Does Decoherence Von Neumann Interpretationrefute

[Alfrez]

Coherence has nothing at all to do with a symmetric arrangement of atoms.

It only means that you maintain the superposition (i.e., an approximately pure state rather than a mixture) long enough to be able to perform experiments with it. Decoherence means that the density matrix degenerates from a rank 1 matrix (corresponding to a pure state) to a diagonal matrix under the influence of noise from the environment. This degeneration is a continuous process that takes some time. If one can keep the interaction with the environment tiny, this time is very long, but it becomes smaller exponentially with the size of the system. This is a theoretically and experimentally very well established fact.

Nothing in quantum mechanics forbids an ensemble of cars to exist in a superposition. But decoherence would turn it in next to no time into a classical mixture. In practice, one cannot prepare such superpositions for large objects, because they degenerate even before they are created.

They are planning to send a virus in double slit. So you are saying that even though the virus is very complex and not uniform. It can still be in coherent state if it is shielded from the environment? Now why haven't they performed it yet? They can shield buckyball but not virus, why?

But then, Decoherence is not proven yet. It is still possible everything is as the Copenhagen says.. meaning classical object can't be quantum. It is only in Decoherence concept where it is possible because the wave function *allegedly* never collapse. So your statement a chair can be in superposition if it could be shielded from environment is just speculations and not a definite sure thing, right? Only if Decoherence is proven that the statement can be true.

 

[A. Neumaier]

They are planning to send a virus in double slit. So you are saying that even though the virus is very complex and not uniform. It can still be in coherent state if it is shielded from the environment? Now why haven't they performed it yet? They can shield buckyball but not virus, why?

A virus is MUCH bigger than a buckyball; so it requires far more experimental ingenuity to do interference experiments with it. The effort scales with a nontrivial power of the mass, not only linearly.

But then, Decoherence is not proven yet.

You err. Decoherence is extremely well established, both theoretically and experimentally.

It is still possible everything is as the Copenhagen says.. meaning classical object can't be quantum. It is only in Decoherence concept where it is possible because the wave function *allegedly* never collapse. So your statement a chair can be in superposition if it could be shielded from environment is just speculations and not a definite sure thing, right? Only if Decoherence is proven that the statement can be true.

Copenhagen does not say that classical objects cannot be quantum. It only says that they must be macroscopic. So there is nothing to speculate about.

 

[Alfrez]

Then it is a classical case of Wigner's friend experiment, explained here:
http://en.wikipedia.org/wiki/Wigner's_friend#Wigner.27s_friend_in_Many_Worlds

I noticed you and Fredrik (is it mainstream now?) seem to model the superpositions in say the double slit experiment as only of 2 possible consequences. One is that each state has own copy.. that is.. in other Worlds. Second is to interpret everything as just for calculations with no actual ontology. But there is another way to look at it. We can say that during superposition, the particle doesn't exist as a particle at all.. that is.. there is really no position... this means spacetime before measurement doesn't exist as a definite lorentz metric. This is one way to make sense out of it.

The consequence of this is that before measurement, say you were the particle being sent to a double slit (or doors) experiment and if you were sufficiently shielded from the environment, you would not experience a frog world view where you only see a history of you passing thru one slit while the other copies pass thru other slits and angles and are in other worlds (birds eye view). Instead what could happen is that when a particle (or even macroscopic object) is shielded from environment. Up-down state doesn't exist so I can imagine myself as pure ghost like as I travel thru the slits. Why is this not possible?? Hope Fredrik can comment too as he holds views similar to yours which I wonder is some kind of Many Worlds bias. A neo enhanced Copenhagen like I mentioned may be valid too.

 

[Alfrez]

A virus is MUCH bigger than a buckyball; so it requires far more experimental ingenuity to do interference experiments with it. The effort scales with a nontrivial power of the mass, not only linearly.



You err. Decoherence is extremely well established, both theoretically and experimentally.



Copenhagen does not say that classical objects cannot be quantum. It only says that they must be macroscopic. So there is nothing to speculate about.

