I Schrodinger's cat, the multiverse and isolated systems

[quantumfunction]

I know the debate about Schrodinger's cat is usually about things like consciousness but I want to talk about what it might say about isolated systems.

Does the wave function of isolated systems remain in a superposition of observable states no matter how large the system gets?

Say you have the radioactive material isolated from the cat in the box and the box the cat is isolated from the outside environment, wouldn't a live/dead cat be two observable states of an isolated system until the box is open and the wave function collapses locally?

This collapse isn't just because of the Scientist opening the box, but the state of the cat interacts with his lab, the car on the highway and the entire observable universe.

So if an isolated system remains isolated do all probable states of that isolated system occur?

If you extrapolate that out to the universe and the universe is an isolated system doesn't that mean that every probable universe exist because there's nothing external to the universe to collapse it's wave function.

I was reading a paper where Max Tegmark said this was a postulate of Everett.

All isolated systems evolve according to the Schrodinger's equation.

So our universe could be an observable state of an isolated system and if this observable state is isolated then you can have probable states within probable states. This would occur maybe for trillions of years until two observable states of the isolated system interacted and maybe you get something like a big bang and everything reboots.

I saw where Penrose talks of Objective Reduction where isolated systems self collapse after they reach a certain threshold due to quantum gravity but I haven't seen much evidence for that. I think Tegmark may have a point if the universe is an isolated system.

 

[rootone]

...
If you extrapolate that out to the universe and the universe is an isolated system...

If you use the definition of 'Universe' as meaning 'everything that exists', then an isolated system is what it is.

Incidentally there is no underlying assumption in QM that the results of experiments have something to do with consciousness.

 

[bhobba]

Does the wave function of isolated systems remain in a superposition of observable states no matter how large the system gets?.

Unless interacted with - of course.

All an observation is is an interaction.

As far as the universe is concerned by definition it can't interact with anything so you can't observe it.

Thanks
Bill

 

[Derek Potter]

Unless interacted with - of course.
All an observation is is an interaction.
As far as the universe is concerned by definition it can't interact with anything so you can't observe it.
Thanks
Bill

So the universe's state cannot collapse even in Copenhagen.
Nevertheless, the state space can be factorized an almost infinite number of ways making it possible for an observer (one subsystem) to interact with another. Collapse is then not objective but is how a subsystem's state appears to behave when there is an observation.
I believe the OP was talking about these improper collapses, to coin a phrase, :) under a factorization of the universe's state space, not about literally observing the universe as a whole.

Does the wave function of isolated systems remain in a superposition of observable states no matter how large the system gets?

Nobody knows. But there is nothing in the standard formulations of QM to suggest anything otherwise.

So if an isolated system remains isolated do all probable states of that isolated system occur?

Every *possible* state. Yes.

If you extrapolate that out to the universe and the universe is an isolated system doesn't that mean that every probable universe exist because there's nothing external to the universe to collapse it's wave function.

Not every interpretation even has wavefunction collapse, observer or no observer. But one should not think of this humungous superposition as being every *possible* universe existing alongside each other. Instead, each possible "world of observations" exists in the one superposition. Just as Schrodinger's Cat isn't two cats but one cat in two states. Which, for the purists, are of course entangled with those of the observer and the environment.

I was reading a paper where Max Tegmark said this was a postulate of Everett.
All isolated systems evolve according to the Schrodinger's equation.
So our universe could be an observable state of an isolated system and if this observable state is isolated then you can have probable states within probable states. This would occur maybe for trillions of years until two observable states of the isolated system interacted and maybe you get something like a big bang and everything reboots.
I saw where Penrose talks of Objective Reduction where isolated systems self collapse after they reach a certain threshold due to quantum gravity but I haven't seen much evidence for that. I think Tegmark may have a point if the universe is an isolated system.

I haven't read much Tegmark but I understand that he says there is no reason to assume that "our" universe has a monopoly on existence. The maths of physics, QM in this context, allows a vast space of possible universes and it it is perfectly possible that they all exist or don't exist to the same extent.

I can't comment on the cosmological implications of Tegmark or of OR. The only time I heard of the universe rebooting was in Doctor Who :)

 

[bhobba]

So the universe's state cannot collapse even in Copenhagen.

No - and obviously so.

Thanks
Bill

 

[alexepascual]

I know the debate about Schrodinger's cat is usually about things like consciousness but I want to talk about what it might say about isolated systems.

