# Length contraction in a block universe must be an illusion

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23 minutes ago, beecee said:

The length contraction is real in those circumstances, as there would also be a related dilation with the aspect of time.

In what circumstances are you referring to?

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2 minutes ago, 34student said:

In what circumstances are you referring to?

Length contraction [space] and time are interchangeable. Neither are illusions and both depend on one's frame of reference, all of which are as valid as each other.

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43 minutes ago, md65536 said:

Don't you have to choose your coordinates for such a block universe? Then you can measure the distance between points with the same T value.

For example, choose coordinates for the block universe where T corresponds with a clock that is stationary relative to the train. Take a pair of events with the same T value, one at the front of the train and one at the back. You can find the proper length of this train, say 100 m.

Or choose coordinates where T' corresponds with Bob's proper time and find 2 different events with the same T' and find that the distance between those 2 events is 1 m.

The aliens would also have to choose a set of coordinates, and could measure the length contraction of the train relative to its proper length.

For every t (time) there is a corresponding function S(t) (static universe).  That is all there is in a block universe.  If you agree, continue reading.

For some t's between 2050 and 2100 Bob sees the train as 1 meter.  But from Earth, people see the train as 100 meters for all t's.

There cannot be two S(t)'s for the same t in a block universe in this example.

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3 minutes ago, 34student said:

For some t's between 2050 and 2100 Bob sees the train as 1 meter.  But from Earth, people see the train as 100 meters for all t's.

How is this possible unless Bob is moving relative to the earth?

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45 minutes ago, beecee said:

Length contraction [space] and time are interchangeable. Neither are illusions and both depend on one's frame of reference, all of which are as valid as each other.

If you want to help me understand, please address my OP.  Where is it flawed?

1 minute ago, swansont said:

How is this possible unless Bob is moving relative to the earth?

Yes, Bob is travelling relative to the Earth/train.  What's the problem?

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7 minutes ago, 34student said:

Yes, Bob is travelling relative to the Earth/train.  What's the problem?

The part where you said “Nothing moves in a block universe.” Or maybe where you said Bob is moving.

Which it?

9 minutes ago, 34student said:

If you want to help me understand, please address my OP.  Where is it flawed?

Issues were raised, AFAICT you’ve ignored them.

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8 minutes ago, swansont said:

The part where you said “Nothing moves in a block universe.” Or maybe where you said Bob is moving.

Which it?

Issues were raised, AFAICT you’ve ignored them.

I have to speak in a "Newtonian language" to explain the block universe.  But the answer to your question is "Nothing moves in a block universe".  Don't you notice that nobody else is raising this issue except you?

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27 minutes ago, 34student said:

I have to speak in a "Newtonian language" to explain the block universe.  But the answer to your question is "Nothing moves in a block universe".  Don't you notice that nobody else is raising this issue except you?

1. That’s how this works. People see I’ve raised the issue, and they refrain from being repetitive. and

2. That’s not an actual rebuttal of the issue, it’s dodging it.

So if nothing moves, how can there be time dilation or length contraction?

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3 minutes ago, swansont said:

1. That’s how this works. People see I’ve raised the issue, and they refrain from being repetitive. and

2. That’s not an actual rebuttal of the issue, it’s dodging it.

So if nothing moves, how can there be time dilation or length contraction?

I just explained this to you.  These are Newtonian terms for simplicity.

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1 hour ago, 34student said:

If you want to help me understand, please address my OP.  Where is it flawed?

1 hour ago, beecee said:

The fact that space and time are interchangeable and the evidence is conclusive that time dilation is real, and relative, means that space [length] also is relative.

and I also gave an excellent link by a reputable physicist.

If I can add more, while I aint no physicist/scientist, you seem to be using Newtonian in one instance, then GR in another. Not sure if that  is allowed.

47 minutes ago, 34student said:

Don't you notice that nobody else is raising this issue except you?

Just as you seem to be the only one questioning the evidenced based aspect of length contraction.

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24 minutes ago, beecee said:

and I also gave an excellent link by a reputable physicist.

If I can add more, while I aint no physicist/scientist, you seem to be using Newtonian in one instance, then GR in another. Not sure if that  is allowed.

Just as you seem to be the only one questioning the evidenced based aspect of length contraction.

Thank you for your link to the physicist, but I am looking for an understanding of SR through my OP.

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15 minutes ago, 34student said:

Thank you for your link to the physicist, but I am looking for an understanding of SR through my OP.

SR is simply a subset of GR. GR was formulated in 1916, more the a 100 years ago, and has been tested, and tested again and again, and its prediction keep on keeping on.eg: gravitational waves discoveries. While like all theories it has limitations, at the instant of the BB and the core of BH'S, it is totally valid within its domain.

