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

[transcend_all]

I've read several descriptions of the Schrodinger's cat thought experiment, but I've never heard anyone discuss whether the cat qualifies as an observer that can collapse the superposition of states. This seems like too simple a question not to have been raised before, but I've never head anyone raise it.

If it is, how is the thought experiment valid? If the cat being aware of its own death or continued life can collapse the superposition, then the cat is either alive or dead and not in a superposition of states.

If it is not, that raises the question of what qualifies as an observer that can collapse the superposition. Do you have to be human to be able to observe a superposition of states such that the superposition will collapse? That seems like an absurdity.

 

[MarcStone]

Ill take a crack at this question...

Schrodinger's cat box...is...a horrible horrible analogy.

I think that half the reason people can't grasp high level physics is that physicists are terrible at creating analogies. I remember back in circa 1988 I read an old book on "relativity"...I was cross-eyed for a week. Anyways...

You can't ascribe the "cat" to having "consciousness" or have "observer" properties. In other words...there is no such thing as the damn cat! What this analogy is attempting to describe is a "unit of space" within the probability wave of an (electron/proton)...for a given "unit of space" here...the (electron/proton) "does" and "does not" exist...it is a "probability"...this (existence/non existence) per "unit space" for the electron dose not have whiskers...does not have a shiny coat..does not have sharp claws...and certainly does not have consciousness...incidentally it cannot be an observer either. Does that help?

 

[Eynstone]

The cat, as I see it, is a quantum object and not an observer in the experiment.
One doesn't have to be a 'living' being to be an observer either. ;)
The cat could always know whether it's dead by appealing to complimentarity!

 

[haael]

The answer for this question depends strongly on interpretation of QM. In fact, this is the very essence of "interpretation" - how microscopic QM laws interact with macroscopic classical world.

 

[Zarqon]

One major issue here is that for any object, macroscopic or otherwise, to be entangled, it has to be cooled close to it's ground state, such that the motion that comes from heat does not decohere the quantum state. In the case of the cat, the very brain functions that we would use to define the consciousness of the cat, is enough to cause decoherence, and one thus needs to cool below the limit where these occur.

Therefore I think one could never talk about the cat being conscious of it's own superposition, as a lack of consciousness seems to be a prerequisite for any object that is to be a part of a quantum state.

 

[Ken Natton]

The first point of reference with Schrödinger’s Cat is to understand that Schrödinger himself did not intend to create a philosophical monster that would leave Stephen Hawking reaching for his firearm. Schrödinger intended his thought experiment to highlight what he perceived as the absurdity of what is known as the Copenhagen Interpretation of quantum theory. But in point of fact, the thought experiment is useful in demonstrating the real point.

The second point of reference then, is to grasp that a great proportion of what is spoken about Schrödinger’s cat is pretentious nonsense, hence Mr Hawking’s eroding patience. A significant further proportion of the philosophising is perfectly earnest, but just as misguided. And the key thing is to realize that all of this is just philosophising, it is not science.

I am reading a book at the moment called ‘Quantum, A Guide for the Perplexed’, by Jim Al Khalili, a man who is beginning to emerge as one of the key conduits between cutting edge physical science and genuinely interested lay men and women such as myself. The book as a whole is a wonderful overview of exactly what is the source of some of the more challenging theories, such as the ’many worlds theory’. But he also includes an excellent demystification of Schrödinger’s cat. At risk of breaching copyright, I will mention that he suggests replacing the cat with a human being, and replacing the poisonous gas with some anaesthetic. The point not being sensibilities about killing a human being, the point being that the idea of a superposition of dead and alive is replaced by a superposition of being conscious and not conscious, and the key new element being, after the experiment is over, you can ask the experimental subject what happened. The point is, a bit like length contraction and time dilation being only relative to the stationary observer, the superposition only exists for the observer outside the box. As Al Khalili says, if we dig up some ancient rock and find a fault line caused by the release of an alpha particle when a radioactive nucleus decayed, the idea that that fault has existed in a superposition of having been there and not having been there until we dug it up and observed it is easy to dismiss. Clearly, at some point in geological history, the nucleus decayed, the alpha particle cut its fault trace, and it lay there unobserved until we dug it up.