If we think about the box isolating the cat from the rest of the environment and any "observer", then environmental decoherence would be prevented. Then we could think about the cat as being in both states at the same time but as far as I know, the only way that is being used to confirm superposition nowadays is by observing interference. In this case, I think as the cat and whatever else inside the box is macroscopic, you would not be able to see interference when some time in the future we make a measurement. Let's say that we don't see interference because the wavelength becomes too short and/or the phases disrupted by the interaction of the original microscopic quantum system with the immediate (inside the box) macroscopic surroundings. We could still think about a kind of superposition different form the typical quantum superposition in which we can observe interference. I think this could be described according to what some call an "improper mixture" and would correspond to a reduced density matrix where all the diagonal elements are still there.
Of course it can be said that in practice it is impossible to make the box to prevent any leakage of information to the outside. But if we ignore that practical difficulty and imagine an ideal experiment in which the walls of the box achieve such insulating power, then it would be interesting to know what people adhering to different interpretations think about it. What do you think guys? (if there is a girl on this thread please forgive me for my sexist expression).

 

[bhobba]

If we think about the box isolating the cat from the rest of the environment and any "observer", then environmental decoherence would be prevented. Then we could think about the cat as being in both states at the same time

That's incorrect. The cat can't be isolated from the environment and remain a cat eg it must breathe air.

And it is entangled with the atomic source which means it is not in a superposition by the definition of entanglement - in fact its in a mixed state of dead and alive meaning it is either dead or alive - not in some weird combination of the two.

Thanks
Bill

 

[Derek Potter]

That's incorrect. The cat can't be isolated from the environment and remain a cat eg it must breathe air.

And it is entangled with the atomic source which means it is not in a superposition by the definition of entanglement - in fact its in a mixed state of dead and alive meaning it is either dead or alive - not in some weird combination of the two.

Thanks
Bill

Even without Alexepascual's isolating box, if one considers the system of [particle plus cat plus observer plus environment] then, under the assumed unitary evolution, the state of this system does evolve to a superposition of
|everything that follows from the particle being emitted> or "|dead>" for short
and
|everything that follows from the particle not being emitted> or "|alive>" for short
which is just as weird a combination as the cat itself being in a pure superposition.

Would you not agree?

 

[bhobba]

Even without Alexepascual's isolating box, if one considers the system of [particle plus cat plus observer plus environment] then, under the assumed unitary evolution, the state of this system does evolve to a superposition of

This has been discussed many many times. I have even posted the math. For the umpteenth time, but from past experience it won't be the last, if you observe inside the system things do not remain in superposition - its a mixed state.

You can do a google search and find where I went through the math.

The solution to the whole thing in the ignorance ensemble interpretation is that the observation occurs just after decoherene. In Schroedinger's Cat the earliest point decoherence occurs is at the particle detector. The superposition of particle detected, not detected is converted into a mixed state and that mixed state is interpreted as a proper one so it no longer a superposition - but it is an actual state - not detected or detected.

Now to someone observing it outside - everything continues on just the same - what they observe is also in a mixed state. The issue comes if they were to observe everything including the particle source - but that would be a totally different set-up.

Thanks
Bill

 

[alexepascual]

That's incorrect. The cat can't be isolated from the environment and remain a cat eg it must breathe air.

Well, it depends on what we mean by environment. I was using the word environment to refer to everything outside the box as once a signal leaks out of the box it is supposedly "uncontrollable" and we can't "erase" the information that has leaked out. According to Environmentally Induced Decoherence (at least as presented by Zurek) it is this uncontrollable leakage of information that produces decoherence. Now let's go back to the practical issue. I got a solution. We can put an oxygen tube inside the box and a small CO2 absorber. We can also put some toy for the cat to play so that he/she doesn't get bored. We would have to select a cat that is not claustrophobic. So Bhobba your statement is incorrect, the cat can continue alive for some time within the box.

 

[alexepascual]

This has been discussed many many times. I have even posted the math. For the umpteenth time, but from past experience it won't be the last, if you observe inside the system things do not remain in superposition - its a mixed state.

You make it sound as if you are getting tired of talking about the same things. But I suspect that on the other hand in some way you enjoy it.
So let me see if I understand your position or interpretation. You are saying that as soon as the microscopic quantum system interacts with the macroscopic detector, the system-instrument-cat (and whatever else inside the box) are in a proper mixed state where the only reason we keep all values on the diagonal of the density matrix is because we don't "know" the actual value but one of those values has already been selected. In other words there is already definiteness, but on the other hand ignorance.

 

[Feeble Wonk]

...it is entangled with the atomic source which means it is not in a superposition by the definition of entanglement - in fact its in a mixed state of dead and alive meaning it is either dead or alive - not in some weird combination of the two.

