Relativity and shared realities (split from clocks, rulers...)

[VandD]

The weird thing happens when the clocks are reunified because the symmetry of Relativity is broken: it should have been that both clocks see the other as ticking slower. While in the famous twin paradox, there is no such a symmetry. There is a "preferred" clock at rest and an "unpreferred" clock in motion. This second clock observes exactly the contrary of what Relativity tells us.

Pure nonsense.

To help you I add a diagram for the rocket not returning back home.

In both diagrams I show where and when -per rocker frame i.o.w. the red 3D spaces of simultaneous events- the earth clock ticks slower (see blue).

But... In the first diagram the added earth clock ticking of 3.6 years (= 10 – 6.4 ) is a result of the rocket changing direction in 4D spacetime.

As long as you refuse to understand 4D spacetime you'll never understand SR.

But no offence it seems you are not interested in learning how SR works. And it won't help you by repeatring us a hundred times that proper length is all there is.

Do you actually see and understand what the diagrams show?

 

Edited September 4, 2016 by VandD

[michel123456]

Pure nonsense.

To help you I add a diagram for the rocket not returning back home.

In both diagrams I show where and when -per rocker frame i.o.w. the red 3D spaces of simultaneous events- the earth clock ticks slower (see blue).

But... In the first diagram the added earth clock ticking of 3.6 years (= 10 – 6.4 ) is a result of the rocket changing direction in 4D spacetime.

As long as you refuse to understand 4D spacetime you'll never understand SR.

But no offence it seems you are not interested in learning how SR works. And it won't help you by repeatring us a hundred times that proper length is all there is.

Do you actually see and understand what the diagrams show?

 

The right diagram makes perfect sense. No problem here.

 

The left diagram makes no sense at all.

1.Why are the red lines reversed in the upper part?(it looks to me as if past & future were reversed and that makes no sense to me but obviously I must miss something) -edit- the observer gets information from the past (the lower part of the diagram) no matter its direction of motion.

2. Why are 2 red lines in the middle not exactly at 45 degrees (as if SOL was not =c)

3. What is the gap between below 3.2years and up 3.2 years? (does the rocket "miss" something of earth history while making the turnaround?)

 

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

(edited)- twice.

Edited September 4, 2016 by michel123456

[studiot]

I have to say that spacetime diagrams help some and hinder others.

 

They are not necessary to understanding or working things out.

 

 

studiot

In neither thread is anyone prepared to work properly through this.

[VandD]

Yes I missed that and I still do. The observed object has the same length in both cases (but I must miss something)

Glad you accept you missed something.

You said: "Because as you have all agreed when the ships are put side by side, they have the same length".

This is when the ships are AT REST relative to each other.

They have NOT the same length when they move relative to each other, as shown correcly in bvr's drawings (see his 2. sketches)

When both astronauts cross they are not in the same set of simultaneous events.

In fact you don't understand relativity of simultaneity, correct?

 

 

 

The right diagram makes perfect sense. No problem here.

 

The left diagram makes no sense at all.

1.Why are the red lines reversed in the upper part?

Because the traveler is going left, flying toward the earth.

In that case the simultaneity line is reversed. Lorents transformations and Minkowski diagrams work that way

 

2. Why are 2 red lines in the middle not exactly at 45 degrees (as if SOL was not =c)

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

(edited)- twice.

Wait a second. Read what I wrote. I told you that the green and red lines are the frames of SIMULTANEITY. These are not the paths of light (I left these out but I can add them if you want. Give me some time I'll do it so that you can see the difference.)

 

3. What is the gap between below 3.2years and up 3.2 years? (does the rocket "miss" something of earth history while making the turnaround?)

 

 

 

No, while turning, the rocket catches up on what's happening on earth in a fast way The total earth worldline of 10 years lays out there in 4D spacetime, and by travelling away and then getting back he ends up at 2017 earth clock.

[swansont]

 

My objection is that it is not possible for the ruler/ship/train to be physically large/short/shorter all at the same time. To me, there must be only one single physical entity.

This "physical entity" is the one that you draw in the diagram.

It is the ruler/ship/train as measured at rest in its own frame.

 

 

This is not a physics argument. Do you have a physics-based reason that backs this up?

[michel123456]

OK one by one in red fonts inside your comments below

Glad you accept you missed something.

You're welcome. Simply when I don't understand something I say "I don't understand". I don't pretend to understand. Sorry for being exhausting.

You said: "Because as you have all agreed when the ships are put side by side, they have the same length".

