Media : Physics/Quantum

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~~~Imported from [Wikipedia:Quantum_mechanics mechanics Wikipedia] on 2009-02-22~~~

'''Quantum''' mechanics is a set of principles underlying the most fundamental known description of all physical systems at the microscopic scale (at the Videx:atomic level). Notable amongst these principles are both a dual [Videx:wave wave]-like and particle-like behavior of Videx:matter and Videx:radiation, and prediction of probabilities in situations where classical Media:physics predicts certainties. Classical physics can be derived as a good approximation to quantum physics, typically in circumstances with large numbers of Videx:particles.

== Interpretation of quantum mechanics ==

~~~Imported from [Wikipedia:Interpretation_of_quantum_mechanics Wikipedia] on 2009-04-10~~~

An interpretation of quantum mechanics is a statement which attempts to explain how quantum mechanics informs our understanding of nature. Although quantum mechanics has received thorough experimental testing, many of these experiments are open to different interpretations. There exist a number of contending schools of thought, differing over whether quantum mechanics can be understood to be deterministic, which elements of quantum mechanics can be considered "real", and other matters.

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The most common interpretations are summarized here (however, the assignment of values in the table is not without controversy, for the precise meanings of some of the concepts involved are unclear and, in fact, the subject of the very controversy itself):

No experimental evidence exists that would distinguish between the interpretations listed. To that extent, the physical theory stands, and is consistent, with itself and with reality; troubles come only when one attempts to "interpret" it. Nevertheless, there is active research in attempting to come up with experimental tests which would allow differences between the interpretations to be experimentally tested.

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<th>Interpretation</th>

<th><a href="http://en.wikipedia.org/wiki/Determinism" title="Determinism" style="color:#4400AA;font-weight:bold;">Deterministic?</a></th>

<th>Wavefunction 

real?</th>

<th>Unique 

history?</th>

<th><a href="http://en.wikipedia.org/wiki/Hidden_variable_theory" title="Hidden variable theory" style="color:#4400AA;font-weight:bold;">Hidden 

variables?</a></th>

<th><a href="http://en.wikipedia.org/wiki/Wavefunction_collapse" title="Wavefunction collapse" style="color:#4400AA;font-weight:bold;">Collapsing 

wavefunctions?</a></th>

<th>Observer 

role?</th>

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<td bgcolor="lightgrey"><a href="http://en.wikipedia.org/wiki/Copenhagen_interpretation_of_quantum_mechanics" title="Copenhagen interpretation of quantum mechanics" style="color:#4400AA;font-weight:bold;">Copenhagen interpretation</a> 

(Waveform not real)</td>

<td bgcolor="pink">No</td>

<td bgcolor="pink">No</td>

<td bgcolor="lightgreen">Yes</td>

<td bgcolor="pink">No</td>

<td bgcolor="white">NA</td>

<td bgcolor="white">NA</td>

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<td bgcolor="lightgrey"><a href="http://en.wikipedia.org/wiki/Ensemble_Interpretation" title="Ensemble Interpretation" style="color:#4400AA;font-weight:bold;">Ensemble interpretation</a> 

(Waveform not real)</td>

<td bgcolor="pink">No</td>

<td bgcolor="pink">No</td>

<td bgcolor="lightgreen">Yes</td>

<td bgcolor="yellow">Agnostic</td>

<td bgcolor="pink">No</td>

<td bgcolor="pink">None</td>

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<td bgcolor="lightgrey"><a href="http://en.wikipedia.org/wiki/Copenhagen_interpretation_of_quantum_mechanics" title="Copenhagen interpretation of quantum mechanics" style="color:#4400AA;font-weight:bold;">Copenhagen interpretation</a> 

(Waveform real) 

<a href="http://en.wikipedia.org/wiki/Objective_collapse_theories" title="Objective collapse theories" style="color:#4400AA;font-weight:bold;">Objective collapse theories</a></td>

<td bgcolor="pink">No</td>

<td bgcolor="lightgreen">Yes</td>

<td bgcolor="lightgreen">Yes</td>

<td bgcolor="pink">No</td>

<td bgcolor="lightgreen">Yes</td>

<td bgcolor="pink">None</td>

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<td bgcolor="lightgrey"><a href="http://en.wikipedia.org/wiki/Consistent_histories" title="Consistent histories" style="color:#4400AA;font-weight:bold;">Consistent histories</a> 

(Decoherent approach)</td>

<td bgcolor="yellow">Agnostic1</td>

<td bgcolor="yellow">Agnostic1</td>

<td bgcolor="pink">No</td>

<td bgcolor="pink">No</td>

<td bgcolor="pink">No</td>

<td bgcolor="yellow">Interpretational2</td>

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<td bgcolor="lightgrey"><a href="http://en.wikipedia.org/wiki/Quantum_logic" title="Quantum logic" style="color:#4400AA;font-weight:bold;">Quantum logic</a></td>

<td bgcolor="yellow">Agnostic</td>

<td bgcolor="yellow">Agnostic</td>

<td bgcolor="lightgreen">Yes3</td>

<td bgcolor="pink">No</td>

<td bgcolor="pink">No</td>

<td bgcolor="yellow">Interpretational2</td>

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<td bgcolor="lightgrey"><a href="http://en.wikipedia.org/wiki/Many-worlds_interpretation" title="Many-worlds interpretation" style="color:#4400AA;font-weight:bold;">Many-worlds interpretation</a> 