 

[Hurkyl]

"The cat is alive" is a random true/false variable with some probability of being true and some probability of being false. (we don't have enough control of the environment to look at the experiment in another fashion)

We know the following true/false variables are true with near certainty:

• If the cat is alive, it knows its alive.
• If the cat is dead, it doesn't know it's dead.

(given, of course, the presumption that cats are self-aware, etc)

If the cat is in a superposition, that doesn't change anything.

• If we opened the box to see a live cat, then all future experiments we do will be consistent with that observation.
• If we opened the box to see a live cat, then all future experiments we do will be consistent with that observation.

These are also random variables that are true with near certainty. If the cat is in a superposition, that doesn't change anything.


It is an impossibility to observe multiple "branches" of a superposition. The experiments we do to measure superposition is not to directly confirm it, but prepare lots of identical experiments, and show the results could only be explained if there was a superposition involved.

Superpositions only seem weird when you don't realize there's a difference between what we, as hypothetical "godlike" observers with access to all of the mathematical details of a wave-function can see, versus what an observer stuck within the universe described by a wave-function is capable of seeing.

I.E. the cat is both dead and alive. No observer will see both. There is the hypothetical possibility of an incredibly complex (or unlikely) experiment whose results depend on the superposition -- but such an experiment will never see the cat as being both dead and alive: it will just be studying a different aspect of the problem that cannot be analyzed in terms of a dead branch and a living branch.

(Of course, in reality, collapse interpretations might turn out to be right and superpositions really don't propagate)

 

[GeorgCantor]

The double slit experiment done with fullerenes and the quantum eraser give support to the idea that there is no cat before you inquire about it, i.e. open the lid and look.

 

[BruceG]

One major issue here is that for any object, macroscopic or otherwise, to be entangled, it has to be cooled close to it's ground state, such that the motion that comes from heat does not decohere the quantum state. In the case of the cat, the very brain functions that we would use to define the consciousness of the cat, is enough to cause decoherence, and one thus needs to cool below the limit where these occur.

Therefore I think one could never talk about the cat being conscious of it's own superposition, as a lack of consciousness seems to be a prerequisite for any object that is to be a part of a quantum state.

I concur with this answer.
I was totally baffled by the cat problem for many years until I read about decoherence theory, then quantum theory all made sense to me.

The point is that if an entangled state of live-cat/dead-cat were ever to form, then on microscopic timescales it would immediately decohere into either a definite macroscopic dead cat or a definite macroscopic live cat. As such the language of macroscopic physics applies to the cat, and we can make an objective statement about the state of the cat.
It does not depend on subjective observation.

As such the question as posed does not apply.

 

[GeorgCantor]

I concur with this answer.
I was totally baffled by the cat problem for many years until I read about decoherence theory, then quantum theory all made sense to me.

If quantum theory makes sense to you, that's a very sure sign you still have a lot to learn. Or probably think and contemplate. Or a combination of both.

The point is that if an entangled state of live-cat/dead-cat were ever to form, then on microscopic timescales it would immediately decohere into either a definite macroscopic dead cat or a definite macroscopic live cat. As such the language of macroscopic physics applies to the cat, and we can make an objective statement about the state of the cat.
It does not depend on subjective observation.

As such the question as posed does not apply.

I'll cut right to the chase on this. There is no coming back to the old concepts of objects with properties in time and space, this is certain. We are in the mids of a paradigm shift and although it's not exactly clear how everything should fit in a coherent picture, it's clear how everything will NOT.

This common-sense view of reality that made sense to you is a total misconception.

Any time you use a concept that involves or implies the term "superposition", you aren't talking of objects with properties in time and space(which happen to be the picture of reality that you appear to have made sense of).

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. Anything that can be in superposition is not an object, it's an event, and there isn't anything in this 'universe' that cannot potentially be in superpositional state.

