Is a length contraction just a visual thing?

[absolute-space]

You have been given ample evidence that you are incorrect.

May I suggest you learn to read and stop making accusation that are not even there to begin with. What exactly do you think I am incorrect about? I have not inferred anything is incorrect. As for evidence, you have provided no physical evidence but only words which mean very little in respect of physical evidence.

 

[absolute-space]

Given that you have been holding back here, why don't you tell us what you already know, to save us all some time. For example, do you know about muon decay observations? If not, Google it, read up on it and let us know how it works out for you.

Likewise, why not just answer the question and provide any experimental evidence you have of an object contracting in physical length?

Provide the evidence and your justification of the physical contraction and then I will believe in a physical length contraction as well of the visual contraction.

I have suggested an experiment using sensors that would without doubt show any change in length relative to the stationary observer.

My belief of the ''fact'' is withheld until an experiment like the suggested is performed.

 

[origin]

May I suggest you learn to read and stop making accusation that are not even there to begin with.

But you did make an incorrect statement.

What exactly do you think I am incorrect about?

I included your quote stating that you think length contraction is just a visual thing. I stated that you are incorrect - was that not clear enough?

I have not inferred anything is incorrect.

Of course you have.

As for evidence, you have provided no physical evidence but only words which mean very little in respect of physical evidence.

Oh come on, there is no evidence that you will accept, your mind is made up. You don't like what relativity has shown us about reality so you have decided to ignore it and live in a fantasy world. That is your choice, but don't expect us to abandon reason and join in your fantasy.

Just another example showing that arguing with a crank is a waste of time.

 

[absolute-space]

I included your quote stating that you think length contraction is just a visual thing. I stated that you are incorrect - was that not clear enough?
.

You reply with more accusation, the only relevance to the thread is the above sentence. Yes I said I think that length contraction is a visual thing, not an illusion , a visual thing to be clear. You posted early in the thread, do not forget the ruler contracts to, insinuating the actual physical condition of the object changed in length. My opinion is it does not, your opinion is it does, the burden of proof is on you to show it does , it is not for me to convince you it doesn't .

If I had posted something of such, ''photons do not exist'', you would ask me to provide proof and evidence, so I am asking for your proof.

 

[exchemist]

I have read every single post from every poster in this thread, it is you that needs to learn some decorum, you obviously have not read the thread, the train sensor example was only a page or so back. It is not on me to keep repeating myself sir, it is on you to read the entire thread if you have interest in the discussion.

But he has replied to that, saying the same as what I said, has he not?

 

[absolute-space]

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 .

But he has replied to that, saying the same as what I said, has he not?

I have spent the time and gone back, I think I may of read it wrongly , my apologies .

 

[absolute-space]

The first is a very ingenious scenario but I think the problem is that you cannot answer it using special relativity, because the train is accelerating (motion in a circle). My understanding is that Special Relativity only works in situations in which there is no acceleration. I think you need General Relativity to deal with your scenario (and please do not ask me how that works - as a chemist I can get my head round Special Relativity but tensor maths is not something I've ever learned.)

The second, involving only linear motion, is easier. As I understand it, an observer on the "stationary" train will see the "speeding" one foreshortened, so that the when the fronts are aligned the rear of the "speeding" one is in front of the rear of the "stationary" one. An observer on the "speeding" one will the same thing applying to the "stationary" train, i.e. when the fronts are aligned the rear of the "stationary one is in front of that of the "speeding" one. Each sees the other foreshortened.

In fact, the interesting thing about this is that the instant at which the ends are aligned appears to occur earlier than the instant when the fronts are aligned but each observer will see the end of the other train aligning earlier. I rather think this is an example of the "relativity of simultaneity", which no doubt you have encountered in your reading.

But I'd be happy to have a real physicist take over the explanation as I'm far from expert on this subject.

There is no problem with the train travelling a constant speed, but obviously it has to accelerate first to get to a speed.

 

[exchemist]

There is no problem with the train travelling a constant speed, but obviously it has to accelerate first to get to a speed.

Fine so how about focusing on your second scenario, which can as you say be treated as a constant velocity scenario? This is what I have tried to do and what Q-reeus has tried also to do.

As I say, has he not answered this, in a way that is consistent with what I said about it? Are you OK with those answers or, if not, what further difficulties do you see?

 

[krash661]

Having a bad spelling day, just like that poster I was referring to? Notice I ended with to, not too.

It was actually referring to your buddy, and his false charge of 'never link anything from a text-book, but simply wiki only' as per a post on p16 in:
http://www.sciforums.com/threads/gravity-waves-detected-for-the-first-time-ever.154848/
Yet never once complained about your chronic use of and reliance on web references. Nice to have such selective and discrete buddies, huh.

