• Either CS (coordinate system) could be used with equal justification. The two sentences: the sun is at rest and the earth moves, or the sun moves and the earth is at rest, would simply mean two different conventions concerning two different CS

    Albert Einstein: Either CS (coordinate system) could be used with equal justification. The two sentences: the sun is at rest and the earth moves, or the sun moves and the earth is at rest, would simply mean two different conventions concerning two different CS