Einstein's 1918 idiocy (the "enough strangeness" below) was not a whim - its fabrication was the only way to save relativity. Without recourse to "enough strangeness", the theory is obviously absurd - either twin sees his brother age more slowly:

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

Pentcho Valev