[Jaaanosik (OP)]

... as per the parent thread:

Hi all,
Is the Lorentz Contraction real or not real.
What a beautiful 'can of warms' we got open here.
We all want to find out the truth.
If we come close to finding out the truth we will also find the answer to the question of this thread: Is angular momentum frame dependent?

I suggest we all put aside our convictions what is the correct answer and we develop an argument together; we find the answer together.
There are good points on both sides, to show that the LC is not real and also to show that the LC is real.
First, let us discuss how we can show the LC is not real.
I'll make a statement and I suggest we get an agreement if the statement can lead towards the answer.
If we say yes, then we will analyze and prove the statement.

If the Special Relativity is reciprocal then the Lorentz Contraction is not real.

Please, let us discuss the statement above. Do we agree it is a true statement?
Jano

If the Special Relativity is reciprocal then the Lorentz Contraction is not real.

Please, let us discuss the statement above. Do we agree it is a true statement?
Jano

What do you mean by special relativity being "reciprocal"?

Two inertial observers see each other clocks going slower.
Two inertial observers see each other Lorentz Contracted.
Whatever the first inertial observer can say about the second one then the second observer can say the same things about the first one.
There is no preferred reference frame.
Jano

[Kryptid]

Both observers are correct and length contraction is real.

[Jaaanosik (OP)]

Both observers are correct and length contraction is real.

They cannot be both real because of the Twin paradox.
If two twins meet again and there is a delta of their clocks then this proves the LC is real and this proves the SR is not reciprocal.

If we can show the Twin paradox stays as a paradox then the SR is reciprocal and LC is not real.
Jano

[Kryptid]

The twin paradox is not actually a paradox. Length contraction is real in both frames.

[Bored chemist]

They cannot be both real because of the Twin paradox.

If you were stood next to either of them you would agree that what they see is real.

The twin paradox is not  symmetrical. Only one twin experiences the acceleration of the ship. So it's not really a paradox.

[CPT ArkAngel]

They must be in the same frame at the start to synchronized a common proper clock to validate the reality of time dilation. The time dilation corresponds to the difference of the total length of the two different paths from the point of view of the meeting point. This time dilation is measured so it is absolutely real. When the paths are symmetrical, meaning their acceleration are equal and opposite at all time from the point of view of the meeting point, there is an apparent time dilation for sure but there is no way to say it is real or not because when they meet they have the same age, but within Special Relativity it must be real. Special relativity is consistent but you must know who is accelerating. One feels the acceleration, the other not.

[Kryptid]

[Halc]

There are good points on both sides, to show that the LC is not real and also to show that the LC is real.
First, let us discuss how we can show the LC is not real.
I'll make a statement and I suggest we get an agreement if the statement can lead towards the answer.
If we say yes, then we will analyze and prove the statement.

If the Special Relativity is reciprocal then the Lorentz Contraction is not real.
1) You'd have to show that SR is reciprocal in all cases, not just one. It isn't.
2) I don't agree with your statement at all. SR could be completely reciprocal and LC could still be real.

What do you mean by special relativity being "reciprocal"?

Two inertial observers see each other clocks going slower.
Two inertial observers see each other Lorentz Contracted.

This is one example, which doesn't define what you mean by reciprocal. It helps I suppose.

Whatever the first inertial observer can say about the second one then the second observer can say the same things about the first one.

That's clearly not always true.

There is no preferred reference frame.

It can be shown that if there is a preferred reference frame, there is no local way to detect it. This fact has nothing to do with LC being real or SR being reciprocal.

They cannot be both real because of the Twin paradox.

The twins scenario is not symmetric. If I smash my finger and have a broken bone and you don't, it doesn't prove that SR isn't reciprocal. It isn't, but not because of the finger.

The rotating examples is where all observers agree on real length contraction.  I can have two identical circular wedding rings, and if I spin one fast enough, length contraction will let me pass the spinning one through the other. All observers will agree that I did that, so LC is real.  Simple as that.

[Colin2B]

If the Special Relativity is reciprocal then the Lorentz Contraction is not real.

Please, let us discuss the statement above. Do we agree it is a true statement?

No, we do not agree. There is no reason to suggest it is.

Two inertial observers see each other clocks going slower.
Two inertial observers see each other Lorentz Contracted.
Whatever the first inertial observer can say about the second one then the second
observer can say the same things about the first one.

All these statements refer to inertial observers and inertial reference frames. If you introduce accelerating frames you will find that when the observers come together in a common, local frame they will not agree on the amount of time each has experienced, nor will they agree on the amount of distance the traveller has covered - due to length contraction.

There is no preferred reference frame.

All inertial frames are preferred frames in SR, accelerating frames are not.

Time dilation/length contraction is real and relativistic effects have been verified by experiment eg in particle accelerators. If Einstein had not discovered relativity its existence would have become obvious with the advent of particle physics.
 

[yor_on]

Myself it's a question of logic versus magic. I expect this universes to consist of a logic.. It may not fit what we once observed, times gone, but it needs logic to make me happy. It's a very centric view but it's also the one mathematics expect to be true.

[Jaaanosik (OP)]

Here is one figure, I hope this helps with the definition of what the reciprocal means.



What do you see?
It appears to me that trains 90 degree beam propagates at c/2 for the platform observer.
... and platform 90 degree beam propagates at c/2 for the train observer.

This is the definition of reciprocal in my view.
Do we have an agreement?
Jano

[Colin2B]

This is the definition of reciprocal in my view.
Do we have an agreement?

