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Does this experiment demonstrate that conscoiusness causes collapse?

  1. Jan 28, 2010 #1
  2. jcsd
  3. Jan 28, 2010 #2


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    This experiment does NOT demonstrate that consciousness causes collapse. It is not important whether you KNOW the information, but whether you CAN know it in principle.
    (Let me use a classical analogy: When the book is written, then you can know information in principle, but it does not mean that you know that information. The existence of the book has nothing to do with consciousness.)
  4. Jan 28, 2010 #3
    But what does it matter if the data of the which-path information is maintained on a hard drive or deleted off it... I don't see how a simple change in the magnetic state of the hard disk could change the results of this experiment.
  5. Jan 28, 2010 #4


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    The hard disc is not essential. The essential information is encoded in the wave function describing the quantum particles. Certain manipulations (insertions or removal of the "eraser") change the wave function. You may think of wave function as a "quantum book", which behaves very differently from the classical book.
  6. Jan 28, 2010 #5
    So you have two identical double slit experiments, both recording which-path information.

    a) In one of these experiments, after the shooting of the electrons at the two slots, the data of the which-path information is deleted.

    b) In the other experiment, the data is kept then analysed afterwards.

    Everything that the wavefunction encountered in both a) and b) were absolutely identical, except one produced an interference pattern and one didn't...

    I'm still mighty confused as I can only see one thing that could cause this.

    You make it sound as if the "eraser" is a thing after the two slits effecting change on the wavefunction. The wording of the source says "But, we will erase the data obtained from the electron detectors at the slits before we analyze the data from the back wall."
  7. Jan 28, 2010 #6


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    Demystifier is correct. The only thing that matters is whether you COULD in principle determine the which-path information. You don't need to look at that information. You can throw it away and never look at it and you will still get results consistent with knowledge of the which-path. There are specific versions of double slit experiments that demonstrate this clearly.
  8. Jan 28, 2010 #7
    Ok thanks for making this clearer guys.

    Buy, why does this matter?

    What does it matter whether the which path data is stored thus the experimenter COULD determine which-path information (collapse), or if this data is deleted and the experimenter COULDN'T (thus no collapse). Why would the existence of the data or the non-existence of it have a causal influence on the wavefunction...
    I don't see any fundamental difference here.
  9. Jan 28, 2010 #8
    Reread point 4. of that source i provided in my first post.

    "Suppose we take our modified double slit set up -- with electron detectors at the slits -- and still leave everything intact. And we will still keep the electron detectors at the slits turned on, so that they will be doing whatever they do to detect electrons at the slits. And we will record the count at the slits, so that we will be able to obtain the results. But (this gets a little complicated), we will
    (1) mix the data from the slits with additional, irrelevant garbage data, and record the combined (and incomprehensible) data;
    (2) design a program to analyze data coming from the slits in one of two ways, either
    . (a) filtering out the garbage data so that we will be able to obtain clean results of electrons going through the slits, or
    . (b) analyzing the mixed-up data so that we will not be able to obtain the results of electrons going through the slits; and
    (3) leave it up to a visiting politician which way we actually analyze the data from the slits.

    The result upon final analysis by method (2)(a): a particle clumping pattern appears from the data.
    The result upon final analysis by method (2)(b): an interference pattern appears from the data."

    What on earth does physical reality care if we mix random numbers in with the data to make it incorrect or if we don't mix random numbers into it and keep it legitimate... How does the act of muddling the data to make it non-representative of what really happened have a causal impact on the wavefunction - whether it collapses or not..? Physical reality doesn't give a damn if a scientist comes along and ruins the data so he can't view it anymore. Do you see why I'm having trouble here?
  10. Jan 28, 2010 #9


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    I am not god, and so cannot explain why. Nonetheless, that is the rule. Here is a specific example:

    Take 2 entangled photons and run them each through a double slit setup. There will be NO interference for either. The reason is that in principle, you could learn about Alice's photon from Bob, and vice versa. Yet neither of them are checked. But you could have determined the which-path, so no pattern results.
  11. Jan 28, 2010 #10
    It's a real mystery! Thankyou for clearing it up drchinese & demystifier.
    Last edited: Jan 28, 2010
  12. Jan 28, 2010 #11


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    Check out this commentary on the Kim-Scully PRL paper from 2000. It is from the same website linked by the OP, and the situation is *far* more clearly explained, with appropriate reference to the experimental science.


    I think that the confusing point in the description from the OP's original link is that it seems to suggest that the information recorded at D0 would be changed based on the decision to look at which-path data at some later time. However, one can see from the experiment that this is not the case ... an interference pattern is recorded at D0 no matter what happens later, this is because there is no which-path information encoded on the signal there.

    So, there is no issue of conciousness at all ... if which-path info has been measured, the discrete-particle results are observed, if which-path info is unknown, then an interference pattern is observed.

    My understanding of this is that the beamsplitter between D1 and D2 acts analogously to the middle filter in the triple Stern-Gerlach experiment (e.g. bottom panel of http://commons.wikimedia.org/wiki/File:Sg-seq.svg" [Broken]). Basically it can be seen as a "measurement" that mixes the information from the two paths, so that even though each photon came from a distinct path, it will be detected in one of the two measurement states (D1 and D2) with equal probability.
    Last edited by a moderator: May 4, 2017
  13. Jan 28, 2010 #12
    That's a different experiment I think, i'll read it tomorrow. concerning my original link;

    The source says that the back wall is never looked at before the decision to delete the data is made. If the experimenter chooses to delete the data, an interference pattern is made. If the experimenter chooses to either observe, or simply leave the data untouched, discrete-particle results are observed.

