Lorentz contraction of box filled with gas

[Dale]

So using PV=nRT, where both Volume and Temperature decrease, Pressure remains constant.

It is fairly dangerous to use the standard form of laws in SR and simply assume that they still remain valid.

Here is P a 4-scalar or is it a tensor? If it is a 4-scalar then what is the corresponding 4-vector of which P is the norm? V is notoriously difficult to define in SR due to issues of simultaneity, usually I think it is a timelike 4-vector. So if V is a 4-vector and P is a tensor or a scalar then is T a 4-vector?

I don't know the answer to any of these, but using the ideal gas law in SR is not a simple matter of writing the traditional expression.

 

[peter0302]

Well, I asked earlier if PV=nRT held in SR and no one answered.

BTW, V and P are both scalar.

 

[1effect]

"Lorentz Contraction of Flux Quanta Observed in Experiments with Annular Josephson Tunnel Junctions", A. Laub et al., Phys. Rev. Lett. 75, 1372 - 1375 (1995).

Zz.

There are some serious problems with the author's claims. The factor in their paper is
sqrt(1-v^2/cbar^2) where cbar is the speed of light in their junction
(about 0.05 c). True Lorentz contraction involves the vacuum speed of
light, c, not cbar.

 

[Xeinstein]

More correctly said:

-the modern view is that the contraction is not physical, it is just a geometric (trigonemetric) artifact of the Lorentz-Einstein transforms : http://en.wikipedia.org/wiki/Length_contraction#A_trigonometric_effect.3F

-we do not have any experimental confirmation to the contrary :
http://www.edu-observatory.org/physics-faq/Relativity/SR/experiments.html#Length_Contraction

That's nonsense
Lorentz-contraction is "Real" in any sense of the word you can think of

 

[matheinste]

Hello all.

i am a little confused by all these knowledgeable arguments for and against various effects due to relatively moving systems. My understanding is that the effects such as time dilation, length contraction etc are results of a transformation of the fundamental dimensions of spacetime, at least i think that is what is predicted by relativity. IF this is true then surely all physical dimensions and derived units change pro rata and basically everything is conserved. This is a rather naive view but is it more or less correct.

Matheinste.

 

[1effect]

Hello all.

i am a little confused by all these knowledgeable arguments for and against various effects due to relatively moving systems. My understanding is that the effects such as time dilation, length contraction etc are results of a transformation of the fundamental dimensions of spacetime, at least i think that is what is predicted by relativity. IF this is true then surely all physical dimensions and derived units change pro rata and basically everything is conserved. This is a rather naive view but is it more or less correct.

Matheinste.

As measured by a distant observer in relative motion, distances shrink, frequencies change (relativistic Doppler effect). The objects themselves do not shrink.

 

[matheinste]

Hello 1effect.

Still confused. I cannot see how distances shrink but objects do not. The dimensions of an object are the measurements of its extension in space and these extensions in space are, surely, distances.

I do of course realize that for an observer in his own frame the action of his being observed has no effect on his own observations and so neither distances or sizes of objects or perception of time change for him.

I need to clear up the fundamentals before i can progress with my queries and my immediate question is are the changes in distance and time fundamental transformations in the values of the dimensions of spacetime. I believe they are.

Thankyou for your reply. Matheinste.

 

[1effect]

Hello 1effect.
I need to clear up the fundamentals before i can progress with my queries and my immediate question is are the changes in distance and time fundamental transformations in the values of the dimensions of spacetime. I believe they are.

Thankyou for your reply. Matheinste.

Yes, they are indeed fundamental transformations in the values of the dimensions.

 

[matheinste]

Hello 1effect.

I am still not happy with the answer but it is a bit unfair of me to continue this discussion in someone elses thread so i will probably start a new one by again asking the same question.

Matheinste.

 

[1effect]

So I suppose we all agree that the moving box does contract in the "lab-frame" in which the box is moving. It takes 100 replies to get to this point or conclusion. We are making progress.
Now the next question is this: will the box compress the gas in it? In other word, will the gas resist the contraction of the box as Lorentz-contraction demands?

You have received the answers several times already : "no" and "no"

 

[Xeinstein]

You have received the answers several times already : "no" and "no"

Do you realize you are probably the only person in this thread/forum claim length does Not contract in the observer frame in which the box is moving? If that's the case, then you are seriously mistaken. For the 5-th time

In the following quote, kev explains why you are mistaken:

If by \Delta V=0 you are saying that change in volume due to relative motion is zero, then that implies that change in length due to relative motion is also zero and you are seriously mistaken.

If change in length (length contraction) is imaginary then change in clock rate (time dilation) is also imaginary, because they go hand in hand. There is plenty of experimental evidence that time dilation is not imaginary.

You might have noticed that Einstein and Lorentz state that L = L_o \sqrt(1-v^2/c^2) and not L=L_o which is what \Delta V=0 and \Delta L=0 implies.

Why does Special Relativity have all those those complicated transformation formulas if no real physical transformations occur? Why does anybody bother if they are all imaginary and have no consequences? Kind of makes relativity pointless.

What's Lorentz-contraction? Is it an illusion or is it real?
First, we need to know how to measure the length of a moving object? It's not straightforward as you might think. To properly measure the length of a moving object, we must measure the position of both ends at the same time in our inertial frame. However, an observer at rest on the moving object would not agree that the measurements were made at the same time. The observer at rest with respect to the moving object, using her own clocks, would say that the position of the front end was measured at an earlier time than the position of the back end. So both agree that a measurement of length of a moving rod yields a shorter length than the measurement made in the frame of the rod. This is called the Lorentz contraction. This contraction is real in any sense of the word you can think of.

