Quantum Mechanics I: Interpretations

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Quantum Mechanics IInterpretations

• by
• Robert Nemiroff
• Michigan Technological University

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Physics X About This Course

• Pronounced "Fiziks Ecks"
• Reviews the coolest concepts in physics
• Being taught for credit at Michigan Tech
• Michigan Tech course PH4999
• Aimed at upper level physics majors
• Light on math, heavy on concepts
• Anyone anywhere is welcome
• No textbook required
• Wikipedia, web links, and lectures only

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Uncertainty PrincipleInterpretations

• There are MANY interpretations of quantum
  mechanics, but only a few will be reviewed here
• Copenhagen Interpretation
• Many Worlds Interpretation
• Ensemble Interpretation
• Hidden Variables

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Uncertainty PrincipleCopenhagen Interpretation

• Most quoted interpretation convention.
• No single statement defines it.
• Defining properties sometimes unclear.
• Systems described by wave function(s)
• Wave functions are probabilistic
• particles do not have an exact position
• uncertainty principle always holds
• Wave functions "collapse" when an observer makes
  a measurement

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Uncertainty Principle Many Worlds Interpretation

• Every possible quantum measurement outcome occurs
• each outcome is realized in a different universe
• these universes do not communicate
• together, these universes compose a metaverse
• No observer-triggered wave function collapse
• therefore different from the Copenhagen
  interpretation
• incorporates "decoherence" instead

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Uncertainty Principle Ensemble Interpretation

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• QM wavefunctions only apply to particle ensembles
• does not apply to individual particles
• each particle in ensemble is "prepared" the same
• supported, at times, by Einstein
• avoids some single-particle philosophy debates
• can attribute probability to classical ignorance,
  not QM indeterminancy

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Uncertainty PrincipleHidden Variables

• Uncertainty caused by untracked complexity
• Universe classical but influenced by unseen
  variables
• not unlike matter before atoms discovered
• Once endorsed by Einstein
• Origin of "God does not play dice." phrase
• Fundamentally different than standard QM
  uncertainty
• universe completely deterministic
• allows a "first mover" type God
• Might demand faster than light communication
• Bell realized HV makes different statistical
  predictions
• QM found right, HV wrong by modern tests