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

[michel123456]

I didn't figure it was a so difficult question...

[VandD]

Screen Shot 09-04-16 at 07.52 PMb.jpg

 

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?

No. What you show is not what is meant by time dilation (time slowing).

The time dilation is here:

 

For RED simultaneity: When red clock indicates 2015, the green clock indicates 2013.4

I.ow. when the red clock ticked from 2007 to 2015 (8 years), the green clock ticked from 2007 to 2013.4 (=6,4 years). This is also what gamma tells us for v=.6c:

8 / 1.25 = 6.4

 

For GREEN simultaneity: When green clock indicates 2015, the red clock indicates 2013.4

I.o.w. when the green clock ticked from 2007 to 2015 (8 years), the red clock ticked from 2007 to 2013.4 (=6,4 years). This is also what gamma tells us for v=.6c:

8 / 1.25 = 6.4

 

A. s. o.

For example: (not made bold in the diagram)

For GREEN simultaneity: When green clock indicates 2013.4, the red clock indicates ... 2012.12. Can you find which green simultaneity line I'm talking about?

When the green clock ticked from 2007 to 2013.4 (6.4 years), the red clock ticked from 2007 to 2012.12 (=4.12 years). This is also what gamma tells us for v=.6c:

6.4 / 1.25 = 4.12

Edited September 4, 2016 by VandD

[Mordred]

I didn't see your question. I was between windows looking for a good article. I'll let Vand's answer stand. Read the article to answer his questions. Pay attention to the details on the numerous axis...

 

The article gives a good geometric relation summary covering details not included in the above Loedel diagram.

 

(it will also give everyone a common set of reference points (labels) to work from...)

Edited September 4, 2016 by Mordred

[michel123456]

No. What you show is not what is meant by time dilation (time slowing).

The time dilation is here:

 

For RED simultaneity: When red clock indicates 2015, the green clock indicates 2013.4

I.ow. when the red clock ticked from 2007 to 2015 (8 years), the green clock ticked from 2007 to 2013.4 (=6,4 years). This is also what gamma tells us for v=.6c:

8 / 1.25 = 6.4

 

For GREEN simultaneity: When green clock indicates 2015, the red clock indicates 2013.4

I.o.w. when the green clock ticked from 2007 to 2015 (8 years), the red clock ticked from 2007 to 2013.4 (=6,4 years). This is also what gamma tells us for v=.6c:

8 / 1.25 = 6.4

 

A. s. o.

For example: (not made bold in the diagram)

For GREEN simultaneity: When green clock indicates 2013.4, the red clock indicates ... 2012.12. Can you find which green simultaneity line I'm talking about?

When the green clock ticked from 2007 to 2013.4 (6.4 years), the red clock ticked from 2007 to 2012.12 (=4.12 years). This is also what gamma tells us for v=.6c:

6.4 / 1.25 = 4.12

Thank you.

IOW (please correct me) time dilation is not about what one observes, because one cannot directly observes through simultaneity.

edit

I mean, the red observer at red 2015 cannot see the green guy at green 2013.4.

Edited September 4, 2016 by michel123456

[VandD]

Thank you.

IOW (please correct me) time dilation is not about what one observes, because one cannot directly observes through simultaneity.

edit

I mean, the red observer at red 2015 cannot see the green guy at green 2013.4.

Correct, because for the green guy to see the green 2013.4 he has to wait until the light from that green 2013.4 clock gets to him, and that's long after 2015.

 

But red can SEE the green time dilation in a different set-up. Let's hope I don't push it too far for you at this stage: For example. Let the clock start at a distance left from red. Then when the green clock reaches him, there will be less time on that green clock than the time on his red clock. He sees it at an inch from his nose and can even feel the hands of the clock if he wants to. But... the tricky thing is that red first has to make sure his red clock and the still spatially removed green clock start ticking simultaneously. So he has first to go through the synchonization procedure... But that's another story.

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

@Michel:

I would like to highlight the following in that paper:

 

 

For the traveler the earth HAS TO tick faster when traveler is turning, because when back home the earth observer is older than traveler.

That's what's happening when moving around in 4D spacetime .

Edited September 4, 2016 by VandD

[Mordred]

+1 on pointing out a key detail.

