Relativity of simultaneity and one-way speed of light

[Mordred]

As someone who hasn't gotten involved in this thread. I would like to see the equations in support of a particular viewpoint rather than bickering amongst each other.

 

A good math argument is far more effective than mere name calling.

Which quite frankly accomplishes nothing

Edited September 3, 2015 by Mordred

[david345]

Where did they get this absolute clock capable of measuring absolute time? Declaring two clocks the same is not equal to a universal time the same for all.

Edited September 3, 2015 by david345

[md65536]

As someone who hasn't gotten involved in this thread. I would like to see the equations in support of a particular viewpoint rather than bickering amongst each other.

 

A good math argument is far more effective than mere name calling.

Which quite frankly accomplishes nothing

Would some references suffice? I've cited a couple in support of my position. Edited September 3, 2015 by md65536

[Mordred]

Would some references suffice? I've cited a couple in support of my position.

Preferably peer reviewed, wiki isn't 100% on numerous articles.

 

While I'm aware there is some debate on whether or not the Michelson Morley test truly tests the one way speed of light or not. There has been numerous alternative and more advanced tests since then.

 

Here is one such recommended test.

 

http://arxiv.org/pdf/physics/0609202

[Andromacus]

I think it would indeed help to use math arguments.

Basically a simultaneity convention is no more than the choice of coordinate systems one decides to use for a certain problem.

The Einstein sync amounts to the usual inertial coordinates of Newtonian mechanics. These are orthonormal coordinates and are the natural ones in a flat space.

Other choices of simultaneity are no more than choosing other coordinates, it shouldn't be a problem what coordinates to use except some may adapt better to certain problems or geometries, in this sense as I commented inertial coordinates are the best suited for flat spacetime.

As long as one is consistent with the use of coordinates of course, one cannot mix different coordinates for the same problem or risks getting contradictory answers. This mixing of coordinates is happenning here, as can be seen in any Minkowski diagram of a change of frames..

Now for instance non-inertial coordinates are curvilinear, we'll left those aside as this issue doesn't concern non-inertial frames(there is no accelerations or gravity involved).

We also have non-orthogonal coordinates like the ones used in Minkowski diagrams to depict the frames not at rest.

So these non-orthogonal coordinates are the ones used when a simultaneity convention different to the one required by Einstein's sync (that had to be orthogonal remember?). This is the case everytime a change of frame(Lorentz transformation) is invoked, in order to have relative simultaneities for each frame.

Now since here we are always dealing with inertial frames, and transformation between frames must preserve the Lorentzian concept of orthogonality wich is differetnfrom the euclidean concept it is usually accepted the use of non-orthogonal axes in Minkowski diagrams for the frame not considered at rest, but again what characterizes an inertial frame is the orthonormality i,e. perpendivular axes for x and t.

 

So one of the frames in the transformation must use non-orthogonal coordinates(giving anisotropic speed of light), and please realize what this implies, this implies that for the frame not using orthogonal coordinates the one-way speed cannot be equal to the round-trip speed of light, and this forces us to say that the one-way speed is unmeasurable to avoid direct contradiction, since the round-trip speed is considered isotropic. We may gree that light speed shouldn't be at the same time isotropic and anisotropic right?

 

Now this simple fact has been repeatedly ignored by all those who claim they are fine with a non-conventional standard Einstein sync, and don't find any problem with sayin one-way speed is perfectly measurable.

 

The reason SR is contradictory is that both sides can find arguments within the theory to say they are right, but we all know this cannot be true, it is much more likely both sides(conventionalists and non-conventionalists) and therefore SR are wrong somewhere.

 

 

Edit I was going to include a Minkowski diagram but it seems I'm not allowed.

Edited September 3, 2015 by Andromacus

[md65536]

It seems no one on the non-conventionality side is getting it so I'll try to explain.

 

 

Einstein's definition of simultaneity and the clock synchronization method it enables, allow us to define whether two distant events are simultaneous in a given inertial frame. Yet, there is no way to say for sure that the two events really "are" simultaneous independent of the definitions. The answer to that is in the realm of metaphysics. There is no way to measure it without using some assumption that is equivalent to assuming the simultaneity definition. Even if multiple conventions give the same answer, that doesn't tell you that it truly "is". This doesn't matter in science, because Einstein's definition works perfectly fine, and the measurements are useful whether or not the events truly "are" simultaneous in some philosophical sense, while the answer to something that can't be measured isn't useful.

