Is MWI Self-Contradictory and Does Time Travel Need a New Approach?

[Hurkyl]

Well yea, if the lottery only has 2 balls and you get one, I get one, but I have 90% chance of getting the ball, but you only got 10% of getting the ball, yet both of us have a 100% chance of getting the ball.
Are you starting to see the error of your thinking?

Now imagine one person getting a ball, but what color it is is given by a probability distribution, rather than a definite outcome.

 

[Varon]

Let's try this clear statement by Barrett:

"In order to capture the usual predictions of quantum mechanics, one would like to say that the probability that I would end up in the world described by the first term is 1/4 and the probability that I will end up in the world described by the second term is 3/4. If one could say this, then one would have an explanation for the fact that I get results that tend to be close to the usual statistical predictions of quantum mechanics. But, as Albert and Loewer point out, on the splitting-words theory, as it stands, one cannot say say. Rather, the splitting-worlds theory tells me that both worlds are equally real and that there will be a fully real copy of me in each world, so presumably neither has a better claim than the other to being the one that I end up experiencing."

[...]

"DeWitt seems to have noticed that the splitting-worlds theory alone did not explain why one should expect the usual quantum statistics. After presenting his interpretation of probability, he confessed that

The alert reader may not object that the above argument in circular, that in order to derive the physical probability interpretation of quantum mechanics, based on sequences of observations, we have introduced a nonphysical probability concept, namely that of the measure of a subspace in Hilbert Space. (DeWitt and Graham 1973: 163)

And he continued:

It should be stressed that no element of the superposition is, in the end, excluded. All the worlds are there, even those in which everything goes wrong and all the statistical laws break down. (186; see also 163)."

~~~~~~~~~~~~~~~~~~~~~~~~~

Now Hurkyl, JesseM, Dmittry and other Many worlders. How do you make the splitting worlds exhibit the correct quantum statistics? In the above example. If there is probability of the outcomes being 1/4 and 3/4. But the world splitting is equal. How do you make it match the quantum statistics. You can't say the world is real in one 1/4 of the time and the real 3/4 of the time. All worlds or branches are real the same time.

This question bugs me for weeks. So what's the solution?

 

[Hurkyl]

How do you make the splitting worlds exhibit the correct quantum statistics?
...
This question bugs me for weeks. So what's the solution?

Nobody knows. It would be really neat if you could arrange for them to be equal or simply related, but there is no prior reason why they should have anything to do with each other.

 

[Varon]

Nobody knows. It would be really neat if you could arrange for them to be equal or simply related, but there is no prior reason why they should have anything to do with each other.

Then why entertain Many Worlds. Maybe because we hope ways could be made someday to make the splitting worlds match the quantum statistics?

Or if you are saying they don't necessarily have to match. Then Many worlds doesn't match the predictions of standard QM or Copenhagen. Then we may as well just stick to Copenhagen and accept the ad hocness of Collapse as part of the world.

 

[Hurkyl]

Then why entertain Many Worlds.

Because MWI is the interpretation that asserts "reality is described by quantum states that undergo unitary evolution". (full stop)

TBH, the only good^* reasons I know not to entertain MWI is pessimism that quantum mechanics won't extend beyond microscopic scales, and an old no-go theorem that unitary evolution cannot turn a pure state into a mixed state has been rendered irrelevant by relative states and especially by decoherence.

*: meaning not based on availability of learning materials or based on misconceptions of the interpretation (or on faulty logic) or things like these

 

[Varon]

Because MWI is the interpretation that asserts "reality is described by quantum states that undergo unitary evolution". (full stop)

TBH, the only good^* reasons I know not to entertain MWI is pessimism that quantum mechanics won't extend beyond microscopic scales, and an old no-go theorem that unitary evolution cannot turn a pure state into a mixed state has been rendered inapplicable relative states and especially by decoherence.

*: meaning not based on availability of learning materials or based on misconceptions of the interpretation (or on faulty logic) or things like these

In both MWI and Copenhagen. What constitutes a measurement is a mystery. So you are kinda saying that if we can solve one of them.. we can apply it to the other in full force?.

 

[Demystifier]

Ok, but let's assume consciousness isn't any mysterious at all.
Functionalism, that's it. A system that is aware, nothing more, nothingless.