 

in figure 8 above the turn around hyperbolic curve is detailed below.

 

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

[Tim88]

 

Sorry, Tim, I see what you mean. Try this.

 

Actually, Tim, the frame of the clock(s) is of vital importance which are most certainly not present at all events in all frames, which they would be (could be) if they were present in all frames. I was not referring to Einsteins paper but the paintball games posts in this thread.

 

[..]

 

Sorry I did not look in detail at the paintball games posts. It just sounded (and still does) as if you claimed that in SR a clock can somehow move outside of a reference frame. A reference frame in SR spans the whole universe; it's impossible to not be present in it.

[studiot]

 

Sorry I did not look in detail at the paintball games posts. It just sounded (and still does) as if you claimed that in SR a clock can somehow move outside of a reference frame. A reference frame in SR spans the whole universe; it's impossible to not be present in it.

 

Being present in a frame is not the same as being present at all (significant) events.

I say significant to distinguish between events of interest and the rest of the points in spacetime since an event is a point in spacetime.

 

Your original claim was that all clocks were present at all events as well as in all frames.

 

For any observer, Spacetime has timelike zones at which it is possible to be present at both events and spacelike zones for which it is not.

 

So in the twins, significant events are

 

P leaving Earth

Q turning around

R return to Earth

 

The rocket clock is present at all three P, Q and R

 

The Earth clock is only present at two, P and R.

 

This is just a more formal way to explaining the asymmetry than my original offering which was essentially, the rocket went somewhere, the Earth did not.

Edited September 5, 2016 by studiot

[Tim88]

Concerning the bold black text above: The ruler can expand? More than what is measured at rest in its own frame?

 

Concerning the blue text : many many reasons (like you said the laws of optics) make us observe the world with paramorphosis. Relativity is another effect.

 

About clocks, there is nothing weird into observing a clock retarding on others.

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.

 

Sorry, I realize now that my clarification was too terse. Call S0 the ECI system of the Earth, and S1 the rest system of the traveler when he is on the outbound leg, traveling at constant speed away from Earth. As determined with S1, a ruler of the traveler while still on Earth is approximately at rest in S0; it is contracted in the direction of motion.

 

When the traveler comes at rest in S1, his ruler expands to its rest length. According to other systems it changes lengths in other ways. Nevertheless, according to all reference systems in which the laws of physics are valid, its length changes along the direction of change of motion. This is necessary in order to be consistent with the measured effects on clock counts, such as with atomic clocks, and the measured lack of effect of rotating Michelson-Morley type of instruments when in different states of motion.

 

I now coloured part of your text in blue; and I dare say that your interpretation of SR disagrees with SR. It's probably an interpretation bug. According to SR, the laws of optics hold perfectly in the "rest" system of your choice; there is no optical distortion due to some magical SR influence, if that is what you have in mind with "observe the world with paramorphosis".

 

One of the papers that I recalled when I wrote that some people argue that relativistic effects are "physically real", analysed reflecting light rays from a moving mirror (moving at an angle with respect to its reflecting surface). By means of the Huygens construction the author found, unsurprisingly, that in order to obey the PoR, the moving mirror (in rest in S1) has to be length contracted according to the rest system S0.

S0 and S1 disagree which one, if any, corresponds to reality; but they agree that a mirror that accelerates from one state of motion to a new state of motion, also undergoes a change in equilibrium shape. And that shape change is not mysterious, it can be understood as due to a change of electromagnetic equilibrium positions of its atoms (Bell elaborated on that in his physics lectures). As a matter of fact, that this could be the case was one of the first hypotheses that lead to SR, and it was inferred from calculations by Heaviside which showed that the electric force range of electrons is reduced in the direction of motion (he found, based on Maxwell, the exact formula that in modern textbooks is derived from SR).

 

Edit: I forgot to comment on the last part. I consider the papers by Einstein and Langevin to which I referred earlier, very much "what relativity tells us". And those papers already describe precisely that absolute effect!

 

Maybe the problem is just related to the name "relativity theory". Einstein attempted to make all forms of motion "relative" by means of GR, but it did not totally catch on and already was not "relative" in the sense of "nothing happens". Nevertheless that name stuck, and may be the prime cause of misunderstanding.

