Can Schrodinger's cat apply to things other than alive/dead?

[Sundown444]

We know of Schrodinger's cat analogy, where a cat in a box that has a gas tube with deadly gas (or whatever it is) is both alive and dead at the same time until observed. Does it work on anything else? Like something is big or small, near or far, tall or short, red or blue, etc. at the same time until it is observed by the viewer?

 

[mfb]

It does not work with a cat. You can make that analogy with whatever you want, of course, but you cannot make that experiment with an actual cat. Decoherence prevents that. You need something as isolated from the environment as possible, and without too many relevant internal degrees of freedom. In general this is easier with smaller objects such as individual atoms.

 

[sophiecentaur]

It does not work with a cat. You can make that analogy with whatever you want, of course, but you cannot make that experiment with an actual cat. Decoherence prevents that. You need something as isolated from the environment as possible, and without too many relevant internal degrees of freedom. In general this is easier with smaller objects such as individual atoms.

++
The Cat Analogy was just that - an analogy. As with many such analogies, it was taken by the ill informed masses (thanks to journalists and bad teaching) and applied way outside of its real meaning. Another similar bit of nonsense is to try to apply a De Broglie wavelength idea to an elephant running at a door.

 

[Sundown444]

I always knew that my understanding could have been wrong, so I decided to ask to make sure. Looks like I got more of an answer than I bargained for.

 

[Cutter Ketch]

Well, yes. I mean the cat is an analogy to illustrate a startling truth of quantum mechanics that happens all the time on the very small scale.

However I think you’ve missed the point a bit. A real cat in a real box is not really in a mixed state until you open the box. Even though you don’t know whether the cat is alive or dead, you know that in reality it must be one or the other. It is the fact that you know this that he is driving at. He is contrasting the “normal” behavior of macroscopic things in the everyday world (cats in boxes) with the counterintuitive world of the very small. No one would think the cat is in some bizarre state where it is both simultaneously alive and dead. That would be crazy. Then he tells you that is exactly what happens in quantum mechanical mixed states. (Not actually cats, but measurable physical quantities of small particles). It’s analogous to the cat being simultaneously alive and dead which you know doesn't happen in the macroscopic world. Mind blown. What is crazy and unthinkable for cats and boxes is the way things actually work on the very small scale.

Now you may have heard of the long running debate between Einstein and DeBroglie and friends on one side and Neil’s Bohr and Scroedinger and crew on the other. Well this is what they were debating. Einstein argued that quantum mechanics a convenient mathematical way to keep score when you don’t know whether the “cat” is alive or dead, but in some unknown underlying reality the cat is certainly one or the other. Bohr and Schroedinger argued that it isn’t just score keeping. The mixed states are the real physical truth. To resolve this people went looking for experiments where the two concepts would give a different result. Bell’s theorem pointed to how this could be done. And over the years many Bell tests have been performed. All showed that there isn’t a hidden reality. The particles really are in mixed states.

 

[ZapperZ]

We know of Schrodinger's cat analogy, where a cat in a box that has a gas tube with deadly gas (or whatever it is) is both alive and dead at the same time until observed. Does it work on anything else? Like something is big or small, near or far, tall or short, red or blue, etc. at the same time until it is observed by the viewer?

You need to understand what the Schrodinger Cat analogy is trying to illustrate. It is trying to illustrate quantum superposition.

Quantum superposition occurs in numerous cases, especially in chemistry. It is also the basis of all those entanglement experiments, because without the presence of quantum superposition, all those measurements will be no different than the classical measurements that make use of conservation of momentum/angular momentum/etc. The the Delft/Stony Brook experiments that I've cited many times, it is the superposition of supercurrents going in opposite directions. And without you realizing it, the double slit experiment itself is analogous to the Schrodinger Cat situation, because the double slit is illustrating the outcome of a superposition of two separate paths!

So yes, there are numerous clear demonstrations of the Schrodinger Cat experiments.

Zz.

 

[SlowThinker]

It does not work with a cat. You can make that analogy with whatever you want, of course, but you cannot make that experiment with an actual cat. Decoherence prevents that. You need something as isolated from the environment as possible, and without too many relevant internal degrees of freedom. In general this is easier with smaller objects such as individual atoms.

Here on PF I often read that the Schrödinger's cat doesn't work, but never understood why.
Is the objection only that the box is usually not perfect? It is obviously assumed that the box is perfect, otherwise there's no point in having a box in the first place.
If we could measure something that would say if the cat is alive, it would be the same as opening the box.

So, assuming the box insulates its content perfectly, is Schrödinger's cat both dead and alive, or not?
I'd say a perfect box could in theory be built.

 

[mfb]

There cannot be a perfect box, and the cat is not perfect either. To get a decoherence time long enough the cat has to be very close to 0 K, and that corresponds to a dead cat. Even if we hand wave the difficulties with the box away the cat is either dead or alive - we just don't know it yet. You can't make superposition experiments with the cat. You can't even get a cat in a single known quantum state.