Do you then see how it is incoherent to say there are 2 outcomes, a observer in both, but one is higher probability?

Well, if one accepts functionalism (which I don't, but it doesn't matter here), and if one assumes that there is nothing else in the world but a wave function, and if no other assumptions are taken, THEN it is hard to see how probability could by anything else but 50:50. Yet, even though it is hard to see it, I have no idea how to formalize this argument. If you do, then you have a NEW argument against MWI possibly stronger than any other existing one, in which case you should publish it. But if it merely "seems obvious" to you (as it seems to me) without being able to formalize it, then, unfortunately, it is not good enough.

 

[Dmitry67]

I must admit I understood nothing of what you just said :P
I'm sure someone else will and comment on it tho
But could you explain it a little less technical?

Then how could you deny the commonly accepted (check wiki) point of view that Decoherence DOES explain the appearance of collapse?

Anyway, looks like you had stopped denying that but you're are attacking MWI on purely Born rule, is that correct?

 

[Dmitry67]

As we are discussing MWI here, does anyone see additional beauty of MWI because it explains Bell/EPR in a locally realistic (*) way?

(*) I know that not all definitions of 'realism' classify MWI as 'realistic', but in some wider sense it is definitely realistic.

 

[Fyzix]

Then how could you deny the commonly accepted (check wiki) point of view that Decoherence DOES explain the appearance of collapse?

Anyway, looks like you had stopped denying that but you're are attacking MWI on purely Born rule, is that correct?

I don't see how decoherence not being sufficient to explain determinate outcomes had anything to do with his statement ?

No, my position on that is still the same.
I've given you tons of information as to why it doesn't work, citing a lot of physicists and philosophers, yet you don't see the point they are getting across, so I stopped trying:P

By the way, whether MWI is truly local or not is still far from decided.

Ruth E Kastner made a paper refuting Deutsch's work on this: http://arxiv.org/ftp/arxiv/papers/1011/1011.3078.pdf

 

[Fyzix]

Now imagine one person getting a ball, but what color it is is given by a probability distribution, rather than a definite outcome.

No, this doesn't work.
Remember it's the SAME person getting both balls.

 

[Dmitry67]

I've given you tons of information as to why it doesn't work, citing a lot of physicists and philosophers, yet you don't see the point they are getting across, so I stopped trying:P

So far I've seen only 2 ways how you tried to attack MWI:

1. Born rule - ridiculous 'lottery' argument, discussed above.
2. Not related to the Born rule - different variations of the same:

Preassumption that there exist some kind of ('hard', 'clean', 'definite', 'final', 'complete', 'real' - words you used) separation between the 'branches'. Based on that (false) assumption you try different attempts of reductio ad absurdum: for example, assuming that there is a 'hard' border which separates different 'branches' you can show that the position of that border is not covariant.

 

[Fyzix]

So far I've seen only 2 ways how you tried to attack MWI:

1. Born rule - ridiculous 'lottery' argument, discussed above.

Ridiculous lottery argument which you have not been able to refute?
Ok...
Then again you think consciousness is something special, so I can see how you may somehow magically get around this problem.

Preassumption that there exist some kind of ('hard', 'clean', 'definite', 'final', 'complete', 'real' - words you used) separation between the 'branches'. Based on that (false) assumption you try different attempts of reductio ad absurdum: for example, assuming that there is a 'hard' border which separates different 'branches' you can show that the position of that border is not covariant.

This just proves you haven't understood the arguments and points put forth.

 

[Demystifier]

As we are discussing MWI here, does anyone see additional beauty of MWI because it explains Bell/EPR in a locally realistic (*) way?

According to MWI, reality does not exist in the 4-dimensional spacetime, but in the infinite dimensional Hilbert space, or as a special case, in the many-dimensional configuration space of particle positions. It is this "weird" highly dimensional space on which MWI is local. But on this space, Bohmian mechanics is also local. Therefore, Bohmian mechanics is not less local than MWI.

 

[Fyzix]

Demystifier, I just remember a question I wanted to ask you the other day:

Why do you prefer normal Bohmian over the "Many Bohmian Worlds" that Jeffrey Barrett once suggested as a potential solution to the problems "pure MWI" faces?
I know Jacques Mallah also consider this to be a potential solution to pure MWI's problems.

