Why exactly cannot cat be in a superposition state?

[Genady]

5 minutes ago, joigus said:

The latter actually represents two cats; one dead, the other alive.

Yes, you're right. There is no even way to represent an impossible state like |alive and dead at the same time〉. Like a state of electron's spin being |up and down at the same time〉.

If an electron spin were |up and down at the same time〉, we could add them and would get the total electron spin = 0. But electron can't have spin 0!

Got it:

spin |left〉 = |←〉

spin |right〉 = |→〉

spin |left and right at the same time〉 = |↔〉

 

[Markus Hanke]

To be honest, I’m not sure what the main point of this discussion actually is - in Schrödinger’s scenario, the radioisotope that sets of the mechanism is never in any superposition relative to the cat; at any given time it has either decayed or it has not. Likewise, the cat is not in any superposition, it’s just that its state is unknown until the box is opened. This was not intended as a real-world example of quantum superposition, but merely as an analogy to demonstrate the basic idea - the uncertainty here is merely epistemic, but not ontological.

I still maintain that for all intents and purposes, in the real world, decoherence prevents a system the size of a cat to be in a superposition for any reasonable amount of time (I’d guesstimate no longer than perhaps 10^-30s or so). And that’s not even considering how you establish such a superposition in the first place, before decoherence.

[MigL]

15 hours ago, studiot said:

Your calculation of probabilities is flawed.

Oh, I don't know.
Isn't it just like playing the lottery ?
The two possible outcomes are , you win, or, you lose.
And since there has to be one of the two outcomes, your chances of winning are 1 in two.

have I been deluding myself all this time, playing the lottery, when my chaces of winning were much, much, smaller ?
😄  😂

[Genady]

11 minutes ago, Markus Hanke said:

To be honest, I’m not sure what the main point of this discussion actually is - in Schrödinger’s scenario, the radioisotope that sets of the mechanism is never in any superposition relative to the cat; at any given time it has either decayed or it has not. Likewise, the cat is not in any superposition, it’s just that its state is unknown until the box is opened. This was not intended as a real-world example of quantum superposition, but merely as an analogy to demonstrate the basic idea - the uncertainty here is merely epistemic, but not ontological.

I still maintain that for all intents and purposes, in the real world, decoherence prevents a system the size of a cat to be in a superposition for any reasonable amount of time (I’d guesstimate no longer than perhaps 10^-30s or so). And that’s not even considering how you establish such a superposition in the first place, before decoherence.

1. It was not about the original Schrödinger’s scenario. I have described way back, up in the thread, scenario which is based on a photon in a genuine superposition state. In this scenario, the unitary evolution establishes a superposition state of the cat.  

2. Yes, perhaps after it gets established, the state quickly drifts away from being a quantum superposition and becomes a set of classical probabilities, either dead or alive. This happens due to interactions with classically probabilistic environment and, I think, this can be analyzed using a density matrix. This was not a point of the question. The point was that a macroscopic body can be in a state of quantum superposition and could stay in such state in principle, albeit it is difficult to maintain it in practice. 

3. As I see it, the question is answered.

[studiot]

There seems to be some confusion concerning the difference between superposition and entanglement.

Quote

Superposition of two state means a quantum system is in two state at a time. But,entanglement says the correlation of two or more system in a ensemble. Which means even if two two system are spatially seperated the measurement of any observable will be effected by the other.

_{12 May 2014}

 

Are quantum entanglement and superposition principle the same?

www.researchgate.net › post › Are_quantum_entanglement_and_superposi...

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Is quantum entanglement the same as superposition?

Quantum entanglement is known to be the exchange of quantum information between two particles at a distance, while quantum superposition is known to be the uncertainty of a particle (or particles) being in several states at once (which could also involve the exchange of quantum information for a particle that is known ...

_{22 Nov 2014}

https://physics.stackexchange.com/questions/148131/can-quantum-entanglement-and-quantum-superposition-be-considered-the-same-phenom

Members should also note that neither entanglement nor superposition are considered to be a simple state.

A bit of googling might help them understand the notion of product states, if and when they occur.

Edited January 29, 2022 by studiot

[MigL]

3 hours ago, studiot said:

Quantum entanglement is known to be the exchange of quantum information between two particles at a distance

I know what you are trying to say, but that sentence is misleading to the average person.
There is no exchange of information.

[studiot]

1 hour ago, MigL said:

I know what you are trying to say, but that sentence is misleading to the average person.
There is no exchange of information.

Thank you for your reply but the quoted piece are not my wording, which is why they are in a quote box.

There was much more to look at in both the links.

