There are two experiments that are often used to explain Quantum Mechanics: the two-slit experiment and the EPR paradox. I am curious what would happen if you combined them.
Imagine an experiment where you fire pairs of entangled particles at two simultaneous two-slit setups. If you used detectors, you could find out how the entangled particles' paths correlate. Perhaps you'd be able to deduce, based on the result of one detector, which slit the other particle went through. Now, if you were to run the experiments with a detector on one side and no detector on the other side, would the unobserved particles still form an interference pattern, even though you know which slit they would have went through?
My intuition is that the answer is yes. Despite being entangled, the particles should not have correlated actions, otherwise we would have invented faster-that-light communication. You could create a device that constantly fired entangled particles toward two far-apart worlds, and if one world suddenly started observing the particles on their side, the particles arriving at the other world would instantly cease to create an interference pattern.