Is a length contraction just a visual thing?

[exchemist]

Thank you for your video link which the narrator explains time dilation, but explains very little on length contraction. I have noticed some rather strange posts from members, which I will choose to ignore as they are seemingly being aimed personally towards myself and have no relevance to the question I have asked.
I have not stated that I am any sort of expert, I have neither asked to learn, I have my own education preference of the original author.

http://www.bartleby.com/173/

Post four from James-''I think most physicists would be inclined to say that the length contraction of the object is a real effect'' implying the object does contract

In post five I say
''I do not mention the length contraction as being an illusion, I asked whether or not it was a visual thing or a thing subject to the actual object decreasing in length''

In post eight , origin replies this ''Don't forget their rulers have shrunk too!'' implying the object does contract

Then you post - ''Length contraction can be viewed as a kind of perspective illusion, as long as you recognize that illusions are still showing you something real (just unexpected).''implying the object doesn't contract

This is a bit confusing and contradictory , who's answer shall I take to be correct?

Actually I think this is a tricky thing. As the effect is only seen from the viewpoint of an observer who is in motion relative to the object observed, you cannot "freeze" the system while you carry out measurements on it at leisure. But calling it a "visual thing" is not right, because any form of information transfer between object and observer will be subject to the same phenomenon. So that makes it "real", rather than a "trick of the light".

(When origin points out the "rulers have shrunk too", he is arguing the object has NOT contracted from the viewpoint of someone travelling with the object, while from the viewpoint of the observer moving relative to the object, BOTH the object AND any mean of determining its length that moves with it have shrunk in proportion.)

 

[krash661]

Great!!!! So you accept length contraction.

you should have said " physical " length contraction. and yes, i think this is azo.
azo's typical argument is that it is simply, only, a visual contraction and not a physical contraction. but then when one ask him too show the math, he will simply divert and initiate the insulting of actual scientist.
it is a pity that no one here can see his so-called thought experiment(which is an obvious flawed attempt from the instant beginning of his thought experiment) of this with geometry and proof/postulates.

 

[absolute-space]

Great!!!! So you accept length contraction.

There was never a point in this thread where I said I did not accept length contraction, on the very first page , post 5 , I posted - ''We do without doubt observe a ''visual'' length contraction of an object moving parallel away from a ''stationary'' observer who is at rest in an inertial reference frame.''

My question was never of a denial of the observation or maths, my question was asking if the actual objects length contracted. The answers I have received seem muddled . confused and contradictory to the original post of James.

 

[absolute-space]

you should have said " physical " length contraction. and yes, i think this is azo.
azo's typical argument is that it is simply, only, a visual contraction and not a physical contraction. but then when one ask him too show the math, he will simply divert and initiate the insulting of actual scientist.
it is a pity that no one here can see his so-called thought experiment(which is an obvious flawed attempt from the instant beginning of his thought experiment) of this with geometry and proof/postulates.

My apologies , I never considered to put physical length and no, I am not this Azo you keep referring to.

 

[krash661]

azo--display your pictorial with the conclusions exact as too the other site, here-- in this moment.
and if you are not azo-- that is fine, i have been wrong before-- but there is very similar conduct here.

 

[Russ_Watters]

I will answer this as it ask's a direct question rather than making a presumption, thank for you asking, I am interested in discussing the question, is there anything wrong in that on a discussion forum?

Yes. First off, it isn't true: when you ask a question, you get answers. So you aren't really discussing the question, you are discussing the answers. So that leads to the second problem: when you already have/think you know the answer and you don't provide it, you are being dishonest. When you ask a question without further explanation, it is natural for people to assume you don't know and want to be taught the answer. That's why this thread looks like trolling/sandbagging.

 

[Russ_Watters]

There was no agenda in my user name, it was the first name I thought of, it means nothing.

Scientists don't believe in coincidences, so you'll have a hard time convincing anyone that that's true.

There was never a point in this thread where I said I did not accept length contraction, on the very first page , post 5 , I posted - ''We do without doubt observe a ''visual'' length contraction of an object moving parallel away from a ''stationary'' observer who is at rest in an inertial reference frame.'

That appears to me to be a very carefully worded dodge, curiously discarding your own previous colloquial words in the OP. So you really should explicitly answer your own question: do you think length contraction is "just a visual thing"?

Given the wording of the OP, the wording there and your username, you certainly do appear to believe length contraction is a "visual thing" that doesn't actually "happen" in reality. IE, you subscribe to the discarded concept of absolute space. Am I right?

 

[paddoboy]

There was never a point in this thread where I said I did not accept length contraction, on the very first page , post 5 , I posted - ''We do without doubt observe a ''visual'' length contraction of an object moving parallel away from a ''stationary'' observer who is at rest in an inertial reference frame.''

