Does Schrodinger's cat know whether it's dead?

[ZapperZ]

If you read back into the thread, you'll see that the decoherence issue wasn't raised by me. My point, which is still valid, is that decoherence doesn't restore the realism Einstein was looking for - objects in space and time with definite properties. Einstein believed an underlying theory could eventually be uncovered, which after Bell-Aspect seems quite an untenable position.

What i said in response to the assertion that decoherence restores quantum theory to a theory that makes sense is(words by word):







What exactly are you asking me to do? And what do you object to in the above passage?

I was talking of superpositions and what they mean for the nature and structure of matter. If you have something to contribute to what it means for matter to be in all possible states at once, by all means do so.


What i said was a logical extension of what Schrodinger's cat experiment was supposed to prove, that the cat doesn't exist in a definite state UNTIL after the lid is open. How is this different from what i said about superpositions prior to decoherence, i.e.:

Cat -- Not-cat

Fullerene-- Not fullerene (experimentally verified though still not fully understood, or rather simply ignored)

Object -- Not object


If you wish to say that superpositions have a reality of their own, i'd very much like to see the evidence for that. Until then, matter existing in all possible states at once belongs only to the configuration space, i.e. it isn't real.

There is a serious misunderstanding here on what, in physics, is meant by "realism". There is also a misunderstanding on what a superposition actually says, and I think you've taken it a step too far beyond that.

Realism, as described by Tony Leggett, is nothing more than a description that the object has a definite property at all times. When you toss a coin and let it land, BUT, before you look at it, the coin has a definite property of being either UP or DOWN, but not both. It is just that you just don't know what it is, so you say it has a probability of being one or the other. Realism exists here.

This is not the same for a QM particle. The superposition principle describe a particle having BOTH orthogonal states simultaneously. In the SQUID experiments of Delft/Stony Brook, the superposition of the supercurrent in both directions gave rise to the coherence gap. The magnitude of the coherence gap directly tells us that this is a consequence of the supercurrent having both opposite direction simultaneously, and not simply a fraction going one way, while the rest going the opposite way. This observation is an indication that realism doesn't quite apply in this situation.

Note that these are NOT my definitions, nor something that I made up on my own to suit my needs. Throughout the years, I've given many references to the usage of these concepts (some are even listed in the Noteworthy papers thread in the General Physics forum).

For some odd reason, you have taken this to way beyond what it says. The cat DOES exist. The thought experiment is pointing out that the orthogonal states of {dead, alive} are in a superposition, i.e. it produces an absurd situation where the cat is BOTH dead AND alive simultaneously, as described by the wave function. How this superposition somehow implies that "... you aren't talking of objects with properties in time and space... " is beyond me, especially considering that the wavefunction contains both time and spatial description. Just because a system consisting more than one particle exists in "configuration space" doesn't mean that it doesn't exist in space and time! After all, the Hamiltonian is described using space and time! So that claim is very puzzling.

A system that goes into a superposition, or that can be put in superposition, or that might EVER potentially be in superpositional states, is NOT something to be made sense of. The human mind DOESN'T and CANNOT comprehend de-localized, physical objects with indefinite properties.

Common sense is nothing more than an accumulation of knowledge. I don't know which human you are claiming that cannot comprehend superposition, but I have no trouble with it, and people that I encounter professionally have no issues with it either. Take note that we have already accepted such a concept even BEFORE QM came along. Superposition of waves resulting in constructive and destructive interference was EASILY comprehended. No one claimed that those didn't make any "sense". Furthermore, we can certainly comprehend delocalized objects. A supercurrent is totally delocalized, which gives it the long-range coherence.

You need to separate what you are not capable of accepting/understanding, with the rest of the human population, especially with what physicists already know and understand.

Zz.

 

[GeorgCantor]

There is a serious misunderstanding here on what, in physics, is meant by "realism". There is also a misunderstanding on what a superposition actually says, and I think you've taken it a step too far beyond that.

Realism, as described by Tony Leggett, is nothing more than a description that the object has a definite property at all times. When you toss a coin and let it land, BUT, before you look at it, the coin has a definite property of being either UP or DOWN, but not both. It is just that you just don't know what it is, so you say it has a probability of being one or the other. Realism exists here.

This is not the same for a QM particle. The superposition principle describe a particle having BOTH orthogonal states simultaneously. In the SQUID experiments of Delft/Stony Brook, the superposition of the supercurrent in both directions gave rise to the coherence gap. The magnitude of the coherence gap directly tells us that this is a consequence of the supercurrent having both opposite direction simultaneously, and not simply a fraction going one way, while the rest going the opposite way. This observation is an indication that realism doesn't quite apply in this situation.

Note that these are NOT my definitions, nor something that I made up on my own to suit my needs. Throughout the years, I've given many references to the usage of these concepts (some are even listed in the Noteworthy papers thread in the General Physics forum).

Agreed, however...

For some odd reason, you have taken this to way beyond what it says.

Whether the cat exists while in a state of all possible superpositions is interpretation-dependent and after Bell, the options are quite limited. As you are well aware, you either toss relativity(or claim it's incomplete) in favor of non-local influences(this essentially would be just an assumption, not proof or evidence) or you learn to accept that systems in superpositions do not have definite properties and by extension - their own existence - until a measurement/decoherence takes place. This seems a very logical statement to make.

The cat DOES exist. The thought experiment is pointing out that the orthogonal states of {dead, alive} are in a superposition, i.e. it produces an absurd situation where the cat is BOTH dead AND alive simultaneously, as described by the wave function. How this superposition somehow implies that "... you aren't talking of objects with properties in time and space... " is beyond me, especially considering that the wavefunction contains both time and spatial description.

But the wave function doesn't live in classical 3D space but in Hilbert space. Cats in Hilbert space are not cats, agree? What would Bell say about cats in Hilbert space after his introduced his theorem? Is there an underlying reality where the cat exists prior to measurement/decoherence? And if there is, what kind of reality would that have to be?