If you still think qt makes sense to you, you need to go back and re-think "the physical matter in superposition" issue. Today, tomorrow or in a month, when you have figured out what is really happeneing, you'll surely go down the drain into a blind alley from which nobody has escaped, as Feynman liked to say.

Realism, in the physics sense, is dead and so is the Newtonian universe of our perception. It's not to be made sense of, unless you are ready to believe the unbelievable.

 

[JoeDawg]

That seems like an absurdity.

The cat is either dead or asleep.

 

[BruceG]

If quantum theory makes sense to you, that's a very sure sign you still have a lot to learn. Or probably think and contemplate. Or a combination of both.

I'll cut right to the chase on this. There is no coming back to the old concepts of objects with properties in time and space, this is certain. We are in the mids of a paradigm shift and although it's not exactly clear how everything should fit in a coherent picture, it's clear how everything will NOT.

This common-sense view of reality that made sense to you is a total misconception.
...
Realism, in the physics sense, is dead and so is the Newtonian universe of our perception. It's not to be made sense of, unless you are ready to believe the unbelievable.

At the microscopic level I agree with you - quantum physics has revealed a form of reality totally remote from our intuitions. OK - I don't really 'understand' this - but I get how the maths works.

But we were talking about a macroscopic object (the cat). A necessary requirement of any interpretation of quantum mechanics is that it MUST recreate the "common-sense view of reality" at the macroscopic level with "objects with properties in time and space".

Decoherence theory seems to provide this missing link making quauntum theory more understandable. Feynman, for all his genius, was as far as I know unaware of this theory.

 

[GeorgCantor]

But we were talking about a macroscopic object (the cat). A necessary requirement of any interpretation of quantum mechanics is that it MUST recreate the "common-sense view of reality" at the macroscopic level with "objects with properties in time and space".

OK, but none of the interpretations do. We are used to thinking in terms of physical structues in space and time, whereas the whole notion of "physical structures" goes to trash assoon as you introduce superpositions. There are very obvious conceptual problems with the notions of space and time as well, and it will take nothing short of demolishing and re-bulding the entire 'universe' anew with wholly different basic constituents to restore the Newtonian universe of perception.

Decoherence theory seems to provide this missing link making quauntum theory more understandable. Feynman, for all his genius, was as far as I know unaware of this theory.

Only slightly more 'understandable', yes. Take a closer look and the common-sense reality is still not there, it's as far away as it can ever be. As i said earlier, "objects" that can be put in superpositions cannot be regarded as objects. They are registered events(detections).

 

[imiyakawa]

[on superpositions] A necessary requirement of any interpretation of quantum mechanics is that it MUST recreate the "common-sense view of reality" at the macroscopic level with "objects with properties in time and space".

Decoherence theory seems to provide this missing link making quauntum theory more understandable.

I've not read decoherence. In my short conversations with a physicist I asked what occurred during reduction to what seems to be discrete-state during measurement. He stated that what's occurring is the wavefunction is simply bunching up to a pointer like state during thermal interaction.

Doesn't this mean that there still isn't this nice, understandable point particle universe even at the large scale? And doesn't this fact actually support Georg's view of the conceptual confusion that should be here? Aren't there still large scale superpositions with decoherence, just not in the same way (at all) as a molecule may be superposed in near absolute zero temperature?

 

[JoeDawg]

demolishing and re-bulding the entire 'universe' anew with wholly different basic constituents to restore the Newtonian universe of perception.

Wow, you're such a drama queen. It means rebuilding the theory to include quantum weirdness and our everyday experience. That doesn't mean our everyday experience isn't real, or the way we describe it is no longer valid. This is what you call 'throwing out the baby with the bathwater'. A paradigm shift doesn't mean starting from scratch. It means... shifting to a different framework... changing some assumptions.

Gravity doesn't stop working just because we don't have a TOE.

QM can give us insights, but the Newtonian universe we experience isn't going anywhere, its just not the complete picture. In fact, what we experience is just as essential to understanding the complete picture.