My question was never of a denial of the observation or maths, my question was asking if the actual objects length contracted. The answers I have received seem muddled . confused and contradictory to the original post of James.

James said....

I think most physicists would be inclined to say that the length contraction of the object is a real effect.

My question to you, if you believe it is an illusion, is: what test would you propose to distinguish between a real contraction and an illusory one? If you can't suggest such a test, then the question itself may not be very meaningful.

And I also said that any and all frames of references are as valid as each other.
I see no confusion in any of the answers you have been given.

 

[absolute-space]

Yes. First off, it isn't true: when you ask a question, you get answers. So you aren't really discussing the question, you are discussing the answers. So that leads to the second problem: when you already have/think you know the answer and you don't provide it, you are being dishonest. When you ask a question without further explanation, it is natural for people to assume you don't know and want to be taught the answer. That's why this thread looks like trolling/sandbagging.

Looks like, is obviously not like, as for the rest it ''looks like'' bickering, If you asked me a question and I gave you the answer, you would want to explore the answer if like minded. If I think I know the answer, that is irrelevant to comparing your answers to my own interpretation of the answer I have read for clarification of my own interpretation. I understand a visual length contraction , evidential by sight. I ask you , does the actual physical length of the object contract? my reason for asking, contradictory answers I have found leaving me confused about the answer.

 

[absolute-space]

Scientists don't believe in coincidences, so you'll have a hard time convincing anyone that that's true.

Do you think length contraction is "just a visual thing"?

My answer to this depends on the context it is been used for, if my answer is being associated to relative motion, then yes I think length contraction is just a visual thing relative to light angles and distance . If we were talking about the Earth's shape, or gases etc then yes I would agree in a physical length contraction or physical length expansion.

Given the wording of the OP, the wording there and your username, you certainly do appear to believe length contraction is a "visual thing" that doesn't actually "happen" in reality. IE, you subscribe to the discarded concept of absolute space. Am I right?

I am not sure how to answer this, the visual length contraction happens in reality, as for the concept of absolute space, to be honest, I do not even know what that means.

 

[absolute-space]

absolute-space:


That's good question. To answer it, you need to understand the circumstances under which length contraction occurs. For simplicity, I only discuss special relativity here.

Length contraction is observed when the reference frame of the observer is changed. If you measure the length of an object that is stationary relative to you, the length you measure is what is known as the object's rest length. If you measure the length of the same object when it is moving past you at constant speed, you measure a shorter length than the rest length, due to relativistic effects.

You are asking whether this contraction is real or just a kind of visual illusion, in effect. The contraction that you measure for moving objects is the same however you measure it. The only thing that matters is your frame of reference as an observer - or, to put it another way, the relative speed between you and the object being measured. If you leave the object alone and just move yourself, you'll still see the length contraction of the object.

I think most physicists would be inclined to say that the length contraction of the object is a real effect.

My question to you, if you believe it is an illusion, is: what test would you propose to distinguish between a real contraction and an illusory one? If you can't suggest such a test, then the question itself may not be very meaningful.

It took me a few hours of thought to give you an answer you asked for. You asked for a test to distinguish between a real contraction and an illusionary contraction . Now I have had a think , it seems quite simple really .
An observer stands in the center of a circle. Around the circle is a circular train track, on the track is a train that's length of carriages and engine is equal to the circumference of the circle, the train starts to accelerate around the track , relative to the observer , the circle is constant

Even simpler, a train is stationary a mile up the track, down the track, an equal length train is about to come speeding past, when the front of the speeding train is level with the front of the stationary train, the rears should align .

 

[Billy T]

Perhaps it may help absolute-space to recognize that to observers in a frame traveling fast and in the same direction as along his back bone when he is standing straight, he is very contracted (yet feels no force pushing his head towards his feet.) I. e. they would measure him as pancake shaped - much fatter than he is tall. And that really is his shape in their frame.

I liked absolute-space's example of a fast train on circular track. To make it better, assume it was initially stationary on the track and the front of the locomotive was physically connected the end of the last car and then the train accelerates up to relativistic speed.

This is a much cleaner puzzle* than the better know problem of the relativistic tank traveling a C/2 in you frame (some tread stationary on the ground and top part of the tread advancing at C?)

* I don't fully understand this but note SR does not apply as no car of the train is traveling in an inertial frame. We need an analysis in GR, and that is too hard for me.

 

[iceaura]

I understand a visual length contraction , evidential by sight. I ask you , does the actual physical length of the object contract?

The physical length will be different as measured by different observers at rest and not at rest with respect to the object.

The measurement technique - sight, etc - does not matter. The observer can use whatever measurement equipment and methods they regard as best.