Are you believing in the many world hypothesis? If you do, you could be justfied in saying that superpositions of physical matter make sense and are understood, and by extension physical objects exist in space and time, but it involves making the assumption that physical space is Hilbert space and the dramatic, sci-fi assumption that there are 8 billion trillion worlds. If this is the case, it's equally valid to say that making a number of 'appropriate' assumptions, one can prove anything, even that which is impossible.

Just because a system consisting more than one particle exists in "configuration space" doesn't mean that it doesn't exist in space and time! After all, the Hamiltonian is described using space and time! So that claim is very puzzling.

"Real", macroscopic, Newtonian objects do not seem to display quantum mechanical features such as superposition. There is a clear-cut dissonance between quantum mechanics and Newtonian physics, where only one configuration occurs(and by logical extension can be said to 'exist'). I have no idea what it means to assert that a bacteria, or a molecule or a human can exist in all possible states described by probability amplitudes at once in time and space. Can you elaborate? Seems like you are introducing a new meaning to the word "exist" that will hardly be found in regular dictionaries(unless they were written by particle physicists for particle physicists, who all agreed on a particular interpretation).

Common sense is nothing more than an accumulation of knowledge. I don't know which human you are claiming that cannot comprehend superposition, but I have no trouble with it, and people that I encounter professionally have no issues with it either.

Schoroedinger surely rings a bell(among others), since he was the author of what has turned to be called the Schroedinger's Cat paradox. And you could say, he was also a professional(and a Nobel prize winner).

Take note that we have already accepted such a concept even BEFORE QM came along. Superposition of waves resulting in constructive and destructive interference was EASILY comprehended. No one claimed that those didn't make any "sense". Furthermore, we can certainly comprehend delocalized objects. A supercurrent is totally delocalized, which gives it the long-range coherence.

You need to separate what you are not capable of accepting/understanding, with the rest of the human population, especially with what physicists already know and understand.

Zz.

My point was about the physical nature of matter and while constructive and destructive inteference of EM waves might be easier to imagine, it isn't so with matter waves. Unless you let go of realism, which more and more physicists after Bell seem to have no problem with.

If i were to sum up my point in one single sentence, it would be - "superpositions of quantum states pose a great challenge to our common-sense picture of physical matter(and by extension of all reality)". If you are denying this, you are denying the existence of the measurement problem and at least half of quantum theory(i.e. the "transition" from fields to single outcomes, aka "matter").


Here is a good question for you. The van der Waals radius of a C60 molecule is about 1 nanometer, the distance between the slits is 50nm( roughly 25 times the size of c60). It's very puzzling what would make someone claim that the unobserved 'entity' that went through both slits was a c60 molecule(that exists at all times)? Remember the c6o molecule is supposed to be a physical object(matter).

http://www.users.csbsju.edu/~frioux/two-slit/c60-slit.htm


The wave function of my body is gradually soaked in around me into space. Yet i claim that that wavefunction is not me, as there is no way to keep my physical processes functioning, and consequently i can't be alive and exist in all possible states at once...

How is this "taking it too far"?

 

[ZapperZ]

Whether the cat exists while in a state of all possible superpositions is interpretation-dependent and after Bell, the options are quite limited. As you are well aware, you either toss relativity(or claim it's incomplete) in favor of non-local influences(this essentially would be just an assumption, not proof or evidence) or you learn to accept that systems in superpositions do not have definite properties and by extension - their own existence - until a measurement/decoherence takes place. This seems a very logical statement to make.

This is a misrepresentation of quantum entanglement. If you look at all the experiments that reported on the Bell-type experiment, NONE OF THEM claim of violation of SR. Why do you think that is?

In a quantum entanglement measurement, no signal of any kind travels from one of the entangled entity to the other at a speed faster than c. This is a very crucial point. In fact, you can't use quantum entanglement to send communications faster than c!

Now, you can measure the responses made by, say, a bipartite pair, and show that they react at a rate faster than c. But in SR, it is the speed of a signal, or information, that is the limiting factor, and that cannot exceed c in the present-day formulation.

So no, no one other than you is tossing out SR based on all the Bell-type experiments. So here is an example of you extending something beyond what it says.

But the wave function doesn't live in classical 3D space but in Hilbert space.

The basis functions are in Hilbert space, but the basis themselves have spatial and temporal dependence. So how does this allows you to draw a conclusion that such a thing doesn't exist in space and time? This already doesn't make any sense since you have not only a spatial operator that measure the position of an object, but one can also transform from real space into momentum space and in reverse. When I construct, say, the Bloch wavefunction, what do you think defines the periodicity of the potential?

Are you believing in the many world hypothesis?

Er... don't jump to conclusions here. Again, you are bringing something and putting words into my mouth. I'm asking you to justify what you said. I have no desire to justify your imagination of what you THINK I said.

"Real", macroscopic, Newtonian objects do not seem to display quantum mechanical features such as superposition. There is a clear-cut dissonance between quantum mechanics and Newtonian physics, where only one configuration occurs(and by logical extension can be said to 'exist'). I have no idea what it means to assert that a bacteria, or a molecule or a human can exist in all possible states described by probability amplitudes at once in time and space. Can you elaborate? Seems like you are introducing a new meaning to the word "exist" that will hardly be found in regular dictionaries(unless they were written by particle physicists for particle physicists, who all agreed on a particular interpretation).

1. Tony Leggett is NOT a particle physicist. In fact, he is in the same field as I am, condensed matter physics. This is the physics of materials, i.e. the stuff that you are using NOW. So none of the stuff we are talking about is "esoteric", and in fact, many of the most amazing indication of quantum phenomena came out of condensed matter experiment. Don't believe me? Look at Carver Mead's article on "Collective Electrodynamics", where he flat-out claim that the most convincing and clearest evidence of quantum mechanics at the macroscopic scale is superconductivity, not some "particle physics" experiments!

2. If you have looked at any of my writings on the quantum-classical boundary, you would have noticed that I claim that they are different from each other, and that the separation between the two at the mesoscopic scale is still unknown, i.e. we don't know if they are truly separated by something similar to a phase transition (i.e. many state variables change discontinuously through the transition), or that this is a smooth crossover. Decoherence is one way out, but it is NOT the only way out. Again, one of the papers I've highlighted in the Noteworthy thread is a paper that shows that our coarse-grained measurement of a quantum system can recover the classical state that we are familiar with. In other words, when we look at a cow from very far (i.e. our observation isn't very detailed), then we get back the sphere!

