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Is it Information or Interaction that Observes ?

  1. Oct 29, 2011 #1
    Is it "Information" or "Interaction" that "Observes"?

    First off, I know there are many questions on this forum in regards to "does consciousness collapse the wavefunction" and I admit that this is roughly the same question in a different way. I wanted to approach this in a new topic though because I wanted to focus this question specifically.

    The question then is in the title. Does the "collapse" occur under "observation" strictly because there is an interaction, or is it because there is an interaction that specifically gives information and what defines "information"? To clarify the analogy we could compared the first case to that of a photon bouncing off of an electron. The "interaction" would thus alter the trajectory/momentum of the electron. A case of "information" would occur if the bouncing off of the photon was measured in order to tell us a bit about the electron's speed or position.

    I think this question is important because, via our current paradigm, we're a bit biased towards trying to find the most materialistic/deterministic explanation possible (i.e. the one closer to the former situation, where a result is based on a reaction).

    But going to the double slit experiment, I do not see how we can suppose the effect due to a physical interaction of any sort. Even such an obvious interaction as hitting an electron passing through either slit with a photon does not satisfy the necessary conditions to alter its trajectory through that slit. And furthermore, the slit apparatus itself is within reach of our electron's probability range! It too interacts, but it does not appear to be what determines the trajectory.

    We then are forced to include that it must be an interaction specifying information, but here's where it gets confusing to me. What is information? The universe has no reason to say that a few dots on a detector foil is "information" as we do. To the universe, the electron hitting the slit shield itself could be "information." The electron bouncing interminably around in the container, getting absorbed, remitted and so on could be "information." I see no reason why, to the universe, the detector foil should not be in a superposition of states even with the measurement device (also in superposition) in front of one slit. If the universe didn't care where the electron was before it hit the foil or "measurer" (a good example of this being the effect-->cause type experiments) then why should we presume it so anthropomorphic to care about the detector foil or our device near the slit?

    To perhaps go back how I admitted this is largely the age-old question in a different way. It seems to me that we mistakenly attribute our measuring devices as giving information in the universe when, in truth, they are only giving information to us.
    Last edited: Oct 29, 2011
  2. jcsd
  3. Oct 30, 2011 #2
    Re: Is it "Information" or "Interaction" that "Observes"?

    "Does the "collapse" occur under "observation" strictly because there is an interaction, or.."
    You seem to assume that wave function collapse is a real event, but most interpretations of QM don't see it that way, e.g. see the table here: http://en.wikipedia.org/wiki/Interpretations_of_quantum_mechanics#Comparison

    See http://en.wikipedia.org/wiki/Quantum_decoherence "Decoherence does not generate actual wave function collapse. It only provides an explanation for the _appearance_ of wavefunction collapse"

    Also see: http://en.wikipedia.org/wiki/Quantum_decoherence#Measurement

    In short, you're using an outdated concept.

    I'll try a summary and let me know if it makes sense to you:

    1. Particles occupy all possible paths (or states) with differing weights, so any arbitrary event has a weight which is the sum of all the possible states. This is well established by Feynman.
    2. When simple particles interact with a large collection of particles, the simple particle decoheres and becomes 'entangled' with the large collection. Which is just a fancy way of saying that each possible state of the simple particle becomes linked to a different state of the large collection in such a way that the sum of all possible states of the large collection is independent between its states. It is as though each state of the large collection becomes orthogonal so that there is no further communication between the separate instances of the large collection.
    3. So we still have a superposition of states for the full large collection of particles, so no collapse at all, but each state for the large collection is independent and so isolated. Now imagine that you are part of that large collection of particles, you would only experience one of those independent states since they don't interact. So you only see a single outcome corresponding to the respective state of the simple particle.

    It is no more meaningful to ask 'why do I specifically experience state 1 rather than state 2' than it is to ask 'why do I experience being me rather than someone else'.
  4. Oct 30, 2011 #3
  5. Oct 30, 2011 #4
    Re: Is it "Information" or "Interaction" that "Observes"?