Decoded: You had not read it through nor grasped it's philosophy before posting. And think that 'validating length contraction' excuses the unnecessary baggage his approach introduces. As usual, ever so kind and gentle and understanding - toward yourself that is. Do carry on.

comical more pathetic nonsense-- how typical.
also--since when have you ever typed " carry on" except when you seen me type it too you.

 

[origin]

Yes I said I think that length contraction is a visual thing, not an illusion , a visual thing to be clear.

Which is wrong.

You posted early in the thread, do not forget the ruler contracts to, insinuating the actual physical condition of the object changed in length.

I didn't insinuate anything. I clearly stated that there is a change in length.

My opinion is it does not,

Which, to be blunt, is the worthless opinion of layman who does not have the education to have a worthwhile opinion.

your opinion is it does, the burden of proof is on you to show it does , it is not for me to convince you it doesn't .

The proof is Special Relativity and the experiments that all support SR. By the way, since you are taking the counter position the burden of proof is on you.

If I had posted something of such, ''photons do not exist'', you would ask me to provide proof and evidence, so I am asking for your proof.

You have been given ample proof which you ignore because of you don't like the implications of SR.

You're like all the other cranks that come here trying to disprove relativity with your arm waving misconceptions. We have seen it all before, you might as well be proclaiming the world is flat...

 

[krash661]

Still have the totally wrong conceptual outlook. Some folks decry use of Wiki and Youtube but correctly used they can both be great resources. I suggest you run through the entries here:
https://www.youtube.com/results?search_query=relativity of length contraction&spfreload=10
And find the one that finally makes good intuitive sense. Everything exists within spacetime and is subject to it's transformation rules. No exceptions possible (leaving aside controversial issues like 'entanglement' that one or two here build so much into).

on a graduate level and also most of the time on a undergraduate level-- you are required not too use wiki.

 

[absolute-space]

Fine so how about focusing on your second scenario, which can as you say be treated as a constant velocity scenario? This is what I have tried to do and what Q-reeus has tried also to do.

As I say, has he not answered this, in a way that is consistent with what I said about it? Are you OK with those answers or, if not, what further difficulties do you see?

Your version is correct and Q-reeus version is correct, but neither correct unless we conduct the actual experiment.

The experiment is simple , two aligned lengths, 4 aligned sensors, observers, add motion, result

 

[absolute-space]

Which is wrong.

I didn't insinuate anything. I clearly stated that there is a change in length.

Which, to be blunt, is the worthless opinion of layman who does not have the education to have a worthwhile opinion.

The proof is Special Relativity and the experiments that all support SR. By the way, since you are taking the counter position the burden of proof is on you.

You have been given ample proof which you ignore because of you don't like the implications of SR.

You're like all the other cranks that come here trying to disprove relativity with your arm waving misconceptions. We have seen it all before, you might as well be proclaiming the world is flat...

If you are insisting the physical length changes then prove it with an experiment?

Prove the pirate ship ride at a fair, swinging left and right contracts in physical length?

 

[exchemist]

Your version is correct and Q-reeus version is correct, but neither correct unless we conduct the actual experiment.

The experiment is simple , two aligned lengths, 4 aligned sensors, observers, add motion, result

Not sure why you insist on an experiment. The theory of relativity is one of the most over-determined theories in physics. Every time a measurement has been made, of whatever sort, it has been found to predict the outcome correctly. Personally I think doing yet another experiment of this sort would be a sheer waste of time.

 

[absolute-space]

Not sure why you insist on an experiment. The theory of relativity is one of the most over-determined theories in physics. Every time a measurement has been made, of whatever sort, it has been found to predict the outcome correctly. Personally I think doing yet another experiment of this sort would be a sheer waste of time.

Can I ask as an experiment ever been done of this sort experiment that shows without doubt one way or another if the actual physical length contract?

 

[Confused2]

The second, involving only linear motion, is easier. As I understand it, an observer on the "stationary" train will see the "speeding" one foreshortened, so that the when the fronts are aligned the rear of the "speeding" one is in front of the rear of the "stationary" one. An observer on the "speeding" one will the same thing applying to the "stationary" train, i.e. when the fronts are aligned the rear of the "stationary one is in front of that of the "speeding" one. Each sees the other foreshortened.

In fact, the interesting thing about this is that the instant at which the ends are aligned appears to occur earlier than the instant when the fronts are aligned but each observer will see the end of the other train aligning earlier. I rather think this is an example of the "relativity of simultaneity", which no doubt you have encountered in your reading.

The times would either be recorded at the point of measurement by synchronised clocks ( https://en.wikipedia.org/wiki/Einstein_synchronisation ) or any signal transmission delays allowed for so that the 'earlier' and 'later' are independant of the position of 'the observer'.

 

[origin]

If you are insisting the physical length changes then prove it with an experiment?