Edited September 5, 2016 by Tim88

[michel123456]

 

Sorry, I realize now that my clarification was too terse. Call S0 the ECI system of the Earth, and S1 the rest system of the traveler when he is on the outbound leg, traveling at constant speed away from Earth. As determined with S1, a ruler of the traveler while still on Earth is approximately at rest in S0; it is contracted in the direction of motion.

 

When the traveler comes at rest in S1, his ruler expands to its rest length. According to other systems it changes lengths in other ways. Nevertheless, according to all reference systems in which the laws of physics are valid, its length changes along the direction of change of motion. This is necessary in order to be consistent with the measured effects on clock counts, such as with atomic clocks, and the measured lack of effect of rotating Michelson-Morley type of instruments when in different states of motion.

 

I now coloured part of your text in blue; and I dare say that your interpretation of SR disagrees with SR. It's probably an interpretation bug. According to SR, the laws of optics hold perfectly in the "rest" system of your choice; there is no optical distortion due to some magical SR influence, if that is what you have in mind with "observe the world with paramorphosis".

 

One of the papers that I recalled when I wrote that some people argue that relativistic effects are "physically real", analysed reflecting light rays from a moving mirror (moving at an angle with respect to its reflecting surface). By means of the Huygens construction the author found, unsurprisingly, that in order to obey the PoR, the moving mirror (in rest in S1) has to be length contracted according to the rest system S0.

S0 and S1 disagree which one, if any, corresponds to reality; but they agree that a mirror that accelerates from one state of motion to a new state of motion, also undergoes a change in equilibrium shape. And that shape change is not mysterious, it can be understood as due to a change of electromagnetic equilibrium positions of its atoms (Bell elaborated on that in his physics lectures). As a matter of fact, that this could be the case was one of the first hypotheses that lead to SR, and it was inferred from calculations by Heaviside which showed that the electric force range of electrons is reduced in the direction of motion (he found, based on Maxwell, the exact formula that in modern textbooks is derived from SR).

 

Edit: I forgot to comment on the last part. I consider the papers by Einstein and Langevin to which I referred earlier, very much "what relativity tells us". And those papers already describe precisely that absolute effect!

 

Maybe the problem is just related to the name "relativity theory". Einstein attempted to make all forms of motion "relative" by means of GR, but it did not totally catch on and already was not "relative" in the sense of "nothing happens". Nevertheless that name stuck, and may be the prime cause of misunderstanding.

What blows my mind is this:

_You have explained the thing with S0 and S1.

but there can be millions of S (S2,S3,S4,S5,...) for which the contraction will be different.

How in the hell can it be possible that all these contractions happen inside the same object at the same time (as you said,that the electromagnetic equilibrium positions of its atoms change in many ways at the same time)!

 

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

 

To me the situation is simple: there is only one object with a "zero configuration" as observed at rest. For all other FOR S1, S2, S3, there are different "configurations" of the object, that are relative. Like Kinetic energy is relative.

And the observations must be symmetric: in your example of the mirror, is it also proved that the Earth was contracted as seen by the mirror? Because if it is not, you have a problem.

Correct, because for the green guy to see the green 2013.4 he has to wait until the light from that green 2013.4 clock gets to him, and that's long after 2015.

 

But red can SEE the green time dilation in a different set-up. Let's hope I don't push it too far for you at this stage: For example. Let the clock start at a distance left from red. Then when the green clock reaches him, there will be less time on that green clock than the time on his red clock. He sees it at an inch from his nose and can even feel the hands of the clock if he wants to. But... the tricky thing is that red first has to make sure his red clock and the still spatially removed green clock start ticking simultaneously. So he has first to go through the synchonization procedure... But that's another story.

@Michel:

I would like to highlight the following in that paper:

 

 

For the traveler the earth HAS TO tick faster when traveler is turning, because when back home the earth observer is older than traveler.

That's what's happening when moving around in 4D spacetime .

"dials in" a quickly incrementing sequence of dates " is an euphemism for "ticking faster". I thought it was not possible.

[Tim88]

What blows my mind is this:

_You have explained the thing with S0 and S1.

but there can be millions of S (S2,S3,S4,S5,...) for which the contraction will be different.

