Is relativity of simultaneity measurable?

[Neddy Bate]

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.

I did some quick calculations, and it looks like the reference frame of the Apollo spacecraft would have measured events on the moon and on earth as being about 40 microseconds apart, (for the case where said events would be simultaneous in the reference frame of the moon-earth system.) I did not include the effects of gravity though, just the spacial separation of the earth & moon, and the speed of the Apollo spacecraft. I don't know if they had clocks capable of measuring to 40 microsecond accuracy aboard the Apollo, but we certainly have them now.

 

[ash64449]

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?

Of course I agree!! This is what i wanted to explain.. But reached somewhere else...

 

[ash64449]

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?

Agree.But They would be comfortable. Because they know that cause of it!!!

 

[ash64449]

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.

Yeah!! I agree too!!! It does represent elapsed "Co-ordinate time".

But i have a question.... What were we arguing about actually???

 

[ash64449]

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.

YES!!!! This is the one that i wanted!!! At last you agree!!

Note: I didn't argue in reality whether RoS is measurable. I saw somewhere in your post that you used to say the above as representing proper time. So i argued against it. Only that.. Nothing else.

 

[Neddy Bate]

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?

Of course I agree!!

Excellent. So there is no need to talk about the proper time elapsed between the lighting strikes. Are there any proper times which you think are pertinent to this discussion?

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.

Yeah!! I agree too!!! It does represent elapsed "Co-ordinate time".

Please note that I am saying those coordinate times are what would be measured in the train frame.

But i have a question.... What were we arguing about actually???

We are arguing because you said those coordinate times could not be measured!!!! Look here:

But observers can only measure "proper" time and Not "co-ordinate" time.

So, now, do we finally agree that the coordinate times which I calculated represent the times of the lighting strikes, as measured by the train frame? And if so, do we finally agree that RoS is measurable?

 

[ash64449]

We are arguing because you said those coordinate times could not be measured!!!! Look here:

I have mistaken.. Sorry for that response.

So, now, do we finally agree that the coordinate times which I calculated represent the times of the lighting strikes, as measured by the train frame? And if so, do we finally agree that RoS is measurable?

Well, Note directly measurable. I mean both observers need to come together for final results.

So,indeed this way Relativity Of Simultaneity is measurable Indirectly.

 

[Layman]

Time dilation itself is measurable. There was a famous experiment where they took atomic clocks around the world in an airplane. The clocks where then compared after the flight was over next to each other (same frame of reference). So then the time dilation or difference between the clocks was not only noticed while in flight, but also after the clocks where both set at rest. I would think that this would mean that it is a real effect and not just an illusion caused by differences in motion. Otherwise the clocks would only look to be out of sync during the flight and not when they came back together.

I don't see a clear distinction of why you mention Relativity of Simultaneity and not just the time dilation itself as being measurable. Does this imply that you are assuming that there are different forms of time dilation? There should be only one.

 

[ash64449]

I don't see a clear distinction of why you mention Relativity of Simultaneity and not just the time dilation itself as being measurable. Does this imply that you are assuming that there are different forms of time dilation? There should be only one.

Yeah.. Time dilation is about change in coordinate time of different reference frame depends on their state of motion observed in a frame of reference.

I agree RoS is measurable indirectly.

 

[ash64449]

Time dilation itself is measurable. There was a famous experiment where they took atomic clocks around the world in an airplane. The clocks where then compared after the flight was over next to each other (same frame of reference). So then the time dilation or difference between the clocks was not only noticed while in flight, but also after the clocks where both set at rest. I would think that this would mean that it is a real effect and not just an illusion caused by differences in motion. Otherwise the clocks would only look to be out of sync during the flight and not when they came back together.

It was measurable because airplane was accelerating. So persons in the airplane and the person on earth have different proper times.

And that's what the clocks measured.

 

[Layman]

Yeah.. Time dilation is about change in coordinate time of different reference frame depends on their state of motion observed in a frame of reference.

I think Relativity of Simultaneity over simplifies the actual cause of time dilation. If it was like you say just a change in how two coordinate systems observe each other then you would think that the atomic clocks in the mentioned experiment wouldn't read different times after set back on the ground at rest relative to each other. But they did, and science dictates fact based off actual experiments.

I agree it is measurable indirectly.

I don't agree, as I just mentioned that was measured directly from experiment. Wasn't sure if you were trying to make a distinction between time dilation caused by relative motion or time dilation caused by acceleration or gravity. To me any other type of distinction is irrelevant.

The atomic clocks directly measured that difference between relative motion and acceleration. As they sat next to each other at rest they were reading different times.