And, Schrodinger's cat is an analogy, which means it can be useful, but is not definitive.

 

[GeorgCantor]

Wow, you're such a drama queen. It means rebuilding the theory to include quantum weirdness and our everyday experience. That doesn't mean our everyday experience isn't real, or the way we describe it is no longer valid. This is what you call 'throwing out the baby with the bathwater'. A paradigm shift doesn't mean starting from scratch. It means... shifting to a different framework... changing some assumptions.

If that theory is going to include physical structures with definite properties in space and time, that theory is going to be WRONG, as it won't be confirmed in experiments. As far as i am aware, there is no such theory in development, and there is no hint of motivation to pursue something that appears so patently absurd, given the experimental verification of qm and gr.

Your common-sense is generally the least reliable tool to understand reality, it's on par with the biblical account of creation, if not much worse(given that there are "common-sense" theories that the Earth is flat, or that the Sun orbits the Earth.)

Gravity doesn't stop working just because we don't have a TOE.

QM can give us insights, but the Newtonian universe we experience isn't going anywhere, its just not the complete picture. In fact, what we experience is just as essential to understanding the complete picture.

True, it isn't going anywhere, but the Newtonain picture of the universe is actually SPECTACULARLY WRONG, as long as we are talking about the God's veiw of the universe. Actually, the single most expensive and elaborate piece of equipment on Earth - the LHC - works because relativity is incorporated into it(very high speed and very high energies is not where relativity is simply visible, it's where relativistic effects are PREDOMINENT).

And, Schrodinger's cat is an analogy, which means it can be useful, but is not definitive.

You have not understood the cat analogy, and if you think i am a drama queen, you've hardly understood anything. The upcoming paradigm shift is not going to be about minor adjustments to current theories. But if you wish to believe you live in a Newtonian universe, so be it, there are people who believe in the flat Earth.

BTW, everybody is confused. Think about it.

A paradigm shift doesn't mean starting from scratch. It means... shifting to a different framework... changing some assumptions.

When you discard the realism assumption, it means starting from scratch. One of the hardest problems before string theorists(according to Greene and others) is to make ST background-independent and to account for the emergence of spacetime from ?.

Wow, you're such a drama queen. It means rebuilding the theory to include quantum weirdness and our everyday experience.

Would you want to "rebuild the theory" to also include yet another idea from our everyday experience - that the Earth is flat?

You can try here and browse the experimental evidence along with their Wiki and their newly opened flat-Earth shop:

http://theflatEarth'society.org/cms/


The 'drama part' or what might seem like strong wording is supposed to challenge those who believe in realism and objects with properties in space and time. I am genuinely curious what others have to say in defence of such a position.

 

[BruceG]

I've not read decoherence.

Doesn't this mean that there still isn't this nice, understandable point particle universe even at the large scale? And doesn't this fact actually support Georg's view of the conceptual confusion that should be here? Aren't there still large scale superpositions with decoherence, just not in the same way (at all) as a molecule may be superposed in near absolute zero temperature?

You seem to have grasped exacly the same issues out of decoherence as I have (despite claiming to not have read it!)

So yes, I think you, I and Georg can agree that decoherence makes things slightly better, but is still baffling.

This is as far as I got with it before I gave up:
- Decoherence does still leave superpositions at the macro-scale.
- The good news is though that you don't get the nasty coupling terms which makes quantum theory so weird (I rely on you understanding what I'm talking about here)
- What this does is make things look a bit more like standard statistical physics (there is a 50% chance the cat is alive, 50% chance the cat is dead -but then that is no different from any statistical physics when the inputs are unknown)
BUT
- we still need to try and make sense of where the macro-state which didn't happen went (ok so we later learn the cat is actually dead, so what of the live cat).
-it is so tempting at this point (and this is actually what I do to stay sane) to invoke the multi-universe interpretation : so I really believe another universe exists somewhere with a live cat (and then another me observing that and so on).
BUT
-I know I shouldn't : talk of such multiverses is metaphysical nonsense: how could I ever verify this. Popper would turn in his grave.

