Clocks, rulers... and an issue for relativity

[VandD]

 

You basically have the choice between block universe and presentism.

Einstein's SR is block universe. The presentism alternative is linked to an ether and/or a preferred frame. There is no such thing.

Here I have made a slight change to the diagram, so that the contraction on the left side (the muon's frame) is more evident.

 

Screen Shot 09-06-16 at 07.56 PM2.jpg

 

 

 

Think about this one:

 

Screenshots teken here. I added notes to the diagram for clarity.

Edited September 7, 2016 by VandD

[Tim88]

Einstein's SR is block universe. The presentism alternative is linked to an ether and/or a preferred frame. There is no such thing.

[..]

 

Einstein's SR was first agnostic as he tried to get rid of the ether, next he expressed support for the Lorentz ether, and later, in a letter to family of a lost friend, he expressed belief in the block universe as it corresponds to eternalism. Scientists are forced to reject what logical reasoning obliges them to reject, but there always remains freedom of models.

 

Concerning your comments on your diagram, note that in the real world clocks don't always express proper time but are tuned to the reference system for which they service - this is in particular the case with GPS clocks.

 

[edit: removed comment of little relevance]

Edited September 8, 2016 by Tim88

[robinpike]

 

So to the next step that I want to understand. (Apologies if I my phrasing is not always as it should be - I am trying my best to use the correct terms.)

 

When the travelling clock is at rest and next to a stationary clock, the two clocks can synchronize with each other. At this point, we / all observers can note that their routes through space-time must be the same, that is they have the same spatial co-ordinates and their progress along their timelines stay abreast with each other.

 

Note here that the travelling clock is always 'at rest' in its own frame, even when it is moving so the underlined statement is incomplete. It is better phrased

When the travelling clock is at rest in the frame of the the stay-at-home clock, and next to it.

 

The travelling clock then goes on its round trip, eventually returning back to the stationary clock and halting alongside that clock. At this point, we / all observers can note that their routes through space-time must again be the same, that is they have the same spatial co-ordinates and their progress along their timelines stay abreast with each other.

 

From experiment, we also know that the travelling clock will have lost time compared to the stay at home clock.

 

What I would like confirmed is how the travelling clock lost time. My naive deduction is that during its journey, the travelling clock was on a shorter route through space-time than the stay at home clock?

 

So first point, is that the correct explanation?

 

Yes the two underlined statements go hand-in-hand as they amount to the same thing so I would not say that one is the cause of the other.

The proof of this is quite easy, given the Lorenz transformation.

 

And thinking ahead, assuming that is the correct explanation, then I note this point...

 

For an observer, who by misfortune did not see the travelling clock start its journey, and only sees the travelling clock coasting through space away from the stationary clock (or towards it if it is on the return leg of its round trip), that observer is therefore unable to determine if it is the 'travelling' clock on a shorter route through space-time, or whether it is the 'stationary' clock that is on the shorter route through space-time. Despite this unfortunate observer not being able to deduce (or measure) which is which, it does not alter that it is the travelling clock that is on the shorter route through space-time.

 

I can't see any good reason why a third observer could not deduce which clock is stay-at-home and which is going on a journey by sufficient observation.

Clearly this third observer must be in a class frame of his own.

This is because the traveler visits events not visited by the stay-at-home observer, as I mentioned before.

 

 

I think I have just realized why this discussion has become so difficult to resolve. When I used the description ‘unfortunate observer’, the responses just used ‘observer’. I wondered why?

 

Could this be because the equations of relativity don’t care about the history of the travelling clock and don't care about which part of the observed value is apparent / real? The equations describe what is being observed now (by an observer), but they do not break the observed value into an apparent value and a real value. (Of course, real effects are not denied by the equations, such as when the travelling clock is compared to the stay at home clock at the end of its round trip.)

 

So when I asked “how does the travelling clock lose time?” how can the equations of relativity reveal how? Sure an explanation could be inferred from the equations, such as shorter route through space-time, or the travelling clock ticks at a slower rate, or its length contracts, or a combination of all of those perhaps – but the equations cannot be used to deduce with certainty the answer?

 

Does the above make sense?

Edited September 8, 2016 by robinpike

[swansont]

I think I have just realized why this discussion has become so difficult to resolve. When I used the description ‘unfortunate observer’, the responses just used ‘observer’. I wondered why?

