I am still not happy about the acceleration argument. Consider this thought experiment. A spacecraft passes the Earth at 60% of c. On the craft is a pair of twins. As the craft passes the Earth, one twin heads for Earth in a shuttle, and lands. The craft continues. Later, it executes a wide turn with no change of speed. Obviously, the manoeuvre causes a velocity change, but this is kept to a minimum, and is probably no greater than the positive and negative acceleration experienced by the other twin. After a journey of 10 light years the craft passes Earth, as it does so, time dilation tells us that the twin on the space craft is younger than the one on Earth, but how can this be attributed to acceleration?

There never was nothing.