Wheeler's Delayed Choice Experiment

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Main Question or Discussion Point

Wheeler's delayed choice experiment is a thought experiment proposed by John Archibald Wheeler in 1978. Wheeler proposed a variation of the famous double-slit experiment of quantum physics, one in which the method of detection can be changed after the photon passes the double slit, so as to delay the choice of whether to detect the path of the particle, or detect its interference with itself.

Since the measurement itself seems to determine how the particle passes through the double slits, and thus its state as a wave or particle, Wheeler's thought experiment has been useful in trying to understand certain strange properties of quantum particles. An implementation of the experiment in 2007 showed that the act of observation ultimately decides whether the photon will behave as a particle or wave, verifying the unintuitive results of the thought experiment.

My question is:

What does Wheeler mean in regards to "Act of Observation"? Is he talking about a sentient being observing, or is he saying "observer" as in an interaction between particles or instruments?
 

Answers and Replies

  • #2
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Bumping this. I would like to know what Wheeler is implying about the act of observation. I am pretty sure he means with detectors or instruments, and not that of a sentient being's knowledge of the particle. Is this correct? Someone who knows what they're talking about please respond. :)
 
  • #3
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Disclaimer - I am not a science grad student!

As far as I have read, you are right. "Act of observation" doesnt stand for observations by a sapient human. In an electron double slit experiment, usually a photon is bumped to the electron to know its position/momentum. And that is how the "act of observation" is done. So in the natural world, any stray photon hitting the electron collapses its state, thus causing decoherence.

As said, what I have explained above are from science popularisation books/blogs.
Others would correct me or to add to mine accordingly.

Thanks
 
  • #4
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Werunom,

Thanks for the response. I agree with you too that this is the case, but I would like it to come from someone who has a degree in quantum physics or has at least a lot of expertise to verify the claims being made on what Wheeler meant by "act of observation"
 

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