[guest39538]

The clocks are never out of synchronisation if the clock is being used correctly i.e 1=1

If you move one clock relative to another, you will necessarily push them out of synchronisation - the only issue is how much, with faster speeds of movement pushing them out of sync by more.

I understand the distance contractions/expansions would cause an issue in timing, sorry I thought you were trying to still say there was a time dilation.

Moving a clock slows its ticking. If you want to drag length-contraction in too, then it reduces the slowing of the ticking (by making it the same no matter which way the clock is aligned), but you still have slowed ticking while the clock's moving.

But all the slowed ticking means is the timing mechanism is out of synchronisation, there is no actual physical length contraction, there is just more or less distance the light has to travel from or .  This in no way affects the rate of time it affects the rate of timing.  It is not much difference to when a timing belt slips and a car misfires. 

The clocks only become out of synchronisation because they are not very good clocks.

[Bored chemist]

The clocks are never out of synchronisation if the clock is being used correctly i.e 1=1

If you move one clock relative to another, you will necessarily push them out of synchronisation - the only issue is how much, with faster speeds of movement pushing them out of sync by more.

Aha!
Progress!
Imagine that I repeat the thought experiment I did earlier (the one where I was carrying a clock round on a bicycle).
I repeat it several times, but I use different modes of transport..
With  a space ship, the difference between the "expected" value for m and 10,000 is larger tan when I use a jet plane.
And that, in turn is bigger than when I use a bike.
The version where I uses continental drift to move the clocks gives a result even closer to 10,000.

So, I can measure the 1 way speed of light by extrapolation of the speed as I move the clocks slower.
In the limit I can calculate it for moving the clocks at zero speed.

Is there any reason to suppose that, if I did that, the limiting value I would get for the 1 way speed of light was any different from C?

[GoC]

So, I can measure the 1 way speed of light by extrapolation of the speed as I move the clocks slower

When you move a clock it is not measuring the speed of light. It is measuring the distance light travels through space. Speed does not matter on the Earth from the continental drift to a light beam. All clocks tick at the same rate at sea level. Simultaneity of relativity does not consider time of movement a factor. Frequency of light does not change the speed of light but it does affect the tick rate of a clock. This affect causes clocks to measure distance indirectly as simultaneity of relativity.

[Bored chemist]

When you move a clock it is not measuring the speed of light.

How fortunate, then, that nobody said it was. Why did you raise the issue?

Measuring the speed of light is when I measure the time it takes for light to travel through a known distance- from 1 clock to the other.
"All clocks tick at the same rate at sea level."
Moving ones don't.
That's the whole damned point.

[GoC]

Measuring the speed of light is when I measure the time it takes for light to travel through a known distance- from 1 clock to the other."All clocks tick at the same rate at sea level."Moving ones don't.That's the whole damned point.

Of course. But speed between clock positions does not affect the difference in reading on the moved clock.

[guest39538]

So, I can measure the 1 way speed of light by extrapolation of the speed as I move the clocks slower

When you move a clock it is not measuring the speed of light. It is measuring the distance light travels through space. Speed does not matter on the Earth from the continental drift to a light beam. All clocks tick at the same rate at sea level. Simultaneity of relativity does not consider time of movement a factor. Frequency of light does not change the speed of light but it does affect the tick rate of a clock. This affect causes clocks to measure distance indirectly as simultaneity of relativity.

Simultaneity of clocks at rest in an  inertia reference frames is directly related to the mass of the inertia reference frame.  If m1 is different to m2, the clocks on m1 and m2 will tick differently.   I consider this is all simultaneity is .

[Bored chemist]

OK, so which of these is true?

But speed between clock positions does not affect the difference in reading on the moved clock.

the only issue is how much, with faster speeds of movement pushing them out of sync by more.

[David Cooper]

Imagine three clocks that are sitting together. They are wired together and connected to a button which can be used to synchronise them all. We press the button, then we send two of the clocks away in opposite directions. If the central clock is not moving through space, the other two clocks will tick more slowly as they are moved through space. TheBox doesn't seem to understand this point, but if you move the clocks at the speed of light they will stop functioning completely while they're being moved, so if you move them one lightsecond of distance away and then leave them there, the two clocks that you've moved will start ticking again, but they're both one second behind the central clock. The two outer clocks are synchronised with each other, but they're not synchronised any more with the central clock.