So that I where I leave it for other to enlighten someday.

 

[JoeDawg]

If that theory is going to include physical structures with definite properties in space and time, that theory is going to be WRONG, as it won't be confirmed in experiments.

You're missing the point. Newtonian mechanics describes the world enough for most people. Its not a common sense argument, its a utility argument.

as we are talking about the God's veiw of the universe.

Since when are we talking about god?? Or do you have a QM interpretation for gods?

Actually, the single most expensive and elaborate piece of equipment on Earth...

isn't useful if my car runs out of gas.

But if you wish to believe you live in a Newtonian universe, so be it, there are people who believe in the flat Earth.

Actually, it slopes down towards a lake where I live.

BTW, everybody is confused. Think about it.

Except you of course, you KNOW I'm wrong. Not that you have understood even a bit of what I said. You're too focused on being right.

When you discard the realism assumption, it means starting from scratch.

That's crap.

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

Scientific realism in classical (i.e. pre-quantum) physics has remained compatible with the naïve realism of everyday thinking on the whole; whereas it has proven impossible to find any consistent way to visualize the world underlying quantum theory in terms of our pictures in the everyday world. The general conclusion is that in quantum theory naïve realism, although necessary at the level of observations, fails at the microscopic level.

You're just an obsessive reductionist.

those who believe in realism and objects with properties in space and time.

Space and time are descriptive of observation, which means they are real enough. The fact observations on the quantum level require different descriptions should neither be surprising or problematic.

Even something as basic as atomic theory shows that everyday objects are not as they appear... that is... they are not 'solid' in the way people used to think of them. That doesn't mean they aren't solid in some fashion.

 

[GeorgCantor]

Even something as basic as atomic theory shows that everyday objects are not as they appear... that is... they are not 'solid' in the way people used to think of them. That doesn't mean they aren't solid in some fashion.

Yes, exactly. I don't deny that they seem solid in some fashion, it would have been ludicrious if i had. My point was about realism as defined in physics - that objects have definite properties at ALL times(the elements of reality as per the EPR argument). On the one hand we have much experimental evidence and a mathematical theorem that this is not the case(the cat is not always there), on the other hand we have common-sense and everyday experience that contradict this. It seems one has to leave one's sanity at the door, or make many new assumptions(though now is the least appropriate time for more controversial assumptions) - like the many world hypothesis, the ftl pilot-wave hypothesis(relativity theory wrong/incomplete), etc.

BTW, the God's view of the universe is the same as saying 'reality', as the term 'universe' is becoming increasingly misleading. Gotta love how there is always talk of 'reality' in the quantum physics forum and talk of 'universe' in the cosmology forum.

 

[JoeDawg]

Yes, exactly. I don't deny that they seem solid in some fashion, it would have been ludicrious if i had. My point was about realism as defined in physics - that objects have definite properties at ALL times(the elements of reality as per the EPR argument).

I think you are defining realism very narrowly.
Its philosophical history is much more complex.

and everyday experience that contradict this.

Which means our understanding of QM and everyday experience, and how they relate is lacking. Not that one obliterates the other.

When our understanding of matter shifted from particles to wave/particles, it didn't mean that describing matter as particles was no longer useful, it just means the some assumptions changed and our understanding became broader.

BTW, the God's view of the universe is the same as saying 'reality', as the term 'universe' is becoming increasingly misleading.

Again, 'reality' is another word loaded with history. Idealism and phenomenology have been around for quite a while. QM is really just part of an ongoing discussion.

Gotta love how there is always talk of 'reality' in the quantum physics forum and talk of 'universe' in the cosmology forum.

Its a paradigm shift, it happens often when you move from one science... one scientific framework... to another. Or really any field of study... to another.

 

[imiyakawa]

On the one hand we have much experimental evidence ... on the other hand we have common-sense and everyday experience that contradict this.

