How can Schrödinger's Cat be both alive and dead?

[bhobba]

Since in the thought experiment we cannot look into the box then unless we can demonstrate that generally a wave function can collapse without a measurement taking place we simply must assume the cat is in superposition.

Its not. Long before the vial breaks etc decoherence occurs (evidently a few stray photons or even a single oxygen atom is enough to cause decoherence) and the particle is in an improper mixed state. It is perfectly legitimate to assume the improper mixed state is an actual mixed state meaning the particle really is there prior to detection by the particle detector. That's when the observation occurs - not when the box is opened. Most definitely the cat is not in some weird state of superposition - the particle prior to decoherence - yes - but that occurs very very quickly. All you have to do is assume the improper mixed state is an actual mixed state - no mathematical analysis or observation can prove you wrong and all this weirdness goes away. Other ways to resolve it are via Many Worlds and Decoherent Histories - but to me the easiest and simplest solution is this simple interpretation of decoherence. Why anyone want's to maintain the cat is in some weird state of superposition is beyond me.

Thanks
Bill

 

[bhobba]

First: What about the cat? Isn't it an observer?

Yea - but if its dead it can't really observe anything. However important semantic issue. We have observations in QM which semantically makes people think you must have an observer - in fact in QM an observation is anything that registers in the macro world. The particle detector is where that occurs first and is the observation that collapses the wavefunction - but with decoherence taken into account it is perfectly legitimate to assume, since decoherence would have occurred well before being detected by the particle detector, the particle was there prior to observation. In interpretations that use decoherence that's when the observation occurs and decoherence occurs very very quickly. The exception is Many Worlds when the mixed state of decoherence continues evolving regardless.

Thanks
Bill

 

[bhobba]

So it is clear, at least to me, that size isn't the issue, but rather the ability to have every part of that object in coherence is the most significant obstacle to observing quantum effects at large scales.

Very true - or at least its clear to me as well.

But for a live and dead cat in our normal macro environment as envisioned in this experiment they do not interfere - decoherence is well and truly in force in that situation - and just as an aside it is actually quite hard to show superposition effects for macro objects - but as you point out - correctly - it can be done. At any time the cat is alive or dead (ignoring of course the time it takes the cat to die via the gas) not in some superposition. The 'measurement' and 'collapse' in this thought experiment occurs at the particle detector - not the cat. Thats where the 'weirdness' lies.

Thanks
Bill

 

[1977ub]

Quantum Suicide & Immortality
http://en.wikipedia.org/wiki/Quantum_suicide_and_immortality

 

[Crazymechanic]

As to Zapper for your last post I agree and actually this is the way police has been chasing killers and suspects for many decades , they never try to interfere with the criminal rather they measure what his actions are and stay under the radar so that he wouldn't understand that his being chased.And this all just for the sake of getting enough evidence.
The scientists too try to preserve the original state of things so that they could see the outcomes without disturbing the "main element"

But I would have to argue that it is actually not superposition in the way we want to see it.Now you said that by measuring A you don't have to necessarily destroy B or collapse B wave function.
Ok I can agree to that but just because you haven't interfered with a state that doesn't mean the state hasn't got some properties already to it.AKA just because we haven't or can't see in the "box" without destroying it 's state of things doesn't mean that the state has all the possible outcomes at once.
i think rather QM is like a tiger in the jungle , he lives his own life and nobody knows what is he doing or where he is, now we can search for some indirect clues and judge by those the life of the tiger and his eating and living standards or we can directly approach him and disturb his natural "wave function" and measure a result , either way he has had his own life even when we were not around and now when we are around he just is in a certain given situation and chooses a certain given action and as with tigers so they say with bees you never know what they will do so unless you "measure" you can't be sure of the state their in.

Also I don't like when they say that upon measurement the system has to choose a state to be in but I find that kinda stupid , the atom or system or whatever you call it doesn't have to choose or think or whatever we say it does it just is in a certain state all the time and upon measurement there is a great chance that some interaction can or will occur and it will now be in a different state and that will be the final state that will show the measurement outcome.
The atom or elementary particles are not some self aware things (to our best understanding) that can choose.

Now ok theoretically let's assume we could put objects of billions of atoms in superposition under some extremely tight conditions at laboratory at near absolute zero temperatures now the meaning dead or alive would loose it's meaning because who has seen a living organism able to stay alive at temperatures when particles themselves almoust "freeze" ? :D
And we wouldn't say the state of dead or alive to a copper wire or a old tv set would we?
So to make the experiment is impossible even if we could achieve the right conditions under them the cat would die even before the atom would have ever got the chance to decay.

Now pardon me if I am wrong but currents passing around a loop at almoust absolute zero temperatures is not that perfect of a cat in a box proof it's rather a proof that if you can put particles and atoms in tightly controlled conditions then you can make them stay in a certain state but they are still one state at the time not in all possible sates at once right? Right.

 

[ZapperZ]

Crazymechanic: you are contradicting the content of several published papers that I cited. I suggest you submit a rebuttal to those papers and get them published first, or else what you are trying to do is considered unpublished speculation.

