Applying Schrodinger's Cat Experiment

[noname2020x]

I know that Schrodinger's Cat experiment is a thought experiment, but why not apply it and see if sound waves are impacted by quantum uncertainty. If the cat, or any other animal dies you can make it sound off by a heart rate monitor or something else. Would this act remove the uncertainty aspect of the experiment?

 

[Bill_K]

Schrodinger's Cat requires that the cat must be completely isolated from the outside. That means you can't listen for the cat to meow, weigh the box, shake it, monitor its temperature, etc.

 

[jtbell]

you can't listen for the cat to meow

i.e. it has to be in a vacuum (which would use up some of its nine lives )

monitor its temperature

which (the cat being in a vacuum) could reveal itself only via radiation. To prevent radiation, the cat would have to be at absolute zero, which means using up the rest of its lives.

 

[noname2020x]

So uncertainty is dictated by observation as in the double slit experiment. Is that what I am understanding? Only observation after the fact determines the actual result?

 

[markb287]

Schrodinger's Cat requires that the cat must be completely isolated from the outside. That means you can't listen for the cat to meow, weigh the box, shake it, monitor its temperature, etc.

Would this not mean that you have to place the cat into a position of uncertainty, a position where the experimenter must be uncertain whether or not the cat is alive or dead in order for the cat to be "said" to be both dead and alive? That would seem to imply that it is not the decay of the radioactive atom that produces the results of the experiment, but it is the experimenter.

Taking this back to the double slit experiment, this conclusion would also seem to imply that it is not the electron beam which produces the interference pattern, but the experimenter, who, in order to produce the interference pattern, must not be able to "measure" the "electrons" passing through the two slits.

In other words, could we not say that it is the experimenter's uncertainty that produces the superposition of states (dead and alive; interference pattern), rather than the subjects of the experiment (the radioactive atom/cat; the electron beam)?

 

[DrChinese]

... In other words, could we not say that it is the experimenter's uncertainty that produces the superposition of states (dead and alive; interference pattern), rather than the subjects of the experiment (the radioactive atom/cat; the electron beam)?

Welcome to PhysicsForums, markb287!

In a sense, that is correct. The experimenter creates what is sometimes called a measurement (or observation) context. That context, when properly arranged, creates a situation in which the superposition can exist. For a double slit experiment, that means a context where the which-slit information is obscured to get the interference pattern.

In essence, the number of target outcomes (relative to some source) is somehow restricted, controlled or funneled. Other outcomes are then ignored.

 

[markb287]

Welcome to PhysicsForums, markb287!

In a sense, that is correct. The experimenter creates what is sometimes called a measurement (or observation) context. That context, when properly arranged, creates a situation in which the superposition can exist. For a double slit experiment, that means a context where the which-slit information is obscured to get the interference pattern.

In essence, the number of target outcomes (relative to some source) is somehow restricted, controlled or funneled. Other outcomes are then ignored.

Thank you, DrChinese, for your response and welcome!

Going further, could we not also say that electrons (or protons, neutrons, photons, etc.) are neither particles nor waves, but are simply, for lack of better words, "quantum stuff" or "subatomic stuff" that, when placed in situations of relative certainty (e.g. turning on the light to observe which slit they went through), produce results consistent with what we can describe as particle behavior, and that, when placed in situations of uncertainty (e.g. we turn off the light), produce results consistent with what we can describe as wave behavior?

In other words, can we say that electrons only act as particles when placed in situations of relative certainty and only act as waves when placed in situations of uncertainty?

I apologize if my questions sound very picky, repetitive, or haven't taken the conclusion very far. I just want to be as concise as possible because I think it is the language behind quantum mechanics that makes the subject even more difficult to understand than it already is.

 

[BruceW]

So uncertainty is dictated by observation as in the double slit experiment. Is that what I am understanding? Only observation after the fact determines the actual result?

Yeah. The principle is that the state is not originally in an eigenstate of the quantity we are measuring, so when we make a measurement, the state changes (with some probability) to one of the eigenstates associated with the observable quantity.

Whether the same principles of quantum mechanics applies to dead or alive cats is still untested. But also, it has not been disproven. But also, it would be very difficult to make an experiment that actually puts a cat into a pure quantum state which is not an eigenstate of "dead or alive".