I don't see how everyday experience contradicts a viewpoint such as decoherence. The electric force of much of macro interaction is still there, i.e. the table is still "solid". Things are still hard (hand can't pass through them because of charge repulsion). The brain should still work as it is for practical purposes not structurally altered by not being composed of pure point particles. So the macro world's hardness and solidity isn't a problem under decoherence.

IF we look to decoherence,
-I see and recognize the conceptual block posed by QM (constant superpositions).
-I don't see the difficulty of macro hardness or the illusion of atomism arising from the perspective of the extremely large.

 

[GeorgCantor]

I don't see how everyday experience contradicts a viewpoint such as decoherence. The electric force of much of macro interaction is still there, i.e. the table is still "solid". Things are still hard (hand can't pass through them because of charge repulsion). The brain should still work as it is for practical purposes not structurally altered by not being composed of pure point particles. So the macro world's hardness and solidity isn't a problem under decoherence.

IF we look to decoherence,
-I see and recognize the conceptual block posed by QM (constant superpositions).
-I don't see the difficulty of macro hardness or the illusion of atomism arising from the perspective of the extremely large.

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.

Superpositions are an established experimental fact, there is no question about it. The remaining question is the realism that Einstein liked to believe in. The one that we now have solid evidence to be a misconception.

So the macro world's hardness and solidity isn't a problem under decoherence.

You miss the point. Coherent and decoherent wave structures mean essentially - object/not-object, physical structure/non-physical structure, probable-actual, there--not-there, cat--non-cat, c60--no c60, matter--non matter.

Decoherence actually provide evidence that there are no physical structures in space and time, i.e. Einstein's idea of realism is wrong and hence matter(physical structures) are actually events, not objects with properties.

Outside decoherence, say the double slit experiment, you have fullerenes(physical structures) and de-localized wave-like entities(non-fullerenes).


You can't have a transistor made without superpositions, and although certainly useful, they do destroy the realism of perception. I would say that superpositions invite total insanity if you really give it much thought. The whole notion of physical structure is a misnomer and we need a considerable adjustment on the way we view reality.

I don't see how everyday experience contradicts a viewpoint such as decoherence.

Am i the only one that perceives a world of objects that there all the time, and that cannot magically vanish under certain circumstances, losing all their defining characteristics?

If you take relativity and superpositions seriously, you can only conclude that Einstein's realism is completely dead.

 

[GeorgCantor]

When our understanding of matter shifted from particles to wave/particles, it didn't mean that describing matter as particles was no longer useful, it just means the some assumptions changed and our understanding became broader.

The notion of "partciles" is a misnomer, particles that are not spatially extended cannot be spatially represented, except as a probability cloud. We basically don't know what we are talking about, as matter has dissolved into a ghostly substance. It's not that now "our understanding became broader" as you say, we basically have no understanding of what matter really is(and it's quite worthy of making a drama on it since we can no longer answer a simple question like "what the hell is really going on?").

 

[JoeDawg]

Am i the only one that perceives a world of objects that there all the time, and that cannot magically vanish under certain circumstances, losing all their defining characteristics?

But it is not magic. Newton didn't understand gravity, he just described it, and he was criticized for his claims of 'action at a distance'. It made no sense, until Einstein.

The fact that QM seems insane and magical to you doesn't mean that it, in fact, is. It just means you (most everyone I'd say) don't understand it.

http://en.wikipedia.org/wiki/Argume...ent_from_incredulity_.2F_Lack_of_imagination"

Changing the word from object to event may change the theory behind it, but it hardly makes objects disappear. It just more clearly defines what they are, or rather what they do.

Describing objects in Newtonian terms is valid, because its useful, even if its not complete or definitive.

 

[imiyakawa]

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.

It blows my mind as well.

It doesn't blow my mind as to why I have the illusion of atomism and point particles on the large scale. Decoherence explains that extremely nicely.

You miss the point. Coherent and decoherent wave structures mean essentially - object/not-object, physical structure/non-physical structure, probable-actual, there--not-there, cat--non-cat, c60--no c60, matter--non matter.