You mention BH's earlier [I think] and while GR does predict BH's, it is not applicable at the core of the hole we chose to label a singularity. A singularity as defined by the failure of GR at that point, not a singularity as defined by infinite spacetime curvature and density, of which most all physicists reject. Which tells me that we have matter/energy there in an unknown state and possibly a surface of sorts

Edited by beecee
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4 minutes ago, beecee said:

SR is simply a subset of GR. GR was formulated in 1916, more the a 100 years ago, and has been tested, and tested again and again, and its prediction keep on keeping on.eg: gravitational waves discoveries. While like all theories it has limitations, at the instant of the BB and the core of BH'S, it is totally valid within its domain.

You mention BH's earlier [I think] and while GR does predict BH's, it is not applicable at the core of the hole we chose to label a singularity. A singularity as defined by the failure of GR at that point, not a singularity as defined by infinite spacetime curvature and density, of which most all physicists reject. Which tells me that we have matter/energy there in an unknown state and possibly a surface of sorts

I did not mention BH's.

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On 10/27/2021 at 2:22 AM, 34student said:

The year is 2050.  Bob goes close to light speed in his ship.  He sees a 100 meter train contract to 1 meter.  He gets back from his trip in the year 2100.

Are you saying he gets back in his ship after biologically aging 50 years and as supported by his on board ship clocks? How much time has passed on Earth?

On 10/27/2021 at 2:22 AM, 34student said:

Aliens from another dimension are looking at our block universe from 2050 to 2100.  Will they see a 100 meter train or a 1 meter train or something else?

100 metre train I believe.

On 10/27/2021 at 2:22 AM, 34student said:

This is meant to support the argument that length contraction is an illusion and not actually happening.

It seems to me to support the argument that time dilation and length contraction are dependent on one's frame of reference.

I can't see a problem.

6 minutes ago, 34student said:

I did not mention BH's.

Sorry, I was thinking of another that is also apparently questioning mainstream results.

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20 minutes ago, beecee said:

Are you saying he gets back in his ship after biologically aging 50 years and as supported by his on board ship clocks? How much time has passed on Earth?

When he comes back, it is 2100 on Earth.  To him, it's (I am not doing the actual calculation) 2051.  So let's say one year passed for him on the ship.

24 minutes ago, beecee said:

100 metre train I believe.

Then you are on my side of the argument.  The train becoming 1 meter is just an illusion for Bob.

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20 minutes ago, 34student said:

When he comes back, it is 2100 on Earth.  To him, it's (I am not doing the actual calculation) 2051.  So let's say one year passed for him on the ship.

Close enough and understood.

21 minutes ago, 34student said:

Then you are on my side of the argument.  The train becoming 1 meter is just an illusion for Bob.

☺️ No, I'm on the side of the fact that all frames of references are as valid as each other. That does not equate to it being an illusion.

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4 hours ago, 34student said:

For every t (time) there is a corresponding function S(t) (static universe).  That is all there is in a block universe.  If you agree, continue reading.

For some t's between 2050 and 2100 Bob sees the train as 1 meter.  But from Earth, people see the train as 100 meters for all t's.

There cannot be two S(t)'s for the same t in a block universe in this example.

Then S(t) is a hypersurface of events representing a single moment?

How do you determine t? It sounds like you're implying it uses dates according to a clock on Earth? What if you have a block universe with all of the same events, but with a t value that corresponds with Bob's clock?

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6 hours ago, md65536 said:

Don't you have to choose your coordinates for such a block universe? Then you can measure the distance between points with the same T value.

You can choose foliations with the same T value for your frame, but that will be different from a foliation from another observer's frame. All are equally valid.

The 'Block' Universe model is essentially devoid of time, as past, present and future are all present in the 'Block'.
It is sometimes known as 'eternalism'; see here

The worldline of an event does not move; it is already there.

10 hours ago, 34student said:

You didn't explain why; please explain why.  Note that a God's eye view of the block universe would have no effect on it.

16 hours ago, Markus Hanke said:

Note that the geometric length of the world line itself does not change - all observers agree on it. They are just looking at the same thing from a different angle in spacetime - quite literally so.

This statement supports my argument that length contraction is not actually happening and is just an illusion.

I think you should read up on the Block Universe model; you don't seem to understand it.

Edited by MigL
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2 hours ago, md65536 said:

Then S(t) is a hypersurface of events representing a single moment?

How do you determine t? It sounds like you're implying it uses dates according to a clock on Earth? What if you have a block universe with all of the same events, but with a t value that corresponds with Bob's clock?

Bob and Earth begin with the same t value.  When Bob returns, his t value is the same as Earth's t value when t was 2051.  For some of that year, according to Bob's clock, the train was 1 meter.  But from 2050 to 2051 on Earth, the train was never 1 meter.

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1 hour ago, MigL said:

The 'Block' Universe model is essentially devoid of time, as past, present and future are all present in the 'Block'. [...]

The worldline of an event does not move; it is already there.

Do you mean worldline of an object? An event is a single point in spacetime (and in the "block") and many worldlines can pass through it.

