Fig. 2.

Illustration of the Gedankenexperiment. In each round n = 0, 1, 2, … of the experiment, agent $\overline{F}$ tosses a coin and, depending on the outcome r, polarises a spin particle S in a particular direction. Agent F then measures the vertical polarisation z of S. Later, agents $\overline{W}$ and $W$ measure the entire labs $\overline{L}$ and $L$ (where the latter includes S) to obtain outcomes $\overline{w}$ and w, respectively. For the analysis of the experiment, we assume that all agents are aware of the entire procedure as specified in Box 1, but they are located at different places and therefore make different observations. Agent F, for instance, observes z but has no direct access to r. She may however use quantum theory to draw conclusions about r