Is relativity of simultaneity measurable?

[Neddy Bate]

Lightning strikes are simultaneous in the embankment and not for the train frame. No use of this to prove that Lorentz transformation is equation for measuring proper time.

Thank you for answering. I agree that the train frame measures the lighting strikes as non-simultaneous. That is what I calculated here:

$$t'_L = \gamma(t - \frac{vx_L}{c^2})$$

$$t'_R = \gamma(t - \frac{vx_R}{c^2})$$

Where:
$$x_L$$ is the location of the LEFT lightning strike, as measured in the ground frame
$$x_R$$ is the location of the RIGHT lightning strike, as measured in the ground frame
$$t$$ is the time that BOTH lightning strikes occur, as measured in the ground frame, (as they are defined to be simultaneous in this experiment)

Please note that the experiment is set up such that:
$$x_L \neq x_R$$
Therefore:
$$t'_L \neq t'_R$$

Now, if you think those are not the proper times for the lighting strikes in the train frame, then please show me your calculations.

 

[ash64449]

Thank you for answering. I agree that the train frame measures the lighting strikes as non-simultaneous. That is what I calculated here:



Now, if you think those are not the proper times for the lighting strikes in the train frame, then please show me your calculations.

Those calculations are correct!! but you are wrong in saying that time you calculated is "proper time"

I say "coordinate" time. Understood?? You misunderstood Lorentz Transformation that Time Transformation of Lorentz transformation measures Proper time.

But its not. It measures coordinate time.

Understood what i said?

You cannot oppose this. Because it is a fact. Not anything of my invention at all...

Come on.. I am not here discussing who is wrong and who is correct? I am saying what is "actually".

Another evidence: If proper time is invariant,why need Lorentz Transformation??!!!

Sure that leads to the answer that Lorentz Transformation measures coordinate time.

 

[Neddy Bate]

Those calculations are correct!! but you are wrong in saying that time you calculated is "proper time"

I say "coordinate" time. Understood?? You misunderstood Lorentz Transformation that Time Transformation of Lorentz transformation measures Proper time.

But its not. It measures coordinate time.

Understood what i said?

You cannot oppose this. Because it is a fact. Not anything of my invention at all...

Come on.. I am not here discussing who is wrong and who is correct? I am saying what is "actually".

Another evidence: If proper time is invariant,why need Lorentz Transformation??!!!

Sure that leads to the answer that Lorentz Transformation measures coordinate time.

If you agree that my calculations are correct, then that is what the train frame measures, (contradicting your claim that coordinate time is not measurable). If you think the proper time is something else, then show me the calculation.

 

[ash64449]

If you agree that my calculations are correct, then that is what the train frame measures, (contradicting your claim that coordinate time is not measurable). If you think the proper time is something else, then show me the calculation.

No. You don't understand a bit what i said!!!

Lorentz Transformation helps to find out coordinate time and coordinate position of the event.

Observers DON'T Measure coordinate time,They Measure Only THEIR PROPER TIME which is invariant.

So It is impossible to measure coordinate time of SPATIALLY Separated event.

DO you know what is coordinate time and how you differentiate a proper time from coordinate time??

Here is the answer: The Time that is measured in the clock is called proper time.

Think of Two Observers Having clocks. They measure their own PROPER Time... But...

They are unable to MEASURE "COMMON" Time for both A and B observers. Just Think How can observer B measure "common" time of his and Distant observer A?

That is coordinate Time . And the difference in timing of events in different reference frame is because of difference in 'common time' for A and B and 'common time' for observer C and D.(for example.)

And comes because of differences in definition of Simultaneity.. Please read Einstein's 1905 paper... First two chapters are enough to get to the conclusion.


OK. LET ME TALK YOUR WAY: DO you agree that proper time is INVARIANT?

 

[eram]

No. You don't understand a bit what i said!!!

Lorentz Transformation helps to find out coordinate time and coordinate position of the event.

Observers DON'T Measure coordinate time,They Measure Only THEIR PROPER TIME which is invariant.

So It is impossible to measure coordinate time of SPATIALLY Separated event.