3. I used the term "real" to mean something to be physically meaningful/significant. See G. Giuliani, Eur. J. Phys. 31 871 (2010).

My point was about the physical nature of matter and while constructive and destructive inteference of EM waves might be easier to imagine, it isn't so with matter waves. Unless you let go of realism, which more and more physicists after Bell seem to have no problem with.

This automatically falsified your claim that the human brain can't fathom or understand with such a concept, unless, of course, you don't consider "more and more physicists" as belonging to the human specie.

Have you ever considered that familiarity breeds acceptance? We are more familiar with classical wave superposition. We are not familiar with quantum superposition. Is your difficulty in accepting the latter because you are not familiar with it? How often do you encounter it? How often do you do experiments in which these QM properties jump up at you? So the problem here may not be with the QM formalism, it could be YOU!

Here is a good question for you. The van der Waals radius of a C60 molecule is about 1 nanometer, the distance between the slits is 50nm( roughly 25 times the size of c60). It's very puzzling what would make someone claim that the unobserved 'entity' that went through both slits was a c60 molecule(that exists at all times)? Remember the c6o molecule is supposed to be a physical object(matter).

http://www.users.csbsju.edu/~frioux/two-slit/c60-slit.htmThe wave function of my body is gradually soaked in around me into space. Yet i claim that that wavefunction is not me, as there is no way to keep my physical processes functioning, and consequently i can't be alive and exist in all possible states at once...

How is this "taking it too far"?

Here's a question for you. Look at the experiment, and see what they have to prepare the C60 molecule to make it undergo such an experiment. Hint: if they do this at room temperature, they won't see the interference effect.

This is where you your misunderstanding of what "coherence" mean comes into play, because you do not realize that every part of the C60 molecules have to be in coherence with each other. It is why a soccer ball cannot undergo such a process. Think of how difficult it is to get each part of a macroscopic object to be in coherence with each other.

In the Delft/Stony Brook book experiment, they managed to make 10^11 particles to undergo the Schrodinger Cat state experiment. 10^11! Think about it. What this means is that 10^11 particles have to be in a complete coherent state! If they are not, the effect is gone!

What you are taking too far is the meaning of superposition at the quantum scale. I am not a fan of applying rules at a scale where they haven't been shown to work. Deepak Chopra is notorious for doing such a thing, and I'm hoping that you don't do the same thing. This isn't about quantum rules working at the classical scale. This is about misrepresenting quantum rules at the quantum scale!

Zz.

 

[GeorgCantor]

This is a misrepresentation of quantum entanglement. If you look at all the experiments that reported on the Bell-type experiment, NONE OF THEM claim of violation of SR. Why do you think that is?

Yes, but Bell did make 2 common-sense assumptions - that of locality and realism that he proved one of them or both were inconsistent with qm. If you look back at my posts, you'll see that i always expressed great reservations about nonlocal influencing in pilot-wave theories. In this thread it was me who brought up the notion that the most elaborate piece of equipment the LHC works because SR is accurate, hence the universe is not Newtonian. The issue that came up here centered around the assumption of realism, and whether objects with properties exist in space and time(to which i objected multiple times).

In a quantum entanglement measurement, no signal of any kind travels from one of the entangled entity to the other at a speed faster than c. This is a very crucial point. In fact, you can't use quantum entanglement to send communications faster than c!

Now, you can measure the responses made by, say, a bipartite pair, and show that they react at a rate faster than c. But in SR, it is the speed of a signal, or information, that is the limiting factor, and that cannot exceed c in the present-day formulation.

No doubt about it. They wouldn't spend 10 billion euro public money on a wrong theory.

So no, no one other than you is tossing out SR based on all the Bell-type experiments. So here is an example of you extending something beyond what it says.

Slow down, I said the opposite. I don't like making assumptions, like that of nonlocality. Nonlocal influences don't exist as far as i am concerned.

The basis functions are in Hilbert space, but the basis themselves have spatial and temporal dependence. So how does this allows you to draw a conclusion that such a thing doesn't exist in space and time?

Because as somebody already asked me in this thread, the standard definition of "physical structure" that i use doesn't fit the observed effect of superpositions of states.

This already doesn't make any sense since you have not only a spatial operator that measure the position of an object, but one can also transform from real space into momentum space and in reverse. When I construct, say, the Bloch wavefunction, what do you think defines the periodicity of the potential?

I don't question that there is clear correspondence between the formalism and the outcomes of measurements. I deny that probability amplitudes are objects(physical structures).

1. Tony Leggett is NOT a particle physicist. In fact, he is in the same field as I am, condensed matter physics. This is the physics of materials, i.e. the stuff that you are using NOW. So none of the stuff we are talking about is "esoteric", and in fact, many of the most amazing indication of quantum phenomena came out of condensed matter experiment. Don't believe me? Look at Carver Mead's article on "Collective Electrodynamics", where he flat-out claim that the most convincing and clearest evidence of quantum mechanics at the macroscopic scale is superconductivity, not some "particle physics" experiments!

2. If you have looked at any of my writings on the quantum-classical boundary, you would have noticed that I claim that they are different from each other, and that the separation between the two at the mesoscopic scale is still unknown, i.e. we don't know if they are truly separated by something similar to a phase transition (i.e. many state variables change discontinuously through the transition), or that this is a smooth crossover. Decoherence is one way out, but it is NOT the only way out. Again, one of the papers I've highlighted in the Noteworthy thread is a paper that shows that our coarse-grained measurement of a quantum system can recover the classical state that we are familiar with. In other words, when we look at a cow from very far (i.e. our observation isn't very detailed), then we get back the sphere!

3. I used the term "real" to mean something to be physically meaningful/significant. See G. Giuliani, Eur. J. Phys. 31 871 (2010).

Good. A recent poll indicated that the majority of the interviewed chose "none of the available interpretations". Seems like the most reasonable position to me.

