# Length contraction in a block universe must be an illusion

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25 minutes ago, 34student said:

So if there are 10 cars to the train, are you saying that there actually are 20 cars?

Could you please stop taking what is said and twisting it to fit your existing misunderstanding? It's been repeated ad nauseam that that there's only one train.

2 hours ago, 34student said:

Now here is my question that will either put my issue to rest for me or keep me wondering.  If the particle is at x1 for Bob, and x2 for people on Earth, does the particle necessarily have to go through x1 and x2 (not necessarily in this sequence)?

No, because those are 2 different coordinate systems. For example, the front of the train can be at rest at x2=0 for the coordinate system of an observer at the front of the train, while Bob might use a coordinate system where his ship is at the origin and the location of the front of the train is x1=several light years and changing. If the front of the train enters a tunnel, that's an event. Everyone agrees that the location of the front of the train coincides with the location of the entrance of the tunnel when it enters, but that could be at x2=0 and x1=several light years. Though it might make more sense with all the other basic stuff about relativity that I'm sure you've read, if you called them x and x' to denote that they're different coordinate systems.

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1 hour ago, 34student said:

So if there are 10 cars to the train, are you saying that there actually are 20 cars?

Nope

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13 hours ago, 34student said:

With world lines in mind, this means that there are at least 2 trains in existence (and probably many more from other frames of reference).  Do you agree?

No - there is only one train, but many observers. The property of “length” is not intrinsic to the train - instead, it describes a relationship between the train and a specific observer.

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On 10/29/2021 at 5:34 PM, md65536 said:

Could you please stop taking what is said and twisting it to fit your existing misunderstanding? It's been repeated ad nauseam that that there's only one train.

No, because those are 2 different coordinate systems. For example, the front of the train can be at rest at x2=0 for the coordinate system of an observer at the front of the train, while Bob might use a coordinate system where his ship is at the origin and the location of the front of the train is x1=several light years and changing. If the front of the train enters a tunnel, that's an event. Everyone agrees that the location of the front of the train coincides with the location of the entrance of the tunnel when it enters, but that could be at x2=0 and x1=several light years. Though it might make more sense with all the other basic stuff about relativity that I'm sure you've read, if you called them x and x' to denote that they're different coordinate systems.

Is the world line of the particle 1 meter away from the world line of a particle at the other end of the train?

Edited by 34student
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4 minutes ago, 34student said:

Is the world line of the particle 1 meter away from the world line of a particle at the other end of the train?

Once again you are trying to impose absolute measurements on something.

Take a metre rule.

In its own frame it is exactly one metre long   - if it is an end standard if you know what I mean  - ask if you don't.

In most most (but not all ) frames it has a different length.

There is no such thing as an absolute metre.

Now if you measure other objects in the same frame as the metre rule, for instance trains, atoms and so on you will find them all scaled by the same factor.

The only things you will come up with the same numbers for are electric charges and numbers of those atoms, trains etc.

I started to tell you about this near the beginning of this thread and understanding this is the key to understanding Special Relativity.

Most other stuff ( including the maths) can be derived fairly easily from this.

World lines are artificial constructs like graphs of stocks and shares - useful in their own way, but not the be-all and end-all of relativity.

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15 minutes ago, studiot said:

Once again you are trying to impose absolute measurements on something.

Take a metre rule.

In its own frame it is exactly one metre long   - if it is an end standard if you know what I mean  - ask if you don't.

In most most (but not all ) frames it has a different length.

There is no such thing as an absolute metre.

Now if you measure other objects in the same frame as the metre rule, for instance trains, atoms and so on you will find them all scaled by the same factor.

The only things you will come up with the same numbers for are electric charges and numbers of those atoms, trains etc.

I started to tell you about this near the beginning of this thread and understanding this is the key to understanding Special Relativity.

Most other stuff ( including the maths) can be derived fairly easily from this.

World lines are artificial constructs like graphs of stocks and shares - useful in their own way, but not the be-all and end-all of relativity.

I am told on this forum that each particle has only one world line each.  Do you agree?

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39 minutes ago, 34student said:

I am told on this forum that each particle has only one world line each.  Do you agree?

Yes that is correct.

That is because the word 'particle' is short for the true phrase 'point particle' which has a special meaning in Physics.

But once again there are many things to know about relativity before you bother with world lines.

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33 minutes ago, studiot said:

Yes that is correct.

That is because the word 'particle' is short for the true phrase 'point particle' which has a special meaning in Physics.

But once again there are many things to know about relativity before you bother with world lines.

Ok, now, are the particles on each side of the 1 meter long train, also have world lines that are one meter apart?

Edited by 34student
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On 10/26/2021 at 5:22 PM, 34student said:

He sees a 100 meter train contract to 1 meter.

And

1 hour ago, 34student said:

Ok, now, are the particles on each side of the 1 meter long train, also have world lines that are one meter apart?