DO you know what is coordinate time and how you differentiate a proper time from coordinate time??

Here is the answer: The Time that is measured in the clock is called proper time.

Think of Two Observers Having clocks. They measure their own PROPER Time... But...

They are unable to MEASURE "COMMON" Time for both A and B observers. Just Think How can observer B measure "common" time of his and Distant observer A?

That is coordinate Time . And the difference in timing of events in different reference frame is because of difference in 'common time' for A and B and 'common time' for observer C and D.(for example.)

And comes because of differences in definition of Simultaneity.. Please read Einstein's 1905 paper... First two chapters are enough to get to the conclusion.


OK. LET ME TALK YOUR WAY: DO you agree that proper time is INVARIANT?

Now not too long ago you were almost entirely clueless (and I think you still pretty much are). You should really tone it down regardless.

 

[ash64449]

Now not too long ago you were almost entirely clueless (and I think you still pretty much are). You should really tone it down regardless.

What am i clueless about?

 

[eram]

What am i clueless about?

You know a bit here and there, and there are a lot of gaps to be filled. And language is still a barrier. So I would suggest you do things one step at a time, don't bite off more than you can chew.

 

[ash64449]

You know a bit here and there, and there are a lot of gaps to be filled. And language is still a barrier. So I would suggest you do things one step at a time, don't bite off more than you can chew.

What is the gap? Don't you agree that Lorentz Transformation is about coordinate time or to understand what are the coordinates of the same event for another reference frame when you know the values for your own reference frame? Time coordinate is the one used for This transformation. Don't you agree?

 

[Fednis48]

As much as I was having trouble understanding ash up to this page, he's definitely correct here. The proper time between two events is defined as the time between them as measured by an inertial clock that is present at both events. By this definition, it doesn't make sense to talk about the proper time between two space-like separated events (like the lightning strikes), because it is impossible for one clock to be present at both.

Neddy Bate, the opposite is true for you: as far as I could tell you were spot-on with everything up until the last couple of pages, but you're misusing the term "proper time". If two events occur at different locations in a given frame, then their times in that frame are not proper times. You're correct that your Lorentz transform gives the times that an observer in the train frame would measure (as long as you're willing to accept some clock synchronization scheme so that he/she can time two space-like separated events). But it's a mistake to call those times proper.

That said, I don't see how this has any effect on Neddy Bate's central conclusion. Again, as long as we are willing to accept Einstein clock synchronization as legitimate (and we wore that caveat into the ground many pages ago), there's no reason why coordinate time can't be used to measure RoS.

 

[Neddy Bate]

As much as I was having trouble understanding ash up to this page, he's definitely correct here. The proper time between two events is defined as the time between them as measured by an inertial clock that is present at both events. By this definition, it doesn't make sense to talk about the proper time between two space-like separated events (like the lightning strikes), because it is impossible for one clock to be present at both.

Neddy Bate, the opposite is true for you: as far as I could tell you were spot-on with everything up until the last couple of pages, but you're misusing the term "proper time". If two events occur at different locations in a given frame, then their times in that frame are not proper times. You're correct that your Lorentz transform gives the times that an observer in the train frame would measure (as long as you're willing to accept some clock synchronization scheme so that he/she can time two space-like separated events). But it's a mistake to call those times proper.

That said, I don't see how this has any effect on Neddy Bate's central conclusion. Again, as long as we are willing to accept Einstein clock synchronization as legitimate (and we wore that caveat into the ground many pages ago), there's no reason why coordinate time can't be used to measure RoS.

Thanks for trying to sort this out. Please consider that ash64449 insists that only proper times can be measured, that coordinate times cannot be measured, and that RoS cannot be measured because it involves coordinate times. So, when you agree with me that the train frame does measure the coordinate times that I calculated, you are saying ash64449 is incorrect, not the other way around.