You mentioned if a chair could be isolated from enviroment, it can be sent thru the slits in a macro double slit experiment. But isn't it that the de broglie wavelength of massive object are so small, how can it still interfere? This is Copenhagen concept which many scientists like DrChinese still hold. Say, in Decoherence, what is the de broglie wavelength of the chair, before and after isolated from environment.. are their changes to the values depending on whether it is isolated or not??

 

[Alfrez]

Coherence has nothing at all to do with a symmetric arrangement of atoms.

It only means that you maintain the superposition (i.e., an approximately pure state rather than a mixture) long enough to be able to perform experiments with it. Decoherence means that the density matrix degenerates from a rank 1 matrix (corresponding to a pure state) to a diagonal matrix under the influence of noise from the environment. This degeneration is a continuous process that takes some time. If one can keep the interaction with the environment tiny, this time is very long, but it becomes smaller exponentially with the size of the system. This is a theoretically and experimentally very well established fact.

Nothing in quantum mechanics forbids an ensemble of cars to exist in a superposition. But decoherence would turn it in next to no time into a classical mixture. In practice, one cannot prepare such superpositions for large objects, because they degenerate even before they are created.

About pure state and mixed state. So key to successful superposition is to create pure state. Buckyball is pure state. But you also said a chair or even car can exist in superposition... How can you create a pure state of the chair or car supposed isolation from the environment could be done (which is very hard if not impossible). But for theoretical understanding let's supposed the system is isolated from the environment, can't it be that inside the car, the dashboard or gear is interacting with noises from inside the car itself? So it can never be in pure state so no superposition is possible because the complex parts can itself be the source of noises amongst themselves. Or let's take the example of a fixed object like chair. Say it is composed of plastic, metal, rubber and wood. Can a pure state be created out of it? (Let's assume environment isolation were possible for sake of discussion of noises within the object itself).

In simple terms.. Can a rubber, a metal, a wood, a plastic be each in pure state and when combining them still be in pure state and not mixed state?? I think the reason why the Buckyball is easy is because of the uniformity which is easy to create pure state. I don't know how you can model a chair as pure state too. Pls. explain. Thanks.

 

[A. Neumaier]

You mentioned if a chair could be isolated from enviroment, it can be sent thru the slits in a macro double slit experiment. But isn't it that the de broglie wavelength of massive object are so small, how can it still interfere?

The possibility of existing in a superposition is independent of a particular method of checking it (by a double slit experiment, say). The difficulty of performing an experiment increases with mass for many different reasons, of which what you mention may be one.

 

[A. Neumaier]

About pure state and mixed state. So key to successful superposition is to create pure state.

Yes.

Buckyball is pure state.

No. Typically a buckyball is in a thermal (i.e., mixed) state. To prepare it in an approximately pure state is already a lot of work.

But you also said a chair or even car can exist in superposition... How can you create a pure state of the chair or car supposed isolation from the environment could be done (which is very hard if not impossible).

yes.

But for theoretical understanding let's supposed the system is isolated from the environment, can't it be that inside the car, the dashboard or gear is interacting with noises from inside the car itself?

This noise must be regarded as part of the car; then it doesn't matter. (But if the noise can escape the car then it is interaction with the environment, which decoheres the car.
You see, one would need a car perfectly insulated against escaping noises, escaping light,
escaping energy, escaping CO_2 from the combustion... Impossible to build...

So it can never be in pure state so no superposition is possible because the complex parts can itself be the source of noises amongst themselves. Or let's take the example of a fixed object like chair. Say it is composed of plastic, metal, rubber and wood. Can a pure state be created out of it? (Let's assume environment isolation were possible for sake of discussion of noises within the object itself).

The usual way of creating a pure state out of a mixed state is by filtering all parts except the desired pure part. This can be done for photons but I have no idea how to do it
(even in principle) for chairs. There are no polarisation filters for chairs.

So one would have to create the chair directly in a pure state...

But I won't continue discussing such hypothetical settings.

 

[Alfrez]

There is nothing bizarre in von Neumann's statements. So there is nothing to refute.
You only need to upgrade your understanding of what the terms mean.