Because there's no particular importance attached to that description?

 

So when I asked “how does the travelling clock lose time?” how can the equations of relativity reveal how? Sure an explanation could be inferred from the equations, such as shorter route through space-time, or the travelling clock ticks at a slower rate, or its length contracts, or a combination of all of those perhaps – but the equations cannot be used to deduce with certainty the answer?

 

Does the above make sense?

No, it doesn't. The equations of relativity are used to analyze the twins paradox, so the obvious conclusion is that the can be used to deduce with certainty the answer. However, they can't indicate what misconceptions you are holding on to that prevent you from seeing this.

[Tim88]

 

I think I have just realized why this discussion has become so difficult to resolve. When I used the description ‘unfortunate observer’, the responses just used ‘observer’. I wondered why?

 

Could this be because the equations of relativity don’t care about the history of the travelling clock and don't care about which part of the observed value is apparent / real? The equations describe what is being observed now (by an observer), but they do not break the observed value into an apparent value and a real value. (Of course, real effects are not denied by the equations, such as when the travelling clock is compared to the stay at home clock at the end of its round trip.)

 

So when I asked “how does the travelling clock lose time?” how can the equations of relativity reveal how? Sure an explanation could be inferred from the equations, such as shorter route through space-time, or the travelling clock ticks at a slower rate, or its length contracts, or a combination of all of those perhaps – but the equations cannot be used to deduce with certainty the answer?

 

Does the above make sense?

 

That makes perfect sense to me. However, a thorough analysis of the meaning and consequences of those equations is certainly helpful to deduce what is going on and it serves to weed out interpretations that are incompatible with SR.

[robinpike]

Because there's no particular importance attached to that description?

 

 

No, it doesn't. The equations of relativity are used to analyze the twins paradox, so the obvious conclusion is that the can be used to deduce with certainty the answer. However, they can't indicate what misconceptions you are holding on to that prevent you from seeing this.

 

Swansont - I do not understand how the equations distinguish between an apparent value and a real value? When you say the 'answer', to what question?

 

I can understand for the question: How much time did the travelling clock lose? But what if the question is: How did the travelling clock lose time? What is the answer (with certainty) to that question?

Edited September 8, 2016 by robinpike

[studiot]

Robin,

 

It took quite a while for you to reply to my last post, and sadly when it came I cannot see any correspondence between my post and your reply.

Any correspondence may be real, but is not apparent to me.

 

So I cannot tell if you have accepted my comments.

 

Your reply introduced the following new question(s)

 

 

robinpike post#180

 

So when I asked “how does the travelling clock lose time?” how can the equations of relativity reveal how? Sure an explanation could be inferred from the equations, such as shorter route through space-time, or the travelling clock ticks at a slower rate, or its length contracts, or a combination of all of those perhaps – but the equations cannot be used to deduce with certainty the answer?

Does the above make sense?

 

The equations of relativity, as you call them, and observed measurements are similar to my comment from post#172

 

They go hand in hand.

 

In other words they are developed together and both brought into convergence together.

That is the scientific process.

 

So no you do not deduce one from the other, but each confirmation (match) between the two aspects strengthens the theory,

just as any contradiction between the two requires us to investigate further.

 

As far as I can see classification of effects into real and apparent is artificial and leads to misunderstandings.

[robinpike]

Robin,

 

It took quite a while for you to reply to my last post, and sadly when it came I cannot see any correspondence between my post and your reply.

Any correspondence may be real, but is not apparent to me.

 

So I cannot tell if you have accepted my comments.

 

Your reply introduced the following new question(s)

 

 

The equations of relativity, as you call them, and observed measurements are similar to my comment from post#172

 

They go hand in hand.

 

In other words they are developed together and both brought into convergence together.

That is the scientific process.

 

So no you do not deduce one from the other, but each confirmation (match) between the two aspects strengthens the theory,

just as any contradiction between the two requires us to investigate further.

 

As far as I can see classification of effects into real and apparent is artificial and leads to misunderstandings.

 

Well, maybe it leads to questions rather than misunderstandings. An effect that is classified as real and an effect that is classified as apparent are not artificial classifications - apparent and real mean different things. I think a better way to state this would be to say that apparent and real effects are both in the classification relativistic?

[swansont]

Swansont - I do not understand how the equations distinguish between an apparent value and a real value? When you say the 'answer', to what question?