If we move the clocks out more slowly, we allow them to tick while they're moving, and the slower we move them out to their destinations, the less far behind they will lag in their ticking behind the central clock, but there will always be a lag. The two outer clocks will be synchronised with each other though without any such lag, so that should give you a clue as to a better method for synchronising clocks - if you're using two of them, you have to move both of them in opposite directions the same distance and at the same speed.

If you can get that idea into your head, the next thing to consider is what happens the system isn't stationary. When you move the clocks apart, one of them may be moving faster through space than the other, so that means it will tick more slowly than the other while they're being moved into position from the central point. That adjusts the synchronisation. We can still do this with three clocks so that we keep a central clock which never accelerated. The faster we move the clocks apart, the further out of sync the central clock will be with the outer two, but we can work out how to correct for that to remove that additional lag for the outer clocks, thereby getting them all to the same synchronisation they would have if we had somehow been able to move the clocks apart infinitely slowly. The clocks are not in sync though, because the one that moved fastest through space lags behind the other two, and the clock that moved the opposite way will be ahead of the other two with its timings (after the correction has been made either to the central clock or the two outer clocks). This difference in synchronisation will guarantee that when you use these synchronised clocks (which will only be displaying the same time simultaneously if the system is stationary), your attempted measurement of the one-way speed of light will always produce the answer c regardless of the actual speed of light relative to the system.

[GoC]

Imagine three clocks that are sitting together. They are wired together and connected to a button which can be used to synchronise them all.

That is impossible if you understand relativity.

If we move the clocks out more slowly, we allow them to tick while they're moving, and the slower we move them out to their destinations, the less far behind they will lag in their ticking behind the central clock, but there will always be a lag. The two outer clocks will be synchronised with each other though without any such lag, so that should give you a clue as to a better method for synchronising clocks - if you're using two of them, you have to move both of them in opposite directions the same distance and at the same speed.

Are we in the solar system? How fast is the solar system spinning? Are we in a galaxy? How fast is the galaxy spinning? Are you going with the spin or against the spin? How do you determine not moving?

The clocks are not in sync though, because the one that moved fastest through space lags behind the other two,

Your clock is a measure of distance by distance. One light second distance from rest no matter how fast or how slow will register one second difference. The electron in your clock measures the distance in reduction of tick rate due to further distance for the constant electron to travel through. Electron distance is confounded with the distance the light goes through.

[David Cooper]

Imagine three clocks that are sitting together. They are wired together and connected to a button which can be used to synchronise them all.

That is impossible if you understand relativity.

If you happen to be moving through space at 99.9999c there will be a big synchronisation error as the clocks can never quite be in a single location no matter how close together you put them, but this will be a trivial error compared with the synchronisation differences once the clocks have been moved apart. For this reason, it is generally considered possible to synchronise two (or more) clocks at a single location.

Are we in the solar system? How fast is the solar system spinning? Are we in a galaxy? How fast is the galaxy spinning? Are you going with the spin or against the spin? How do you determine not moving?

Bored chemist referred to a flat world to eliminate such problems from his scenario. He could alternatively have put the system in deep space. If you're working in a lab though and only want to move the clocks from the middle to the ends of the room, any rotations of the lab are unimportant so long as the clocks are always aligned on a straight line. If you want to work on the Earth's surface and move the clocks thousands of miles apart, you can't going to end up with all three clocks in a straight line, so you can't do the synchronisation this way. It's a good idea though if you understand the difficulties of synchronising clocks on a straight line first before you start trying to understand the extra complications of moving them round a curved surface of a spinning object.

The clocks are not in sync though, because the one that moved fastest through space lags behind the other two,

Your clock is a measure of distance by distance. One light second distance from rest no matter how fast or how slow will register one second difference. The electron in your clock measures the distance in reduction of tick rate due to further distance for the constant electron to travel through. Electron distance is confounded with the distance the light goes through.

Does what you've said negate what I said in some way? Two clocks moved in opposite directions, but one was moving faster through space, so its asserted time lags behind that of the other clock.

[Bored chemist]

Imagine three clocks that are sitting together. They are wired together and connected to a button which can be used to synchronise them all. We press the button, then we send two of the clocks away in opposite directions. If the central clock is not moving through space, the other two clocks will tick more slowly as they are moved through space. TheBox doesn't seem to understand this point, but if you move the clocks at the speed of light they will stop functioning completely while they're being moved, so if you move them one lightsecond of distance away and then leave them there, the two clocks that you've moved will start ticking again, but they're both one second behind the central clock. The two outer clocks are synchronised with each other, but they're not synchronised any more with the central clock.

