Quantum uncertainty, and Schrodinger's cat

[Juma]

Betting isn't closed until the box is open. Now, if you want to influence the odds a bit... just stall.

Isn't the box essentially 'open' in the instance that the camera/recorder is imbedded and observing/recording?

The camera doesnt make any difference. But to actually get an image you need ligth. But the photons will interact with the objects.

 

[Jesse]

Isn't the box essentially 'open' in the instance that the camera/recorder is imbedded and observing/recording?

I think most physicists would say that in an experiment where some measuring-system records the information but this information is later erased in an unrecoverable way before the box is opened (as in my last post about waiting billions of years to open the box so the atoms the cat was made of would have time to go to maximum entropy), then from the perspective of outside measurers you have to assume that no "collapse" of the wavefunction ever occurred before the box was opened, regardless of what was inside the box. This would apply even if it had been a conscious human inside the box--and in fact there is an analogue of the Schroedinger's cat thought-experiment known as Wigner's friend which imagines a person in the box who, like the cat, must be treated as being in quantum state that's a superposition of "alive" and "dead" (Wigner, the physicist who put forward this thought-experiment, came to the conclusion that consciousness caused an objective collapse of the wavefunction, but I think few physicists today would see this as a likely answer, especially in an information-erasure experiment where it could lead to different predictions about the actual measurement results than treating the person in the perfectly isolated box as a normal quantum system would).

 

[Juma]

Isn't the box essentially 'open' in the instance that the camera/recorder is imbedded and observing/recording?

I think most physicists would say that in an experiment where some measuring-system records the information but this information is later erased in an unrecoverable way before the box is opened (as in my last post about waiting billions of years to open the box so the atoms the cat was made of would have time to go to maximum entropy), then from the perspective of outside measurers you have to assume that no "collapse" of the wavefunction ever occurred before the box was opened, regardless of what was inside the box. This would apply even if it had been a conscious human inside the box--and in fact there is an analogue of the Schroedinger's cat thought-experiment known as Wigner's friend which imagines a person in the box who, like the cat, must be treated as being in quantum state that's a superposition of "alive" and "dead" (Wigner, the physicist who put forward this thought-experiment, came to the conclusion that consciousness caused an objective collapse of the wavefunction, but I think few physicists today would see this as a likely answer, especially in an information-erasure experiment where it could lead to different predictions about the actual measurement results than treating the person in the perfectly isolated box as a normal quantum system would).

Bullshit.

Take a well known example: the double slit experiment: to measure position you need to change the system => new behavior.

Same in the box: to measure you need to change the system and that is what vhanges the result. Not some "wavecollapse"

 

[Kharakov]

You could have the Wigner's friend in a viewing room in the box with its own air, so that the friend observes whether the cat dies or not, and then tells people when they open the door.

 

[Jesse]

I think most physicists would say that in an experiment where some measuring-system records the information but this information is later erased in an unrecoverable way before the box is opened (as in my last post about waiting billions of years to open the box so the atoms the cat was made of would have time to go to maximum entropy), then from the perspective of outside measurers you have to assume that no "collapse" of the wavefunction ever occurred before the box was opened, regardless of what was inside the box. This would apply even if it had been a conscious human inside the box--and in fact there is an analogue of the Schroedinger's cat thought-experiment known as Wigner's friend which imagines a person in the box who, like the cat, must be treated as being in quantum state that's a superposition of "alive" and "dead" (Wigner, the physicist who put forward this thought-experiment, came to the conclusion that consciousness caused an objective collapse of the wavefunction, but I think few physicists today would see this as a likely answer, especially in an information-erasure experiment where it could lead to different predictions about the actual measurement results than treating the person in the perfectly isolated box as a normal quantum system would).

Bullshit.

Take a well known example: the double slit experiment: to measure position you need to change the system => new behavior.

Same in the box: to measure you need to change the system and that is what vhanges the result. Not some "wavecollapse"

I never said anything about there being an actual physical process called "wave collapse", I just said that in the Wigner's friend thought experiment you could get the wrong prediction if you assumed the friend's measurements inside the box did collapse the wavefunction, which argues against the notion of any objective "collapse" associated with measurement. That said, your own interpretation is problematic as well, since if you treat measurement as being no different from any other quantum interaction, then measurement just produces an entangled state that involves a superposition of both measurement results (and indeed, this is how you would have to model Wigner's friend according to the quantum rules, assuming the box was really 100% isolated from its external environment, which isn't possible in practice). Also, there are forms of passive measurement that produce the same result--for example, in the double-slit experiment you could just put shutters over each slit which alternate which one is closed, then by looking at the timing of each electron that hits the screen you could determine which slit was open at the time it passed the location of the slits, and thereby "measure" which slit it went through. This will destroy the double-slit interference pattern as well, even though if you imagine the electron as a classical entity, one might naively think this should make no difference since a classical entity wouldn't change its behavior when passing through an open slit depending on whether another, faraway slit was open (as in the standard double-slit experiment where they're both open at all times) or closed (as in this variation on the double-slit experiment).

