On Saturday, November 3, 2018 at 3:50:30 PM UTC-5, agrays...@gmail.com 
> On Thursday, November 1, 2018 at 11:22:46 PM UTC, Pierz wrote:
>> On Monday, October 15, 2018 at 9:40:39 PM UTC+11, agrays...@gmail.com 
>> wrote:
>>> On Sunday, October 14, 2018 at 5:08:42 PM UTC, smitra wrote:
>>>> On 14-10-2018 15:24, agrays...@gmail.com wrote: 
>>>> > In a two state system, such as a qubit, what forces the 
>>>> interpretation 
>>>> > that the system is in both states simultaneously before measurement, 
>>>> > versus the interpretation that we just don't what state it's in 
>>>> before 
>>>> > measurement? Is the latter interpretation equivalent to Einstein 
>>>> > Realism? And if so, is this the interpretation allegedly falsified by 
>>>> > Bell experiments? AG 
>>>> It is indeed inconsistent with QM itself as Bell has shown. Experiments 
>>>> have later demonstrated that the Bell inequalities are violated in 
>>>> precisely the way predicted by QM.  This then rules out local hidden 
>>>> variables, therefore the information about the outcome of a measurement 
>>>> is not already present locally in the environment. 
>>>> Saibal 
>>> What puzzles me is this; why would the Founders assume that a system in 
>>> a superposition is in all component states simultaneously -- contradicting 
>>> the intuitive appeal of Einstein realism -- when that assumption is not 
>>> used in calculating probabilities (since the component states are 
>>> orthogonal)? AG 
>> I think because of interference. Consider the paradigmatic double slit, 
>> with the single electron going through it. It sure looks like the electron 
>> was in two place at once, doesn't it?
> *Yes, that's my assessment how the erroneous interpretation took hold, but 
> only if you restrict yourself to the particle interpretation. If the 
> electron travels as a wave, it can go through both slits simultaneously and 
> interfere with itself. This is my preferred interpretation; the only one 
> that makes sense. AG*
> I'm not sure what you mean by "that assumption is not used in calculating 
>> probabilities". 
> *If the operator whose eigenvalues are being measured has a well defined 
> mathematical form -- e.g., not like |alive> -- it has specific eigenvectors 
> and eigenvalues, and the state function can be written as superposition of 
> these eigenvectors. It can be shown that eigenvectors with distinct 
> eigenvalues are orthogonal, meaning the Kronecker delta applies to their 
> mutual inner products. Therefore, to calculate the probability of observing 
> a particular eigenvalue, one must take the inner product of the wf with the 
> eigenvector which has that eigenvalue. Due to the orthogonality, all terms 
> drop out except for the term in the superposition which contains the 
> eigenvector whose eigenvalue you want to measure. As you should see, there 
> is nothing in this process of calculating probabilities that in any way 
> implies, assumes, or uses, the concept that the system is simultaneously in 
> ALL component states of the superposition (written as a sum of 
> eigenvectors). AG*
>> If you take a sum-over-histories approach it's explicitly assumed the 
>> electron went via all possible paths.
> *I don't know that method, but offhand POSSIBLE PATHS might have nothing 
> to do with, and possibly independent of SUPERPOSITIONS OF STATE. AG*
> I don't see what the orthogonality of the basis vectors (and hence 
>> component states) has to do with the question of interpretation of 
>> superposition. 
> *Explained in detail above. AG*
> Clearly the system will be measured in only one state, and this is what 
>> the orthogonal vectors represent. However the quantum state itself 
>> typically spans more than one dimension of the vector space - that's what a 
>> superposition is. However I think when physicists say that the 
>> superposition is in all states simultaneously, it's only in a manner of 
>> speaking - a way of conveying the mathematical situation in natural 
>> language that is inherently classical. 
> *It's a totally misleading way to discuss the quantum superpositions.  
> Even classically, say for the vector space of "little pointy things" in a 
> plane, each vector can be expressed in uncountably many bases, both 
> orthogonal and non-orthogonal. So to claim that one basis is somehow 
> preferred, and the vector being expressed as a sum or superposition in that 
> basis, is simultaneously in all components of that particular basis, make 
> no sense whatsoever. AG*
> Reading Born's exchange of letters with Einstein (I'm proud to say Born 
>> was my great grandfather), it's clear that Born had a conception of QM that 
>> was still very realistic in the Einstein sense. Though they disagreed 
>> significantly and somewhat heatedly, Born still seems to have regarded QM 
>> probabilities as classical probabilities in disguise.
> *Einstein realism seems to have been falsified due to Bell experiments. If 
> that's the case, it would mean that BEFORE measurement of a quantum system, 
> it is not only NOT in all states of a superposition simultaneously for the 
> reasons I have argued (nothing to do with Bell), but ALSO has no local 
> preexisting value. AG*
> I don't think he would ever have endorsed the notion that a particle is 
>> truly in all of the states of the superposition simultaneously. 
> *Thanks for your input. AG *

The (complex-number-weighted) "path"s of the path integral 
(sum-over-histories) formulation are all that are needed to define 
superpositions. "Einstein realism" is restored if *retrocausality* (the 
path futures can *stochastically* influence the path pasts) is allowed.

- pt

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