Quantum uncertainty, and Schrodinger's cat

[Speakpigeon]

A cat can either be alive or dead.

It cannot be both.

If anybody thinks differently provide the evidence of a cat that is both dead and alive.

Strickly speaking it could be something else since there is no science precluding some other state(s).

But I would agree that, at least in the sense of the Schrödinger's experiment, the cat cannot be both dead and alive.
EB

 

[Speakpigeon]

Well, it is one interpretation. Another interpretation is the "many-worlds" interpretation, in which the universe splits and becomes two universes, one in which the cat is alive, and another in which it is dead. Win something in the not-so-absurd department, lose a little in the parsimonious department!

Quantum physics is bafling. The many-worlds interpretation of it seems to fulfill a longing for realism, i.e. there would have to be actual "parallel" universes and almost each event in each universe would create more of them, all as real as each other. Yet, this interpretation is only necessary (or appears to be so) if one wants to insist on the realism of the solution. So, yes, fulfiling that longing, like so many other, does not come cheap.
EB

 

[Speakpigeon]

Whether a cat can be both alive and dead is a matter for biology not physics.

But all one has to do is produce a cat that is both alive and dead to demonstrate my error.

"..the 'paradox' is only a conflict between reality and your feeling of what reality 'ought to be.'"
~ Richard Feynman,


To produce the cat would collapse the wave function so its physical state would be settled. You don't seem to understand (no surprise) what the Copenhagen interpretation is even addressing.

Feynman's remark doesn't apply here since we don't know what is the reality of the cat before opening the box. The contradiction in some descriptions of this situation is that of the description. It's not that of the reality of the situation.
EB

 

[PyramidHead]

I must admit to some ignorance about quantum electrodynamics, but if a cat that is neither (a better word than 'both' I think) alive nor dead is a necessary outcome of the theory, then it would be hard to deny it without denying the whole theory. As I understand, quantum electrodynamics is the most accurate scientific model of reality ever devised, in terms of the predictions it makes about empirically observable phenomena.

You are expressing faith.

Unlike many atheists, I'm not scared of that word. I have a lot of faith in quantum electrodynamics because people smarter than me, with much greater stake in being accurate and vulnerability to being proven wrong, attest to its high degree of accuracy in reputable circles.

I suspect you feel the same way about chemistry: without having to verify it yourself, you accept that a molecule of water is made up of two hydrogen atoms and an oxygen atom.

All I am saying is that if quantum electrodynamics necessarily implies the indeterminate state of a cat in Schrodinger's box, that prediction should be given more weight than one that is not backed by such a successful scientific theory.

I don't share your faith.

I suggest you try to educate yourself on the matter. Quantum mechanics is notorious for two reasons: it is both extremely counterintuitive and extremely likely to be correct. It really doesn't have a precedent in the scientific world, which is why people get so excited about it.

As you have gifted me with your unsolicited opinion of my mindset, allow me to return the favor. You appear to have no curiosity whatsoever about the world you inhabit. If I were to guess at your priorities, you seem to automatically reject any concept that cannot be expressed in two or three lines separated by white space. Reality does not naturally occur in stanza-sized chunks. Sometimes, you need to get past your initial reaction and see where all the threads of evidence (not just the ones that can be rendered as haikus) converge.

 

[Speakpigeon]

According to the famous thought experiment, Schrodinger's Cat exists in a quantum uncertain state until the box is opened, and can thus be both alive and dead.

I've run into someone who insists that this is a logical contradiction, and thus that not only the cat, but quantum uncertainty itself, is impossible.

Logic is secondary to a reality,

I don't think that's true. I think you couldn't justify this claim.

if reality does not fit your logic then it's your logic at fault, not the reality.

That would be true but it doesn't apply to Schrödinger's cat since the experiment is such that the observer doesn't know what is the reality of the situation inside the box. So you cannot claim to know that logic could not fit the reality.

So logic is fine with QM.

See?
EB

 

[Speakpigeon]

Maybe some other option? (note: "Yahweh collapses the wave function" is not a viable option, of course ).

Are you saying Yahweh has no brain?! Grrrr....
EB

 

[Starr]

The corresponding wavelength for a big object is so tiny as to vanish for all practical purposes. This was thought to be why we do not experience weird quantum effects in our everyday lives. The Schrodinger's Cat thought experiment is to show that the stuff classical mechanics applies to being big doesn't prevent quantum effects from dominating, by having the classical state of the cat, completely determined by the quantum state of a radioactive nuclei. Since the nuclei is in a superposition, the cat must also be in a superposition, and only "collapse" to a determined state upon taking a measurement.

