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Problems with Many Worlds Interpretation

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Demystifier
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Nov2-12, 03:46 AM
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Quote Quote by Dmitry67 View Post
But why do you need to separate the worlds?
To explain the illusion of wave-function collapse, which, indeed, is the main motivation for studying many worlds in the first place.
Demystifier
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Nov2-12, 03:52 AM
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Quote Quote by Hurkyl View Post
But we can distinguish between symmetries that preserve the laws of physics and those that do not. This is the most important idea behind a symmetry based analysis of physical theories.
He discusses that issue as well. What matters in MWI is not the Hamiltonian (with its symmetries), but the wave function (as a function of time). If you know the wave function, you don't need the Hamiltonian. A wave function is a particular solution, and in general it does not have any symmetries which the Hamiltonian does.
Dmitry67
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Nov2-12, 03:53 AM
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BTW, what is the current position of BM with the issue about the cosmology. AFAIK, there is a hidden rest frame in BM, right? But in expanding Universe no objects 'at rest' in some frame can have timelike worldlines globally. For example, lets say that here, on Earth, the hidden rest frame is the same as 'rest to CMB'. So we have a 'hidden' center of the universe in BM :) But outside of our hubble space the 'NOW' in the hidden rest frame, normally spacelike, becomes timelike.
Demystifier
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Nov2-12, 03:57 AM
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Quote Quote by bohm2 View Post
In case others haven't come across the papers, note that Schwindt does mention and references 2 authors (M. Dugic and J. Jeknic-Dugic) that made the same argument. On of the papers by these 2 authors was posted previously in this thread. I believe that Ilja Schmelzer also makes a similar argument in some of his papers.
As I said, his (Schwindt's) argument is not new, but in my opinion, nobody before presented this argument in such a clear form.

In particular, his analogies (with Minkowski space in strange coordinates, as well as with classical phase space) are brilliant. Also, his terminology (nirvana and samara basis) is fun.
Dmitry67
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Nov2-12, 03:59 AM
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Quote Quote by Demystifier View Post
To explain the illusion of wave-function collapse, which, indeed, is the main motivation for studying many worlds in the first place.
Demystifier, could you explain it in more details?

Decoherence shows that taking some basis and somehow isolating somehow 2 systems (observer and the cat), we can explain what an observer perceive.

I am putting a stress on the words some/somehow, because in fact, these parameters are free, decoherence doesn't put any constraint to limit your choice (expect the observer must have high number degrees of freedom).

WHY do you need any constrains on these parameters?
Demystifier
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Nov2-12, 04:03 AM
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Quote Quote by Dmitry67 View Post
BTW, what is the current position of BM with the issue about the cosmology. AFAIK, there is a hidden rest frame in BM, right? But in expanding Universe no objects 'at rest' in some frame can have timelike worldlines globally. For example, lets say that here, on Earth, the hidden rest frame is the same as 'rest to CMB'. So we have a 'hidden' center of the universe in BM :) But outside of our hubble space the 'NOW' in the hidden rest frame, normally spacelike, becomes timelike.
You misunderstood something about general relativity. In the fame in which CMB is homogeneous and isotropic, there is no center of the Universe, there is no horizon, and the notion of "hubble space" does not make sense.
Demystifier
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Nov2-12, 04:12 AM
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Quote Quote by Dmitry67 View Post
Demystifier, could you explain it in more details?

Decoherence shows that taking some basis and somehow isolating somehow 2 systems (observer and the cat), we can explain what an observer perceive.

I am putting a stress on the words some/somehow, because in fact, these parameters are free, decoherence doesn't put any constraint to limit your choice (expect the observer must have high number degrees of freedom).

