Coordinate Transformation versus Change of Synchrony Convention

  • #1
GeneSnider
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Rather than adding to this already long thread, I chose to start a new thread.

Thought Experiment

In this post, s is distance, t1, is the time of transmission, t2 is the time of reflection and t3 is the time of reception. All cases assume an orthogonal coordinate system.

Case 1:
From a God's eye point of view, a laser pulse bounced off of a retroreflector on the moon will have these time stamps:
t1=0, t2=1.25, t3=2.5


Case 2:
Coordinate Transformation
In transformed coordinates where the transformation is T = T' + T * C / S the time stamps are:
t1 = 0 = 1.25, t3 = 2.5

Case 3:
When C is C/2 away from the earth and C/0 towards the observer, the time stamps are:
t1 = 0, t2 = 1.25, t3=2.5

If we watch the clocks from a God's eye point of view, the only difference is that in Cases 1 and 2, the time of flight is equal on both legs of the journey. In Case 3, the time of flight on both legs of the journey is not equal.

Historical Perspective

Einstein, Riechenbach and Gruenbaum never mentioned coordinate transformations in their work. The earliest paper I can find proposing this thesis is Edwards 1963 paper in 'American Journal of Physics'. Winnie popularized the idea in his two paper article in the 1970 'The Philosophy of Science Journal Association'.

Equations

I would like to see someone derive the cavity resonator equation under the conditions of Case 3.

ω101=[(πc/a)2+(πc/d)2]0.5

This equation shows that it is theoretically possible to measure e using a missile projectile and only one clock.

Rearranging Reichenbach's equation e = (t3 - t1) / (t2 - t1).

e = t3 / (t2 - 2 * t1))

Supporting article

The only supporting paper I've found so far is:
R. Anderson, I. Vetharaniam, and G. E. Stedman, Conventionality of synchronization,
gauge dependence and test theories of relativity, Physics Reports 295, 93180 (1998).
He provides no supporting evidence or a proof. This purpose of this post is to fill in the blanks.

Minkowski Diagram

To construct a Minkowski diagram, start with an XY plane and an orthogonal T axis. Obviously for the case where the speed of light C/2 away from an observer located at the origin and C/0 toward the observer located at the origin, the slope is C/2 for the forward light cone and the slope for the backward light cone is C/0. This corresponds to Einstein's alternate synchrony convention published in his 1905 paper.

A Paradox

Consider observer 1 located at the origin. Another observer is located at event 2 sometime in the future of observer 1. When an event occurs at observer 2's location, observer 1 will never be aware of it. However any event occurring at the location of observer 1 will always be seen by observer 2.
The only symmetrical case is when the light cones are parallel, which means the only possible solution is that the speed of light is isotropic.

Conclusion

A coordinate transformation is not equivalent to a change of synchrony convention.

Respectfully,
Gene Snider
 
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  • #2
GeneSnider said:
From a God's eye point of view
What does this mean? There is no "God's eye point of view" in relativity--no reference frame is the "true" one. All frames are equally valid.

GeneSnider said:
In transformed coordinates where the transformation is T = T' + T * C / S
Where did you get this transformation from and why do you think it means anything? It's certainly not a Lorentz transformation.

GeneSnider said:
When C is C/2 away from the earth and C/0 towards the observer
What does this even mean?

GeneSnider said:
Einstein, Riechenbach and Gruenbaum never mentioned coordinate transformations in their work.
What are you talking about? One of Einstein's classic 1905 papers explicitly derives the Lorentz transformation.

GeneSnider said:
The earliest paper I can find proposing this thesis is Edwards 1969 paper in 'American Journal of Physics'. Winnie popularized the idea in his two paper article in the 1970 'The Philosophy of Science Journal Association'.
These references are too vague. Please give specific titles and journal volumes/pages.

GeneSnider said:
The only supporting paper I've found so far is:
R. Anderson, I. Vetharaniam, and G. E. Stedman, Conventionality of synchronization,
gauge dependence and test theories of relativity, Physics Reports 295, 93180 (1998).
What do you think this paper is "supporting"?