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You could have the Wigner's friend in a viewing room in the box with its own air, so that the friend observes whether the cat dies or not, and then tells people when they open the door.

Sure, but that's why I said you can only see the rationale for saying that the measuring-system (whether the cat or Wigner's friend) was in a superposition state if you consider an experiment in which the information has been erased by the time the outside observer opens the box/room.

 

[Kharakov]

Betting isn't closed until the box is open. Now, if you want to influence the odds a bit... just stall.

Isn't the box essentially 'open' in the instance that the camera/recorder is imbedded and observing/recording?

Within the box it evolves classically, outside (where it cannot be observed) it evolves quantumally. So in a sense, yes.

 

[Kharakov]

Sure, but that's why I said you can only see the rationale for saying that the measuring-system (whether the cat or Wigner's friend) was in a superposition state if you consider an experiment in which the information has been erased by the time the outside observer opens the box/room.

I got it. Here is an example that loosely correlates: if we wait until the friend and the cat are mush (say a billion years like your example) even if there is a time limit on the detector (say 1 day, if it decays after that, nothing happens), we won't be able to tell if the detector detected decay or decay was just a consequence of time. In other words, quantum erasure.

 

[ryan]

Isn't the box essentially 'open' in the instance that the camera/recorder is imbedded and observing/recording?

Within the box it evolves classically, outside (where it cannot be observed) it evolves quantumally. So in a sense, yes.

If I observe what is in the box with a camera while the cat experiences its fate, then, of course, I will see A or B. But if I am not observing what the recorder observes, then the recorder is suspended in a superposition too. Eventually when I watch what the video recorded, only then does the final outcome come known to me.

Furthermore, once I see the video, the cat is in a fixed state; let's say it's alive. But for anyone else who has had no connection to me, the video, or any other connection that could cause decoherence since the experiment, they could find out that the cat is actually dead. Meanwhile, everyone in my world agrees that the cat is alive.

So, I do not see any other explanation other than the many worlds interpretation.

The only way this makes sense to me is that there are only subjective realities - no this has nothing to do with the other threads.

 

[Jesse]

Sure, but that's why I said you can only see the rationale for saying that the measuring-system (whether the cat or Wigner's friend) was in a superposition state if you consider an experiment in which the information has been erased by the time the outside observer opens the box/room.

I got it. Here is an example that loosely correlates: if we wait until the friend and the cat are mush (say a billion years like your example) even if there is a time limit on the detector (say 1 day, if it decays after that, nothing happens), we won't be able to tell if the detector detected decay or decay was just a consequence of time. In other words, quantum erasure.

Yes, exactly. And in that case, if we measure the precise quantum state of all the particles in the mush, then right before we measure the probability distribution for different precise states may be different then it would be if we had assumed the friend and cat had to be either definitely alive or definitely dead a billion years earlier, and calculated the probabilities for different mush states a billion years later based on that assumption (in technical terms this would mean treating the final probability distribution on different mush states as a mixed state rather than a pure quantum state).

 

[untermensche]

I don't see how anything can happen without "detection".

If an atom decays then its electrical properties change, its gravitational properties will change, and all other matter in the box will be able to "detect" those changes.

 

[ryan]

I don't see how anything can happen without "detection".

If an atom decays then its electrical properties change, its gravitational properties will change, and all other matter in the box will be able to "detect" those changes.

Those effects might be too small to have a physical effect on anything at the quantum level.

 

[Speakpigeon]

Ehh, if you don't know who won the match, and your buddy hasn't looked, you can still bet based on the knowledge you have. The QM knowledge is simply half-life in this case- if you make it so there is an even 50% chance that the atom decays, you're both idiots for making the bet, even more so for killing a fucking cat to make a bet. That's the relevance.

You don't know until you opened the box. Something definitely happened. The cat is definitely a fucking observer, as is the radiation detector, etc. There is no great fucking mystery- although maybe the universe, spacetime, God, or someone else reserves the right to choose paths 'til the last possible second.

Its an experiment that was changed when a camera was embedded inside the box making the outside observer irrelevant. The box is a metaphor for not having the capacity to measure something. Change the metaphor to a camera inside a box and neither the box nor the observer are necessary, Experiment over when camera records the decay (cat's death).

The guy outside remains an observer. The point is that he won't have access to the inside of the box until the box is opened so until then he has to rely on quantum calculus of probabilities to tell him the range of possibilities. Until the box is opened, this range uncludes a dead cat and a live cat. For the camera inside the box, clearly it will record what is going on. However, for the outside obsever, the two states in superposition describing the inside of the box will include each one a camera, one recording a dead cat, the other recording a live cat. On opening the box, the observer will only see one camera.

