[deleted]
Eckard,
You wrote, "I didn't pay attention to the question of what I consider inconsistent SR related conventionality. Of course, due to the simple Doppler effect each twin perceives the pulse frequency of the other one slower and not higher if the distance between the twins increases while higher if they move towards each other."
As I implied, those who don't understand relativity in the first place won't be swayed by explanations that follow directly from the model. Even though relativity clearly illustrates that all motion is relative and there is no preferred Galilean frame of reference, there just has to be "something else" that "makes sense" to one's naive sensibilities. I see it in this forum time after time.
The Doppler effect has nothing to do with the twin problem. RELATIVE motion between the twins in straight line acceleration where each sees the other as staying young (though in their own respective frames they see themselves age normally) implies that there is no preferred Doppler frame. There is no objective third observer, in other words (which is another error some forum participants consistently make).
Only when the traveling twin reverses course, does the aging of each twin appear asymmetrical, because the curved path the traveling twin takes on return to his sister implies decreasing increments of spacetime between them. Now there IS an (arbitrary) fixed reference frame, that of the stay at home twin. That is, the traveling twin speeded up his own aging process (relative to his twin) only at the period of negative acceleration in reversing course; otherwise, his (relative) motion preserves some of the youth that his sister lost.
The physics is straightforward, and I think that's all I have to say about it.
Tom