If we move the clocks out more slowly, we allow them to tick while they're moving, and the slower we move them out to their destinations, the less far behind they will lag in their ticking behind the central clock, but there will always be a lag. The two outer clocks will be synchronised with each other though without any such lag, so that should give you a clue as to a better method for synchronising clocks - if you're using two of them, you have to move both of them in opposite directions the same distance and at the same speed.

If you can get that idea into your head,

I can get it into my head just fine that your plan to synchronise the clocks won't work because there is a delay (typically the product of the square root of dielectric constant of the insulation on the wires and the distance divided by c IIRC).
So you are not actually synchronising the clocks with the one in the middle- we know there's a delay.
The delay may well be the same in each direction but, as you can reduce it to zero by moving them slowly...
Adding a 3rd clock doesn't really seem to add anything.

Re " if you move the clocks at the speed of light they will stop functioning completely while they're being moved, "
Then don't.
Why choose the state of affairs where the error you introduce is as big as possible?
Why not move them slowly so they stay (arbitrarily close to) synchronised?

[David Cooper]

I can get it into my head just fine that your plan to synchronise the clocks won't work because there is a delay (typically the product of the square root of dielectric constant of the insulation on the wires and the distance divided by c IIRC).

How are you synchronising them then when you have two clocks together? Are you pressing buttons on both of them and getting an error of up to a tenth of a second instead of using one button to start both? I can assure you that my way of doing it is more accurate. The big question though is about getting clocks synchronised at a distance and the errors that necessarily find their way into that, so the trivial business of how synchronising clocks at a single location is done is a trivial sideshow.

So you are not actually synchronising the clocks with the one in the middle- we know there's a delay.
The delay may well be the same in each direction but, as you can reduce it to zero by moving them slowly...
Adding a 3rd clock doesn't really seem to add anything.

I brought the third clock into this to try to help you see how awful your synchronisation method is. If you synchronise the three clocks at the central location, you can then move two of them away from there in opposite directions at the same speed to get them where you want them to be. Those two clocks are now as just about as well synchronised with each other as they can be, but only if the system happens to be stationary rather than moving fast through space. The middle clock though is badly synchronised with them, and the faster you moved the other two clocks into position, the worse the synchronisation with the middle clock will be. You only have two clocks, and one of them is being treated like my middle clock, so you're getting the huge error in your synchronisation instead of the minimal error with my two outer clocks. If you know how fast you moved your moving clock relative to your stationary clock though, you can adjust the timing of one or other of them to correct that synchronisation, at which point your clocks can be just as well synchronised as my pair of moved clocks. In both cases though, even that superior synchronisation will be affected by the movement of the system through space, so one clock's time may be far ahead of the other, which is why when you use them to attempt to measure the one-way speed of light, you are guaranteed to get the value c regardless of the actual speed of the light that you're timing relative to the system.

Re " if you move the clocks at the speed of light they will stop functioning completely while they're being moved, "
Then don't.

Imagine a light clock aligned with the direction you're moving it in. If you move this clock at c, the clock will stop clicking throughout the time you're moving it because the light would have to travel faster than c in order to complete a circuit (and thereby to tick). All clocks are limited in the same way, slowed to the same extent by their movement through space.

Why choose the state of affairs where the error you introduce is as big as possible?
Why not move them slowly so they stay (arbitrarily close to) synchronised?

The faster you move your only moved clock into position, the sooner you can start using your clocks to make measurements. It would be stupid to take a million years to move your clock into position just to minimise a predictable error which you can simply adjust for. That error is a complication which you want to eliminate, and it's a diversion away from the nature of the real error that you cannot correct for - the undetectable error affects all methods of synchronisation and it affects them equally. It's caused by the communication delay in one direction being longer than in the opposite direction if the system is moving through space.

[guest39538]

Imagine three clocks that are sitting together. They are wired together and connected to a button which can be used to synchronise them all. We press the button, then we send two of the clocks away in opposite directions. If the central clock is not moving through space, the other two clocks will tick more slowly as they are moved through space. TheBox doesn't seem to understand this point,

Of course I understand this point and I also understand this point to be incorrect which you do not. 