However, at the risk of giving untermensche ammunition, it is not correct to say that the cat being simultaneously alive and dead is an absolute logical consequence of Quantum Mechanics being true. It would be a consequence of the Copenhagen Interpretation of Quantum Mechanics being true. The reason is that only by measuring a quantum system does the wave function "collapse" into a determinate observable state under that interpretation. However there are other interpretations of Quantum Mechanics, which could also be true, which do not have this result. Someone already mentioned the Everett interpretation (many-worlds). In this interpretation, everything is completely deterministic, and the cat is either alive or dead in whatever branch of the wave function you occupy, even before you open the box. It is just the fact that it is impossible for you to know which branch you are in that prevents you from deducing the state of the cat before you open the box. Another "interpretation" (in this case actually a completely different theory, that produces equivalent predictions to at least non-relativistic QM), is De Broglie-Bohm Theory, which asserts that there are real particles, which always have real positions, and there is a "quantum force" which is what the wave function is describing. In this theory the cat would also be either alive or dead, and it is only our ignorance of initial particle positions that prevents us from being able to predict which. Another interpretation which I like, but which has a tendency to give me headaches if I think about it to long, is the Relational Interpretation. This one sort of goes in the opposite direction, proposing a world which makes Schrodinger's Cat look passe. In this interpretation nothing has an inherent state. The state of a system is only defined in relation to another system. So under this interpretation, the nuclei, the cat, and the person, are all valid observers. Ignoring the nuclei as observer, the cat observes the nuclei and "knows" whether it decayed or not. To the cat, there is no superposition. To the person outside, viewing the cat+nuclei as a system, there is a superposition. It isn't until you open the box that the superposition you have "collapses" to match whatever the cat measured in the box. This doesn't mean that the cat collapsed the wave function, and you just don't know about it. What it very oddly, and unintuitively means, is that the nuclei is in a definite state in relation to the cat, but is still in a superposition (along with the cat) in relation to the outside observer. Like I said, headaches..... There are other interpretations, or alternative formulations as well. Objective Collapse theories postulate an actual physical process that collapses the wave function, rather than the ill-defined concept of "measurement".

The ultimate problem, is that Quantum Mechanics is not a theory that really describes the world. Something must be happening in each individual experiment, but Quantum Mechanics can't tell us what, it can only tell what we should see over time from a large number of identical preparations of the experiment. QM is just a set of algorithms for making (very good) predictions about the world. What is the wave function? It is a method of figuring out how probabilities of various measurements evolve over time. Standard QM does not imbue it with any sort of realness, it is merely tool. Certain interpretations of QM, such as Everett and DeBroglie-Bohm, do imbue it with realness. Not worrying about this is one of the reason the physics of the past century was so successful. Physicists worried that there was no good ontology for Quantum Mechanics fell by the wayside, as those who followed the advice of the Instrumentalist Interpretation (i.e. no interpretation) to "shut up and calculate" made great strides forward.

So, TLDR: Whether the cat is in a superposition until you open the box is a matter of the interpretation of Quantum Mechanics. Nearly all interpretations will produce the same results as standard QM, so you can't tell one way or the other which is right.

 

[barbos]

Logic is secondary to a reality,

I don't think that's true. I think you couldn't justify this claim.

Logic is human construct purpose of which is to make sense of reality.

if reality does not fit your logic then it's your logic at fault, not the reality.

That would be true but it doesn't apply to Schrödinger's cat since the experiment is such that the observer doesn't know what is the reality of the situation inside the box. So you cannot claim to know that logic could not fit the reality.

Reality of the situation is that cat is in superposition state.

So logic is fine with QM.

See?
EB

Yes, correct logic is fine with QM.

 

[untermensche]

A cat can either be alive or dead.

It cannot be both.

If anybody thinks differently provide the evidence of a cat that is both dead and alive.

Strickly speaking it could be something else since there is no science precluding some other state(s).

But I would agree that, at least in the sense of the Schrödinger's experiment, the cat cannot be both dead and alive.
EB

I don't know.

Death is the complete absence of life.