Worldlines still exist in the block, and one's proper time is an invariant length of the world line. Different coordinate times can be defined (including just using T to represent time) and the coordinate times between distant events can be calculated in the block. I don't understand what you mean by it being "devoid of time", since all the measures of time are still there. Some philosophical "flow or time" or whatever might be taken out, but time in SR and GR is the measurement, not the concept.

6 minutes ago, 34student said:

Bob and Earth begin with the same t value.  When Bob returns, his t value is the same as Earth's t value when t was 2051.  For some of that year, according to Bob's clock, the train was 1 meter.  But from 2050 to 2051 on Earth, the train was never 1 meter.

Where's the problem? You're using coordinate time t to be the time in Earth's frame. You're stating that the length of the train is relative, and depends on the observer (ie. reference frame). That agrees with observation. That agrees with relativity. Nothing there implies illusion.

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15 hours ago, 34student said:

This statement supports my argument that length contraction is not actually happening and is just an illusion.

No it doesn’t, because the geometric length of a world line in spacetime is not identical to an observer’s measurement of spatial length - as I have pointed out in my post.

21 hours ago, studiot said:

It is worth noting that there is a difference between a projection (called resolved parts in my attachment) and a component.

You are correct of course, my use of terminology was sloppy. Thanks for pointing it out!

8 hours ago, 34student said:

The train becoming 1 meter is just an illusion for Bob.

Length contraction - like time dilation - has real-world physical consequences that are directly detectable, so the very notion of it being illusory isn’t tenable.

- The classic example being of course atmospheric muons

- Another classic example is the change in interaction cross section of relativistically colliding gold ions at the RHIC

- Magnetic forces on test particles passing currents at relativistic speeds (Purcell, Electricity and Magnetism)

- Flux quanta in Josephson Tunnel Junctions

- Changes in ionisation energy levels for relativistically moving particles

Among many others. None of these things are ‘illusions’, these are very real, directly detectable phenomena that are direct consequences of relativistic physics; some of these are relevant to engineering applications.

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10 hours ago, 34student said:

Thank you for your link to the physicist, but I am looking for an understanding of SR through my OP.

5 hours ago, 34student said:

Bob and Earth begin with the same t value.  When Bob returns, his t value is the same as Earth's t value when t was 2051.  For some of that year, according to Bob's clock, the train was 1 meter.  But from 2050 to 2051 on Earth, the train was never 1 meter.

This seems to me to be the key to unlocking understanding of SR for you.

Some of us find thought experiments such as the one you describe add to the confusion, rather than dispel it.

Please bear in mind that it is not physically possible for Bob to directly observe the measurements you describe.
He can, however calculate the effects in his own terms.

Modern derivations of SR are much simpler than the original, which is comparatively quite hard to follow.

Modern derivations start with the idea that different observers will make different measurements on the same phenomenon.

They then go with the notion of finding something that 'observers' can agree about and establishing the maths that yields the same values.

In other words, the Maths follows the Physics.

The something that can be agreed upon is called an invariant.

An invariant is the same for all observers.

Do you want to develop this route to understanding SR  ?

Note GR and SR are actually different; understaning GR requires further considerations.

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11 hours ago, 34student said:

I just explained this to you.  These are Newtonian terms for simplicity.

Contradictions are not simple. It's not surprising that they arise because we are discussing special relativity, which is not Newtonian, and you can't mix-and-match models in this way. (it can lead to contradictions)

It could be that whatever questions/confusion you have arise from such contradictions. What is needed is a self-consistent picture of what is going one. Newtonian physics is, and so is SR. The latter matches observation, the former fails to do so under situations like we are discussing.

10 hours ago, 34student said:

The train becoming 1 meter is just an illusion for Bob.

Are you going to address my example of kinetic energy, and whether that is an illusion for Bob?

The issue is that length and time are absolutes in a Newtonian world, so we aren't used to thinking of them as variables. But you can derive the effects, as Einstein did, based on c being invariant — which is another thing that we're not used to in Newtonian physics — and you can also look at the experiments that confirm it. Most of them involve time, because time is easier to measure at the precision demanded by such experiments.

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10 hours ago, md65536 said:

I don't understand what you mean by it being "devoid of time", since all the measures of time are still there.

Sorry, md65536, obviously it cannot be devoid of time as that is a component of its dimensionality.
It is devoid of time passage.
From the link I previously provided          Eternalism (philosophy of time) - Wikipedia

"It is sometimes referred to as the "block time" or "block universe" theory due to its description of space-time as an unchanging four-dimensional "block", as opposed to the view of the world as a three-dimensional space modulated by the passage of time."

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11 hours ago, md65536 said:

Where's the problem? You're using coordinate time t to be the time in Earth's frame. You're stating that the length of the train is relative, and depends on the observer (ie. reference frame). That agrees with observation. That agrees with relativity. Nothing there implies illusion.

During the year 2050, was the train 1 meter or 100 meters?

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