 

If you argue that one of the related quantities (simultaneity, synchronization, speed, delay of light, etc) truly "is" the only possible physical reality, you can effectively derive that Einstein's simultaneity convention "is" in fact the only real one, even though such a fact can't be measured without effectively assuming it. That makes it a crackpot argument.

 

I don't think anyone here arguing on the non-conventionality side is a crackpot, in the sense of knowingly promoting a position that contradicts science. I think the crackpot ideas on this side come from a lack of understanding.

[Mordred]

My recommendation is to gather data and peer review articles on the various tests and examine each. Then compare the accuracy of each.

Edit didn't see your last post

Edited September 3, 2015 by Mordred

[Andromacus]

It seems no one on the non-conventionality side is getting it so I'll try to explain.

 

 

Einstein's definition of simultaneity and the clock synchronization method it enables, allow us to define whether two distant events are simultaneous in a given inertial frame. Yet, there is no way to say for sure that the two events really "are" simultaneous independent of the definitions. The answer to that is in the realm of metaphysics. There is no way to measure it without using some assumption that is equivalent to assuming the simultaneity definition. Even if multiple conventions give the same answer, that doesn't tell you that it truly "is". This doesn't matter in science, because Einstein's definition works perfectly fine, and the measurements are useful whether or not the events truly "are" simultaneous in some philosophical sense, while the answer to something that can't be measured isn't useful.

 

If you argue that one of the related quantities (simultaneity, synchronization, speed, delay of light, etc) truly "is" the only possible physical reality, you can effectively derive that Einstein's simultaneity convention "is" in fact the only real one, even though such a fact can't be measured without effectively assuming it. That makes it a crackpot argument.

 

I don't think anyone here arguing on the non-conventionality side is a crackpot, in the sense of knowingly promoting a position that contradicts science. I think the crackpot ideas on this side come from a lack of understanding.

I'm intrigued about your position in this thread. Sometimes I think you are quite aware of the contradiction I'm bringing in like in this post you seem to. Other times it seems you are saying the opposite and in the meantime you bash everyone in sight. I truly don't know yet what your position is.

[md65536]

Here is one such recommended test.

 

http://arxiv.org/pdf/physics/0609202

This seems rather ambiguous because they mention the issue but don't seem to address it. They mention the "problem of simultaneity", quote Einstein suggesting it is merely a convention, mention the "problem of clock synchronization" but no resolution, and cite a reference that says the one way speed of light can't be tested, except that it is phrased ambiguously as though suggesting it no longer applies:

 

The importance of the test of the one-way speed of light can never be overestimated because the

isotropy of the one-way speed of light not only is the foundation of the principle of the constancy of the

speed of light, but also is the core of the problem of simultaneity. It was stated by Einstein: “That light

requires the same time to traverse the path A → M as for the path B → M is in reality neither a supposition

nor a hypothesis about the physical nature of light, but a stipulation which I can make of my own freewill

in order to arrive at a definition of simultaneity.” (M is the mid-point of line AB.) [20] The test of the one-

way speed of light is difficult because the clock type of the experiments has the problem of the clock

synchronization and the interference type of the experiments has the problem of the closed light path.

Sometime it was even claimed that the one-way speed of light cannot be tested by the experiments [21].

Regardless, it is generally agreed that the one-way speed of light is measurable given synchronized clocks, with respect to the particular sync convention.

I'm intrigued about your position in this thread. Sometimes I think you are quite aware of the contradiction I'm bringing in like in this post you seem to. Other times it seems you are saying the opposite and in the meantime you bash everyone in sight. I truly don't know yet what your position is.

It's so hard to try to argue a mainstream position on a poorly understood issue around here without being called a dick, rude, and being accused of bashing.

 

I'm not aware of the contradiction you're bringing up. I think it's based on a fundamental lack of understanding of SR. Sorry to say that, like I said I think your understanding of the philosophical, conventionality of simultaneity side of things is the best that I've seen, but your examples of alternative simultaneities, and claims that the Lorentz transformation require them, contradict SR. At best I think you'll have to show an alternative simultaneity is in agreement with experimentally verified predictions of SR. I don't think anyone has a hope of finding a contradiction in SR by using SR incorrectly, and with a decent understanding of SR it becomes hard to see any weakness where there is a possibility of contradiction.

 

My position is that Einstein's convention has never been proven non-conventional.