To say that consciousness collapses the wave function is equivalent to say that it takes consciousness to interpret the universe and change the interpretation when new information arrives.



Instead of modeling the system by a superposition in the absence of information, you model it by one of the participating eigenstates if a measurement result becomes known. Clearly, modeling reality (and changing the model) is a conscious activity and requires a consciousness.

This is nothing mysterious, and happens also in classical physics once you have a stochastic dynamics, where the collapse is called conditional probability.

Moreover, it has nothing to do with superluminal changes, since once one changes a molde to describe something, everything in the model changes instantaneously, although the system modeled isn't changed at all.
This already happens when you apply a coordinate transformation in a classical system...



What do you mean by ''in limbo''? The inside of the moon has lots of meaningful properties even in the absence of a sharp position (which it doesn't even have classically, by the way). Note that being in a superposition only means that there is no exact value of the position, not that there is no position at all. In particular, there is a mean position and a mean square deviation form this position, which together is adequate for most purposes.



Blood vessels work quite well without each of their atonms having precise positions to 10^1000 decimals of accuracy.

You are right that Neumann original meaning of consciousness collapsing the wave function was only related to pure mathematical interpretation. Meaning he didn't believe there was an objective reality to the wave function and one can move the Neumann cut of the collapse anywhere for calculation purposes only. It's a stretch for some to interpret Neumann wordings as saying there is an objective collapse where consciousness caused the collapse literally.. which is not the case. With this historical vagueness in perspective. It is very possible Mind doesn't have anything to do with Quantum Mechanics. Maybe the brain produce the mind as emergence. Thanks guys for all the clarifications.

 

[StevieTNZ]

I have only read page one of this thread, but, remember a non-local universe means that if a collapse occurs somewhere in it, the whole universe stops being a superposition.

"It means that underneath the ocean where human consciousness is not present, the water only exist as possibilities. This means the weight of the water at the surface can fall down to the limbo region." - and so would the rest of the universe exist in possibility. If 'part' of the universe collapses, then the rest does too.

Also, reading this book published by Princeton University Press, decoherence does not falsify that there still exists a superposition. Remember, the wave function equation doesn't collapse. Take it to the logical conclusion. Still a superposition.

 

[StevieTNZ]

Also, I like to think of it as, if decoherence chooses which possibility exists, then we have no control over the world - i.e. will this be a red piece of paper, or a blue piece of paper. That would be chosen for us.

Edit: reading the other pages of this thread now. Very interesting discussion. Find a lot of points that I myself have come to conclude through logic, so it's good to know there is someone out there that is thinking along the same lines as me!

 

[A. Neumaier]

I have only read page one of this thread, but, remember a non-local universe means that if a collapse occurs somewhere in it, the whole universe stops being a superposition.

One cannot collapse it since nobody can observe the whole universe.
So your statement is empty.

 

[StevieTNZ]

You don't need to observe the whole universe. Just part of it. Remember non-locality?

If an 'observation' was made in the place where Pluto is now, then the rest of the universe collapses because of entanglement. Pluto doesn't stop being a superposition while the rest of the universe continues to be.

 

[A. Neumaier]

You don't need to observe the whole universe. Just part of it. Remember non-locality?

If an 'observation' was made in the place where Pluto is now, then the rest of the universe collapses because of entanglement. Pluto doesn't stop being a superposition while the rest of the universe continues to be.

Only your logic collapses.

The state of a system cannot collapse through the observation of a subsystem. Indeed, since your fictitious claim cannot even be translated into a formal statement, it is impossible to give it an interpretation of it in terms of quantum mechanics.

 

[StevieTNZ]

Are you trying to say entanglement is not a fact?

 

[A. Neumaier]

Are you trying to say entanglement is not a fact?

How on Earth can you read such a strange assertion into my statements?

Entanglement, collapse, and decoherence are very different things, though there are relations between them. I am using my words with care not to mix things up.

