B How do we identify a stationary system?

[PeterDonis]

This is necessary to communication accurate local times between A and B, in order to synchronizing their clocks.

No, you have it backwards. You have to synchronize the clocks at A and B first in order to communicate accurate local times between A and B according to a particular inertial frame. How you synchronize the clocks at A and B determines which inertial frame the times on the clocks correspond to.

 

[Sagittarius A-Star]

A is a light source B is a mirror, so t A, t B, and t ′A are the times of emission, reflection and return respectively.
You can adjust the distance between and the times of A and B, but that is irrelevant to the purpose of the definition, and testing it, which it to find out if the time for light to travel from A to B is equal to the time for it to travel from B to A.

This is necessary to communication accurate local times between A and B, in order to synchronizing their clocks.

The isotropy of the one-way-speed is only a convention. In his popular book from 1916, Einstein wrote in part 1, section 8:

That light requires the same time to traverse the path $A \rightarrow M$ as for the path $B \rightarrow M$ 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."

Source:
https://en.wikisource.org/wiki/Rela..._I#Section_8_-_On_the_Idea_of_Time_in_Physics

 

[Dale]

Yes I will learn from the answers.

If you wish to learn from the answers, as you stated that you did, then please pay attention. When I say “you are missing the point” I am not inviting you to argue. I am telling you that the past 118 years of scientists have learned something about this and you have missed the lesson that we have learned. Whole books and many follow-up papers have delved into this topic in exceptional depth, and you did not understand the concept correctly. To learn you will need to abandon your erroneous concept and learn the correct one.

You can adjust the distance between and the times of A and B, but that is irrelevant to the purpose of the definition,

No. As I stated, the purpose is to establish how two distant clocks can be synchronized. Yes, you can also adjust the distance, but doing so does not change the synchronization status. It is only adjusting $t_B$ that will change the synchronization.

and testing it, which it to find out if the time for light to travel from A to B is equal to the time for it to travel from B to A.

We are not testing the invariance of $c$, that is already postulated. We are exploring the practical consequences and utility of the invariance of $c$. The useful consequence of the invariance of $c$ is an operational method for synchronizing distant clocks.

 

[Ibix]

How did Einstein synchronize his clocks in the stationary system unless he “assumes” a privileged, absolute state of rest?

He synchronised his clocks by adjusting one of them until they both agree on the lag of the other. Any pair of clocks that are mutually at rest can do this. Two pairs of clocks synchronised this way that are not at rest with respect to the other pair (i.e. clocks A and B move with speed v and are synchronised by their own measure, clocks C and D move with speed u and are synchronised by their own measure) will not agree on the same synchronisation.

Some of you are trying to teach Einstein, not me.

No - you have not understood what Einstein is saying, so you see conflict between what we say and your misunderstanding of what he said.

I think we have already agreed this equality is not found in their measures. And no matter how much we adjust the times on either clock, the time of a light path from A to B will never be the same as the time of a light path B to A when AB is a rigid rod in motion.

Nobody agrees with you on this, not here and not Einstein.

 

[Sagittarius A-Star]

So my question #2 is:
How did Einstein synchronize his clocks in the stationary system unless he “assumes” a privileged, absolute state of rest?

Only clocks at rest in the "stationary system" can be synchronized with reference to the "stationary system".

 

[Ibix]

Only clocks at rest in the "stationary system" can be synchronized with reference to the "stationary system".

A bit of care needed with that statement. Clocks in the same state of motion can be synchronised in the sense that they show the same time as each other according to any frame's simultaneity convention (edit: which will not match their own frame's synchronisation convention). They don't tick at the correct rate except in their own rest frame, of course.

 

[Sagittarius A-Star]

They don't tick at the correct rate except in their own rest frame, of course.

Yes. About this, Einstein 1905 creates confusion, see:
https://www.physicsforums.com/threads/sr-which-clock-was-slower.993341/post-6392678

 

[CClyde]

He synchronised his clocks by adjusting one of them until they both agree on the lag of the other.

If that can be done it would certainly answer my question
Can you tell me how that is done?

 

[Ibix]

If that can be done it would certainly answer my question
Can you tell me how that is done?

Um... You look at the other clock and see how far out of sync it appears to be. Then you go to the other clock and see how far out the first one appears. Whichever one lags more, you reset it by the half the difference in the apparent lags. Job done. It's not rocket science. It's pretty much how you sync your wristwatch to a wall clock, if you have an old school one that doesn't do it itself.

 

[Ibix]

So, say I stand at clock A. It reads 12.00.00, and clock B reads (from this distance) 12.00.04. Then I go over to clock B. Time has passed and it now reads 1.00.00 and clock A reads 12.59.54. That's a ten second difference in the apparent lag (+4 vs -6) so I step the lead clock back by five seconds. You should be able to see that they now both appear one second slow seen from the other clock, which implies they are synchronised, but the further clock appears slow due to light speed lag over a one light second separation.

 

[malawi_glenn]

Some of you are trying to teach Einstein, not me.

Einstein is dead, we can't teach him.
What we can teach you is how you have misunderstood the arguments of Einstein.

 

[Ibix]

Yes. About this, Einstein 1905 creates confusion, see:
https://www.physicsforums.com/threads/sr-which-clock-was-slower.993341/post-6392678

Agreed. In the century plus since the paper was published it's become clear that there are less convoluted ways of getting to Einstein's results.

 

[PeterDonis]

Thread closed for moderation.

 

[PeterDonis]

After moderator review, the thread will remain closed as the OP is now taking a temporary vacation.