Personally I think it truly is conventional, and that physically meaningful simultaneity is merely a local measurement, something more like in general relativity, but I won't argue that because I'm not aware of anything to back it up.

Edited September 3, 2015 by md65536

[Andromacus]

 

your examples of alternative simultaneities, and claims that the Lorentz transformation require them, contradict SR. At best I think you'll have to show an alternative simultaneity is in agreement with experimentally verified predictions of SR.

This shows you haven't understood what I'm saying(I'll be more tolerant than you and refrain from saying that means you don't have a clue about what you are saying or SR). Try my previous post. I'm willing to carry the blame for your(or others) not understanding my point anyway. Communication in a forum has its drawbacks.

 

[studiot]

 

So one of the frames in the transformation must use non-orthogonal coordinates(giving anisotropic speed of light), and please realize what this implies, this implies that for the frame not using orthogonal coordinates the one-way speed cannot be equal to the round-trip speed of light, and this forces us to say that the one-way speed is unmeasurable to avoid direct contradiction, since the round-trip speed is considered isotropic. We may gree that light speed shouldn't be at the same time isotropic and anisotropic right?

 

Let us at least get our terminology correct, perhaps English is not your first language.

 

Can time or a timelike axis be isotropic or anisotropic or is that reserved for space and spacelike continua since they have more than one axis.

 

Should you not be using the term homogeneous?

 

The contention that we must assume or declare time and timelike axes to be homogeneous is correct

to ensure that transit time for A to B is the same as for B to A or the midpoint if you want to use the formula mentioned earlier.

[Andromacus]

A clear explanation of how SR's relativity of simultaneity requires the different frames to disagree about sync chronization of clocks(alternative simultaneities) can be read here:http://www.pitt.edu/~jdnorton/teaching/HPS_0410/chapters/Special_relativity_rel_sim/index.html

 

Let us at least get our terminology correct, perhaps English is not your first language.

 

Can time or a timelike axis be isotropic or anisotropic or is that reserved for space and spacelike continua since they have more than one axis.

 

Should you not be using the term homogeneous?

 

The contention that we must assume or declare time and timelike axes to be homogeneous is correct

to ensure that transit time for A to B is the same as for B to A or the midpoint if you want to use the formula mentioned earlier.

Orthonormality refers to both the time and space axis(inertial coordinates) in a minkowski diagram. We are restricting here to the one dimensional case for simplicity, by isotropy we refer to the perpendicularity of the axes that allows the standard synchronization, that is isotropic(speed from A to B in the x axis is eqaul to that from B to A).. I'm not sure what you mean by isotropy or anisotropy of just one axis, one needs two axes to define perpendicularity.

Edited September 3, 2015 by Andromacus

[swansont]

 

As long as one is consistent with the use of coordinates of course, one cannot mix different coordinates for the same problem or risks getting contradictory answers. This mixing of coordinates is happenning here, as can be seen in any Minkowski diagram of a change of frames..

 

How so? In SR you can't synchronize clocks in different frames. Einstein synchronization only happens in a single frame. So where is this mixing happening?

[md65536]

A clear explanation of how SR's relativity of simultaneity requires the different frames to disagree about sync chronization of clocks(alternative simultaneities) can be read here:http://www.pitt.edu/~jdnorton/teaching/HPS_0410/chapters/Special_relativity_rel_sim/index.html

Relativity of simultaneity and conventionality of simultaneity aren't the same thing. Your link's referring to the former.

 

In SR you have eg. the embankment frame, with 2 Einstein-synchronized clocks. Those clocks aren't synchronized in the train frame (they might be according to some alternative convention, I'm not sure, but your link doesn't show that).

 

In the train frame, some other pair of clocks will be synchronized. However, in SR they will be synchronized using the same convention (it is still Einstein-synchronization).

 

The measure of simultaneity is relative, and different in the different frames. The definition of simultaneity used is the same in the different frames.

 

 

 

Other definitions of simultaneity may work, but they're not needed or used in SR. We don't say that the embankment's clocks are "synchronized according to an alternative simultaneity convention" in the train frame, meaning that they read the same time according to some other set of rules, we say they are "not synchronized", meaning they are not reading the same time.

Edited September 4, 2015 by md65536

[Mordred]

This seems rather ambiguous because they mention the issue but don't seem to address it. They mention the "problem of simultaneity", quote Einstein suggesting it is merely a convention, mention the "problem of clock synchronization" but no resolution, and cite a reference that says the one way speed of light can't be tested.

