Did I miss the point of Schrodinger's Cat?

[BobbyJoeCool]

Experts... feel free to be completly... free in expressing your disapointment in me for asking this question...

 

But there's something I don't understand... The cat is potentially alive and dead at the same time until observed by an outside observer. What exactly does this prove? All it seems to prove to me is that Man is exerting his superiority over the universe, and that the cat is not dead until a Man observes it to be true. I mean, the cat is either dead or alive. Just because no one knows, only makes it unknown. Or is that the point.

[ydoaPs]

the point of the experiment is that a particle is in multiple states until it interacts with another particle.

[BobbyJoeCool]

specifically what are you talking about.. I assume you mean the particle that, when it decays, kills the cat. But what does it interact with? Right now I just assume it's right in front of my nose, but I just can't see it.

[ydoaPs]

no, that's not what i meant.

 

the cat represents the particle and the observation represents another particle interacting with the first.

[BobbyJoeCool]

I guess this is just above my understanding then, because I just don't see what you're saying. I just see someone saying that until they observe something, it has and hasn't happened. whereas from our POV this is true, but it either has or hasn't happened. Right?

[ydoaPs]

particles states are undetermined until they are forced to be. until an interaction, a particle only has a probability of having any state.

[BobbyJoeCool]

but even though you and I don't know what the state is, it still has one. We just don't know what it is. The probablility that it decayed is irrelevent to whether or not it actually has. It has a state, observed or not, it still has it's state. but what it sound like to me (and this is why I don't understand it I guess), is that he's saying that we don't know what it's state is until we know what it is. Just in fancy sciency terms...

[ydoaPs]

no, it doesn't.

[BobbyJoeCool]

as I said, I guess it's above my head.

[matt grime]

the cat is alive or dead... can you prove that? without opening the box? do you know? how do you know?

 

think on it as a metaphor if you will. classically the cat is alive or dead, one or t'other though we know not. but not in the QM model. remember these are just models, and it turns out that the QM model is the correct (or the best we have) at the (sub)atomic scale. apologies if i'm offending the experts here; i am not one.

 

take the two slits experiment. though i know not the details it is possible to fire a photon (or was it an electron) at two slits and to show it simultaneously passes through both slits which classically it couldn't do, since it must pass through one or the other.

 

this, i am sure, is a gross misrepresentation of it. there are, if i recall correctly, two different interpretations of "the cat", the danish and the other one. try reading some essays on them.

[swansont]

but even though you and I don't know what the state is, it still has one. We just don't know what it is. The probablility that it decayed is irrelevent to whether or not it actually has. It has a state, observed or not, it still has it's state. but what it sound like to me (and this is why I don't understand it I guess), is that he's saying that we don't know what it's state is until we know what it is. Just in fancy sciency terms...

 

No, actually, that's one of the strange things about QM. Its not "in one state but you can't tell" - it actually is in both states. In the latter condition you get interference effects of the two states, which are observed, and you wouldn't get them in the former condition.

[[Tycho?]]

Experts... feel free to be completly... free in expressing your disapointment in me for asking this question...

 

But there's something I don't understand... The cat is potentially alive and dead at the same time until observed by an outside observer. What exactly does this prove? All it seems to prove to me is that Man is exerting his superiority over the universe' date=' and that the cat is not dead until a Man observes it to be true. I mean, the cat is either dead or alive. Just because no one knows, only makes it unknown. Or is that the point.[/quote']

 

 

Yeah you did miss the point. With these sort of quantum interactions, the theory goes that it is not decided until one observes it. So in this thought experiment is neither dead nor alive until it is observed, and not even the universe "knows" the actual state of the cat, its undecided until its observed.

 

This was probably thought up not as a way of explaining quantum theory but of showing how incomplete it was. These quantum interactions are super small scale, the like decay of a single atomic nucleus, which I belive is what was used in the thought experiment. However, it seems rather abusurd to carry this reasoning over to a macroscopic level of an actual cat. It seems unlikely a cat can be in some wierd state of dead and alive; its either alive or dead.