 

[Speakpigeon]

It doesn't matter how you try to couch an unsupported claim.

Without evidence to support it I have no reason to believe in beasts such as cats that are both alive and dead.

I don't think you understand the Schrödinger's cat thought experiment:

1) The cat in the experiment is placed in a 'box' (an unobservable location),

2) The 'box' also contains a mechanism that will, with 100% certainty, kill the cat if a certain quantum event (eg the decay of a radioactive particle), which has a 50% chance of happening, occurs.

3) We know from Quantum theory that it is only possible to correctly predict the future state of a quantum system in which such an event may have occurred, by considering the event (in this case, the radioactive decay) to exist in a superimposed state of both having occurred and having not occurred, until such time as an observation 'collapses the wave function', to produce only one of the two possible outcomes.

1, 2 and 3 are not in dispute; 1 and 2 are premises of the experiment, and 3 is amongst the best supported facts in all of science today.

4) Given 3 and 2, we can say with confidence that the only way to correctly model the future state of the system before it is observed, is to consider it as existing in superimposed states of both possible outcomes having occurred; and that this superposition of states must apply not only to the microscopic event (the radioactive decay), but also to the macroscopic event (the life or death of the cat).

This thought experiment was specifically designed to highlight the fact that the observed reality at the quantum level is both transferable to the macroscopic level, and completely at odds with our understanding of reality. In other words, it is exactly as reasonable to think of a cat that is both dead and alive, as it is to think of a radioactive material that has both decayed and not decayed, or an electron that is both over here and over there at the same time - and it is demonstrable that these are irretrievably connected states of affairs. If it is possible for electrons to be in two places at once, then it is also possible for cats to be both alive and dead simultaneously (and the life or death of the cat in this thought experiment is merely a place-holder - for all probabilistic events at all scales - and has nothing to do with life per se, so it is not a biological question).

Now, one can (and clearly you do) try to resolve this by simply declaring that at all scales, probabilistic events are immediately resolved - the radioactive decay either happens OR it does not; the electron passes through slit A OR slit B; the cat is alive OR dead.

But we know from experiment, and from Quantum theory, that this is not true. We know (with as great a degree of certainty as we have ever known anything), that the radioactive decay BOTH happens AND it does not; and that the electron passes through BOTH slit A AND slit B, unless and until an observation is made to determine which of these actually occurred. The only logical conclusions we can therefore reach, are that either the cat is BOTH alive AND dead, or that Quantum theory is completely wrong.

It seems unreasonable to throw out the single best supported scientific theory in history, simply because we don't like the un-testable and unobservable consequences that this theory has for reality.

What seems illogical in your presentation of QM is the apparent claim that there just one cat in two logically incompatible states (or one electron in two different places at the same time). If you want to insist on this formulation, then untermensche is correct, you are claiming that a contradiction is true.

Alternatively, you could try to see where the problem might be (instead of, somehow, inside untermensche).

For example, I don't think that QM explicitly tells you that there is just one cat (in two incompatible states), or even that there is any cat (for example, there are maybe two wave functions but no actual cat). In all the descriptions and explanations I have looked at, not one scientist ever insisted that, actually, there would be one cat in two incompatible states. This formulation seems to appear as a sort of sloppy short-cut for saying that there are two wave functions. In other words, the "one cat, two states" is not science, it's just sloppy wording from scientists.
EB

 

[skepticalbip]

"..the 'paradox' is only a conflict between reality and your feeling of what reality 'ought to be.'"
~ Richard Feynman,


To produce the cat would collapse the wave function so its physical state would be settled. You don't seem to understand (no surprise) what the Copenhagen interpretation is even addressing.

Feynman's remark doesn't apply here since we don't know what is the reality of the cat before opening the box. The contradiction in some descriptions of this situation is that of the description. It's not that of the reality of the situation.
EB

That is an argument you would have to take up with Feynman. I stand by my statement that producing the cat would collapse the wave function so set the physical state of the cat. I also stand by my view that Unter- shows no sign of having a clue what the Copenhagen interpretation is addressing.

 

[Speakpigeon]

I'm really looking forward to the day that untermensche backs down from one of his 'grand proclamations of obvious truth'.

I advise against holding your breath.

Yeah, he could end up both dead and alive.
EB

 

[barbos]

and the cat is either alive or dead in whatever branch of the wave function you occupy, even before you open the box. It is just the fact that it is impossible for you to know which branch you are in that prevents you from deducing the state of the cat before you open the box.

