Consider three widely separated galaxies in an expanding universe. Imagine that you are located in galaxy 1 and observe that both galaxies 2 and 3 are moving away from you. If you asked an observer in galaxy 3 to describe how galaxy 2 appears to move, what would he or she say?


  1. Answer:

    The observer will say that galaxy 2 is moving away from galaxy 3 where he stands.


    Since the galaxies are expanding, each one would move away from the others. Observers on all three galaxies have their frame of reference fixed on their own galaxies. Judging from their own galaxies, each observer will perceive the other galaxies moving away from his/or galaxy.

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