My point was about the physical nature of matter and while constructive and destructive inteference of EM waves might be easier to imagine, it isn't so with matter waves. Unless you let go of realism, which more and more physicists after Bell seem to have no problem with.

This automatically falsified your claim that the human brain can't fathom or understand with such a concept, unless, of course, you don't consider "more and more physicists" as belonging to the human specie.

This is the central point - that of the contextuality of GR and QM and the rejection of realism. As soon as we denounce realism, we have to accept the unacceptable, that objects are not objects with fixed properties existing in space and time, but that which we measure/collapse in our inertial frame, that which decoheres from all possible superpositional states, etc.

When you do a measurement, you get particles, atoms, molecules...

It takes a leap of faith to say there exist objects with fixed properties prior to a measurement and this is contradicted by SR as well. Your acceptance that realism might be wrong, suggests that we need a new definition of physical objects, that will depart the Newtonian picture. That picture might be already there among your collegues, but it's not there, out on the street. That the world may not be out there at all times with definite properties is not even remotely considered by the general population.

What you are taking too far is the meaning of superposition at the quantum scale. I am not a fan of applying rules at a scale where they haven't been shown to work. Deepak Chopra is notorious for doing such a thing, and I'm hoping that you don't do the same thing. This isn't about quantum rules working at the classical scale. This is about misrepresenting quantum rules at the quantum scale!

Zz.

I am not sure myself if macro objects can be shown to display interference effects but quantum field theory works just fine on the macro scale AFAIK(and it's not a theory that confirmes the Realism assumption of objects with properties existing at all times). It's only a conceptual difficulty in relating fields to uhhmm... 'observations' seems like the least misleading term.

 

[BruceG]

Now if someone is willing to entertain the notion that decoherence explains what it means for a cat to have decohered and treat it as a common-sense object in space and time, i'd like to see it done in this thread. I'd like to see explantion on how single outomes are actualized.

As I started this sub-thread off, I'd like another go at this. I've found this succinct account by Terry Gannon [Moonshine beyond the monster p.245]

"[Decoherence] alone doesn't resolve the measurement problem. At best decoherence can only explain why macroscopically distinct states in superposition don't 'see' each other. A (perhaps overly zealous) application of quantum mechanics insists that macroscopic superpositions must occur; from this, the 'Many-Worlds' interpretation is inevitable. The explanation for the mysterious wave-function collapse then would be that measurement entangles the microscopic quantum system with a macroscopic system.. Each coupled state ('world') in this superposition would decohere from the others, and so the various quantum states could no longer 'see' each other. It would be as if at the moment of measurement, the universe split into parallel universes, one for each possible experimental outcome."

I re-assert that this makes sense to me and allows me to continue being a realist. So its very tempting to take this interpretation.

 

[apeiron]

I re-assert that this makes sense to me and allows me to continue being a realist. So its very tempting to take this interpretation.

Decoherence has the right feel for an interpretation because it does not seek to erradicate quantum weirdness but instead tames it, pushes it to the margin of the real.

There were three early reactions to the shocks of QM - denial, exaggeration and agnosticism. So either a search for a way out that preserved locality, crispness, and other properties deemed essential to Newtonian/Einsteinian mechanics, or - Georg's position - a call for complete ontological revolution where perhaps even human consciousness was needed to observe reality into existence, or a pragmatic "we can't understand, so shut up and calculate".

None of these three responses seem commonsensical. You have to respond to the experimental verification of QM, but in a way that preserves the well-supported formalisms of Newton, Einstein (and Boltzmann - never forget thermodynamics).

We already treat relativity as a "weirdness" that occurs at the global limit of Newtonian mechanics. It exists, but only at the margins of our "realistic" experience of the world - ie: our mesoscopic viewpoint standing bang in the middle of things.

In the same way, QM is the weirdness at we find down at the local scale, when things are very small or hot. Decoherence is a way of both accepting that QM is "everywhere" in the classically real world (just as relativity is), and yet also only nakedly apparent in all its glorious weirdness at the very margins.

Decoherence itself is not yet a complete answer as, in my understanding, the formalism smears the weirdness out rather successfully so that it is marginalised, but it does not yet do the same job for observation - the collapse part of the story.

On the other hand, achieving actual complete collapse would be an erradication of the weirdness, and so actually this should not be the aim anyway? If the QM weirdness is being pushed to the very edge of the field of view, then so is the final collapse issue. It too ceases to become a source of ontological concern. Everything can be vague at the margins, so long as it looks crisp and solid across the many orders of flat spatiotemporal scale that make up our "reality".

 

[GeorgCantor]

As I started this sub-thread off, I'd like another go at this. I've found this succinct account by Terry Gannon [Moonshine beyond the monster p.245]

"[Decoherence] alone doesn't resolve the measurement problem. At best decoherence can only explain why macroscopically distinct states in superposition don't 'see' each other. A (perhaps overly zealous) application of quantum mechanics insists that macroscopic superpositions must occur; from this, the 'Many-Worlds' interpretation is inevitable. The explanation for the mysterious wave-function collapse then would be that measurement entangles the microscopic quantum system with a macroscopic system.. Each coupled state ('world') in this superposition would decohere from the others, and so the various quantum states could no longer 'see' each other. It would be as if at the moment of measurement, the universe split into parallel universes, one for each possible experimental outcome."

I re-assert that this makes sense to me and allows me to continue being a realist. So its very tempting to take this interpretation.

Actually, you have to be a really weak realist, as under the MWI there are no objects with absolute properties in spacetime, PRIOR to a universe split. The best one can say is that there exists a wave "structure" of all possible events that become to look like "objects" only at the split. Three seconds into the future from now, there is not be a single object in existence(just a coherent wave structure). The notion that the universe splits instantaneously/nonlocally is another challenge to the idea of realism, if you really get down to it.

Zeilinger's position that what exists "out there" is information seems to be the only somewhat common-sensical explanation of reality. But take a second look at it, and it stops being common-sensical too.

 

[BruceG]

Actually, you have to be a really weak realist.