 

[DrChinese]

Thank you, DrChinese, for your response and welcome!

Going further, could we not also say that electrons (or protons, neutrons, photons, etc.) are neither particles nor waves, but are simply, for lack of better words, "quantum stuff" or "subatomic stuff" that, when placed in situations of relative certainty (e.g. turning on the light to observe which slit they went through), produce results consistent with what we can describe as particle behavior, and that, when placed in situations of uncertainty (e.g. we turn off the light), produce results consistent with what we can describe as wave behavior?

In other words, can we say that electrons only act as particles when placed in situations of relative certainty and only act as waves when placed in situations of uncertainty?

I apologize if my questions sound very picky, repetitive, or haven't taken the conclusion very far. I just want to be as concise as possible because I think it is the language behind quantum mechanics that makes the subject even more difficult to understand than it already is.

Sure, fine descriptions!

However, usually one says a quantum object is like a particle when it's position is relatively certain but it's momentum is not. And vice versa for a wave, uncertain position and more certain momentum.

 

[markb287]

Sure, fine descriptions!

However, usually one says a quantum object is like a particle when it's position is relatively certain but it's momentum is not. And vice versa for a wave, uncertain position and more certain momentum.

I see. So let me modify my statement:

Electrons (or any quantum object) exhibit particle behavior when they are in a situation where their position is relatively certain, but their momentum is not; and they exhibit wave behavior when their momentum is relatively certain, but their position is not.

The main point behind this is that quantum objects are neither particles nor waves, but are simply phenomena that exhibit particle or wave behavior according to the experimenter's degree of measurable certainty. In other words, their behavior is dependent upon the experimenter's uncertainty in some aspect (position or momentum).

In addition, as per Bohr's Complementarity Principle as well as Heisenberg's Uncertainty Principle, an electron cannot exhibit particle behavior and wave behavior at the same time. Rather, the behavior is mutually exclusive, dependent on the type of experiment you conduct (relative certainty in measuring position requires uncertainty in measuring momentum, and vice versa).

So let's return back to the double slit experiment/Schrodinger's Cat experiment. If we place the electron beam (or the cat) in a position of uncertainty with regards to its position or state (i.e. turn the light off; isolate the cat), so that we cannot measure its position or state, thereby producing wave behavior as well as excluding the possibility of producing particle behavior, what point is there in interpreting the interference pattern or superposition as a probability of the electron's arrival or the cat's state? Wouldn't the term "probability" be a misnomer, since the electron (or the cat) doesn't express a position (particle behavior) when placed in a position of uncertainty, since the behavior of positionality cannot be produced?

It would seem to me that since the electron's position is held in a position of uncertainty, the electron doesn't express positionality. And it is this uncertainty with regards to positionality that actually produces the interference pattern.

In other words, there is no "probability of the electron's arrival" because the electron doesn't express an arrival (i.e. its arrival is not being measured). The only value expressed is the momentum of the electron beam, to the degree to which it can be measured by the backdrop.

Unless, of course, the backdrop re-establishes relative certainty with respect to the electron's position. Would this be the case? If not, the question as to what the wave function actually represents is, I believe, still left unanswered by quantum mechanics.

 

[mfb]

If you could isolate/freeze/... the cat sufficient to get a superposition of two different cat states, you could do interference experiments with cats. You have to describe it as superposition and not as probabilities of (cat lives) and (cat is dead).

While position and momentum uncertainty have some relation to particle-like and wave-like behavior, they are not the same.

 

[markb287]

While position and momentum uncertainty have some relation to particle-like and wave-like behavior, they are not the same.

You are right. Position is not the same as particle-behavior, nor is momentum wave-like behavior. However, the act of measuring the position of a quantum object produces particle-behavior in that object, just as the act of measuring the momentum of a quantum object produces wave-behavior. When you use an apparatus to see if the electron is passing through slit A or slit B, you are treating the electron as a particle, which it ends up acting as (i.e. you can tell whether or not it passed through slit A or slit B).

However, it only acts this way when you treat it like a particle. If you don't, then it produces an interference pattern, acting as a wave. My argument is that the probabilistic interpretation, which reads the interference pattern as a probability of the electron's arrival on the backdrop, is not adequate, since an electron cannot be said to have an "arrival" -- i.e. since its positionality depends upon our ability to measure it.

