As Einstein argued long ago, the quantum physics of his era - that is, the single-global-world interpretation of quantum physics, in which experiments have single unique random results - violates Special Relativity; it imposes a preferred space of simultaneity and requires a mysterious influence to be transmitted faster than light; which mysterious influence can never be used to transmit any useful information.
That's not quite right, there is no preferred frame and no influence is transmitted. Until the results of the spacelike-separated measurements are compared, one observer cannot know if the other even measured anything. All they know is that, if the other guy measured everything properly, the results must agree when they compare them later. You can visualize this outcome with collapse or with many worlds, whatever you are comfortable with.
I guess the confusion comes from the counterfactuals: people talk about the other measurement as if it were an objective reality before they learn about it. You can reasonably hope that the other measurement happened as planned, but you cannot know it for sure until you get the record of it some time later. Only then it becomes a part of your world.
Today's post, Spooky Action at a Distance: The No-Communication Theorem was originally published on 05 May 2008. A summary (taken from the LW wiki):
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This post is part of the Rerunning the Sequences series, where we'll be going through Eliezer Yudkowsky's old posts in order so that people who are interested can (re-)read and discuss them. The previous post was Bell's Theorem: No EPR "Reality", and you can use the sequence_reruns tag or rss feed to follow the rest of the series.
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