Doublethink in Divine Albert's World II
The acceleration suffered by the travelling twin is responsible for her youthfulness. The turning-around period is essential:
John Norton: "Then, at the end of the outward leg, the traveler abruptly changes motion, accelerating sharply to adopt a new inertial motion directed back to earth. What comes now is the key part of the analysis. The effect of the change of motion is to alter completely the traveler's judgment of simultaneity. The traveler's hypersurfaces of simultaneity now flip up dramatically. Moments after the turn-around, when the travelers clock reads just after 2 days, the traveler will judge the stay-at-home twin's clock to read just after 7 days. That is, the traveler will judge the stay-at-home twin's clock to have jumped suddenly from reading 1 day to reading 7 days. This huge jump puts the stay-at-home twin's clock so far ahead of the traveler's that it is now possible for the stay-at-home twin's clock to be ahead of the travelers when they reunite."
The acceleration suffered by the travelling twin is not responsible for her youthfulness. The turning-around period can be ignored:
Gary W. Gibbons FRS: "In other words, by simply staying at home Jack has aged relative to Jill. There is no paradox because the lives of the twins are not strictly symmetrical. This might lead one to suspect that the accelerations suffered by Jill might be responsible for the effect. However this is simply not plausible because using identical accelerating phases of her trip, she could have travelled twice as far. This would give twice the amount of time gained."
The acceleration suffered by the travelling twin is responsible for her youthfulness. The turning-around period is essential. On the other hand a discussion of acceleration is not required to quantitatively understand the paradox, that is, the turning-around period can be ignored, insofar as there are scenarios in which there is no acceleration at all:
Introduction to Classical Mechanics With Problems and Solutions, David Morin, Cambridge University Press, Chapter 11, p. 14: "Example (Twin paradox): Twin A stays on the earth, while twin B flies quickly to a distant star and back. Show that B is younger than A when they meet up again. (...) For the entire outward and return parts of the trip, B does observe A's clock running slow, but enough strangeness occurs during the turning-around period to make A end up older. Note, however, that a discussion of acceleration is not required to quantitatively understand the paradox, as Problem 11.2 shows."
Why do Einsteinians practice doublethink so diligently? Because that's the way ahah ahah they like it, ahah ahah.
Pentcho Valev