SOURCE
Heavy ions that are spherical when at rest should assume the form of "pancakes" or flat disks when traveling nearly at the speed of light. And in fact, the results obtained from particle collisions can only be explained when the increased nucleon density due to length contraction is considered.

What is that you say? You won't accept that evidence. Imagine my surprise!!

Prove the pirate ship ride at a fair, swinging left and right contracts in physical length?

$$L=L_o \sqrt{1-\frac{v^2}{c^2}}$$

What is that you say? You won't accept that because it is only math. Imagine my surprise!!

You cranks are so boring and science is so interesting...

 

[exchemist]

Can I ask as an experiment ever been done of this sort experiment that shows without doubt one way or another if the actual physical length contract?

See Origin's reply. It is hard to do except with subatomic particles, as the speeds involved have to be so high that the energy, time and length required to accelerate them limits the size of the test objects that can be considered in practice, but that's life ( and that of course is why these effects were not predicted until the early c.20th, when the speed of light could be measured accurately for this first time in history.)

 

[rpenner]

In science, a theory is a framework for predicting the behavior of a wide class of phenomena within a certain domain. So the physical theory of special relativity is supported by a great number of empirical observations. The reality of length contraction is a necessary consequence of those empirical observations as it is an elementary consequence of treating two coordinate systems as equally applicable (Principle of Relativity) and endorsing Newton's principle of Inertial and the observation that all observers see the speed of a particular beam of light in vacuum as traveling at the same speed, c.

Definition of inertial frame of reference: All bodies in inertial motion describe linear relations in space-time coordinates.
Definition of two bodies in same state of inertial motion: Relative to a third body or inertial coordinate system, they have the same velocity as a vector.
Definition of length of a material body in a uniform state of inertial motion: The difference in position of its two ends as measured simultaneously.

Thus we have for a body in a state of inertial motion described by velocity $$\vec{u}$$ in a certain inertial coordinate system, the following linear relationship for it's endpoints A and B:

$$\vec{x}_{A,1} - \vec{u} t_{A,1} = \vec{x}_{A,2} - \vec{u} t_{A,2} \\ \vec{x}_{B,3} - \vec{u} t_{B,3} = \vec{x}_{B,4} - \vec{u} t_{B,4} $$

...

We can simplify this somewhat if we use the property of real numbers that there is a zero, thus our coordinate system has an origin, even if this origin is purely a fiction of mathematical convenience.

Then $$\vec{x}_{A,1} - \vec{u} t_{A,1} = \vec{x}_{A,2} - \vec{u} t_{A,2} = \vec{x}_{A,0} \\ \vec{x}_{B,3} - \vec{u} t_{B,3} = \vec{x}_{B,4} - \vec{u} t_{B,4} = \vec{x}_{B,0}$$
...
And the length measured between comoving endpoints A and B at any one time is:
$$ L_{AB} = \left| \vec{x}_{B,0} - \vec{x}_{A,0} \right|$$

So the question of this thread is what is the length of the same material body in a coordinate system where it is not moving.
Newton and Special Relativity give different answers.

For special relativity we can transform space-time points $$( \vec{x}_{A,1} , t_{A,1} ) , \; ( \vec{x}_{A,2} , t_{A,2} ) , \; ( \vec{x}_{B,3} , t_{B,3} ) , \; ( \vec{x}_{B,4} , t_{B,4} ) $$ and recalculate the length in the new coordinates.

...
So if $$\left( \vec{x}_{B,0} - \vec{x}_{A,0} \right) \cdot \vec{u} = 0$$ then the motion was perpendicular to the length and there is no change in the length measured.
But if the directions are parallel, the length measure in the coordinate system where the object is not moving is greater than in the coordinate system where the length was moving with velocity u.
$$ L'_{AB} = \frac{1}{\sqrt{1 - \frac{u^2}{c^2}}} L_{AB} > L_{AB}$$.

So if you accept that the length of a moving object is a thing, then length contraction is real, not illusory, in special relativity.

That's not an illusion. The object is shorter when length and its non-zero motion are not perpendicular. The choice of which coordinates to use is a choice, but that choice has consequences if you want to talk about things like length. It turns out that length is not fundamental in special relativity, because it is a geometry which preserves the space-time interval $$ c^2 (\Delta t)^2 - ( \Delta \vec{x})^2$$ and not length $$ | \Delta \vec{x} | $$.

 

[Russ_Watters]

Likewise, why not just answer the question and provide any experimental evidence you have of an object contracting in physical length?

Because it appears your purpose here is to troll and waste peoples' time. That annoys people.

Provide the evidence and your justification of the physical contraction and then I will believe in a physical length contraction as well of the visual contraction.

I just did. You won't even say if you were aware of it, so for now I see no reason to explain further!

I havesuggested an experiment using sensors that would without doubt show any change in lengthrelative to the stationary observer.

The one with the train on the first page? It doesn't address length contraction for what it is.