This is when the ships are AT REST relative to each other.

Yes.

They have NOT the same length when they move relative to each other, as shown correcly in bvr's drawings (see his 2. sketches)

I agree they are not observed & measured as having the same length.

When both astronauts cross they are not in the same set of simultaneous events.

Yes I understand that.

In fact you don't understand relativity of simultaneity, correct?

That is very possible.

 

 

 

Because the traveler is going left, flying toward the earth.

In that case the simultaneity line is reversed. Lorents transformations and Minkowski diagrams work that way

I am surprised that does not make rise your eyebrows. Why should simultaneity line change?

 

Wait a second. Read what I wrote. I told you that the green and red lines are the frames of SIMULTANEITY. These are not the paths of light (I left these out but I can add them if you want. Give me some time I'll do it so that you can see the difference.)

Yes I understand that it is not the path of light. The line depicts when 2 events are appearing simultanate. The direction of simultaneity should be always at 45 angles because simultaneity is ruled by SOL. A simultaneity line at any other angle does not make sense (to me)

 

 

 

No, while turning, the rocket catches up on what's happening on earth in a fast way

When scientist smiles during an explanation, something is wrong. And this is total nonsense. That would mean the rocket observing the clocks on earth jiggling at an hilarious rate (instead of ticking slower).

 

The total earth worldline of 10 years lays out there in 4D spacetime, and by travelling away and then getting back he ends up at 2017 earth clock.

I will show another diagram.

Edited September 4, 2016 by michel123456

[VandD]

The diagrams with light paths:

 

[michel123456]

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

Here you are:

 

 

In this diagram, there is no time dilation as per Einstein. There is only a rotation. And the result is also that the traveller observes the time on Earth clicking slowly: when the time on the rocket is 2017, the time on Earth is only June of 2011.

And this diagram is fully reversible. It is symmetric, one can flip flop the Earth & the rocket without any contradiction.

The diagrams with light paths:

 

So that seems to be my error: your simultanity lines are not at 45 degrees, parallel to SOL. Why? And what gives you the angle?

[VandD]

OK one by one in red fonts inside your comments below

The line depicts when 2 events are appearing simultanate. The direction of simultaneity should be always at 45 angles because simultaneity is ruled by SOL. A simultaneity line at any other angle does not make sense (to me)

 

Nonsense. A light path is not a simultaneity line. In a Minkowski diagram a light path is always at 45°. Not the simultaneity lines.

Please return back to your SR books. Learn what events are, what simultaneity means, and how constant speed of light is measured. Etc etc. Until then it's hopeless to continue this discussion.

 

Please use proper quotation method. Unless moderator allows different colors when answering?

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

Here you are:

 

Screen Shot 09-04-16 at 03.45 PM.JPG

 

In this diagram, there is no time dilation as per Einstein. There is only a rotation. And the result is also that the traveller observes the time on Earth clicking slowly: when the time on the rocket is 2017, the time on Earth is only June of 2011.

And this diagram is fully reversible. It is symmetric, one can flip flop the Earth & the rocket without any contradiction.

 

 

What you draw is what is seen by the observer. That's not time dilation. Time dilation is what's happening with time indication on clocks as per reference frame. In your case you don't even draw the reference frame of the traveler. Where is it?

 

You probably make the mistake that because a Minkowski diagram shows greater time units on the rocket worldline THIS meaning time dilation. It's not.

To avoid different time unit lengths one can draw a Loedel diagram. I prefer loedel diagrams for the simple reason people misread the greater time unit lengths lenths as being time dilation.

The problem is that the loedel diagram is not that good in showing the full twin story in one diagram. You have to cut it in two, one for outbound, one inbound.

Are you interested in a Loedel diagram (same unit lengths) showing time dilation for the right diagram?

So that seems to be my error: your simultanity lines are not at 45 degrees, parallel to SOL. Why? And what gives you the angle?

The relative speed between frames.

[Endy0816]

You see things sped up as you move to intersect the Earth.

[michel123456]

 

Nonsense. A light path is not a simultaneity line. In a Minkowski diagram a light path is always at 45°. Not the simultaneity lines.

Please return back to your SR books. Learn what events are, what simultaneity means, and how constant speed of light is measured. Etc etc. Until then it's hopeless to continue this discussion.

 

Please use proper quotation method. Unless moderator allows different colors when answering?

 

What you draw is what is seen by the observer. That's not time dilation. Time dilation is what's happening with time indication on clocks as per reference frame. In your case you don't even draw the reference frame of the traveler. Where is it?