How in the hell can it be possible that all these contractions happen inside the same object at the same time (as you said,that the electromagnetic equilibrium positions of its atoms change in many ways at the same time)!

 

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

 

To me the situation is simple: there is only one object with a "zero configuration" as observed at rest. For all other FOR S1, S2, S3, there are different "configurations" of the object, that are relative. Like Kinetic energy is relative.

And the observations must be symmetric: in your example of the mirror, is it also proved that the Earth was contracted as seen by the mirror? Because if it is not, you have a problem.

 

Oops I slightly missed the target when I wrote that relativity "already was not "relative" in the sense of "nothing happens""; I intended to refer to your preceding post, by emphasizing that relativity already was not "relative" in the sense of "all observations are symmetrical".

 

Then concerning "there can be millions of S (S2,S3,S4,S5,...) for which the contraction will be different", that is exactly the point. All those perceived contractions are mutually exclusive; at best one of those viewpoints can correspond to reality. In Newtonian mechanics this also played, but it was less striking (according to different reference systems, the kinetic energy increases or decreases; who is right? and the rotating bucket physically rotates relative to which frame?).

Thus I did not say that the electromagnetic equilibrium positions of its atoms change in many ways at the same time; to the contrary, one can at most accept one such view as reality, only we cannot know which one, if any.

 

Newton therefore postulated the existence of absolute space, and built up his theory from that assumption. The SR equivalent of that is the Lorentz ether; did you know that the Lorentz transformations were first derived based on that concept? It works and it makes SR perfectly understandable, without anything looking paradoxical.

 

However, the Lorentz ether implies a hidden physical difference between inertial frames, so that the mathematical symmetry of observations between inertial frames would not correspond to hidden reality. A way out is Minkowski's 4D Spacetime: in that view of reality, all inertial frames are truly on equal footing. An acceleration nevertheless corresponds to curved trajectory, so that symmetry is also naturally broken by acceleration with that view. A disadvantage is that time must then be regarded as somewhat the same physical thing as length; some people even would like to give time and length the same units.

 

We cannot know from measurements which worldview is correct (and possibly they are both wrong), but either of them works as a functional model of the "relativistic" world so that we can make sense of the phenomena. Regretfully neither of them fully solves the riddles of quantum mechanics, but it's already great to end confusions of SR.

 

Your "zero configuration" is usually called "proper length, rate etc; it corresponds with the viewpoint that the object is in rest. However I doubt that you think that everything is all the time in rest!

 

And yes, although not in that article, but in one of the year 18xx by Lorentz, it is shown that similarly the moving Earth must be contracted relative to the stationary ether. Replace the term "stationary ether" by the frame which you by chance called for example S3, and you arrive at SR.

 

[edit: additional remark] The original point of the Lorentz transformations by Lorentz and Poincare, was to explain how motion could affect a reference system in such a way, that if one assumes it be not in motion but in rest, the observed phenomena do not show any error from making that assumption. It appears as if rulers of other systems (even those in "true rest") are length contracted, and clocks of other systems are slow.

Next, the same philosophical change occurred as with Newton's mechanics: textbooks often fail to mention conceptual models that are not necessary for describing the phenomena, as they are arguably not part of physics. Thus usually no mention is made of the absolute or true rest model (or even it is falsely claimed that it was disproved!), and neither is Minsowski's physical Spacetime model discussed, according to which the separate concepts of "time" and "space" should be abandoned. "Shut up and calculate"!

Edited September 5, 2016 by Tim88

[VandD]

What blows my mind is this:

_You have explained the thing with S0 and S1.

but there can be millions of S (S2,S3,S4,S5,...) for which the contraction will be different.

How in the hell can it be possible that all these contractions happen inside the same object at the same time (as you said,that the electromagnetic equilibrium positions of its atoms change in many ways at the same time)!

 

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

 

To me the situation is simple: there is only one object with a "zero configuration" as observed at rest. For all other FOR S1, S2, S3, there are different "configurations" of the object, that are relative. Like Kinetic energy is relative.

And the observations must be symmetric: in your example of the mirror, is it also proved that the Earth was contracted as seen by the mirror? Because if it is not, you have a problem.

"dials in" a quickly incrementing sequence of dates " is an euphemism for "ticking faster". I thought it was not possible.

