# Re: Entanglement

```From: <agrayson2...@gmail.com <mailto:agrayson2...@gmail.com>>
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On Thursday, April 12, 2018 at 10:12:58 PM UTC, agrays...@gmail.com <mailto:agrays...@gmail.com> wrote:
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On Thursday, April 12, 2018 at 9:26:53 PM UTC, Brent wrote:

On 4/12/2018 12:44 PM, agrays...@gmail.com wrote:
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```        *Let's simplify the model. Instead of a Nitrogen molecule,
consider a free electron at rest in some frame. Its only
degree of freedom is spin IIUC. Is it your claim that this
electron become entangled with its environment via its spin
WF, which is a superposition of UP and DN? Does this spin WF
participate in the entanglement? TIA, AG*
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The electron's spin dof can only become entangled with the
environment by an interaction with the environment.

Brent

Does that happen spontaneously, in the absence of a measurement? AG

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If entanglement of a system with the environment requires measurement, and if virtually everything in the physical world is entangled with the environment, aka "the world" -- which seems to be the prevailing belief -- what concept of measurement do we need to explain this? AG
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As has been explained, entanglement is the consequence of any interaction whatsoever. Measurement is just a particular kind of interaction, one that is controlled and monitored, but otherwise not special.
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Consider a scattering interaction between two billiard balls. If you know their initial momenta, and you know that momentum is conserved, then because of the entanglement, if you measure the momentum of one particle, you immediately know the momentum of the other, no matter how far away it is (provided there have been no intervening interactions). Entanglement is not just a quantum phenomenon, though quantum entanglement does have some non-classical features. (Such as violating the Bell inequalities.)
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Bruce

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