 

You probably make the mistake that because a Minkowski diagram shows greater time units on the rocket worldline THIS meaning time dilation. It's not.

To avoid different time unit lengths one can draw a Loedel diagram. I prefer loedel diagrams for the simple reason people misread the greater time unit lengths lenths as being time dilation.

The problem is that the loedel diagram is not that good in showing the full twin story in one diagram. You have to cut it in two, one for outbound, one inbound.

Are you interested in a Loedel diagram (same unit lengths) showing time dilation for the right diagram?

I will do that.

And yes it is read as time dilation.

And yes i am always interested.

[VandD]

 

And yes it is read as time dilation.

 

It's not. But I forgive you because it's a classic mistake a lot of people people make.

I will show you loedel diagram: same unit lengths and showing time dilation. Watch it.

[Mordred]

Yes I missed that and I still do. The observed object has the same length in both cases (but I must miss something)

 

I have understood that a clock doesn't tick "so faster than I thought it was", i.e. that the clock that clicked slower only regains its original clicking rate (maybe wrong wording here). As for the rest I don't understand where I am misunderstanding spacetime diagrams.

Im glad to see you learned that portion. I admit the math I posted isn't the easiest to understand.

It's not. But I forgive you because it's a classic mistake a lot of people people make.

I will show you loedel diagram: same unit lengths and showing time dilation. Watch it.

A very common mistake, lets hope your wording and example helps. Good idea on the Loedel diagrams.

[VandD]

Here it is.

The time dilation is not what a black light path connect. For time dilay read green and red lines of simultaneity.

Also check with gamma factor for .6c. For red the green clock ticks 1.25 slower. For green the red clock ticks 1.25 slower. Does your diagram show this?

 

 

 

 

 

 

[Mordred]

Michel pay close attention to the value of gamma to the observed time dilation. This is extremely important. Look at both formulas, time dilation and length contraction. They both contain the same gamma term.

 

One source of confusion on the diagrams on the right is the seperation distance portion. This seperation distance isn't the time dilation though it includes that aspect it doesn't show the details on seperation distance and time dilation into distinctive parts.

 

(the Author probably assumed you would infer that from the equations)

 

The Loedel diagram on the left is a good idea to help show this aspect.

 

as mentioned the confused aspects on lightpath is often confused. Its not uncommon to miss the portion on seperation distance that corresponds to just the spatial 3d components, from the time dilation influence on the seperation distance.

Edited September 4, 2016 by Mordred

[studiot]

I honestly think that the diagrams you guys are bandying about are far too complicated for first understanding.

 

In particular they run for way too many years.

A few years are sufficient to establish the principles.

[Mordred]

true, but were using the diagrams Michel posted. Your correct that we don't need the extra years on the diagram to show the principle. Still its an excellent point.

Edited September 4, 2016 by Mordred

[studiot]

true, but were using the diagrams Michel posted. Your correct that we don't need the extra years on the diagram to show the principle. Still its an excellent point.

 

Yes I was including Michel in the 'you guys'. (Would I ever exclude him?)

 

The problem with those diagrams is that, whilst they are an excellent summary to someone familiar with this stuff,

they contain a lot of information and there is no explanation as to where any of it comes from.

 

Hence all the toing and froing about this in the posts.

 

Thanks for the vote.

[Mordred]

 

Yes I was including Michel in the 'you guys'. (Would I ever exclude him?)

 

The problem with those diagrams is that, whilst they are an excellent summary to someone familiar with this stuff,

they contain a lot of information and there is no explanation as to where any of it comes from.

 

Hence all the toing and froing about this in the posts.

 

Thanks for the vote.

agreed, relying on diagrams for relativity is a poor way to learn relativity. Too often the focus is on the end results. Ignoring the mathematical steps to generate that diagram.

Unfortunately too often details are missing by over reliance on the diagrams.

Edited September 4, 2016 by Mordred

[studiot]

It takes students studying this about 12 weeks to make their way through a basic course.

And those students are already au fait with a good deal of Physics ie they are Physics students.

 

Yes my offered analysis, that nobody seems to want, contains some simple arithmetic but it is perfectly possible to perform graphical constructions with gamma/lerontz built in to avoid even this.

Russell shows a simple one in his elementary ABCs of Relativity.

 

In fact graphical construction was once de rigeur in most engineering design offices for many tasks we now undertake by calculation.

I have some old books that show how to extract roots, solve algebraic equations, perform graphical integration and differentiation etc etc.