 

[sophiecentaur]

There cannot be a perfect box, and the cat is not perfect either. To get a decoherence time long enough the cat has to be very close to 0 K, and that corresponds to a dead cat. Even if we hand wave the difficulties with the box away the cat is either dead or alive - we just don't know it yet. You can't make superposition experiments with the cat. You can't even get a cat in a single known quantum state.

All those caveats go to demonstrate that the analogy is open to misinterpretation and over simplification. It is not treated with the right reservations by most people who quote it. But the original scenario does, in fact start with a simple binary condition which is subject to the condition. The cat's contribution is just to act as a measuring device which 'records' the state of the nucleus that's being observed.

 

[YoungPhysicist]

Speaking of Schrodinger's cat, is there the specific action required to be considered as OBSERVE ?
In the analogy, the cat's state is determined when a person observed it. But a camera waiting outside of the box should do just the same.

 

[DrClaude]

Speaking of Schrodinger's cat, is there the specific action required to be considered as OBSERVE ?
In the analogy, the cat's state is determined when a person observed it. But a camera waiting outside of the box should do just the same.

Any strong coupling with a big enough system (big = many degrees of freedom) will lead to decoherence and can be considered, in some sense, as an observation. Even the emission of a single photon, which will effectively coupe the system to the EM field, can be sufficient.

 

[richrf]

The "measurement issue' which is at the heart of the Schrodinger's Cat thought experiment, is a manifestation of the so-called Copenhagen Interpretation of Quantum Wave Theory. Three problem disappears if one adopts the Bohm-DeBroglie or Everett Many-Universes models/interpretations. My preference is the Bohm-DeBroglie, since it is real (no superposition of states or wave collapse), and it successfully predicted nonlocality which is a major plus in its favor.

 

[mfb]

My preference is the Bohm-DeBroglie, since it is real (no superposition of states or wave collapse)

You have a superposition of states via the guide wave which is still real.

and it successfully predicted nonlocality which is a major plus in its favor.

How is predicting something that cannot be observed a plus? MWI is a local interpretation. If quantum mechanics would be inherently nonlocal then there couldn't be local interpretations.

 

[richrf]

You have a superposition of states via the guide wave which is still real.How is predicting something that cannot be observed a plus? MWI is a local interpretation. If quantum mechanics would be inherently nonlocal then there couldn't be local interpretations.

The nature of the Quantum Potential is subject to interpretation. There is no reason to suggest it is a superposition of states. Bohm describes it differently. Suffice to say everything is real and there is no collapse, and whether or not anyone peeks into the box, the cat is already dead or alive depending upon a very real decay.

The MW interpretation is untestable so nothing much can be said about it. However, in the world/universe that we live in, nonlocality had been experimently verified and Bohmian Mechanics is the lone quantum theory that makes nonlocality an integral part of the theory. It appears there may be some important applications if this feature in the area of information security.

 

[mfb]

The MW interpretation is untestable so nothing much can be said about it.

All interpretations are untestable in their differences.

However, in the world/universe that we live in, nonlocality had been experimently verified

If that would be true MWI would be ruled out. Publish such a revolutionary result if you have it!
No, what has been ruled out is a combination of locality, causality and getting a unique result. MWI clearly doesn't have the latter but it is local and in agreement with all measurements.

and Bohmian Mechanics is the lone quantum theory that makes nonlocality an integral part of the theory

See above: That is a downside. Bohmian mechanics needs something that doesn't have to be there.

 

[jartsa]

It does not work with a cat. You can make that analogy with whatever you want, of course, but you cannot make that experiment with an actual cat. Decoherence prevents that. You need something as isolated from the environment as possible, and without too many relevant internal degrees of freedom. In general this is easier with smaller objects such as individual atoms.

Decoherence results in two thing with different phases.

If decorence works in this case, then there are two things in this case.

Thing 1: Cat that is alive.

Thing 2: Cat that is dead.

 

[richrf]

All interpretations are untestable in their differences.If that would be true MWI would be ruled out. Publish such a revolutionary result if you have it!
No, what has been ruled out is a combination of locality, causality and getting a unique result. MWI clearly doesn't have the latter but it is local and in agreement with all measurements.See above: That is a downside. Bohmian mechanics needs something that doesn't have to be there.

There are enough unique qualities of Bohm's Quantum Theory to make it treatable as different from other quantum theories. It was the specific prediction that the Quantum Potential is non-local in nature that led to its far too premature rejection by the great scientists of that period. However, as fate would have it, it also peaked the interest of John Bell that would set off a chain of events (highly suppressed by academia) that led the Bell's Theorem and subsequent experiments that confirmed non-locality. While non-locality may be superfluous to some it is highly relevant to the universe as it operates, which makes Bohm's model ever more interesting.

 

[bobob]

Schroedinger's cat has to be one of the most misapplied and worst analogies ever posed. First of all, alive and dead are not eigenstates of anything. Alive and dead aren't even a reliable macroscopic description of an organism. At best, doctors use some guidelines to determine that under certain circumstances, recovery is not going to happen, but when a doctor tells a heart attack patient he/she was dead for a few minutes, it doesn't mean the EMT's resurrected the patient. It does not make much sense to speak of a superposion of two states that cannot even be defined in general terms much less be given mathematical rigor.