As far as the term "proper time" is concerned: If the definition is that which you have provided, (that a single inertial clock must be present at both events), then indeed there is no proper time between the lightning strikes in Einstein's thought experiment. I might add here that this would further contradict ash64449's claim that only proper times can ever be measured, because in this case there wouldn't be any proper times. However, if the definition of coordinate time is that which I have provided...


http://en.wikipedia.org/wiki/Coordinate_time

"In the special case of an inertial observer in special relativity, by convention the coordinate time at an event is the same as the proper time measured by a clock that is at the same location as the event, that is stationary relative to the observer and that has been synchronised to the observer's clock using the Einstein synchronisation convention."​

...then it seems to me that my calculated coordinate times $$t'_L$$ and $$t'_R$$ are also "proper times" because clocks on the train which are Einstein synchronized and co-located with the lightning events would measure the times that I calculated. That is, those clocks fulfill the requirements of the above special case. In this context, "proper time" seems to be defined differently than your definition, because it seems to apply to a single event. Actually, the two events in this context are the beginning of the experiment (when the clock was set to zero), and the measurement of the event. In that context, all E-synched clocks display proper times, and perhaps that is why ash64449 insists that only proper times can be measured.

Regardless of whether my times are proper times or not, they are certainly times which can be measured, in direct contradiction to ash64449's claims.

 

[Tach]

Pretty much everyone seems to have agreed that relativity of simultaneity (RoS) is not technically measurable, because to measure simultaneity one needs a clock synchronization scheme. For reasons explained in the links in post 95, clock synch schemes are inherently untestable, so RoS is also untestable by extension.

Correct. The thread should have closed here.

The debate is still going on about whether the one-way speed of light (OWLS) can be measured experimentally.

This is incorrect, there is no debate on this subject, OWLS is not measurable. What is measurable is OWLS anisotropy.

I think I speak for everyone in the thread except Tach when I say that the links in post 95 all seem to indicate that the isotropy of OWLS is equivalient to the validity of Einstein clock synchronization (E-synch), so if E-synch is untestable, it follows that the isotropy of OWLS (or at least, the absence of certain classes of OWLS anisotropy) must be untestable as well. Tach has been arguing against this by citing a frankly jaw-dropping number of papers which he claims measure the isotropy of OWLS.

Ain't mainstream science a bitch? Anyways, I think that you should open a separate thread about OWLS anisotropy-constraining experiments. This thread has run its course, the answer to the title question is "no".

 

[Fednis48]

Neddy Bate: I definitely agree that ash was wrong in pretty much all of his substantive conclusions. I just wanted to step in and correct an issue of vocabulary. I'm glad you provided the Wikipedia definition you did, but I think it's actually more a statement of convention than an actual definition:

"In the special case of an inertial observer in special relativity, by convention the coordinate time at an event is the same as the proper time measured by a clock that is at the same location as the event, that is stationary relative to the observer and that has been synchronised to the observer's clock using the Einstein synchronisation convention."​

Since we can set the zeros of our clocks at arbitrary times, it makes sense come up with a convention by which we can zero clocks in different frames consistently. The above is apparently such a convention, and I didn't know about it until now. But measuring RoS depends more on the time interval between events than the raw time-coordinates of the events individually, and I am quite certain that proper time interval is not the same as coordinate time interval. If nothing else, proper time interval is invariant while coordinate time interval is not, so they can't be the same thing.

Tach: Welcome back. I agree that if it is to be discussed further at all, the measurability of OWLS should be migrated to a separate thread. I'm pretty exhausted on the issue so I won't start such a thread, but if you do I'll be sure to chime in.

 

[Neddy Bate]

Neddy Bate: I definitely agree that ash was wrong in pretty much all of his substantive conclusions. I just wanted to step in and correct an issue of vocabulary.

Yes, your point is well-taken. I should have just stuck with my original claim that the coordinate times of the lighting strikes would be measurable in both frames. But when I saw the special-case definition of coordinate time, I thought I could use that to support the idea that the times I calculated are meaningful (if not proper) times.