What is an apparent value and what is a real value? That seems to be a false distinction you introduced. One of those misconceptions I mentioned.

 

I can understand for the question: How much time did the travelling clock lose? But what if the question is: How did the travelling clock lose time? What is the answer (with certainty) to that question?

How did it lose time? It ran slower. For details, see the relativity equations that confirm this.

Well, maybe it leads to questions rather than misunderstandings. An effect that is classified as real and an effect that is classified as apparent are not artificial classifications - apparent and real mean different things. I think a better way to state this would be to say that apparent and real effects are both in the classification relativistic?

But where in relativity is it stated that this is a legitimate distinction?

[robinpike]

What is an apparent value and what is a real value? That seems to be a false distinction you introduced. One of those misconceptions I mentioned.

 

 

How did it lose time? It ran slower. For details, see the relativity equations that confirm this.

 

But where in relativity is it stated that this is a legitimate distinction?

 

Dictionary definition: Apparent - seeming real or true, but not necessarily so.

 

Dictionary definition: real - actually existing as a thing or occurring in fact; not imagined or supposed.

 

An apparent value is different to a real value by definition.

 

Swansont are you being deliberately obtuse? Yes I know the travelling clock ran slower. I asked how (not what). What you have done is replied a 'what' reply to a 'how' question!? For example: How does gravity work? And the reply: It pulls you towards the ground. Does not answer the How question!

 

Relativity equations do not distinguish between apparent or real - relativity is a set of equations that equate to what is measured.

Edited September 8, 2016 by robinpike

[swansont]

Dictionary definition: Apparent - seeming real or true, but not necessarily so.

 

Dictionary definition: real - actually existing as a thing or occurring in fact; not imagined or supposed.

 

An apparent value is different to a real value by definition.

 

I know they are different, but I want to know what they mean (or you think they mean) in this context. You were the one who introduced this terminology. What would be a real time and what would be an apparent time? What is it about relativity that suggests that the equations would give you illusory values?

 

Swansont are you being deliberately obtuse? Yes I know the travelling clock ran slower. I asked how (not what). What you have done is replied a 'what' reply to a 'how' question!? For example: How does gravity work? And the reply: It pulls you towards the ground. Does not answer the How question!

 

Relativity equations do not distinguish between apparent or real - relativity is a set of equations that equate to what is measured.

Science doesn't address the how question you pose. We do not know how mass attracts other mass (or curves spacetime). We know that it does.

 

We don't know why the speed of light is invariant, or has the value that it does. We know the ramifications on how time and distance behave.

 

So one might inquire as to whether you were being deliberately obtuse in asking a question that science simply doesn't address.

[Tim88]

 

I know they are different, but I want to know what they mean (or you think they mean) in this context. You were the one who introduced this terminology. What would be a real time and what would be an apparent time? What is it about relativity that suggests that the equations would give you illusory values?

 

Science doesn't address the how question you pose. We do not know how mass attracts other mass (or curves spacetime). We know that it does.

 

We don't know why the speed of light is invariant, or has the value that it does. We know the ramifications on how time and distance behave.

 

So one might inquire as to whether you were being deliberately obtuse in asking a question that science simply doesn't address.

 

A few people in this thread pretended that science does address his questions. Perhaps it warrants a discussion in the philosophy forum, where, I suppose, every scientific question goes that experiments cannot answer.

[robinpike]

 

I know they are different, but I want to know what they mean (or you think they mean) in this context. You were the one who introduced this terminology. What would be a real time and what would be an apparent time? What is it about relativity that suggests that the equations would give you illusory values?

 

Science doesn't address the how question you pose. We do not know how mass attracts other mass (or curves spacetime). We know that it does.

 

We don't know why the speed of light is invariant, or has the value that it does. We know the ramifications on how time and distance behave.

 

So one might inquire as to whether you were being deliberately obtuse in asking a question that science simply doesn't address.

 

Swansont - I agree. Let me think about how to state the questions so that they are not misunderstood / discussed at cross purposes. I don't want this to just peter out - I want to understand that there is no (logical) issue with relativity, or if there is, then what is the argument that reveals that logical issue.

 

PS Studiot - I haven't been ignoring you! A lot of cross purpose replies were happening (inadvertently) and I couldn't delve into everything that was being suggested, while I was trying to figure out why.