 

[Demystifier]

Demystifier, I just remember a question I wanted to ask you the other day:

Why do you prefer normal Bohmian over the "Many Bohmian Worlds" that Jeffrey Barrett once suggested as a potential solution to the problems "pure MWI" faces?
I know Jacques Mallah also consider this to be a potential solution to pure MWI's problems.

Yes, I have also been thinking about many Bohmian worlds (MBW) as a compromise between BM and MWI. The main problem I see is the following: If many Bohmian worlds exist, then why do we see only one? (Decoherence provides an answer for standard MWI, but not for MBW.)

 

[Dmitry67]

Ridiculous lottery argument which you have not been able to refute?

There was already a reply in this thread:

Putnam's argument is wrong because of the lottery thing. The "number of worlds" -- if that phrase even makes sense -- has absolutely no reason to coincide with any probability that is supposed to have bearing on reality.

 

[Fyzix]

Dmitry, we have alraedy discussed this.
If you are goin to assume that consciousness is just something that arises in the physical brain (functionalism) this argument by Hurkyl does NOT work.

 

[Dmitry67]

Fyzix,

1. Regarding the Born rule, I see 2 options
1a. In fact, Born rule is an illusion, created by consiousness;
1b. MWI will be able somehow to 'prove' Born rule is MWI-compatible form (like Hurkyl had formulated)
have I ever told you that MWI had already solved the problem with the MWI Rule? No.

2. All other aspects of reality, specifically:
A. Why do we observer only one branch?
B. Why we don't feel ourselves being split?
C. Why do we see definite outcomes?
etc etc
All these things are successfully explained by the Decoherence.

You are making wide and fuzzy statements like 'decoherence is not enough!' without providing any details, this is why we are returning back again and again to the point where I try to understand, are we talkign about the Born rule or your favourite 'branching' stuff.

 

[Fyzix]

Let's make it simple then, when this thread stops talking about Born Rule, we can move over to the ontological aspect, ok?
I have given you sources, Tim Maudlin, Jeffrey Barrett, MJ Donald etc. so don't claim I haven't given you any details, I've written long posts to you and given you sources for all claims...

However back to Born Rule:

You are doing science wrong, you have started out with a model and then you try to find facts that fit it.
Right now science is telling us MWI can't make sense of Born Rule, thus must be wrong!
You say "Nono, I like MWI so reality must be wrong"

Your assumption that consciousness can explain this is WAY more of a violation of Occam Razor than any other interpretation.

You also didn't answer Demystifiers statement that MWI isn't more local than Bohm in the sense you tried to argue...

To me it's blatantly obvious that you just like MWI and therfefor you are willing to ignore problems that show it isn't right / is incomplete.

 

[Dmitry67]

1. I need to think about Demystifier's argument before I reply.
2. Yes, it is obvious that I like MWI, like it is obvious that you hate it. But how does it change the facts and observations?

I talk about observations (post #69, item B), I ask you about wha is not in agreement with the observations? You reply in emotional manner about 'love' and 'hatred'. If your statement is refuted on page N, you simply repeat it on page N+1!

Right now science is telling us MWI can't make sense of Born Rule, thus must be wrong!

It was show in this thread that this logic is WRONG! There are many things science can't explain, but it does not make it "wrong". Demystifier had provided an example in post #20. Did it help?

 

[Fyzix]

No it was shown that his argument only works if you assume that consciousness is something special...
Your impossible to argue with...

 

[Dmitry67]

Shown by whom? Where?
Anyway, I am happy that at least you had abandoned the stuff with the 'picture of spacetime unzipping', 'clean and complete separation', 'problems with SR', so now your critics is focused solely on the Born rule.

 

[Dmitry67]

According to MWI, reality does not exist in the 4-dimensional spacetime, but in the infinite dimensional Hilbert space, or as a special case, in the many-dimensional configuration space of particle positions. It is this "weird" highly dimensional space on which MWI is local. But on this space, Bohmian mechanics is also local. Therefore, Bohmian mechanics is not less local than MWI.

Well, let's say it differently. In MWI, "reality" exist in Hilbert space, but it can be also 'mapped' into our physical 4D space (in a given basis). Such mapping can create multiple (almost) non-interacting 'branches', occupying the same physical space. If we can create a transformation from one to another, based on MUCH you can't say what is 'more' real. I hope you agree.

