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Schrödinger's cat


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#1    Mr. Fahrenheit

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Posted 06 August 2006 - 05:37 AM

Okay, I stumbled upon this about an hour ago (curiously having never heard about it before) and rather than just silently wonder about this, I decided to make a topic about it.

What exactly is the paradox involved?

Once the experiment begins, either:

A) The nucleus decays, the gas is released, the cat dies

Or:

B) The nucleus does not decay, the gas is not released, the cat lives.

Apparently, the question raised is something to the effect of: Are the objects involved in the experiment hanging between states of being?

Which, in my mind, is a resounding no.

Does the fact that the result of the experiment is unknown  create a problem? I don't see how. For example, if I flip a coin, and it lands at the bottom of a dark, empty well, does that coin become lodged in between the realms of heads and tails?

Am I just stupid?

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Edited by Mr. Fahrenheit, 06 August 2006 - 07:23 AM.


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#2    Startraveler

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Posted 06 August 2006 - 06:15 AM

The paradox arises from possible interpretations of the way things work in quantum mechanics. A quantum system evolves very smoothly through time in a superposition of states, meaning the nucleus here is in some sense both decayed and not decayed at once. At some point something special takes place--this is usually called a measurement though you shouldn't take that to mean a human being is needed--and the system collapses down to a single state.

Now if you happen to be of the view that a measurement has to be a human being (i.e. a conscious being) observing or collecting data then this Schroedinger's cat situation is an odd one. Until a person observes the system it remains in a superposition of states--the nucleus is both decayed and not. But this is set up so that this quantum strangeness manifests itself in the macroscopic world (which, of course, it usually doesn't). The cat's health is very much affected by the state of that nucleus. Thus if you're of the opinion no measurement has taken place then the nucleus--and by extension the cat's life--must remain in some limbo. And the idea of a cat being both alive and dead at once is very bizarre (though, of course, so is the idea of a nucleus being in multiple states at once).

Of course the whole exercise is just part of a bigger point: no one really understands what's really going on when it comes to quantum mechanics. That's why all these interpretations have sprung up to try and make sense of what these quantum rules are trying to tell us about the universe.



#3    Mr. Fahrenheit

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Posted 06 August 2006 - 07:21 AM

Thanks for answering. This still leaves me with a fiew questions, though.

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The paradox arises from possible interpretations of the way things work in quantum mechanics. A quantum system evolves very smoothly through time in a superposition of states, meaning the nucleus here is in some sense both decayed and not decayed at once. At some point something special takes place--this is usually called a measurement though you shouldn't take that to mean a human being is needed--and the system collapses down to a single state.

This is mostly what I don't understand. Aren't things one way or the other? Is there really an instant during every change where objects are in some ethereal limbo between two states? Or does it only apply to certain situations?

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The paradox arises from possible interpretations of the way things work in quantum mechanics.

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though you shouldn't take that to mean a human being is needed

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Now if you happen to be of the view that a measurement has to be a human being (i.e. a conscious being) observing or collecting data then this Schroedinger's cat situation is an odd one. Until a person observes the system it remains in a superposition of states--the nucleus is both decayed and not.

So, was I correct with my assumption that it is only the perception of the observer that creates the paradox? Is it simply not knowing whether or not the cat is dead that creates the idea of being between states?
Is there something huge that I'm missing, because the few things I've quoted above seem to conflict, slightly.
I'm reminded of the Ray Bradbury short story "No Particular Night or Morning". In it, a man believes that objects and people cease to exist when they are not around for him to see. Is this train of thought similar?

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Of course the whole exercise is just part of a bigger point: no one really understands what's really going on when it comes to quantum mechanics. That's why all these interpretations have sprung up to try and make sense of what these quantum rules are trying to tell us about the universe.

So (keep in mind this is just conjecture), what if everyone was wrong and things change the way most people think of them outside of such abstract experiments, changing the way they change and not morphing between the two states we acknoweledge and into a wacky in-between idea?

