Parallel universe theory in quantum mechanics

FrumiousBandersnatch

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Now THIS I would consider non-mainstream science. And it impacts theology:

Parallel Universes and the Many-Worlds Theory - Universe Today


We have a small number of respected physicists--and by "respected" I mean these are the same physicists who brought about the field of Quantum Mechanics in the first place, and had their peers experimentally verify their claims--theorize that every time you measure a quantum particle, you spawn a parallel universe. In other words if an unknown quantum particle is positive half the time and negative half the time, as soon as you measure it, you spawn off two universes: one where it is positive, the other where it is negative. Which naturally results in an extremely high number of parallel universes.
Strictly speaking, you don't get branching of the wavefunction every time a particle is measured, but only when it is in a superposition of states. So the second and third times (and on) that you measure it, you'll get the same result each time - until it interacts with another particle in a superposition and becomes entangled.

This parallel universe by definition has to interact with this one, since the measurement of the particle in this universe caused it. So that means, in theory, experimental physicists ought to be able to come up with an experiment which tests the theory.
No, the opposite is true - a branch becomes a separate universe when it can no longer interfere with the others. This occurs when the alternate results of the interaction spread out into the environment, becoming irrevocably entangled with the wider world. This is known as 'decoherence' and is what leads to the causal separation of the branches.

The initial superposition of the particle is like the thin end of the wedge between worlds - when something interacts with the particle it joins the superposition, then whatever interacts with that also joins, until you have a cascade of superpositions - decoherence. At that point the different outcomes of the original interaction have become separate branches of the whole wavefunction that can no longer interact; these are the separate 'worlds'. It's really all one universe with a single wavefunction that is branched a vast number of times.

This, if true, could seriously impact theology, since this could make us all human Schroedinger's Cats, where if we die we go to Heaven and Hell at the same time. Or in 50% of the parallel universes you go to Hell, and the other 50% you go to Heaven. But then again maybe we don't really understand what exactly a said "parallel universe" is.
That would only be true if Heaven and Hell were in a 50:50 superposition, or you had an inevitable interaction with some other 50:50 quantum superposition that would somehow determine which way you'd go. It's almost as implausible as the idea of Heaven and Hell itself...
 
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FrumiousBandersnatch

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P.S. Schrodinger's cat is a ruse. It makes a category error conflating ontology (what is) with epistemology (what one can know). Some think he did this on purpose to mock his fellow QM practitioners due to their lack of philosophy of science acumen.
As I understand it, Schrodinger's Cat was intended to point out the ridiculous implications of the Copenhagen interpretation idea of requiring a conscious observer to collapse the wavefunction. It was a jibe at those who suggested the observer decided 'what is' by his/her observation.

Clearly, the epistemological version wouldn't be at all controversial - you simply don't know what's happened until you look. It would appear that, in the real world, both would occur - something would collapse the wavefunction at some point so the cat becomes either alive or dead (by the Copenhagen interpretation), and the conscious observer would not know the outcome until he/she looked in the box.
 
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FrumiousBandersnatch

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You want an experiment to test this? A few years ago Life Magazine did a cover story on children who had been resuscitated from the dead. They chose very young children because they didn't want them influenced by what they had read or been taught. They chose children from all over the world, different family backgrounds, religions, cultures, languages, etc. The children were asked to draw a picture of what they saw, and they had experiences of meeting Jesus, even if their religion was not Christian. This to me demonstrates another "universe".
I'd really like to see that article or the paper it was presumably based on.

I would suggest it's pretty much impossible that children old enough to be able to draw anything recognisable will not have been enculturated - the process starts well before physical coordination does. And how you can distinguish a drawing of Jesus from one of Nana, Teecher, Daddy, or for that matter, Mohammed, at that age is a puzzle - so how could the researchers know the figure was Jesus unless the children themselves already knew who Jesus was... etc.

Colour me deeply sceptical.
 
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ZNP

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I'd really like to see that article or the paper it was presumably based on.

I would suggest it's pretty much impossible that children old enough to be able to draw anything recognisable will not have been enculturated - the process starts well before physical coordination does. And how you can distinguish a drawing of Jesus from one of Nana, Teecher, Daddy, or for that matter, Mohammed, at that age is a puzzle - so how could the researchers know the figure was Jesus unless the children themselves already knew who Jesus was... etc.

