B Is velocity the reason for the time dilation effect?

[Sagittarius A-Star]

Sabine Hossenfelder used this convention in her (rather poor) "I explain relativity" video.

No, she doesn't (see below).

I had no idea it had been used by Rindler. I have to say I don't like it. "Time dilation" and "real time dilation" seems to me like "mass" and "relativistic mass" - an obvious source of confusion.

Rindler didn't distinguish between "Time dilation" and "real time dilation". He wrote that time dilation is a real effect.

 

[PeterDonis]

Rindler uses the twin paradox as argument, that time dilation in general is no accident of convention.

No, not "time dilation in general"--only "time dilation" by Rindler's definition. Which, as has already been said, is what we in this thread have called "differential aging"--i.e., an invariant. He is not saying that "time dilation" by the other definition (the frame-dependent one) is "no accident of convention".

Rindler didn't distinguish between "Time dilation" and "real time dilation". He wrote that time dilation is a real effect.

Whether RIndler explicitly distinguished the two meanings of the term "time dilation" is irrelevant. He explicitly defined what he meant by the term, and, as above, it is what we are calling "differential aging". That is the only kind of "time dilation" that he claimed was a "real effect".

 

[PeterDonis]

In this case it's magnitude depends on a convention, but not it's existence at certain velocities.

If by this you mean that there will be a difference in time dilation factor between two worldlines in any frame, that is not correct. Given two inertial worldlines in flat spacetime, their time dilation factors will be the same in the inertial frame called the Loedel frame, in which each worldline is moving at the same speed, but in opposite directions. AFAIK it is possible more generally to construct a coordinate chart such that both of a given pair of worldlines, which need not be inertial (and the spacetime need not be flat), will have the same relationship of proper time to coordinate time, but in general the chart will not correspond to an inertial frame.

 

[Sagittarius A-Star]

He is not saying that "time dilation" by the other definition (the frame-dependent one) is "no accident of convention".

He describes in his scenario the differential aging as a two-way time dilation. Logically, the resulting age difference must be the sum of the (frame-dependent) time-dilations in forward and backward direction. Therefore it is not possible to define the clock-synchronization for his reference-frame in such a way, that the (frame-dependent) time-dilations in both directions disappear.

 

[PeterDonis]

He describes in his scenario the differential aging as a two-way time dilation.

No, he uses the term "time dilation" to mean what we are calling "differential aging".

Logically, the resulting age difference must be the sum of the (frame-dependent) time-dilations in forward and backward direction. Therefore it is not possible to define the clock-synchronization for his reference-frame in such a way, that the (frame-dependent) time-dilations in both directions disappear.

Sorry, but at this point you are simply repeating errors. Look up the term "Loedel diagram".

 

[PeterDonis]

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