[BobbyJoeCool]

it actually is in both states.

 

I don't see how that's possible. and, this doesn't seem to help me much at all... is there like a website or a book about schrodinger's cat that might help me understand this concept?

[BobbyJoeCool]

']Yeah you did miss the point. With these sort of quantum interactions' date=' the theory goes that it is not decided until one observes it. So in this thought experiment is neither dead nor alive until it is observed, and not even the universe "knows" the actual state of the cat, its undecided until its observed.

 

This was probably thought up not as a way of explaining quantum theory but of showing how incomplete it was. These quantum interactions are super small scale, the like decay of a single atomic nucleus, which I belive is what was used in the thought experiment. However, it seems rather abusurd to carry this reasoning over to a macroscopic level of an actual cat. It seems unlikely a cat can be in some wierd state of dead and alive; its either alive or dead.[/quote']

 

I think I understand now... the cat represents a single molicule of matter of some sort that is in an unknown state, and the decay of a different atom (which the rate of decay of an element is known, but which specific atoms of the element decays at random) and that since the "box" in which it is contained cannot be entered or exited by anything...

 

right track or no?

 

 

btw... Tycho? As in Marathon, a game made by Bungie? The Avatar shows the same symbol that Tycho was, so I just assume.

[blike]

I don't see how that's possible.

I recommend a book titled "Quantum: A Guide for the Perplexed" by Jim Al-Khalili. It helped me immensly with all of the quantum weirdness.

[timo]

the point of the experiment is that a particle is in multiple states until it interacts with another particle.

It [particle, cat, whatever'] is not "in one state but you can't tell" - it actually is in both states.

Strictly speaking you are both wrong. A quantum mechanical system allways is in a single definite state. The state just isn´t nessecarily an eigenstate to the observable you are going to measure. This is what leads to the unpredictability of the measuring process (which I did not fully understand up to today) because a QM axiom claims that after the measurement the system will be in an eigenstate to the eigenvalue maesured. But the system still is in a single definite state at any time.

This may sound pedantic but I feel that this "the system is in multiple states at once"-thinking is one of the biggest hindrances for understanding QM - you can only understand such statements if you know that you have to interpret "it is in both states" as "its state is non-perpedicular to both states". Not that I´m saying you don´t know what you were saying. I just wouldn´t understand your statements correctly if I didn´t know QM.

 

 

EDIT: I found a quote from the original paper on the german version of wikipedia. Seems like Schroedinger introduced this though experiment to show that QM effects which usually are important at very small size-scales (and therefore leave you with the "you can´t see it anyways"-excuse if something doesn´t seem to make sense) can be transferred to macroscopic, easily observable systems. It seems that he did this to show that QM makes absurd predictions (the cat being neither dead not alive unless the box is opened). As the example seems to be chosen to show the absurdity of QM, there´s not much learning effect to be expected from it.

[[Tycho?]]

I think I understand now... the cat represents a single molicule of matter of some sort that is in an unknown state' date=' and the decay of a different atom (which the rate of decay of an element is known, but which specific atoms of the element decays at random) and that since the "box" in which it is contained cannot be entered or exited by anything...

 

right track or no?

 

 

btw... Tycho? As in Marathon, a game made by Bungie? The Avatar shows the same symbol that Tycho was, so I just assume.[/quote']

 

 

Yeah from marathon, love that game. More specifically the writing of the game.

[BobbyJoeCool]

'']Yeah from marathon, love that game. More specifically the writing of the game.

 

I really liked being able to design your own world using Forge. it was so mcuh fun. I miss Marathon now, I can't play it on my OS X...

[swansont]

Strictly speaking you are both wrong. A quantum mechanical system allways is in a single definite state. The state just isn´t nessecarily an eigenstate to the observable you are going to measure. This is what leads to the unpredictability of the measuring process (which I did not fully understand up to today) because a QM axiom claims that after the measurement the system will be in an eigenstate to the eigenvalue maesured. But the system still is in a single definite state at any time.

