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Several interpretations have been advanced to explain how wavefunctions "collapse" to yield the observable world we see.

Several interpretations have been advanced to explain how wavefunctions "collapse" to yield the observable world we see.

* The "hidden variable" interpretation<ref>http://www.reasons.org/resources/non-staff-papers/the-metaphysics-of-quantum-mechanics</ref> says that there is actually a [[determinism|deterministic]] way to predict where the wavefunction will collapse; we simply have not discovered it.  [[Von Neumann]] attempted to prove that there is no such way; however, [[John Stuart Bell]] pointed out an error in his proof.

* The "hidden variable" interpretation<ref>http://www.reasons.org/resources/non-staff-papers/the-metaphysics-of-quantum-mechanics</ref> says that there is actually a [[determinism|deterministic]] way to predict where the wavefunction will collapse; we simply have not discovered it.  [[John von Neumann]] attempted to prove that there is no such way; however, [[John Stuart Bell]] pointed out an error in his proof.

* The many-worlds interpretation says that each particle does show up at every possible location on its wavefunction; it simply does so in alternate universes.  Thus, myriads of alternate universes are invisibly branching off of our universe every moment.

* The many-worlds interpretation says that each particle does show up at every possible location on its wavefunction; it simply does so in alternate universes.  Thus, myriads of alternate universes are invisibly branching off of our universe every moment.

* The currently prevailing interpretation, the Copenhagen interpretation, states that the wavefunctions do ''not'' collapse until someone observes the particle at a certain location; until someone observes it, it exists in a quantum indeterminate state of simultaneously being everywhere in the universe.  However, [[Schrodinger]], with [[Schrodinger's cat|his famous cat experiment]], raised the obvious question: who, or what, constitutes an observer? What distinguishes an observer from the system being observed? In essence, the Copenhagen Interpretation requires a [[soul]] or something else to distinguish observers from inanimate matter.

* The currently prevailing interpretation, the Copenhagen interpretation, states that the wavefunctions do ''not'' collapse until the particle is observed at a certain location; until it is observed, it exists in a quantum indeterminate state of simultaneously being everywhere in the universe.  However, [[Schrodinger]], with [[Schroedinger's Cat|his famous thought experiment]], raised the obvious question: who, or what, constitutes an observer? What distinguishes an observer from the system being observed? This distinction is highly complex, requiring the use of ''quantum decoherence theory'', parts of which are not entirely agreed upon. In particular, quantum decoherence theory posits the possibility of "weak measurements", which can indirectly provide "weak" information about a particle ''without'' collapsing it.<ref>http://quanta.ws/ojs/index.php/quanta/article/view/14/21</ref>

==Applications==

==Applications==