In the last question, do you mean a 100m long train (proper length), a 1m long train (proper length), special relativity length contraction of 100m to 1m (measured in some frame of reference)? Or something else?

Proper length or rest length is the length of an object in the object's rest frame. (https://en.wikipedia.org/wiki/Proper_length)

Edited by Ghideon
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58 minutes ago, 34student said:

Ok, now, are the particles on each side of the 1 meter long train, also have world lines that are one meter apart?

You have just asked this and been told my answer.

The question as it stands is meaningless.

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45 minutes ago, Ghideon said:

And

In the last question, do you mean a 100m long train (proper length), a 1m long train (proper length), special relativity length contraction of 100m to 1m (measured in some frame of reference)? Or something else?

Proper length or rest length is the length of an object in the object's rest frame. (https://en.wikipedia.org/wiki/Proper_length)

A train with a proper length of 100m.  This is from the example that I gave in my OP.

46 minutes ago, studiot said:

You have just asked this and been told my answer.

The question as it stands is meaningless.

So we can say that the particles are 1 meter apart, but we can't know if their world lines are 1 meter apart?  Why not?

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27 minutes ago, 34student said:

So we can say that the particles are 1 meter apart, but we can't know if their world lines are 1 meter apart?  Why not?

There is some frame of reference S where a 100m long train (proper length) will have the length 1m according to special relativity. If the question "world lines are 1 meter apart" is physically meaningful, can you explain how?

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4 minutes ago, Ghideon said:

There is some frame of reference S where a 100m long train (proper length) will have the length 1m according to special relativity. If the question "world lines are 1 meter apart" is physically meaningful, can you explain how?

Since the particles are 1 meter apart and they travel along world lines through time, then doesn't that imply that their world lines are also 1 meter apart?

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35 minutes ago, 34student said:

Since the particles are 1 meter apart and they travel along world lines through time, then doesn't that imply that their world lines are also 1 meter apart?

Your line of questions shows you're not going to understand the answers. Why don't you start with simpler concepts first and understand them before talking about world lines?

The world line of a particle is made up of all the events in the particle's entire lifetime. You're asking for the distance between two arbitrary lines. I think what you're really asking for is the distance between particular pairs of events on those world lines, but you're not specifying that unambiguously.

If you're using coordinates where Bob's world line remains fixed at one x,y,z location and only varies in T, then (based on the situation you've implied), the distance between a given event at time T1 on the world line of the front of the train, and an event at the same time T1 on the world line of the back of the train, will be 1 m apart. If you use other coordinates, you'll get other answers.

If you're talking about measurements in the block universe, you should specify what coordinates you're using. If you're talking about observations, you should make it clear what frame of reference you're using. If you're measuring the distance between 2 objects over their entire lifetimes (ie. world line) you should make it clear what time you're talking about. And if you're talking about a single moment across a distance, to even make sense of that requires the set of coordinates or frame of reference! If you want specific answers, your questions have to make sense, and they haven't been.

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29 minutes ago, md65536 said:

Your line of questions shows you're not going to understand the answers. Why don't you start with simpler concepts first and understand them before talking about world lines?

Thank you.

But I don't think the OP means the same sort of distance as you do, since he is measuring in metres.

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12 minutes ago, studiot said:

But I don't think the OP means the same sort of distance as you do, since he is measuring in metres.

I did mean the same thing, but failed to state it. I should have said I meant the spatial distance between two events at the same time in a particular frame of reference. Did I imply the invariant length of a spacetime interval?

...thus proving my point that you have to specify these details for things to make sense to others!

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4 hours ago, 34student said:

Since the particles are 1 meter apart and they travel along world lines through time, then doesn't that imply that their world lines are also 1 meter apart?

The particles are one meter apart as seen from a specific frame of reference. A different observer will measure a different distance. All observers are right, in their own frames. A specific Length is thus a relational property, and not somehow intrinsic to the object.

I guess-timate that this has been pointed out now at least ~10 times or so, in different ways be different posters.

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4 hours ago, md65536 said:

Your line of questions shows you're not going to understand the answers. Why don't you start with simpler concepts first and understand them before talking about world lines?

The world line of a particle is made up of all the events in the particle's entire lifetime. You're asking for the distance between two arbitrary lines. I think what you're really asking for is the distance between particular pairs of events on those world lines, but you're not specifying that unambiguously.

If you're using coordinates where Bob's world line remains fixed at one x,y,z location and only varies in T, then (based on the situation you've implied), the distance between a given event at time T1 on the world line of the front of the train, and an event at the same time T1 on the world line of the back of the train, will be 1 m apart. If you use other coordinates, you'll get other answers.

