Improbability of the Many-Worlds Interpretation?

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No. Or at least, if you're going to allow for that possibility, then you are allowing for possibilities that invalidate our belief in past data, and that version of the MWI undermines itself, as I argued in post #24. The chance that enough of the molecules will happen to all have tunneled into the "can't fire" state, and none of them will have tunneled back into the "can fire" state, at the exact instant that you try to fire the bullet, is comparable to the chance that @DrChinese actually was president of the US 5 minutes ago, but then a quantum fluctuation happened that changed everything on Earth, including all of our memories, to the state we all perceive and remember now. And if you allow for possibilities like that, all bets are off and there's no point in doing science at all.
I don't think taking MWI literally requires the assumption that every massive tunneling event is realized. Incredibly unlikely things might not be stable enough to form recognizable branches, the interference effects might be too strong before they fully split, or they might not contain something that can be considered a future version of one's self, so must be ignored.

Looking at it backwards is also helpful. Maybe there is a very small contribution to my current state from almost-orthogonal past states where Dr. Chinese was president. But that past state is so incompatible with my current personal state (containing my memories) the contribution will be too small to notice.

I'm not suggesting these are solved problems, because I suspect one needs to really understand how people perceive the world and form their sense of self to fully connect objective unitary evolution to the subjective experience of life inside that universe.
 
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"Everything" and "rules" meaning what exactly?

I also wouldn't connect a clarification request from me about what exactly you were referring to to be related in any way to what physicists think about or don't think about. I just wasn't sure precisely what you meant.
I see; sometimes I'm just surprised by what things I say turn out to be least clear :) I meant once you have a way to try every possible program, you have the power to do (almost) anything not ruled out by the laws of physics.
 

Hans de Vries

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Perhaps you should read this first:
It might save you from tilting at straw men.
I know Sean Carrol's arguments but quote:

Sean Carrol said:
Everett, by contrast, says that the universe splits in two: in one the cat is awake, and in the other the cat is asleep. Once split, the universes go their own ways, never to interact with each other again.
I don't see how Sean Carrol's following arguments help in anyway:

1) All universes are in superposition and superposition is normal in QM
2) In any universe all particles are entangled so they can't interact with particles in other universes.
3) And because of decoherence particles in one universe do not interfere with particles in other universes.

- At the end you need the same amount of independent universes. Since the splitting started right at the big bang we can be assured that universes are totally different from each other.

- The entanglement claim does not hold. Only certain properties can be entangled and momentum is not one of them. You can reflect entangled photons on mirrors, guide them through glass fiber and so on. I don't see how entanglement justifies the claim that particles can not interact with each other anymore. It's just a subset of their properties that is entangled.

- Also the decoherence argument for non-interference runs counter to accepted physics. A particle in two worlds may obtain different momentum states in each world. In QED, and subsequently QFT, a particle in a superposition of 2 momentum states gives rise to interference currents which are the source of the bosons of the Standard model.

The rest of the article is rather denigrating and political. It goes about the skeptics emotional states: "angry", "denial" and finally "acceptance". The latter is of course to accept the Everettian MWI approach and to forget the "silly" objections.


Finally: I do not choose sides with any of the quantum philosophical interpretations, simple because I'm highly skeptical to all of them :smile:
 

PeroK

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I know Sean Carrol's arguments but quote:



I don't see how Sean Carrol's following arguments help in anyway:

1) All universes are in superposition and superposition is normal in QM
2) In any universe all particles are entangled so they can't interact with particles in other universes.
3) And because of decoherence particles in one universe do not interfere with particles in other universes.
I must confess, I find this post quite bizarre. I'm not an advocate of MWI, nor do I know the Carrol piece particularly well. But, my first reaction was "I didn't think he said any of that". So, I went back to his blog, and nothing you ascribe to him he actually says!

Those three points, as far as I can tell, are entirely your own invention!

My understanding of Carrol's argument (reading what he actually says) is:

Fundamentally, despite its name, in MWI there is only one universe. But, it contains ultimately a superposition of all (measurement) outcomes. Like orthodox QM does before you measure it. Unlike orthodox QM, the superposition is never resolved, but continues indefinitely.