Zz.

 

[DrChinese]

...

But I would have to argue that it is actually not superposition in the way we want to see it.Now you said that by measuring A you don't have to necessarily destroy B or collapse B wave function.
Ok I can agree to that but just because you haven't interfered with a state that doesn't mean the state hasn't got some properties already to it.AKA just because we haven't or can't see in the "box" without destroying it 's state of things doesn't mean that the state has all the possible outcomes at once.

i think rather QM is like a tiger in the jungle , he lives his own life and nobody knows what is he doing or where he is, now we can search for some indirect clues and judge by those the life of the tiger and his eating and living standards or we can directly approach him and disturb his natural "wave function" and measure a result , either way he has had his own life even when we were not around and now when we are around he just is in a certain given situation and chooses a certain given action and as with tigers so they say with bees you never know what they will do so unless you "measure" you can't be sure of the state their in.

...

If you look at your reasoning carefully, you are actually assuming that which you are trying to prove. On the other hand, every single piece of experimental evidence points in the opposite direction.

 

[Crazymechanic]

Hmm okay fair critique, i re read my post one more time as I was writing in the morning a little sleepy but yet I can't find where is all the wrong things that I have said ??

@DrChinese now isn't every one even those who go out and publish a theory assuming what they prove? We all have somekind of a natural bias towards some opinion (not speaking about crackpots here ) all reasonable people do have some assumptions based on some either proven or very likely to happen logic.
Now quantum mechanics so happens to be one of the subfields in physics that is very tied up with assumptions and philosophy actually.because as other forum members before me on this thread pointed out and quit rightly that there are a lot of things we put forward without empirical evidence , sometimes we get the evidence after decades sometimes there is a great chance for us to never get it due to physical laws or the way nature works.

Now call me crazy (which I am actually) but the only thing in my post I could find that would be the object of ZapperZ and DrChinese objection is the fact that I stated that I "believe" that quantum states exist before we even look at them and take a measurement, rather the measurement only collapses the state in which they were and a new one emerges due to the measurement being an interaction in QM.
Now what is so contradicting there ?

 

[DrChinese]

... @DrChinese now isn't every one even those who go out and publish a theory assuming what they prove? ...

No, of course not. And certainly any working assumptions one makes is not an argument in its favor. And throwing out only the evidence that works against your assumption is the first step of a crackpot. You have been around here enough to know that experimental results are given a great deal of weight.

 

[Nugatory]

I "believe" that quantum states exist before we even look at them and take a measurement, rather the measurement only collapses the state in which they were and a new one emerges due to the measurement being an interaction in QM.
Now what is so contradicting there ?

That was at one time a quite respectable position; seeing as how it was at one time Einstein's position, you're in good company .

But would you continue to maintain this position after we've done experiments that yield results that cannot be produced by ANY state that exists before the measurement? The Bell experiments are getting pretty damned convincing these days.

 

[Crazymechanic]

Well yes I do believe empirical evidence is the backbone of physics , ok I guess I'll take another look on the recent papers both linked in this thread or in other sources.As I am not the top person that follows everything quantum mechanical rather the basic rules and the logic or common sense as much as there is any in the case of QM.

So just in case the "up to date" conclusion about the cat in he box or any other state of superposition is that basically the observer made collapse of the system at a given point is also the moment when the system takes a certain shape aka state and before that not only we have no way of knowing what is happening in the "box" but there is a great chance that maybe there is no result in the box and the result become instant and defined in the very moment when there is an observer around to witness ?

 

[Nugatory]

So just in case the "up to date" conclusion about the cat in he box or any other state of superposition is that basically the observer made collapse of the system at a given point is also the moment when the system takes a certain shape aka state and before that not only we have no way of knowing what is happening in the "box" but there is a great chance that maybe there is no result in the box and the result become instant and defined in the very moment when there is an observer around to witness ?

The observer is not needed; the superposition goes away when it interacts with the larger environment around it, as it would with just about any measurement or interaction with any measuring apparatus.

Worth remembering about the Schrodinger's cat thought experiment: Schrodinger invented it as a criticism of the then-standard interpretation of QM. The point of the cat in the box is that something had to be wrong with the way that QM introduced this boundary between the macroscopic/classical world and the microscopic/quantum world.

 

[Crazymechanic]

Well I wasn't actually thinking about the observer as somebody specific , I do know that in QM an observer to collapse a state can be pretty much any interaction that the particle or atom or system encounters in it's way.

But this semantic doesn't change the main though of my previous question which with all respect you didn't answer.