Not quite. In MWI "collapse" is replaced with "branching" or "decoherence" which happens when you open the box and interact with cats wavefunction. Before that it's superposition.

 

[Speakpigeon]

So, TLDR: Whether the cat is in a superposition until you open the box is a matter of the interpretation of Quantum Mechanics. Nearly all interpretations will produce the same results as standard QM, so you can't tell one way or the other which is right.

Yeah, so there is this superposition of interpretations and they are all correct and not correct at the same time...
EB

 

[Speakpigeon]

Strickly speaking it could be something else since there is no science precluding some other state(s).

But I would agree that, at least in the sense of the Schrödinger's experiment, the cat cannot be both dead and alive.
EB

I don't know.

Nor do I.

Death is the complete absence of life.

I don't think science has any fundamental definition of death v. life. Instead, there has been a constant shift throughout history of where the threshold might be. It's a pragmatic view and in the past some people who were regarded as dead would now be regarded as still alive (and maybe some cases would be the reverse). So there is a time interval when we don't really know if the person is dead or is alive and even if science can furhter narrow that window I think there will always be one, and with it, people who cannot be said to be nor dead, nor alive.

But I agree with you as to Schrödinger's cat because the situation is one where the cat is either really-really dead or really-really alive.
EB

 

[Speakpigeon]

Feynman's remark doesn't apply here since we don't know what is the reality of the cat before opening the box. The contradiction in some descriptions of this situation is that of the description. It's not that of the reality of the situation.
EB

That is an argument you would have to take up with Feynman.

Ok, I'll give him a call tonight.

I stand by my statement that producing the cat would collapse the wave function so set the physical state of the cat.

Sure.

I also stand by my view that Unter- shows no sign of having a clue what the Copenhagen interpretation is addressing.

Maybe his point isn't about the Copenhagen interpretation or even about Schrödinger's cat thought experiment or even about QM. I agree with him that one cat cannot be dead and alive at the same time and this has nothing to do with QM. The fault may lie with the way people choose to phrase their understanding of QM.
EB

 

[Valjean]

With the Standard Interpretation, dead or alive doesn't really apply to the "cat" in the box. In the box is an indeterminate field of catness potential (maybe). It's you who chooses the contents when you open the box.

 

[Juma]

"..the 'paradox' is only a conflict between reality and your feeling of what reality 'ought to be.'"
~ Richard Feynman,


To produce the cat would collapse the wave function so its physical state would be settled. You don't seem to understand (no surprise) what the Copenhagen interpretation is even addressing.

Feynman's remark doesn't apply here since we don't know what is the reality of the cat before opening the box. The contradiction in some descriptions of this situation is that of the description. It's not that of the reality of the situation.
EB

You seem to indicate that the multistate is just a matter of uncertainty. That is wrong. The quantum multistate is really all states at the same time.

 

[Starr]

and the cat is either alive or dead in whatever branch of the wave function you occupy, even before you open the box. It is just the fact that it is impossible for you to know which branch you are in that prevents you from deducing the state of the cat before you open the box.

Not quite. In MWI "collapse" is replaced with "branching" or "decoherence" which happens when you open the box and interact with cats wavefunction. Before that it's superposition.

Ahh, you are quite right, I haven't read up on MWI in awhile and messed up the details there a bit.

 

[untermensche]

I don't know.

Nor do I.

Death is the complete absence of life.

I don't think science has any fundamental definition of death v. life. Instead, there has been a constant shift throughout history of where the threshold might be. It's a pragmatic view and in the past some people who were regarded as dead would now be regarded as still alive (and maybe some cases would be the reverse). So there is a time interval when we don't really know if the person is dead or is alive and even if science can furhter narrow that window I think there will always be one, and with it, people who cannot be said to be nor dead, nor alive.

But I agree with you as to Schrödinger's cat because the situation is one where the cat is either really-really dead or really-really alive.
EB

In terms of something like a cat you could reduce it to the cellular level.

Then a dead cat is a cat where no "cat cells" are alive. Clinical death may come before this but this is ultimate death or as you say really-really dead.

If you do this then the fuzziness is not very fuzzy. It is not hard to tell the difference between a living cat cell and a dead cat cell.

So in this case death would be the complete absence of life.