It simply "appears" on the backdrop as the backdrop measures its position.

 

[mfb]

If you measure the slit (but not the precise position in the slit), you still get interference: single-slit interference. It is not "particle OR wave", you always have both.

since an electron cannot be said to have an "arrival"

There is some time where the electron arrived in every interpretation.

 

[dlgoff]

If you could isolate/freeze/... the cat sufficient to get a superposition of two different cat states, you could do interference experiments with cats.

OMG :rofl:

I'd love the those interference patterns on a screen.

 

[markb287]

If you measure the slit (but not the precise position in the slit), you still get interference: single-slit interference. It is not "particle OR wave", you always have both.

You are right -- it is not "particle OR wave." However, it is producing particle-behavior OR producing wave-behavior. You cannot produce both particle results AND wave results at the same time. This is inherent in both the Principle of Complementarity and the Principle of Uncertainty.

There is some time where the electron arrived in every interpretation.

This is because physicists still are relying on the idea of electron as particle. Even the Born interpretation does this. But there's no sense in talking about an electron "arriving" at the screen when its position -- between the time we stop measuring and the time it appears on the screen -- is fundamentally uncertain. Uncertainty is a state of existence that we can produce experimentally, and it is our job not to "deal" with the state of uncertainty by using probabilities, but to understand it.

 

[mfb]

You are right -- it is not "particle OR wave." However, it is producing particle-behavior OR producing wave-behavior. You cannot produce both particle results AND wave results at the same time. This is inherent in both the Principle of Complementarity and the Principle of Uncertainty.

No, it is just a language thing. No physical law has "particle" or "wave" in its formulas.

This is because physicists still are relying on the idea of electron as particle.

You can consider the time when the wave, probability distribution or whatever arrived, it does not matter. They are just models, using different words to describe the same experimental result.

 

[markb287]

No, it is just a language thing. No physical law has "particle" or "wave" in its formulas.

That's because no physical law has "formulas." The formulas are "just a language thing" also.

You can consider the time when the wave, probability distribution or whatever arrived, it does not matter. They are just models, using different words to describe the same experimental result.

The issue is not whether the models describe the same experimental results. I could provide many different models that describe the results of any experiment. The issue is whether or not the model helps produce a better understanding of the results. That's the whole game of science.

 

[mfb]

That's because no physical law has "formulas." The formulas are "just a language thing" also.

Formulas require interpretation, too, but they are way better than english (or any other spoken language). Their language is mathematics, this avoids ambiguity.

The issue is not whether the models describe the same experimental results. I could provide many different models that describe the results of any experiment.

If they have a similar complexity (easier=better of course) and applicability range as to the current ones: Publish them.

 

[markb287]

Formulas require interpretation, too, but they are way better than english (or any other spoken language). Their language is mathematics, this avoids ambiguity.

Mathematics, on its own, cannot avoid ambiguity; it is only the context of the communication that can do that. If we don't have the same context for understanding the communication (e.g. that electrons are neither particles nor waves; that electrons do not "arrive" at the screen, and therefore do not express a probability of arrival when they are not measured, etc.), then we will be misunderstanding each other or the results.

If they have a similar complexity (easier=better of course) and applicability range as to the current ones: Publish them.

To publish them requires actually having ideas, which I don't (I have only suspicions and hypotheses, but nothing even close to being publishable). I simply wish to establish for my own understanding what it is that we can reasonably conclude from the experimental results of the double-slit experiment in order to establish what is possible or not possible to interpret.

 

[mfb]

Mathematics, on its own, cannot avoid ambiguity; it is only the context of the communication that can do that.

Well, let me phrase it differently: mathematics allows to communicate without ambiguity.

If we don't have the same context for understanding the communication (e.g. that electrons are neither particles nor waves; that electrons do not "arrive" at the screen, and therefore do not express a probability of arrival when they are not measured, etc.), then we will be misunderstanding each other or the results.

This can happen if you do not use mathematics.

To publish them requires actually having ideas, which I don't (I have only suspicions and hypotheses, but nothing even close to being publishable).

In other words, you do not have new good models.
Finding good models is a hard part of science. And if you include the relation between models and experimental results, it is the interesting part of science.

