# Multiple processes interpretation

Hi pf,

there was an article in the Stanford encyclopedia about QM that was rewritten.
it quoted a "multiprocess" interpretation differing from Everett's one which could be related to Bohm's interpretation. it is no more there.
i am wondering if there are interpretatins where different results for a unique measurement can coincide (like in Everett)

PeterDonis
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2020 Award
there was an article in the Stanford encyclopedia about QM that was rewritten.

Sorry
i have no link. it was a remark in a conversation with somebody who did not remember!

i think that unitarity is central in QM and that collapse does not occur.

GR authorizes closed time loops (time reversal is not requested for going to the starting point of spacetime). Have theoricists analyzed the consequences in QM ?

this helps me to think that the diagonal density matrix that we get at the end of one measurement has the same status than a table of percentages of the atoms in the universe !

Consider a particle which is an eigenvector in a measurement it could evolve unitarily and come back in time as another eigenvector to the same measurement device and so on.
Of course as the eigenvectors are orthogonal we would have the same situations as in the Everett branches.

The percentages can also be obtained from loops in the Feynmann integration paths if we take into account the returning paths.

PeterDonis
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2020 Award

Then we can't discuss whatever interpretation you were referring to, since we don't have a source we can use to tell us what that interpretation says.

i think that unitarity is central in QM and that collapse does not occur.

This is one possible interpretation of QM, yes.

GR authorizes closed time loops (time reversal is not requested for going to the starting point of spacetime). Have theoricists analyzed the consequences in QM ?

Yes. The main result is the Novikov self-consistency principle:

https://en.wikipedia.org/wiki/Novikov_self-consistency_principle

Consider a particle which is an eigenvector in a measurement it could evolve unitarily and come back in time as another eigenvector to the same measurement device

No, it couldn't, because that would violate the above principle.

Hi pf,

there was an article in the Stanford encyclopedia about QM that was rewritten.
it quoted a "multiprocess" interpretation differing from Everett's one which could be related to Bohm's interpretation. it is no more there.
i am wondering if there are interpretatins where different results for a unique measurement can coincide (like in Everett)
It sounds like you're thinking of the "Many Interacting Worlds" (as opposed to "Many Worlds") interpretation:
https://arxiv.org/abs/1402.6144
https://arxiv.org/abs/1403.0014

No, it couldn't, because that would violate the above principle.

I think that as the returning particle is in an orthogonal state to its previous state it cannot interact with it so no paradox can come from this
but it is true that it interacts diffierently with the measuring device. A paradox may appear here.
but as i said there is no collapse at any moment. I wonder if there is a paradox without collapse.

can we object to MWI that different results for the measurement is a paradox?

thank you jimmy
i am going to give these links to my friend

mfb
Mentor
can we object to MWI that different results for the measurement is a paradox?
No, because it is consistent with observations.

i think that there is no paradox here
consider the simplest case of a young experiment with a screen and only one hole H
i consider possible loops passing by the source S the hole H and a point A on the screen (with no collapse there) and then the returning path to S (backward in time
i can write such a loop as
$$\langle S(o)|O(t) \rangle \langle O(t)|A(T) \rangle \langle A(T)|O(t) \rangle \langle O(t)|S(0) \rangle$$
here we consider loops notations and not complex numbers
"after" that we can consider another loop passing by anoter point B on the screen and so on.

we can use now the feynmann path calculus to give a weight to all these loops (the notations are now complex numbers. This enables us to get the density matrix
$$\Sigma_x p(x) [x \rangle \langle x|$$
we had no collapse at all but a density matrix;
at this level there is no spot on the screen and no paradox
It would be the same with 2 slits;
Different weights for the loops would give interferences or no interferences or partial interferences.

is not this mainstream?

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PeterDonis
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2020 Award
is not this mainstream?

I can't tell because it doesn't make sense. Nor does it appear to be related to the topic of this thread.

PeterDonis
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2020 Award
Since no reference can be provided, this thread is closed.