I'm sorry to note that you are guilty of at least one of the two pieces of sloppyness I am trying to highlight here.

Firstly the quote says quantum information, not just information.

Secondly I am trying to say that pieces of different notions are being pieced together/mixed up when they should not be, in this case the characteristics of entanglement and

superposition along with the issue of quantum and not quantum matters.

Also the issue of coherence (and decoherence) are being ignored, except in swansont's pointed questions.

 

[MigL]

OK, I read the link ( although I do know the difference )

The line you quoted is from a posed question.
A given answer provides the quote

"Now you really shouldn't think of entanglement as exchange of information, because it happens instantaneously and it is impossible to transmit information instantaneously. Again, it is also impossible to transmit information instantaneously by collapsing the superposition."

[johnsankey]

I know using the Everett formulation of QM, based upon knowledge,  isn't popular but it really does simplify a number of questions that are confusing with the other formulations.

If you follow the information, Schrödinger's cat is in one state, either alive or dead - it's us, our knowledge, outside the cat's closed box that's in two states because we don't know.

I discuss this in more detail at url deleted

 

[swansont]

12 hours ago, johnsankey said:

I know using the Everett formulation of QM, based upon knowledge,  isn't popular but it really does simplify a number of questions that are confusing with the other formulations.

If you follow the information, Schrödinger's cat is in one state, either alive or dead - it's us, our knowledge, outside the cat's closed box that's in two states because we don't know.

I discuss this in more detail at url deleted

 

!

Moderator Note

The discussion should take place here.

 

[johnsankey]

Here is a human analogy of Schrödinger's cat:

Suppose that your significant other is visiting the next town and, on the radio, you hear that half that town has been blown up by a gas leak. By the time you hear the news, your other is only in one state. One way or another, the explosion is complete. But, you sure aren't in one state! Half of you is worried that your bed won't be warm tonight, the other half is worried that the breakfast argument will be continued at dinner. You phone your nurturing parent for some solace, and promptly create a pair of worlds at the other end of the telephone line...

Finally, you get that phone call, from your s.o. or from the police. One way or another, you make your quantum jump and one of your states (worlds) dissolves from reality. Gradually, your family and friends follow suit as they talk to you. Of course, years later, you can still run into someone who asks "Did your ? ?" But, once everyone who interacted with any of you when you were in two pieces (in superposed states) has heard the news, or has passed on to that other world, your world is back to being one again with regard to that particular matter.

That's what happens to quantum particles. Quantum worlds fade from existence as fast as new ones are created. Schrödinger's cat is in one state - it's us, our knowledge, outside the cat's closed box that's in two states. But you'd never guess that from Schrödinger's formulation. You have to follow the information.

An 'observer' can be as small as a single radioactive nucleus - things our size and complexity are not required. In fact, any two even partially-correlated quanta can 'observe' another single quantum. In the limit, quantum mechanics is a continuous function.

[swansont]

Many worlds is an interpretation of QM rather than being QM theory, but if you think the cat is in one state but we just don't know about it, that sounds like a hidden variable theory, and that runs afoul of Bell inequality experiments.

[johnsankey]

Schrödinger, Heisenberg and Everett are mathematical formulations of QM. They are formulations, not separate theories, because they are exactly equivalent mathematically. Any criticism of one is a criticism of them all.

[swansont]

1 hour ago, johnsankey said:

Schrödinger, Heisenberg and Everett are mathematical formulations of QM. They are formulations, not separate theories, because they are exactly equivalent mathematically. Any criticism of one is a criticism of them all.

They are indeed equivalent mathematically, which is why you can't say one has to be taken as true and the others as false. Meaning that the view that the cat is in a superposition of states and the wave function collapses is a valid way of looking at the problem.

So that leads me to think that your view is not actually what the many-worlds interpretation actually says. 

[johnsankey]

swansont: To a mathematician, all 3 formulations say the same thing. However, I'm a physicist who focuses on reality, what I can observe.

To me (with a twinkle in my eye 😉): One formulation, due to Schrödinger, is based upon space-time, wave patterns, and makes the universe look continuous. Like, really continuous. Schrödinger functions have no boundary - each one fills all of possible space if you wait long enough. A second, Heisenberg, is based upon observable energy movement, quantum jumps, and makes the universe look like particles. In this view, all particles but one are made of other particles - the universe is the ultimate particle. The third, Everett, is based upon information, and makes the universe look sensible - like we think we are.

My human analogy of the cat is based on Everett's formulation; I'm not claiming that the E. formulation "says it". I hope that helps you to understand my approach; of course you don't have to agree with it!