On Monday, June 10, 2019 at 7:39:55 AM UTC-5, Lawrence Crowell wrote:
>
> On Sunday, June 9, 2019 at 11:52:02 PM UTC-5, Bruce wrote:
>>
>> On Wed, Jun 5, 2019 at 11:25 PM Philip Thrift <cloud...@gmail.com> wrote:
>>
>>> On Wednesday, June 5, 2019 at 7:56:41 AM UTC-5, Philip Thrift wrote:
>>>>
>>>> On Wednesday, June 5, 2019 at 6:45:32 AM UTC-5, Lawrence Crowell wrote:
>>>>>
>>>>> On Tuesday, June 4, 2019 at 10:22:51 PM UTC-5, Bruce wrote:
>>>>>>
>>>>>> On Wed, Jun 5, 2019 at 1:15 PM Philip Thrift <cloud...@gmail.com>
>>>>>> wrote:
>>>>>>
>>>>>>>
>>>>>>> As for quantum stochastic retrodependency (which physicists avoid
>>>>>>> like vampires avoid sunlight), it simplifies the "puzzles" of QM,
>>>>>>> meaning
>>>>>>> that, for the most part, the articles you see talking about the "spooky
>>>>>>> action at a distance" or "many wolds" of QM you can dump in the
>>>>>>> trashcan
>>>>>>> and save a lot of time!
>>>>>>>
>>>>>>
>>>>>> The trouble is that these retrocausal "explanations" do not actually
>>>>>> explain anything! They sound like they should: "The formation of the EPR
>>>>>> pair depends on the future setting of the polarises as well as on the
>>>>>> state
>>>>>> preparation." (Or something similar). But no detailed dynamics are ever
>>>>>> given, and the supposed explanation is even more mystical than "spooky
>>>>>> action at a distance...."
>>>>>>
>>>>>> Bruce
>>>>>>
>>>>>
>>>>> Bingo --- ting ding ting ding ... . Thanks Bruce. Since QM is time
>>>>> symmetric or invariant in its form with respect to time direction whether
>>>>> you define time forwards or backwards, or do so for some partition of a
>>>>> density matrix or wave, makes no difference. Retrocausality in effect
>>>>> solves nothing. Nonlocality and the contextual nature of QM, eg the
>>>>> Mermin-Peres square that gives Kochen-Specker, have no definition with
>>>>> respect to any time direction. If you have locality in QM then it is
>>>>> still
>>>>> not possible to think meaningfully of counterfactual definiteness (CFD),
>>>>> or
>>>>> if QM is regarded as nonlocal only then can you have CFD, such as with
>>>>> Many
>>>>> Worlds Interpretation. It makes no difference whether the observables
>>>>> measured are considered forwards or backwards evolving.
>>>>>
>>>>> LC
>>>>>
>>>>
>>>>
>>>> Retrocausality in effect solves nothing.
>>>>
>>>> It solves wasting any time reading papers about QM many worlds,
>>>> non-locality, all the nonsense you read today.
>>>>
>>>> [If one views QM as a generalized measure on a space of histories, then
>>>> one sees not only how quantal processes differ from classical stochastic
>>>> processes (the main difference, they satisfy different sum rules), but
>>>> also
>>>> how closely the two resemble each other.]
>>>> via Rafael Sorkin
>>>>
>>>> @philipthrift
>>>>
>>>
>>>
>>> Anyway, as you know well, I "adopted" the retrocausal view 20 years ago
>>> via* Victor J. Stenger,* who pointed of course to Huw Price.
>>>
>>
>>
>> Apart from not solving anything, and the problem of the absence of any
>> dynamical explanation as to how retrocausality might work to eliminate
>> non-locality, the real problem is that retrocausal explanations have been
>> ruled out experimentally.
>>
>> The seminal experiment by Aspect, et al., published in 1982 really put
>> the last nail in the coffin of retrocausal explanations. The point is that
>> in Aspect's experiment, the polariser settings were chosen while the
>> photons were in flight -- in other words, at some time after the singlet
>> pair was created. So there is no way the photons, travelling back in time
>> at the speed of light, could ever reach the original singlet state after
>> they had detected the polariser setting. The best they could do would be to
>> carry the polariser setting back half way, but no way could they reach back
>> to the interaction that created the original singlet state.
>>
>> So all these years, Huw Price and his cronies have been talking absolute
>> rubbish -- their theory has already been falsified by experiment.
>>
>> Bruce
>>
>
> A little thought should indicate this. Quantum mechanics is invariant with
> respect to time direction. This then means whether you consider the causal
> direction of a Greens function forwards or backwards it makes no
> difference. In fact a standard Green's function is of the form
>
> G(x,x',t,t') = 1/4π (|x – x'|^2 - |t - t'|^2)^{-1}
>
> so how in the hell can any signal with a propagator that is time reversal
> invariant have any measurable impact of this sort? If this were the case,
> that a preferred time direction in QM absorbed the appearance of
> nonlocality, this would imply QM is not time direction invariant.
>
> I agree Price, Wharton, and other have been wasting their time. When
> Stenger wrote about this idea I arm wrestled with him. It is just patently
> wrong that one can do this. In fact one can't try to reconstruct
> nonlocality with tachyons, and this has been tried.
>
> LC
>
Very funny. Totally non-sequitur, as usual.
Retrocasation in quantum computing:
*A Retrocausal Model of the Quantum Computational Speedup*
in
AAAS Pacific Division
2016 San Diego Meeting
Symposium Abstracts
*Quantum Retrocausation III*
https://pdfs.semanticscholar.org/4e9f/f4d375626b2cd051b49dda2047b040d8e9b5.pdf
Bob, the problem setter, hides a ball in one of four drawers. Alice, the
problem solver, is to locate it. Quantumly, this can be done by opening
just one drawer. We explain this quantum speedup with retrocausality.
The initial measurement randomly selects a drawer number out of a mixture
of the four possible numbers. Bob unitarily sends it into the desired
number of the drawer with the ball. This yields the algorithm input state
to Bob and any external observer, not to Alice. It would tell her the
solution of the problem before she opens any drawer. To Alice, the
projection of the quantum state induced by the initial measurement should
be retarded to the end of her search. The input state to her remains the
mixed one. Alice sends it unitarily into a mixture of tensor products, each
a drawer number and the corresponding solution. She reads – measures – the
solution corresponding to the number chosen by Bob.
Mathematically, this final measurement could select back in time any part
of the random outcome of the initial measurement. The assumption it selects
half of it explains the speedup. This projects the input state to Alice on
one of lower entropy where she knows half of the information that specifies
the number of the drawer with the ball. The quantum algorithm is a sum over
classical histories in each of which Alice knows in advance one of the
possible halves of the information and opens only the drawers required to
find the other half. A similar explanation applies to quantum oracle
computing.
*Reversing cause and effect is no trouble for quantum computers*
https://phys.org/news/2018-07-reversing-effect-quantum.html
https://journals.aps.org/prx/abstract/10.1103/PhysRevX.8.031013
Causal asymmetry is one of the great surprises in predictive modeling: The
memory required to predict the future differs from the memory required to
retrodict the past. There is a privileged temporal direction for modeling a
stochastic process where memory costs are minimal. Models operating in the
other direction incur an unavoidable memory overhead. Here, we show that
this overhead can vanish when quantum models are allowed. Quantum models
forced to run in the less-natural temporal direction not only surpass their
optimal classical counterparts but also any classical model running in
reverse time. This holds even when the memory overhead is unbounded,
resulting in quantum models with unbounded memory advantage.
@philipthrfit
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