I know the superposition goes away under interaction just as you get dressed whenever you get out on street but the question was is there a state before the collapse before the small subsystems encounters the larger one or so?
is there a chance that a quantum system is at a certain state before it ever encounters something in it's way I do know that there is zero chance of us ever knowing if it had some state prior to the one we measured upon interaction because superposition is basically telling that before the measurement the system can be in either one of the possible states which I objected to as saying that how can something be in many states at once , that was the one of main arguments about this thread in general it was also what I asked and assumed and said and it was also the thing about which ZapperZ and Dr Chinese made me some critique.
@DrChinese well empirical evidence do play a huge role so is there any real physical evidence for superposition other than the mathematical outcomes we get when solving equations in a theory we made about quantum mechanics that is just like most of the physics theories almoust or partly right.
Now I'm not trying to deny basic physics or being a crackpot rather just squeezing the last juice out of this thread to put it to rest

Now I would be honored to hear some opinion from these fellow members also from you Nugatory. :)

 

[BruceW]

What do you mean by "is in a state before collapse" ? Do you mean like (for example) an electron in orbit around the hydrogen having a specific position, even though the position has not been measured? This is a 'hidden variable theory'. And there is nothing wrong with it per se. But as others have probably already said, hidden variable theories are not favoured because many consider them to be a very not useful way to interpret quantum mechanics. And also, some hidden variable theories actually make different predictions to quantum mechanics. But there are hidden variable theories which make the same predictions as standard quantum mechanics (and are therefore an 'interpretation' of quantum mechanics, really).

edit: this is my understanding of it anyway. I was never taught about the interpretations of quantum mechanics, only how to apply it to basic problems. So I am not 100% sure about the definitions of various interpretations.

 

[bhobba]

So just in case the "up to date" conclusion about the cat in he box or any other state of superposition is that basically the observer made collapse of the system at a given point is also the moment when the system takes a certain shape aka state and before that not only we have no way of knowing what is happening in the "box" but there is a great chance that maybe there is no result in the box and the result become instant and defined in the very moment when there is an observer around to witness ?

The 'up to date' conclusion of how an observation causes collapse, or even if it occurs at all, is entirely interpretation dependant. The least favored one these days is that an observer caused it or was required to be around to witness it - it for example makes a mockery of computer science and the objective existence of information in a computer system if taken to an extreme. The last great holdout to that view was probably Wigner but even he changed his mind when he heard about some early work on decoherence by Zurek. The modern champion of it is Hameroff and Penrose:
http://www.quantumconsciousness.org/index.html

But it is very much a minority view.

Thanks
Bill

 

[bhobba]

What do you mean by "is in a state before collapse" ?

I think he means the discontinuous change in state caused by observation.

I was never taught about the interpretations of quantum mechanics, only how to apply it to basic problems. So I am not 100% sure about the definitions of various interpretations.

Probably a wise move of those that designed the courses you learned it from or the books you chose if self taught like me.

The usual issue with interpretation is how to overcome some of the weirdness of the formalism such as between observations the state changes continuously and deterministically but when an observation occurs it changes randomly and discontinuously. The other issue is what Kochen-Specker tells us. It basically means, without other factors taken into account, such as decoherence, the outcome of an observation can't be there prior to observation. Of modern times, while not solving the previous issues to everyone's satisfaction, decoherence has shed a lot of light on it and research is ongoing.

My suggestion to those interested in, or simply want to investigate interpretations, is to get Decoherence and the Quantum-to-Classical Transition by Maximilian Schlosshauer:
https://www.amazon.com/dp/B000SJ155C/?tag=pfamazon01-20

It isn't a book about interpretations per-se but it does examine them quite well in the light of decoherence. And even aside from its application to interpretations its a very interesting area anyway. I have a copy and along with Ballentines book - QM - A Modern Development made a big impact on my understanding of what's going on in QM.

Thanks
Bill

 

[Crazymechanic]

pretty close with your post Bruce.
Well I guess hidden variables or not they are favoured or dismissed rather based on how they work out in terms of equations than what seems logic or not.
just like any other physics theory he language is math.
Actually in QM we have limited capabilities of "seeing" what's going on so I guess we have to rely on math heavily.
it just so happens to be that math is not my best friend around and I rather make my assumptions based on the opinions of people "who know things" or the insiders and my personal common sense and some philosophy.
Well @bhobba the fact that upon measurement the state changes unpredictably is not a problem because the fact that every measurement is also an interaction in QM is fine.It also follow the logic based on what we have seen.The problem as always is with the things we haven't or can't directly or indirectly see or tell.This is the place where people go like "hey opinions" and as in every place some consider their opinion better and etc etc.
So how we find out what happens at the states before measurement I guess we haven't , we just made an opinion and some math and found that happy and good.
Actually I don't care for a certain opinion in QM is not like having a debate about your wifes cooking level.
I just want the truth and if the truth is that we yet don't know then let it be.

@ZapperZ the link you gave """http://physicsworld.com/cws/article/news/2010/mar/18/quantum-effect-spotted-in-a-visible-object"""
it is said there that quote """the team measured the quantum state of the resonator by connecting it electrically to a superconducting quantum bit or "qubit" --connecting it electrically is the key point here I guess.

So basically what they did is they made a supersmall tuning fork with the right materials that would have great qm properties at temperatures almoust absolute zero to see quantum properties undisturbed by any thermal action no mater how small.
But isn't the qubit that is connected electrically even though superconducting at such temperatures isn't the measurement still a state collapse? because even if the temperatures are good to not have any disturbance from outside the qubit itself is the observer in this case.
So how did they came to conclude that the resonator has a excitation and hasn't one at the same time ,I guess they first measured the qubit and it showed no excitation and then measured it again and it showed an excitation probably from some kind of a interaction with the qubit's own electrical impulse or whatever is there so isn't this still just measuring one object at different states but not both in the same time?