Again, sorry. I feel as if I am operating at a lower level than you are, what you're saying probably makes more sense than what I'm saying.



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#4    ArgenVert

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Posted 06 August 2006 - 07:27 AM

It's not meant to be taken literally, because as you said, the cat won't really hang in an in-between state until you open the box. It's meant as a metaphor for the particle/wave duality of small matter, usually photons. Because it is a particle you can predict where it is going to be, but since it is also a wave of probability you can never truly know where it is until you look inside the box. But because of the observer effect your observation has also become involed in the experiment and it is no longer objective.

Hope I didn't confuse anybody too much.  tongue.gif

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#5    Mr. Fahrenheit

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Posted 06 August 2006 - 07:35 AM

So, what you're saying is...this experiment means nothing?
Really, after re-reading the posts, everything that the experiment depends on to mean anything is all just people with hypotheses on how things work, and this is on about the eight fringe of "if"s.

Know what I mean?


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#6    Startraveler

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Posted 06 August 2006 - 08:06 AM

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This is mostly what I don't understand. Aren't things one way or the other?


In the quantum world, no. As a system evolves it's described by what's known as the Schroedinger equation. At that point we can only talk about probabilities--probabilities of what state we'll find the system in when we look (i.e. perform a measurement). These probabilities, however, aren't just some consequence of us not knowing what state the system is in (like when you role dice, don't look at them, and then talk about the probability of rolling so-and-so), they're somewhat more disconcerting. The reason we have to talk in probabilities is that the system doesn't have any one definite state at that point and really is somehow spread out across all possibilities (though spread more thinly over the more likely states, etc).

That's one of the most important and bitter pills to swallow when it comes to quantum mechanics. Things really aren't one way or the other for whatever reason. And how they go from that to being in one particular state is probably the central conundrum of it all.

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Is there really an instant during every change where objects are in some ethereal limbo between two states? Or does it only apply to certain situations?


We're talking about quantum phenomena here. For complicated macroscopic systems the quantum rules generally don't quite work. So if you're flipping a coin it's either heads or tails, it's not in a superposition of the states.


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So, was I correct with my assumption that it is only the perception of the observer that creates the paradox? Is it simply not knowing whether or not the cat is dead that creates the idea of being between states?


Technically there's no paradox here, it's just a very strange situation. And to repeat something I said in the paragraph above this one, it's not a matter of us lacking knowledge. The nucleus isn't said to be in a superposition because we're not sure prior to taking a measurement what state it'll be in; rather, it's said to be in a superposition of states because it's really spread out over any and all possible states, being a little bit in each one.

The really weird part of the cat scenario is that this quantum strangeness is seemingly allowed to spill into the macroscopic world (because whether the cat lives or dies is tied in to the state of that nucleus) so that the cat itself exists in a superposition of states. If the nucleus doesn't actually exist in one particular state at that time then how we can the cat be said to?

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So (keep in mind this is just conjecture), what if everyone was wrong and things change the way most people think of them outside of such abstract experiments, changing the way they change and not morphing between the two states we acknoweledge and into a wacky in-between idea?


Remember this is all basically just a quantum thing; you generally don't have to worry about people or things going into some strange kind of superposition every time you shut your eyes. On the quantum level, at least, the fact that a particle doesn't exist in one definite state prior to some kind of measuring event is pretty well verified by the observation of phenomena like quantum tunneling.

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Again, sorry. I feel as if I am operating at a lower level than you are, what you're saying probably makes more sense than what I'm saying.


You don't have anything to apologize for, these are some of the strangest concepts ever stumbled over by man.



#7    ArgenVert

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Posted 06 August 2006 - 08:08 AM

Quote

So, what you're saying is...this experiment means nothing?
Really, after re-reading the posts, everything that the experiment depends on to mean anything is all just people with hypotheses on how things work, and this is on about the eight fringe of "if"s.

Know what I mean?


