"The wavefunction never collapses"

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PeterDonis said:
What we really need is a theory in which "spacetime geometry" is not built into the foundations at all, but emerges from something else. That's what, for example, loop quantum gravity is trying to do. (String theory? Not really. It still assumes a background--it's just a background with 10 or 11 or 26 or whatever dimensions instead of 4. It doesn't discard the concept completely at the foundational level.)
In string theory (M), are 10+1 dimensions "assumed" in the same way that 3+1 dimensions are assumed in GR?

I understood that problems in string theory have solutions if and only if the problem is embedded in a spacetime with a specific number of dimensions. Unlike other theories where spacetime is a rather malleable tool, in string theory the number of dimensions of spacetime is a consequence, eliminating loopholes. Isn't that emergent? (that the dimensionality of spacetime arises as a necessary consequence to solve something)
 
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javisot said:
In string theory (M), are 10+1 dimensions "assumed" in the same way that 3+1 dimensions are assumed in GR?
There are restrictions, at least according to string theorists, regarding what numbers of dimensions allow solutions, yes. But the point is that there is still an underlying spacetime manifold. The spacetime manifold doesn't emerge from something else; it's a fundamental aspect of the theory that's just put in by hand. The only thing the theory predicts is how many dimensions it has to have in order for there to be solutions.

javisot said:
in string theory the number of dimensions of spacetime is a consequence
The number of dimensions is, yes, but the fact that you're using a spacetime manifold at all is not. See above.
 
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haushofer said:
Of course nature "views them as incompatible"; our current theories are just not yet able to distinguish them.
I don’t at all see this as true. Certainly not “of course”. Simply saying “of course” is not at all convincing.

What actual evidence do you have from nature that indicates that nature views different interpretations of QM as incompatible?

I know lots of people who view them as incompatible. And I know lots of people who believe that nature shares their view. But so far I have seen no indication that nature views different interpretations as incompatible.
 
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Dale said:
I know lots of people who view them as incompatible. And I know lots of people who believe that nature shares their view. But so far I have seen no indication that nature views different interpretations as incompatible.
I agree with your point and would add that if by "compatible" we mean being able to explain the same results, then MWI and Copenhagen are compatible.

If by "compatible" we mean something more complex than simply being able to explain the same results, then MWI might not be compatible (depending on the exact requirements for compatibility).
 
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Dale said:
I don’t at all see this as true. Certainly not “of course”. Simply saying “of course” is not at all convincing.

What actual evidence do you have from nature that indicates that nature views different interpretations of QM as incompatible?

I know lots of people who view them as incompatible. And I know lots of people who believe that nature shares their view. But so far I have seen no indication that nature views different interpretations as incompatible.
I think the whole discussion about how gravity fits in here at least suggests that they aren't necessarily all compatible.

Penrose's interpretation is radically different. At this point we don't have any experiment to decide but I personally think it is worth thinking about the implications of the different "interpretations".
 
jbergman said:
I think the whole discussion about how gravity fits in here at least suggests that they aren't necessarily all compatible
That is a far cry from “of course nature views them as incompatible”.
 
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jbergman said:
Penrose's interpretation is radically different. At this point we don't have any experiment to decide but I personally think it is worth thinking about the implications of the different "interpretations".
By Penrose interpretation do you mean the Penrose-Diosi model where gravity causes collapse?

That one should actually make some different predictions from standard QM, it just does so at a scale that's not easy to access and there's some parameters that can be tweaked. The simplest version of that theory seems to have been falsified. There's another thread around here on it.

I believe the GRW collapse theories are also in a similar situation.

The above are called theories since they make some different predictions than standard QM so they don't seem to be interpretations.
 
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Dale said:
I don’t at all see this as true. Certainly not “of course”. Simply saying “of course” is not at all convincing.

What actual evidence do you have from nature that indicates that nature views different interpretations of QM as incompatible?

I know lots of people who view them as incompatible. And I know lots of people who believe that nature shares their view. But so far I have seen no indication that nature views different interpretations as incompatible.
I merely regarded that statement that in the end one "interpretation" (theory) turns out to be the right one.
 
The wavefunction doesn't "collapse", instead the observer's Dirac current (the physical matter current) becomes entangled with the measurement apparatus and environment, and the reading is confined to one branch of the entanglement, so from inside that branch you see only one outcome.
 
danieltanfh95 said:
The wavefunction doesn't "collapse", instead the observer's Dirac current (the physical matter current) becomes entangled with the measurement apparatus and environment, and the reading is confined to one branch of the entanglement, so from inside that branch you see only one outcome.
To repeat something that I believe was said much earlier in this thread, this is true in the MWI, but it is not true in some other QM interpretations.
 
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haushofer said:
I merely regarded that statement that in the end one "interpretation" (theory) turns out to be the right one.
And my point is that “right” in this context is not a statement about nature.
 
jbergman said:
This blog post details an interpretation that is kind of like a rigorous Copenhagen Interpretation based on Decoherence.

https://deivondrago.substack.com/p/zureka-a-way-forward-to-solving-the
While the blog presents a defensible summary of Zurek, its framing is misleading since the package is really a restatement of the same problem with newer vocabulary:

1. It packages the definite-outcomes residual as "empirically inert philosophy," which assumes no physical closure exists, but I show above that taking the matter field to be physical + standard decoherence directly presents a physical closure.
2. It presents decoherence + envariance as the only "conservative upgrade" path, but the Bell-beable / primitive-ontology lineage is equally conservative and does close the definite-outcomes gap. This is missing from the literature review here.
3. It labels the package "a way forward to solving the thorniest issues" but does not even solve the thorniest issue (definite outcomes), and envariance-to-Born remains contested (Schlosshauer, Barnum).
 
danieltanfh95 said:
This framing only assumes decoherence
No, what I quoted from you assumes more than that.

danieltanfh95 said:
it does not require MWI's ontological commitment that all other branches are equally "real".
If you did not intend to claim this, then your post was extremely poorly worded, since what you wrote does claim it.
 
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I want to additionally note that photons and other fundamental bosons cannot be SR-observers because they lack the positive-definite localizable density that a worldline requires, and thus involving them as an observer in the standard decoherence picture is undefined.
 
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danieltanfh95 said:
I want to additionally note that photons and other fundamental bosons cannot be SR-observers because they lack the positive-definite localizable density that a worldline requires, and thus involving them as an observer in the standard decoherence picture is undefined.

I think you would benefit from reading:
https://www.amazon.com.au/Decoherence-Quantum-Classical-Maximilian-Schlosshauer/dp/3540357734

For example, photons from the CBMR are enough to decohere dust particles and give them a definite position.

That book is an example of a reference suitable for this forum; personal theories are not, unless published in peer-reviewed journals.

Thanks
Bill