I'm glad you provided the Wikipedia definition you did, but I think it's actually more a statement of convention than an actual definition:

"In the special case of an inertial observer in special relativity, by convention the coordinate time at an event is the same as the proper time measured by a clock that is at the same location as the event, that is stationary relative to the observer and that has been synchronised to the observer's clock using the Einstein synchronisation convention."​

Since we can set the zeros of our clocks at arbitrary times, it makes sense come up with a convention by which we can zero clocks in different frames consistently. The above is apparently such a convention, and I didn't know about it until now.

The Lorentz transforms are easiest to use if the clock at rest with $$x=0$$ and the clock at rest with $$x'=0$$ both display $$t=0$$ and $$t'=0$$ (respectively) at the time when they are co-located with each other. Even if that never happened in reality, it is best if that happened at the "theoretical" beginning of the experiment. They also require that all clocks are Einstein synchronized in their own rest frames. So, those are the conventions that we tend to adhere to in order to make using the Lorentz transforms as simple as possible.

But measuring RoS depends more on the time interval between events than the raw time-coordinates of the events individually,

Well, if one frame measures two events to have the same time coordinate, and if the other frame measures those same two events to have two different time coordinates, then RoS has been measured. The interval itself does not matter, as long as it is non-zero in one frame, and zero in the other.

and I am quite certain that proper time interval is not the same as coordinate time interval. If nothing else, proper time interval is invariant while coordinate time interval is not, so they can't be the same thing.

I agree that they are not the same thing. But, given the conventions we tend to adhere to, the time displayed on any E-synched clock does represent the proper time that has elapsed since that clock was set to zero at the "theoretical" beginning of the experiment. That is one of the things which makes the times displayed on clocks meaningful.

 

[ash64449]

Thanks for trying to sort this out. Please consider that ash64449 insists that only proper times can be measured, that coordinate times cannot be measured, and that RoS cannot be measured because it involves coordinate times. So, when you agree with me that the train frame does measure the coordinate times that I calculated, you are saying ash64449 is incorrect, not the other way around.

As far as the term "proper time" is concerned: If the definition is that which you have provided, (that a single inertial clock must be present at both events), then indeed there is no proper time between the lightning strikes in Einstein's thought experiment. I might add here that this would further contradict ash64449's claim that only proper times can ever be measured, because in this case there wouldn't be any proper times. However, if the definition of coordinate time is that which I have provided...


http://en.wikipedia.org/wiki/Coordinate_time

"In the special case of an inertial observer in special relativity, by convention the coordinate time at an event is the same as the proper time measured by a clock that is at the same location as the event, that is stationary relative to the observer and that has been synchronised to the observer's clock using the Einstein synchronisation convention."​

...then it seems to me that my calculated coordinate times $$t'_L$$ and $$t'_R$$ are also "proper times" because clocks on the train which are Einstein synchronized and co-located with the lightning events would measure the times that I calculated. That is, those clocks fulfill the requirements of the above special case. In this context, "proper time" seems to be defined differently than your definition, because it seems to apply to a single event. Actually, the two events in this context are the beginning of the experiment (when the clock was set to zero), and the measurement of the event. In that context, all E-synched clocks display proper times, and perhaps that is why ash64449 insists that only proper times can be measured.

Regardless of whether my times are proper times or not, they are certainly times which can be measured, in direct contradiction to ash64449's claims.

Well, Did i say that we cannot measure coordinate time?

 

[ash64449]

Neddy Bate: I definitely agree that ash was wrong in pretty much all of his substantive conclusions.

Where was i wrong?? As far as i saw Neddy Bete's today's post.. I do agree with him.

 

[ash64449]

...then it seems to me that my calculated coordinate times $$t'_L$$ and $$t'_R$$ are also "proper times" because clocks on the train which are Einstein synchronized and co-located with the lightning events would measure the times that I calculated. That is, those clocks fulfill the requirements of the above special case. In this context, "proper time" seems to be defined differently than your definition, because it seems to apply to a single event. Actually, the two events in this context are the beginning of the experiment (when the clock was set to zero), and the measurement of the event. In that context, all E-synched clocks display proper times, and perhaps that is why ash64449 insists that only proper times can be measured.
.

