terrell rotation, he sees the same thing but at a different angle.

> Now, regardless of whether or
>> not they take their respective pictures at the same time, what will the pictures show?
>

In my changed statement of the problem, they don't actually get taken at the same time -- but they do both record the same event, namely, the event at which the center of the pole is at the center of the barn. However, the recorded events at the ends of the pole will not be the same in the two images, due to the relativity of simultaneity, and this accounts for the differences that I describe below.

Will the runners picture show a

>> pole much longer than the barn?
>

Yes, or rather that's what his accomplice's picture will show.

(As an aside for more advanced readers, yes, I'm aware of Penrose-Terrell rotation. It's true that the image will present the illusion that the barn is rotated rather than contracted; however, in the present case it will be clear that the barn is not *really* rotated since the pole will manifestly be sticking out of both doors in the image.)

Will the

>> barn-viewer's picture show a pole much shorter and able to fit inside the barn?
>

Yes.

--
David Hartley


8 Length Contraction is WRONG

Van: "Bilge"
Onderwerp: Re: Length Contraction is WRONG
Datum: zondag 14 april 2002 11:25

Oriel36 left bird droppings:

>

Wonderful!,now take the next step and apply it to cosmic expansion in

OK.


9 Length Contraction is WRONG

Van: "Oriel36"
Onderwerp: Re: Length Contraction is WRONG
Datum: zondag 14 april 2002 19:43

root@radioactivex.lebesque-al.net (Bilge) wrote in message news:...
> Oriel36 left bird droppings:

> >Wonderful!,now take the next step and apply it to cosmic expansion in

OK.

Simple,is'nt it !,so simple in fact that with one stroke you can do away with time dilation and at the same time infer rotation from acceleration.

Imagine if the SRist existed back at the time of Copernicus,he would have got nowhere with a heliocentric system as the SRist is concerned only with what the observer 'sees',likewise if the SRist sees cosmic expansion and it is accelerating then that is what it actually is doing.Numbskulls !,you don't have the intellectual strenght to infer indirectly that acceleration is not what it 'appears' nor that in a rotating system the distance covered increases from center to outer rim and therefore looks like acceleration.

Science used to be great at figuring out indirectly what was actually happening,Copernicus is one,Ole Roemer is another and his discerment that light covers a finite distance for each second that elapses through observing the trajectory of Io .Is'nt it amazing that dark matter is used in an attempt to explain away acceleration or that the missing mass is derived from a superficial observation of what the cosmos looks like,truly you are hopeless cases.

Mental midgets who are truly happy in ignorance is such a waste of a life,despite the sanitised image of science (at least in this area ) presented to the mainstream public behind it are small minds and even though true contention is enjoyable and work does get done by this means,the shelf life of SR expired long ago with nothing fresh to take its place nor will grovelling minds like yours allow it.

You knew what I was saying in regards to a second and varying distances through rotation yet you do not give a damn,even your opponents are mute on the topic where rotation can be infered from acceleration by reducing speed to 'distance covered' and SR cannot operate without 'speed'.


10 Length Contraction is WRONG

Van: "Bilge"
Onderwerp: Re: Length Contraction is WRONG
Datum: zondag 14 april 2002 23:52

Oriel36 said some stuff about Re: Length Contraction is WRONG to usenet:
> root@radioactivex.lebesque-al.net (Bilge) wrote in message news: ...
>> Oriel36 left bird droppings:

> >Wonderful!,now take the next step and apply it to cosmic expansion in

OK.

>

Simple,is'nt it !,so simple in fact that with one stroke you can do away with time dilation and at the same time infer rotation from acceleration.

Incorrect.


11 Length Contraction is WRONG

Van: "Nicolaas Vroom"
Onderwerp: Re: Length Contraction is WRONG
Datum: maandag 15 april 2002 17:59

"ripzone23" schreef in bericht news:a97b71$2pj$1@persian.noc.ucla.edu...
>

I still had one question concerning the barn & pole "paradox". What would happen if the runner took a "snapshot" of the barn and pole when he was at the exact center of the barn (no closing doors involved) and the barn viewer did the same? Now, regardless of whether or not they take their respective pictures at the same time, what will the pictures show? Will the runners picture show a pole much longer than the barn? Will the barn-viewer's picture show a pole much shorter and able to fit inside the barn?

The difficulty I have is that it seems to me that the center of the barn is THE center of the barn regardless of viewer.

Also, if this question is answered by the simultaneity clause, let me put a twist in. What if the barn viewer is standing at the center of the barn and the runner crashes into him, and at that exact moment of impact, a picture is taken by barn viewer and runner, what will the picture show? Will the runners pole be sticking out past the barn door, or will the pole fit exactly in the barn?

> How would you be able to tell who was moving and who was standing still?
You can not

>
IMO what you have are two rods and two observers at the middle of each rod.

One rod (observer) is fixed (at rest) = Barn
One rod (observer) is moving with a speed v in the rest frame.

When the moving observer MO meets at meeting point MP the fixed observer FO then the MO makes a picture and the FO makes a picture.

IMO if they both make the picture in the same direction the pictures (no delay) will be identical because the pictures will be taken at the same place and moment.
That means IMO the pictures are independent of who takes them (at MP)

   A-------MO-------B     moving  ---->
A----------FO---------B   fix
           MP
In reality MO should make a picture in direction A (against direction of movement)
FO should make a picture in direction B (in direction of movement) and you should compare the two pictures.

On both pictures you will see the ends of each rod (the points A or B) but you can not say were they are in radial direction.

To get more about the pictures you should place clocks at each end (and one at MO and FO)
Suppose the length of each rod is 2 light minutes and MO meets FO at 12:00:00 at FOs fixed watch than at the picture in A direction you will see 11:59:00 at the A end of the fixed rod. at the picture in B direction you will see 11:59:00 at the B end of the fixed rod.

ie the time for the fixed rod is identical.

For the moving rod the result is "identical".
That means Suppose the length of each rod is 2 light minutes and MO meets FO at 11:00:00 at MOs moving watch than at the picture in A direction you will see 10:59:00 at the A end of the moving rod. at the picture in B direction you will see 10:59:00 at the B end of the moving rod.

Please study: http://users.pandora.be/nicvroom/calc1.htm

In order to understand this result it is important to take clock synchronisation into account. http://users.pandora.be/nicvroom/length3.htm#clsync

I hope this helps

Nick


12 Length Contraction is WRONG

Van: "ripzone23"
Onderwerp: Re: Length Contraction is WRONG
Datum: dinsdag 16 april 2002 22:16

Thank you to everyone who answered my questions. I sort of figured out on my own that there is no real way to tell who is moving based on my examples; I just didn't have to time to follow up and let you all know.

One final question: I would assume that if the runner collided with the barn viewer, at the moment of impact, the two should agree on measurement and KE would be exchanged. (I know, I'm being overly simplistic, bear with me.) Would this be approx. accurate?


Created: 16 April 2002

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