QUANTUM MECHANICS I:INTERPRETATIONS

byRobert Nemiroff

Michigan Technological University

Physics X: About This Course

• Pronounced "Fiziks Ecks"• Reviews the coolest concepts in physics • Being taught for credit at Michigan Tech

o Michigan Tech course PH4999o Aimed at upper level physics majorso Light on math, heavy on concepts o Anyone anywhere is welcome

• No textbook requiredo Wikipedia, web links, and lectures only

UNCERTAINTY PRINCIPLE:INTERPRETATIONS

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

UNCERTAINTY PRINCIPLE:COPENHAGEN INTERPRETATION

• Most quoted interpretation convention.• No single statement defines it.

o Defining properties sometimes unclear.• Systems described by wave function(s)• Wave functions are probabilistic

o particles do not have an exact position o uncertainty principle always holds

• Wave functions "collapse" when an observer makes a measurement

UNCERTAINTY PRINCIPLE: MANY WORLDS INTERPRETATION

• Every possible quantum measurement outcome occurso each outcome is realized in a different universeo these universes do not communicateo together, these universes compose a metaverse

• No observer-triggered wave function collapseo therefore different from the Copenhagen interpretationo incorporates "decoherence" instead

UNCERTAINTY PRINCIPLE: ENSEMBLE INTERPRETATION

   • QM wavefunctions only apply to particle ensembles

o does not apply to individual particleso each particle in ensemble is "prepared" the sameo supported, at times, by Einsteino avoids some single-particle philosophy debateso can attribute probability to classical ignorance, not QM indeterminancy

UNCERTAINTY PRINCIPLE:HIDDEN VARIABLES

• Uncertainty caused by untracked complexity• Universe classical but influenced by unseen variables

o not unlike matter before atoms discovered• Once endorsed by Einstein

o Origin of "God does not play dice." phrase• Fundamentally different than standard QM uncertainty

o universe completely deterministic allows a "first mover" type God

• Might demand faster than light communication• Bell realized HV makes different statistical predictions

o QM found right, HV wrong by modern tests