>>11161344You can solve it entirely within the framework of special relativity by carefully jumping between inertial reference frames.
Physically, you can imagine an inertial ship heading out from Earth. After exactly one year proper time, another inertial ship heading in the opposite direction passes by. This ship synchronizes its clock to the reading of the first ship (1 year), and then continues toward Earth, reaching Earth when the clock marks 2 years. Nothing accelerates in this scenario, but you still get the disagreement between ship time and Earth-based time.
