That part I understand, but what confuses me is that as I hear it described, the two frames of…
Dark Jaguar
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The spaceship sees time pass more slowly on Earth, just as Earth sees time pass more slowly on the spaceship. For the spaceship to actually come back to Earth and compare clocks, it has to accelerate, which breaks the symmetry of the scenario, and also means that we need general relativity to explain it, not just special relativity.

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