Colour me deeply sceptical.
I didn't say they were old enough to draw pictures when they were resuscitated but when Life interviewed them.
 
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FrumiousBandersnatch

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I didn't say they were old enough to draw pictures when they were resuscitated but when Life interviewed them.
It becomes less plausible with detail... memories, in particular early childhood memories, are unreliable and malleable enough without leaving a significant interval before recording them. Coherent episodic memories are poorly encoded earlier than about 3 yrs, and rarely able to be recalled.
 
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ZNP

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It becomes less plausible with detail... memories, in particular early childhood memories, are unreliable and malleable enough without leaving a significant interval before recording them. Coherent episodic memories are poorly encoded earlier than about 3 yrs, and rarely able to be recalled.
OK, here is my total recollection. I was teaching English in Taiwan at the time, prior to 1995 but after 1987. The school I was at gave us articles to read to the class, we read this article. At the time it was just me and one other student (this was an adult class at night and he was the first to arrive). I asked him what he thought of the article and he said he agreed with it. I found that strange since he had already told me he was a Buddhist, so I asked why he agreed. He said that he had been in the military and had also died in the hospital and then been resuscitated. He said when he had died he had met Jesus. That was very surprising since he was a Buddhist, so I asked him about this. He said he had visited some churches after this happened but couldn't understand what they were talking about, so he was a Buddhist that believed he would see Jesus when he died.
 
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FrumiousBandersnatch

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OK, here is my total recollection. I was teaching English in Taiwan at the time, prior to 1995 but after 1987. The school I was at gave us articles to read to the class, we read this article. At the time it was just me and one other student (this was an adult class at night and he was the first to arrive). I asked him what he thought of the article and he said he agreed with it. I found that strange since he had already told me he was a Buddhist, so I asked why he agreed. He said that he had been in the military and had also died in the hospital and then been resuscitated. He said when he had died he had met Jesus. That was very surprising since he was a Buddhist, so I asked him about this. He said he had visited some churches after this happened but couldn't understand what they were talking about, so he was a Buddhist that believed he would see Jesus when he died.
OK; I'd still like to see the article or paper, get the details of what they did - it simply doesn't sound like a sensible experiment ¯\_(ツ)_/¯
 
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Halbhh

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Strictly speaking, you don't get branching of the wavefunction every time a particle is measured, but only when it is in a superposition of states. So the second and third times (and on) that you measure it, you'll get the same result each time - until it interacts with another particle in a superposition and becomes entangled.

No, the opposite is true - a branch becomes a separate universe when it can no longer interfere with the others. This occurs when the alternate results of the interaction spread out into the environment, becoming irrevocably entangled with the wider world. This is known as 'decoherence' and is what leads to the causal separation of the branches.

The initial superposition of the particle is like the thin end of the wedge between worlds - when something interacts with the particle it joins the superposition, then whatever interacts with that also joins, until you have a cascade of superpositions - decoherence. At that point the different outcomes of the original interaction have become separate branches of the whole wavefunction that can no longer interact; these are the separate 'worlds'. It's really all one universe with a single wavefunction that is branched a vast number of times.

That would only be true if Heaven and Hell were in a 50:50 superposition, or you had an inevitable interaction with some other 50:50 quantum superposition that would somehow determine which way you'd go. It's almost as implausible as the idea of Heaven and Hell itself...
Understanding it, Many Worlds seems just as ad hoc as any other interpretation to me, without any reason to think it more likely than any of the competing theories. It has no special supporting evidence. If it were 1 of only 1 or 2 competing theories, one could take it more seriously. It seems much more ad hoc than pilot waves or other theories like darwinism for instance. So, I think of it as unlikely. Until something gets unique supporting evidence (that other theories don't fit), there is no favorite.
Interpretations of quantum mechanics - Wikipedia
 
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FrumiousBandersnatch

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Understanding it, Many Worlds seems just as ad hoc as any other interpretation to me, without any reason to think it more likely than any of the competing theories. It has no special supporting evidence. If it were 1 of only 1 or 2 competing theories, one could take it more seriously. It seems much more ad hoc than pilot waves or other theories like darwinism for instance. So, I think of it as unlikely. Until something gets unique supporting evidence (that other theories don't fit), there is no favorite.
Interpretations of quantum mechanics - Wikipedia
These aren't theories, they're generally called 'interpretations'; they're ways of describing in physical terms what is described by the mathematics of the quantum formalism. In principle, they should all conform to that formalism. The only evidence for any of them is QM itself.