Yes, I'm happy being a weak realist in the general philosophical sense of not being an idealist: I can think about the evolution of the universe in a deterministic objective way existing independent of human observation of it. Decoherence + many-worlds at least does this, however crudely.

 

[ZapperZ]

Yes, but Bell did make 2 common-sense assumptions - that of locality and realism that he proved one of them or both were inconsistent with qm. If you look back at my posts, you'll see that i always expressed great reservations about nonlocal influencing in pilot-wave theories. In this thread it was me who brought up the notion that the most elaborate piece of equipment the LHC works because SR is accurate, hence the universe is not Newtonian. The issue that came up here centered around the assumption of realism, and whether objects with properties exist in space and time(to which i objected multiple times).

I work at a particle accelerator. I don't need to go to the LHC to show that SR is accurate.

Secondly, are you sure you know what is meant by "realism" as applied within this context? For example, is your definition of realism consistent with not only Bell, but also with the papers dealing with such issues? Read:

A.J. Leggett, Rep. Prog. Phys. v.71, p.022001 (2008)
S. Groeblacher et al., Nature v.446, p.871 (2007).

The problem here is the way you are "interpreting" what a "superposition of states" mean. I still don't think you know what it is, so I'm going to ask a very direct question via an example.

I have a system consisting of two orthogonal states |1> and |2>. The wavefunction describing the system is

$$\psi = a_1|1> + a_2|2>$$

where the a's are the normalized amplitude for each state.

Please tell me what this is saying to you.

Zz.

 

[GeorgCantor]

Secondly, are you sure you know what is meant by "realism" as applied within this context? For example, is your definition of realism consistent with not only Bell, but also with the papers dealing with such issues? Read:

A.J. Leggett, Rep. Prog. Phys. v.71, p.022001 (2008)
S. Groeblacher et al., Nature v.446, p.871 (2007).

I haven't finished reading yet but i wonder what you will say ontologically(how it pertains to the real world) about the cat from this paragraph:


"This state clearly exhibits several quantum phase-space interference fringes between the 'dead' and 'alive' components, and is large enough to become useful for quantum information processing and experimental tests of quantum theory."


Does the cat exist in both states at once and how does the notion of coarse-graininess solve the dead/alive cat paradox?



EDIT: I could only find abstracts from those papers, but found this article referenced by you as a summation of the points(supposedly) raised in the paper:

http://physicsworld.com/cws/article/news/27640


which seems to be consistent with what i stated in the beginning in this thread about realism.

"Now physicists from Austria claim to have performed an experiment that rules out a broad class of hidden-variables theories that focus on realism -- giving the uneasy consequence that reality does not exist when we are not observing it (Nature 446 871)."

The problem here is the way you are "interpreting" what a "superposition of states" mean. I still don't think you know what it is, so I'm going to ask a very direct question via an example.

I have a system consisting of two orthogonal states |1> and |2>. The wavefunction describing the system is

$$\psi = a_1|1> + a_2|2>$$

where the a's are the normalized amplitude for each state.

Please tell me what this is saying to you.

Zz.

The system's probability to be in state one is a1 and a2 to be in state 2. Their sum describes the superposition of the two states(the simultaneous existence of both states).

It's the standard procedure to consider that that which goes through both slits at the double slit, is a probability wave, since the interference pattern is perfectly accounted for by solving the Schroedinger equation. From here a probability wave cannot be regarded as an object, unless we make a few assumptions, or make up a new definition of what we mean by object.

 

[ZapperZ]

I haven't finished reading yet but i wonder what you will say ontologically(how it pertains to the real world) about the cat from this paragraph:


"This state clearly exhibits several quantum phase-space interference fringes between the 'dead' and 'alive' components, and is large enough to become useful for quantum information processing and experimental tests of quantum theory."


Does the cat exist in both states at once and how does the notion of coarse-graininess solve the dead/alive cat paradox?

We have a failure to communicate here. I've been telling you since the first time I ventured into this thread on why your argument that things just don't exist, especially in space and time, is false simply based on the superposition principle. The Schrodinger Cat experiments are showing that the "orthogonal" states are there simultaneously! Again, look at what I've written, especially when I was discussing the Delft/Stony Brook experiment. Remember, I said that the supercurrent exists in BOTH OPPOSITE DIRECTIONS SIMULTANEOUSLY.

EDIT: I could only find abstracts from those papers, but found this article referenced by you as a summation of the points(supposedly) raised in the paper:

http://physicsworld.com/cws/article/news/27640


which seems to be consistent with what i stated in the beginning in this thread about realism.

No way!

First of all, you are quoting a popular article for the general public that is now a 2nd hand source. Secondly, how could you use such sources and phrase as if they are biblical quotes? If this is a reflection of how you acquire your information (and I'm beginning to suspect that it is), no wonder you have such a view!

The system's probability to be in state one is a1 and a2 to be in state 2. Their sum describes the superposition of the two states(the simultaneous existence of both states).

It's the standard procedure to consider that that which goes through both slits at the double slit, is a probability wave, since the interference pattern is perfectly accounted for by solving the Schroedinger equation. From here a probability wave cannot be regarded as an object, unless we make a few assumptions, or make up a new definition of what we mean by object.

I would not nitpick the fact that the "probability" is the square of the amplitudes, rather than the amplitudes themselves. But you never answered my question. I asked:

"Please tell me what this is saying to you."

Zz.

 

[GeorgCantor]

I would not nitpick the fact that the "probability" is the square of the amplitudes, rather than the amplitudes themselves. But you never answered my question. I asked:

"Please tell me what this is saying to you."

Zz.

That the system can be said to exist in both a1 and a2 states simultaneously. Interference is the result of superpositions of two or more waves(say passing through the double slit experiment). When performing a certain measurement on a quantum state, the result is described by a probability distribution, however we don't observe superpositions, objects in superpositions are not real(do not exist) until the state vector reduction that describes the evolution of the system.

We have a failure to communicate here. I've been telling you since the first time I ventured into this thread on why your argument that things just don't exist, especially in space and time, is false simply based on the superposition principle. The Schrodinger Cat experiments are showing that the "orthogonal" states are there simultaneously!