Pardon me if I am wrong but this sounds like seeing one is sleeping then coming again in the same way but accidentally making a little noise somewhere on the floor that I;'m not even aware of but which wakes the person up and now I see him awake , and after ten minutes maybe he would fall asleep again.The interaction is always there but without it I would not know if he is asleep or awake.
Ok please comment if you find it worthwhile P.S. Even though philosophy is forbidden on PF it is kinda funny to see that the QM section is one of the sections here where thread end up from some maths to pure philosophy , I think there is a good reason why...
I have seen many long threads here like that some of them even copied out because they were too long to read.

 

[jambaugh]

One problem is in the phrase "superposition of states". Quantum superposition reflects the resolution of a given "state" in a specific basis ("of states"). The "presence" of superposition is in the relationship between the observed system mode and the choice one makes of basis. You can always pick your basis so that there is no superposition. It is like choosing principle axes for the moment of inertia tensor so it becomes diagonal or more aptly resolving a general motion as a "superposition" of horizontal and vertical motions when we resolve a displacement vector in a given basis.

In short don't inadvertently think that "being in a superposition" is a physical property of either the Cat or of an atom. Superpositions arise specifically as a relationship between measurement devices. (e.g. the device measuring position of a particle and the device measuring momentum of a particle.) Superposition then arises when we try to reconcile facts observed from one device with predictions about what will be observed by a complementary device. A definite outcome of one resolves as a superposition of outcomes for the other. Nowhere in that is the system itself in some "weird superposition".

State vectors represent states of knowledge about the system not states of the system! (Orthodox Interpretation.)

 

[f95toli]

In short don't inadvertently think that "being in a superposition" is a physical property of either the Cat or of an atom. Superpositions arise specifically as a relationship between measurement devices. (e.g. the device measuring position of a particle and the device measuring momentum of a particle.)

I sort of agree with this. However, there are plenty of cases where it is -in my view- quite clear what the states that are in a superposition correspond to classically.
An obvious example would be a flux qubit, where the two states correspond to a current flowing clockwise or anti-clockwise.
Another example would be the orignal solid state qubit which was a charge qubit, here the two states correspond to 0 or 1 extra electrons on a mesoscopic island. There are many other cases, mostly from solid state QIP.

The reason or why these examples are -in my view- much more illuminating than examples from atomic physics or optics, is that the states that are put into a superposition also exist classically (if you want your qubit to become a classical system you can just warm it up a bit), whereas there is no such thing as a classical atom or photon.

Hence, any explanation that tries to avoid "quantum weirdness" for solid state QIP devices becomes pretty convoluted.

 

[jambaugh]

I sort of agree with this. However, there are plenty of cases where it is -in my view- quite clear what the states that are in a superposition correspond to classically.
An obvious example would be a flux qubit, where the two states correspond to a current flowing clockwise or anti-clockwise.
Another example [...]

The reason or why these examples are -in my view- much more illuminating than examples from atomic physics or optics, is that the states that are put into a superposition also exist classically (if you want your qubit to become a classical system you can just warm it up a bit), whereas there is no such thing as a classical atom or photon.

Hence, any explanation that tries to avoid "quantum weirdness" for solid state QIP devices becomes pretty convoluted.

I'm not sure I see the issue. Again "in a superposition" is just relative to choice of observables.
A definite spin z-up electron, which we can quite clearly understand in terms of the classical analogue of a rotating mass, is also in a superposition of spin x-"up" and spin-x "down" states. Saying it is "in superposition" or "not" is simply a question of which component is being classically analogized.

Secondly the "quantum weirdness" is imnsho not to be avoided but understood. And that understanding starts with not thinking of "being in a superposition" as if it were some system switch we can turn on or off. I think too many people working in quantum information get caught up in that point. Clearly in a classical computer one wants to be very conscious of the state of the state machine. But that is just the wrong way to think in QM and hence in quantum computing. It is, I think, better to use a communications channel paradigm rather than state machine when invoking e.g. qubits. (The spin of) An electron can be though of as a binary channel able to encode a classical bit in one of a continuum of ways. The quantum comes into play when one is writing in one basis and reading in a different one... and even more fun playing with many qubits which can not only be encoded in many ways but factored into components in many different ways hence we get entanglement phenomena.

 

[BruceW]

I'm not sure I see the issue. Again "in a superposition" is just relative to choice of observables.
A definite spin z-up electron, which we can quite clearly understand in terms of the classical analogue of a rotating mass, is also in a superposition of spin x-"up" and spin-x "down" states. Saying it is "in superposition" or "not" is simply a question of which component is being classically analogized.

Yes, so in this sense, the electron would be in a superposition of x-spin eigenstates. And also, the electron is in a single z eigenstate. What is wrong with these statements? It seems arbitrary to me to separate "state of knowledge of the system" and "state of the system". Why separate these two concepts? They are identical to me.