Are you still pretending that the contraction of a train is nothing real?

 

Let a small car stay at rest on road. An 'observer' (let's call him Mr Magoo) stands at rest relative to the car. He spreads his arms so that he can feel the front and rear of the car simultaneously (and his nose feels the middle of the car). No doubt about it: that car is physically present as a real object in his 3D real world.

 

Now Mr Magoo will move at different speeds.

For each speed Mr Magoo physically feels the car at a different length: for each different speed he has to spread his arms at different length in order to touch the front and rear of the car simultaneously (and his nose feels the middle of the car). No doubt about it: at each different speed a real short car of different length is physically present in Mr Magoo's 3D real world of simultaneous events.

Edited September 5, 2016 by VandD

[Tim88]

[..] [About the textbook:]

"dials in" a quickly incrementing sequence of dates " is an euphemism for "ticking faster". I thought it was not possible.

 

 

I would say that such an observation is merely the effect of acceleration of the traveler. "Her point of view", according to which the earth twin ages very rapidly during turnaround, is not physically valid in SR.

 

As the related switch of reference system implies the claim to be in rest before and after the turnaround, it is just as "possible" that the far away earth clock instantly ticks faster due to the traveler's rocket engines firing, as the corresponding instant change of velocity of the rest of the universe (and zero change of the traveler's speed!).

 

Messy accounting is avoided by either:

 

- sticking to one reference system

or

- explicitly accounting for the effects from acceleration and the switch from one reference system to the next one

 

The observed phenomena during and after acceleration are due to things happening to the accelerated object, and not due to things happening to the non-accelerating objects.

 

(slight improvement in phrasing)

Edited September 5, 2016 by Tim88

[michel123456]

 

Are you still pretending that the contraction of a train is nothing real?

 

Let a small car stay at rest on road. An 'observer' (let's call him Mr Magoo) stands at rest relative to the car. He spreads his arms so that he can feel the front and rear of the car simultaneously (and his nose feels the middle of the car). No doubt about it: that car is physically present as a real object in his 3D real world.

 

Now Mr Magoo will move at different speeds.

For each speed Mr Magoo physically feels the car at a different length: for each different speed he has to spread his arms at different length in order to touch the front and rear of the car simultaneously (and his nose feels the middle of the car). No doubt about it: at each different speed a real short car of different length is physically present in Mr Magoo's 3D real world of simultaneous events.

This is wrong.

Mr Magoo is (being observed) contracting as well. He feels nothing.

 

I would say that such an "observation" is very much nonphysical; it's merely the effect of switching ("jumping") between reference systems.

 

As this switch of reference system implies the claim to be in rest before and after the turnaround, it is just as "possible" that the far away earth clock instantly ticks faster due to the traveler's rocket engines firing, as the corresponding instant change of velocity of the rest of the universe (and zero change of the traveler's speed!).

 

Such a messy accounting is avoided by either:

 

- sticking to one reference system

or

- explicitly accounting for the switch from one reference system to the next, or for the effects from acceleration.

 

The observed phenomena during and after acceleration are due to things happening to the accelerated object, and not due to things happening to the non-accelerating objects.

I have a deal to propose for you:

I will agree with that if you agree that in no way an observer can make things happen in an object just by looking at it.

 

Oops I slightly missed the target when I wrote that relativity "already was not "relative" in the sense of "nothing happens""; I intended to refer to your preceding post, by emphasizing that relativity already was not "relative" in the sense of "all observations are symmetrical".

 

Then concerning "there can be millions of S (S2,S3,S4,S5,...) for which the contraction will be different", that is exactly the point. All those perceived contractions are mutually exclusive; at best one of those viewpoints can correspond to reality. In Newtonian mechanics this also played, but it was less striking (according to different reference systems, the kinetic energy increases or decreases; who is right? and the rotating bucket physically rotates relative to which frame?).

Thus I did not say that the electromagnetic equilibrium positions of its atoms change in many ways at the same time; to the contrary, one can at most accept one such view as reality, only we cannot know which one, if any.

 

Newton therefore postulated the existence of absolute space, and built up his theory from that assumption. The SR equivalent of that is the Lorentz ether; did you know that the Lorentz transformations were first derived based on that concept? It works and it makes SR perfectly understandable, without anything looking paradoxical.

