In 1918 Einstein devised an idiotic hoax. As the traveling twin turns around and experiences acceleration, a HOMOGENEOUS gravitational field emerges which instantly reaches the distant stay-at-home twin and makes him age very fast during the turning-around period. The hoax is so idiotic that most Einsteinians avoid any discussion of it. Yet some teach it quite diligently, without mentioning the HOMOGENEOUS gravitational field:

David Morin, Introduction to Classical Mechanics With Problems and Solutions, Chapter 11, p. 14: "Twin A stays on the earth, while twin B flies quickly to a distant star and back. [...] 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." http://www.people.fas.harvard.edu/~djmorin/chap11.pdf

Physics Girl (4:30): "One last question. What's happening to the clocks during the period of acceleration? We still get time dilation, but we have to use a different set of rules from the general relativity. General relativity states that clocks runs slower in accelerated reference frames. So while your twin is turning around, her clock runs slower, and she sees the same thing. She sees your clock running faster than hers, so you're aging quicker.. It's during this period of acceleration that you become the older twin." https://www.youtube.com/watch?v=ERgwVm9qWKA

"At the same time, the twin in the spaceship considers himself to be the stationary twin, and therefore as he looks back towards Earth he sees his brother ageing more slowly than himself. [...] When the twin in the spaceship turns around to make his journey home, the shift in his frame of reference causes his perception of his brother's age to change rapidly: he sees his brother getting suddenly older. This means that when the twins are finally reunited, the stay-at-home twin is the older of the two." https://hubpages.com/education/Twin-Paradox

John Norton: "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." http://www.pitt.edu/~jdnorton/teachi...yon/index.html

What forced Einstein to resort to an obvious idiocy? He was in danger. He had already predicted, in 1905, that the traveling twin remains younger (more precisely, that the moving clock runs more slowly), and the prediction had been totally unjustified. In 1918 he almost admitted that but informed the gullible world that his general relativity did solve the problem:

Albert Einstein 1918: "A homogeneous gravitational field appears, that is directed towards the positive x-axis. Clock U1 is accelerated in the direction of the positive x-axis until it has reached the velocity v, then the gravitational field disappears again. An external force, acting upon U2 in the negative direction of the x-axis prevents U2 from being set in motion by the gravitational field. [...] 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." http://sciliterature.50webs.com/Dialog.htm

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