So while what you said is true in Hilbert space, in physical space all 'influences' are limited to the light cones. So MWI provides 'stronger' locality then BM, where 'particles' affect each other FTL in physical space.

Am I right?

 

[Hurkyl]

No, this doesn't work.
Remember it's the SAME person getting both balls.

No, it's the same person getting one ball. And the physical state is a probability distribution over two colors, rather than a definite choice of color.

(For reference, a probability distribution, in this case, means nothing beyond assigning a non-negative number to each color so that the numbers add to 1)

This is what the negation of definite outcomes means. (Well, technically, asserting the existence of a probability distribution over the outcomes is stronger than merely asserting there isn't a definite outcome)

 

[Hurkyl]

According to MWI, reality does not exist in the 4-dimensional spacetime, but in the infinite dimensional Hilbert space, or as a special case, in the many-dimensional configuration space of particle positions. It is this "weird" highly dimensional space on which MWI is local. But on this space, Bohmian mechanics is also local. Therefore, Bohmian mechanics is not less local than MWI.

No, he really meant local in the usual sense of Minkowski space. One can identify space-time by operators that relate to position in space-time, and the time-evolution really is locally realistic^*, at least assuming something resembling these axioms.

*: Defining "realistic" to mean that any physically meaningful calculation is completely determined by the quantum state. (Indefiniteness is a key here -- assuming definite outcomes would require a hidden variable to decide how to collapse)

 

[Demystifier]

Well, let's say it differently. In MWI, "reality" exist in Hilbert space, but it can be also 'mapped' into our physical 4D space (in a given basis). Such mapping can create multiple (almost) non-interacting 'branches', occupying the same physical space. If we can create a transformation from one to another, based on MUCH you can't say what is 'more' real. I hope you agree.

So while what you said is true in Hilbert space, in physical space all 'influences' are limited to the light cones. So MWI provides 'stronger' locality then BM, where 'particles' affect each other FTL in physical space.

Am I right?

I think you are only partially right. The crucial question is whether reality in the Hilbert space can be mapped into the 4D spacetime. It can, but only on the macroscopic level when decoherence takes place. In a more general context, there is nothing "physical" about the 4D spacetime that our intuition is used to. Thus, at the fundamental level, the 4D world does not exist in any meaningful sense, so the world cannot be local on that space.

By the way, when decoherence takes place, at the macroscopic level Bohmian mechanics can also be well approximated by classical local laws of motion. Thus, I can conclude again that BM is not less local than MWI.

 

[Demystifier]

No, he really meant local in the usual sense of Minkowski space. One can identify space-time by operators that relate to position in space-time, and the time-evolution really is locally realistic^*, at least assuming something resembling these axioms.

*: Defining "realistic" to mean that any physically meaningful calculation is completely determined by the quantum state. (Indefiniteness is a key here -- assuming definite outcomes would require a hidden variable to decide how to collapse)

I would say that this (more or less standard) view of quantum theory is NOT the many-world view of quantum theory. In particular, your definition of reality above, which may be fine by itself, is NOT the many-world definition of reality. In MWI spacetime is NOT identified with operators that relate to position in space-time. In MWI, operators do not exist in an ontological sense. Only wave functions do.

 

[Varon]

Something I don't quite get. When do branches get separated. Is it after what is equivalent to Collapse.. where instead of Collapse the branches split off and all real?

But before Collapse, the particles are in superposition, so what happens during superposition? Like are the branches active before collapse? If only after, then superposition prior to collapse is as mysterious as Copenhagen?

 

[Demystifier]

Varon, in MWI there is no collapse. The split is described by the Schrodinger equation itself, or more precisely by the theory of decoherence emerging from the Schrodinger equation.

 

[Varon]

Varon, in MWI there is no collapse. The split is described by the Schrodinger equation itself, or more precisely by the theory of decoherence emerging from the Schrodinger equation.

I know. But before split or decoherence, the system is in superposition.. What happens inside this superposition?

 

[Hurkyl]

Something I don't quite get. When do branches get separated. Is it after what is equivalent to Collapse.. where instead of Collapse the branches split off and all real?