Sorry to side track the discussion, but I'm hoping that this point helps me get a better handle on the general concept... which is the logical differentiation between "pure", "mixed" and "proper" quantum states. Please correct me where I'm wrong...

In superposition, which is a "pure" state, the cat is dead AND alive (and I am simply accepting for the sake of discussion that the cat IS in superposition here).

If we accept Bhobba's assertion that decoherence, even in the "isolated" system, prevents the cat from being in superposition (and I'm assuming that this does in fact cause "collapse" of the cat's quantum state), then the cat would be in a "proper", "mixed" state... meaning that the critter is dead OR alive, but we just don't know which.

Is that correct?

 

[alexepascual]

Even without Alexepascual's isolating box, if one considers the system of [particle plus cat plus observer plus environment] then, under the assumed unitary evolution, the state of this system does evolve to a superposition of everything that follows from the particle being |emitted> or "|dead>" for short and everything that follows from the particle not being emitted> or "|alive>" for short which is just as weird a combination as the cat itself being in a pure superposition. Would you not agree?

Let's see Derek what Bhobba thinks. I think that according to a more "many worlds" like interpretation, when the outside environment gets entangled with the cat, then a human observer also gets entangled with it. So you can say that the observer is in a state of superposition, but to each "version" of the observer, there is only one outcome and as Bohbba said the cat assumes a definite macroscopic state. The picture I proposed, was as the original poster did, to think of the box as isolating the inside of the box from the outside to prevent entanglement with the outside environment and with the observer. I was under the impression that in those circumstances, even other interpretations besides "many worlds" might see the cat as in a state of superposition. But this would be a superposition different from the one we are used to in quantum mechanics as it would not show any interference effects when measured. If we don't want to call it a superposition, we could always call it "indefiniteness". But for Bhbba, if I interpret him correctly, that's not the case and even if the inside of the box is isolated from the outside, as soon as the quantum system makes contact with the macroscopic instrument and we wait a little for the poison vial to break, the quantum system, the instrument and the cat assume a definite state. Well, I understand, the cat according to this view is always in a definite state because it is a macroscopic object. My view is different as you can see.

 

[alexepascual]

Sorry to side track the discussion, but I'm hoping that this point helps me get a better handle on the general concept... which is the logical differentiation between "pure", "mixed" and "proper" quantum states. Please correct me where I'm wrong...
In superposition, which is a "pure" state, the cat is dead AND alive (and I am simply accepting for the sake of discussion that the cat IS in superposition here).
If we accept Bhobba's assertion that decoherence, even in the "isolated" system, prevents the cat from being in superposition (and I'm assuming that this does in fact cause "collapse" of the cat's quantum state), then the cat would be in a "proper", "mixed" state... meaning that the critter is dead OR alive, but we just don't know which.
Is that correct?

Feeble, In my opinion your conclusion is correct if (as you said) we accept Bhobbas' assertion.

 

[bhobba]

In other words there is already definiteness, but on the other hand ignorance.

I am saying the ignorance is in how an improper mixed state becomes a proper one. Here is the detail:
http://philsci-archive.pitt.edu/5439/1/Decoherence_Essay_arXiv_version.pdf

Look up the ignorance interpretation in the above.

The observation occurs at the particle detector. Everything is common-sense classical from that point on. Opening or closing the lid makes no difference to anything. Decoherence breaks the von-neumann chain by placing the cut at the earliest point decoherence occurs which in Schroedinger's cat is at the particle detector.

Thanks
Bill

 

[bhobba]

I was using the word environment to refer to everything outside the box as once a signal leaks out of the box it is supposedly "uncontrollable" and we can't "erase" the information that has leaked out.

You are talking about Zurecks Quantum Darwinism. I am talking about the ignorance ensemble interpretation which is much simpler. The mystery occurs at the earliest point decoerence happens - which is at the particle detector. Everything is classical from that point on.

Thanks
Bill

 

[bhobba]

Is that correct?

No.

The trouble is the answer is technical and can't be explained in lay terms. You simply have to accept that this weird thing known as a superposition gets converted into this less weird thing called a mixed state by decoherence.

Thanks
Bill

 

[Feeble Wonk]

Is my mistake in the "proper" designation after decoherence?

 

[bhobba]

Is my mistake in the "proper" designation after decoherence?

Yes - its interpreted as a proper mixed state - its really a improper one.