Edited September 8, 2016 by robinpike

[swansont]

I don't want this to just peter out - I want to understand that there is no (logical) issue with relativity, or if there is, then what is the argument that reveals that logical issue.

 

 

The fact that the experiment and theory agree should indicate that there isn't. Even if they didn't, the math is internally consistent. So any potential illogic is in some artificial constraint that you are putting on the problem. Common ones I have seen at SFN are assuming simultaneity or any of the measurable quantities (e.g. length, time) are absolute

[michel123456]

Einstein's SR is block universe. The presentism alternative is linked to an ether and/or a preferred frame. There is no such thing.

 

Think about this one:

 

Screenshots teken here. I added notes to the diagram for clarity.

I have to admit that is not so easy to grasp

 

Question below:

 

C, where the Earth's worldline intersects the x′-axis, corresponds in S′ to the position of Earth simultaneous with the emergence of the muon. Length L₀=AB in S is longer than length L′=AC in S′.

 

I don't get this last one because it is stated at the beginning that:

The muon rests in S′, its worldline is the ct′-axis.

 

So, if the muon is at rest in S', what distance did it travel in S'? The distance AC in S' is the distance traveled by the muon at rest?

Edited September 8, 2016 by michel123456

[swansont]

 

So, if the muon is at rest in S', what distance did it travel in S'? The distance AC in S' is the distance traveled by the muon at rest?

 

 

The earth is moving for someone in the muon rest frame. 2 km, per the original statement of the problem. 7.1 km using the numbers in that graphs (since they use a different v)

[michel123456]

 

 

The earth is moving for someone in the muon rest frame. 2 km, per the original statement of the problem. 7.1 km using the numbers in that graphs (since they use a different v)

Ok. So it is the distance traveled by the atmosphere as seen from the muon frame at rest.

-------------------------------

But the diagram does not depict what one sees. The diagram is a graph of the algebraic equations, showing that it is all geometry.

 

What I say is very simple:

The earthling sees a muon traveling a 10 km path through atmosphere. The earthling knows that for the muon, this same path represents only 2 km. That means the path is contracted, and the muon is contracted also.

 

But the earthling doesn't see 2km, he sees 10 km.

As such, the earthling does not see the muon contracted. Because the muon contracted corresponds to 2 km. And the earthling does not see 2 km.

 

Is that so complicated?

[swansont]

Ok. So it is the distance traveled by the atmosphere as seen from the muon frame at rest.

-------------------------------

But the diagram does not depict what one sees. The diagram is a graph of the algebraic equations, showing that it is all geometry.

 

What I say is very simple:

The earthling sees a muon traveling a 10 km path through atmosphere. The earthling knows that for the muon, this same path represents only 2 km. That means the path is contracted, and the muon is contracted also.

 

But the earthling doesn't see 2km, he sees 10 km.

As such, the earthling does not see the muon contracted. Because the muon contracted corresponds to 2 km. And the earthling does not see 2 km.

 

Is that so complicated?

 

 

It's not an issue of being complicated, it's just wrong.

 

The earthling does not see that atmosphere contracted to 2 km because the atmosphere is not moving at 0.995c. The atmosphere is in the rest frame.

 

The earth would see the muon contracted by a factor of 5 if that were measurable, but it's not.

[VandD]

But what if the question is: How did the travelling clock lose time? What is the answer (with certainty) to that question?

To keep speed of light constant in all intertial frames. Check f.ex. light clock experiment.

 

Relativity of simultaneity, time dilation, length contraction are all a result of constant c.

I have to admit that is not so easy to grasp

 

I think you have to face the fact that you miss some fundamental elementary knowledge about SR to discuss this kind of exercise and diagrams.

Why don't you take a brake, surf a bit on the internet, learn about relativity of simultaneity etc, and how to read and draw all that in some preliminary spacetime diagrams?

[michel123456]

 

 

It's not an issue of being complicated, it's just wrong.

 

The earthling does not see that atmosphere contracted to 2 km because the atmosphere is not moving at 0.995c. The atmosphere is in the rest frame.

 

The earth would see the muon contracted by a factor of 5 if that were measurable, but it's not.

So you believe that from frame S (Earth) the muon's proper length is observed?

[Tim88]

[..]

