I just took the relativity quiz here: https://www.physicsforums.com/quiz.php?quizid=28 and I goofed on question 10. Could someone explain it to me? Below I've posted what the review of the quiz said about question 10 along with some of the previous questions for context. This seems to conflict with what I've read about GR. In one of Einstein's thought experiments he imagined a man in a chest with a rope tied to the top being pulled with a constant acceleration in one direction. Einstein said: - Relativity: The Special and General Theory, Section 20 This seems to support that Stella can call herself at rest. The only argument I can think of is that Stella's acceleration would generally be thought to not be constant and maybe that's why we can't call her at rest. Although it is possible for Stella to go from moving away from Earth, come to a stop, and return to Earth with a constant acceleration, maybe the question was taking the most likely situation in which Stella changes her acceleration multiple times during the course of the trip, and this is why she can't call herself at rest. The only other reason I can think of why Stella can't call herself at rest is if modern physics has replaced the conclusions of Einstein's acclerated chest thought experiment, and it's more acceptable now to call such "gravitational fields" that aren't the result of matter an indication of change in motion. Can someone clear this up for me?