Decoherence actually provide evidence that there are no physical structures in space and time, i.e. Einstein's idea of realism is wrong and hence matter(physical structures) are actually events, not objects with properties.

You quoted me:
"So the macro world's (perceived) hardness and solidity isn't a problem under decoherence."

You said I've missed the point. Have I? I clearly stated that superpositions are a huge conceptual issue. My only assertion that you quoted was that the emergence of the macro world as we perceive it is not a problem - one can easily see how the feeling of hardness, fullness, definiteness arises.

And I wouldn't say (without great care) that decoherence "provides evidence that there aren't physical structures". It depends on how you define a physical structure.

 

[GeorgCantor]

And I wouldn't say (without great care) that decoherence "provides evidence that there aren't physical structures". It depends on how you define a physical structure.

I define 'physical structure' as in the physics sense -- the specific arrangment of constituent parts, that has observable attrubutes like Size, Mass, Position, Momentum and forces holding the structure together. Example:


http://img375.imageshack.us/img375/97/colorbuckyball.jpg

Uploaded with ImageShack.us




Example of superposition of states(unobservable by definition):



















A physical structure that does not retain its physical defining characteristics at all times cannot unambiguously be regarded as a physical structure. The only definition that is not misleading is to call it 'event', isn't it?

You said I've missed the point. Have I? I clearly stated that superpositions are a huge conceptual issue. My only assertion that you quoted was that the emergence of the macro world as we perceive it is not a problem - one can easily see how the feeling of hardness, fullness, definiteness arises.

Okay, but it's not very obvious, as the exact underlying mechanism is still not there, but it's easier on the brain, than say a wave that sends signals ftl and directs particles(and fewer assumptions seem to be made).

 

[ZapperZ]

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.

Can you make an exact citation where decoherence claims such a thing, i.e. it doesn't say that matter are "there all the time with properties in space"?

You miss the point. Coherent and decoherent wave structures mean essentially - object/not-object, physical structure/non-physical structure, probable-actual, there--not-there, cat--non-cat, c60--no c60, matter--non matter.

Er... what exactly do you mean by "coherent" and "decoherent" here? This is not how it is defined in physics.

Zz.

 

[imiyakawa]

I define 'physical structure' as in the physics sense -- the specific arrangment of constituent parts, that has observable attrubutes like Size, Mass, Position, Momentum and forces holding the structure together.

Ok yes by that definition you are 100% correct.

A physical structure that does not retain its physical defining characteristics at all times cannot unambiguously be regarded as a physical structure. The only definition that is not misleading is to call it 'event', isn't it?

I suppose, if you wish to be technically correct and you adhere to the definition of a physical structure that you adhere to.

Okay, but it's not very obvious, as the exact underlying mechanism is still not there, but it's easier on the brain, than say a wave that sends signals ftl and directs particles(and fewer assumptions seem to be made).

My only claim was that the feeling of objects as definite, hard and "solid" things is not difficult to envisage as arising from decoherence. If you push your hand onto the table, nothing in decoherence predicts anything other than an electric repulsion that your brain perceives as hardness. The macro world, as we perceive it, is supposed to be perceived that way. It's what one expects from decoherence.

I share your views on superpositions, coupling, etc.

 

[GeorgCantor]

Can you make an exact citation where decoherence claims such a thing, i.e. it doesn't say that matter are "there all the time with properties in space"?

"Quantum superposition refers to the quantum mechanical property which states that all particles exist in not one state but all possible states at once. Due to this property, to completely describe a particle one must include a description of every possible state and the probability of the particle being in that state."


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





Matter(c60 molecules) causing interference pattern due to superposition of states:



"Recent studies have revealed that interference is not restricted solely to elementary particles such as protons, neutrons, and electrons. Specifically, it has been shown that large molecular structures like fullerene (C60) also produce interference patterns."


http://en.wikipedia.org/wiki/Double-slit_experiment





"Collisional decoherence observed in matter wave interferometry"


http://www.ncbi.nlm.nih.gov/pubmed/12731960




How is an object in superposition an object? That's what i said in the the text you quoted. Do you consider probability clouds to be objects?[/quote]

Er... what exactly do you mean by "coherent" and "decoherent" here? This is not how it is defined in physics.