Somewhat. With the cat metaphor it is more philosohpical than anything else, because the cat won't linger in-between. However, with electrons and photons the problem is a real one.

There this thing called the double-slit experiment, in which a device fires off a single photon (or electron) at a time towards a wall with two narrow, parallel slits in it. It is then measured on a wall on the other side of the slitted wall where they land. Sounds pretty simple right? Mind you this is only one particle at a time. Since it is a particle you can perdict a range of places it will be. After firing many particles, you'd assume that the opposite wall would be 'painted' in a solid band at the same height as the two slits.

Oddly enough, you get verticle bands of light and dark. This is because the particle changed into a wave of probability as it passed through the slotted wall. This interference pattern shows that light is a wave even though it was orginally a particle.

To investigate farther people have put measuring devices in the slits to register the particles as they pass through. However, once the particles are being observed passing through, they no longer appear as bands of interferrence! You get the solid band that you predicted in the beginning! w00t.gif

Basically, if you are observing it passing through the slits, it acts the way you'd expect it too. Like a particle. If you aren't observing it pass through, it acts like a wave and appears in the probable places. This is astounding, because the only thing different is the observing scientist. The mere act of taking a look inside the box changes the way matter acts.

Personally, I don't think that means nothing.  thumbsup.gif

Futher reading:
http://en.wikipedia.org/wiki/Copenhagen_Interpretation

http://en.wikipedia.org/wiki/Double-slit_experiment

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#8    Mr. Fahrenheit

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Posted 06 August 2006 - 08:15 AM

Aw, blessed are us simple minded folks.
I guess I'll just never fully understand hmm.gif

I just don't get how it being possible for something to be one way somehow alters its state.

I'll post again sometime tomorow. It's 4 AM here.


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#9    Poetic Reven

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Posted 06 August 2006 - 02:19 PM

No... Just flat out... no.  I have never believed in "inbetween". Either it is, or it isnt. Besides, if it lingered inbetween it would be a zombie cat. w00t.gif

P.S. No one really did this with any cats did they?

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#10    Raptor

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Posted 06 August 2006 - 03:08 PM

Quote


No... Just flat out... no.  I have never believed in "inbetween". Either it is, or it isnt. Besides, if it lingered inbetween it would be a zombie cat. w00t.gif


On the quantum scale superposition does occur, which just means while something is not being observed and it's state is unknown, it's in all possible states at once.

The Schrödinger cat experiment involves taking a sealed box and putting a cat inside with a vial of poisonous gas. A trigger (a quantum particle) is put on the vial so that it will break open depending on the state of the particle. Say, if the particle is on the left side of the box the vial will break and kill the cat, if it's on the right side it won't break open and the cat will survive. While the particle can't be observed the particle is in all states, it's on the left and right side at the same time, meaning the vial will break and remain unbroken at the same time, meaning the cat would theoretically be killed and remain living at the same time.  wacko.gif

(I think that's right anyway, someone please tell me if I'm wrong. yes.gif)


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P.S. No one really did this with any cats did they?


laugh.gif It's just an analogy to try and explain some aspects of quantum physics, not something which is actually done. thumbsup.gif


#11    TooFarGone

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Posted 06 August 2006 - 04:32 PM

The whole thing is rather confusing to me......probably because I have yet to take physics in school, and have only a BASIC understanding of these things....

But it was worth reading the link, just to see that Einstien had wrote "blown to bits" tongue.gif

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#12    Poetic Reven

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Posted 07 August 2006 - 01:38 AM

Ah well. I still have no belief in inbetween. I don't look at it as a matter of "the cat is both dead and alive". I look at it as, Is the cat Dead Or Alive? I almost never reference something to be both. Just like the question that askes me if the cup if half full or half empty. My answer is always "A cup can only be full when its at max capacity, so even when one ounce is missing, the cup is actually in a way empty. At which point I go and fill the cup up again" grin2.gif

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#13    mklsgl

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Posted 07 August 2006 - 02:59 AM

Really want to comprehend this? Then read Ursula Le Guin's "Schrodinger's Cat."