Let me take three light clocks ,
the distance between the mirrors on  clock one is a Planck length .
the distance between the mirrors on clock two is 1 mm
the distance between the mirrors on clock three is 1cm

Oh look I have just created different tick rates by adding distance the light has to travel between ticks.


Let us start again and measure time correctly.

I have again 3 light clocks,
the distance between the mirrors on  clock one is a Planck length .
the distance between the mirrors on clock two is a Planck length
the distance between the mirrors on clock three is a  Planck length

Oh look we are now synchronous


Sorry for being ''cocky'' David, but quite clearly you do not understand relative correctness.

[David Cooper]

Imagine three clocks that are sitting together. They are wired together and connected to a button which can be used to synchronise them all. We press the button, then we send two of the clocks away in opposite directions. If the central clock is not moving through space, the other two clocks will tick more slowly as they are moved through space. TheBox doesn't seem to understand this point,

Of course I understand this point and I also understand this point to be incorrect which you do not.

The "this point" in the bit you've quoted points forwards to the rest of the content of the same sentence where the point is made much more clearly for you - if you could move the clocks at the speed of light, they would stop ticking altogether (while being moved). If you move them at a little bit less than the speed of light they may struggle to complete a single tick while being moved. The slower you move them, the more quickly they will tick while being moved, but they will always be ticking more slowly than the stationary clock while they are moving. I've shown you the proof of this a multitude of times in another thread and you stubbornly refuse to accept it, even though you seemed to agree with every step of the argument along the way, so it's entirely a matter of you having a belief which you are not prepared to part with no matter how much it is shown to be wrong, and there's no fix for that.

Let me take three light clocks ,
the distance between the mirrors on  clock one is a Planck length .
the distance between the mirrors on clock two is 1 mm
the distance between the mirrors on clock three is 1cm

Oh look I have just created different tick rates by adding distance the light has to travel between ticks.

And moving a clock will increase the communication distances too.

Let us start again and measure time correctly.

I have again 3 light clocks,
the distance between the mirrors on  clock one is a Planck length .
the distance between the mirrors on clock two is a Planck length
the distance between the mirrors on clock three is a  Planck length

Oh look we are now synchronous

And now you've just introduced a length-contraction much stronger than the one that everyone else accepts, and you've added a width-contraction to it too! But you won't recognise that because you're a magical thinker.

Sorry for being ''cocky'' David, but quite clearly you do not understand relative correctness.

If you base your physics in magic, that's entirely up to you, but it means you're just one more artist making Turner-Prize-winning works out of elephant dung.

[guest39538]

Imagine three clocks that are sitting together. They are wired together and connected to a button which can be used to synchronise them all. We press the button, then we send two of the clocks away in opposite directions. If the central clock is not moving through space, the other two clocks will tick more slowly as they are moved through space. TheBox doesn't seem to understand this point,

Of course I understand this point and I also understand this point to be incorrect which you do not.

The "this point" in the bit you've quoted points forwards to the rest of the content of the same sentence where the point is made much more clearly for you - if you could move the clocks at the speed of light, they would stop ticking altogether (while being moved). If you move them at a little bit less than the speed of light they may struggle to complete a single tick while being moved. The slower you move them, the more quickly they will tick while being moved, but they will always be ticking more slowly than the stationary clock while they are moving. I've shown you the proof of this a multitude of times in another thread and you stubbornly refuse to accept it, even though you seemed to agree with every step of the argument along the way, so it's entirely a matter of you having a belief which you are not prepared to part with no matter how much it is shown to be wrong, and there's no fix for that.

Let me take three light clocks ,
the distance between the mirrors on  clock one is a Planck length .
the distance between the mirrors on clock two is 1 mm
the distance between the mirrors on clock three is 1cm

Oh look I have just created different tick rates by adding distance the light has to travel between ticks.

And moving a clock will increase the communication distances too.

Let us start again and measure time correctly.

I have again 3 light clocks,
the distance between the mirrors on  clock one is a Planck length .
the distance between the mirrors on clock two is a Planck length
the distance between the mirrors on clock three is a  Planck length

Oh look we are now synchronous

And now you've just introduced a length-contraction much stronger than the one that everyone else accepts, and you've added a width-contraction to it too! But you won't recognise that because you're a magical thinker.

Sorry for being ''cocky'' David, but quite clearly you do not understand relative correctness.