 

However, the Lorentz ether implies a hidden physical difference between inertial frames, so that the mathematical symmetry of observations between inertial frames would not correspond to hidden reality. A way out is Minkowski's 4D Spacetime: in that view of reality, all inertial frames are truly on equal footing. An acceleration nevertheless corresponds to curved trajectory, so that symmetry is also naturally broken by acceleration with that view. A disadvantage is that time must then be regarded as somewhat the same physical thing as length; some people even would like to give time and length the same units.

 

We cannot know from measurements which worldview is correct (and possibly they are both wrong), but either of them works as a functional model of the "relativistic" world so that we can make sense of the phenomena. Regretfully neither of them fully solves the riddles of quantum mechanics, but it's already great to end confusions of SR.

 

Your "zero configuration" is usually called "proper length, rate etc; it corresponds with the viewpoint that the object is in rest. However I doubt that you think that everything is all the time in rest!

 

And yes, although not in that article, but in one of the year 18xx by Lorentz, it is shown that similarly the moving Earth must be contracted relative to the stationary ether. Replace the term "stationary ether" by the frame which you by chance called for example S3, and you arrive at SR.

 

[edit: additional remark] The original point of the Lorentz transformations by Lorentz and Poincare, was to explain how motion could affect a reference system in such a way, that if one assumes it be not in motion but in rest, the observed phenomena do not show any error from making that assumption. It appears as if rulers of other systems (even those in "true rest") are length contracted, and clocks of other systems are slow.

Next, the same philosophical change occurred as with Newton's mechanics: textbooks often fail to mention conceptual models that are not necessary for describing the phenomena, as they are arguably not part of physics. Thus usually no mention is made of the absolute or true rest model (or even it is falsely claimed that it was disproved!), and neither is Minsowski's physical Spacetime model discussed, according to which the separate concepts of "time" and "space" should be abandoned. "Shut up and calculate"!

Excellent point about Newton mechanics: nobody is arguing that a body "has" kinetic energy. Nobody is asking "who is right?" because the simple answer is that kinetic energy is relative.

But I argue that the body to which this kinetic energy is linked is a body that "exists" and "has" dimensions. It is not a body that "has" multiple lengths at the same time according to the state of motion of its observers. And if another observer arrives, the body doesn't change length.

And exactly as in the case of kinetic energy, there is a "zero" point, which corresponds to the frame at rest. In this frame, kinetic energy is zero, the length is maximum, the ticking rate is minimum, and rest mass is defined.

Edited September 5, 2016 by michel123456

[Tim88]

This is wrong.

Mr Magoo is (being observed) contracting as well. He feels nothing.

I have a deal to propose for you:

I will agree with that if you agree that in no way an observer can make things happen in an object just by looking at it.

Excellent point about Newton mechanics: nobody is arguing that a body "has" kinetic energy. Nobody is asking "who is right?" because the simple answer is that kinetic energy is relative.

But I argue that the body to which this kinetic energy is linked is a body that "exists" and "has" dimensions. It is not a body that "has" multiple lengths at the same time according to the state of motion of its observers. And if another observer arrives, the body doesn't change length.

And exactly as in the case of kinetic energy, there is a "zero" point, which corresponds to the frame at rest. In this frame, kinetic energy is zero, the length is maximum, the ticking rate is minimum, and rest mass is defined.

 

Concerning Mr Magoo I disagree with VandD's phrasing: distant simultaneity is a mere convention, and thus I would not use the word "real" there. However I do agree with his(/her) description of phenomena! I'll let him elaborate.

 

1. Further we certainly agree that in no way an observer can make things happen in an object just by looking at it; that was exactly my point (note that it appears that QM disagrees somewhat; but it's definitely so in SR). Sorry if my phrasing was ambiguous for you! I even wrote a paper about that (correcting an accepted error in the literature) in the European Journal of Physics; I can send it to you if you like.

 

2. Now, concerning your preference of using proper measures only: I can understand that, as it looks "cleaner". However, that preference could possibly hinder understanding of how there could be any absolute effects, and how to correctly account for effects from motion. More importantly, it could result in conflict with the just established point 1. here above, if you think that the"proper" point of view is always what should be considered "physical reality".