WHY do you need any constrains on these parameters?
The point is that you have to do it somehow. (Unlike you, I emphasize the word "have"). On the other hand, MWI in its minimal form (i.e., without the additional structure) tells you that you shouldn't, because otherwise you ruin the mathematical structure of MWI. That is the problem.
Dmitry67
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Nov2-12, 04:16 AM
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Quote Quote by Demystifier View Post
You misunderstood something about general relativity. In the fame in which CMB is homogeneous and isotropic, there is no center of the Universe, there is no horizon, and the notion of "hubble space" does not make sense.
Of course I understand it - you had probably misunderstood my post.
But I've heard that BM has a special rest frame, is it true?
Dmitry67
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Nov2-12, 04:18 AM
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Quote Quote by Demystifier View Post
The point is that you have to do it somehow. (Unlike you, I emphasize the word "have"). On the other hand, MWI in its minimal form (i.e., without the additional structure) tells you that you shouldn't, because otherwise you ruin the mathematical structure of MWI. That is the problem.
No, it doesn't say that you shouldn't.
It says that you can do it any way you want
Feel the difference.
Demystifier
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Nov2-12, 04:19 AM
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Quote Quote by Dmitry67 View Post
But I've heard that BM has a special rest frame, is it true?
Some variants do, some variants don't.
Dmitry67
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Nov2-12, 04:22 AM
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Quote Quote by Demystifier View Post
Some variants do, some variants don't.
Hm...
Then how many flavors of BM exist,
and are all of them compatible?
Of course, I am interested only in relativistic BM
Demystifier
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Nov2-12, 04:25 AM
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Quote Quote by Dmitry67 View Post
No, it doesn't say that you shouldn't.
It says that you can do it any way you want
Feel the difference.
Yes, Schwindt discusses that variant of MWI too. In second paragraph of Sec. 5 he says:
"The Many World Interpretation is therefore rather a No World Interpretation (accord-
ing to the simple factorization), or a Many Many Worlds Interpretation (because each of
the arbitrary more complicated factorizations tells a different story about Many Worlds
[7])."

But the many-many world interpretation is certainly not how most MWI experts see MWI, because they typically believe that decoherence fixes the basis. What Schwindt shows is that it doesn't.
Demystifier
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Nov2-12, 04:27 AM
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Quote Quote by Dmitry67 View Post
Hm...
Then how many flavors of BM exist,
and are all of them compatible?
Of course, I am interested only in relativistic BM
There are a few of them. They are not intrinsically equivalent, but they all reproduce standard measurable predictions of relativistic quantum theory.
Dmitry67
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Nov2-12, 04:30 AM
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Exactly! But one story is special for you, because of your consciousness.
So we have a constructive disagreement - our axioms are different, I assume a special role of consciousness aka 'qualia'.
Demystifier
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Nov2-12, 04:37 AM
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Quote Quote by Dmitry67 View Post
Exactly! But one story is special for you, because of your consciousness.
So we have a constructive disagreement - our axioms are different, I assume a special role of consciousness aka 'qualia'.
I don't have a problem with your axioms, indeed they seem viable to me. My point is that your additional consciousness axiom makes the total axiomatic system more complicated than typical MWI-believers would like. So you are a not-typical MWI-believer, which I think is good.
Dmitry67
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Nov2-12, 04:53 AM
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Thank you. Minor question about BM: say, there are 2 observers in 2 different inertial frames. Do they agree on the 'trajectories' of BM 'particles'? (Of course, they can't observe these trajectories because they are hidden, but observers can calculate them).

Probably they would agree in BM flavor with hidden special rest frame, but what's about flavor without special hidden rest frame?
Ilja
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Nov2-12, 04:53 AM
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Quote Quote by Dmitry67 View Post
Of course I understand it - you had probably misunderstood my post.
But I've heard that BM has a special rest frame, is it true?
Yes it has. Some people try to get rid of it, but I don't think it is a good idea (sorry, Demystifier).

But to have a preferred frame in cosmology does not mean that there has to be a hidden center of the universe. It is simply a preferred foliation in the GR sense, not an inertial frame in the SR sense.

Trajectories in different frames are trajectories with completely different initial values and there is no reason at all to suspect that they have something in common. But observers will not think that their own rest frame, based on the quite arbitrary Einstein synchronization, has some relation with the hidden preferred rest frame. So I think they will agree that the CMB frame is the closest candidate for the hidden preferred frame and use it, independend of their own speed, for computations.
Demystifier
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Nov2-12, 05:06 AM
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Quote Quote by Dmitry67 View Post
Thank you. Minor question about BM: say, there are 2 observers in 2 different inertial frames. Do they agree on the 'trajectories' of BM 'particles'? (Of course, they can't observe these trajectories because they are hidden, but observers can calculate them).

Probably they would agree in BM flavor with hidden special rest frame, but what's about flavor without special hidden rest frame?
The two observers agree on the trajectories, both with and without special hidden rest frame.


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