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

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

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

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

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

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

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

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

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

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.

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

dlgoff

OMG

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

markb287

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.

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

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

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

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

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.