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Interpretations of QM?

  1. Dec 6, 2003 #1
    I just wanted to ask How many interpretations of QM are there and which one is considered best by the scientific community?

    P.S.: Is there need for any QM interpretation et all?
  2. jcsd
  3. Dec 6, 2003 #2

    In David Griffiths book on quantum mechanics he breaks people into three groups, and I paraphrase:

    1. The realists. Where was a quantum particle just before you measured it and collapsed the wave function? An infinitesimal distance away from where you measured it. This implies that quamtum mechanics is an incomplete theory and that there are hidden variables that would give us more information about the particle (ie its exact position).

    2. The orthodox position. The particle really wasn't anywhere. It was the act of measuring that produced its exact location. There are various definitions of "measurement", but the main idea is the particle didn't have a definite position before the wavefunction collapsed.

    3. Agnostic. Doesn't make sense to ask a question, that you cant know the answer to. In other words, asking where the particle was BEFORE the measurement is just not a question worth spending time on.

    With the discovery by Bell in 1964 that it makes a measurable difference if the particle had an exact position before the measurement or not, agnosticism kind of evaporated and most physicists these days take the orthodox view which is supported by experiment.
  4. Dec 8, 2003 #3
    Ok, my list:
    1) Copenhagen intepretation
    2) Many worlds interpretation
    3) Many-minds interpretation
    4) Transactional interpretation
    5) Modal interpretation
    6) Decoherence
    7) Everett's relative state
    8) Bohmian mechanics
    9) Zeilinger's principle
    10) Relational quantum mechanics

    I think that decoherence is the most sound of these proposals
    Last edited: Dec 8, 2003
  5. Dec 8, 2003 #4


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    Usually the term many worlds interpretaion is applied to a whole set of interpretaions including the many minds interpretaion and Everett's interpretaion, which as it was the first (explicity, as I have seen it argued that techincally Bohmian mechanics is a many worlds interpretation) many worlds interpretation is sometimes just called the many worlds interpretaion though the orginal many worlds interpretaion is a variation on it.

    Anyway suffice to say there are so many different inerpretions of quantum mechanics and they can be put into broad groups, with overlap, such as:


    many worlds


    pschyo-physical parallellism


    I wouldn't call decohernce a seperate interpretion as it fits into just about interpretation.
  6. Dec 8, 2003 #5
    do you know if the Consistent histories interpretation can be included inside some of the 10 interpretations of my list, or form another different interpretation?

    Also, I would like that you clarify where exactly you classify decoherence
  7. Dec 8, 2003 #6


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    Well decohernce can be put into just about any quantum interpretaion, it's more a process than an actual interpretation.
  8. Dec 8, 2003 #7
    True, but there are some people (notably Zurek) who think environmental decoherence ALONE can provide an explanation of quantum mechanics. In this sense it can be regarded as a separate interpretation.

    No-one has mentioned "spontaneous-collapse" models yet, although you might want to put them in the "realist" category. However, there is a distinction to be made between whether you are being realist about particle properties (e.g. positions as in Bohmian mechanics) or wave-properties (as in spontaneous collapse models). You could also be realist about something much more abstract, such as quantum logic, but these interpretations usually end up having a somewhat positivist flavour that makes the 'realist' label a bit of a misnomer.

    There is also something called the "new orthodoxy", which is a modern non-interpretation designed to replace the Copenhagen non-interpretation. Copenhagen is actually untenable nowadays because it postulates a divide between the classical and quantum worlds, without saying where this divide is to be found. However, as experimentalists can now do quantum mechanics with macroscopic systems it doesn't really make sense to have this divide at all. Therefore, the "new orthodoxy" runs something like:

    A) Quantum mechanics applies to all systems in the whole universe.

    B) We don't see Schrodinger's cat in a superposition because of environmental decoherence.

    C) The wavefunction appears to collapse in a measurement due to the same sort of effect.

    Of these three, (C) is the most problematic, but it allows most researchers to get on with their work without worrying about foundational issues, much as Copenhagen did for most of the 20th century.
  9. Dec 8, 2003 #8
    hehehe... the copenhagen non-interpretation. i like that.
  10. Dec 12, 2003 #9
    I discovered today another interpretation of quantum mechanics, is called mangled worlds quantum mechanics, and is a variation of the many worlds interpretation
  11. Dec 26, 2003 #10
    Yet another interpretation of QM, the zitterbewegung interpretation
  12. Dec 28, 2003 #11


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    Another one: The "Ithaca" interpretation, by N.David Mermin.
  13. Dec 29, 2003 #12


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    In the sense that the predictions of QM in it's application to ordinary physical systems don't depend on interpretation, whatever apparent conceptual advantages some might have over others, deciding between them is arguably not a scientific problem.

    Environmental decoherence - which is more than mere interpretation - is the most important idea to emerge over the last 25 years and is believed responsible for the emergence of classicality in macroscopic quantum systems.

    However, among the most serious and puzzling problems in fundamental physics are those that arise when one tries to apply QM to the entire universe. The problem is that the universe by definition is everything, so in explaining the emergence of classicality from some quantum cosmological initial state, ideas like environmental decoherence can't be used and there are currently no convincing ideas on the subject.
    Last edited: Dec 29, 2003
  14. Jan 1, 2004 #13
    What about the many-histories interpretation? (Is not the same as the many-worlds interpretation)
    Last edited: Jan 1, 2004
  15. Jan 1, 2004 #14
    - The ensemble interpretation. I've just discovered that this is the interpretation accepted by Einstein
    - Quantum causal histories. This interpretation is due to Fotini Markopoulou
    - The Bare theory. This interpretation is due to David Albert
  16. Jan 1, 2004 #15
    The SonyCam interpretation.
    A Sony cam recorder is put inside the Schrodinger cat's box. The cam registers when the cat dies. No superposition. The outside observer was ignorent but the SonyCam registered. Inside reality.
  17. Jan 1, 2004 #16


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    Observation is observation. Measurement is measurement. No consciousness required. Do you think the physicists crawl into the target chambers at CERN while the beam is running to make the wave functions collapse?
  18. Jan 1, 2004 #17
    Richard, because they want to know what comes out? But is it due causality or because they don't know what may come out?
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