 

[AVentura]

If I accelerated a train to a relativistic speed I would observe a contraction of its length.

But if I accelerate two electrons (or atoms) independently at the same rate I do not observe the distance between them to reduce at all from what it was when they were moving slowly. (Picture two separate Linacs aligned on the same axis, their electrons will not affect one another, otherwise Linacs in different hospitals would be pulling each other's electrons out of their guides!)

Why the two different results? Because the atoms in the train are in a lattice. If you try to accelerate the front of the train independently of the back you will rip it in half. But an observer who is already moving the same direction as the train would claim the front started first, and that's why it ripped in half; no paradox. But the train will rip in half.

 

[granpa]

when an objects moves it really does contract or at least it occupies less space (same thing?). but to that object the rest of the universe appears to be moving and therefore contracted. did the universe contract just because this one object moved? of course not.

the length of an object is the distance between the front and back at one instantaneous moment. imagine that the object is moving past a line of stationary, perfectly synchronized clocks. since, to the moving object, the clocks APPEAR (even after compensating for light travel time) to be out of synch, the line of clocks will also appear to be shorter.

so length contraction is both real and illusory. the moving object really contracts. while everything else only appears to the moving object to contract.

this is similar to the twin paradox where only one of the twin actually ages less even though it appears as though both are time dilated.

 

[matheinste]

Hello granpa.

--------- contraction is both real and illusory. the moving object really contracts. while everything else only appears to the moving object to contract.---------


Length contraction, like time dilation in SR is symmetric. Both observers in relative motion see length contract and time dilate in the other frame. In their own frame of course they see nothing change.

Matheinste.



-----so length contraction is both real and illusory. the moving object really contracts. while everything else only appears to the moving object to contract.-----

 

[granpa]

thats what i said

 

[matheinste]

Hello granpa.

I messed up the last post. The bottom line should not be there i was just pointing out that you were wrong by quoting your words.

This is how it was meant to read. Sorry for the mix up.

To quote your words!

-----so length contraction is both real and illusory. the moving object really contracts. while everything else only appears to the moving object to contract.-----

That is incorrect

My reply!

Length contraction, like time dilation in SR is symmetric. Both observers in relative motion see length contract and time dilate in the other frame. In their own frame of course they see nothing change.

Matheinste.

 

[granpa]

there is no contradiction. both see length contraction and time dilation

one sees a real contraction and the other sees an illusory contraction due to loss of simultaneity.

it is of course absolutely impossible to know which is which.

 

[matheinste]

Hello granpa.

They cannot be real and illusory. Both are real.

Matheinste.

 

[granpa]

care to point out the flaw in my reasoning?

 

[AVentura]

when an objects moves it really does contract or at least it occupies less space (same thing?)

what if you don't let it. do you think it would be ripped apart?

 

[granpa]

what difference does it make?

 

[matheinste]

Hello granpa.

You say ----the moving object really contracts.----

True. But bear in mind that each observer regards the other as moving relative to him so the words moving and stationary only have a relative meaning in his sense.

You say ---everything else only appears to the moving object to contract. ----

Everything else ( moving relative to other observer, or object ) not only appears to contract, it too really contracts. But, again bear in mind, that to each observer the other is regarded as moving.

Matheinste

 

[granpa]

relativity does not say that there is no absolute velocity. it just says that you can't determine what it is without ftl travel.

 

[matheinste]

Hello granpa.

----relativity does not say that there is no absolute velocity. it just says that you can't determine what it is without ftl travel.------

Complete nonsense. Buy a book and read it.

Matheinste.

 

[Mentz114]

relativity does not say that there is no absolute velocity. it just says that you can't determine what it is without ftl travel.

Can you expand on this ? Are you saying that absolute motion could be detected if you had ftl travel ?

 

[granpa]

well suppose you could communicate instantly with any part of the universe or at least with arbitrarily small delay. that would allow you to know the absolute time.

if you know absolute time then you should be able to determine absolute velocity simply by looking at your time dilation.

https://www.physicsforums.com/showthread.php?t=235621

of course, there is no way to do either. some people do suggest that quantum entanglement might allow ftl communication but the consensus seems to be that it cant.

 

[yuiop]

Hello granpa.

----relativity does not say that there is no absolute velocity. it just says that you can't determine what it is without ftl travel.------

Complete nonsense. Buy a book and read it.

Matheinste.

Grandpa is "sort of right". Relativity does not rule out an absolute reference frame of the type proposed by Lorentz (where clocks moving relative to the absolute vacuum time dilate and rulers moving relative to the absolute vacuum length contract), it just says it can not be detected and that there "is no need of one".

 

[AVentura]

what difference does it make?

to what were you referring?

 

[yuiop]

when an objects moves it really does contract or at least it occupies less space (same thing?).

what if you don't let it. do you think it would be ripped apart?

Bell's spaceships paradox says yes, it will be ripped apart.

 

[AVentura]

Bell's spaceships paradox says yes, it will be ripped apart.

thanks, I have been thinking about this for years but didn't know what it was called. (they didn't cover this in my master's program)

but I don't think most Physicist would agree with Bell (none of my professors would have). I got in lots of arguments.

The wikipedia entry on Bell's spaceships paradox says that CERN put together a think tank that disagreed with Bell. What was their argument?