My preference is the Bohm-DeBroglie, since it is real (no superposition of states or wave collapse), and it successfully predicted nonlocality which is a major plus in its favor.

I'm not sure why you consider a prediction of non-locality a success. Standard quantum mechanics is a local theory. I'd call a prediction of non-locality a failure, especially given that it conflicts with relativity.

 

[Demystifier]

I'm not sure why you consider a prediction of non-locality a success. Standard quantum mechanics is a local theory. I'd call a prediction of non-locality a failure, especially given that it conflicts with relativity.

Have you ever heard about the Bell theorem?

 

[mfb]

There are enough unique qualities of Bohm's Quantum Theory to make it treatable as different from other quantum theories.

It doesn't make different predictions for experiments.

Bell's Theorem and subsequent experiments that confirmed non-locality.

See above: It doesn't.

Collapse interpretations are non-local as well. This is nothing special about dBB. But why would you prefer a non-local interpretation if there are local interpretations consistent with experiments? You are needlessly adding something that cannot be verified, not even in principle.

 

[bobob]

Have you ever heard about the Bell theorem?

Sure and standard quantum mechanics is a local theory.

 

[Demystifier]

Sure and standard quantum mechanics is a local theory.

With nonlocal correlations.

 

[Grinkle]

We know of Schrodinger's cat analogy, where a cat in a box that has a gas tube with deadly gas (or whatever it is) is both alive and dead at the same time until observed. Does it work on anything else? Like something is big or small, near or far, tall or short, red or blue, etc. at the same time until it is observed by the viewer?

This thread helped me, fwiw.

https://www.physicsforums.com/threa...a-non-dertministic-state.951750/#post-6028117

 

[Grinkle]

To get a decoherence time long enough the cat has to be very close to 0 K, and that corresponds to a dead cat.

Or something not recognizable at all? I can make a geeky joke and say "What does a decoherent cat look like"? but behind that joke is the question of what would result after the system stops being decoherent. Would you be looking at anything macroscopic, or would you get a bunch of particles that didn't resemble anything, let alone a cat?

 

[bob012345]

Schrodinger actually came up with the cat analogy as a critique of certain interpretations of QM and it was never meant literally. All the players at the time knew that. But over time it's become one of the most abused and misleading concepts used for popularizing and teaching QM and should now, finally, be abandoned.

 

[richrf]

Schrodinger actually came up with the cat analogy as a critique of certain interpretations of QM and it was never meant literally. All the players at the time knew that. But over time it's become one of the most abused and misleading concepts used for popularizing and teaching QM and should now, finally, be abandoned.

The thought experiment developed by Schrodinger was directed at the Copenhagen set of Interpretations and it is a question that will not go away. It it is as relevant today as it was back then. What is the meaning of the wave collapse? What is it that is collapsing and what it's it precisely that causes this collapse. The question can only be ignored or be replaced by another Interpretation.

Now, this may be more of a philosophical question than one of physics, but that depends upon what one believes is the nature of physics.

 

[bob012345]

The thought experiment developed by Schrodinger was directed at the Copenhagen set of Interpretations and it is a question that will not go away. It it is as relevant today as it was back then. What is the meaning of the wave collapse? What is it that is collapsing and what it's it precisely that causes this collapse. The question can only be ignored or be replaced by another Interpretation.

Now, this may be more of a philosophical question than one of physics, but that depends upon what one believes is the nature of physics.

Good question since a wave function is usually thought of as a purely mathematical entity yet the concept of collapse definitely suggests a physical entity. I usually get in trouble asking too much about what really happens so I won't.

 

[bobob]

With nonlocal correlations.

Saying a correlation is local or non local has no meaning.

 

[mfb]

Or something not recognizable at all? I can make a geeky joke and say "What does a decoherent cat look like"? but behind that joke is the question of what would result after the system stops being decoherent. Would you be looking at anything macroscopic, or would you get a bunch of particles that didn't resemble anything, let alone a cat?

Decoherence is irreversible by definition.

 

[Demystifier]

Saying a correlation is local or non local has no meaning.

So how would you call a correlation that violates Bell inequality?

 

[Grinkle]

Decoherence is irreversible by definition.

Right, thanks for noting that.

 

[jartsa]

It does not work with a cat. You can make that analogy with whatever you want, of course, but you cannot make that experiment with an actual cat. Decoherence prevents that. You need something as isolated from the environment as possible, and without too many relevant internal degrees of freedom. In general this is easier with smaller objects such as individual atoms.

Oh now the Schrodinger's cat story/analogy/experiment/thought experiment is a quantum interference experiment, although Schrodinger does not say anything about interference. Let's put a radioactive atom in a box made of steel, and the box we put in such place where there is a few light minutes of empty space around the box. After a minute the box will be in these states:

many states where the box knows that the atom decayed at time one second
.
.
.
many states where the box knows that the atom decayed at time two seconds
.
.
.
many states where the box knows that the atom has not decayed yet