Re: Sync two clocks

Am Samstag000024, 24.08.2024 um 10:02 schrieb Mikko:
...

How is it possible to fail to understand this?
>
If we have two stationary clocks in an inertial frame,
 and clock A shows tA = t1 when it emits light,
 and clock B shows tB = t1 + td when the light hits it,
 and clock A shows tA'= t1 + 2⋅td when it is hit by the reflected light,
>
then tA, tB, tA', t1 and td are all proper times which are frame
independent (invariants) and "the same for all".
>
 tB − tA = t'A − tB = td
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The transit time td is a frame independent invariant and
the same in both directions, which means that the clocks according
to Einstein's _definition_ are synchronous in the inertial frame.

>
You introduced t_d or 'transit time' (aka 'delay'), while Einstein didn't use any of these terms.

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Einstein used tB - tA and similar expressions. Nothing else needs be
said about delays. The equation tB − tA = t'A − tB and the text that
describes the situation and defines what tA, t'A and tB mean define
clearly and unambiguously what simultaneity and synchronity mean.

>
But this has nothing to do with synchronicity, but with a process to turn remote clocks to the same time value.

 That is the same thing. Two clocks are sychronous if and only if the
show the same at the same time.

Well, I would agree on that.
But what do you mean with 'at the same time'?
As I see it, we need to adress the so called 'hyperplane of the present' with 'at the same time'.
This is the set of events, which would require an infinetely fast signal, to recognize them at the same time.
Since no such signal exists, the hyperplane of the present is mainly invisible.
What we actually see, like in the nicht sky and call 'universe', is visible, hence does not belong to the hyperplane of the present.
Therefore, synchronization with light signals isn't a very good idea, because it is light what we see and light would not allow infinite fast communication.
That's why we need some means, to compensate the delay, caused by the finite speed of light.
This compensation isn't that difficult, because we could easily measure the delay and use this value for compesation.
BUT: Einstein didn't do this nor even mentioned this requirement.

 

Time is not equal to what clocks say, because clocks are measuring devices, which measure time, but do not determine, what the measured quantity is.

 The intent is to adjust the clocks so that the value shown is the time,
or at least to find out the difference so that the time can be inferred
from the shown value.

The 'value shown' isn't time, neither.
In physics I would distinguish between a quantity we like to measure, the measuring device and the value shown by that device.
In case of time we have a clock as device to measure that quantity and the positions of its hand as shown value.
But the positions of the hands are not time, but the outcome of a certain measurement (contrary to what Einstein had written).

The process to synchronize clocks require technical means, which are here light signals:
>
The clock at some point A emmits a timing signal, which a remote clock receives a little time later, because such signals have finite speed.

 And also a light signal to the opposite direction.

Sure, the process should produce the same setting, if it is initiated from the other side.
But Einstein's process would not fullfil this requirement, because it was based on one frame of reference and the observations from there.
The obvious step would be, that the delay was measured and the measured value used to compensate this delay.
Since Einstein didn't mention anything like this, his method would not produce symmetric snychronization.

Now it should be obvious, that the remote clock had to compensate this delay, because otherwise it would not show the time of the master clock, but an asynchronous value.

 And in order to do that, the delay needs be known. Therefore the requirement
to adjust so that the apparent delay is the same in both directions.
 

For uncertain reasons Einstein had not mentioned this requirement at all, even if transit time per se was actually mentionend.

 For obvious reason, Einstein required what he required.

Well, yes, but we are not discussing what Einstein wanted, but what he wrote in this particular article.
If he forgot to mention his requirements, then they are not there.
And what is not there where it should be, that does not exist in the context of this paper.
TH