Physics:Quantum Measurement problem - Revision history

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	'''Measurement problem''' ~~is a Book I topic in the Quantum Collection. Quantum~~ Measurement problem is a central conceptual issue in quantum mechanics concerning how definite outcomes arise from probabilistic quantum states. While the wave function evolves deterministically according to the Schrödinger equation, measurements yield single, definite results rather than superpositions. This raises the fundamental question: how does a superposition of many possible outcomes reduce to a single observed reality? Quantum Measurement problem is a central conceptual issue in quantum mechanics concerning how definite outcomes arise from probabilistic quantum states. While the wave function evolves deterministically according to the Schrödinger equation, measurements yield single, definite results rather than superpositions. This raises the fundamental question: how does a superposition of many possible outcomes reduce to a single observed reality?		'''Measurement problem''' quantum Measurement problem is a central conceptual issue in quantum mechanics concerning how definite outcomes arise from probabilistic quantum states. While the wave function evolves deterministically according to the Schrödinger equation, measurements yield single, definite results rather than superpositions. This raises the fundamental question: how does a superposition of many possible outcomes reduce to a single observed reality? Quantum Measurement problem is a central conceptual issue in quantum mechanics concerning how definite outcomes arise from probabilistic quantum states. While the wave function evolves deterministically according to the Schrödinger equation, measurements yield single, definite results rather than superpositions. This raises the fundamental question: how does a superposition of many possible outcomes reduce to a single observed reality? In quantum theory, the state of a system is described by a wave function that evolves deterministically:
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	{{Short description\|Fundamental problem concerning the emergence of definite outcomes in quantum measurements}}		{{Short description\|Fundamental problem concerning the emergence of definite outcomes in quantum measurements}}

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	'''~~Quantum~~ Measurement problem''' is a central conceptual issue in ~~[[Physics:Quantum mechanics\|~~quantum mechanics]] concerning how definite outcomes arise from probabilistic quantum states. While the ~~[[Physics:Wave function\|~~wave function]] evolves deterministically according to the ~~[[Physics:Schrödinger equation\|~~Schrödinger equation]], measurements yield single, definite results rather than superpositions.~~<ref name="Weinberg1998">{{cite book \|title=The Oxford History~~ of the Twentieth Century \|first=Steven \|last=Weinberg \|year=1998 \|publisher=Oxford University Press \|isbn=0-19-820428-0}}</ref><ref name="Zurek2003">{{cite journal \|last=Zurek \|first=Wojciech H. \|title=Decoherence, ~~einselection~~, ~~and the quantum origins of the classical \|journal=Reviews of Modern Physics \|volume=75 \|issue=3 \|pages=715–775 \|year=2003 \|doi=10.1103/RevModPhys.75~~.~~715}}</ref>~~		'''Measurement problem''' is a Book I topic in the Quantum Collection. Quantum Measurement problem is a central conceptual issue in quantum mechanics concerning how definite outcomes arise from probabilistic quantum states. While the wave function evolves deterministically according to the Schrödinger equation, measurements yield single, definite results rather than superpositions. This raises the fundamental question: how does a superposition of many possible outcomes reduce to a single observed reality? Quantum Measurement problem is a central conceptual issue in quantum mechanics concerning how definite outcomes arise from probabilistic quantum states. While the wave function evolves deterministically according to the Schrödinger equation, measurements yield single, definite results rather than superpositions. This raises the fundamental question: how does a superposition of many possible outcomes reduce to a single observed reality?

