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  1. Nov 8, 2003 #1
    Why one past?

    Quantum theory is very successful in describing bits of matter as clouds (probability distributions).

    Ironically, it is the proximity of one cloud to another that constrains the shape and size of each cloud.

    These constraints pile one upon another, ultimately constraining the quantum world until on large scale it becomes the world of our everyday experience.

    However, quantum theory says that underneath it all, the quanta are ultimately unconstrained. For instance, if a photon from a distant star ultimately hits a photo receptor in your eye, then in some sense that same photon did not hit your eye, or even the earth and is still flying through space.

    This multiple existence of quanta is the very basis of quantum computers.

    So it seems clear to me that our solid existence is ultimately a self-consistent set of constraints/observations on quanta.

    In fact, it seems that the defining characteristic of our experiential world is that all observations are consistent, whereas in the quantum world, all quanta are ultimately not consitent.

    Let me come back at the photon and the photo receptor in order to clarify this point: When the photon interacts with the photoreceptor, this sets off a chain of events that result in a memory of the initial quantum interaction. Such memories are self consistent. Think of it as information. Our universe is built of layer upon layer of self consistent memory or information. The memories record past quantum interactions and are built via a series of ongoing quantum interactions. Each of these interactions is consistent in terms of the interactions that preceeded it, and at the same time each of these interactions is one of an arbitrary number of possibilities. The constraints are determined by what happened in the past.

    Our experiential universe is nothing more than a set of information, memories of past quantum interactions. As individuals, we are nothing more than the sum of our past memories. The defining characterisic here is that all of these memories record the same past. But quantum theory tells us that there are an arbitrary number of different pasts. Why does our experiential reality choose just one?

    I've been trying to come up with a conceptual framework, the beginning of a mathematical description for this concept.

    Can anyone out there help?
    Last edited: Nov 9, 2003
  2. jcsd
  3. Nov 8, 2003 #2

    The above isn't correct. Photons due have the property of seeming to taking many different paths (all paths!) but this is when unobserved. By receiving a photon in your eye, you 'collapse the wave function' of it - ie it goes from a possibility of many states to one defined state.

  4. Nov 8, 2003 #3
    What you describe is one conceptual framework.

    This is a popular framework because it feels consistent with our experential reality.

    However, what collapses is not the wave, but our conception of it. The wave becomes constrained by an observation in our experiential domain, our universe.

    The question is not about the wave, but why it appears to becomes constraned this way. In other words, why does our experiential domain exist at all within the much larger quantum fuzz.
  5. Nov 12, 2003 #4
    Re: Why one past?

    I think I understand what you mean. I posted a very similar question some time ago, before the relaunch of PF.

    Went like this:
    "Any detector, even our body, is just a system of particles obeying the rules of quantum theory. So there's actually no reason why wavefunctions should ever collapse. Instead, everything should be a superposition of possible states, i.e., a superposition of wavefunctions, propagating continously in accordance to Schrödinger's (or whatever) equation, without ever collapsing." - The so-called 'many-worlds theory'.

    People on this forum convinced me that there are several flaws in this argument. The most important one seemed to me the concept of 'entanglement' or 'decoherence'. IOW, as you take into account larger and larger systems, you can't assume any more that the state of the system is a linear (coherent) superposition of the subsystems' states. This leads to a more and more 'classical' behavior of the larger system, until at least, in the experiential domain, you have a definite measurement and not a superposition.
  6. Nov 12, 2003 #5


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    arcnets - many worlds theory is a valid interpretation of quantum mechanics and your statement is valid. It's just a case of do you prefer the problems (ontological and otherwise) that the CI brings compared to those that the MWI brings.
  7. Nov 12, 2003 #6
    I'm not sure what CI stands for. Persumably something about collapsing wave functions.

    Decoherence is a concept that derives from a belief that particles fall out of some sort of quantum fuzzy state when they are observed. This is the collapsing wave idea. But this has never made much sense to me. Quantum theory math all deals with waves and the theory works very well. The idea that the waves collapes is a conceptual crutch. What happens is that the observed freedom of a particular particle is constrained via observation. But those constraints are a function of the observing reference frame. The rule is that all observations in one reference frame, one universe, must be consistent.

    Our experiential universe, our reference frame devolves from the quantum world by the application of the one simple rule listed above, but there is no theory that explains why. This is a major hole in physics theory.
  8. Nov 12, 2003 #7


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    CI is the Copenhagen interpretation, which is the convential interpreation. The collapse of the wavefunction is observable, so any QM intepretation must explain it.
  9. Nov 13, 2003 #8
    Yes. One of the problems is, that both quantum theory and relativity use 'observers'. But the concepts are not the same. They rather contradict each other.
    For instance, a statement like 'two wavefunctions collapse at the same time' makes so sense in relativity, since another observer may not see those events at the same time.
    Similarly, the expression 'the same past' is problematic.
  10. Nov 13, 2003 #9


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    The two concepts don't really contradict each other, special relativty can be integrated into quantum mechanics using the Dirac equation, they are two very differnt and unrlated concepts. In relativty a rest frame is well defined (and is easily related to other ret frames via tensors) whereas a in QM a measuremnt is not a well defined concept.

    A big problem in QM is that you have two different forms of time-dependence, the unitary evolution of the time-dependet Schroedinger equation and the collapse of the wavefunction.
  11. Nov 14, 2003 #10
    I refer to the past as a history of quantum interactions or observations that constrain the state of particles, giving rise to persisent information or memory.

    The guiding rule here is that such interactions build upon one another, have a causal connection, are consistent.

    Relativity and time dialation are not an issue because we are not talking about simultinaity here, but rather about the order in which things happen. The indivdual quantum interactions themselves happen in a very small space and therefore, for most situations, the affects of relativity may be neglected. However, when considering quanta traveling over vast distances to interact, the rules of relativity govern the order in which various interactions may occur.
    Last edited: Nov 15, 2003
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