Thanks
Bill

 

[Feeble Wonk]

That's what I thought... and that's where my cognitive wheels grind to a halt. >_<

I have a rough idea that it has something to do with diagonalizing through density matrices of potential quantum states... none of which I understand.

But, my primary question is this... Does the "improper" mixed state imply that it's not arrived at by an ACTUAL quantum state "collapse" (assuming that such a thing really occurs)?

 

[bhobba]

But, my primary question is this... Does the "improper" mixed state imply that it's not arrived at by an ACTUAL quantum state "collapse" (assuming that such a thing really occurs)?

That's correct - an improper mixed state observationally is exactly the same as collapse - but it really isn't. Interpreting it as a proper one is exactly the same as collapse. In fact how an improper mixed state becomes a proper one is the modern version of collapse ie the measurement problem. It colloquially is called why do we get any outcomes at all. Some say it resolved nothing - but being part of decoherence has REASONABLY solved the following issues:

1. The preferred basis problem.
2. Why its so hard to observe interference effects

Note the use of the word REASONABLE - there are a few issues around it like the so called factorisation issue and some key theorems are lacking.

What it hasn't solved is - why do we get outcomes at all.

Thanks
Bill

 

[Feeble Wonk]

...being part of decoherence has REASONABLY solved the following issues:

1. The preferred basis problem.
2. Why its so hard to observe interference effects

Note the use of the word REASONABLE - there are a few issues around it like the so called factorisation issue and some key theorems are lacking.

What it hasn't solved is - why do we get outcomes at all.

I think I'm hanging on so far. But, I'd like to make sure I have the general idea right for your point #1...

The preferred basis issue refers to the variable "observable" by which the quantum state is reduced. Is that correct?

 

[bhobba]

The preferred basis issue refers to the variable "observable" by which the quantum state is reduced. Is that correct?

Yes. For example in a position measurement why does it measure position and not say momentum.

Thanks
Bill

 

[Feeble Wonk]

Yes. For example in a position measurement why does it measure position and not say momentum.

OK. I'm afraid that this is where my mathematical ineptitude is going to bite my gluteal tissue, but...

My understanding is that there are "observables" that can not, even in principle, be observed simultaneously (such as your examples of position and momentum). And, it seems to me that "which" of these observables is selected as the preferred basis might well have a significant effect on the unitary evolution of a system's wave function. Is there any way in the world you can try to explain to me (remembering my mathematical limitations) HOW decoherence selects the preferred basis?

 

[bhobba]

HOW decoherence selects the preferred basis?

Sorry - that is some deep math.

What I can say is it turns out most of the time position is singled out because interactions are usually radially symmetric - but the reason is in the math.

Thanks
Bill

 

[Feeble Wonk]

Sorry - that is some deep math.

What I can say is it turns out most of the time position is singled out because interactions are usually radially symmetric - but the reason is in the math.

>_< I was afraid you were going to say something like that.

 

[Feeble Wonk]

That's correct - an improper mixed state observationally is exactly the same as collapse - but it really isn't. Interpreting it as a proper one is exactly the same as collapse. In fact how an improper mixed state becomes a proper one is the modern version of collapse ie the measurement problem.

This part is still confusing me. If I've understood you correctly, the mixed state is "improper" because it has not yet actually collapsed.

Is that correct?

 

[bhobba]

This part is still confusing me. If I've understood you correctly, the mixed state is "improper" because it has not yet actually collapsed.

No. Its improper because its prepared differently to a proper one where collapse would have occurred. There is no way to tell the difference. It may be collapsed or not - its unknown. I assume however it is. Also if it is collapsed there is no mechanism for that - that's the ignorance bit.

Thanks
Bill

 

[Feeble Wonk]

No. Its improper because its prepared differently to a proper one where collapse would have occurred. There is no way to tell the difference. It may be collapsed or not - its unknown. I assume however it is. Also if it is collapsed there is no mechanism for that - that's the ignorance bit.

Thanks
Bill

I'm not sure I'm following you here. I think I need to better understand your definition of the term "prepared" in this context.

 

[bhobba]

I'm not sure I'm following you here. I think I need to better understand your definition of the term "prepared" in this context.

Here is one way to create a mixed state. Randomly select a pure state. There is a pure state there - but its unknown what it is. Such are called proper mixed states. Another way to create a mixed state is from decoherence. Such are called improper. Now there is no way to tell the difference between the two. It may be like a proper one and a pure state is there - but we don't know which one - or not. We simply don't know. We are ignorant - hence the name ignorance interpretation. If it was a proper mixed state collapse would have occurred - the state that's observed is there before observation - everything is sweet. So the interpretation simply assumes it is.

