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The experiment says that if I split a photon into two coherent entangled photons, one towards a double-slit, one towards a which-way detector, I can control whether

  • the interference pattern appears by choosing either detecting which way the photon came through or
  • destroying the information about the photon, even if the detector/destroyer is further away than the double slit screen.

Does it imply that I can know about whether the which-way information will be detected or not even before it is detected?

Suppose I have a person controlling the detector 10 ly away from the slits, and the double-slit setup immediately in front. Then just by looking at the screen, will I be able to know whether the person 10ly away decides to observe or not 10 years before he even decides it? I am quite uncomfortable with this thought.

HolgerFiedler
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Jeffrey Suen
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1 Answers1

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No, you cannot use this to communicate faster than light, or get information from the future. I tried to think a way to do that. Turns out, you need to analyse both sets of data from both sites to get to see if interference patterns appears or not. At the double-slit site, you get mush (no interference), only by combination, careful analysis of correlation might the interference pattern might emerge.

So when bringing together both sides, it's clearly already beyond the time delay of the choice and slower than light.

Ng Xin Zhao
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