This may sound pedantic but I feel that this "the system is in multiple states at once"-thinking is one of the biggest hindrances for understanding QM - you can only understand such statements if you know that you have to interpret "it is in both states" as "its state is non-perpedicular to both states". Not that I´m saying you don´t know what you were saying. I just wouldn´t understand your statements correctly if I didn´t know QM.

 

 

But then you have the problem that once you make the measurement, the particle must be in a superposition in the other basis that you've described. I don't see how that necessarily improves the situation. In the basis in which I observe, the particle is in a superposition of states.

 

As far as "I just wouldn´t understand your statements correctly if I didn´t know QM." goes, I see your point and agree. OTOH, a random someone who pops into an internet science forum and starts asking questions about QM and expects to fully understand the answers without any grounding in the subject (and unwilling to spend the few years of physics classes it would take to get that grounding) has an unreasonable set of expectations.

[timo]

But then you have the problem that once you make the measurement, the particle must be in a superposition in the other basis that you've described. I don't see how that necessarily improves the situation. In the basis in which I observe, the particle is in a superposition of states.

I can only speak for me, here. But I get much less headaches from the idea of describing a vector with a linear combination of base vectors than from particles being in two states simultaneously.

I also wouldn´t have commented on "superposition of states" . But "is in both states" strictly speaking means "|dead> = |state> = |alive>" while superposition correctly sais "|state> = a|dead> + b|alive>".

As said, this might seem a bit pedantic. But I feel that the distinction between being in a certain state or having a non-vanishing projection on that state can be crucial for understanding QM (though, I wouldn´t know a good example atm).

 

A random someone who pops into an internet science forum and starts asking questions about QM and expects to fully understand the answers without any grounding in the subject (and unwilling to spend the few years of physics classes it would take to get that grounding) has an unreasonable set of expectations.

That´s true of course. But in this case the statement doesn´t really seem to apply as from his profile Bobby actually is going to spend (or allready did spend) some years learning QM.

Of course, you could say "go to your classes or read a book instead of asking here" but this attitude would imho reduce this forum to posts about the morals of atheists and ways to disprove relativity. Providing someone with incorrect ideas, regardless wheter this was because of an incorrect statement or a correct statement that was misinterpreted, can severely reduce the effectivity of learning physics if the person sticks to them too hard.

E.g. I read somewhere that in QFT you replace the states with theit creation and annhilation operators. For several years I was completely unable to see the point in QFT or to even make any sense of it (how can QM without states work?). Then, not too long ago, I read a paper that explicitely described how to obtain the S-matrix by pulling out particles of the inital and the final state, leaving the vaccuum state (so there still are states in QFT!) by using these operators. At this point it made "click" and I suddenly understood a lot of what made absolutely no sense to me before. And the main hindrance for understanding QFT was that "replace the fields by their operators" statement which isn´t even incorrect if you know what´s meant.

[ydoaPs]

one of swansont's cartoons:

[eon_rider]

LOL... very funny cartoon.

 

as to the question of possible states.

 

" T.M wrote "No, actually, that's one of the strange things about QM. Its not "in one state but you can't tell" - it actually is in both states"

 

 

Correct me if I’m wrong, but...

 

Others keep talking about 2 possible states, but my understanding is that the particle (or cat) can be in not 2 states or 4 states or 10 states (I sound like I’m selling a set of steak knives on T.V. ) but an infinite amount of possible states until you take the top off the box. The whole 2 state thing was just to simplify but the cat could have turned into a giraffe, or a planet, or a sea monkey or whatever. (this correlates to all the possible states of the particle some how...lol... )

 

Is that somewhat correct?

[swansont]

Correct me if I’m wrong' date=' but...