In the infamous cat experiment, there is only ever one cat. It's the state (of the particles that make up the cat) that is in superposition; not that an extra cat has been brought into existence. When you open the box, in orthodox QM the state resolves itself in one or the other. In MWI, the two possibilities continue to exist, in some sense - but, through decoherence, there is no subsequent mixing of the two possibilities

It's the branches of the wave function that decohere, so that they do not in general interfere with each other. Not that new universes of trillions of particles are continuously created.

PS the crux of Carrol's argument is here (direct quotation, with my underlines):

"All of this exposition is building up to the following point: in order to describe a quantum state that includes two non-interacting “worlds” as in (2), we didn’t have to add anything at all to our description of the universe, unlike the classical case. All of the ingredients were already there!"
 
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Hans de Vries

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I must confess, I find this post quite bizarre. I'm not an advocate of MWI, nor do I know the Carrol piece particularly well. But, my first reaction was "I didn't think he said any of that". So, I went back to his blog, and nothing you ascribe to him he actually says!

Those three points, as far as I can tell, are entirely your own invention!
I would urge you to read carefully through the text as accurate and painstakingly as I have done (and anybody can do in the link at the bottom), before you come out in the aggressive way you did. Lets carefully go through the 3 statements (as I ascribed them to Carrol) one by one:

1) All universes are in superposition and superposition is normal in QM

First Carrol comes up with the theory that both particle and observer (apparatus or human) are in a superposition state with different versions of them self:

Sean Carrol said:
But there is clearly another possibility. If the particle can be in a superposition of two states, then so can the apparatus......What would it be like to live in a world with the kind of quantum state we have written in (2)? It might seem a bit unrealistic at first glance; after all, when we observe real-world quantum systems it always feels like we see one outcome or the other. We never think that we ourselves are in a superposition of having achieved different measurement outcomes.
If the human being is already in superposition after the split then both human beings need their own versions of the universe because:
Sean Carrol said:
Everett, by contrast, says that the universe splits in two: in one the cat is awake, and in the other the cat is asleep. Once split, the universes go their own ways, never to interact with each other again.

2) In any universe all particles are entangled so they can't interact with particles in other universes.

Sean Carrol said:
But there is clearly another possibility. If the particle can be in a superposition of two states, then so can the apparatus............. There are more things in the universe than our particle and the measuring apparatus; there is the rest of the Earth, and for that matter everything in outer space. That stuff — group it all together and call it the “environment” ............ We expect the apparatus to quickly become entangled with the environment, if only because photons and air molecules in the environment will keep bumping into the apparatus. As a result, even though a state of this form is in a superposition, the two different pieces (one with the particle spin-up, one with the particle spin-down) will never be able to interfere with each other
Here we see that the apparatus (or human observer) is expected by Carrol to become entangled with the environment which includes "everything in outer space". The second odd thing here is that, while Carrol mentions entanglement, A particle spin-up never interferes with particle spin-down because the two states are orthogonal. This is a very well known property of the Dirac field!! Entanglement has nothing to do with this !!

3) And because of decoherence particles in one universe do not interfere with particles in other universes.

Sean Carrol said:
This is where the magic of decoherence comes in......... As a result, even though a state of this form is in a superposition, the two different pieces (one with the particle spin-up, one with the particle spin-down) will never be able to interfere with each other. Interference (different parts of the wave function canceling each other out) demands a precise alignment of the quantum states, and once we lose information into the environment that (interference) becomes impossible. That’s decoherence
Here Carrol blames decoherence for the loss of interference between the two states in superposition.

My advice would be (to Carrol as well) : Study at least QED.


 
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I don't think taking MWI literally requires the assumption that every massive tunneling event is realized
Perhaps not, but many MWI proponents seem to talk as if it does.
 
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Only certain properties can be entangled and momentum is not one of them.
Where are you getting this from? Momentum can certainly be entangled. To give just two examples: in a Stern-Gerlach apparatus, the momentum of a particle like an electron is entangled with its spin; and in a process where two photons are created by particle-antiparticle pair annihilation, the momenta of the two photons are entangled since they must sum to zero in the center of mass frame.
 

Hans de Vries

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Where are you getting this from? Momentum can certainly be entangled. To give just two examples: in a Stern-Gerlach apparatus, the momentum of a particle like an electron is entangled with its spin;

and in a process where two photons are created by particle-antiparticle pair annihilation, the momenta of the two photons are entangled since they must sum to zero in the center of mass frame.
It's not as simple as just energy conservation. Do you have an example of a correlation experiment using momentum as an entangled quantum state?
 