Zz.

Gradual loss of quantum interference.

 

[ZapperZ]

"Quantum superposition refers to the quantum mechanical property which states that all particles exist in not one state but all possible states at once. Due to this property, to completely describe a particle one must include a description of every possible state and the probability of the particle being in that state."http://en.wikipedia.org/wiki/Quantum_superpositionMatter(c60 molecules) causing interference pattern due to superposition of states:
"Recent studies have revealed that interference is not restricted solely to elementary particles such as protons, neutrons, and electrons. Specifically, it has been shown that large molecular structures like fullerene (C60) also produce interference patterns."http://en.wikipedia.org/wiki/Double-slit_experiment"Collisional decoherence observed in matter wave interferometry"http://www.ncbi.nlm.nih.gov/pubmed/12731960

You've just given me a lesson on what I already know (I am a physicist). I need the exact source where decoherence says what you claimed it says. Decoherence is NOT superposition, even though superposition plays a role. All you've given me are stuff about superposition, which is not what I asked for.

Gradual loss of quantum interference.

And whose definition is this? Yours? It certainly isn't from physics/mathematics. If this is what you are using, but basing you continue to link it to physics papers and phenomena, then you are mixing things and changing the definition on the fly. This is not kosher.

Zz.

 

[GeorgCantor]

You've just given me a lesson on what I already know (I am a physicist). I need the exact source where decoherence says what you claimed it says. Decoherence is NOT superposition, even though superposition plays a role. All you've given me are stuff about superposition, which is not what I asked for.

In the strict sense, decoherence is about transitioning from pure, coherent superpositional states to mixed states due to interaction with the environement. The issue i raised was more based towards the nature of superpositions(and what they say about matter), than the mechanism underlying decoherence.

I asked a question that you didn't see?/address in my previous post:

How is an object in superposition an object? That's what i said in the the text you quoted. Do you consider probability clouds to be objects?

 

[ZapperZ]

In the strict sense, decoherence is about transitioning from pure, coherent superpositional states to mixed states due to interaction with the environement. The issue i raised was more based towards the nature of superpositions(and what they say about matter), than the mechanism underlying decoherence.

So how does this ties in with YOUR interpretation that I questioned? You still haven't given me a proper citation to any sources that support such a statement. Do you need a reminder of what I was asking for?

I asked a question that you didn't see?/address in my previous post:

I didn't address it because I didn't make such a point. I didn't realize that I had to defend something that I never said. You are confusing the fact that it was you who made definitive statements about certain things. That is why I wanted to know what possible sources you could have used to arrive at such a conclusion, which, based on my understanding, is incorrect.

Zz.

 

[GeorgCantor]

So how does this ties in with YOUR interpretation that I questioned? You still haven't given me a proper citation to any sources that support such a statement. Do you need a reminder of what I was asking for?

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):

"Any time you use a concept that involves or implies the term "superposition", you aren't talking of objects with properties in time and space(which happen to be the picture of reality that you appear to have made sense of).

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. Anything that can be in superposition is not an object, it's an event, and there isn't anything in this 'universe' that cannot potentially be in superpositional state."

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.

 

[imiyakawa]

What i said in response to the assertion that decoherence restores quantum theory to a theory that makes sense is

I didn't assert this, but anyways, carry on. :)

 

[GeorgCantor]

I didn't assert this, but anyways, carry on. :)

No, that wasn't you. That was BruceG:

I was totally baffled by the cat problem for many years until I read about decoherence theory, then quantum theory all made sense to me.

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, how mass/energy is conserved(it isn't in superpositions), how a decohered cat is somehow an object existing in space and time. The underlying mechanism behind decoherence isn't there yet.

The whole notion of objects, cats and so on, existing in space and time with definite properties in completely untenable and Zz knows this quite well. He's picking on definitions and semantics, which i am obviously not good at(English is not my native language).