The USP for 'Many Worlds' is that it is the simplest interpretation, i.e. it adds nothing to the quantum formalism, whereas the other mainstream interpretations introduce unexplained ad-hoc extras. For example, the Copenhagen variations introduce the idea of wavefunction collapse, an instantaneous change of state of the wavefunction, which doesn't appear at all in the formalism. All that's needed for MW is to accept the wavefunction as a complete description of the state of things in the world, which it appears to be, and follow its unitary evolution according to the Schrodinger equation.

The QM formalism describes how quantum systems in superposition interact - they become 'entangled' - their states combine additively so that their wavefunctions (actually parts of the universal wavefunction) must be considered together, i.e. they become a single quantum system. So, for example, particle A in a superposition of spin-up and spin-down, might interact and become entangled with particle B, so that the resulting system is described by a combination of [spin-up A with B] and [spin-down A with B] (in bra–ket notation, something like this: ⎥A↑〉⎥B〉 + ⎥A↓〉⎥B〉. These X states represent the vectors in Hilbert space).

This should be the same for all interpretations, but it's how this situation then develops that shows the differences. In MW, this process simply continues deterministically, with more and more particles joining the entanglement until the superposed states rapidly become so entangled with the environment they can no longer interfere with each other, becoming separate non-interacting branches of the wavefunction that continue to develop independently, i.e. effectively separate 'worlds'. This process is called decoherence. In Copenhagen interpretations, when systems large enough to be described classically (a rather fuzzy boundary), e.g. a person or a measuring device, interact with a quantum system in superposition, the wavefunction instantaneously 'collapses' so that all but one of the superposed states (randomly) cease to exist.

So Copenhagen accounts for our macro-scale observation of a single outcome for a quantum measurement by somehow throwing away all but one state of the superposition, whereas Many Worlds says the observer simply joins the superposition like any other quantum system, branching with it and participating in each of the non-interacting branches that result.

For its supporters, the simplicity of MW makes it preferable to wavefunction collapse interpretations and the tricky additional questions that accompany them.

Whether we can ever determine which interpretation (if any) reflects what 'really' happens is a moot point, but MW would be falsified if wavefunction collapse could be demonstrated or shown to be necessary...
 
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Halbhh

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These aren't theories, they're generally called 'interpretations'; they're ways of describing in physical terms what is described by the mathematics of the quantum formalism. In principle, they should all conform to that formalism. The only evidence for any of them is QM itself.

The USP for 'Many Worlds' is that it is the simplest interpretation, i.e. it adds nothing to the quantum formalism, whereas the other mainstream interpretations introduce unexplained ad-hoc extras. For example, the Copenhagen variations introduce the idea of wavefunction collapse, an instantaneous change of state of the wavefunction, which doesn't appear at all in the formalism. All that's needed for MW is to accept the wavefunction as a complete description of the state of things in the world, which it appears to be, and follow its unitary evolution according to the Schrodinger equation.

The QM formalism describes how quantum systems in superposition interact - they become 'entangled' - their states combine additively so that their wavefunctions (actually parts of the universal wavefunction) must be considered together, i.e. they become a single quantum system. So, for example, particle A in a superposition of spin-up and spin-down, might interact and become entangled with particle B, so that the resulting system is described by a combination of [spin-up A with B] and [spin-down A with B] (in bra–ket notation, something like this: ⎥A↑〉⎥B〉 + ⎥A↓〉⎥B〉. These X states represent the vectors in Hilbert space).

This should be the same for all interpretations, but it's how this situation then develops that shows the differences. In MW, this process simply continues deterministically, with more and more particles joining the entanglement until the superposed states rapidly become so entangled with the environment they can no longer interfere with each other, becoming separate non-interacting branches of the wavefunction that continue to develop independently, i.e. effectively separate 'worlds'. This process is called decoherence. In Copenhagen interpretations, when systems large enough to be described classically (a rather fuzzy boundary), e.g. a person or a measuring device, interact with a quantum system in superposition, the wavefunction instantaneously 'collapses' so that all but one of the superposed states (randomly) cease to exist.

So Copenhagen accounts for our macro-scale observation of a single outcome for a quantum measurement by somehow throwing away all but one state of the superposition, whereas Many Worlds says the observer simply joins the superposition like any other quantum system, branching with it and participating in each of the non-interacting branches that result.