Whether before opening the box there is just one camera or two in superposition, it seems we don't know.
EB

 

[Speakpigeon]

Within the box it evolves classically, outside (where it cannot be observed) it evolves quantumally. So in a sense, yes.

If I observe what is in the box with a camera while the cat experiences its fate, then, of course, I will see A or B. But if I am not observing what the recorder observes, then the recorder is suspended in a superposition too. Eventually when I watch what the video recorded, only then does the final outcome come known to me.

Furthermore, once I see the video, the cat is in a fixed state; let's say it's alive. But for anyone else who has had no connection to me, the video, or any other connection that could cause decoherence since the experiment, they could find out that the cat is actually dead. Meanwhile, everyone in my world agrees that the cat is alive.

So, I do not see any other explanation other than the many worlds interpretation.

The only way this makes sense to me is that there are only subjective realities - no this has nothing to do with the other threads.

Why subjective?

It's not a matter of observation, it's a matter of interaction as you indeed seem to have understood.

Observation always requires an interaction but an interaction may not qualify as an observation*. So even if the observer abstains from looking at the recording made by the camera or even inside the opened box, there is nonetheless an interaction (photons, gaz molecules spreading out, etc.) so the observer (his body) will interact unless specifically protected...

(*) Strictly speaking of course, the way the body of the abstaining observer is affected by the inside of the box spilling out could be used, if only in principle, to tell us whether the cat was dead or alive on opening the box. This might qualify as a recording of sort and as an observation... but then subjectivity would clearly be beside the point.
EB

 

[Speakpigeon]

I don't see how anything can happen without "detection".

If an atom decays then its electrical properties change, its gravitational properties will change, and all other matter in the box will be able to "detect" those changes.

That would be true for the camera (as it would be for the decay detector). But the thought experiment assumes that until the box is opened there's no interaction between the observer outside the box and whatever is inside the box. So, for him at least, there's superposition of a dead cat and a cat alive and obviously there would have to be a superposition of two cameras, one for each cat, one recording a dead cat, one recording a live cat. For each camera, the cat would be in one state, definitely dead or definitely alive, and that's what it would be recording.
EB

 

[untermensche]

I don't see how anything can happen without "detection".

If an atom decays then its electrical properties change, its gravitational properties will change, and all other matter in the box will be able to "detect" those changes.

That would be true for the camera (as it would be for the decay detector). But the thought experiment assumes that until the box is opened there's no interaction between the observer outside the box and whatever is inside the box. So, for him at least, there's superposition of a dead cat and a cat alive and obviously there would have to be a superposition of two cameras, one for each cat, one recording a dead cat, one recording a live cat. For each camera, the cat would be in one state, definitely dead or definitely alive, and that's what it would be recording.
EB

How is this state of "no interaction" achieved?

 

[Jesse]

How is this state of "no interaction" achieved?

It's a thought-experiment, so it doesn't really have to be realizable in practice, it just has to respect the known fundamental laws of physics. But if we ever figure out a way to design a large quantum computer, we could imagine simulating an isolated Schroedinger's cat-like system on such a computer--by necessity the "qubits" that make up a quantum computer have to be isolated from interactions with the external environment that produce decoherence (occasional environmental interactions can apparently be compensated for using quantum error correction techniques, as described in this article), and some progress has been made in isolating small numbers of qubits using special types of physical systems that are more easily isolated than most (often involving supercold temperatures so that environmental interactions due to random thermal motions of particles will be minimized). For example, this article has links to some articles about a "superconducting circuit with nine qubits" with effective quantum error correction.

 

[Speakpigeon]

How is this state of "no interaction" achieved?

Everybody here seems to accept that this experiment couldn't be conducted in practice.

I also seem to remember an article saying that this kind of setup would be definitely too large to allow isolation from the environment. Uh-uh.


Still, Schrödinger's point was to emphasise the absurdity of having a really cool cat both dead and alive and people still get excited about this today. But the same idea is examplified just the same by individual particles, like electrons etc, in two superposed states. So we could also have two particles, one playing the cool cat, the other the recording system, with some lab dude loafing about in the role of the observer. But I won't say more until I'm reassured I'll get my share of the Nobel prize.
EB

 

[skepticalbip]

How is this state of "no interaction" achieved?

Everybody here seems to accept that this experiment couldn't be conducted in practice.

I also seem to remember an article saying that this kind of setup would be definitely too large to allow isolation from the environment. Uh-uh.