 

[Layman]

It was measurable because airplane was accelerating. So persons in the airplane and the person on earth have different proper times.

And that's what the clocks measured.

No, they didn't only measure the acceleration. If they did, the planes would have only had to have taken off and then immediately landed again and then measure the same difference in their readings. The effect is so small they had to fly the planes around the globe.

 

[ash64449]

I think Relativity of Simultaneity over simplifies the actual cause of time dilation.

RoS does not 'cause' Time Dilation.

If it was like you say just a change in how two coordinate systems observe each other then you would think that the atomic clocks in the mentioned experiment wouldn't read different times after set back on the ground at rest relative to each other. But they did, and science dictates fact based off actual experiments.

They read different times because airplane was accelerating so both of them have different proper times,That's what clocks measured.

I don't agree, as I just mentioned that was measured directly from experiment. Wasn't sure if you were trying to make a distinction between time dilation caused by relative motion or time dilation caused by acceleration or gravity. To me any other type of distinction is irrelevant.
As they sat next to each other at rest they were reading different times.

See the above statement

 

[ash64449]

No, they didn't only measure the acceleration. If they did, the planes would have only had to have taken off and then immediately landed again and then measure the same difference in their readings. The effect is so small they had to fly the planes around the globe.

What are you trying to say? I only said they have different proper times. that's all.

 

[Layman]

RoS does not 'cause' Time Dilation.

That's a new one I haven't heard before. Last time I checked it was the Holy Grail of physics.

They read different times because airplane was accelerating so both of them have different proper times,That's what clocks measured.

Acceleration only determines what clock actually reads slower when they come back together. If a clock is sent on a plane for a trip that last 24 hours it will not be off by as much as a clock that has been sent on a plane for 48 hours.

 

[Layman]

What are you trying to say? I only said they have different proper times. that's all.

That clocks in different frames of references traveling at a relative speed to each other actually tick at different rates.

 

[ash64449]

That clocks in different frames of references traveling at a relative speed to each other actually tick at different rates.

You cannot use the word "actually".

Let me say why. An object is observed to move at 0.6c in one frame of reference and in other frame of reference it is observed that the same object moves 0.8c in other frame of reference.

What is the "actual" time measured by the clock of that object?!!!

So you cannot use the word "actual" because Time Dilation is coordinate effect or effect that depends on two frames of coordinate systems. that's why Time is Relative!!! Got that?

Clocks measured different time because both of them have followed different proper time. Why different proper time?? Because air plane is accelerating. It is a distinguishable quantity.

Do you know the difference between the proper time and coordinate time?

 

[ash64449]

Acceleration only determines what clock actually reads slower when they come back together. If a clock is sent on a plane for a trip that last 24 hours it will not be off by as much as a clock that has been sent on a plane for 48 hours.

Yes. see above. acceleration causes difference in proper time. same as what i said. I went a little "deep". That's all.

 

[ash64449]

That's a new one I haven't heard before. Last time I checked it was the Holy Grail of physics.

Sorry, What are you trying to say from this statement? You should be straightforward. Don't make us to understand indirectly.

 

[Layman]

You cannot use the word "actually".

I just did and you actually did too.

Let me say why. An object is observed to move at 0.6c in one frame of reference and in other frame of reference it is observed that the same object moves 0.8c in other frame of reference.

So then how could the object that is moving at 0.8 c actually measure the same speed of light? It would actually have to measure time differently in order to measure it traveling the same speed that the object moving at 0.6 c would measure it.

Time would have to actually go slower and the distance would actually have to be shorter in order for two objects moving at different speeds to actually measure the same object from both frames actually traveling at the same speed.

What is the "actual" time measured by the clock of that object?!!!

The amount of time it would take to actually measure the correct speed of light.

So you cannot use the word "actual" because Time Dilation is coordinate effect or effect that depends on two frames of coordinate systems. that's why Time is Relative!!! Got that?

If I couldn't use the word actual and it was something that was actually happening then I would never be able to prove my point that was actually what was going on. Got that?

Clocks measured different time because both of them have followed different proper time.

I think they actually tick at different rates because of the proper time. There wouldn't be a need for a proper time if they didn't actually tick at different rates.

Do you know the difference between the proper time and coordinate time?

In the theory of relativity, it is convenient to express results in terms of a spacetime coordinate system relative to an implied observer. In many (but not all) coordinate systems, an event is specified by one time coordinate and three spatial coordinates. The time specified by the time coordinate is referred to as coordinate time to distinguish it from proper 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.