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Schrodenger's cat

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#1 cavefrog

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Posted 03 May 2013 - 10:56 PM

I know I am in way over my head here, but I gotta ask someone! what is it that I am not seeing about this cat? If an atom decays, the cat is dead. well , that's easy enough. and if an atom does not decay, the cat is not dead. that seems to be another easy. so where is the overlap of the cat being BOTH dead and alive at the same time? is it the speed in which an atom MIGHT decay?
as I said, I am trying to understand something probably way over my head, so if someone cares to answer, please try to use layman's terms.

Thanks, Theo

#2 llanitedave

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Posted 03 May 2013 - 11:28 PM

Because the state of decay is not determined until you open the lid to check. According to the way it's usually explained, the two states of the atom are in superposition until observed, not either decayed or not, but both decayed AND not. Therefore, the cat is to be considered simultaneously both dead and alive until you open the box to check.

Since nobody has actually done the experiment, the example is a bit metaphorical. Schrodinger would probably be charged with animal cruelty if he really tried it.

#3 StarmanDan

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Posted 04 May 2013 - 01:44 AM

Indeed. The trick is that we are seeing the experiment from our perspective not the cat's or the atom's. Since we can't make an observation of the result of the experiment without looking into the box, we can't say anything about the state of the cat or the atom. Therefore we say that the cat is both alive and dead and the atom has both decayed and not decayed until we open the box to find out how the thing played out.

#4 JAT Observatory

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Posted 04 May 2013 - 09:01 AM

Ah...it all makes sense now.. the light is both on and off in the refrigerator until we open the door to check.

#5 llanitedave

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Posted 04 May 2013 - 09:18 AM

What Shrodinger neglected to consider, though, is that the cat is also an observer.

#6 TVG

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Posted 04 May 2013 - 12:01 PM

I never understood how the experiment would know it was being observed. A simplified way of indirectly observing would be a video camera, would there be a difference? How about a sensor of some kind that only picked up biological decaying gases in dead animals? Would one be able to measure a difference initially or could the cat be measured as both dead and alive after the sensor registered but not after an observer read the sensor?

Todd

#7 TVG

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Posted 04 May 2013 - 12:03 PM

Doesn't the "double slit" experiment address a similar paradox in a much more humane way?

Todd

#8 dickbill

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Posted 04 May 2013 - 01:19 PM

Ah, the video camera issue! first, to see anything you'll need light, and with a gas sensor you'll need something coming out (gas, odor, sound) from the cat. These would make the wave function collapse, as 'they' say.
So maybe a more usefull description of the system would be a cat enclosed with a geiger and a radioactive element with nothing else that coud leak information about the cat: no light, no gas leaking out of the cat etc., before we open the box.
Second, a video camera per se is not an observer. It takes some intelligence in front of the screen to decide if the set of colored pixels displayed onscreen actually means anything informative or represent a cat, dead or alive. Without this intelligence, pre-programmed or not, the camera just project pixels without any signification or information.
Then, maybe we should introduce some entropy considerations. The system enclosed with the cat is entirely described by a set of bits. Without an observer or a program capable to analyse the image on the camera, the bits displayed on screen are not really extracted and are still part of the cat system. Then, since no information is extracted, the entropy of the system does not change.
If the entropy does not change, isn't the arrow of time frozen?
The problem is that, as Dave said, the cat is an observer too and extract information from itself: he changes the entropy of its own system and that ruins the experiment. So the cat, or any living/thermodynamic machine is very inapropriate for this experiment in fact.

Now, what happens when the image is analysed by a human or a computer program a posteriori? does the change in entropy goes 'back in time'...?

#9 Sean Cunneen

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Posted 04 May 2013 - 02:29 PM

What Shrodinger neglected to consider, though, is that the cat is also an observer.


False(in my best Dwight Schrute voice)

Dead cats cannot observe anything but dead mice.

#10 JAT Observatory

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Posted 04 May 2013 - 04:30 PM

Doesn't the "double slit" experiment address a similar paradox in a much more humane way?

Todd


Yes but each single particle can only be observed once per slit, with the cat you have at least 9 opportunities if the cat was new at the start of the experiment!

#11 jchaller

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Posted 04 May 2013 - 05:11 PM

Wouldn't we have to open the box 9 times to see if the cat was really dead?

