Try this thought experiment.

 

If 2 identical clocks are synchronised and then accelerated from rest to nearly C. One of them is then stopped and the other carries on at a constant velocity for a certain time period. The second one is the decelerated to a stop and accelerated back to nearly C towards the first. As it approaches the first clock accelerates up to nearly C, so they are travelling together back to the original start position where the both decelerate together to a stop.

 

Would the clocks be synchronised.

 

If no, why not, because the only lack of symmetry is the length of time that one moved away from the other, at close to C, and who can say which one was travelling.

 

If they are synchronised is time reletive to velocity?

Would the clocks be synchronised.

No

 

If no, why not, because the only lack of symmetry is the length of time that one moved away from the other, at close to C,

There is also lack of symmetry in their acceleration.

 

and who can say which one was travelling.

you did, from your initial/final position.

All you appear to have done is take the twin paradox and put in some common movement that should affect the clocks in an identical fashion.

Try this thought experiment.[/b']?

 

No question in my mind that in this thought experiment the clock that went further will be "younger", primarily due to the due to the SR effect. The GR effects could be symmetrical.

 

I do wonder: What is the "BEST" experimental evidence to support this. All evidence I have seen has a major GR component chomping into any margin of error.

 

It is impossible to get any results on SR without being exposed to some GR effects. The best we can hope for is to make them symmetrical (with respect to what though, time or distance etc.) or to factor them out based on theory.

 

It is also impossible to make them perfectly symmetrical or you would be duplicating the same test. No comparison could be made.

 

Apologies if any of that does not make sense.