No, we do not. Your diagram doesn’t make sense, nor does it define reciprocal.

[David Cooper]

No, it is not reciprocal. We can see this in a case where one clock travels round and round in circles with another clock in the centre of the circle. Let's say that these clocks are in spaceships with the circling one always moving at 0.866c relative to the central one. If they are transmitting video to each other, the crew of the central ship will see the people in the other ship living in slow motion, and their clock will confirm it, ticking half as often as the central ship's clock. However, in the circling ship, when they watch the video coming from the central ship, they see the people in it moving about very fast, and they see that the clock there is ticking at twice the rate of their own clock. So it is not symmetrical.

How do defenders of STR deal with this? They assert that STR can't handle it because of the involvement of acceleration and that you have to switch to GTR, but that's a bogus argument. You can eliminate the accelerations by having lots of other clocks moving at 0.866c along tangents to the circle make timings of the almost exactly the same course by acting as a relay team, passing a virtual baton to each other when they pass each other. Here's an animation of it magicschoolbook.com/science/STR-disproof-5.html to help you visualise it correctly. These clocks moving along tangents to the curve tick at the same rate as the circling clock while they accompany it during their leg of the relay. No matter which frame of reference you use to analyse this, you determine that the clocks moving along tangents are ticking on average at half the rate of the central clock. That is not symmetrical. There are certainly some clocks in there that are not accelerating at any point which are ticking slower than the central clock, even though there is no possible mechanism in STR to allow them to do so.

[Kryptid]

passing a virtual baton to each other when they pass each other.

The act of "passing the baton" will require acceleration, because the direction that the mass-energy aboard the ship is moving will change every time a signal (which must be composed of that same mass-energy) is passed from one ship to the other.

[Jaaanosik (OP)]

This is the definition of reciprocal in my view.
Do we have an agreement?

No, we do not. Your diagram doesn’t make sense, nor does it define reciprocal.

What is wrong with the diagram?
What does not make sense?
Please, be more specific.
The diagram is kind of self explanatory, isn't it?
Jano

[Jaaanosik (OP)]

No, it is not reciprocal. We can see this in a case where one clock travels round and round in circles with another clock in the centre of the circle. Let's say that these clocks are in spaceships with the circling one always moving at 0.866c relative to the central one. If they are transmitting video to each other, the crew of the central ship will see the people in the other ship living in slow motion, and their clock will confirm it, ticking half as often as the central ship's clock. However, in the circling ship, when they watch the video coming from the central ship, they see the people in it moving about very fast, and they see that the clock there is ticking at twice the rate of their own clock. So it is not symmetrical.

How do defenders of STR deal with this? They assert that STR can't handle it because of the involvement of acceleration and that you have to switch to GTR, but that's a bogus argument. You can eliminate the accelerations by having lots of other clocks moving at 0.866c along tangents to the circle make timings of the almost exactly the same course by acting as a relay team, passing a virtual baton to each other when they pass each other. Here's an animation of it magicschoolbook.com/science/STR-disproof-5.html to help you visualise it correctly. These clocks moving along tangents to the curve tick at the same rate as the circling clock while they accompany it during their leg of the relay. No matter which frame of reference you use to analyse this, you determine that the clocks moving along tangents are ticking on average at half the rate of the central clock. That is not symmetrical. There are certainly some clocks in there that are not accelerating at any point which are ticking slower than the central clock, even though there is no possible mechanism in STR to allow them to do so.

What are you talking about?
There is no circle in the diagram. Please, stay true what is presented on the diagram,
Jano

[Jaaanosik (OP)]

passing a virtual baton to each other when they pass each other.

The act of "passing the baton" will require acceleration, because the direction that the mass-energy aboard the ship is moving will change every time a signal (which must be composed of that same mass-energy) is passed from one ship to the other.

Whatever David says is not relevant, there is no acceleration involved in the Figure presented,
Jano

[Halc]

David was commenting that there exist scenarios where relativity is not reciprocal. I agree with him on that point. He incorrectly asserts that SR cannot handle acceleration, but is gravity that SR cannot handle.

You simply presented one example that was reciprocal according to your definition, but it isn't always the case as evidenced by David's counter-example and several other counter-examples in the other thread.

Length contraction being real or not does not hinge on this reciprocal property, so I don't know what you think has been illustrated by it all. I thought M-L had a better definition: It is real if there is a real consequence that all observers can agree on, such as one twin being older than another.

[arjeet45o]

The twin paradox is not actually a paradox

[Jaaanosik (OP)]

David was commenting that there exist scenarios where relativity is not reciprocal. I agree with him on that point. He incorrectly asserts that SR cannot handle acceleration, but is gravity that SR cannot handle.

You simply presented one example that was reciprocal according to your definition, but it isn't always the case as evidenced by David's counter-example and several other counter-examples in the other thread.

Length contraction being real or not does not hinge on this reciprocal property, so I don't know what you think has been illustrated by it all. I thought M-L had a better definition: It is real if there is a real consequence that all observers can agree on, such as one twin being older than another.

What is the distance the train observer moved in the platform frame in 2s of the platform time? 1.732cs
What is the distance the platform observer moved in the train frame in 2s' of the train time? 1.732cs'
How is this possible to be true for both observers if there is a length contraction?
We have to go to relativity of simultaneity, clock desynchronization, ... to explain it.
The problem is that whatever explanation is done from the first frame then it can be applied to the second frame in the reciprocal way.
This is the paradox, it does not go away,
Jano