 

Because that textbook fell in the trap of suggesting (although not explicitly claiming) that the "proper Observation" of the traveler during turnaround makes physical sense, despite the fact that it implies instant magical action at a distance (which is not allowed in SR), and despite the fact that it even demands the traveler to quickly and continuously modify clock synchronisations aboard the ship, and then to pretend that nothing happened to her clocks, but that instead a huge instantaneous effect happened to the Earth's clocks!

 

[edit: typo's]

Edited September 5, 2016 by Tim88

[michel123456]

Tim88 +1 for your very explicit and understandable posts.

And I am glad that we agree that in no way an observer can make things happen in an object just by looking at it.

Because sometimes I fell getting crazy reading some very knowledgeable posters seemingly stating otherwise (but that must be me who understands badly).

IOW, I am an observer, I look in my telescope to some distant star. This has no effect upon the star.

If the star looks length contracted to me, it is merely an effect of observation, nothing else. If I start running like the flash, the star will not change length.

[robinpike]

Tim88 +1 for your very explicit and understandable posts.

And I am glad that we agree that in no way an observer can make things happen in an object just by looking at it.

Because sometimes I fell getting crazy reading some very knowledgeable posters seemingly stating otherwise (but that must be me who understands badly).

IOW, I am an observer, I look in my telescope to some distant star. This has no effect upon the star.

If the star looks length contracted to me, it is merely an effect of observation, nothing else. If I start running like the flash, the star will not change length.

 

Michel, we appear to share some common ground on our questions about relativity.

 

Looking back on my questions within my topic, I realize that I have been concerned about the offered explanation(s) finishing with the shorter route through space-time as being real, but earlier in the explanation it relying on the shorter route through space-time as being only apparent - i.e. dependent on which observer is doing the looking?

 

Is this the same sort of concern that you have?

[Mordred]

Maybe a simple statement may help.

 

" Every observed measurement is real from the perspective of the observer."

 

without throwing in time dilation or length contraction we can see this when one measures speed or percieved size of an object or even the percieved color (frequency of light) the percieved blackbody temperature will even be affected.

 

Its funny no one has any problem accepting observer perceptions in these cases. Yet the observers in relativity follow precisely the same rules. With or without time dilation.

 

"The key statement is measurement according to an observer" which measurement is more real is impossible to determine. All measurements involve an observer point of view.

 

A preferred frame would be a philosophical choice. There is no mathematical means to prove one observer is more accurate than the other.

Edited September 5, 2016 by Mordred

[michel123456]

 

Michel, we appear to share some common ground on our questions about relativity.

 

Looking back on my questions within my topic, I realize that I have been concerned about the offered explanation(s) finishing with the shorter route through space-time as being real, but earlier in the explanation it relying on the shorter route through space-time as being only apparent - i.e. dependent on which observer is doing the looking?

 

Is this the same sort of concern that you have?

I guess but we don't use the same phrasing.

One of the problem of these discussions is language.

Maybe a simple statement may help.

 

" Every observed measurement is real from the perspective of the observer."

 

without throwing in time dilation or length contraction we can see this when one measures speed or percieved size of an object or even the percieved color (frequency of light) the percieved blackbody temperature will even be affected.

 

Its funny no one has any problem accepting observer perceptions in these cases. Yet the observers in relativity follow precisely the same rules. With or without time dilation.

 

"The key statement is measurement according to an observer" which measurement is more real is impossible to determine. All measurements involve an observer point of view.

I agree100%

The "funny thing" is that talking about Relativity, then suddenly the length contraction & time dilation seems to become "real" in such way as if the object was changed by the observer. It is not changed by the observer.

The other "funny thing" is that most physicists will shoot you if you dare to compare relativistic effects to optical effects, or even worse, to optical illusion.

 

I have found an example.

A cube is a geometric object with 6 sides.

However, if you look at a cube you can only, at best, see 3 sides simultanately.(not counting eventual reflections)

So Relativistic physicist say that when you observe 3 sides, the cube "has" 3 sides. That if I turn it exactly facing me, the cube changed and "has" one side. But all physicists in the world agree that in 4d, the cube has 6 faces.