    "And we will still keep the electron detectors at the slits turned on, so that they will be doing whatever they do to detect electrons at the slits. And we will record the count at the slits, so that we will be able to obtain the results. But, we will erase the data obtained from the electron detectors at the slits before we analyze the data from the back wall.

    The result upon analysis: an interference pattern at the back wall."

    If what this source says is correct, I see only two things that could possible cause this.
    (A) Consciousness
    (B) Existence of understandable, not-muddled data. (According to the source, either muddling the data or destroying it means there's an interference pattern)

    This is why I thought this experiment demonstrated that consciousness causes collapse, because I don't see how the data, meaningless without interpretation, could causally affect matter.
    Last edited: Jan 28, 2010
  14. Jan 28, 2010 #13
    According to the source in my OP, this is only true if the which-path info isn't destroyed before viewing the backwall. I don't undestand what could be so special about this data!!
  15. Jan 28, 2010 #14
    From the source:
    the difference is whether the analysis of the results at the back wall is conducted when information about the electrons' positions at the slits is available, or not.

    So, I only see either:
    a) the data is required to exist (#3 in source), be understandable, and not be muddled (#4 in source) OR
    b) a conscious observer has to have the ability to garner this which-path information.

    doesn't a) sound ridiculous to you? I'll repeat what I said before, what does physical reality care if this data is readable. It wouldn't. Data is just a bunch of 0s and 1s, meaningless until we interpret it. Data, meaningless without interpretation, cannot have a causal influence on matter.

    I see no holes in my logic, anyone care to enlighten me?
  16. Jan 28, 2010 #15


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    First of all I haven't read any of the links.

    However, a few years ago there was an experimental group (don't remember where) that were doing experiments in this field and they were claiming all sorts of nonsense; e.g. that it mattered whether or not they looked at the data on the computer. Maybe that is was you are referring to?
    There was -as far as I remember- nothing wrong with the "optical" part of their setup, but it was a clear demonstration of the fact that you don't always have to understand what you are doing in order to perform an experiment...

    Anyway, no conscious has absolutely nothing to do with it. Nor does it matter whether or not we save the data etc...
  17. Jan 28, 2010 #16


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    Nothing is special about the data itself, it doesn;t need to be recorded for the effect to occur. And it doesn't matter whether the which-path info is erased before or after the light hits the backwall. In fact, you can erase it after and it is "as if" the past is changed. It is the context of the complete experiment that matters.
  18. Jan 28, 2010 #17
    If the source isn't bogus, then this is incorrect. When the data is not saved, there's an interference pattern. When the data is saved but then erased, there's an interference pattern. When the data is saved but the muddled, there's an interference pattern.

    When the data is saved, then the backwall is analyzed, there's a discrete-particle result.

    If this source isn't lies, it is evidence tha the von neumann chain does NOT end with the measuring instrument.
  19. Jan 28, 2010 #18


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    I think the issue is that you are taking too much on faith the description of the details of the experiment described in that link you initially posted. Notice that the website author does not post citations directly referring to the results described there .. all of the citations are to "related" experiments, like the one analyzed in the link I posted.

    To my eye there is a lot of fuzzy thinking/analysis going on in the link you posted. For example, there has to my knowledge never been an experiment that worked precisely as he suggests with the cartoons he posted. Specifically, I do not believe anyone has ever measured the same particle both as it traversed the slit, and later at some projection screen. More generally, I do not believe that such an experiment *could* ever be done with QM particles in a meaningful way, due to the complications of carrying out multiple measurements on the same particles.

    All of the experiments that address the issue of delayed choice and quantum erasers involve clever tricks with how the particle is measured *after* it has gone through the slits.

    At any rate, I don't believe any of the allegorical accounts involving erasing data from hard-drives or the choices of visiting politicians, etc., without solid documentation in peer-reviewed literature, which I guess doesn't exist for those accounts. At least it is not given on the website you linked.
  20. Jan 28, 2010 #19
    Then what causes what the experimenters claim:

    Erase which-path information BEFORE backwall observation --> No collapse
    Maintain which-path information until backwall observation --> Collapse

    Muddle data BEFORE backwall observation --> no collapse
    Maintain integrity of data until backwall observation --> collapse

    If this source isn't lies, then what causes collapse has to either be the ability of a conscious being to observe the results, OR the fact that coherent data on the which-path information exists. There exists no other possibilities.
  21. Jan 28, 2010 #20
    I thought these results were too good to be true. Conclusive evidence showing the von neumann chain ended in either readable data or a conscious observer with the ability to read the data sometime in the future.
    Oh well, hopefully someone will try and replicate what this source described.
  22. Jan 28, 2010 #21
    I don't believe that any Interpretation which accepts those consequences allows for them to be observed in more than one state. Even for the MWI, both outcomes are seperated from any one observer, and those observers can never share information.

    To me this comes back to a basic principle: In the real world we rely on classical measuring devices, so issues like quantum erasure or thought experiments can NEVER be performed and observed with meaningful results. As thought experiments they're nifty however.
  23. Jan 28, 2010 #22
    I just wanted to add that 'data erased' is too fuzzy. When one erased data from HDD it is already too late: some portions of HDD are warmer then the others, so theoretically it is possible to recover the information.

    An interesting example is C60 interference with different air pressure: when pressure is high there is no interference (because one can theoretically detect a tiny wind?)
  24. Jan 28, 2010 #23
    Hmmm... I suppose the only true eraser in the universe would be a BH that DOES 'eat' matter and release only HR.
  25. Jan 28, 2010 #24
    True eraser must erase information before it irreversibly dissipate in the environment. I jsut wanted to attract the attention to the fact that the QM meaning of "information is erased" is very different from a common sense meaning (file erased, nobody looked at the detector etc)
  26. Jan 28, 2010 #25
    I've heard that information can escape from the BH via entaglement of HR with what is inside.
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