# Re: Measuring a system in a superposition of states vs in a mixed state

On Tuesday, December 4, 2018 at 10:28:39 PM UTC-6, Philip Thrift wrote:
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> On Tuesday, December 4, 2018 at 3:45:32 PM UTC-6, Bruce wrote:
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>> On Wed, Dec 5, 2018 at 6:58 AM Philip Thrift <cloud...@gmail.com> wrote:
>>
>>>
>>> On Tuesday, December 4, 2018 at 1:53:15 PM UTC-6, Brent wrote:
>>>>
>>>>
>>>> On 12/4/2018 12:25 AM, Philip Thrift wrote:
>>>>
>>>>
>>>> 1. Histories originate at an emitter e and end at screen locations s on
>>>> a screen S.
>>>> 2. At each s there is a history bundle histories(s). A weight w(s) is
>>>> computed from the bundle by summing the unit complex numbers of the
>>>> histories and taking the modulus.
>>>> 3. The weight w(s) is sent back in time over a single history h*(s)
>>>> selected at random (uniformly) from histories(s).
>>>> 4. At e, the weights w(s) on backchannel of h*(s) are received (in the
>>>> "present" time)
>>>> 5. A single history h*(s*) is then selected from the distribution in 4.
>>>>
>>>>
>>>> How is it selected?  Above you said "at random".  But that implies
>>>> there is already a probability measure defined on the histories.  How is
>>>> this probability measure determined?  Or put another way how do you
>>>> determine what histories to consider to form the bundles in step 2?
>>>>
>>>> Brent
>>>>
>>>
>>> Selection happens via quantum Darwinism.
>>>
>>
>>
>> Do you have even the faintest understanding of Quantum Darwinism?
>>
>> Bruce
>>
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> How is *sum over histories with Darwinian selection*  (as defined) not
> quantum Darwinism?
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> Operationally, what is different?
>
> - pt
>

*Sum over histories with Darwinian selection* is consistent with *Quantum
Darwinism as a Darwinian process*  [ https://arxiv.org/abs/1001.0745 ].

- pt

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