# Conventionality and clock symchrnization

1. Feb 22, 2008

### bernhard.rothenstein

Please tell me if "conventionality of dimultaneity" and "Einstein clock synchronization" are one and the same thing?
Please tell me how could be quoted ideas received on the Forum.

2. Feb 23, 2008

### Jorrie

I guess you mean "conventionality of simultaneity"? If so, no, it is not necessarily the same thing. Einstein's method is one (very good) convention, but I think there are others. Here's a good discussion from Stanford Encyclopedia of Philosophy on simultaneity issues.

Jorrie

3. Feb 25, 2008

### DrGreg

In relativity discussions, "Einstein clock synchronization" is usually simply assumed and the question of different synchronizations is never considered. If someone talks about "conventionality of simultaneity" they are considering which parts of relativity depend on a choice of synchronization convention and which do not. Or in the case of the interesting paper quoted by Jorrie, they are considering the philosophical question as to whether or not there is a "natural" synchronization that need not be considered to be a "convention" at all.

Thus you may see statements such as "time dilation and length contraction are conventional" or "the twin paradox has an unconventional solution". The words "conventional" and "unconventional" are being used in an unusual sense here as meaning "dependent on a choice of synchronization convention" or "independent of a choice of synchronization convention".

So the answer to your question is that the two phrases would be used in slightly different contexts. "Conventionality of simultaneity" might often mean "conventionality of Einstein synchronization".

4. Feb 26, 2008

### bernhard.rothenstein

conventionality

t(E)=t(e)+x/c (1)
where t(E) represents the reading of an Einstein synchronized clock located at point (x,0)
t(e) representing the time when the synchronizing agent, propagating with speed c, was emitted.
The single terms on which conventions could be made are x and c.
-If we consider c=infinity we make the everyday clock synchronization proposed by Leubner and discussed in a previous thread.
-If we consider x=0 we obtain the "inertial transformations Selleri" with time transforming
in accordance with time dilation.
-we make the two way light propagation with c, c(+), c(-) considering even infinite values for the propagation speed of the synchronizing signal.
If the statements made above are correct then my problem is if there are other ways to complete the classification made above.
Regards

5. Feb 26, 2008

### DrGreg

If you want your coordinates to be physically meaningful (so x is compatible with "proper length") you have no choice over x.

Yes.

No. I dealt with this in this post.

Yes (if I understand you correctly). The two way speed of light c must be constant (to agree with experiment and SR), but the one-way speeds c+ and c- can be varied, with different synchronisations. Note that 1/c = (1/c+ + 1/c-)/2 (see this post). In more than one spatial dimension it gets more complicated as the speed of light would vary by direction, but the relation above would still hold for any two opposite directions.

I think that probably covers it. In the notation of Stanford Encyclopedia of Philosophy - Conventionality of Simultaneity, varying the value of c+ is equivalent to varying the value of $$\epsilon$$.

Note that, I think, c+ could even vary as a function of position and time, but that would get very complicated to ensure the two-way speed was still constant.