Re: Sync two clocks

Thomas Heger <ttt_heg@web.de> wrote:

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
>
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.

>
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.

Once again, scientific papers were written for collegues who will
understand, and for whom half a hint suffices to see the implications.
They are not written for people like you,
who need a whole book of explanations, fully spelled out,
and then still succeed in not understanding the obvious,

Jan