What I say is that the cube doesn't change, it always has 6 faces, even if you can see only 3, even when you catch it in your own hands. The cube doesn't change because it is observed.

Edited September 5, 2016 by michel123456

[Mordred]

Lets run a Newton example. Observer A holds an object. Observer B is your distant observer. The far away observer will measure the object as being smaller than observer A's measurement.

 

In an everyday sense people have gotten used to these observer perceptions. So we habitually consider Observer A being more accurate. However this is more due to habit than science.

 

Science wishes to mathematically prove one observer as being more accurate.

 

Yet as it turns out, all efforts to mathematically prove one observer as being more accurate than the other is as far as we can tell impossible.

 

That is what is needed for a preferred observer.

Edited September 5, 2016 by Mordred

[VandD]

This is wrong.

No, it's correct.

[michel123456]

No, it's correct.

Mr Magoo is also under the laws of physics.

[VandD]

I guess but we don't use the same phrasing.

One of the problem of these discussions is language.

I agree100%

The "funny thing" is that talking about Relativity, then suddenly the length contraction & time dilation seems to become "real" in such way as if the object was changed by the observer. It is not changed by the observer.

The other "funny thing" is that most physicists will shoot you if you dare to compare relativistic effects to optical effects, or even worse, to optical illusion.

 

I have found an example.

A cube is a geometric object with 6 sides.

However, if you look at a cube you can only, at best, see 3 sides simultanately.(not counting eventual reflections)

So Relativistic physicist say that when you observe 3 sides, the cube "has" 3 sides. That if I turn it exactly facing me, the cube changed and "has" one side. But all physicists in the world agree that in 4d, the cube has 6 faces.

What I say is that the cube doesn't change, it always has 6 faces, even if you can see only 3, even when you catch it in your own hands. The cube doesn't change because it is observed.

Well, actually the 4D train indeed doesn't change. When Mr Magoo moves relative to the train he feels with his hands a different 3D section through that 4D train. You get it?

 

But you pretend there is only a 3D real train and Mr Magoo moving relative to the train 'observes' a distortion of that 3D train. That's wrong. You completely miss the fact that the different section throught the 4D train is a equaly valid different set of simultaneous events.

And if you call one set of simultaneous events 'real', then all the other 3D sections are real as well. You simply have no valid physical reason for believing the contrary.

[Mordred]

I agree100%

The "funny thing" is that talking about Relativity, then suddenly the length contraction & time dilation seems to become "real" in such way as if the object was changed by the observer. It is not changed by the observer.

The other "funny thing" is that most physicists will shoot you if you dare to compare relativistic effects to optical effects, or even worse, to optical illusion.

Science doesn't consider one set of measurements as being more real than the other set of measurements.

 

They are not saying the object shrinks in actuality due to perception. They are stating the measurement of that object is equally valid according to an observer. However in this case the spacetime is Euclidean flat. No dilation

 

Length contraction and time dilation we have proved to have very real consequences. Different age rates for example. How you measure the different rates depends on the observer. In a sense the spacetime geometry itself has really changed.

 

This is the aspect that confuses people. Particularly time dilation.

 

In those Newtonian examples the deviations on measurements is easily understood as a distance relationship.

 

Follows from Pythagoras theory. When you add length contraction and time dilation you deviate from Pythagoras theory. If you study the math, most of the formulas has a connection to Pythagoras.

 

We have shown two clocks will deviate and this deviation has measurable influence that is quite real. The clock actually slows down. This wouldn't occur in a strictly optical illusion.

 

For example muons falling to Earth don't require observers to set time dilation and length contraction. Even when they are not being observed they are still dilated.

 

How do you pass that off as mere optical illusion?

Edited September 5, 2016 by Mordred

[VandD]

Mr Magoo is also under the laws of physics.

Of course, so what?

If you don't accept he feels with his hands in front of him the contracted car, rear and front simultaneously, then you still haven't understood an inch about SR.

 

But don't be desperate. You are not the only one I encounter during the last 25 years thinking that because the length contraction and time dilation is a reciprocal thing between the car passenger and Mr Magoo, it can only be possible if its a visual optical illusion effect.

Do you think Einstein would have spent his time with such a stupid optical illusion effect?

Edited September 5, 2016 by VandD