If you base your physics in magic, that's entirely up to you, but it means you're just one more artist making Turner-Prize-winning works out of elephant dung.

if you could move the clocks at the speed of light, they would stop ticking altogether

And this means nothing except there is nothing to count. Quite clearly my ''magic'' is much more objective than your Myths.

Science is adding a length to contract when there is no length there to begin with.  Time does not move in 1 second jumps, it moves continuous at the smallest rate we can understand time Planck. You carry on believing the subjective thought, the belief you have not being factual.

You are ignorant by the way, you do not want to understand or try to understand.

[dutch]

Multiple people are making large errors in this thread.

Please read the following from Stanford University on this matter. Also note that the burden of proof falls on those who wish to prove the non-conventionality of synchronization.

https://plato.stanford.edu/entries/spacetime-convensimul/

If you can't synchronize clocks without using a convention, then you CANNOT measure the one-way speed of light without circularly referring to that convention. If you can't prove one convention explains more than another (as in verifiable predictions) then all remain valid... regardless of opinion.

But all the slowed ticking means is the timing mechanism is out of synchronisation, there is no actual physical length contraction, there is just more or less distance the light has to travel from  or .  This in no way affects the rate of time it affects the rate of timing.  It is not much difference to when a timing belt slips and a car misfires.

Really? No physical length contraction? Prove it to me.......

 

Aha!
Progress!
Imagine that I repeat the thought experiment I did earlier (the one where I was carrying a clock round on a bicycle).
I repeat it several times, but I use different modes of transport..
With  a space ship, the difference between the "expected" value for m and 10,000 is larger tan when I use a jet plane.
And that, in turn is bigger than when I use a bike.
The version where I uses continental drift to move the clocks gives a result even closer to 10,000.

So, I can measure the 1 way speed of light by extrapolation of the speed as I move the clocks slower.
In the limit I can calculate it for moving the clocks at zero speed.

Is there any reason to suppose that, if I did that, the limiting value I would get for the 1 way speed of light was any different from C?

That's not progress... If two objects accelerate off in opposite directions from one central point by the same amount they will have symmetric Doppler Shifts to the original position. This will have a very real and verifiable effect (symmetric Doppler Shifts verified by central observer). It doesn’t matter what m is in your experiment. When the two clocks go back to a speed of v=0, m could be many values depending on synchronization chosen. Two objects could have their clocks synchronized and they could blast off in opposite directions at 90% the speed of light in the same way relative to their initial location then they stop. Their clocks are STILL SYNCHRONIZED with their initial reference frame if they didn't re-sync (if you use Einstein Synchronization). Sure, their clocks may have ticked at different rates than a clock left at their initial location, but this has no bearing on the problem whatsoever. You could pick any other reference frame to synchronize to and the physics works the same. That we need to have ε =1/2 is a human made condition AKA a convention. The clocks may only tick at 43.5% during their journey but they would still have the same reading relative to each other using the original reference frame throughout the journey (via Einstein Synchronization). 

All other ε are used in Relativity (see the Lorentz Transformation) why do they have to pertain to "other" reference frames? Why does a mile need to be 5,280 feet? Why do some countries drive on the left while others drive on the right? Why do we have to use a base 10 number system? These are all conventions. We could have physics where ε =1/4 or 1/8 but we chose 1/2.

If you move one clock relative to another, you will necessarily push them out of synchronization - the only issue is how much, with faster speeds of movement pushing them out of sync by more.

No, you can accelerate two synchronized clocks from the same location in opposite directions with the same amount of acceleration. You can then decelerate the clocks back so their velocities relative to their initial location is zero. These clocks don't need to be re-synchronized relative to the original frame (assuming they were not re-synced during the trip). Their original synchronization assumed Einstein Synchronization convention and their initial and final velocities are the same. Under acceleration clocks i a moving frame get out of sync with respect to their final reference frame but remain synchronized with the original reference frame (assuming Einstein Clock Synchronization). If the final velocity matches the initial velocity and the trips were symmetric then with the standard convention the clocks may have run slow but they ran slow by the same amount. While the trip is symmetric from the original frame’s view it certainly isn’t from all other reference frames.

The clocks only become out of synchronisation because they are not very good clocks.

Really? Find me better clocks then.

no, you are measuring time by counting at different speeds which is wrong.

What? Why?

[guest39538]

What? Why?