I simply wish to establish for my own understanding what it is that we can reasonably conclude from the experimental results of the double-slit experiment in order to establish what is possible or not possible to interpret.

See interpretations of quantum mechanics.

 

[markb287]

Well, let me phrase it differently: mathematics allows to communicate without ambiguity.

I doubt that. If that were the case, the Born interpretation would have satisfied quantum physicists all on its own. And yet it is a continual problem for physicists and was ever since it was proposed, although the mathematics is all there. This was the case when Heisenberg had developed matrix mechanics to describe quantum phenomena, and when Schrodinger had come up with wave mechanics to do the same. Both had problems knowing how to "interpret" the mathematics -- i.e. to find the right context for understanding the phenomena.

Again, the only way we can get out of that problem is if there is a specific context for understanding the mathematics, and this context must be, by nature, non-mathematical (and non-linguistic, to be exact).

Of course, this is not to say that mathematics is not helpful (it's extremely helpful), but on its own it cannot allow for unambiguous communication.

In other words, you do not have new good models.
Finding good models is a hard part of science. And if you include the relation between models and experimental results, it is the interesting part of science.

I agree completely. But my goal in posting right now is not to establish a model, but, as I just said, to establish what could be usable for a new model, since I'm arguing that the "standard" model is not adequate.

See interpretations of quantum mechanics.

Again, I have read interpretations of quantum mechanics, and none of them seem to me to be adequate, unless there is something that I'm missing.

If so, please illuminate for me.

 

[mfb]

I doubt that. If that were the case, the Born interpretation would have satisfied quantum physicists all on its own. And yet it is a continual problem for physicists and was ever since it was proposed, although the mathematics is all there. This was the case when Heisenberg had developed matrix mechanics to describe quantum phenomena, and when Schrodinger had come up with wave mechanics to do the same. Both had problems knowing how to "interpret" the mathematics -- i.e. to find the right context for understanding the phenomena.

Careful, you are mixing theory and interpretation here. Quantum mechanics is a theory - it is extremely successful, and its results are not ambiguous. Interpretations of quantum mechanics are different - but you do not need them, "shut up and calculate" (with Born rule, not interpretation) works.

I agree completely. But my goal in posting right now is not to establish a model, but, as I just said, to establish what could be usable for a new model, since I'm arguing that the "standard" model is not adequate.

Well, if that would be known, we would have an alternative to QM, I think.

Again, I have read interpretations of quantum mechanics, and none of them seem to me to be adequate, unless there is something that I'm missing.

If so, please illuminate for me.

All of them can be used to do science. They all have some parts which are not intuitive, or parts with unclear mechanisms, but they all work and give correct results.

 

[markb287]

Careful, you are mixing theory and interpretation here. Quantum mechanics is a theory - it is extremely successful, and its results are not ambiguous. Interpretations of quantum mechanics are different - but you do not need them, "shut up and calculate" (with Born rule, not interpretation) works.

I think we have two different "interpretations" for the term "interpretation." An interpretation is simply a statement that expresses some kind of understanding regarding some aspect of something (in this case, nature). It's something you express in order to produce an understanding of some event or phenomena. Interpretations can be proven or unproven.

A scientific theory is quite simply a set of propositions that describe certain aspects of nature and whose truthfulness can be demonstrated experimentally. A proposition (in the context of science) is a declarative statement that expresses a specific interpretation of nature.

So a scientific theory is a type of interpretation. And if a scientific theory doesn't produce a strong enough understanding of some phenomena of nature, then it is not an adequate interpretation, regardless of whether or not it is able to produce reliable experimental results. Newton's theory of gravitation, for example, is able to produce accurate results, but that doesn't mean it was an accurate theory. Accuracy is not simply dependent upon results, but upon understanding. In this way, the probability theory of quantum mechanics is an interpretation. My argument is that it is not an adequate one.

Now, the imperative, "Shut and calculate," is not a theory. It has nothing to do with the theory itself, but with how we should "treat" the theory (i.e. to let it go). Someone could have just as easily told Einstein to "shut and calculate" when it came to discrepancies in Newtonian physics. But that has nothing to do with Newtonian physics itself.