Perhaps there really is miscommunication. What do you mean by 'Cat'? Is this supposed to be a quantum cat existing in all possible states simultaneously? If so, what is your definition of 'exist'? By exist i mean the act of being in space and time with particular properties as in:


1.to have actual being; be: The world exists, whether you like it or not.
2.to have life or animation; live.
3.to continue to be or live: Belief in magic still exists.
4.to have being in a specified place or under certain conditions; be found; occur: Hunger exists in many parts of the world.
5.to achieve the basic needs of existence, as food and shelter: He's not living, he's merely existing.


http://dictionary.reference.com/browse/exist



Mind you, the definition of 'to exist' calls for Actual being, not Potential.



A cat that is dead and alive simultaneously is not a cat. How is this statement supposed to sound weird?



Here is the standard definition for 'cat':

"The cat (Felis catus), also known as the domestic cat or housecat[5] to distinguish it from other felines and felids, is a small domesticated carnivorous mammal that is valued by humans for its companionship and ability to hunt vermin and household pests. Cats have been associated with humans for at least 9,500 years,[6] and are currently the most popular pet in the world."

http://en.wikipedia.org/wiki/Cat



Nowhere will you find a mention of cats in superposition of states. There doesn't exist such a cat, if by cat you mean what wikipedia says.



What makes you say both the Potential and the Actual 'exist'? Is probability an object?

Cats exist in multiple possibilities of realities known as superpositions(until whatever it is you believe in). That doesn't mean they are real or exist in the traditional sense.


And since superposition of possible positions for an electron can be demonstrated by the observed phenomenon quantum tunneling, also in transistors, etc. superpositions are an observed effect. However what they mathematically represent cannot be real, unless you believe in the many world hypothesis(but that has its realism problems too).

 

[Pythagorean]

Perhaps we should derive the superposition principle as a consequence of indistinguishable particles for Georg.

 

[GeorgCantor]

Perhaps we should derive the superposition principle as a consequence of indistinguishable particles for Georg.

The MOST striking feature of quantum mechanics is the existence of superposition states, where an object appears to be in different situations at the same time.


Are you disputing this statement?

 

[Pythagorean]

No, because it was all subjectively stated with words like striking and appears

 

[ZapperZ]

That the system can be said to exist in both a1 and a2 states simultaneously. Interference is the result of superpositions of two or more waves(say passing through the double slit experiment). When performing a certain measurement on a quantum state, the result is described by a probability distribution, however we don't observe superpositions, objects in superpositions are not real(do not exist) until the state vector reduction that describes the evolution of the system.

Actually, the system exists in state |1> and |2>, not a1 and a2. But never mind. What is puzzling is that, how did you jump from what you view as what quantum superposition say, to this:

The problem with decoherence is that it doesn't say that matter(objects) are there all the time with properties in space. On the contrary, though it doesn't explain why we observe exatly what we do, it says that physical structures are not always there. If this doesn't blow one's mind, one must have rocks in his head.

?

Remember, this was my original question/objection!

I have no idea why you decide to give me a lesson in tunneling. Have YOU done any experiment in quantum tunneling? I have.

Zz.

 

[GeorgCantor]

No, because it was all subjectively stated with words like striking and appears

How about now:

"The MOST weird feature of quantum mechanics is the existence of superposition states, which are confirmed by multiple observations, logical inference and millions of practical applications to be evidence that an object was in different situations at the same time."

 

[Pythagorean]

I don't think so. Read the wiki on indistinguishable particles. That's where superposition comes from, and particularly, it's a major difference between classical and quantum particles.

I think you're making a private interpretation about the evidence.

 

[GeorgCantor]

Actually, the system exists in state |1> and |2>, not a1 and a2. But never mind. What is puzzling is that, how did you jump from what you view as what quantum superposition say, to this:

The problem with decoherence is that it doesn't say that matter(objects) are there all the time with properties in space. On the contrary, though it doesn't explain why we observe exatly what we do, it says that physical structures are not always there. If this doesn't blow one's mind, one must have rocks in his head.

Remember, this was my original question/objection!.

Loose language, i guess. I meant to say superpositions, not decoherence(not just decoherence) but i think the point i was making was still comprehensible(or i hope so). My next posts centered around superpositions of cats, etc. That's what it was intended to have meant anyway.

 

[ZapperZ]

Loose language, i guess. I meant to say superpositions, not decoherence(not just decoherence) but i think the point i was making was still comprehensible(or i hope so). My next posts centered around superpositions of cats, etc. That's what it was intended to have meant anyway.

But that makes it even contradictory. Here, you say that the object exists in all the possible orthogonal states:

That the system can be said to exist in both a1 and a2 states simultaneously. Interference is the result of superpositions of two or more waves(say passing through the double slit experiment). When performing a certain measurement on a quantum state, the result is described by a probability distribution, however we don't observe superpositions, objects in superpositions are not real(do not exist) until the state vector reduction that describes the evolution of the system.

But in the quote that I originally objected to, you say they DON'T exists in any of the states!

The problem with decoherence is that it doesn't say that matter(objects) are there all the time with properties in space. On the contrary, though it doesn't explain why we observe exatly what we do, it says that physical structures are not always there. If this doesn't blow one's mind, one must have rocks in his head.

In fact, you claim that it doesn't say that it exist "all the time with properties of space"!

Look at what you wrote and see if it is not only consistent with physics, but consistent with each other.

Zz.

 

[GeorgCantor]

"The MOST weird feature of quantum mechanics is the existence of superposition states, which are confirmed by multiple observations, logical inference and millions of practical applications to be evidence that an object was in different situations at the same time."

I don't think so.Read the wiki on indistinguishable particles. That's where superposition comes from, and particularly, it's a major difference between classical and quantum particles.

I read it, still no reference where superpositions are coming from.

I think you're making a private interpretation about the evidence.

Evidence of what? Of superpositions? And what do you mean by "private" interpretation? That of Standard Quantum Mechanics? If so, then that's got to be a wholly world-wide "private" interpretation of the evidence, taught in ALL the major universities around the world.

That's where superposition comes from, and particularly, it's a major difference between classical and quantum particles.