 

[BruceW]

analogously, vectors are used to describe the electric field. I can say the components of the electric field with respect to some basis are some values. And with respect to another basis, they are some other values. The physical situation can be described by either choice of coordinates, or any other choice.

Edit: I think I see your viewpoint though. In this analogy, would you say the only 'real' thing is the abstract vector (without reference to any basis)?

 

[capcom1983]

There is no cat if it isn't observed it doesn't exist. I love that (it also explains why I'm still 21). The point of this thought experiment is to remove observer with a result that is unknown and immeasurable. I prefer einsteins version with the bomb not poison. If you use a ka atom with a half life of 1600 years (and the cat amazingly lives that long) you still can't say that the atom decayed. So the cat would still be alive (old). Then when you look in the box this could cause the decay thus blowing up the cat.

 

[Omega0]

Edit: I think I see your viewpoint though. In this analogy, would you say the only 'real' thing is the abstract vector (without reference to any basis)?

I guess you got it. It does not matter if we speak about a "z-state". Once again this is just human thinking "oh, okay z-axis directed to heaven". That's it. Look at the description of the state of an electron. It is |UP> or |DOWN>. It's just naming. You can call it |fish> and |lemon>, it is the same, just convention. I believe it is wise to not call the spin of an electron "left" and "right" in the same sense (nevertheless I would say fish an lemon would be better for spin because then you don't get the idea that is has something to do with up and down)-

 

[jambaugh]

Yes, so in this sense, the electron would be in a superposition of x-spin eigenstates. And also, the electron is in a single z eigenstate. What is wrong with these statements? It seems arbitrary to me to separate "state of knowledge of the system" and "state of the system". Why separate these two concepts? They are identical to me.

Yes, I understand and vehemently disagree. The principle point is that what we know about e.g. an electron is how it will behave, its "actuality" not the "reality" of how it "is".

Objective state is to QM as the aether was to SR. Its exactly the excising of this component that "makes" the theory and advance. (And like the aether based SR equivalents you see popping up all the time on this forum you have the objective state based QM equivalents in the form of Many Worlds and Bohm's demonic pilot waves.)

Now just as you can do relativistic physics, carrying out Lorentz transformations properly while believing in an aether, you can likewise do quantum physics while believing the state vector you write down somehow is a representation of the state of reality of the quantum system. But at some points the very existence of these, aether and "state of reality" are articles of faith which cannot be directly known. You know system behavior through devices.

We define time by when a clock goes tick and we define an electron by when an electron detector goes click.

While the post modernists want to vanquish positivism, it is the appropriate paradigm for defining and carrying out science and most especially quantum physics.

 

[BruceW]

I think I see what you mean. In an ideal world, we would never mention the components of the state vector with respect to a basis. And it is only because we relate our theories to actual measurements, that it is useful to talk about the components.

I don't really see the connection to the aether/SR. I'm guessing you mean that when everything could be explained without the aether, then there is no longer a need to hold on to that concept. But this is not analogous to "component representation"/quantum theory because component representation is still useful to us, even though not really a necessary part of the theory. aether theory was no longer useful when SR became fully developed.

Or maybe you mean that QM has not fully developed yet, and when it does, the "component representation" will no longer be useful??!

 

[Crazymechanic]

@jambaugh according to how much I know myself and how much my logic tells me I agree to what you say mostly.This is also one of the things I questioned here before and some people have not yet responded to that.

@BruceW """ "It seems arbitrary to me to separate "state of knowledge of the system" and "state of the system". Why separate these two concepts? They are identical to me."""

Bruce this is where i think it is not like that.
If our state of knowledge about the system would be the whole system then in the middle ages the Earth should have been flat and the sun orbited the Earth and when did that changed , when we made an observation? Now ofcourse you would disagree saying that quantum effects cannot be also the same effects on cosmological scales and yes you would be right but my analogy is more to point out that what we think is not always the whole truth , indeed in most of the cases it's not only half of it.
Now ofcourse it's my personal opinion as on this topic everyone has one of a kind but I do think that QM works just fine with no superpositions and other stuff and does so according to the laws nature has given it.Now the ones who need superpositions and other so called "quantum phenomenon" are us because we don't have he full access to scales so small and so a lack of full information and observation of what's going on.
Now physics and theories to me seems like people and debates if we would somehow have the ability to see through other peoples eyes and think like they do we would immediately understand them and the argument would be gone but because we can't we have to predict and analyze a man's opinion and the way he reacts to draw conclusions about the man and sometimes they are right sometimes not so and sometimes wrong, but the average conclusion about the average human is called psychology and yet no matter how good it is at describing ones behavior and etc you will never know the whole story of a person not being him.
Just like you can never know what it is to be an electron or so.
but ofcourse that doesn't mean we cannot atleast for 95% understand what one is and what it does.
Saying that we have the whole picture would be speculation and saying that what we see is the whole picture and there is nothing more to that would be unprovable hence another speculation.
i think saying that we not yet fully know would be a fair answer the thing is some people don't like these types of answer they get annoyed by them and angry. """ Or maybe you mean that QM has not fully developed yet, and when it does, the "component representation" will no longer be useful??! """

Do you think it is developed fully as of now when I hit the letters on this keyboard? :)

 

[f95toli]

I'm not sure I see the issue. Again "in a superposition" is just relative to choice of observables.
A definite spin z-up electron, which we can quite clearly understand in terms of the classical analogue of a rotating mass, is also in a superposition of spin x-"up" and spin-x "down" states. Saying it is "in superposition" or "not" is simply a question of which component is being classically analogized.