    TGlad, it sounds to me as if you are describing Everett's way at looking at the issue, yes? Regardless, I'm not sure how confident we can conclude a consensus over any individual interpretation of quantum mechanics as, at least in academic environments, there really doesn't seem to be any. I also find it hard to buy into the interpretation you described because it hinges so heavily on the "interaction" as discussed. The wave-function/particle/whatever has an opportunity to interact with physical substance before the detector, yet that is not what makes it "decohere." It seems strongly to me that only situations whereby a certain information (or logic, or consequence) is ascertained that affects this, not just interaction. The question I see then is-- What type of information causes this collapse/decoherrence?

    And Stevie, I appreciate the link, but I'm afraid I've got too many other science textbooks to read at the moment, hah.
  6. Oct 30, 2011 #5
    Re: Is it "Information" or "Interaction" that "Observes"?

    It is only a quick section on the nature of interaction/information. Will probably take about 5 minutes of your time.
  7. Oct 30, 2011 #6
    Re: Is it "Information" or "Interaction" that "Observes"?

    Well it does decohere in this case, I think. For example the path that bounces off a random wall to the detector is not in a coherent state with the path that goes direct.

    It isn't a boolean thing, if a particle interacts with a larger collection of particles then there will be more decoherence between the possible states of the whole system. There is a superposition of these possible collection states but they don't affect each-other overall, so the macroscale appears classical.
    When a photon is detected by an electron in the double-slit, you get decoherence because the electron is connected to a larger system (the rest of the detector), if the photon just was absorbed and emitted by a single electron it wouldn't decohere.

    Well, it is saying nothing more than Feynman's path integral formulation. If one accepta that a particle takes every possible path then it seems that one needs to accept that the particles in our bodies take many different paths, they just don't interact with each-other as much in the macroscopic scale as at the quantum scale.
    Feynman and Everett remind me of Charles Darwin and Thomas Huxley. Darwin did all the work to explain evolution but completely avoided the issue of where humans came from. Huxley made the obvious connection and took the flak as it was so controversial that we could be apes.

    Multiple parallel outcomes would always be controversial, but it is not really even an interpretation, just a logical conclusion of the QM maths right? Hence Hawking described Many Worlds as 'trivially true'.

    Well, ok, but there is a definite leaning... as I showed in the table link, there are 9 interpretations with no 'collapse' and only 5 that include collapse. Of those five, three don't involve humans in collapse, and the remaining two are very old, pre-1933.

    So there is, at least, a strong interpretation that single outcomes (whether that is 'collapse' or decoherence) are nothing to do with humans observing stuff.
    Last edited: Oct 30, 2011
  8. Oct 30, 2011 #7
    Re: Is it "Information" or "Interaction" that "Observes"?

    I'm not sure how it could decohere partly as you are saying. If it decoheres to entangle with a specific "set" within the superpositions, then only that "path" must exist in that...well, let's go ahead and call it a "reality" just for sake of ease. Any interaction before the detector would thus make it decohere, and unless you want to make multiple particles out of one within one reality, I don't see how it could not decohere completely. That's why I point towards information.

    Granted, I'm not suggesting that any sort of multiverse/everett-type theory is wrong. In fact, I should point out that my original question was posed from the perspective of admittedly disregarding it momentarily for the sake of argument. All the same, whereas I see the logic of it, I am unsatisfied by how it seems to try and have its cake and eat it too, without paying for the cake (subjective opinion).

    As for the table, I hear you, but be careful as number of theories has no need to correspond to number of adherents. A parallel would be American political parties for instance.
  9. Oct 30, 2011 #8
    Re: Is it "Information" or "Interaction" that "Observes"?

    I'll try and check it out again. At the time I looked at it, I couldn't find google access, but I frequent Barnes and Noble as a library hah.
  10. Oct 31, 2011 #9
    Re: Is it "Information" or "Interaction" that "Observes"?

    I'll admit that I'm as lost as you (I'm probably more lost actually) as to exactly what causes decoherent states (or 'collapse').
    I have heard that it is interaction with anything which is capable of maintaining a record of that interaction. e.g. if it flips some state permanently.
    But have heard other descriptions too, so would also be interested to get a clearer answer.
  11. Oct 31, 2011 #10
    Re: Is it "Information" or "Interaction" that "Observes"?

    If that explanation you heard were true, it would seem very similar to being an information-deal ordeal like the others. I'm sure we're all actually wrong though anyways :)
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