Very helpful insight, but can you show me specifically where it is explained where "superpositions" come from(from the wiki or other source) before you take the Nobel Prize.

 

[GeorgCantor]

But in the quote that I originally objected to, you say they DON'T exists in any of the states!
Zz.

Yes, that's right. They don't exist as objects but they EXIST as probabilities. I made it clear several times that i was speaking of objects. There is no contradiction(see in the quotes you made the term 'object'),.

 

[Pythagorean]

You must have not read t very thoroughly. Go back and look under "statistical Properties of bosons and fermions".

No need to be hostile. I'm not expecting a nobel prize for something I was taught in the standard coursework and can be found in an introductory text on qm.

 

[ZapperZ]

Yes, that's right. They don't exist as objects but they EXIST as probabilities. I made it clear several times that i was speaking of objects. There is no contradiction(see in the quotes you made the term 'object'),.

But this is what is thoroughly wrong!

Existing as merely "probability" will not produce the coherence gap in the SQUID/Delft experiments! When I tossed a coin, the outcome exists merely as probabilities. You can't do anything with those probabilities other than wait for an actual measurement. This is not true in QM. You can, in fact, detect the superposition of those states, especially via a measurement of a non-commuting observable. The fact that there are such a thing as bonding-antibonding states, the coherence gap, etc.. etc. clearly shows that in those cases, both states EXIST and produced a physically significant outcome of a measurement that would not be there had they not exist.

Since you like to quote PhysicsWorld article, how come you didn't pay any attention to http://physicsworld.com/cws/article/news/2815" ?

In 1935 Erwin Schrodinger proposed a famous thought experiment in which a cat was somehow both alive and dead at the same time. Schrodinger was attempting to demonstrate the limitations of quantum mechanics: quantum particles such as atoms can be in two or more different quantum states at the same time but surely, he argued, a classical object made of a large number of atoms, such as a cat, could not be in two different states. Now Jonathan Friedman and co-workers at the State University of New York (SUNY) in Stony Brook have demonstrated a macroscopic Schrodinger cat state for the first time (Nature 406 43). In their experiment a superconducting device is placed in a quantum superposition of two states: one that corresponds to a current flowing through the device in a clockwise direction, and another that corresponds to an anti-clockwise current.

Nowhere in there is there any implied scenario that it is the probability that is 'existing'. Rather, there is an explicit indication that (i) both properties are simultaneously present and (ii) they are the "object" itself. This review is the Stony Brook's SQUID experiment.

Zz.

 

[GeorgCantor]

But this is what is thoroughly wrong!

Existing as merely "probability" will not produce the coherence gap in the SQUID/Delft experiments! When I tossed a coin, the outcome exists merely as probabilities. You can't do anything with those probabilities other than wait for an actual measurement. This is not true in QM. You can, in fact, detect the superposition of those states, especially via a measurement of a non-commuting observable. The fact that there are such a thing as bonding-antibonding states, the coherence gap, etc.. etc. clearly shows that in those cases, both states EXIST and produced a physically significant outcome of a measurement that would not be there had they not exist.

Since you like to quote PhysicsWorld article, how come you didn't pay any attention to http://physicsworld.com/cws/article/news/2815"?





Nowhere in there is there any implied scenario that it is the probability that is 'existing'. Rather, there is an explicit indication that (i) both properties are simultaneously present and (ii) they are the "object" itself. This review is the Stony Brook's SQUID experiment.

Zz.

Okay, this makes sense and i see the point you were trying to make from the beginning. Assuming that the experiment holds for larger objects, you are justified in saying that the cat(the object 'cat') does exist in all possible states simultaneously.

I've just learned a new definition of 'exist' that makes my bewilderment even greater. Perhaps because my brain got as fuzzy as its quantum states.

 

[GeorgCantor]

You must have not read t very thoroughly. Go back and look under "statistical Properties of bosons and fermions".

No need to be hostile. I'm not expecting a nobel prize for something I was taught in the standard coursework and can be found in an introductory text on qm.

I didn't see it in my quantum physics textbook and i couldn't find mention of derivation of superpositions in Penrose "The Road to Reality".

I took your statement literally and it seemed to strongly imply that it is possible to derive superposition states from more basic principles, which would make quantum mechanics a fully deterministic theory. Of course this can't be done without a TOE, we are adjusting the formalism to what we observe, not vice versa.

 

[Pythagorean]

I didn't see it in my quantum physics textbook and i couldn't find mention of derivation of superpositions in Penrose "The Road to Reality".

I took your statement literally and it seemed to strongly imply that it is possible to derive superposition states from more basic principles, which would make quantum mechanics a fully deterministic theory. Of course this can't be done without a TOE, we are adjusting the formalism to what we observe, not vice versa.

My statement was literal. If you don't want to formally confirm it for yourself form the wiki article:

David Griffith, Introduction to Quantum Mechanics, Section 5.1.1, Two Particle Systems: Bosons and Fermions.

The only reason I press the point is because for me, it was the ah-ha moment when I realized what "superposition of states" really meant. There's also some interesting insights about the uncertainty principle here:

http://en.wikipedia.org/wiki/Uncertainty_principle#Uncertainty_principle_and_observer_effect

 

[apeiron]

Nowhere in there is there any implied scenario that it is the probability that is 'existing'. Rather, there is an explicit indication that (i) both properties are simultaneously present and (ii) they are the "object" itself.

To call the SQUID superposition an object would be misleading as an object is tangible, within the grasp of the senses. And of course the experiment only observes one or other direction of the current. Which is why I presume you put object in quotes. But even then, the superposition does not seem object-like in the sense you appear to mean - a persistent ring of activity.

The situation is just the same as a twin slit superposition. A condition is created in which a current is made to take both paths, resulting in a measurable self-interference, just as the twin slit creates an interference pattern. But would we call the "thing" passing through the twin slit situation a single "object"?

Superposition is a state to which neither the terms exist, nor non-existent, really apply. Georg's problem is that he wants to divide the world into these two strict categories as they are the two options that are possible under realism.

Clearly, he says, something in superposition does not fully exist in the naive realistic sense. But then he jumps to the conclusion, well, superposition must be a state of non-existence.