	This raises the fundamental question: how does a superposition of many possible outcomes reduce to a single observed reality?
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	* A single definite outcome		* A single definite outcome
	* Apparent discontinuity (often called ~~[[Physics:Wave function collapse\|~~wave function collapse]])		* Apparent discontinuity (often called wave function collapse)

	This mismatch between continuous evolution and discrete measurement outcomes defines the measurement problem.<ref name="Weinberg2005">{{cite journal \|last=Weinberg \|first=Steven \|title=Einstein's Mistakes \|journal=Physics Today \|volume=58 \|issue=11 \|pages=31–35 \|year=2005 \|doi=10.1063/1.2155755}}</ref>		This mismatch between continuous evolution and discrete measurement outcomes defines the measurement problem.<ref name="Weinberg2005">{{cite journal \|last=Weinberg \|first=Steven \|title=Einstein's Mistakes \|journal=Physics Today \|volume=58 \|issue=11 \|pages=31–35 \|year=2005 \|doi=10.1063/1.2155755}}</ref>
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	== Schrödinger’s cat paradox ==		== Schrödinger’s cat paradox ==

	The measurement problem is famously illustrated by ~~[[Physics:Schrödinger's cat\|~~Schrödinger’s cat]]:		The measurement problem is famously illustrated by Schrödinger’s cat:

	* A quantum event (e.g., radioactive decay) determines the fate of a cat		* A quantum event (e.g., radioactive decay) determines the fate of a cat
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	=== Copenhagen-type interpretations ===		=== Copenhagen-type interpretations ===

	The ~~[[Physics:~~Copenhagen interpretation~~\|Copenhagen interpretation]]~~ posits:		The Copenhagen interpretation posits:

	* Measurement causes collapse of the wave function		* Measurement causes collapse of the wave function
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	=== Many-worlds interpretation ===		=== Many-worlds interpretation ===

	The ~~[[Physics:Many-worlds interpretation\|~~many-worlds interpretation]] removes collapse entirely:		The many-worlds interpretation removes collapse entirely:

	* The universal wave function always evolves deterministically		* The universal wave function always evolves deterministically
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	* All outcomes occur in separate branches		* All outcomes occur in separate branches

	A key challenge is deriving the ~~[[Physics:~~Born rule~~\|Born rule]]~~ for probabilities.<ref>{{cite encyclopedia \|last=Kent \|first=Adrian \|title=One world versus many \|year=2010 \|publisher=Oxford University Press}}</ref>		A key challenge is deriving the Born rule for probabilities.<ref>{{cite encyclopedia \|last=Kent \|first=Adrian \|title=One world versus many \|year=2010 \|publisher=Oxford University Press}}</ref>

	=== de Broglie–Bohm theory ===		=== de Broglie–Bohm theory ===

	The ~~[[Physics:De Broglie–Bohm theory\|~~pilot-wave theory]] introduces hidden variables:		The pilot-wave theory introduces hidden variables:

	* Particles have definite trajectories		* Particles have definite trajectories
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	=== Objective-collapse models ===		=== Objective-collapse models ===

	~~[[Physics:Objective-collapse theory\|~~Objective-collapse theories]] modify quantum dynamics:		Objective-collapse theories modify quantum dynamics:

	* Collapse occurs spontaneously		* Collapse occurs spontaneously
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	* Predict experimentally testable deviations		* Predict experimentally testable deviations

	Example: ~~[[Physics:Ghirardi–Rimini–Weber theory\|~~GRW theory]].<ref>{{cite journal \|last1=Bassi \|first1=Angelo \|last2=Lochan \|first2=Kinjalk \|last3=Satin \|first3=Seema \|last4=Singh \|first4=Tejinder P. \|last5=Ulbricht \|first5=Hendrik \|title=Models of wave-function collapse \|journal=Reviews of Modern Physics \|volume=85 \|issue=2 \|pages=471–527 \|year=2013 \|doi=10.1103/RevModPhys.85.471}}</ref>		Example: GRW theory.<ref>{{cite journal \|last1=Bassi \|first1=Angelo \|last2=Lochan \|first2=Kinjalk \|last3=Satin \|first3=Seema \|last4=Singh \|first4=Tejinder P. \|last5=Ulbricht \|first5=Hendrik \|title=Models of wave-function collapse \|journal=Reviews of Modern Physics \|volume=85 \|issue=2 \|pages=471–527 \|year=2013 \|doi=10.1103/RevModPhys.85.471}}</ref>