Still, Schrödinger's point was to emphasise the absurdity of having a really cool cat both dead and alive and people still get excited about this today. But the same idea is examplified just the same by individual particles, like electrons etc, in two superposed states. So we could also have two particles, one playing the cool cat, the other the recording system, with some lab dude loafing about in the role of the observer. But I won't say more until I'm reassured I'll get my share of the Nobel prize.
EB

The cat was only a metaphor for the quantum event. What Shrodinger opposed was the idea of a quantum event being in all allowable states at once (superposition) with its final state only set when "observed" (the Copenhagen interpretation). Schrodinger held that, although an event has a probability of being in any given allowed state, it was only in one discrete state - the decay either had not or had occurred and that observation was irrelevant to the quantum state, only necessary to our knowing that state.

ETA:
If, as you seem to be saying, you believe that quantum events are in superposition until "observed" then you are agreeing that the cat is both dead and alive until the box is opened - the cat only being a metaphor for the quantum event and "opening the box" a metaphor for any "observation".

The thought experiment is that the cat's state mirrors the state of the radioactive particle. The cat alive mirroring the decay not yet having occurred. The cat dead mirroring the particle having decayed. What is the state of the cat (which mirrors the quantum event) while the quantum event is in superposition (both having decayed and not yet decayed) as you seem to say is reality?

 

[fromderinside]

Its an experiment that was changed when a camera was embedded inside the box making the outside observer irrelevant. The box is a metaphor for not having the capacity to measure something. Change the metaphor to a camera inside a box and neither the box nor the observer are necessary, Experiment over when camera records the decay (cat's death).

The guy outside remains an observer. The point is that he won't have access to the inside of the box until the box is opened so until then he has to rely on quantum calculus of probabilities to tell him the range of possibilities. Until the box is opened, this range uncludes a dead cat and a live cat. For the camera inside the box, clearly it will record what is going on. However, for the outside obsever, the two states in superposition describing the inside of the box will include each one a camera, one recording a dead cat, the other recording a live cat. On opening the box, the observer will only see one camera.

Whether before opening the box there is just one camera or two in superposition, it seems we don't know.
EB

Have a camera in the box don't need the observer or the box. The camera doesn't know util it has recorded the dead cat or decay.

Point is a camera was added as if to change the problem. It didn't. It changed the mechanism for observing.

 

[Speakpigeon]

The cat was only a metaphor for the quantum event. What Shrodinger opposed was the idea of a quantum event being in all allowable states at once (superposition) with its final state only set when "observed" (the Copenhagen interpretation). Schrodinger held that, although an event has a probability of being in any given allowed state, it was only in one discrete state - the decay either had not or had occurred and that observation was irrelevant to the quantum state, only necessary to our knowing that state.

Ok.

ETA:
If, as you seem to be saying, you believe that quantum events are in superposition until "observed" then you are agreeing that the cat is both dead and alive until the box is opened - the cat only being a metaphor for the quantum event and "opening the box" a metaphor for any "observation".

Not quite.

First, I'm not a scientist, I don't understand how the math of QM was agreed on, and unfortunately I don't have the means to carry out my own experiments. So, I'm a layman commenting on the theory, I'm not pretending to know what is really going on. Still, as I understand it, scientists don't really know yet whether the cat would settle for one possibility, either dead or alive, even before the observer would have a look. But I still don't pretend I know the answer to that.

Second, I'm on record for criticising people, including scientists, who are happy to say that the same atom (or photon, or electron, or cat) is in two incompatible states. Still, I think basically they just don't pay attention to the way they talk. No big deal except that they confuse the man on the street.

Yet, even if we recognise that it is not the case that one atom is ever in two incompatible states, we could still have two real states at the "same time", each somehow issued from the same object (through entanglement I guess). My point is that if this is so then we no longer have one object but two, scientists careless with words notwithstanding. I also understand that this view of two objects in two different states but coming from one object is that of scientists working on the idea of parallel universes (or histories). I don't know who is right but I like the idea.

The thought experiment is that the cat's state mirrors the state of the radioactive particle. The cat alive mirroring the decay not yet having occurred. The cat dead mirroring the particle having decayed. What is the state of the cat (which mirrors the quantum event) while the quantum event is in superposition (both having decayed and not yet decayed) as you seem to say is reality?

As I said plenty of times, the idea is that there is no one cat. There is one cat dead and there is one cat alive, and there is a sort of superposition of the two whereby an observer outside the closed box doesn't know whether the cat would be dead or would be alive if he ever opened the box right there.

I don't pretend I understand the whole of it and I'd be certainly interested if you had an argument showing that the cat is definitely dead or alive even before the observer has a look-in, for example if there is a camera inside the closed box. To me, it's clear that if there can be a superposition of two cats, there can also be a superposition of two cameras, as I already said.

Still, I don't know that the observer would know that there is in the box just one camera or a superposition of two, one cat or a superposition of two, because the box is closed, which is the point of the experiment.
EB