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#12 cavefrog

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Posted 04 May 2013 - 08:00 PM

Doesn't the "double slit" experiment address a similar paradox in a much more humane way?

Todd


the double slit experiment I can somewhat comprehend. It tries to determine whether an item is a particle or a wave, and does not have anything to do with Shrodengers cat. I don't think.

If it is more humane or not is not relevant either because this is a THOUGHT experiment, and being thus, is not meant to be played out.

I still am not getting the point to it however... from what I see, what we are trying to determine is if the atom has decayed or not. so why the poison and cat? If the geiger counter can relay a switch, why can the switch not be just a mark or something to be seen as yea or nay? why all the complication with the cat and poison?

Somewhere this smells of observers effect, but opening the box and observing has no effect on the result. it is a 50 - 50 proposition, the atom will either decay or not, so there is no point to the experiment in the first place. I'm still missing something here.
with guessing about if ANYTHING could happen that has a 50 - 50 chance of happening or not and is equal odds.... does it make it both and neither untill a determination is made?

OK. what I think I am missing is that a particle can be in different states at the same time. so how is this? and are there more states than just two?

I think I stepped in too deep. maybe this can only be explained in mathmatics(?) that I have never (and never will) learned. I kinda did the same thing when I asked questions about absolute zero and entropy!
I do pick up a little here and there on the way through though, so its not a total waste.

Theo

#13 TVG

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Posted 04 May 2013 - 08:37 PM

Yes, you have gotten about as far as I have with these paradoxal thought experiments. The main point being that particles can be in two different states simultaneously tears at the very fabric of my mind.
We humans love dualities, so for now let's just keep it simple with two states, alive/dead or particle/wave. :crazy:
Nine different states of existence, or even infinite states of existence sounds a lot like "many worlds interpretation", which I simultaneously understand and don't understand.

Todd

#14 MRoedel

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Posted 04 May 2013 - 10:42 PM

I don't see how this is any different than saying that a flipped coin is both heads and tails until it hits the ground.

Flipping the coin doesn't send you to the shed to get the shovel half of the time.

#15 TL2101

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Posted 05 May 2013 - 03:33 PM

In the double slit experiment it is the act of actually having the data that collapses the probability wave into the particle not the detector. If the detector is on slot A and the photon goes through slot B the wave will still collapse because we now have the data of which slot the photon traveled through.

I think it's pretty obvious we all live inside some huge quantum computer. :grin:

#16 deSitter

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Posted 05 May 2013 - 10:15 PM

This is one of those things about science popularization that is really annoying. The cat is a diversion, forget about it.

The point being made is that quantum systems are capable of yielding a range of discrete values for measured parameters. The actual value determined by a measurement may be any one of this range, with certain probabilities assigned to the each value. In classical mechanics it is 1 for one thing, and 0 for all the others. In quantum mechanics it is not so.

However, this does NOT apply to any random radioactive atom wandering the universe whose decay may lead to felicide. The rules and results of quantum theory apply to what are called "prepared systems". You cannot make measurements of sufficient accuracy to display the superposition principle (e.g. two-slit experiment) on unprepared systems. So the superposition principle, and its role in the "Copenhagen intepretation" of quantum theory, is worthless for describing individual events that are simply random chance.

The live/dead cat business is just another form of "if a tree falls in the forest..." Such things do nothing to explain quantum theory and are simply mind games.

-drl

#17 dickbill

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Posted 06 May 2013 - 09:32 AM

Apparently you are right. The system works much better without a cat, but how come Schrodinger could not see that?
I think he did. He probably thought that conscient observers have special power over the nature of reality.
Dean Radin has pushed the idea further, using a double slit experiment shielded from evereything oustide, he tried to observe if the wave function of photons collapsed by the sole concentration of human 'meditators', focusing remotely their attention on the slit. You can even do the experimemt online, I did. I don't know what are the results honestly and if he found a correlation between 'observers focusing their attention' and the diffracted or not diffracted figures. But I am pretty sure Radin said that 'trained meditators' show a positve correlation with much higher confidence that untrained meditators. Statisticaly significant or not, i don't know.

#18 Rick Woods

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Posted 06 May 2013 - 10:36 AM

The live/dead cat business is just another form of "if a tree falls in the forest..." Such things do nothing to explain quantum theory and are simply mind games.