Which one of those lengths do you wish to label the "actual length"?

 

[paddoboy]

I am not sure how to answer this, the visual length contraction happens in reality, as for the concept of absolute space, to be honest, I do not even know what that means.

It's easy. There is no absolute space, nor absolute time. Both depend on one's frame of reference, and all frames of references are as valid as each other.
More simply, there is no universal now.
eg:

 

[Russ_Watters]

....as for the concept of absolute space, to be honest, I do not even know what that means.

Heh - yeah, right.

 

[paddoboy]

http://arxiv.org/pdf/1501.05899v1.pdf

Direct calculation of length contraction and clock retardation

Abstract.
For simple electromagnetic models of a rod and a clock, a change of the shape of the rod and of the rate of the clock when they are set in uniform motion is calculated exactly, employing the correct equation of motion of a charged particle in the electromagnetic field and the universal boostability assumption. Thus it is demonstrated that, for the simple system considered, length contraction and clock retardation can be interpreted as dynamical cause-and-effect phenomena, and not as kinematical effects as is usually construed in conventional presentations of Special Relativity. It is argued that the perspectival relativistic change of an object (corresponding to observations from two inertial frames), while certainly an acausal effect, has a dynamical content in the sense that it is tantamount to an actual dynamical change of the object in one frame.

 

[ajanta]

Another thing, simply we know that a black hole can reduce its volume due to its strong gravitational force. And when a electrons is in relativistic speed, the mass(of electron) is increased so its gravitational force is increased too. When a spacecraft travels in high speed, then its mass is increased and I think the attraction force between atoms(of spacecraft) should increase. Does it really reduce its(spacecraft) length, hight, volume etc.......too little ?

 

[Russ_Watters]

One can conceive of simple thought experiments on this issue to get into brass tacks and stop discussing this with vague colloquialisms:

A spaceship takes off from Earth and rapidly accelerates to just under the speed of light (they've found a way to do that without smooshing the passengers). The inertial guidance system in the spaceship tells the pilots (and anyone with a watch can verify it) that they arrived at Alpha Centuari in an hour, traveling just over 1 billion km, which confuses some of them because according to Google, that should put them just past Jupiter, yet here they are at Alpha Centuari.

So are their watches and inertial guidance systems wrong? Or did they really travel only 1 billion km?

 

[Q-reeus]

http://arxiv.org/pdf/1501.05899v1.pdf

Direct calculation of length contraction and clock retardation

Abstract.
For simple electromagnetic models of a rod and a clock, a change of the shape of the rod and of the rate of the clock when they are set in uniform motion is calculated exactly, employing the correct equation of motion of a charged particle in the electromagnetic field and the universal boostability assumption. Thus it is demonstrated that, for the simple system considered, length contraction and clock retardation can be interpreted as dynamical cause-and-effect phenomena, and not as kinematical effects as is usually construed in conventional presentations of Special Relativity. It is argued that the perspectival relativistic change of an object (corresponding to observations from two inertial frames), while certainly an acausal effect, has a dynamical content in the sense that it is tantamount to an actual dynamical change of the object in one frame.

A rather confusing piece that misleadingly disparages the usual simple approaches as 'inadequate', and moreover refers to 'so-called' kinematical effects of SR. But such kinematics is absolutely necessary and fundamental to SR. The author creates 'dynamics' of length contraction by introducing pseudo forces that preserve proper length at each stage of linear acceleration of an object going from a notional rest state to a final constant velocity moving one. While it can be done that way it only adds unnecessary conceptual issues. Simple moral - for such cases where global constraints do not enter, compute all dynamics in the proper frame and Lorentz transform to any other frame of interest. His use of term 'acausal' is also misplaced.

About the sole situation where a genuine dynamical aspect of length contraction enters is in rotating rigid bodies (global constraints) - the so-called Ehrenfest 'paradox':
http://www.physicspages.com/tag/ehrenfests-paradox/
https://en.wikipedia.org/wiki/Ehrenfest_paradox
(I make no apologies for furnishing webpage links - it's the way to go this day and age. Nasty hypocrites fail to realize or acknowledge that and in addition have no issues with their own buddies doing just that continually.)
Did you bother to read it through and actually grasp his approach, before posting it here?

 

[paddoboy]

(I make no apologies for furnishing webpage links - it's the way to go this day and age. Nasty hypocrites fail to realize or acknowledge that and in addition have no issues with their own buddies doing just that continually.)
Did you bother to read it through and actually grasp his approach, before posting it here?

??Who asked you too? The other irrelevant accusations/insinuations are just that and I'll ignore them.
On reading it through, no not entirely, but the reason for posting it was again to refute more anti SR/GR nonsense.
It validates length contraction, and that's the message.