Time moves forward directly proportional to the history created at an infinite speed/rate. Count as fast as you can and see if you can count faster than time passes by. 
It does not matter if you count time past slow or fast, the time passes by immediately always.

[David Cooper]

If you move one clock relative to another, you will necessarily push them out of synchronization - the only issue is how much, with faster speeds of movement pushing them out of sync by more...

No, you can accelerate two synchronized clocks from the same location in opposite directions with the same amount of acceleration.

Which is exactly what I've already explained in earlier posts. If you move one clock relative to another (which it was at rest with and which continues to be unaccelerated), they will go out of sync.

Importantly, if you could move the clocks away from the central location to their new equally distant locations in opposite directions at the speed of light, you would have set up your synchronisation at a distance in the shortest possible time, and we can get the same result in the real universe by sending out synchronisation signals at the speed of light from a central location.

You can also synchronise two clocks by sending a light signal from one to the other and then making the adjustment for the delay in getting light to travel the known distance (by the clocks' rest frame's measurement), so there is no need for anyone to go to the midway point.

You can also synchronise two clocks where you don't know the distance between them by timing the round trip of a light signal to calculate the distance, but that will take twice as long to do (on average).

The simplest way to understand the synchronisation of clocks issue though is to play tennis between the two clocks, sending signals back and forth. The first clock will send a signal and start its clock at 0, then the second clock will start its clock at 1 when it receives the signal. The first clock will reset its clock to 2 when it gets a signal back and it will recalibrate the rate of its timing to tie in with that figure so that it will read 4 when the next signal arrives. The second clock resets its clock to 3 when it receives a second signal and it recalibrates its timing to tie in with the length of the delay such that it will read 5 when the next signal arrives. (These counts are unlikely to be seconds, but they could be used internally while a display in seconds is provided instead.) Importantly though, each clock ticks at regular intervals with one on the even numbers when the signal arrives and the other on the odd numbers. If the clocks are both at rest, both will tick the same number at the same instant. If they are moving, the leading clock will tick late, but it will always tick before the trailing clock makes its tick for the next value. What we have set up is essentially a light clock with one end in each of our two locations.

[Bored chemist]

I can get it into my head just fine that your plan to synchronise the clocks won't work because there is a delay (typically the product of the square root of dielectric constant of the insulation on the wires and the distance divided by c IIRC).

How are you synchronising them then when you have two clocks together? Are you pressing buttons on both of them and getting an error of up to a tenth of a second instead of using one button to start both? I can assure you that my way of doing it is more accurate. The big question though is about getting clocks synchronised at a distance and the errors that necessarily find their way into that, so the trivial business of how synchronising clocks at a single location is done is a trivial sideshow.

So you are not actually synchronising the clocks with the one in the middle- we know there's a delay.
The delay may well be the same in each direction but, as you can reduce it to zero by moving them slowly...
Adding a 3rd clock doesn't really seem to add anything.

I brought the third clock into this to try to help you see how awful your synchronisation method is. If you synchronise the three clocks at the central location, you can then move two of them away from there in opposite directions at the same speed to get them where you want them to be. Those two clocks are now as just about as well synchronised with each other as they can be, but only if the system happens to be stationary rather than moving fast through space. The middle clock though is badly synchronised with them, and the faster you moved the other two clocks into position, the worse the synchronisation with the middle clock will be. You only have two clocks, and one of them is being treated like my middle clock, so you're getting the huge error in your synchronisation instead of the minimal error with my two outer clocks. If you know how fast you moved your moving clock relative to your stationary clock though, you can adjust the timing of one or other of them to correct that synchronisation, at which point your clocks can be just as well synchronised as my pair of moved clocks. In both cases though, even that superior synchronisation will be affected by the movement of the system through space, so one clock's time may be far ahead of the other, which is why when you use them to attempt to measure the one-way speed of light, you are guaranteed to get the value c regardless of the actual speed of the light that you're timing relative to the system.

Re " if you move the clocks at the speed of light they will stop functioning completely while they're being moved, "
Then don't.

Imagine a light clock aligned with the direction you're moving it in. If you move this clock at c, the clock will stop clicking throughout the time you're moving it because the light would have to travel faster than c in order to complete a circuit (and thereby to tick). All clocks are limited in the same way, slowed to the same extent by their movement through space.

Why choose the state of affairs where the error you introduce is as big as possible?
Why not move them slowly so they stay (arbitrarily close to) synchronised?