But before Collapse, the particles are in superposition, so what happens during superposition? Like are the branches active before collapse? If only after, then superposition prior to collapse is as mysterious as Copenhagen?

Maybe it would help to see a mathematical example of how relative state works?

The simplest example, I think, is the quantum state of a qubit and the relative state of its "spin around the z axis".


The state space of a qubit can be described geometrically as the unit ball. The surface, called the Bloch sphere, is the space of pure states -- the ones you're most familiar with as being described by kets in a Hilbert space. For any unit vector v, the point on the sphere it describes represents the qubit state "spin-up along the v-axis".

In this geometric picture, (convex) linear combinations are interpreted in the sense of classical statistics. If P,Q are two points in the unit ball, then aP + bQ is the state that represents a statistical distribution of being in state P with probability a, and state Q with probability b.



The relative state "spin around the z axis" can also be represented geometrically as the interval [-1, 1]. The two endpoints 1 and -1 (the "surface" of the interval) represent "spin up" and "spin down" respectively.

The relationship between the two is the straightforward one: if (x,y,z) is the state of a qubit, then the state of its subsystem "spin around the z axis" is simply z.



Now, "spin around the z axis" is actually really, really simplistic -- it's actually a classical system, and even with a unique choice of 'basis' states! It's a particle that's in a statistical distribution over the possibilities "up" and "down". If we're studying this subsystem, it makes sense to call these two possibilities worlds.




Now, suppose the qubit starts at the North pole -- the state (0,0,1). Let's assume the qubit is a closed system. Time evolution, according to Schrödinger's equation, will move this state around the surface of the sphere -- the state is always a pure state! There are no worlds or anything, there is simply "which axis am I oriented around now?"

But, we might be interested in looking how the "spin around the z axis" subsystem behaves while all of this is happening. It starts off in the "up" state. But as time progresses, it slides back and forth in the interval. The state of this subsystem is (completely) described as being a weighted mixture of the two worlds "up" and "down", the specific weights depending on just where in the interval it is.


Other relevant things are that any operator (acting on the Hilbert space) in the {|z+>, |z->} basis can also be interpreted as acting on the "spin around the z axis" subsystem. e.g. any measurement operation can be described in terms of having some value on the "up" state, and some value on the "down" state, and that's all there is to it. If time evolution was diagonal in that basis, then the state of the "spin around the z axis" subsystem would evolve in a purely classical fashion. In this case it's a rather boring fashion, since "up" can only evolve to "up" and "down" can only evolve to "down", but in general it would be more interesting.

 

[Demystifier]

But before split or decoherence, the system is in superposition.. What happens inside this superposition?

Nothing which could be understood in classical terms. The cat is neither dead nor alive, etc. Fortunately, for macroscopic stuff decoherence is very very fast, so in practice such weird superpositions can never be seen. That's why it is hard to imagine the cat which is neither dead nor alive.

 

[Varon]

Nothing which could be understood in classical terms. The cat is neither dead nor alive, etc. Fortunately, for macroscopic stuff decoherence is very very fast, so in practice such weird superpositions can never be seen. That's why it is hard to imagine the cat which is neither dead nor alive.

So in Many worlds, superposition in one world still exist (before split or decoherence). So Many World Interpretation doesn't make it simplier. It only explains what happens after split or decoherence when branches become separate worlds, but not before. So you still have the mysterious superposition state in one world just like Copenhagen.

 

[Demystifier]

So in Many worlds, superposition in one world still exist (before split or decoherence). So Many World Interpretation doesn't make it simplier. It only explains what happens after split or decoherence when branches become separate worlds, but not before.

No, it describes very well what happens before in mathematical terms, but not in classical terms such as cats.

So you still have the mysterious superposition state in one world just like Copenhagen.

I don't think that superposition is mysterious for Copenhagen. What is mysterious for Copenhagen is how the superposition suddenly ceases to be a superposition. It says - by a measurement - but it does not specify what the measurement is.

 

[Varon]

No, it describes very well what happens before in mathematical terms, but not in classical terms such as cats.


I don't think that superposition is mysterious for Copenhagen. What is mysterious for Copenhagen is how the superposition suddenly ceases to be a superposition. It says - by a measurement - but it does not specify what the measurement is.