GeneSnider said:
To construct a Minkowski diagram, start with an XY plane and an orthogonal T axis. Obviously for the case where the speed of light C/2 away from an observer located at the origin and C/0 toward the observer located at the origin, the slope is C/2 for the forward light cone and the slope for the backward light cone is C/0.
I have no idea what you're talking about here. In a Minkowski diagram, the slopes of light cones are 45 degrees everywhere.

GeneSnider said:
This corresponds to Einstein's alternate synchrony convention published in his 1905 paper.
Einstein published multiple papers in 1905. Please be specific about which one you are referring to and what particular part of it you think gives an "alternate synchrony convention".

GeneSnider said:
A Paradox

Consider observer 1 located at the origin. Another observer is located at event 2 sometime in the future of observer 1. When an event occurs at observer 2's location, observer 1 will never be aware of it.
This is not a paradox at all. It's just you not understanding how spacetime works. Obviously an observer at event 1 cannot be aware of event 2 if event 2 is to the future of event 1.

GeneSnider said:
However any event occurring at the location of observer 1 will always be seen by observer 2.
An event is not a "location". It's a point in spacetime. If event 2 is in the causal future of event 1, then an observer at event 2 can be aware of event 1. (But note the qualifier I put on "future".) Again, there is no paradox here at all.

GeneSnider said:
The only symmetrical case is when the light cones are parallel
Light cones of what?

GeneSnider said:
which means the only possible solution is that the speed of light is isotropic.
If you think this is the only possible "solution" to constructing a coordinate chart, you are egregiously wrong. If not, I have no idea what you think this is the only possible "solution" to.

GeneSnider said:
Conclusion

A coordinate transformation is not equivalent to a change of synchrony convention.
I have no idea why you think this follows from anything you have said.
 
  • #3
PeterDonis: What does this mean? There is no "God's eye point of view" in relativity--no reference frame is the "true" one. All frames are equally valid.
From a God's eye point of view

PeterDonis: Where did you get this transformation from and why do you think it means anything? It's certainly not a Lorentz transformation.
That transformation is used in the literature to transform to a coordinate system where the speed of light is C/2 away from the origin and C/0 towards the origin.
I've seen God's eye point of view in the literature. Another equivalent expression would be omniscient

PeterDonis:
It's the transformation used in the literature to transform a coordinate system to one where the speed of light is C/2 to away from the origin and C/0 towards the origin.

PeterDonis:
I should have changed notation slightly. Here, C is the two-way speed of light and c/2 is the one-way speed of light.

PeterDonis: What are you talking about? One of Einstein's classic 1905 papers explicitly derives the Lorentz transformation.
But he did not use transformed coordinates in while describing his alternative synchrony convention

PeterDonis: These references are too vague. Please give specific titles and journal volumes/pages.

Reference 1
Reference 2
Reference 3

PeterDonis: What do you think this paper is "supporting"?
He is supporting my thesis that a coordinate transformation is not equivalent to a change of synchrony conventions. That is true only if the one-way speed of light is isotropic.

PeterDonis: Light cones of what?
The light cones in a Minkowski diagram to represent the one way speed of light.

PeterDonis: What do you think this paper is "supporting"?
Light cones with a slope of one can only occur if the one-way speed of light is isotropic.

It does.
 
  • #4
One point I forgot to mention, this thesis makes the Conventionality Thesis moot for General Relativity as well as Special Relativity. Do you agree with me on this point?
Regards,
Gene
 
  • #5
GeneSnider said:
In this post, s is distance, t1, is the time of transmission, t2 is the time of reflection and t3 is the time of reception. All cases assume an orthogonal coordinate system.
Case 1:
From a God's eye point of view, a laser pulse bounced off of a retroreflector on the moon will have these time stamps: t1=0, t2=1.25, t3=2.5
Case 2:
Coordinate Transformation
In transformed coordinates where the transformation is T = T' + T * C / S the time stamps are: t1 = 0 = 1.25, t3 = 2.5
Case 3: When C is C/2 away from the earth and C/0 towards the observer, the time stamps are: t1 = 0, t2 = 1.25, t3=2.5
It would be easier to follow the discussion if you would use the forum’s quote feature to distinguish your replies from whatever you’re replying to and use Latex for the mathematical expressions. But I’m doing my best to understand what you’re trying to say here….