If you're talking about measurements in the block universe, you should specify what coordinates you're using. If you're talking about observations, you should make it clear what frame of reference you're using. If you're measuring the distance between 2 objects over their entire lifetimes (ie. world line) you should make it clear what time you're talking about. And if you're talking about a single moment across a distance, to even make sense of that requires the set of coordinates or frame of reference! If you want specific answers, your questions have to make sense, and they haven't been.

Yes, you understand my question.  Now are there also world lines from 2 particles that are 100 meters apart, as measured from an observer on the train?

50 minutes ago, Markus Hanke said:

The particles are one meter apart as seen from a specific frame of reference. A different observer will measure a different distance. All observers are right, in their own frames. A specific Length is thus a relational property, and not somehow intrinsic to the object.

I guess-timate that this has been pointed out now at least ~10 times or so, in different ways be different posters.

53 minutes ago, Markus Hanke said:

The particles are one meter apart as seen from a specific frame of reference. A different observer will measure a different distance. All observers are right, in their own frames. A specific Length is thus a relational property, and not somehow intrinsic to the object.

I guess-timate that this has been pointed out now at least ~10 times or so, in different ways be different posters.

Yet I am told that each particle only has 1 world line.

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There are not more worldlines for different frames.
The 'block' universe is a static universe.
You can have many different 'foliations' of the 4D hypercube, and all are equally valid.
The worldline of an object starts with the formation of that object, and winds through space, and time, to its endpoint, or destruction, of the object.
There is no 'present'. All time that the object exists, and all distances that it travels during its existence, are encompassed by its worldline.
As Marcus has already explained, different frames imply different foliations, resulting in different projections onto the axis of the 4D hypercube, and are the observations ( length contraction/time dilation ) we see in different frames.

I suggest some reading on Special Relativity before you jump to the 'block' universe model.

And NO, there is no valid frame 'outside the universe, or in another 'dimension'.

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31 minutes ago, MigL said:

And NO, there is no valid frame 'outside the universe, or in another 'dimension'.

Ok, then let us just think about some state of the universe S1 at some time T1.

T1 is a moment when the train is 1 meter for Bob.  We can examine this frozen frame of the universe, yes?

If so, then I would think that we can see if the train really is 1 meter.  If this is allowed, continue reading.

Now an observer on the train who is on the train the whole time that Bob is gone will never have a 1 meter train for some interval of time that contains T1.

There seems to be a contradiction here.

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10 minutes ago, 34student said:

There seems to be a contradiction here.

This isn’t a contradiction at all, because these are different observers performing a measurement the outcome of which is observer-dependent, since they’re measuring something that isn’t intrinsic to the train, but describes only their relationship to it.

It seems to me that we are just repeating both question and answer over and over again, to no avail at all it seems. So let me ask you this - are you actually interested in the explanation, or have you made up your mind already that relativity must be wrong? Just be honest.

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1 hour ago, Markus Hanke said:

It seems to me that we are just repeating both question and answer over and over again, to no avail at all it seems. So let me ask you this - are you actually interested in the explanation, or have you made up your mind already that relativity must be wrong? Just be honest.

Yeah agreed, and I'm beginnning to smell an agenda of sorts also.

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27 minutes ago, beecee said:

Yeah agreed, and I'm beginnning to smell an agenda of sorts also.

The very title of the thread already gave it away right from the start, but I had been hoping that explaining the theory plus listing experimental evidence might have had some effect at least. Sadly though, at this point the best term I can think of to describe this thread is ‘sealioning’.

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3 hours ago, Markus Hanke said:

The very title of the thread already gave it away right from the start, but I had been hoping that explaining the theory plus listing experimental evidence might have had some effect at least. Sadly though, at this point the best term I can think of to describe this thread is ‘sealioning’.

Sealioning, gas lighting and so forth.

It's all very sad that the only things I seem to be learning lately are different new words for unpleasant activity.

I have already suggested that you understand the basic principles before proceeding to greater detail.

There are two here.

1.) The Principle of Relativity.

This was actually known long before Einstein and different works have presented it differently, as did Einstein in his turn.

His version is that the laws of Mechanics and of Electrodynamics should appear mathematically in the same form to all observers.

This is very general and too difficult to start with but a consequence is useful and is the version I commend to you.

There are no such things as absolute space or absolute time.

To this Einstein added a second principle and again I will quote it in a suitable form here for your benefit.

2.) The invariability of the speed of light in a vacuum.

Every observer measures the same speed of light relative to himself and also relative to every other observer, irrespecitive of the motion of the source of that light.

As stated above these two Principles generated a restricted form of relativity, called Special Relativity.

A third principle was later introduced to add the laws of gravity to the list and led to General Relativity, which I will not go into further at the moment.

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7 hours ago, 34student said:

Yet I am told that each particle only has 1 world line.

And every observer will agree with this. What it looks like depends on the observer.

Your personal model of how this works is wrong and needs to be abandoned.

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