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## Main Question or Discussion Point

if 2 clocks are synchronised in a stationary frame of refernece and then that frame of ref is accelerated up to a constant velocity will the clocks still be synchronised ?

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if 2 clocks are synchronised in a stationary frame of refernece and then that frame of ref is accelerated up to a constant velocity will the clocks still be synchronised ?

tiny-tim

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if 2 clocks are synchronised in a stationary frame of refernece and then that frame of ref is accelerated up to a constant velocity will the clocks still be synchronised ?

Hi rab99! Welcome to PF!If both of them remain in the same frame, then the answer should be 'yes'. I'm no expert on Relativity, though. It's probably best to wait for a real scientist to weigh in with some answers for you.

Yes, if they're attached to a spaceship, say, and the spaceship accelerates, and then stops accelerating, the clocks should still be synchronised.

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Nice work.

I didn't realize that it could go out of sync under born-rigid acceleration.

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It is a little unclear from your explanation but I interpret it that both Bell and Born cause the clocks to become unsynchronised.

From examining the thread that you referred me to if:

all the appropriate parameters are measured, by the appropriate measuring device, in the appropriate frame, Then the clocks can be adjusted (say by moving the hands on the clock) to allow for the amount they became unsychronised, during the acceleration, to make them synchronised again yeh ?

Of course at a constant velocity contraction is constant and time is constant

I guess the question I want answered is , is it possible to have two clocks perfectly synchronised in a moving frame of reference yes or no? I suspect the answer is yes

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From examining the thread that you referred me to if:

all the appropriate parameters are measured, by the appropriate measuring device, in the appropriate frame, Then the clocks, ONCE THEY ARE AT A CONSTANT VELOCITY, can be adjusted (say by moving the hands on the clock) to allow for the amount they became unsychronised, during the acceleration, to make them synchronised again yeh ?

AND

I guess the question I want answered is , is it possible to have two clocks perfectly synchronised in a CONSTANT VELOCITY moving frame of reference yes or no? I suspect the answer is yes

JesseM

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Well, do you understand about the relativity of simultaneity in relativity which says that different frames define what it means for clocks to be "synchronized" differently? In relativity, if I'm moving inertially and I have two clocks at rest relative to me, I synchronize them in my frame using the "Einstein synchronization convention" which is based on assuming that light moves at the same speed in all directions in my own frame--so, for example, I can set off a flash at the midpoint of the two clocks, and then as long as they both read the same time at the moment the light from the flash hits them, I define them to be "synchronized" in my frame. But it's not hard to see that if each observer synchronizes their own clocks this way, they will say that the clocks of other observers are out-of-sync. For example, say I'm on a rocket which is moving forward in your frame, and I synchronize clocks at the front and back of the rocket by setting off a flash at the midpoint and setting the two clocks to read the same time when the light reaches them. In

From examining the thread that you referred me to if:

all the appropriate parameters are measured, by the appropriate measuring device, in the appropriate frame, Then the clocks, ONCE THEY ARE AT A CONSTANT VELOCITY, can be adjusted (say by moving the hands on the clock) to allow for the amount they became unsychronised, during the acceleration, to make them synchronised again yeh ?

AND

I guess the question I want answered is , is it possible to have two clocks perfectly synchronised in a CONSTANT VELOCITY moving frame of reference yes or no? I suspect the answer is yes

So, the short answer to your question is, yes, whenever two clocks are moving at constant velocity it is always possible to synchronize them in their own rest frame using the Einstein synchronization convention, but this will result in the clocks being out-of-sync in the frame of other observers moving at constant velocity who see the clocks moving relative to themselves.

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and

thru measurement and further adjustment to synchronise the clocks so the observer external to the frame will say they are synchronised

Of course the adjustment for the external observer will be different than the adjustment required for the internal observer

and

of course it is impossible to adjust the clocks so they are simutaneously synchronised for both the internal and external observer if the internal and external observer are in different frames ie frames travelling at a different velocity or direction relative to to each other .... is this correct ?

JesseM

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A "frame" is just a coordinate system, it isn't localized to a particular region of space, so I don't see what you mean when you distinguish "external to the frame" and "in a different frame". But other than that I'd say your correct, it's possible to adjust the clocks so they're synchronized in the rest frame of an observer who sees the clocks as being at rest relative to himself, or it's possible to adjust them so they're synchronized in the rest frame of an observer a different observer who sees the clocks in motion relative to herself, but not both (except in the special case where the observer who sees the clocks in motion sees them moving exactly perpendicular to the axis between the two clocks).

and

thru measurement and further adjustment to synchronise the clocks so the observer external to the frame will say they are synchronised

Of course the adjustment for the external observer will be different than the adjustment required for the internal observer

and

of course it is impossible to adjust the clocks so they are simutaneously synchronised for both the internal and external observer if the internal and external observer are in different frames ie frames travelling at a different velocity or direction relative to to each other .... is this correct ?

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The main thing is it is possible thru measurement and adjustment to make two clocks synchronised wrt any observer, regardless of the frame that they happen to be in

JesseM

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No, you're thinking of "frame" incorrectly. A frame is a coordinate system that fills all of space and time, which may be infinite. When physicists talk about the ship's frame, all that means is a coordinate system in which the ship is at rest--i.e. its coordinate position does not change with the passage of coordinate time in that system. A frame is not localized to any particular region of space.I always think of a frame as being a space ship. One person is standing on the ground observing the space ship moving and there is a person in the space ship. If the clocks are in the space ship then the pseron in the space ship is at rest relative to the clocks the person on the ground is not at rest relative. I guess the inside the space ship is a regoin of space that is a moving frame as opposed to the air just outside the skin of the space ship or the person on the ground?

Clocks are not "in" one frame or another, since every frame covers every region of space, including whatever region the clock is occupying. But yes, any pair of clocks can be synchronized in any frame.rab99 said:The main thing is it is possible thru measurement and adjustment to make two clocks synchronised wrt any observer, regardless of the frame that they happen to be in

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surely there must be as space is continuous

Are coordinate systems just a mathematical construct used to make it easier to visualise reality ?

tiny-tim

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Yes!Are coordinate systems just a mathematical construct used to make it easier to visualise reality ?

Don't get confused between mathematics and reality!

Mathematicians can define anything they like, to make calculation easier!

For example, there's a mathematical singularity at the North pole (of the Earth) … but physicists know there's no singularity there!

JesseM

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I think you're still misunderstanding something here--

surely there must be as space is continuous

Are coordinate systems just a mathematical construct used to make it easier to visualise reality ?

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