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If a monkey was to observe the electron in double slt experiment how would it behave?

  1. Jun 17, 2006 #1
    the title says it all.
     
  2. jcsd
  3. Jun 17, 2006 #2

    mathman

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    What is "it", the monkey or the electron? In any case observed effect doesn't depend on whether or not anyone is watching. The diffraction pattern will appear. I don't know if the monkey cares.
     
  4. Jun 17, 2006 #3

    dav2008

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    The monkey would fling feces at the detector screen.
     
  5. Jun 17, 2006 #4
    dav2008 pretty much nailed the sequence of events.
     
  6. Jun 17, 2006 #5

    HallsofIvy

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    Assuming that "it" is the electron, it would behave the same way if would if you were watching it. What, you thought your were special?
     
  7. Jun 18, 2006 #6
    Is that before or after it types the collected works of Shakespear?
     
  8. Jun 18, 2006 #7
    Well, it's in superposition with a monkey that already has.
     
  9. Jun 19, 2006 #8
    LOL ... thanks for the replies.
     
  10. Jun 21, 2006 #9
    Riiiiiight... laying aside all that, I think that the point is somewhat moot. To know what had happened, you'd have to observe the result post-fact. BAM! Suddenly the monkey is no longer the only observer. Hear that gurgling sound? That's the waveform collapsing.
     
  11. Jun 21, 2006 #10
    My understanding of the currently generally accepted reading of the Copenhagen Interpretation is that that there is nothing special about 'observation' as such, any interaction with the universe at large will collapse the wave function. So any sort of measurement will do it, whether it involves a human, a monkey, an aardvark or just a photon detecting screen.
     
  12. Jun 21, 2006 #11
    It depends on if the monkey can sign or not. If the monkey can't, the wave function collapses as usual. If it can, the wave function collapses and the monkey signs to you, asking what journal the ensuing paper should be presented to, and what order the authors will be listed in.
     
  13. Feb 3, 2012 #12
    Re: if a monkey was to observe the electron in double slt experiment how would it beh

    i don't believe what mumeishi said is true... the delayed choice quantum eraser experiment shows that even after measurement, once the "information" is erased the interference pattern re-emerges... so the awareness of the information is in fact what collapses wave functions. the monkey question is quite significant then... i wonder if there has been an experiment to find out.
     
  14. Feb 4, 2012 #13
    Re: if a monkey was to observe the electron in double slt experiment how would it beh

    So, you do a double slit experiment and see an interference pattern. Fine, you don't know which slit each photon passed through, all makes sense.
    Now you add polarizers behind each slit, orthogonal to each other, and do the experiment again. Each photon can only pass through one slit so the interference pattern disappears. Do YOU know which slit each photon passed through? No, of course not. So why does the interference pattern disappear if you have no knowledge/awareness of the photons' paths?

    Isn't this enough to show that consciousness/awareness has nothing to do with the experimental outcome?

    Here's a site which explains the quantum eraser quite nicely http://www.mathblog.ellerman.org/2011/11/a-common-qm-fallacy/
     
  15. Feb 4, 2012 #14
    Re: if a monkey was to observe the electron in double slt experiment how would it beh

    The interference is still there. It is just hidden. When do you 'erasure of information', two fringes appear.
     
  16. Feb 4, 2012 #15
    Re: if a monkey was to observe the electron in double slt experiment how would it beh

    From Paul Kwiat:
    Bruce Rosenblum is saying what is changed is an unobserved past. We never observed the interference before finding out which way the particle went, or 'erasured' the which-way information. Only if we erase the information and do the appropriate correlations do we see the fringe and anti-fringe.
     
  17. Feb 4, 2012 #16
    Re: if a monkey was to observe the electron in double slt experiment how would it beh

    I think you're talking about the quantum eraser experiment. I was talking about a standard double slit experiment - each particle can only pass through one slit and therefore can't interfere with itself.
     
  18. Feb 4, 2012 #17
    Re: if a monkey was to observe the electron in double slt experiment how would it beh

    I don't get this argument: it's already been shown that something that supposedly has no consciousness, such as a simply machine, can collapse a wave function by means of measurement the same as any other measurement.
     
  19. Feb 4, 2012 #18
    Re: if a monkey was to observe the electron in double slt experiment how would it beh

    "In quantum mechanics, the Heisenberg uncertainty principle states a fundamental limit on the accuracy with which certain pairs of physical properties of a particle, such as position and momentum, can be simultaneously known. In layman's terms, the more precisely one property is measured, the less precisely the other can be controlled, determined, or known."

    "The uncertainty principle states a fundamental property of quantum systems, and is not a statement about the observational success of current technology."."



    http://en.wikipedia.org/wiki/Uncertainty_principle



    The verb "know" only refers to conscious activity. It's part of what mind is.
     
  20. Feb 4, 2012 #19
    Re: if a monkey was to observe the electron in double slt experiment how would it beh

    The reason there is still disagreement as to what constitutes measurement is that it makes no experimental difference according to quantum mechanics. The way QM works under the Copenhagen interpretation is that you have to split the world into two parts, the “observer” or measurement device, and the “observed” or the particles you’re measuring.

    The measurement device is assumed to behave classically. The particles in the observed system are in a superposition of states described by the wave function which keeps evolving until it interacts with the classical measurement device. The question is where to draw the line. You could consider a photon to be the observed system and an atom to be the measuring device, but you can also consider the photon-and-atom system as in a superposition of states, and take a Geiger counter to be the measurement device. So there is this von-Neumann chain, going from elementary particles to Geiger counters to human beings, and we have to decide where to cut it off.

    Von Neumann proved in his famous "Bible" of QM that regardless of where you cut the chain, you would get the same experimental results. But he argued that wherever you cut the chain you have things made out of particles on each side of the cut, so there’s no principled way to place the cut in the middle. So he decided that you should place the cut between the human mind and the human body, because he believed that the mind is non-physical. Hence "consciousness causes collapse" was born. Nowadays, the most popular view is decoherence, where there is no real collapse, it's just that when you have a large number of particles in the environment interacting with the system, the wave function becomes smeared out and looks like it has collapsed. So decoherence gives us a reasonable place to cut the chain, when the number of particles involved reaches a critical number so that interference effect become negligible.
     
  21. Feb 4, 2012 #20
    Re: if a monkey was to observe the electron in double slt experiment how would it beh

    Yeah, an atom *does* technically measure a photon if it absorbs it. You draw the line between measurement and no measurement. If it doesn't collapse it's wave function, it's not a measurement. So if you shine a photon through a prism and the prism doesn't absorb it, then what you get are two polarization angles, the atoms didn't absorb it, so it's still subject to superposition.

    A ruler can measure length, does that mean it has consciousness?
     
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