 

[StevieTNZ]

Then if two 'particles' are entangled, which are on opposite sides of the universe, and one of those particles is observed, then the other one would collapse, no? Or have I been lied to? Because that is what I've come to understand from reading a variety of QM books.

I say are you suggesting entanglement is not a fact due to you denying this previous post:

You don't need to observe the whole universe. Just part of it. Remember non-locality?

If an 'observation' was made in the place where Pluto is now, then the rest of the universe collapses because of entanglement. Pluto doesn't stop being a superposition while the rest of the universe continues to be.

That post relies heavily on what I've read, and I would hope that I have been told the truth. After all, you learn from others and you expect a bit of honesty that it is factual.

If all 'particles' are entangled, then you can apply the above to previous statements I have posted.

 

[Alfrez]

Then if two 'particles' are entangled, which are on opposite sides of the universe, and one of those particles is observed, then the other one would collapse, no? Or have I been lied to? Because that is what I've come to understand from reading a variety of QM books.

You didn't read the QM book property. QM is even stranger than you can possibly imagine. Remember that quantum properties don't exist before measurement, if no one is there on the other side of the universe to measure it, the properties like position doesn't even exist. So there is really no non-locality to it because locality doesn't exist in the first place. It is only upon this realization that you can be said to understand more completely quantum entanglement and Bell's Theorem.

 

[StevieTNZ]

You didn't read the QM book property. QM is even stranger than you can possibly imagine. Remember that quantum properties don't exist before measurement, if no one is there on the other side of the universe to measure it, the properties like position doesn't even exist. So there is really no non-locality to it because locality doesn't exist in the first place. It is only upon this realization that you can be said to understand more completely quantum entanglement and Bell's Theorem.

But if someone were there to measure a particle, then wouldn't the other particle collapse? That's what I'm aiming to say, you don't need to 'observe' (measure) the whole universe to collapse every part of it because you are obviously in one area, the 'wavicle' is now a particle, which is entangled with the rest of the universe, so the other wavicles collapse?

 

[Alfrez]

But if someone were there to measure a particle, then wouldn't the other particle collapse? That's what I'm aiming to say, you don't need to 'observe' (measure) the whole universe to collapse every part of it because you are obviously in one area, the 'wavicle' is now a particle, which is entangled with the rest of the universe, so the other wavicles collapse?

No. Because in entanglement the twin particles don't even exist before one does measurement. You are assuming both particles are sent off to opposite directions like ping pong balls. But no. Only the wave function exist travels. Now if you measure one side, the particle part pops out, but if you didn't measure the opposite side or particle, the particle doesn't exist yet even though the wave function already collapse... it's like it's hold off in a buffer zone and not yet outputted to Spacetime when no one measures it. So the reason you can't collapse the whole universe by collapsing a region is because the wave function can initiate collapse isolation shield courtersy of lorentz metric regional quantum coupling quarantine. Something like that. Hope others can share the right words and mathematical formalisms to use.

 

[A. Neumaier]

But if someone were there to measure a particle, then wouldn't the other particle collapse? That's what I'm aiming to say, you don't need to 'observe' (measure) the whole universe to collapse every part of it because you are obviously in one area, the 'wavicle' is now a particle, which is entangled with the rest of the universe, so the other wavicles collapse?

If you measure a system X and can continue to observe it, the measurement prepares the system X in a new state that (in some approximation) is an eigenstate of the corresponding observable. This is referred to as a collapse.

The measurement does nothing at all to particles far away, no matter how entangled they are with X. But the state of the big system also changes by the measurement, though in a more complex way that cannot be described by the notion of collapse.

Thus if X and Y are entangled and far away from each other, measuring X collapse X but neither Y nor the universe; and measuring Y collapses Y but neither X nor the universe. If you compare the resulting measurements, and make a statistics over sufficiently many such measurements, you get the standard predictions for the behavior of entangled states.

No measurement collapses the whole universe. This can be affected only by God, who runs the whole universe and presumably can collapse it, e.g., by switching it off.

 

[A. Neumaier]

"Everett considers the many worlds as real, in an ontological sense.[...]"
Pls. refute the above if possible using critical arguments..