The faster you move your only moved clock into position, the sooner you can start using your clocks to make measurements. It would be stupid to take a million years to move your clock into position just to minimise a predictable error which you can simply adjust for. That error is a complication which you want to eliminate, and it's a diversion away from the nature of the real error that you cannot correct for - the undetectable error affects all methods of synchronisation and it affects them equally. It's caused by the communication delay in one direction being longer than in the opposite direction if the system is moving through space.

OK, these are those nice clocks you find in thought experiments.
You can synchronise them however you like, including the button on the top.
If they are next to each other  then here's an amusing way to do it.
Turn one of the clocks upside down.
Press its button down on the button of the other clock.
Since both presses are the same event they are necessarily synchronised exactly.

But that's not the point.
It's a thought experiment we don't worry about irrelevant issues like whether my reflexes are good enough to press two buttons in a tenth of a second or what.

Because the two clocks are next to each other it's perfectly simple to synchronise them. Relativity doesn't have any problems with "at the same time" for things that are "in the same place".

Now, do you see that my "awful" synchronisation method is (at the time when I'm synchronising them)  actually mathematically perfect?
You can see how no observer anywhere in the universe, regardless of their speed, acceleration of local gravity will ever see the two clocks -just after I push both buttons in the same place and at the same time- as being anything other than synchronised?

Synchronous is hard in GR.
It can only happen locally.

That's why I choose to set the clocks running at zero in the same place and at the same time.
From the point of view of nearly everybody else in the universe, your "synchronised clocks" are ( or at least may be) never  in step because they are separate in space.
With my approach, once we have two clocks that at least start out  together we can run the experiment where we know how far out of synch the clocks are (because we can calculate it from the way in which we moved one of them).
And we can minimise that change.

We can make it as mall as we like (by moving them a  short distance and/ or slowly).
And then we have two nearly synchronised clocks  which we can set off a flash lamp in front of and look at the delay.
 

[David Cooper]

OK, these are those nice clocks you find in thought experiments.
You can synchronise them however you like, including the button on the top.
If they are next to each other  then here's an amusing way to do it.
Turn one of the clocks upside down.
Press its button down on the button of the other clock.
Since both presses are the same event they are necessarily synchronised exactly.

Try doing that with three clocks, but you've also got the problem that the buttons probably won't "fire" simultaneously, so you're really going to have to smash the clocks together hard to minimise the error.

It's a thought experiment we don't worry about irrelevant issues like whether my reflexes are good enough to press two buttons in a tenth of a second or what.

Then stop obsessing about it - the reason I spelt out a reasonable method was to attempt to ward off any ridiculous diversions of the kind that have subsequently been taken.

Because the two clocks are next to each other it's perfectly simple to synchronise them. Relativity doesn't have any problems with "at the same time" for things that are "in the same place".

You're repeating what I've already said.

Now, do you see that my "awful" synchronisation method is (at the time when I'm synchronising them)  actually mathematically perfect?
You can see how no observer anywhere in the universe, regardless of their speed, acceleration of local gravity will ever see the two clocks -just after I push both buttons in the same place and at the same time- as being anything other than synchronised?

That's not the part of the synchronisation process that I'm calling awful. The awful part is when you move one of them somewhere else and it's movement slows it and leads to its timing lagging by a different amount depending on how quickly you relocated it.

That's why I choose to set the clocks running at zero in the same place and at the same time.
From the point of view of nearly everybody else in the universe, your "synchronised clocks" are ( or at least may be) never  in step because they are separate in space.
With my approach, once we have two clocks that at least start out  together we can run the experiment where we know how far out of synch the clocks are (because we can calculate it from the way in which we moved one of them).
And we can minimise that change.

There are better methods where you don't have to worry about extra errors creeping in from the way you accelerate and decelerate your moving clock, plus complications from little wanders off a straight path vertically and horizontally. You can simply send a flash of light.

We can make it as small as we like (by moving them a  short distance and/ or slowly).

Which you don't need to do as you still have to make a correction, so you might as well make a big correction and move the clock quickly.

And then we have two nearly synchronised clocks  which we can set off a flash lamp in front of and look at the delay.

And at the end of it all, when you time the delay, you get the answer c because you have synchronised clocks with the same time difference between them as with any other valid method so that they will assert the speed is c even if it's actually close to 0 or 2c.