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

[1977ub]

Something.

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

 

[dmriser]

I suppose I take the orthodox viewpoint..

It seems that Omega0 has a reasoning not unlike Einstein with the hidden variable theory. Roughly, the Bell's inequality give an expected degree of correlation for a system that was derived using the assumption of a hidden variable that already has the final state outcome information. These inequalities have been violated by different methods many times. It is now done in undergraduate advanced laboratory courses. The interpretation is simple, the particle is not in a state of ON/OFF, but a superposition of both. Measuring the state collapses the wavefunction and forces the particle to assume a state.

It seems you are describing more of a mixed state rather than a superposition, one in which an ensemble of particles are prepared the same way, you don't know which ones will come up in each state, but you know the distribution, and you know that each particle is definitely in one state or the other.

I could be operating under a false assumption, but from the way I was taught, I thought these things (superposition as a real phenomena) were pretty universally accepted. Is it not the case?

 

[BruceW]

I don't think that Omega0 is talking about hvt's. it seems to me that he is saying that QM "doesn't happen" for things like cats. Without experimental evidence either way, it is difficult to justify either side.

 

[bhobba]

One thing people sometimes forget is that long before it breaks a vial and releases a gas that kills the cat it has registered in the macro world via the particle detector. Its really there you need to look at what's going on and decoherence plays an important part in how they work.

Thanks
Bill

 

[bhobba]

Contrary to popular opinion, the 'cat' is quantum mechanical as well .

Sure - key point though - no interference between the states of a live cat and those of a dead cat.

Thanks
Bill

 

[Omega0]

Okay, I believe I indeed was sort of confusing. The cat is a macroscopic object. I did agree that quantum entanglement exists but too believe that this exists and is stable with a macroscopic object of billions of particles seems to me more than ridiculous. To state that me as an observer of the box which is macroscopic also is the only observer makes no sense. First: What about the cat? Isn't it an observer? If you can show that also molecules interfere in a quantum mechanical sense - what does it prove? Physics is measuring and finding a theory describing. In some points theory leads to new ideas of measurement to prove a theory. QFT is a good example. Nevertheless, to confuse people in mixing macroscopic and quantum world makes here no sense in my eyes.
I think one should clearly separate the realms of the validity in existing theories - everything else is not science.

 

[Passionflower]

I think one should clearly separate the realms of the validity in existing theories - everything else is not science.

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.

That is science, 'to believe it is ridiculous or any other belief about it' is certainly not science.

 

[Omega0]

we simply must assume the cat is in superposition.
That is science

What it scientific in assuming something you can't measure?

 

[Passionflower]

What it scientific in assuming something you can't measure?

That is what we do in QM and very successfully.

 

[Omega0]

That is what we do in QM and very successfully.

Seems I got it wrong! Thought it is a theory based on a rethinking of the measurement process. Are you sure you studied it in detail?

 

[Omega0]

That is what we do in QM and very successfully.

PS: If you feel any uncertainty in your understanding I recommend J.J. Sakurai, "Modern Quantum Mechanics". He explaining the measurement process is a masterpiece in my eyes. Just as a hint. I loved it in my studies.

 

[Passionflower]

Seems I got it wrong! Thought it is a theory based on a rethinking of the measurement process. Are you sure you studied it in detail?

We have a very successful theory about the time evolution of the wave function but we cannot actually measure this just like we cannot measure the state and evolution of the cat but the results of any measurements (using observables) are statistically in accordance with theory.

 

[Omega0]

We have a very successful theory about the time evolution of the wave function but we cannot actually measure this just like we cannot measure the state and evolution of the cat but the results of any measurements (using observables) are statistically in accordance with theory.

So "any measurement" is on a microscopic level, right? You can't find the Eigenstate of the cat but you say that it is determined clearly in the same sense as some atoms are with respect to a quantum entanglement? It is pretty easy, I see... hmmm mightn't it be sort of too easy?
And in the end wrong? If you just say: Well, from our experience this idea holds, the theory works, so just let us expand the theory to the complete universe, to macroscopic bodies, we believe that quantum entanglement now exists for the cat, yeah, let's believe that we have now superpositions of being alive or dead. Is this science? In your eyes?

 

[Passionflower]

So "any measurement" is on a microscopic level, right? You can't find the Eigenstate of the cat but you say that it is determined clearly in the same sense as some atoms are with respect to a quantum entanglement? It is pretty easy, I see... hmmm mightn't it be sort of too easy?
And in the end wrong? If you just say: Well, from our experience this idea holds, the theory works, so just let us expand the theory to the complete universe, to macroscopic bodies, we believe that quantum entanglement now exists for the cat, yeah, let's believe that we have now superpositions of being alive or dead. Is this science? In your eyes?

Yes, we have a theory that works, and unless it is proven by experiments that at a certain scale it no longer works, it should be the prevailing theory.

 

[ZapperZ]

Sometime, a discussion on this forum gets so convoluted, it is difficult to decipher what exactly is the issue here. This appears to be the case here, and I think people are tripping over themselves talking about different things.

Is the issue

(i) the detection of superposition

or is it

(ii) can superposition be detected at the cat/macroscopic level?