When you say “God’s eye view” it seems that you mean “as analyzed by someone who knows the timestamp values ##t_1##, ##t_2##, ##t_3##”?

We can use Minkowski ##(x,t)## coordinates to label the three events (emission, reflection, reception of reflected signal): ##(0,0)##, ##(s,1,25)##, ##(0,2.5)##. Or we can use the transformed coordinate system: ##(0,0)’##, ##(s,2.5)’##, ##(0,2.5)’##. Are these what you mean by case 1 and case 2? These are the same physical situation just described using different coordinates.

Using the case 1 coordinates we calculate the coordinate speed of light in both directions and we get the isotropic result ##c_L=c_R=\frac{\Delta x}{\Delta t}=\frac{s}{1.25}##. Of course it had to turn out that way because we’re calculating the coordinate speed of light using a simultaneity convention in which the speed of light is isotropic.

Using the case 2 coordinates, we calculate the coordinate speed of light in both directions, and of course we will get ##c_L=\frac{\Delta x}{\Delta t}=\frac{s}{2.5}## and ##c_R=\frac{\Delta x}{\Delta t}=\frac{s}{0}##. Again, it had to come out that way because we started from coordinates assigned using a simultaneity convention in which the speed of light is anisotropic.

Case 3 is just case 2 with the simultaneity convention stated explicitly. (If you believe that they are not the same because case 3 includes physical content that case 2 does not, you have missed the point, that one-way speeds are always things that we calculate instead of measuring - although ratios of one-way speeds can be measured).

To construct a Minkowski diagram, start with an XY plane and an orthogonal T axis. Obviously for the case where the speed of light C/2 away from an observer located at the origin and C/0 toward the observer located at the origin, the slope is C/2 for the forward light cone and the slope for the backward light cone is C/0.
That’s not a Minkowski diagram; a Minkowski diagram is a plot of Minkowski ##x## and ##t## coordinates. You can draw an analogous diagram for the transformed coordinates, but in this diagram the causal structure will not be represented by neat 45-degree cones as in a Minkowski diagram.
The apparent paradox that you’ve found will go away once you draw the causal structure properly using the transformed coordinates.
 
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  • #6
GeneSnider said:
One point I forgot to mention, this thesis makes the Conventionality Thesis moot for General Relativity as well as Special Relativity. Do you agree with me on this point?
Regards,
Gene
Tell us what that thesis is and we might be better able to respond.
 
  • #7
One can easily draw a Minkowski diagram and then shear it so that the coordinate speed of light in the new diagram is infinite in one direction. This will manifestly preserve all causal connections, so can introduce no paradoxes.
 
  • #8
GeneSnider said:
I've seen God's eye point of view in the literature.
Where? Be specific. It sounds like an extremely misfortune term that shoukd not be used. I have never heard of it being used in 20 years of teaching relativity.

GeneSnider said:
Another equivalent expression would be omniscient
This doesn’t really help. Still not a standard term.
 
  • #10
GeneSnider said:
This is a Wikipedia article on the one-way speed of light. Is your point that the one-way speed of light (as opposed to the round-trip speed of light) is a convention? If so, you could have said that in one sentence (and it wouldn't be news to anyone). It is not evident from anything you've posted.

GeneSnider said:
These are both to the same paper, which appears to be making the same point as the Wikipedia article above. Again, you could have just said that in one sentence, and it's not evident from anything you've posted.

GeneSnider said:
He is supporting my thesis that a coordinate transformation is not equivalent to a change of synchrony conventions. That is true only if the one-way speed of light is isotropic.
No, it isn't. For example, the transformation from standard Minkowski coordinates to Rindler coordinates does involve a change of synchrony conventions, but the one-way speed of light is not isotropic in Rindler coordinates.
 

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