Thanks
Bill

 

[Feeble Wonk]

Here is one way to create a mixed state. Randomly select a pure state. There is a pure state there - but its unknown what it is. Such are called proper mixed states.

Ugh... I'm getting MORE confused rather than less.

My previous understanding was that the "pure" state was in actual superposition... still in the "and" state, so to speak. In contrast, I thought the "proper mixture" was in an "either/or" state. It's admittedly a subtle difference, but logically significant.

 

[Feeble Wonk]

Or... are you saying that the "proper" mixed state actually contains a "pure" state in addition to a null (nonexistent) state? Nonexistent, in the sense that it MIGHT have been, but it's not.

 

[bhobba]

Or... are you saying that the "proper" mixed state actually contains a "pure" state in addition to a null (nonexistent) state? Nonexistent, in the sense that it MIGHT have been, but it's not.

Its what I said. Imagine you have a heap of pure states that are the possible outcomes of an observation. You randomly select one. There is a pure state there - but because it was randomly selected you don't know which one - only the probability of what it is. That is a proper mixed state.

Thanks
Bill

 

[quantumfunction]

I think the real question is about decoherence and isolated systems.

If the box is an isolated system doesn't the cat and everything in the box become observable states of that isolated system (the box)? If I understand Tegmark and Everett's postulate about isolated systems, it's saying that decoherence doesn't occur if there's nothing external to the isolated system. In this case all observable states of the isolated system would be realized.

So if the universe is an isolated system then our universe would be an observable state of that isolated system because there's nothing external to the universe to interact with so no decoherence.

The reason we can see the wave nature of particles is because they can remain isolated for long periods of time. So in a sense these particles have free will according to the Free Will Theorem.

The free will theorem of John H. Conway and Simon B. Kochen states that, if we have a free will in the sense that our choices are not a function of the past, then, subject to certain assumptions, so must some elementary particles. Conway and Kochen's paper was published in Foundations of Physics in 2006.[1] They published a stronger version of the theorem in 2009.[2]

https://en.wikipedia.org/wiki/Free_will_theorem

A baseball can't remain isolated from it's environment so it's always in one observable state. This would mean classical objects don't have free will. There different states can't exist in the same environment so they're in different universes.

On a side note, this could mean if we have free will it's due to a quantum mind. So on a classical level you have no choice but to go to medical school instead of law school because you're in this observable state of an isolated system. Your quantum mind would be like the isolated particle and experiences a choice between law school and medical school.

I think Tegmark understood this dilemma and he recently proposed that consciousness was a state of matter. I think it makes more sense if consciousness is quantum because that would mean the mind could remain isolated from the environment and could make choices or appear to make choices because it would have a wave nature like an isolated particle.

 

[bhobba]

If the box is an isolated system doesn't the cat and everything in the box become observable states of that isolated system (the box)?.

If the box is an isolated system its the same story. The observation happens at the particle detector - everything is common-sense classical from that point on. The cat lives or dies regardless of if the box is opened, is isolated etc.

Thanks
Bill

 

[quantumfunction]

If the box is an isolated system its the same story. The observation happens at the particle detector - everything is common-sense classical from that point on. The cat lives or dies regardless of if the box is opened, is isolated etc.

I think the point is, there is no common sense classical for an isolated system. You will always be observing one observable state or the other of that system. So it's kind of an illusion that stems from the fact we can't be isolated from the environment long enough to experience or see these other observable states of the isolated system.

So live cat/dead cat or Law School/Medical School would be observable states of an isolated system and there's no decoherence. So decoherence occurs as a system grows in size and can't remain isolated from it's environment for long periods of time. So everything would essentially be quantum and classical objects are just quantum systems that can't be isolated from their environment.

There was a recent study of cesium atoms that showed they don't follow a well defined path. There needs to be more tests done but it could essentially show that what we call common sense classical is really just and observable state of an isolated system and it appears classical because we can't remain isolated from the environment long enough to see other observable states of the isolated system.

http://www.eurekalert.org/pub_releases/2015-01/uob-acb012015.php

Here's another article on the subject

Macrorealism Violated By Cs Atoms

http://www.itec-sde.net/en/posts/macrorealism-violated-by-cs-atoms

Like I said, more tests need to be done but I do think Tegmark is on the right track.

 

[bhobba]

I think the point is, there is no common sense classical for an isolated system.

I have no idea why you would think that. For example astronauts circling the Earth in a space capsule is for all practical purposes an isolated system - everything that goes on there is classical.