Each one of those have different answers. The first one has been discussed ad nauseum in this forum. I had repeatedly mentioned about bonding-antibonding states, the Delft/Stony Brook experiments, etc... etc. There are already many of these types of Schrodinger cat states that have been measured.

http://physicsworld.com/cws/article/news/2815
http://physicsworld.com/cws/article/print/525
http://physicsworld.com/cws/article/news/42019

The second one has also been discussed many times, and the Delft/Stony Brook paper showed the superposition of up to 10^11 particles, which in some scale, is quite macroscopic! The existence of interference experiments with buckyballs and even other larger molecules are clear examples of such huge objects having a superposition of paths. These are not simple experiments, btw, and these are performed under extreme conditions to ensure that all parts of the object are in coherence with each other.

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.

Zz.

 

[Charles Wilson]

Frustrating!
Here's one of the problems: How do we know that the Quantum World maps to the World we live in? If all we have are dials and pointers and screens, then there will ALWAYS be an alternative explanation for what we "observe".

"We opened the box and found the cat was alive AND the poison dispersed". So, did the atom decay or not?
WE DON'T KNOW. The experiment was never about what we could see. That's why a computer screen is as good as - and no worse than - a cat in box. And before you talk of the absurdity of a cat in a box, look at how we used to determine if a woman was pregnant. "Why would a doctor keep a bunch of cute little bunnies? I hope nothing bad happens to them!"

The experiment was about what we could infer from what we assumed was a causal chain from a set of Quantum circumstances.

"Suppose we have an electron..." We are already in a System with this one statement! You write a textbook about Physics. You discuss the Shroedinger Equation and Born's modification. You write that it is very useful and to understand it, you must understand how to normalize the Probability to fit the electron you are examining:
"The Integral from - infinity to + infinity of (Psi) ^2 dx = 1."

This is the normalization condition for finding the electron somewhere along the axis we are observing.

"But the electron has to be SOMEWHERE..." Hence the Integral is set to 1.

That's all Einstein ever needed and we are here denying Einstein and then denying the negation of Einstein.

In short, we continue to argue about the presence of das Noumena within Kantian restrictions and the first person who quotes Hegel loses. We are left with A N Whitehead's criticism of Humean Empiricism: All we can talk about are bees and flowers. There is no "why". All we see are bees landing on flowers. There is nothing else to be said.

[[EDIT: I removed a paragraph sorta' by request. See below.]]

Bell showed that Locality does not provide the results that QM obtains AND QM IS CORRECT.
That's the problem. So how does the QM non-locality map onto a Realistic and/or Local World?

We are only now getting to this examination in Physics.

CW

 

[Omega0]

Yes, we have a theory that works, and unless it is proven by experiments that at a certain scale it no longer works, it should be the prevailing theory.

Good point, you might be right in a sense that a theory which is not wrong in what we know from measurement in small scale might be correct on a bigger scale but this seems to imply that you believe in that this automatically must be valid on bigger scales. So it means that I have to send cats through double slits to measure to find out that on this scale there may be different effects than superposition. In other words: Your believing makes your world complete - but not mine. I am not sure if the theory holds on every scale. I trust in measurement.

 

[ZapperZ]

And on and on. We cannot see, even in principle, Entanglement Correlations. All we have are marks on paper written down from an experiment that flashed red light or green light when a button was pushed. There is no entanglement because marks on paper are not entanglement. The cat cannot be dead and alive but if a Probability Wave is given an OBJECTIVE MEANING then there exists a situation where YOU are dead and alive! "How do you feel?"

This is highly incorrect.

If I have two non-commuting observables, A and B, and [A,B] is not zero, then a measurement of A does NOT collapse anything related to B, and the reverse is also true. So I can easily make some measurement of B, and see if there are particulars of what I measure in which I can detect the effect of A being in a superposition.

This similar concept is what is done in, say, the Delft/Stony Brook experiments. The existence of the coherence energy gap is a DIRECT result of the superposition of the supercurrents! You can verify this by looking at the physics done by Tony Leggett. I really don't need to actually make a measurement of the amount and direction of the current. By not doing that, and measuring something else, I preserved that superposition, and detect its direct effect on another observable.

Zz.

 

[Charles Wilson]

ZapperZ

I have no problem with that! My points are about the development of Thought about QM. I don't doubt QM results. I'm NOT arguing that they are meaningless! That's the point. See my initial post on this on page 1.
The original post was, "I don't understand about Schroedinger's Cat. How can it be both dead and alive?"

Well, if you are looking AT THE CAT, then it cannot be both Dead AND Alive. You can set the experiment so that YOU are seen by others as having to be both dead AND alive. "How do you feel?" For decades, these problems were not dealt with.

Einstein and Bohr went round and round and I think they both missed the action, although I side with Einstein a lot. I don't argue for Local Realism and there are NOW lots of Real Math reasons for denying it, with experiments based on Real Math that give results every time.

My question is still, "How does QM (and non-locality) map onto our perceived World - without the Kantian/Hegelian stuff? By all means, keep posting things that you find!

So, if I still haven't given a coherent answer to what you stated, tell me what I should edit out of my above post and I will be happy to delete or rewrite.

CW

 

[1977ub]

MWI has an infinity of universes where cat is alive, and then a 2nd infinity where they are all dead.

http://en.wikipedia.org/wiki/Many-worlds_interpretation

 

[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.