Before quantum mechanics hit the scene, I would expect most physicists (and people) would have answered the above question with the basic assumption: Two observers see the same result in an experiment because we live in the same universe. Today, most people (and some physicists) would probably still agree with that answer. However, with all the interpretations of quantum mechanics, I would guess that there would be additional responses from physicists such as but not limited to: The question is outside the scope of legitimate questions that physics can answer. Observers don't live in the same universe (for example, each possible outcome creates a new universe). Observers don't observe the same thing (for example, each observation is an imperfect approximation of a mathematical universe). So my questions are: Am I correct that this assumption is now "up for grabs" and being questioned? If so, are the above responses an accurate summary of current responses? Are there any other responses besides the ones above? Has anyone attempted to experimentally show a difference in observations (response 3 above)? I have no agenda with these questions. I am just trying to wrap my head around quantum mechanics and its corresponding interpretations.