Thanks
Bill

 

[quantumfunction]

I have no idea why you would think that. For example astronauts circling the Earth in a space capsule is for all practical purposes an isolated system - everything that goes on there is classical.

No they're not. Everything classical in size in our universe can't remain isolated like subatomic particles. I would like to see the article that says Humans in space are just like photons or electrons. So for larger objects in an observable state of an isolated system your wave nature is essentially zero. As large objects, the wave function can't become large enough for us to see other observable states of the isolated system like for instance an electron.

Here's an article from Nature that talks about this:

Physics: Quantum all the way

Decoherence also predicts that the quantum–classical transition isn't really a matter of size, but of time. The stronger a quantum object's interactions are with its surroundings, the faster decoherence kicks in. So larger objects, which generally have more ways of interacting, decohere almost instantaneously, transforming their quantum character into classical behaviour just as quickly.

http://www.nature.com/news/2008/080430/full/453022a.html

 

[Feeble Wonk]

Its what I said. Imagine you have a heap of pure states that are the possible outcomes of an observation. You randomly select one. There is a pure state there - but because it was randomly selected you don't know which one - only the probability of what it is. That is a proper mixed state.

So, it's more or less what I was thinking. It seems to be a semantic issue, but of fundamental significance.

By this definition, the "proper" MIXED state is not really a "mixture" at all... IF the pure state actually exists, and the previously potential states no longer do. Or, maybe a better way of saying it is... A proper mixed state is a mixture of what IS, and what MIGHT HAVE BEEN, prior to observation of what IS... the "mixture" is completely (and only) a statistical description, and not an ontological depiction of what exists (assuming that ANYTHING actually exists).

I recognize that this phrasing of the issue is probably a little too "metaphysical" for your tastes, but aside from that, is the general idea correct?

 

[bhobba]

I would like to see the article that says Humans in space are just like photons or electrons.

I never said they were - in fact since they behave classically they are nothing like photons and electrons.

And yes everything is quantum - but that doesn't mean objects can't behave classically since its obvious from everyday experience the world around us does.

Thanks
Bill

 

[bhobba]

I recognize that this phrasing of the issue is probably a little too "metaphysical" for your tastes, but aside from that, is the general idea correct?

Its called a mixture for technical reasons to do with generalised probability theory - but what you said is about as good as you will et at the lay level.

Thanks
Bill

 

[DennisN]

Reading this thread made me look around a bit, and I stumbled upon this paper which I had not seen before, which I found interesting enough to mention here, and it may perhaps also be interesting to thread readers... (I have not read the whole paper yet, but I will).

It is about "many worlds of [so-called] causal diamonds", decoherence, eternal inflation, "pocket universes", isolated/closed systems etc:

The Multiverse Interpretation of Quantum Mechanics
Raphael Bousso, Leonard Susskind
(Submitted on 19 May 2011 (v1), last revised 22 Jul 2011 (this version, v3))
Arxiv link: http://arxiv.org/abs/1105.3796
Pdf: http://arxiv.org/pdf/1105.3796v3

Abstract:
We argue that the many-worlds of quantum mechanics and the many worlds of the multiverse are the same thing, and that the multiverse is necessary to give exact operational meaning to probabilistic predictions from quantum mechanics.

Decoherence - the modern version of wave-function collapse - is subjective in that it depends on the choice of a set of unmonitored degrees of freedom, the "environment". In fact decoherence is absent in the complete description of any region larger than the future light-cone of a measurement event. However, if one restricts to the causal diamond - the largest region that can be causally probed - then the boundary of the diamond acts as a one-way membrane and thus provides a preferred choice of environment. We argue that the global multiverse is a representation of the many-worlds (all possible decoherent causal diamond histories) in a single geometry.

We propose that it must be possible in principle to verify quantum-mechanical predictions exactly. This requires not only the existence of exact observables but two additional postulates: a single observer within the universe can access infinitely many identical experiments; and the outcome of each experiment must be completely definite. In causal diamonds with finite surface area, holographic entropy bounds imply that no exact observables exist, and both postulates fail: experiments cannot be repeated infinitely many times; and decoherence is not completely irreversible, so outcomes are not definite. We argue that our postulates can be satisfied in "hats" (supersymmetric multiverse regions with vanishing cosmological constant). We propose a complementarity principle that relates the approximate observables associated with finite causal diamonds to exact observables in the hat.

 

[alexepascual]

I think the point is, there is no common sense classical for an isolated system. You will always be observing one observable state or the other of that system. So it's kind of an illusion that stems from the fact we can't be isolated from the environment long enough to experience or see these other observable states of the isolated system.