True, but my point was that if you e. g have a charge qubit the two states correspond to "0" or "1" electrons on the island these two states can be in a superposition, ¦0> and ¦1>is then most natural basis. There is a difference between this and the spin of an electron where the choice of basis is more arbitrary since spin is a fundamentally QM and also "classically" continous.

Note also that these two states (0 or 1 electron) that also exist classically; it is just that the charge qubit in the classical regime (e.g at high temperatures) is just (essentially) a fancy transitor.
Hence, a charge qubit (or a flux qubit) is a system that is binary in the classical regime. and where the most natural choice of basis in the quantum regime is a one which correponds to these two states.

You are of course free to change basis for whatever system you want, but to me as an experimentalist that is just math: when I design devices I will still think about single electrons moving in and out of an island, or currents flowing in different directions. These electrons and currents are "real" and something I can measure.

 

[bahamagreen]

It is unfortunate that a cat was chosen because the experimental design confounds the interaction between the half life of the radioactive trigger and the half life of the cat itself.

Intrinsic uncertainty can never be overcome as one may never know if a particular cat hasn't already spent some of its nine lives prior to being placed in the box.

The measurement problem occurs because if you repeated kill the cat until all its lives are consumed, you will have counted and verified how many lives it had left, but it's no longer suitable to meet the initial conditions assumed in the experimental design.

Hidden variables in QM arise from sloppy theory, design, and analysis, as when one cannot exclude the influence of past spent cat lives shortening the cat's present half life).

Wheeler's "Many-cats" interpretation of QM is an extreme example of how to address these issues.

 

[bhobba]

Objective state is to QM as the aether was to SR.

I am not a fan, but the MWI has an objective state and is very elegant mathematically. Same with BM - although to me its a kludge and not elegant. I too hold to an interpretation where the state is not objective however I think the issues with interpretation are a bit too subtle for blanket statements like that.

Thanks
Bill

 

[bhobba]

If our state of knowledge about the system would be the whole system then in the middle ages the Earth should have been flat and the sun orbited the Earth and when did that changed , when we made an observation?

You misunderstand state of knowledge. If you consider a quantum state to not be objective and merely an aid to describing the outcome of observations you consider it like probabilities in standard probability theory. Probabilities do not have objective existence like say an electric field but they also help in describing certain situations like rolling a dice. It has nothing to do with false views in the past actually being true.

Can I ask have you actually studied the details of QM? If not that would be a good start in actually understanding the issues involved.

Thanks
Bill

 

[bhobba]

You are of course free to change basis for whatever system you want, but to me as an experimentalist that is just math: when I design devices I will still think about single electrons moving in and out of an island, or currents flowing in different directions. These electrons and currents are "real" and something I can measure.

This is extremely important to modern physics and especially Quantum Mechanics. You are free to change basis, coordinates etc etc to whatever you want - they are simply man made constructs and the laws of nature should not depend on that choice. Certainly some choice often makes a situation easier to understand and analyse but in principle it can be anything.

Imagine a system and an apparatus to observe some property with a digital readout. List the possible outcomes as yi. This by definition is a vector and to bring this out write it as sum yi |bi>. Now we have a problem - the precise |bi> is arbitrary and can be changed to any other basis - but in doing that the yi will change - but the laws of nature can not depend on the choice of basis. To circumvent this problem QM replaces the |bi> by |bi><bi| to give the Hermitian operator sum yi |bi><bi|. This is basis independent and the possible outcomes of the observation are its eigenvalues. In fact this is the first axiom of Ballentines approach to QM found in his book - QM - A Modern Approach. The second axiom, the expected value of an observation is via the usual trace formula Tr(RP) where R is the observable defined above and P the state follows from Gleason's Theorem. It would seem that an arbitrary choice of basis is built right into the foundations of QM.

Thanks
Bill

 

[bhobba]

Hidden variables in QM arise from sloppy theory, design, and analysis, as when one cannot exclude the influence of past spent cat lives shortening the cat's present half life).

BM (Bohmian Mechanics) for example is not the product of 'sloppy theory, design, and analysis'. I don't hold to it but it's perfectly valid.

The issues with interpretation can not be resolved with throwaway lines like that.

Thanks
Bill

 

[akdude1]

Schrodingers was trying to show that the wave function might both collapse and keep going in separate universes but the experiment could be ruined if something as simple as cosmic radiation interacted with anything or if schrodinger were watching the whole experiment would be ruined. In summary Schrodinger said the wave function (in a perfect experiment) could both collapse and continue (again in a perfect world)

 

[bhobba]

Schrodingers was trying to show that the wave function might both collapse and keep going in separate universes

Don't think so - the MWI wasn't even around then.

