David Morin, Introduction to Classical Mechanics, 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." https://scholar.harvard.edu/files/david-morin/files/cmchap11.pdf

This "enough strangeness" sounds too enigmatic. Einstein explains it:

Albert Einstein 1918: "3. A homogenous 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." http://sciliterature.50webs.com/Dialog.htm

That is, as the traveling twin turns around (but considers himself to be at rest), he finds that a homogeneous gravitational field appears and in this homogeneous gravitational field his brother accelerates towards him and reaches speed v. Then the field disappears.

Why is the gravitational field "homogeneous"? Because otherwise it would not go up to the very distant brother and would not cause his acceleration.

The way Einstein brainwashes the world in 1918 is too blatant, even by the standards of the Einstein Cult. David Morin feels some shame (perhaps) and uses the enigmatic euphemism "enough strangeness".

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