Superposition in Copenhagen is not mysterious? It is. Explain how one electron at a time double slit experiment can still interfere with itself. Somehow it becomes a wave in between emission and detection. Let's just focus on Copenhagen whose superposition I assume is similar to the superposition in Many worlds before split or decoherence. Let's avoid Bohmian, your specialization for now.

 

[Varon]

Maybe it would help to see a mathematical example of how relative state works?

The simplest example, I think, is the quantum state of a qubit and the relative state of its "spin around the z axis".


The state space of a qubit can be described geometrically as the unit ball. The surface, called the Bloch sphere, is the space of pure states -- the ones you're most familiar with as being described by kets in a Hilbert space. For any unit vector v, the point on the sphere it describes represents the qubit state "spin-up along the v-axis".

In this geometric picture, (convex) linear combinations are interpreted in the sense of classical statistics. If P,Q are two points in the unit ball, then aP + bQ is the state that represents a statistical distribution of being in state P with probability a, and state Q with probability b.



The relative state "spin around the z axis" can also be represented geometrically as the interval [-1, 1]. The two endpoints 1 and -1 (the "surface" of the interval) represent "spin up" and "spin down" respectively.

The relationship between the two is the straightforward one: if (x,y,z) is the state of a qubit, then the state of its subsystem "spin around the z axis" is simply z.



Now, "spin around the z axis" is actually really, really simplistic -- it's actually a classical system, and even with a unique choice of 'basis' states! It's a particle that's in a statistical distribution over the possibilities "up" and "down". If we're studying this subsystem, it makes sense to call these two possibilities worlds.




Now, suppose the qubit starts at the North pole -- the state (0,0,1). Let's assume the qubit is a closed system. Time evolution, according to Schrödinger's equation, will move this state around the surface of the sphere -- the state is always a pure state! There are no worlds or anything, there is simply "which axis am I oriented around now?"

But, we might be interested in looking how the "spin around the z axis" subsystem behaves while all of this is happening. It starts off in the "up" state. But as time progresses, it slides back and forth in the interval. The state of this subsystem is (completely) described as being a weighted mixture of the two worlds "up" and "down", the specific weights depending on just where in the interval it is.


Other relevant things are that any operator (acting on the Hilbert space) in the {|z+>, |z->} basis can also be interpreted as acting on the "spin around the z axis" subsystem. e.g. any measurement operation can be described in terms of having some value on the "up" state, and some value on the "down" state, and that's all there is to it. If time evolution was diagonal in that basis, then the state of the "spin around the z axis" subsystem would evolve in a purely classical fashion. In this case it's a rather boring fashion, since "up" can only evolve to "up" and "down" can only evolve to "down", but in general it would be more interesting.

Thanks. I'll analyse it sometime after I learned all the maths (so don't make it quite complicated). For now. I just wanted to know if the superposition before split or decoherence in Many Worlds has the same ontology as the superposition of Copenhagen before collapse. I'll explain. Bohr stated that in the absence of measurement to determine position, there is no position. In Many worlds before split or decoherence, does a particle also has no position or does the wave function contain multiple copies of the particles (prior to split or decoherence)?

 

[Demystifier]

Superposition in Copenhagen is not mysterious? It is. Explain how one electron at a time double slit experiment can still interfere with itself. Somehow it becomes a wave in between emission and detection. Let's just focus on Copenhagen whose superposition I assume is similar to the superposition in Many worlds before split or decoherence. Let's avoid Bohmian, your specialization for now.

That's easy. Electron is a wave, so nothing is easier than to interfere with itself. Nothing mysterious.

 

[Demystifier]

In Many worlds before split or decoherence, does a particle also has no position or does the wave function contain multiple copies of the particles (prior to split or decoherence)?

In MWI there are no particles at all. Only waves.

 

[Varon]

In MWI there are no particles at all. Only waves.

If that's true. How come the detector can detect particles if only waves exist?

Anyway. I just read that in a doublet slit experiment in Many Worlds. When an electron is emitted, the electron splits immediately where one goes to the upper slit in one world, the second goes to the lower slit in the other world. And interferences is due to superposition of universes (whatever this means). So when you said only waves are present, this is what propel the electron to their respective places in each universe that can interfere in the screen, isn't it.