The SQUID example, just as much as twin slit experiments, shows that superpositions have physically-measureable consequences. So they exist in some sense. They can occupy a place and a time, as they do for nano-seconds in a super-cooled SQUID ring. But new words would be needed to describe the status of a superposition.

I have already suggested vagueness (vagueness being that to which the law contradiction does not apply - Peirce). But regardless, both existence and non-existence are too strong as descriptions of superpositions.

 

[ZapperZ]

To call the SQUID superposition an object would be misleading as an object is tangible, within the grasp of the senses. And of course the experiment only observes one or other direction of the current. Which is why I presume you put object in quotes. But even then, the superposition does not seem object-like in the sense you appear to mean - a persistent ring of activity.

You are forgetting, or did not know, that a supercurrent is described by a coherent, single wavefunction, i.e. it is a macro-object. The same way that an entangled pair are considered to be "one" object.

The whole point of that experiment is to show that size doesn't matter to show quantum phenomena. If you can make the object's constituents coherent among themselves, then the whole thing is a single quantum object. Again, this is why http://www.pnas.org/content/94/12/6013.short" claims that superconductivity is the clearest manifestation of quantum phenomena at the macroscopic scale. It is the easiest means that we know of to create such "large" quantum object.

The situation is just the same as a twin slit superposition. A condition is created in which a current is made to take both paths, resulting in a measurable self-interference, just as the twin slit creates an interference pattern. But would we call the "thing" passing through the twin slit situation a single "object"?

Yes, I would. Protons and neutrons can do the same thing too. But are you disqualifying them because they are made up of quarks?

Superposition is a state to which neither the terms exist, nor non-existent, really apply. Georg's problem is that he wants to divide the world into these two strict categories as they are the two options that are possible under realism.

Clearly, he says, something in superposition does not fully exist in the naive realistic sense. But then he jumps to the conclusion, well, superposition must be a state of non-existence.

The SQUID example, just as much as twin slit experiments, shows that superpositions have physically-measureable consequences. So they exist in some sense. They can occupy a place and a time, as they do for nano-seconds in a super-cooled SQUID ring. But new words would be needed to describe the status of a superposition.

I have already suggested vagueness (vagueness being that to which the law contradiction does not apply - Peirce). But regardless, both existence and non-existence are too strong as descriptions of superpositions.

I only used the word 'exist' because that seems to be a popular phrase in this subforum. I've already cited a reference for a more useful terminology "physically significant". Still, the issue here is that, even without changing the words and phrase, people need to understand the actual physics involved before trying to describe it in words. The problem with learning and understanding physics through pop science description will not stop with redefining or coming up with a new phrase to replace "exist". I've seen way too many people going off on a tangent in here using various phrases in physics and taking them to mean something else - what I often called the bastardization of physics. There is no substitute to actually understanding the formalism. Period. Anything else is simply a translation of a translation.

Zz.

 

[GeorgCantor]

Nowhere in there is there any implied scenario that it is the probability that is 'existing'. Rather, there is an explicit indication that (i) both properties are simultaneously present and (ii) they are the "object" itself. This review is the Stony Brook's SQUID experiment.

Zz.

When you transition from cat to "they", what happens to the law of conservation of energy?

 

[ZapperZ]

When you transition from cat to "they", what happens to the law of conservation of energy?

The cat IS "they" in that experiment, i.e. a coherent, macroscopic object. So I don't undergo any transition in going from one thing to the same thing. Besides, why is there a "conservation of energy" issue here all of the sudden?

If you are asking about the superconducting transition, that's another topic altogether.

Zz.

 

[apeiron]

You are forgetting, or did not know, that a supercurrent is described by a coherent, single wavefunction, i.e. it is a macro-object. The same way that an entangled pair are considered to be "one" object.

I agree both are object-like in ways, but also say they lack essential attributes of objects - in the ordinary realist sense. The same is true of classical things too, like solitons.

So it would still be nice if there was a way to talk about these things neutrally, rather than worrying about their failure to exist properly, or to be definite somethings.

We call them super-states (yet they seem less than real, even if they have some extraordinary properties). We call them quasi-particles (which is not too bad a term). We call them condensates (which says something directly about the mechanism that forms such states, so that is good). We call them weird (which is bad again as again QM is becoming a challenge to realism rather than the as yet undetermined base of the real).

 

[ZapperZ]

I agree both are object-like in ways, but also say they lack essential attributes of objects - in the ordinary realist sense. The same is true of classical things too, like solitons.

It's hard to force Mother Nature to conform to our prejudices.

We call them super-states (yet they seem less than real, even if they have some extraordinary properties). We call them quasi-particles (which is not too bad a term). We call them condensates (which says something directly about the mechanism that forms such states, so that is good). We call them weird (which is bad again as again QM is becoming a challenge to realism rather than the as yet undetermined base of the real).

Not sure what the point in all of this is. "Quasiparticles" are very much well-defined within the Landau's Fermi Liquid Theory. If you consider the renormalized particle as an object, then I can't see why you can't accept the superfluid as one, considering the latter has a clearer coherence than the latter.

Zz.

 

[apeiron]

It's hard to force Mother Nature to conform to our prejudices.

Which was why I was arguing the opposite - using a language in which the embedded prejudices conform with nature. But I see you have no interest in the topic.

 

[apeiron]

When you transition from cat to "they", what happens to the law of conservation of energy?

Are you now talking about actual cats or examples of QM superpositions like SQUID rings and entangled buckyballs?

Does anyone still think that Schrodinger's cat can be in a state of superposition rather than decoherence? Clearly, what all the QM experiments spell out is how fragile and specific are the conditions for superposition to linger and persist in ways which seem quasi-object like in our classical realm. You need temperatures around absolute zero, or other special material conditions to get quantum condensates of matter.

So to get a cat into superposition, perhaps it would be possible, but only if you, for a start, super-cooled it. At which point, it would be dead for other reasons. And being an inhomogenous mix of atoms, not a collection of identical particles, even dropping a cat in liquid helium is unlikely to bring about a QM coherent state - a QM quasi-object.