 

What I say is very simple:

The earthling sees a muon traveling a 10 km path through atmosphere. The earthling knows that for the muon, this same path represents only 2 km. That means the path is contracted, and the muon is contracted also.

 

But the earthling doesn't see 2km, he sees 10 km.

As such, the earthling does not see the muon contracted. Because the muon contracted corresponds to 2 km. And the earthling does not see 2 km.

 

Is that so complicated?

 

As others already stated, it's wrong: according to the Earth, the Earth's atmosphere is in rest and NOT contracted; the muon is in motion, and therefore contracted.

 

And what of my discussion about relativity of simultaneity? However, all such discussions assume a good understanding of the basic assumptions of SR.

 

Perhaps VandD is right that it's better to read up some more about the basics on Internet. For example you could read about the Michelson-Morley experiment, as it illustrates the practical meaning of both the first postulate (about inertial frames) and the second postulate (about light propagation) as well as length contraction. It was one of the experiments that led to SR. The Wikipedia article is rather good but perhaps overly complex: https://en.wikipedia.org/wiki/Michelson%E2%80%93Morley_experiment

[michel123456]

 

As others already stated, it's wrong: according to the Earth, the Earth's atmosphere is in rest and NOT contracted; the muon is in motion, and therefore contracted.

 

And what of my discussion about relativity of simultaneity? However, all such discussions assume a good understanding of the basic assumptions of SR.

 

Perhaps VandD is right that it's better to read up some more about the basics on Internet. For example you could read about the Michelson-Morley experiment, as it illustrates the practical meaning of both the first postulate (about inertial frames) and the second postulate (about light propagation) as well as length contraction. It was one of the experiments that led to SR. The Wikipedia article is rather good but perhaps overly complex: https://en.wikipedia.org/wiki/Michelson%E2%80%93Morley_experiment

With all my respect maybe you should start to think by yourself instead of repeating other's thoughts.

 

Fact 1: The atmosphere is at rest and 10 km thick. You are observing the muon going through 10km.

 

Fact 2: A contracted muon goes through a 2km atmosphere, not through a 10 km atmosphere.

 

Fact 3: what we call a "contracted muon" is the muon's proper length.

 

Is anything wrong in the above?

Because if nothing is wrong, it comes out that a contracted muon does not go through a 10 km atmosphere, IOW that this observation is impossible.

 

-----------------

edited. Strikethrough useless comment

Edited September 9, 2016 by michel123456

[swansont]

So you believe that from frame S (Earth) the muon's proper length is observed?

 

 

The muon is a point particle, so this is moot. If the muon had a size and we could measure it, it would be contracted, since in the earth's frame the muon is moving.

Fact 1: The atmosphere is at rest and 10 km thick. You are observing the muon going through 10km.

 

Fact 2: A contracted muon goes through a 2km atmosphere, not through a 10 km atmosphere.

 

Fact 3: what we call a "contracted muon" is the muon's proper length.

 

Is anything wrong in the above?

Because if nothing is wrong, it comes out that a contracted muon does not go through a 10 km atmosphere, IOW that this observation is impossible.

 

Yes, something is wrong.

 

The muon is not contracted in its own frame, so the contracted muon is not the proper length. Those are measurements made in two different frames. Only moving things are contracted. The length-contracted muon (as far as that is realizable for a point particle) goes through 10 km of atmosphere, since the frame in which the muon would be contracted is the earth's frame.

[michel123456]

 

 

The muon is a point particle, so this is moot. If the muon had a size and we could measure it, it would be contracted, since in the earth's frame the muon is moving.

 

Yes, something is wrong.

 

The muon is not contracted in its own frame, so the contracted muon is not the proper length. Those are measurements made in two different frames. Only moving things are contracted. The length-contracted muon (as far as that is realizable for a point particle) goes through 10 km of atmosphere, since the frame in which the muon would be contracted is the earth's frame.

That's the point of divergence.

If the muon, in its own frame, travels 2km, then what we call the contracted muon in our frame is the muon's proper length.

 

If we cannot agree on this, then there is no hope.

Edited September 9, 2016 by michel123456

[swansont]

That's the point of divergence.

If the muon, in its own frame, travels 2km, then what we call the contracted muon in our frame is the muon's proper length.

 

If we cannot agree on this, then there is no hope.

 

 

The definition of proper length is the length measured in the rest frame. I agree, if we cannot agree on basic definitions, there is no hope.