 

[BruceW]

I agree with mfb. Mathematics is the least ambiguous part. With pure maths, we have very rigorous definitions and proofs. In physics, we have less rigorous definitions and proofs. (Which is why they are often called 'derivations' rather than strict mathematical proofs). The more we keep to the mathematical side, the more rigorous we stay.

For example, a dirac delta function is a mathematical object. The mathematical formulae associated with it are unambiguous and rigorous. We could then associate it with the 'position' of a 'particle' in our theory. When we do this, there are going to be issues with interpretation, and what it actually is supposed to mean.

Edit: I suppose I am saying that any physical theory has some element of interpretation, and that element is the non-mathematical part. I guess I am agreeing with both of you really. Since it seems mfb is taking 'theory' to mean the very core, most-mathematical part. And markb287 seems to be taking 'theory' in a broader sense.

 

[mfb]

I think we have two different "interpretations" for the term "interpretation." An interpretation is simply a statement that expresses some kind of understanding regarding some aspect of something (in this case, nature). It's something you express in order to produce an understanding of some event or phenomena. Interpretations can be proven or unproven.

There are no proofs in physics.
I use "interpretation" as in interpretations of QM.

A scientific theory is quite simply a set of propositions that describe certain aspects of nature and whose truthfulness can be demonstrated experimentally. A proposition (in the context of science) is a declarative statement that expresses a specific interpretation of nature.

You can fail to falsify a theory, but you cannot prove it - a (useful) theory can be used for an infinite set of predictions, and you cannot perform infinitely many experiments.

In this way, the probability theory of quantum mechanics is an interpretation. My argument is that it is not an adequate one.

There are probabilistic interpretations - and non-probabilistic ones.

Someone could have just as easily told Einstein to "shut and calculate" when it came to discrepancies in Newtonian physics.

No, he could not - Einstein would have gotten wrong results. This quote has a special meaning in quantum mechanics, and its application is unique to QM, where interpretation (see first part) is not trivial. Newtonian gravity and SR/GR do not need a separate interpretations.

 

[markb287]

You can fail to falsify a theory, but you cannot prove it - a (useful) theory can be used for an infinite set of predictions, and you cannot perform infinitely many experiments.

My fault here, my friend. The word I meant to say was "testable," not "proven."

No, he could not - Einstein would have gotten wrong results. This quote has a special meaning in quantum mechanics, and its application is unique to QM, where interpretation (see first part) is not trivial. Newtonian gravity and SR/GR do not need a separate interpretations.

The topic of what a theory "should" do is obviously one that has been argued over and over, especially in the case of quantum mechanics. You seem to be arguing the case for instrumentalism, while I am arguing more for the case for realism.

The mathematics of quantum mechanics is battle-tested, a fact which I am not doubting. The issue is that the mathematics of quantum mechanics itself is not a complete theory. It's simply symbols (variables, operators, numbers, etc.). What makes something a theory is not simply the fact that its claims can be tested, but that its claims can be interpreted as testable, with experiments themselves being interpretations of claims. Conducting a test on the claim, "When I let go of this ball, the ball will accelerate towards the ground at a rate of 9.8 m/s^2," requires an interpretation (i.e. understanding) of how it will even be possible to even test the claim. This understanding is implicit (i.e. contextual), produced from a frame of understanding about the physics/mathematics of the situation that we already have, but still very much present in the theory and is indispensable to it.

My goal is simply to make what is implicit in the double-slit experiment (or Schrodinger's Cat experiment) more explicit so that we can better interpret the results of the experiment and possibly conduct more experiments that can produce more elucidating results. The issue is much more than a "language thing": it is a "context" thing, which is necessary for any viable scientific theory, since the context is what allows us interpret the claim as testable. To say that the interference pattern of the electron beam expresses the probability of an electron's arrival assumes that the electron "arrives" -- i.e. travels from one place to another. But I don't know how to understand this claim if the position of the electron must be uncertain in order to get the interference. And if it's not the probability of "arrival," then what is it the probability of, to be concise?

If you could elucidate this issue for me, I'd be very thankful.

 

[mfb]

In my opinion, this is getting a discussion about words and their meaning only - I'm out.

