2017-12-27 12:05:06 UTC
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
So, all along, the traveling twin observes his stationary brother aging SLOWER (imagine that the spaceship is very long so that, all along, the traveler can check the clock of his brother against his own clocks). Yet, as the traveling twin turns around, "enough strangeness" occurs and the distant stationary twin SUDDENLY gets very old:
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."
"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/teaching/HPS_0410/chapters/spacetime_tachyon/index.html
Do you really believe in the "enough strangeness", Einsteinians?