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Do you have an example of a correlation experiment using momentum as an entangled quantum state?
The first example I gave is an experiment that has been done.

The second example I gave might not have been realized in precisely the form I gave it, but since it's just an example of momentum conservation (not energy conservation), and momentum conservation has been verified by countless experiments, I don't see what the issue is.
 

Hans de Vries

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The first example I gave is an experiment that has been done.

The second example I gave might not have been realized in precisely the form I gave it, but since it's just an example of momentum conservation (not energy conservation), and momentum conservation has been verified by countless experiments, I don't see what the issue is.
Well yes, that is of course that's what I wanted to say: It's more than just momentum conservation.

One would expect at least some "action-at-a-distance" correlation effect in need for an explanation. For instance a higher probability that both green detectors go off or both red detectors go off because the entanglement relation maintains the momentum relation somehow at a distance, even after going through the mirrors. What is entanglement without "action-at-a-distance"? I'm sure if you do this experiment that you won't see this kind of correlation though. It is just some example.
momentum_correlation.jpg


Note that I made the remark to counter the claim suggesting there is no interaction possible when all particles in a superposition states are entangled. This clearly suggests an "action-on-a-distance" for momentum which I do not believe to be correct.
 
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PeroK

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I would urge you to read carefully through the text as accurate and painstakingly as I have done (and anybody can do in the link at the bottom), before you come out in the aggressive way you did. Lets carefully go through the 3 statements (as I ascribed them to Carrol) one by one:

1) All universes are in superposition and superposition is normal in QM
Carrol does not say this.

2) In any universe all particles are entangled so they can't interact with particles in other universes.
Carrol does not say this either. This is your interpretation of MWI.


3) And because of decoherence particles in one universe do not interfere with particles in other universes.
Carrol does not say this either.

I fail to see the connection between Carrol's text and your analysis of it. In fact, your analysis is precisely the misunderstanding of MWI that his blog was intended to address.

You are free to believe that all the advocates of MWI are either mad or ignorant. But, I don't buy that. I don't buy that you know so much more about QM that its professional advocates. Especially, as it seems quite clear to me you are tilting at a straw man of your own creation.
 
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One would expect at least some "action-at-a-distance" correlation effect in need for an explanation.
This is true of any experiment involving spacelike separated measurements on entangled particles, since any such experiment can produce correlations which violate the relevant Bell inequalities.

This clearly suggests an "action-on-a-distance" for momentum which I do not believe to be correct.
Then you evidently don't believe in conservation of momentum, since conservation of momentum plays the same role in an experiment involving momentum entanglement that conservation of angular momentum plays in an experiment involving spin entanglement. The "action at a distance" effect on correlations is the same in both cases.
 

Hans de Vries

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Then you evidently don't believe in conservation of momentum, since conservation of momentum plays the same role in an experiment involving momentum entanglement that conservation of angular momentum plays in an experiment involving spin entanglement. The "action at a distance" effect on correlations is the same in both cases.
Conservation of momentum is maintained at all times, always. One of the most basic laws of nature. Who would ever make such a ridiculous claim?

- Momentum can also be absorbed by the silver mirrors.
- Angular momentum can be absorbed by Wollaston prisms.

So a loss of correlation at the detectors does not violate any conservation laws.
 
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For instance a higher probability that both green detectors go off or both red detectors go off because the entanglement relation maintains the momentum relation somehow at a distance, even after going through the mirrors
The photons can transfer momentum to the mirrors, so once they are involved the momentum of the two photons by themselves is not necessarily conserved.
 
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a loss of correlation at the detectors does not violate any conservation laws
Indeed, as I just posted myself in response to you. Which simply means this experiment is not a good one for testing momentum entanglement. But if you take out the mirrors, and just use pairs of detectors in opposite directions, and do coincidence counting, it is.
 
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It's not clear to me that Michael Price is saying Dr. Chinese is president right now. For me that doesn't make sense, since he clearly isn't president based on the information contained in this lab. I'm not even sure you can compare times between different worlds as they are casually disconnected from the point of branching.
Dr Chinese is President of the US in some parallel timelines right now, in the sense that those timelines use our dating system and show a date of 2019.
 