What he was trying to show is the formalism if blindly followed leads to absurdities like a cat that is in a superposition of partly alive and partly dead. And he is correct - if you are not careful that's exactly the conclusion - but with appropriate care such as understanding exactly where it is observed in the macro world (at the particle detector) the issues vanish. For some reason however some want to draw a different conclusion - don't really know why. To me the issue is not that it can't be resolved, but, as I think it was Einstein that wryly remarked, the ways of doing it were all different. To Einstein this suggested what was happening was far from well understood and QM was incomplete. It is believed by some that Einstein rejected QM, and indeed his views did evolve, but most certainly in his later years he believed it was correct, and wasn't even really worried about its probabilistic nature, but rather it was incomplete. Thats the real import of Schrodinger's Cat - its not that the issue it raises can't be resolved - its there seems to be so many different takes on it.


Thanks
Bill

 

[akdude1]

@bhobba hey man my bad I totally spaced about when Hugh Everette postulated the MWI. Thanks for enlightening me!

 

[Crazymechanic]

@bhobba Nowhere I was saying or intended to say that everything we know about QM states is just a mind construct or mathematics I do believe that there are many so called "variables" that we do measure directly and assign meaning and numbers and states to them.
But all I was trying to say is that there is something we don't know because the way things work forbids us from direct chance of "seeing" it.

 

[bhobba]

But all I was trying to say is that there is something we don't know because the way things work forbids us from direct chance of "seeing" it.

What precisely don't you know if you can't see it? The cat is either alive or dead regardless. Is it the knowledge the cat is alive or dead? Of course you can't see the cat to determine that until you open the box - and the experiment is designed precisely for that - but that's utterly trivial. The issue with Schrodinger's cat is to point out issues of the formalism - its not to show that you have to resort to some weird ideas like 'then in the middle ages the Earth should have been flat and the sun orbited the Earth and when did that changed , when we made an observation?' to resolve it. If you had a machine in their that flipped a coin and you had to open a box to see if it was heads or tails would you evoke similar arguments? To be specific what it highlighted is the need for a quantum based theory of measurement - since then a lot of work has been done on just that - and research is ongoing.

There are many ways to resolve Schrodinger's Cat - I gave one - namely to realize the weirdness resides at the particle detector and not at the cat. Here is another one - in Copenhagen the state is simply a theoretical device to determine the probability of outcomes here in the macro world - it allows us to determine the probability of the cat being dead or alive - but the cat at any time is either dead or alive. The issue with Copenhagen though is it splits the world into a classical macro world and a quantum world - but since the classical macro world is still governed by QM why does it appear to behave differently? Modern research has shown decoherence is the reason. You can have a look at further ways to resolve it here:
http://en.wikipedia.org/wiki/Schrödinger's_cat

Of modern times decoherence is often directly invoked to resolve it (it was not known about at the time it was propsed) - that shows the live and dead states never interfere so it behaves clasically:
http://en.wikipedia.org/wiki/Quantum_mind%E2%80%93body_problem
'Decoherence does not generate literal wave function collapse. Rather, it only provides an explanation for the appearance of wavefunction collapse, as the quantum nature of the system "leaks" into the environment. That is, components of the wavefunction are decoupled from a coherent system, and acquire phases from their immediate surroundings. A total superposition of the universal wavefunction still exists (and remains coherent at the global level), but its fundamentality remains an interpretational issue. "Post-Everett" decoherence also answers the measurement problem, holding that literal wavefunction collapse simply doesn't exist. Rather, decoherence provides an explanation for the transition of the system to a mixture of states that seem to correspond to those states observers perceive. Moreover, our observation tells us that this mixture looks like a proper quantum ensemble in a measurement situation, as we observe that measurements lead to the "realization" of precisely one state in the "ensemble".'

Indeed that link examines the whole mind body thing - it explains while some hold to consciousness being part of QM, it most definitely is not required, not required at all.

Thanks
Bill

 

[Crazymechanic]

@bhobba I don't know why you interpret me again maybe because of the way I word my phrases but I used the flat Earth just as an analogy although I agree in the times of flat Earth it was not because we didn't know which of the scenarios will play out but we just didn't knew and had no devices and maths to prove either one.

The research may be ongoing but it's not like our research will change the laws with which QM plays out , in this case the fact that we already know very well that wave function collapse at measurement.
To say that nature knows what she will "spit out" what state there is going to be and is even before we ever made the "eye contact" well I don't know that would have to mean that nature is self aware. That would be philosophy.
Maybe there is a God behind all of this.Again philosophy.
Well I think this thread is maxed out as there is nothing more fundamental to Schroedingers cat right now that we could add to what we already know.

 

[Charles Wilson]

http://www.nobelprize.org/nobel_prizes/physics/laureates/1954/born-lecture.pdf

I wasn't going to post anymore in fear of the Hounds of Hell nipping at my heels (How can quoting someone's position to develop a point without asserting whether it is your own position be one of the dreaded Thought Crimes in QM-Land?...)