Edited September 4, 2016 by studiot

[Mordred]

I think I may have read some of Russel's work. However it was so long ago I can't be certain.

 

Recalling back when I was one of those students. I found the math steps to generate a spacetime diagram was the only way to truly understand them.

 

Ideally I could show several key confusions by posting several different line elements ds^2. Of course ideally It would be best to cover Pythagoras theory deviations in each example.

 

This was the light switch that gave myself my understanding. To this day I apply this lesson when looking at ds^2 line elements.

1) Euclidean (no dilation)

2) SR Newton limit line element.

3) Schwartzchild metric

4) FLRW metric line element.

 

In each of these cases, deviation from Pythagoras theory has different causes. Identifying those causes is an excellent learning aid. (though not specifically SR), the line elements are compatible under SR.

 

It was funny I missed these aspects during my SR course, even though I was doing the math and generating spacetime diagrams. It wasn't until I started comparing those line elements did I clue in.

 

On a side note, there was a poster in Speculations that was trying to prove expansion as time dilation. If that poster ever looks at the differences between the Schwartchild line element and the FLRW metric. He would realize thats impossible.

 

Unfortunately he failed to see this difference when I pointed it out to him so he has wasted the past 1/2 year in the wrong direction (yes he is still trying)

 

Hint keep track of which coordinates are changing. Which changes are due to gamma and which ones simply change the spatial components.

 

[latex](\acute{t},\acute{x},\acute{y},\acute {z})=(t,x,y,z)[/latex]

 

see my previous posted math for clues.

 

Sorry that math was posted in another recent and related thread.

http://www.scienceforums.net/topic/97871-five-questions-re-sr/#entry939987

Edited September 4, 2016 by Mordred

[michel123456]

It takes students studying this about 12 weeks to make their way through a basic course.

And those students are already au fait with a good deal of Physics ie they are Physics students.

 

Yes my offered analysis, that nobody seems to want, contains some simple arithmetic but it is perfectly possible to perform graphical constructions with gamma/lerontz built in to avoid even this.

Russell shows a simple one in his elementary ABCs of Relativity.

 

In fact graphical construction was once de rigeur in most engineering design offices for many tasks we now undertake by calculation.

I have some old books that show how to extract roots, solve algebraic equations, perform graphical integration and differentiation etc etc.

Unfortunately for me a diagram is the alpha and the omega for understanding. An equation says much more when it is put into a graph.

Here it is.

The time dilation is not what a black light path connect. For time dilay read green and red lines of simultaneity.

Also check with gamma factor for .6c. For red the green clock ticks 1.25 slower. For green the red clock ticks 1.25 slower. Does your diagram show this?

 

 

 

 

 

 

Yes the diagram on the left is more sensible and understandable. Thank you. It is perfectly symmetric, there is no preferred FOR, what observes the one is what observes the other. They are both moving relatively to each other. The numbers from the equation coincide. The gamma factor 1,25 appears somehow evidently. (edit) And also the difference between simultaneity and light ray is shown.

However time dilation is not so evident to detect.

I will post my understanding in a while. Please check if I missed the point again.

Edited September 4, 2016 by michel123456

[Mordred]

Unfortunately for me a diagram is the alpha and the omega for understanding. An equation says much more when it is put into a graph.

Thats fine if the graph shows just the changes due to the formula ie time dilation formula. However the spacetime diagram also shows the changes in the spatial seperation between events due to velocity. As well as changes to direction and acceleration/ deceleration.

 

These are aspects that are overlooked by just looking at the graph. Which is what we trying to get you to distinquish.

Edited September 4, 2016 by Mordred

[michel123456]

 

The blue triangle. It means for the red path that 2 years have passed for him while he sees only one year has passed for the green dot. IOW he is observing the clock on the green path ticking slower.

 

Is that it?

[Mordred]

Be careful here Loedel diagrams can be tricky if you miss the axis details.

 

A good summary is here on arxiv

 

"A Graphical Introduction to Special Relativity Based on a Modern Approach to Minkowski Diagrams"

 

https://www.google.ca/url?sa=t&source=web&rct=j&url=https://arxiv.org/pdf/1508.01968&ved=0ahUKEwjPs4XuoPbOAhVY1mMKHf0cCq0QFghRMA0&usg=AFQjCNGgXcFd5j31T9RqdMZziWfeLeLWGA&sig2=M39ciWw0V6eUwszQDWronw

Edited September 4, 2016 by Mordred