Well, we know already what bhobba thinks. He thinks that the isolated system-detector is in a definite state once the detector has interacted with the quantum system. If I am correct, you (Quantumfuction) and Feeble are more inclined to think that these systems remain in a superposition state.
But another way to interpret the way decoherence takes place (besides the one you describe in the quote above) would be that the inside of the box does not collapse to a definite state just because of uncontrolable leakage of information. The collapse would not be an absolute thing but relative to another system. If you were sitting inside the box (even if you are not a friend of Wigner) you would say that there has been collapse, because you have split into two copies of yourself and have become entangled with the two possible states of the system-detector-cat. So for you inside the box the cat is dead or alive. For someone outside the box as they have not become entangled with the inside of the box, the inside is still in an indefinite state. But we have to consider that a preferred basis has already been chosen and we could represent this as a density matrix with all the element there (two in this case) but to the outside observer which of these diagonal elements will become his/her "reality" remains undefined (not just unknown). The outside observer does not need to be a sentient/conscious being but could just be a measurement device. What do you think Quantumfunction about his way of looking at it?

 

[bhobba]

For someone outside the box as they have not become entangled with the inside of the box, the inside is still in an indefinite state.

In the early days of QM Von Neumann sorted this all out. He showed the cut can be placed anywhere in the Von-Neumann chain. This is nothing new. The question is why do you choose not to place it right after decoherence and instead proceed to espouse such a complicated weird view of the world with information leaking out etc etc.

But regardless of that once the collapse has occurred and inside the box the cat is dead or alive it has occurred period - for observers outside the box - for anyone.

Quantum Darwinism takes a view somewhat like that - but Zureck takes the quantum state as primary and uses it to derive the Born rule via evarience. Because of that he has to be rather tricky about what an observation is - however once you accept the Born rule there is no need for such sophistry.

Personally I take observations as primary and the state emerges from that - see post 137:
https://www.physicsforums.com/threads/the-born-rule-in-many-worlds.763139/page-7

Thanks
Bill

 

[alexepascual]

In the early days of QM Von Neumann sorted this all out. He showed the cut can be placed anywhere in the Von-Neumann chain. This is nothing new. The question is why do you choose not to place it right after decoherence and instead proceed to espouse such a complicated weird view of the world with information leaking out etc etc.

Information leaking out is just the way most environmental decoherence proponents present it, including Zurek. So for these peple, if information "leaks out" and let's say travels away towards some other galaxy, then there is decoherence even if there is no entanglement with the observer. The way I see it is a little diferent. For me is not just the fact that information has gotten out of control by leaking out but that the system has become entangled with the observer.
Is it weird? Maybe, but in my view there is no model (interpretation) that solves all the paradoxes. You may say that the ensemble interpretation solves most paradoxes, but if there is one paradox left, that may be very important.

 

[bhobba]

Information leaking out is just the way most environmental decoherence proponents present it, including Zurek.

I disagree with that.

My bible on this, and many consider it THE book, is Schlosshauer's text:
https://www.amazon.com/dp/3540357734/?tag=pfamazon01-20

That is NOT what generally happens in decoherence - some models yes - but in general no. For example in Schroedingers Cat the decoherence occurs in the particle detector - everything is classical after that.

As I explained previously you are likely thinking of Quantum Darwinian which is a particular interpretation using decoherence and uses ideas like that - it's not a general requirement - not by a long shot.

Thanks
Bill .

 

[alexepascual]

I disagree with that.
My bible on this, and many consider it THE book, is Schlosshauer's text:
https://www.amazon.com/dp/3540357734/?tag=pfamazon01-20
That is NOT what generally happens in decoherence - some models yes - but in general no. For example in Schroedingers Cat the decoherence occurs in the particle detector - everything is classical after that.
As I explained previously you are likely thinking of Quantum Darwinian which is a particular interpretation using decoherence and uses ideas like that - it's not a general requirement - not by a long shot. Thanks
Bill .

I have not read Schlosshawer's book, but some years ago I had read a very complete and long article by him. I though it was a very comprehensive review of the subject. With respect to Quantum Darwinism, I didn't remember much about that concept as I haven't read Zurek's articles for a while, but I just read a little about it and it looks like it refers more to the selection of a preferred pointer basis rather than the selection of a particular eigenvalue of the selected measurement operator involved in the decoherence process. So from what you are saying, you think that Zurek's ideas are not the most popular within the environmental decoherence school right?
At this point Bill I wonder if you think your interpretation solves all the paradoxes of quantum mechanics or you think that there is still something important that is not resolved. I don't mean some technicality but some paradox that is still unexplained. If that's the case, what is that unresolved paradox?