 

[leamphil]

Getting back to the Cat, I have always had a problem with this thought experiment ... the moment when the radioactive decay occurs is unknowable, that I can see, but whether the cat is alive or dead is simply unknown - not the same thing in my mind.

Unlike the experiments where the act of observation introduces uncertainty, measuring whether the cat is alive or dead in no way affects the unknowable moment of radioactive decay so would not affect the situation one way or another.

In my view the whole thing was just a moment of humour between Schrodinger and Einstein ?

One could have exactly the same "unknown" state from tossing a coin - does that mean that to an observer the wavefunction has not collapsed until the result of the toss is revealed ?

 

[markb287]

In my opinion, this is getting a discussion about words and their meaning only - I'm out.

I understand your frustration in this matter and respect your decision to leave this discussion. But my question still stands, and has been left unanswered. I'll restate it for anyone generous enough to reply.

If the value of an electron's position is essentially produced by either the experimenter "looking" at the electron with some apparatus or by the phosphorescent screen, at which the electron "appears" (for lack of better word), and if the interference pattern is essentially produced only when the electron's position is measured when it "appears" at the phosphorescent screen, then isn't the quantum mechanical probability simply an "interpretation" of the electron's movement from the source to the screen?

To say, for example, that, according to the wave function, it is equally probable that the electron passes through both slit A and slit B (or that the cat is both alive and dead), assumes that there was any passing to begin with. This "assumption" is not verified by the experiment, since, according to the Heisenberg principle, position and momentum cannot be measured precisely at the same time, so that we cannot create the interference pattern and measure the electron's precise position before it hits the screen.

My hypothesis is that the terms "arrival," "travel," "passes," etc. are superfluous, adding unnecessary interpretation to the process. All we know is that the source is turned on, we hear some clicks (as per Feynman's description), then detect an interference pattern on the screen. Everything that happens in between is fundamentally uncertain.

If I'm wrong here in my interpretation, please elucidate so I can finally get some sleep. And if you believe this is a stupid discussion and not worth discussing, then I apologize beforehand.

 

[markb287]

One could have exactly the same "unknown" state from tossing a coin - does that mean that to an observer the wavefunction has not collapsed until the result of the toss is revealed ?

It's not the exact same unknown. The unknown from the Heisenberg Uncertainty Principle is qualitatively different (i.e. it is a fundamental characteristic of nature) from the unknown of a coin toss. The unknown of a coin toss is simply ignorance, where it could be known if you have the right calculative ability, while the unknown of a radioactive decay in the nucleus of an atom is in a physical state of uncertainty.

 

[leamphil]

... and the state of the Cat is of the same order as the state of the coin toss (ie. unknown not unknowable).

If you can impose conditions on the Cat to make it unknowable (ie. sealed away somehow) as distinct to unknown, then you could impose those same conditions on the coin toss.

 

[markb287]

... and the state of the Cat is of the same order as the state of the coin toss (ie. unknown not unknowable).

If you can impose conditions on the Cat to make it unknowable (ie. sealed away somehow) as distinct to unknown, then you could impose those same conditions on the coin toss.

This brings up a really good question. I wonder if it is possible to produce the effects of the Uncertainty Principle onto large scale objects by imposing conditions of uncertainty (i.e. complete isolation). Does the Uncertainty Principle only work for the very small, or could it also be applied to the large?

 

[leamphil]

The only guaranteed "complete isolation" I can envisage would arise from being outside the light cone of the observer - with obvious implications on ever finding out the result of any experiment !

 

[leamphil]

One other "complete isolation" scenario (because the physics would prevent any information escaping) would be behind the event horizon of a black hole. If the black hole then evaporated (?) one could then see the result but perhaps, due to time dilation, nothing much would have happened ?

 

[markb287]

The only guaranteed "complete isolation" I can envisage would arise from being outside the light cone of the observer - with obvious implications on ever finding out the result of any experiment !

That's an interesting idea. Physically, we wouldn't have any way of testing whether or not there was a superposition of states. I think Schrodinger's idea was simply to tell us how bizarre the implications of the probability interpretation of the wave equation are (e.g. the idea that a cat, or any organism, could be both dead and alive at the same time). It is not actually an experiment that he thought out, since he was focused simply on the implications themselves. The question is: what would be the "screen" that would allow us to record the interference pattern of a cat being both alive and dead?