That's how it seems to me. It's saying that the observer's degree of ignorance of the state of things somehow affects that state.
I think it's more germane to ask: if you get up in the middle of the night, has or has not the cat honked up a hairball where you will step in it? (You'll soon find out.)

#19 deSitter

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Posted 06 May 2013 - 12:29 PM

The simplest case of a prepared system is light that has passed through a polarizer. Stacked polarizers exhibit all the essential features of quantum theory. If you can get a handle on those, then you are well on your way to being freed from the bogus mysticism of popularizers.

http://www.users.csb...e/POLAR-sup.pdf

http://www.informati...c_3-polarizers/

-drl

#20 Pess

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Posted 06 May 2013 - 02:59 PM

In the simplest terms, the math of Quantum theory states that a quantum particle sits in a state of superposition.

Since quantum particles can be describes as waves or particles the math states that they exist as both until the are measured (observed).

This state is called 'superposition". Since the 'final' state is determined by how the measurement is made.

Schrodenger looked at that and said, 'Well what if we link a non-quantum sized outcome to the outcome of that single quantum particle?' In other words, if the quantum particle decays it triggers the death of a Cat....

Since the end event is triggered by a particle in a superposition state, it follows that the Cat itself exists in a superposition o state (ie: both dead and alive) until a measurement is taken.

Pesse (Schrodenger failed to take into account the nine lives of cats) Mist

#21 dickbill

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Posted 06 May 2013 - 03:56 PM

...yes, until a measurement is taken. That means the geiger itself is enough to impose a single state out of the other possible states, since it makes the first measurement when a decayed particle interact with the detector.
It is however interesting how the quantum indetermination vanishes 'instantly'.

#22 Pess

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Posted 06 May 2013 - 05:23 PM

...yes, until a measurement is taken. That means the geiger itself is enough to impose a single state out of the other possible states, since it makes the first measurement when a decayed particle interact with the detector.
It is however interesting how the quantum indetermination vanishes 'instantly'.


I don't think the terms 'instant', 'now', 'then' 'before' after' have the same meaning at the quantum level as in the macro level.

I believe the proper linguistic description is that the 'waves of probability collapse into a certainty once a measurement is taken'.

So in your slit experiment if you look for the photon behaving as a wave its probability function (wave vs particle) collapses into a wave. If you detect it as a particle its probability function collapses into a particle.

But before the measurement the photon is in both states.

Pesse (Quantum objects have 'nuthing on Sybil) Mist

#23 deSitter

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Posted 06 May 2013 - 07:30 PM

In the simplest terms, the math of Quantum theory states that a quantum particle sits in a state of superposition.

Since quantum particles can be describes as waves or particles the math states that they exist as both until the are measured (observed).

This state is called 'superposition". Since the 'final' state is determined by how the measurement is made.

Schrodenger looked at that and said, 'Well what if we link a non-quantum sized outcome to the outcome of that single quantum particle?' In other words, if the quantum particle decays it triggers the death of a Cat....

Since the end event is triggered by a particle in a superposition state, it follows that the Cat itself exists in a superposition o state (ie: both dead and alive) until a measurement is taken.

Pesse (Schrodenger failed to take into account the nine lives of cats) Mist

ve

You have forgotten how the initial state is prepared. You cannot calculate anything in quantum theory without specifying the initial state. All the stuff about superposition is meaningless without knowledge of the initial state.

-drl

#24 dickbill

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Posted 07 May 2013 - 08:53 AM

"Since quantum particles can be describes as waves or particles the math states that they exist as both until the are measured (observed)."
The first measurement is when a decayed particle interacts with something, therefore the geiger detector is doing the first measurement. The quantum indetermination is lost long before the cat 'status' can be influenced and in no ways this indetermination can be transfered to a macroscopic cat.
Is it true?
Does the wave function of probability collapse completely? or is there a tiny remnant of quantum indetermination that could be transfered to a macroscopic system, either the geiger or the cat? so that instead of saying the cat is 50% dead or 50% alive, we'd say he is 99.999% dead or 99.999% alive.

#25 llanitedave

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Posted 07 May 2013 - 09:15 AM

Whoo-hoo-hoo, look who knows so much. It just so happens that your friend here is only MOSTLY dead. There's a big difference between mostly dead and all dead. Mostly dead is slightly alive. With all dead, well, with all dead there's usually only one thing you can do.

What's that?

Go through his clothes and look for loose change.






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