Yes, I posted this paper as an example of the debate amongst professionals on the validity of one way speed of light tests. I've seen counter arguments on both sides of the fence. This includes such techniques such as two clock synchronization, single clock and Doppler shift tests.

 

As this particular subject isn't my expertise, It would be nice seeing how detailed (including the related math) this thread will get.

 

It's a excellent subject, one that many can learn from. So I'm sort of challenging the debators on this thread to provide a thorough and detailed discussion. With both peer reviewed articles as well as a clear math analysis (pros and cons) of the various tests.

Ps (using math and peer review backing will not be considered a crank. If one provides the proper math and references, any mainstream theory can be examined) it's those that can't do the math or provide supporting evidence that typically fall into that category. Just saying

 

A format I would recommend in light of the above challenge. Post a specific test. Provide a peer review of said test. Then debate that test.

 

This would be an enlightening discussion. One everyone can learn from. This forum has more than enough. Personal opinion lack of support arguments. Make this thread a better example of how to properly debate a subject....

As a side note here is an excellent article on teaching relativity of simultaneity.

http://arxiv.org/pdf/physics/0511062

@ Andromecus here is a link on posting latex on this site.

 

http://www.scienceforums.net/topic/3751-quick-latex-tutorial/page-1#

Edited September 4, 2015 by Mordred

[studiot]

Mordred

 

I would like to see the equations in support of a particular viewpoint rather than bickering amongst each other.

As this particular subject isn't my expertise, It would be nice seeing how detailed (including the related math) this thread will get.

 

 

 

 

 

 

In order to perform more detailed maths it is necessary to distinguish clearly

 

 

Between point properties such as isotropy and interval segment or region properties such as homegeny.

 

The intimate link between space and time which is embodied in Einstein's work

Synchronisation is a point property.

Point properties should not be treated as segment properties and vice versa.

 

 

Einstein

The analysis of the concept of time was my solution. Time cannot be absolutely defined and there is an inseparable between time and signal velocity. With this new concept (My words SR) I could resolve all difficulties for the first time.

 

Which led to the equation for the four dimensional invariant

[math]\Delta {s^2} = {c^2}\Delta {t^2} - \Delta {x^2} - \Delta {y^2} - \Delta {z^2}[/math]

I have emphasised that this all these are segment properties, not point properties.

Both ends of Segments need to be measured in the same reference frame.

Einstein avoids this neatly using swansont's slow transfer method in the Train Thought Experiment.

 

What is meant by 'the speed of light' phase or group velocity?

The path of the light signal, the physical nature of the light and the interaction between the two.

 

Note in particular the stipulation in c (ii) for pulses of light ( as used in Einstein's analysis, but he does not distinguish the difference)

 

We should always remember that all these equations are just models and be sure about their applicability and constraints, and whether these constraints lead to greater errors than our clevel, but over simple model.

Edited September 4, 2015 by studiot

[Andromacus]

 

 

 

 

In order to perform more detailed maths it is necessary to distinguish clearly

 

 

Between point properties such as isotropy and interval segment or region properties such as homegeny.

 

The intimate link between space and time which is embodied in Einstein's work

Synchronisation is a point property.

Point properties should not be treated as segment properties and vice versa.

 

 

As I said inertial coordinates being orthogonal and normalized are both homgeneous and isotropic, and these properties must be preserved by the Lorentzian inertial frame (linear) transformations. But if you look at a minkowski diagram of a frame transformation it is clear that isotropy(i.e. synchronization) is not preserved, changing to non-orthogonal coordinates in one of the frames. This is not a linear transformation. Agree so far?

Edited September 4, 2015 by Andromacus

[studiot]

 

Agree so far?

 

 

Neither agree nor disagree until you publish some maths as requested.

[Andromacus]

 

How so? In SR you can't synchronize clocks in different frames. Einstein synchronization only happens in a single frame. So where is this mixing happening?

The mixing is of inertial and noninertial coordinates when both should be inertial frames, it consist of performing a supposedly lorentz transformation that should preserve orthogonality(isotropy of light with Einstein sync) and getting anisotropic, non-Eisntein sync, non-orthogonal coordinates.for the transformed frame.

 

Neither agree nor disagree until you publish some maths as requested.

I thought this was clear enough as written, they are standard definitions. I tried to include a Minkowski diagram but the system won't let me.

[studiot]

 

I thought this was clear enough as written, they are standard definitions. I tried to include a Minkowski diagram but the system won't let me.