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But I also think you can't just consider classical evolution since inflation. When people perform quantum measurements now, it forms new branches. This is most clearly true when people use quantum outcomes to make macroscopic decisions. It's not clear if you are suggesting an alternative view, where quantum outcomes are overwhelmed by classical evolution and the branch we are living in is actually deterministic.

I also think quantum branching and decoherence is ubiquitous, though it's more controversial. This is based on the only analysis I've seen on the topic, which I linked in the other linked thread, looking at how the average coin flip is an amplification of quantum uncertainty.
Yes, and this branching occurs not just at quantum measurements, but at every entropic event.
PS, nice article.
 
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The point I'm making is that all this blithe talk about "multiple worlds" fails to pay attention to specifically how such multiple worlds get created, if the MWI is true. They don't get created by magic. They don't get created just because we humans can imagine them. They get created by having genuine quantum mechanical uncertainty, "
Of course these multiple worlds (or timelines, as I prefer) don't get created by magic. I am at a loss to see why you thought I said or implied otherwise.
 
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Of course these multiple worlds (or timelines, as I prefer) don't get created by magic. I am at a loss to see why you thought I said or implied otherwise.
So what you contend is essentially that at least one of the branches that branch from THIS exact universe at THIS exact moment will reconfigure all particles in our lightcone to put you in the white house and every citizen of Earth will have their brain (again just particle reconfiguration) filled with memories where Michael Price (or whoever else) as president make sense. Right?
 

Mentz114

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Dr Chinese is President of the US in some parallel timelines right now, in the sense that those timelines use our dating system and show a date of 2019.
How can possibly claim that from the laws of physics ? Are you a clairvoyant now ?

Being so certain in your proclamations is not becoming in a scientist.
 
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Dr Chinese is President of the US in some parallel timelines right now, in the sense that those timelines use our dating system and show a date of 2019.
Sorry, but I've already made several posts explaining why this claim is extremely implausible. I can't prove it's wrong, but you can't prove it's correct either, because neither of us knows the universal wave function and what possibilities it includes.

Of course these multiple worlds (or timelines, as I prefer) don't get created by magic. I am at a loss to see why you thought I said or implied otherwise.
Because you keep helping yourself to extremely extravagant claims like the one quoted at the top of this post. If you want to avoid people thinking that you are making dubious claims, you should not make dubious claims.
 

PeroK

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Sorry, but I've already made several posts explaining why this claim is extremely implausible. I can't prove it's wrong, but you can't prove it's correct either, because neither of us knows the universal wave function and what possibilities it includes.



Because you keep helping yourself to extremely extravagant claims like the one quoted at the top of this post. If you want to avoid people thinking that you are making dubious claims, you should not make dubious claims.
Just to be on the safe side, it might be worth PF putting in some software that plays "Hail to the Chief" everytime @DrChinese makes a post.
 
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this branching occurs not just at quantum measurements, but at every entropic event
First, "entropic event" is not well-defined.

Second, in order for this to justify your much more extravagant claim about there being a world in which @DrChinese is president right now, you have to claim that there is a possible sequence of "entropic events" that can generate, from some common starting point, both the world we are actually in, and an alternate world in which @DrChinese is president right now, but which is similar enough in all other respects to make that description a reasonable one. And you can't possibly justify such a claim; you're just waving your hands and helping yourself to it without any consideration of whether it's actually at all plausible.
 
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How can [you] possibly claim that from the laws of physics ? Are you a clairvoyant now ?

Being so certain in your proclamations is not becoming in a scientist.
This claim, in the context of MWI, is no more extravagant than the claim that such occurrence is possible from a spontaneous random rearrangement of molecules in the Copenhagen interpretation. How this any different from saying that all the gas molecules in a chamber could suddenly bunch up in one small portion of the chamber? Such claims are often made in textbooks and seen as quite unremarkable.
 
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So what you contend is essentially that at least one of the branches that branch from THIS exact universe at THIS exact moment will reconfigure all particles in our lightcone to put you in the white house and every citizen of Earth will have their brain (again just particle reconfiguration) filled with memories where Michael Price (or whoever else) as president make sense. Right?
Sounds about right. In the context of MWI...
 

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