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Another double slit question - noob

  1. Aug 21, 2013 #1
    another double slit question - noob :(

    Hi guys, I never officially studied physics so my knowledge on the topic is limited.

    My understanding of quantum physics in relation to the double slit experiment is the following:
    When you only observe the end result of light, it appears as if it interferes with itself, suggesting its a wave. But when you observe light mid-travel, it collapses into a particle.

    My question: Is it the act of conscious measurement that collapses the wave, or is it simply the fact the light has left a "mark", Regardless of conscious observers or not.

    I understand my terminology may be incorrect, and I might be missing some fundamental information. But, please give it a crack.

    I would appreciate answers in direct response to my question, and on the broader sense of quantum physics.
  2. jcsd
  3. Aug 21, 2013 #2


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    Staff: Mentor

    There's no consciousness involved; it's that the light has interacted with the environment around it, or as you say, "left a mark". If you google for "quantum decoherence" you'll find a bunch of interesting stuff.
  4. Aug 21, 2013 #3
    Decoherence doesn't produce a definite outcome, and it may well be consciousness is necessary. I don't know how Nugatory can rule it out.
    I am currently working on the delayed-choice entanglement swapping experiment and Ghirardi's thought experiment in his book 'Sneaking a Look at God's Cards' to try and pin point where collapse occurs.

    I myself am a believer in the consciousness causes collapse, but very few associate themselves with that solution to the measurement problem. Thus I'm limited to those I can contact for discussion over the topic.
  5. Aug 21, 2013 #4


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    Staff: Mentor

    Decoherence doesn't produce a specific outcome (the particle may still go through one slit or the other) but it does preclude all the outcomes in which the particle can be said to go through both slits - and it does so without ever invoking any consciousness anywhere.
  6. Aug 22, 2013 #5
    If you take the full environment into account, then both slits the photon (or whatever particle) goes through.

    The interference pattern is still present, except it is hidden.
  7. Aug 22, 2013 #6
    I should add that although decoherence does not solve the measurement problem, if you have two terms that are effectively mixtures, then the particle must have gone through one or the other slit. Then you have no measurement problem. But as admitted, decoherence does not solve it, therefore the system is in a superposition of going through both slits.

    The measurement problem is not concerned with what outcome arises; its about how that outcome came about.
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