You can read my refutation of the MWI in Chapter A4 of my theoretical physics FAQ
http://arnold-neumaier.at/physfaq/physics-faq.html#manyworlds
I don't consider it to be a serious interpretation, and won't waste my time on further discussing it.

 

[Alfrez]

You can read my refutation of the MWI in Chapter A4 of my theoretical physics FAQ
http://arnold-neumaier.at/physfaq/physics-faq.html#manyworlds
I don't consider it to be a serious interpretation, and won't waste my time on further discussing it.

I read it and here's a partial refutation of it. You wrote there that

"Q1 Who believes in many-worlds?

many- worlds is most popular amongst scientists
who may rather loosely be described as string theorists or
quantum gravitists/cosmologists. It is less popular
amongst the wider scientific community who mostly
remain in ignorance of it.

String theorists and quantum gravitists/cosmologists are those
physicists farthest removed from experiment and hence most free to
entertain fancy theories without stringent constraints that would
bring them down to earth. That the wider scientific community mostly
ignores MWI is a healthy sign of contact to reality."

Here's the refutation:

http://arxiv.org/PS_cache/quant-ph/pdf/0101/0101077v1.pdf
quoting

"An informal poll taken at a conference on quantum
computation at the Isaac Newton Institute in Cambridge
in July 1999 gave the following results:

~~

Which interpretation of quantum mechanics is closest to your own?
(a) Copenhagen or consistent histories (including postulate of explicit collapse): 4
(b) Modified dynamics (Schroedinger equation modified to give explicit collapse): 4
(c) Many worlds/consistent histories (no collapse): 30
(d) Bohm (an ontological interpretation where an auxiliary “pilot wave” allows particles to have well-defined positions and velocities): 2
(e) None of the above/undecided: 50

The reader is warned of rampant linguistic confusion in this area. It is not uncommon that two physicists who say that they subscribe to the Copenhagen interpretation find themselves disagreeing about what they mean by this. Similarly, some view the “consistent histories”
interpretation (in which the fundamental objects are consistent sets of classical histories) as a fundamentally random theory where God plays dice (as in the recent Physics Today article by Omn`es & Griffith), whereas others view it more as a way of identifing what is classical within the deterministic “many worlds” context. Such issues undoubtedly contributed to the large “undecided” vote on the last question."

--------------

The reason many are going into Many Worlds camp is because of the following. Quoting again from the url:


"The simple double slit interference experiment, hailed by Feynman as the mother of all quantum effects, was successfully repeated for ever larger objects: atoms, small molecules and most recently a carbon-60 Buckey Ball”. After this last feat, Anton Zeilinger’s group in Vienna has even started discussing doing it with a virus. If we imagine, as a Gedanken experiment, that this virus has some primitive kind of consciousness, then the many worlds/many minds interpretation seems unavoidable, as has been emphasized by Dieter Zeh. An extrapolation to superpositions involving other sentient beings such as humans would
then be merely a quantitative rather than a qualitative one."

 

[A. Neumaier]

http://arxiv.org/PS_cache/quant-ph/pdf/0101/0101077v1.pdf
quoting

"Which interpretation of quantum mechanics is closest to your own?
(a) Copenhagen or consistent histories (including postulate of explicit collapse): 4
(b) Modified dynamics (Schroedinger equation modified to give explicit collapse): 4
(c) Many worlds/consistent histories (no collapse): 30
(d) Bohm (an ontological interpretation where an auxiliary “pilot wave” allows particles to have well-defined positions and velocities): 2
(e) None of the above/undecided: 50

This is a very uninformative questionnaire.
The dominant statistical interpretation is not even mentioned (and might figure under either (c) or (e)).
The consistent history interpretation has nothing to do with Everett's MWI, but both are classified together in the single choice (c).
No collapse does not imply either of many worlds or consistent histories, but this seems to be suggested by the choices.

In particular, this gives an upper bound on 30% on supporters of MWI in the particular sample taken, while the only deducible lower bound is 0%.