 

[bhobba]

So from what you are saying, you think that Zurek's ideas are not the most popular within the environmental decoherence school right?

I have no idea how popular they are. Its just he makes use of ideas similar to what you are talking about in his development evarience.

At this point Bill I wonder if you think your interpretation solves all the paradoxes of quantum mechanics or you think that there is still something important that is not resolved. I don't mean some technicality but some paradox that is still unexplained. If that's the case, what is that unresolved paradox?

QM has no paradoxes - just blemishes. By blemishes I mean things like Copenhagen assumes the existence of a commom-sense classical world observations appear in. That means it can't explain such a world because it assumes it from the start. It doesn't invalidate it or anything like that but it is a blemish. Refinements like my ignorance interpretation and decoherent histories fix that particular blemish, but some still remain like why do we get any outcomes at all. Some like BM resolves that one but most interpretations stand powerless before it. I simply assume they exist by interpreting an improper mixed state as a proper one - it doesn't invalidate it or anything like that - and every theory has undefined primitives - again its just nice if there was an explanation.

Thanks
Bill

 

[quantumfunction]

Well, we know already what bhobba thinks. He thinks that the isolated system-detector is in a definite state once the detector has interacted with the quantum system. If I am correct, you (Quantumfuction) and Feeble are more inclined to think that these systems remain in a superposition state. But another way to interpret the way decoherence takes place (besides the one you describe in the quote above) would be that the inside of the box does not collapse to a definite state just because of uncontrolable leakage of information. The collapse would not be an absolute thing but relative to another system. If you were sitting inside the box (even if you are not a friend of Wigner) you would say that there has been collapse, because you have split into two copies of yourself and have become entangled with the two possible states of the system-detector-cat. So for you inside the box the cat is dead or alive. For someone outside the box as they have not become entangled with the inside of the box, the inside is still in an indefinite state. But we have to consider that a preferred basis has already been chosen and we could represent this as a density matrix with all the element there (two in this case) but to the outside observer which of these diagonal elements will become his/her "reality" remains undefined (not just unknown). The outside observer does not need to be a sentient/conscious being but could just be a measurement device. What do you think Quantumfunction about his way of looking at it?

Good points.

Like I said, this is more about isolated systems than it is about decoherence. Decoherence can occur in the box but if the box is an isolated system, then live cat/dead cat both exist in the box.

If the box is all there is, there's nowhere for the wave function to go that's external to the box. The cat isn't in a pure state of live cat/dead cat but a mixed state of life cat or dead cat but both observable states exist in the box if the hypothetical box is isolated and there isn't any space external to the box to interact with.

When the Scientist opens the box, he's in an observable state of either live cat/happy Scientist or dead cat/sad Scientist. This extends to the guy on the highway whose happy cause girlfriend said yes to Marriage or sad guy on the highway cause girlfriend said no. This just means the state of the cat becomes entangled with the entire universe.

So for an isolated system there is no deoherence. Within the isolated system you have observable states that become large enough to where there's decoherence that occurs relative to each system in that observable state like cats, dogs, humans and planets.

So you have a global wave function that evolves according to Schrodinger's equation and never "collapses" because there's nothing external to the universe that can interact with it. So it goes back to Everett's postulate.

All isolated systems evolve according to the Schrodinger's equation.

Now, Penrose understands this and Tegmark and Penrose agree in principle. Penrose just thinks there's a self collapse or what he calls Objective Reduction which simply says that instead of all of these possible states evolving, they reach a threshold he calls the one graviton level and at this threshold all states collapse except 1. So you have one state that's cyclical instead of many states that are parallel. I think Penrose will run into trouble if they keep doing test with Cs atoms and larger objects that violate macrorealism. Penrose depends on classical objects having a definite path.

 

[bhobba]

Decoherence can occur in the box but if the box is an isolated system, then live cat/dead cat both exist in the box.

That's impossible.

Cats can not be in a superposition of alive/dead. For example to be alive it must breath air that quickly decoheres it. The differences in the processes going on in a live and dead cat are such that its impossible for them to be in superposition any more than you can be in a superposition with the person next to you in a checkout line. This is the efficiency of a measurement device issue - some macroscopic states due to their nature will give unambiguous results - a live and dead cat is one of those - like a 1 or 0 appearing on a computer screen.

Thanks
Bill