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How did the concept of quantum entanglement arise?


geordief
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How did it come about that  2  particles  were considered to be entangled?

What were the preconditions for this to occur?

I imagine (I am just guessing) that there was a theory and that this theory was confirmed when its predictions  were observed.

How was the theory arrived at?

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As far as I know, entanglement is a fundamental aspect of Quantum Mechanics, where the quantum state of each particle affected cannot be described independently of the state of the others in the grouping.
IOW, the states ( such as position, momentum, spin, polarization ) of theaffected particles in the 'entangled' grouping are represented by a single mathematical wave function, until 'decoherence' occurs due to an interaction.

It was 'accepted' theory, until A Einstein, B Podolsky and N Rosen proposed the EPR paradox which violated local realism and/or causality; the original "spooky action at a distance", and Einstein's ( and Shroedinger's ) belief that unknown 'hidden' variables were involved.
J Bell put the 'nail in the coffin' to hidden variable theories, and this year's Nobel Prize winners, J Clauser, A Aspect and A Zeilinger, have been recognized for estabilishing that there is no local reality.

See here      Quantum entanglement - Wikipedia

Edited by MigL
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6 minutes ago, MigL said:

As far as I know, entanglement is a fundamental aspect of Quantum Mechanics, where the quantum state of each particle affected cannot be described independently of the state of the others in the grouping.
IOW, the states ( such as position, momentum, spin, polarization ) of theaffected particles in the 'entangled' grouping are repItresented by a single mathematical wave function, until 'decoherence' occurs due to an interaction.

It was 'accepted' theory, until A Einstein, B Podolsky and N Rosen proposed the EPR paradox which violated local realism and/or causality; the original "spooky action at a distance", and Einstein's ( and Shroedinger's ) belief that unknown 'hidden' variables were involved.
J Bell put the 'nail in the coffin' to hidden variable theories, and this year's Nobel Prize winners, J Clauser, A Aspect and A Zeilinger, have been recognized for estabilishing that there is no local reality.

See here      Quantum entanglement - Wikipedia

Thanks,I will take a look tomorrow. 

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19 hours ago, geordief said:

Thanks,I will take a look tomorrow. 

 

19 hours ago, geordief said:

Thanks,I will take a look tomorrow. 

OK I can see that the maths involved in Bell's theorem is too hard for me  to follow for now (even though I have come across the notation** used  in the past)

I see there are a few ways that entanglement can arise and learn now that it was considered  by Evin Schodinger (sp?) to be absolutely  central to QM.

 

I will just keep at it and maybe it will become clearer eventually. 

 

** I think it looked like a tensor or a cross product they were  using  before I gave up trying to follow.

 

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It was almost certainly the tensor product. The statement "these two particles are entangled" is, more formally, "the combined state of these two particles is not a pure tensor element in the tensor product of the state spaces of each element separately".

While I don't know the history itself, entanglement itself is a rather natural aspect of the fact that quantum physics is fundamentally linear, and that the tensor product is the "natural" way of dealing with bilinearity.

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