I wonder if what I just mentioned is a Dewitt version or original Everett version (not likely). How do you create an Everett version out of the double slit experiment?

 

[Demystifier]

If that's true. How come the detector can detect particles if only waves exist?

According to MWI, detector does not detect particles. It detects localized waves, which people like to call "particles". The localization itself is described and explained by decoherence.

 

[Varon]

According to MWI, detector does not detect particles. It detects localized waves, which people like to call "particles". The localization itself is described and explained by decoherence.

You are kidding right?

In Many worlds. I have never heard it stated that particles are localized waves (shades of Schroedinger). In MWI. Particles exist at all times.. only duplicated during split or after decoherence. What version MWI are you talking about anyway?

 

[Demystifier]

You are kidding right?

In Many worlds. I have never heard it stated that particles are localized waves (shades of Schroedinger). In MWI. Particles exist at all times.. only duplicated during split or after decoherence. What version MWI are you talking about anyway?

I believe you have seriously misunderstood something about MWI.

 

[Varon]

I believe you have seriously misunderstood something about MWI.

Ok. I'll re-read the books about it. Maybe it is because it's called a Universal
Wavefunction... but we clearly have particles... so what happened to the particles inside the wavefunction. If the wavefunction is the particle. So I am a wave function? I'll consider you not kidding. Anyway. I'll look into it.

 

[Dmitry67]

Absolutely serious.
Photon wave hits 10 megapixel digital camera matrix. It decoheres into 10 millions of states where only one cell is affected. This is what we call a 'photon'

 

[Varon]

According to MWI, detector does not detect particles. It detects localized waves, which people like to call "particles". The localization itself is described and explained by decoherence.

Ok. After preferred basis chosen, one of the eigenvalues corresponds to our world. Here an electron is a wave. We are told an electron is a point particle. So in the MWI counterpart, what is the length of the Universal Wavefunction wavelength corresponding to the electron?

 

[Varon]

Absolutely serious.
Photon wave hits 10 megapixel digital camera matrix. It decoheres into 10 millions of states where only one cell is affected. This is what we call a 'photon'

In Copenhagen, collapse chooses one of the eigenvalues which becomes a particle.

In Many worlds, after decoherence and basis chosen, one of the eigenvalues correspond to our world.

In both cases, one of the eigenvalues is chosen.

This means Copenhagen and Many worlds are equivalent in one of the eigenvalues chosen. So how come is one call a particle, the other a wave. Maybe a particle in Copenhagen is also a localize wave just like in Many Worlds?

Anyway. What is the length of the wavelenth corresponding to one of the eigenvalues in Many worlds and Copenhagen?

 

[Dmitry67]

In both cases, one of the eigenvalues is chosen.

No.
In MWI, there is a symmery between all outcomes (ignoring their probability or, how it is better to be called in MWI, "intensity of existence")
ALL outcomes exist.
This is very important.
No specific outcome is "chosen"

However, as observers remember only the past, not the future, and as they effectively lose an ability to 'communicate' with the 'other branches', all observers (in every branch) have an illusion, they 'their' outcome is the only one which exist.

 

[Dmitry67]

Ok. After preferred basis chosen, one of the eigenvalues corresponds to our world. Here an electron is a wave. We are told an electron is a point particle. So in the MWI counterpart, what is the length of the Universal Wavefunction wavelength corresponding to the electron?

The same as in QM.
MWI is a 'pure' QM - MWI does not have any additional assumptions, on the contrary, it is a claim that no additional assumptions are needed.

 

[Varon]

No.
In MWI, there is a symmery between all outcomes (ignoring their probability or, how it is better to be called in MWI, "intensity of existence")
ALL outcomes exist.
This is very important.
No specific outcome is "chosen"

However, as observers remember only the past, not the future, and as they effectively lose an ability to 'communicate' with the 'other branches', all observers (in every branch) have an illusion, they 'their' outcome is the only one which exist.

I know. It's just a bad choice of words when I said one of the eigenvalues is chosen. What I meant was our branch only experience one of the eigenvalues and all outcomes exist. Since all are wave, I'm asking what is the wavelength of the particle in this sense. So it's the same de Broglie wavelength? But this is based on wavelengh = h/momentum. Is there another formula that only inputs the particle existence without regards to momentum?