	== Role of decoherence ==		== Role of decoherence ==
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	It remains one of the most important unresolved issues in the foundations of physics, closely linked to:		It remains one of the most important unresolved issues in the foundations of physics, closely linked to:

	* ~~[[Physics:~~Interpretations of quantum mechanics~~\|Interpretations of quantum mechanics]]~~		* Interpretations of quantum mechanics
	* [[Physics:Quantum decoherence\|Decoherence theory]]		* [[Physics:Quantum decoherence\|Decoherence theory]]
	* [[Physics:Quantum information theory\|Quantum information]]		* [[Physics:Quantum information theory\|Quantum information]]

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	{{Sourceattribution\|Physics:Quantum Measurement problem\|1}}		{{Sourceattribution\|Physics:Quantum Measurement problem\|1}}

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	'''Quantum Measurement problem''' is a central conceptual issue in [[Physics:Quantum mechanics\|quantum mechanics]] concerning how definite outcomes arise from probabilistic quantum states. While the [[Physics:Wave function\|wave function]] evolves deterministically according to the [[Physics:Schrödinger equation\|Schrödinger equation]], measurements yield single, definite results rather than superpositions.<ref name="Weinberg1998">{{cite book \|title=The Oxford History of the Twentieth Century \|first=Steven \|last=Weinberg \|year=1998 \|publisher=Oxford University Press \|isbn=0-19-820428-0}}</ref><ref name="Zurek2003">{{cite journal \|last=Zurek \|first=Wojciech H. \|title=Decoherence, einselection, and the quantum origins of the classical \|journal=Reviews of Modern Physics \|volume=75 \|issue=3 \|pages=715–775 \|year=2003 \|doi=10.1103/RevModPhys.75.715}}</ref>		'''Quantum Measurement problem''' is a central conceptual issue in [[Physics:Quantum mechanics\|quantum mechanics]] concerning how definite outcomes arise from probabilistic quantum states. While the [[Physics:Wave function\|wave function]] evolves deterministically according to the [[Physics:Schrödinger equation\|Schrödinger equation]], measurements yield single, definite results rather than superpositions.<ref name="Weinberg1998">{{cite book \|title=The Oxford History of the Twentieth Century \|first=Steven \|last=Weinberg \|year=1998 \|publisher=Oxford University Press \|isbn=0-19-820428-0}}</ref><ref name="Zurek2003">{{cite journal \|last=Zurek \|first=Wojciech H. \|title=Decoherence, einselection, and the quantum origins of the classical \|journal=Reviews of Modern Physics \|volume=75 \|issue=3 \|pages=715–775 \|year=2003 \|doi=10.1103/RevModPhys.75.715}}</ref>

	This raises the fundamental question: how does a superposition of many possible outcomes reduce to a single observed reality?		This raises the fundamental question: how does a superposition of many possible outcomes reduce to a single observed reality?
	[[File:Quantum_measurement_problem.jpg\|thumb\|~~400px~~\|~~Conceptual illustration of the quantum measurement~~ problem~~: a superposed quantum state yielding a single classical outcome upon observation, often represented by Schrödinger’s cat~~.]]		</div>

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			[[File:Quantum_measurement_problem.jpg\|thumb\|280px\|Quantum Measurement problem.]]
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	== Deterministic evolution vs measurement ==		== Deterministic evolution vs measurement ==

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	{{Quantum article nav\|previous=Physics:Quantum Uncertainty principle\|previous label=Uncertainty principle\|next=Physics:Quantum Bell's theorem\|next label=Bell's theorem}}		{{Quantum article nav\|previous=Physics:Quantum Uncertainty principle\|previous label=Uncertainty principle\|next=Physics:Quantum Bell's theorem\|next label=Bell's theorem}}

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	[[author\|Harold Foppele}}		[[author\|Harold Foppele}}

			{{Author\|Harold Foppele}}

	{{Sourceattribution\|Physics:Quantum Measurement problem\|1}}		{{Sourceattribution\|Physics:Quantum Measurement problem\|1}}