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The quantum eraser double slit experiment shows that interference pattern is destroyed not by interacting with the quantum particle, but rather by getting which path information. In this experiment even if you interact with the quantum particle but later erase the which path information, you still get interference pattern.

How can this fact be reconciled with many worlds interpretation? Why would just marking an atom make it stop interfering with other universes? Why would erasing this information make it interfere again?

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    $\begingroup$ There is no issue here. Every interpretation of quantum mechanics can explain delayed eraser experiments, because they do not contain any quantum measurements. In the absence of measurements all interpretations agree the dynamics is governed by the Schrodinger equation, which is the only thing you need to explain the experiment. $\endgroup$ – knzhou Apr 17 '18 at 12:07
  • $\begingroup$ I always thought the Quantum Boiling Pot did the same, because you could select which universe you wanted. But then someone who understood MWI fixed that for me. $\endgroup$ – Maury Markowitz Apr 17 '18 at 12:07
  • $\begingroup$ I don't think you understand my question. I get why for example in consistent histories interpretation erasing /not erasing information could make a difference. But I don't understand why erasing info or not should impact if atom interefere with atoms in different universes or not. $\endgroup$ – Michał Sykutera Apr 17 '18 at 18:33
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In the double slit quantum eraser experiment one observable of the photon, its polarization has its value changed depending on the value of another observable, which path it is on.

Since the polarization and path can be adjusted independently they are effectively different systems within the same photon. So this experiment is a case where interference in one system is prevented by information being transferred to another system. This can be accounted for in quantum mechanics without introducing a collapse postulate, see

https://arxiv.org/abs/1212.3245

If that transfer of information is undone, as in the eraser experiment, then so is the change that prevented the interference.

The many worlds interpretation (MWI) sez that the existence of parallel universes is an implication of quantum mechanics without a collapse postulate. So the outcome of the eraser experiment is entirely consistent with the MWI.

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This is an excellent question. With the many worlds interpretation, a single our universe photon passes through one slit in the double slit experiment accompanied by trillions of shadow photons in different universes. These shadow photons interfere with the path of the photon deflecting it’s path. When repeated thousands of times you get the the many stripes pattern on the photo sensitive screen. A switched on measuring divine affects the interference between the shadow photons and our world photon. Switched on interference continues, switch off the device and interference returns. It is clear the live components of the device affect the shadow photons.: simple even if I can say precisely why. I’ve also avoided apparent justifying jargon in this explanation.

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    $\begingroup$ This answer is completely wrong, and its content has nothing to do with the actual many-worlds interpretation. $\endgroup$ – Emilio Pisanty Apr 30 '19 at 6:06
  • $\begingroup$ All the same, welcome to Physics Stack Exchange, William. $\endgroup$ – StudyStudy Apr 30 '19 at 16:02
  • $\begingroup$ I wouldn‘t say it has nothing to do with many-worlds. David Deutsch, one of the main proponents of MWI also uses similar explanations of interactions between photons in different parallel universes in his book ‚the fabric of reality‘. I don‘t think this interpretation/visualization is completely off the rails $\endgroup$ – matthias_buehlmann Feb 22 at 5:24

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