In his 1918 paper:

http://en.wikisource.org/wiki/Dialog...f_rela tivity
Dialog about Objections against the Theory of Relativity, by Albert Einstein

Einstein shows that, if the turn-around acceleration suffered by the travelling twin is ignored, the travelling twin returns both younger (as judged from the sedentary twin's system) and older (as judged from the travelling twin's system) than his sedentary brother. This is obviously fatal for his theory so Einstein is forced to introduce an ad hoc absurdity (there is no other way to save relativity): According to the travelling twin, the sedentary twin's clock runs slow all along but "this is more than compensated" when the traveller sharply turns around and experiences acceleration in the process:

Albert Einstein: "During the partial processes 2 [traveller moves with constant speed away from sedentary brother] and 4 [traveller moves with constant speed towards sedentary brother] the clock U1 [the sedentary twin's clock], going at a velocity v, runs indeed at a slower pace than the resting clock U2 [the travelling twin's clock]. However, this is more than compensated by a faster pace of U1 during partial process 3 [traveller sharply turns around]. According to the general theory of relativity, a clock will go faster the higher the gravitational potential of the location where it is located, and during partial process 3 U2 happens to be located at a higher gravitational potential than U1. The calculation shows that this speeding ahead constitutes exactly twice as much as the lagging behind during the partial processes 2 and 4."

It is easy to show that the turn-around acceleration has nothing to do with the youthfulness of the travelling twin:

http://www.damtp.cam.ac.uk/research/...tivity2010.pdf
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."

There are even scenarios where there is no turn-around acceleration at all and yet the travelling twin proves younger at the end of the journey:

http://www.people.fas.harvard.edu/~djmorin/book.html
Introduction to Classical Mechanics With Problems and Solutions, David Morin, Cambridge University Press, Chapter 11, p. 44: "Modified twin paradox *** Consider the following variation of the twin paradox. A, B, and C each have a clock. In A's reference frame, B flies past A with speed v to the right. When B passes A, they both set their clocks to zero. Also, in A's reference frame, C starts far to the right and moves to the left with speed v. When B and C pass each other, C sets his clock to read the same as B's. Finally, when C passes A, they compare the readings on their clocks."

Conclusion: The turn-around acceleration is irrelevant and can and should be ignored. On the other hand, it is the only salvation - without the miraculous "more than compensation" caused by the turn-around acceleration, the twin paradox is a blatant absurdity: the travelling twin returns both younger (as judged from the sedentary twin's system) and older (as judged from the travelling twin's system) than his sedentary brother.

Pentcho Valev