Maybe this might help.

Born gives a great deal of useful historical info, especially at the beginning. The development of |Psi|^2 is worth the price of admission all by itself.

CW

 

[alweiss]

I know that so far as we know, it's impossible to figure this out, but is it possible that in a superposition, the atom(or whatever particle, in this case a cat) becomes two atoms once interaction with anything is blocked off, and then once a photon of light is sent some type of force pushed one cat away, leaving just the one cat in one state?

 

[ZapperZ]

I know that so far as we know, it's impossible to figure this out, but is it possible that in a superposition, the atom(or whatever particle, in this case a cat) becomes two atoms once interaction with anything is blocked off, and then once a photon of light is sent some type of force pushed one cat away, leaving just the one cat in one state?

Then you have misunderstood the superposition principle. What is in superposition is NOT the cat, or the atom, but rather a property of the cat or atom. This property, described by an observable, is the one that is in superposition, not the whole cat or atom.

By creating a duplicate system, you've created a whole slew of problems, including several conservation violations.

Zz.

 

[alweiss]

Thanks for the clarification !

 

[StarsRuler]

The cat is a macroscopical system with the precision for decide if he is alive. He is an observer, alive or dead, the system decohere in a very short time. There is no superposition with the cat. We can let an isolated closed box but the cat is alive or dead . It is question to do the calculations

 

[audioloop]

the pertinent question is if persist superposition (a linear principle, i.e. not change)
on macroscopic objects ?
to answer that, what is need is experimental testing.

 

[bahamagreen]

BM (Bohmian Mechanics) for example is not the product of 'sloppy theory, design, and analysis'. I don't hold to it but it's perfectly valid.

The issues with interpretation can not be resolved with throwaway lines like that.

Thanks
Bill

Why do I get the idea that you did not read my post? (#79) ;)

 

[bhobba]

Why do I get the idea that you did not read my post? (#79) ;)

Well let's see:

The measurement problem occurs because if you repeated kill the cat until all its lives are consumed, you will have counted and verified how many lives it had left, but it's no longer suitable to meet the initial conditions assumed in the experimental design.

All its lives consumed? Hmmmmm.

Maybe its not me reading it, which I did, maybe its what you are saying.

Thanks
Bill

 

[bhobba]

The cat is a macroscopical system with the precision for decide if he is alive. He is an observer, alive or dead, the system decohere in a very short time. There is no superposition with the cat. We can let an isolated closed box but the cat is alive or dead . It is question to do the calculations

In QM an observation does not require an observer. An observation is whenever a quantum process makes its mark here in the macro world, which in this setup occurs at the particle detector. Schrodinger's Cat never was an issue for Copenhagen - its solution within Copenhagen was utterly trivial. The issue with Schrodinger's Cat was, and always has been, pointing to the need of a fully quantum theory of measurement rather than the fundamental split Copenhagen makes between the quantum and the macro world.

I suspect you know that though and it was just the way you expressed it.

Your observations about decoherence are spot on - and is part of the modern view of Schrodengers Cat that reflects the work that has been done with developing that quantum theory of measurement since Schrodinger proposed his famous (infamous?) thought experiment.

Pop Sci accounts IMHO are responsible for much of the misunderstanding about this thought experiment.

Thanks
Bill

 

[bhobba]

the pertinent question is if persist superposition (a linear principle, i.e. not change) on macroscopic objects ? to answer that, what is need is experimental testing.

The cat is obviously not in a superposition of alive and dead.

However it is well known that once entanglement with the environment is removed, which is difficult, but not impossible, to do, (it usually means it must be kept ultra cold - most entanglement is via some kind of 'heat bath') quantum effects reassert themselves even for macro objects. And indeed some strange quantum effects have been observed with macro objects, and undoubtedly future experiments will reveal even more eg:
http://www.scientificamerican.com/article.cfm?id=quantum-microphone

Although I have a bone to pick with the article:
'As to how the day-to-day reality of objects that we observe, such as furniture and fruit, emerges from such a different and exotic quantum world, that remains a mystery'.

That's not quite true - how classical behavior emerges is pretty well understood - environmental decoherence has shed a lot of light on it - but some issues do remain such as the so called factoring problem (there are others as well, and most good textbooks allude to them - but strangely, and I am not quite sure why this is, it may be for a deep reason or evidence of nothing at all, they do not talk about the factoring problem - I have only seen discussions here about it - interesting). I believe, and I think most physicists also believe, this is more along the lines of dotting the i's and crossing the t's so to speak and they will be resolved - but really who knows what the future will bring.

But that is not what is going on here. The cat and the rest of the paraphernalia of this thought experiment are entangled with each other and the environment - specifically its not done at an ultra cold temperature near absolute zero.

Thanks
Bill

 

[audioloop]

quantum effects reassert themselves even for macro objects.

That's not quite true - how classical behavior emerges is pretty well understood

valid to 430 atoms (experimental limit).

i am talking about 10 ²⁰ atoms.