Yes. This does makes sense.. I mean we will be able to measure coordinate time. Well,the reason i argued with you is that you said that Lorentz Transformation is about knowing proper time. But it's not. It is about measuring MAINLY Time coordinate. Understood?

 

[Neddy Bate]

Yes. This does makes sense.. I mean we will be able to measure coordinate time. Well,the reason i argued with you is that you said that Lorentz Transformation is about knowing proper time. But it's not. It is about measuring MAINLY Time coordinate. Understood?

I am very happy that we finally agree! My whole point was that the train measures two different times $$t'_L$$ and $$t'_R$$ for the lightning strikes, and the embankment measures a single time $$t$$ for the lightning strikes. So, do you agree that this means we can measured RoS?

 

[OnlyMe]

I am very happy that we finally agree! My whole point was that the train measures two different times $$t'_L$$ and $$t'_R$$ for the lightning strikes, and the embankment measures a single time $$t$$ for the lightning strikes. So, do you agree that this means we can measured RoS?

Neddy, I started out with Einstein's 1920 hypothetical because it included a train with a classical velocity and I had hoped that there would be an analog that would work out... After reading the paper you referenced I saw that, that was an error. The reason is that at classical velocities even given today's clocks and synchronization, the measurement and systemic error, would very likely be greater than any difference in the measurement of time, between the two frames.

That leaves only a relativistic analog as a possible test and relativistic velocities are not possible, for things like clocks and measuring devices, let alone observers. Which leaves the comparison to one arrived at by way of Lorentz transformation etc... And there's the nut.., transformations are not measurements.

I think Pete was right, when he limited his case to in principle measureable, rather than suggesting any practical test.

The key point is in defining what is acceptable as measurement, in both frames.

 

[ash64449]

I am very happy that we finally agree! My whole point was that the train measures two different times $$t'_L$$ and $$t'_R$$ for the lightning strikes, and the embankment measures a single time $$t$$ for the lightning strikes. So, do you agree that this means we can measured RoS?

Yes, I agree that train measure different 'time coordinate'[important one: not 'proper time' Agree?(note also before answering that coordinate time cannot always be equal to proper time)] compared to embankment frame.

You began after that train frames are synchronized. So clock that measures is coordinate time and not proper time and as a result:

The embankment frame will say that clocks are not synchronized in the train frame.

Agree?

 

[Neddy Bate]

Yes, I agree that train measure different 'time coordinate'[important one: not 'proper time' Agree?(note also before answering that coordinate time cannot always be equal to proper time)] compared to embankment frame.

I agree that the time coordinates $$t'_L = \gamma(t - \frac{vx_L}{c^2})$$ and $$t'_R = \gamma(t - \frac{vx_R}{c^2})$$ are coordinate times.

I also agree that $$t'_L-t'_R = \gamma(t - \frac{vx_L}{c^2}) - \gamma(t - \frac{vx_R}{c^2})$$ does NOT represent the proper time elapsed between the two lighting strikes.

However, I still maintain that $$t'_L-t'_R = \gamma(t - \frac{vx_L}{c^2}) - \gamma(t - \frac{vx_R}{c^2})$$ DOES represent the elapsed time between the two lighting strikes, as measured by the train frame.


Please note that the same thing applies to the embankment frame. The time coordinate $$t$$ is a coordinate time. Since both lightning strikes happen at the same time, $$t - t$$ represents the elapsed time between the two lighting strikes, as measured by the embankment frame. But $$t - t$$ does NOT represent the proper time elapsed between the two lighting strikes.

As Fednis48 explained, it does not make sense to talk about the proper time elapsed between the two lighting strikes. Elapsed proper time must be measured by a single inertial clock co-located with both events. No such clock would be possible in this case, because it would have to travel instantaneously between $$x_L$$ and $$x_R$$. Do you agree?

You began after that train frames are synchronized. So clock that measures is coordinate time and not proper time and as a result:

The embankment frame will say that clocks are not synchronized in the train frame.

Agree?

Yes, I agree. But the train frame would argue that the clocks at rest with the train ARE synchronized, and that the clocks at rest with the embankment frame are not synchronized. Do you agree?