 

 

I am sorry you can't include your diagram, have you asked a mod (eg swansont) for help?

 

If you can email it to me I will post it for you.

 

As regards the other part of your reply,

 

I feel I am wasting my time discussing since I have addressed each and every one of your points as well as offering some of my own.

 

So far all I have received in return is a derogatory comment about my understanding.

 

I have seen nothing to indicate that you understand the difference between homogeny and isotropy in you use of the terms and you have not replied to my pointing this out.

 

As an example, the pressure in my glass of beer is isotropic but not homogeneous.

[Andromacus]

Relativity of simultaneity and conventionality of simultaneity aren't the same thing. Your link's referring to the former.

From post one I have been saying the contradiction lies in the relativity of simultaneity. It is of couse related to the different synchronization in the different frames, not in the same frame. Read the title of the thread.

 

 

I have seen nothing to indicate that you understand the difference between homogeny and isotropy in you use of the terms and you have not replied to my pointing this out.

I don't know what you want me to say nor why it is so important to you to talk about homogeneity.

Isotropy is spherical symmetry, a point property in Euclidean geometry as you said. Homogeneity refers to space translation invariance and therefore involves more than one point. The isotropy and homogeneity in classical mechanics and in SR results from using flat geometry. Cartesian, and inertial minkowski coordinates are naturally orthonormal and homogeneous and isotropic and this must be preserved by linear transformations.

Edited September 4, 2015 by Andromacus

[swansont]

The mixing is of inertial and noninertial coordinates when both should be inertial frames, it consist of performing a supposedly lorentz transformation that should preserve orthogonality(isotropy of light with Einstein sync) and getting anisotropic, non-Eisntein sync, non-orthogonal coordinates.for the transformed frame.

 

I don't understand your issue. There is no Lorentz transform or transformed frame for an Einstein synchronization. There is no synchronization possible with a transformed frame in SR. If you are mixing frames you are doing something that's not allowed.

[Andromacus]

 

I don't understand your issue. There is no Lorentz transform or transformed frame for an Einstein synchronization. There is no synchronization possible with a transformed frame in SR. If you are mixing frames you are doing something that's not allowed.

No, not for a synchronization, I'm talking about the regular Lorentz transformation between frames as seen in the usual Minkowski diagram.

Ok, so this is the usual minkowski diagram of a lorentz transformations. The black axes represent the inertial frame at rest and it's compatible with isotropy of light and Einstein sync. The red axes represent in theory the Lorentz transformed inertial frame. But it is evident that non-orthogonal coordiantes cannot represent an inertial frame. This is usually dodged by saying the non-orthogonal coodinates are actually how one observer perceives the other. And symmetrically if we go to the rest frame of the red axes observer they are also orthogonal. But this clearly is not mathematically demonstrable since we cannot put both observers at rest except at the origin, however we are drawing conclusion about simultaneity from this diagram with the miixed coordinates, that should only be used for ilustrative purposes, not to draw physical conclusions. The red axes that give an anitropic c are giving a coordinate velocity that cannot be used to extract physical consequences about simultaneity.

 

Some will say this is just a drawback of the 2D representation but when going to 4-space the restriction persists that the time coordinate must be orthogonal to the spatial hypersurface(Minkowski space is static wich implies this).

[swansont]

No, not for a synchronization, I'm talking about the regular Lorentz transformation between frames as seen in the usual Minkowski diagram.

 

OK. I got the wrong impression from a previous post.

[md65536]

Which led to the equation for the four dimensional invariant

[math]\Delta {s^2} = {c^2}\Delta {t^2} - \Delta {x^2} - \Delta {y^2} - \Delta {z^2}[/math]

I have emphasised that this all these are segment properties, not point properties.

Both ends of Segments need to be measured in the same reference frame.

I still think that this is consistent with Einstein's definition of simultaneity and with the convention used to define it.

I don't see how it shows an improvement over Einstein.

 

 

 

 

Einstein's definition of simultaneity is the standard definition still used today.

Einstein used a convention in his definition, he did not claim the definition derived from experimental observation or from assumption.

No one in history has provided a better definition, without a convention, that has replaced Einstein's as the accepted standard.

No one has proven Einstein wrong or improved upon his definition.

 

Unfortunately I'm deficient in maths to be able to express any of these statements in equations. If anyone has an equation that shows any of the statements are wrong, then I concede utter defeat.