(Decoherent approach)</td>

<td bgcolor="lightgreen">Yes</td>

<td bgcolor="lightgreen">Yes</td>

<td bgcolor="pink">No</td>

<td bgcolor="pink">No</td>

<td bgcolor="pink">No</td>

<td bgcolor="pink">None</td>

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<td bgcolor="lightgrey">Stochastic mechanics</td>

<td bgcolor="pink">No</td>

<td bgcolor="pink">No</td>

<td bgcolor="lightgreen">Yes</td>

<td bgcolor="pink">No</td>

<td bgcolor="pink">No</td>

<td bgcolor="pink">None</td>

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<td bgcolor="lightgrey"><a href="http://en.wikipedia.org/wiki/Many-minds_interpretation" title="Many-minds interpretation" style="color:#4400AA;font-weight:bold;">Many-minds interpretation</a></td>

<td bgcolor="lightgreen">Yes</td>

<td bgcolor="lightgreen">Yes</td>

<td bgcolor="pink">No</td>

<td bgcolor="pink">No</td>

<td bgcolor="pink">No</td>

<td bgcolor="yellow">Interpretational4</td>

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<td bgcolor="lightgrey"><a href="http://en.wikipedia.org/wiki/Bohm_interpretation" title="Bohm interpretation" style="color:#4400AA;font-weight:bold;">Bohm-de Broglie interpretation</a> 

("Pilot-wave" approach)</td>

<td bgcolor="lightgreen">Yes</td>

<td bgcolor="lightgreen">Yes5</td>

<td bgcolor="lightgreen">Yes6</td>

<td bgcolor="lightgreen">Yes</td>

<td bgcolor="pink">No</td>

<td bgcolor="pink">None</td>

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<td bgcolor="lightgrey"><a href="http://en.wikipedia.org/wiki/Transactional_interpretation" title="Transactional interpretation" style="color:#4400AA;font-weight:bold;">Transactional interpretation</a></td>

<td bgcolor="pink">No</td>

<td bgcolor="lightgreen">Yes</td>

<td bgcolor="lightgreen">Yes</td>

<td bgcolor="pink">No</td>

<td bgcolor="lightgreen">Yes7</td>

<td bgcolor="pink">None</td>

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<td bgcolor="lightgrey"><a href="http://en.wikipedia.org/wiki/Copenhagen_interpretation_of_quantum_mechanics" title="Copenhagen interpretation of quantum mechanics" style="color:#4400AA;font-weight:bold;">Copenhagen interpretation</a> 

(Waveform real) 

<a href="http://en.wikipedia.org/wiki/Anthropic_principle" title="Anthropic principle" style="color:#4400AA;font-weight:bold;">PAP</a></td>

<td bgcolor="pink">No</td>

<td bgcolor="lightgreen">Yes</td>

<td bgcolor="lightgreen">Yes</td>

<td bgcolor="pink">No</td>

<td bgcolor="lightgreen">Yes</td>

<td bgcolor="lightgreen">Causal</td>

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<td bgcolor="lightgrey"><a href="http://en.wikipedia.org/wiki/Relational_quantum_mechanics" title="Relational quantum mechanics" style="color:#4400AA;font-weight:bold;">Relational 

Quantum Mechanics</a></td>

<td bgcolor="pink">No</td>

<td bgcolor="lightgreen">Yes</td>

<td bgcolor="yellow">Agnostic8</td>

<td bgcolor="pink">No</td>

<td bgcolor="lightgreen">Yes9</td>

<td bgcolor="pink">None</td>

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<td bgcolor="lightgrey"><a href="http://en.wikipedia.org/wiki/Theory_of_incomplete_measurements" title="Theory of incomplete measurements" style="color:#4400AA;font-weight:bold;">Incomplete 

measurements</a></td>

<td bgcolor="pink">No</td>

<td bgcolor="pink">No10</td>

<td bgcolor="lightgreen">Yes</td>

<td bgcolor="pink">No</td>

<td bgcolor="lightgreen">Yes10</td>

<td bgcolor="yellow">Interpretational2</td>

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<blockquote>

<ol>

<li>If wavefunction is real then this becomes the many-worlds interpretation. If wavefunction less than real, but more than just information, then Zurek calls this the "existential interpretation".

<li>Quantum mechanics is regarded as a way of predicting observations, or a theory of measurement.

<li>But quantum logic is more limited in applicability than Coherent Histories.

<li>Observers separate the universal wavefunction into orthogonal sets of experiences.

<li>Both particle AND guiding wavefunction are real.

<li>Unique particle history, but multiple wave histories.

<li>In the TI the collapse of the state vector is interpreted as the completion of the transaction between emitter and absorber.

<li>Comparing histories between systems in this interpretation has no well-defined meaning.

<li>Any physical interaction is treated as a collapse event relative to the systems involved, not just macroscopic or conscious observers.

<li>The nature and collapse of the wavefunction are derived, not axiomatic.

</ol>

</blockquote>

Each interpretation has many variants. It is difficult to get a precise definition of the Copenhagen interpretation. In the table above, two variants are shown: one that regards the waveform as being a tool for calculating probabilities only, and the other regards the waveform as an "element of reality".

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#MAGIC Videx q=quantum

[[[ +++"No experimental evidence exists that would distinguish between the interpretations of quantum mechanics. To that extent, the physical theory stands, and is consistent, with itself and with reality; troubles come only when one attempts to "interpret" it. Nevertheless, there is active research..."+++ ]]]