For its supporters, the simplicity of MW makes it preferable to wavefunction collapse interpretations and the tricky additional questions that accompany them.

Whether we can ever determine which interpretation (if any) reflects what 'really' happens is a moot point, but MW would be falsified if wavefunction collapse could be demonstrated or shown to be necessary...
Would it help if I let you know you've told me nothing new to me? Just don't waste time explaining basic stuff someone that learned some QM and read since would already know. (though it's odd you think Many Worlds is simpler than Copenhagen itself)

Where does MW has any special support to give it more credibility than competing theories? just simplicity? Not very convincing.

We are still waiting for any evidence that supports any of the various interpretation theories uniquely.

It is fun tho to point out that if we prefer to say a new theory is a hypothesis that makes specific unique predictions other theories do not, then anything not doing that tempts us to wonder if it is....what's that wording....ah, "not even wrong" heh heh :) So, what are the unique observable in principle predictions of MW and I wonder if they are going to be testable?
 
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FrumiousBandersnatch

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Would it help if I let you know you've told me nothing new to me? Just don't waste time explaining basic stuff someone that learned some QM and read since would already know.
Not everyone who reads these forums knows the basics of QM.

(though it's odd you think Many Worlds is simpler than Copenhagen itself)
Why do you think that's odd? MW follows the unadorned formalism with no ad-hoc additions, Copenhagen adds wavefunction collapse to the formalism.

Where does MW has any special support to give it more credibility than competing theories? just simplicity? Not very convincing.

We are still waiting for any evidence that supports any of the various interpretation theories uniquely.
I already said the only evidence any of them have is QM itself.

It is fun tho to point out that if we prefer to say a new theory is a hypothesis that makes specific unique predictions other theories do not, then anything not doing that tempts us to wonder if it is....what's that wording....ah, "not even wrong" heh heh :) So, what are the unique observable in principle predictions of MW and I wonder if they are going to be testable?
As I already said, they're not theories or testable hypotheses, they're more conceptual models.
 
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Halbhh

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Not everyone who reads these forums knows the basics of QM.

Why do you think that's odd? MW follows the unadorned formalism with no ad-hoc additions, Copenhagen adds wavefunction collapse to the formalism.

I already said the only evidence any of them have is QM itself.

As I already said, they're not theories or testable hypotheses, they're more conceptual models.
I've been taking a look today at simply extending Copenhagen with decoherence:
Consistent histories - Wikipedia
 
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FrumiousBandersnatch

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I've been taking a look today at simply extending Copenhagen with decoherence:
Consistent histories - Wikipedia
Yes, that's an interesting project - although it's arguable whether it's still part of the Copenhagen canon when wavefunction collapse is no longer required and it achieves the single, unitary wavefunction evolution that is shared by Many Worlds.
 
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Halbhh

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FrumiousBandersnatch

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I don't tend to form conclusions quickly, but tend to gather more. This was interesting:

https://phys.org/news/2019-09-atoms-quantum-superposition.html
Yes, this is beginning to make some collapse interpretations look less likely, but there's still a long way to go. I suspect diminishing returns in the difficulty of producing and observing massive superpositions will set in well before it casts serious doubt on spontaneous collapse, which has been suggested to occur at around 100 million years per particle.
 
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usexpat97

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I was in a lab this week and talking to a guy, and a couple interesting things came up:

1) the quantum superposition they achieve is not ephemeral. They can maintain it as long as they want--they just have to constantly intervene, and not let nature decohere it.

2) they are confident that they can actively observe a process in the middle of decohering. And maybe even inject a little energy bias in the middle. Which in my mind, contradicts the double-slit experiment.
 
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FrumiousBandersnatch

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I was in a lab this week and talking to a guy, and a couple interesting things came up:

1) the quantum superposition they achieve is not ephemeral. They can maintain it as long as they want--they just have to constantly intervene, and not let nature decohere it.
Yes, this is sometimes called the 'quantum watched kettle' (which never collapses/decoheres).

2) they are confident that they can actively observe a process in the middle of decohering. And maybe even inject a little energy bias in the middle. Which in my mind, contradicts the double-slit experiment.
What do you mean by 'contradicts the double-slit experiment'? The double-slit experiment is empirically demonstrable...
 
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