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#14    DarbyII

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Posted 07 August 2006 - 05:30 AM

Quote


Okay, I stumbled upon this about an hour ago (curiously having never heard about it before) and rather than just silently wonder about this, I decided to make a topic about it.

What exactly is the paradox involved?

Once the experiment begins, either:

A) The nucleus decays, the gas is released, the cat dies

Or:

cool.gif The nucleus does not decay, the gas is not released, the cat lives.

Apparently, the question raised is something to the effect of: Are the objects involved in the experiment hanging between states of being?

Which, in my mind, is a resounding no.

Does the fact that the result of the experiment is unknown  create a problem? I don't see how. For example, if I flip a coin, and it lands at the bottom of a dark, empty well, does that coin become lodged in between the realms of heads and tails?

Am I just stupid?

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Farenheit,

In 1935 when Schrodinger proposed this thought experiment he was purposely (and humorously) stating a paradox to show that quantum mechanics, as it was formalized at that time, was incomplete.  He was asking the question, how large does a system have to be before quantum effects no longer predominate and classical effects take over.  We know that a single subatomic particle or a photon's actions are wholly dominated by quantum mechanics.  A cat, box, geiger counter, a cannister of poison gas and a ponderable mass of radioactive material is a system of molecules that is dominated by classical mechanics.  

In this case irreversible classical thermodynamic events occured.  A nucleus decayed, a geiger counter clicked, a gunpowder charge exploded and a bullet flew.  Assuming that it hit its target, the bullet terminated the cat in a very irreversible way by causing the release of a lethal dose of prussic acid..

Real, rather than gedanken, cats are either dead or alive - not a mixture of both.  All  we need to do is ask the cat. wink2.gif  We don't have to wait to open the door to the box.  If we wait for several days after the geiger counter has close to a 100% probability of firing the detonator to the gas cannister (the nucleus decays) we will have one very dead, very ripe cat.  It won't wait in a mixed state for us to look.

We run into big problems when we try to apply quantum mechanics, a description of the micro world, to large masses, a description of the macro or classical world.

Quantum mechanics is correct in the sense that it makes good predictions about the outcomes of subatomic events.  The real question is why this is so.

Edited by DarbyII, 07 August 2006 - 05:35 AM.


#15    Poetic Reven

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Posted 07 August 2006 - 05:36 AM

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Farenheit,

In 1935 when Schrodinger proposed this thought experiment he was purposely (and humorously) stating a paradox to show that quantum mechanics, as it was formalized at that time, was incomplete.  He was asking the question, how large does a system have to be before quantum effects no longer predominate and classical effects take over.  We know that a single subatomic particle or a photon's actions are wholly dominated by quantum mechanics.  A cat, box, geiger counter, a cannister of poison gas and a ponderable mass of radioactive material is a system of molecules that is dominated by classical mechanics.  

In this case irreversible classical thermodynamic events occured.  A nucleus decayed, a geiger counter clicked, a gunpowder charge exploded and a bullet flew.  Assuming that it hit its target, the bullet terminated the cat in a very irreversible way.

Real, rather than gedanken, cats are either dead or alive - not a mixture of both.  All  we need to do is ask the cat. wink2.gif  We don't have to wait to open the door to the box.  If we wait for several days after the geiger counter has close to a 100% probability of firing the detonator to the gas cannister (the nucleus decays) we will have one very dead, very ripe cat.  It won't wait in a mixed state for us to look.

We run into big problems when we try to apply quantum mechanics, a description of the micro world, to large masses (the macro or classical world).

Quantum mechanics is correct in the sense that it makes good predictions about the outcomes of subatomic events.  The real question is why this is so.


Thankyou! thumbsup.gif  Thank you for stating exactly what I wanted to say! thumbup.gif  Congrats on having higher intellect! w00t.gif


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