 

Others keep talking about 2 possible states, but my understanding is that the particle (or cat) can be in not 2 states or 4 states or 10 states (I sound like I’m selling a set of steak knives on T.V. ) [b']but an infinite amount of possible states[/b] until you take the top off the box. The whole 2 state thing was just to simplify but the cat could have turned into a giraffe, or a planet, or a sea monkey or whatever. (this correlates to all the possible states of the particle some how...lol... )

 

Is that somewhat correct?

 

No. How many states are possible depends on the system. In this case, the observation is either alive or dead, and those are the only possibilities.

 

In the very strange situation where one might think the cat could transform into a giraffe or other living creature, it is also possible to envision a way of testing for that, like getting a DNA sample, in a way that does not indicate whether it is alive. Under that set of circumstances you could do this transformation test without collapsing the alive vs dead wave function. These measurement operators would then have to commute.

[DQW]

Others keep talking about 2 possible states' date=' but my understanding is that the particle (or cat) can be in not 2 states or 4 states or 10 states (I sound like I’m selling a set of steak knives on T.V. ) [b']but an infinite amount of possible states[/b] until you take the top off the box. The whole 2 state thing was just to simplify but the cat could have turned into a giraffe, or a planet, or a sea monkey or whatever. (this correlates to all the possible states of the particle some how...lol... )

 

Is that somewhat correct?

The number of "states" is merely the number of dimensions in the space that describes the outcomes of an observation. Naturally, this depends on the "thing" that you are trying to observe or the property that is being measured.

 

If you are trying to observe the aliveness of the cat, this is a two-state system (or a binary valued observable) : the cat is either alive, or it is not - and both outcomes are allowed by the physics of the problem. Hence, in the absense of a measurement, the "aliveness of the cat" (not the cat itself) may be described as being in a superposition of two states (it is the property which is in a superposition of states).

 

Now the "physical nature of the cat" is not a space with infinite dimensions, simply because science does not allow it. Mass conservation, thermodynamics, etc. forbid the cat from turning into a sea monkey or an old man in a hat, so these are not allowed states in the space of "the physical nature of the cat". This space is spanned by only one state : "cattiness".

 

(The subspace of the other states is a zero-matrix)

[eon_rider]

No. How many states are possible depends on the system. In this case, the observation is either alive or dead, and those are the only possibilities.

 

Got it. Thanks.

 

If you are trying to observe the aliveness of the cat, this is a two-state system (or a binary valued observable) : the cat is either alive, or it is not - and both outcomes are allowed by the physics of the problem. Hence, in the absense of a measurement, the "aliveness of the cat" (not the cat itself) may be described as being in a superposition of two states (it is the property which is in a superposition of states).

 

Now the "physical nature of the cat" is not a space with infinite dimensions, simply because science does not allow it. Mass conservation, thermodynamics, etc. forbid the cat from turning into a sea monkey or an old man in a hat, so these are not allowed states in the space of "the physical nature of the cat". This space is spanned by only one state : "cattiness".

 

Ok. It's a two state system. (a zero or one. Cat's alive or it's not)

got it. Glad to know that Quantum Physics is not that weird.

Pretty normal stuff.

 

best

 

eon

 

EDITED TO ADD:

 

SWANSONT WROTE: it is also possible to envision a way of testing for that, like getting a DNA sample, in a way that does not indicate whether it is alive. Under that set of circumstances you could do this transformation test without collapsing the alive vs dead wave function

 

1 )How would one possibly get that information without opening the box?

If you poked a hole in the side of the box and extracted some DNA you'd be interfering with the state of the binary system? Wouldn't you? So how could one get that DNA with out interfering with the system? (and collapsing the alive vs dead wave function.)

 

I certainly don't know the answer.

 

2) A totally different question. What if it was not a binary system? Could one create a non-binary system where the object in the box was unknown, and one was attempting to postulate what might be in the box before I observe it?

Then could the possibilities theoretically be infinite? Proving without the observer the true state of any matter in the universe is unknowable? (and totally dependant on the function of the observer or the act of being observed?)

 

The first question is more serious.

The second question is just for fun.