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Post by Progenitor A on Oct 30, 2010 8:36:58 GMT 1
Reality Check –Schrodingers Cat
There is much talk on this board about the Copenhagen interpretation of QM, in particular the ‘superposition principle’ is often quoted to support some QM ideas and experimental results.
In short the ‘superposition principle’ applied to QM maintains that for as long as subatomic particles are not observed they have multiple characteristics, the most famous characteristic is for an electron, photon etc. to be in two or more places at once and to be spinning cw, acw and every other orientation simultaneously.
Unfortunately these superpositions can never be observed because as Bohr maintains, as soon as look at one of these particles they assume just one of the superposition states.
Although these assumptions help to explain some experimental results, they are full of contradictions and absurdities. Moreover the Copenhagen interpretation of QM is not necessary to QM as there are other interpretations that do not rely on these superpositions.
With QM, you simply choose whichever model actually suits your temperament, and if the Copenhagen Interpretation makes you feel good, then so be it, use that interpretation, but be aware of the absurdities that it produces
Now the Austrian gentleman Mr Schrodinger.
He proposed the wave function that was accepted by Bohr and became part and parcel of the Copenhagen interpretation (Bohr was, of course, Danish)
However Schrodinger was horrified by the inherent absurdities of the Copenhagen interpretation and devised his famous though experiment involving the Cat in order to ridicule it.
In summary, a single atom with a half-life of 10 mins is placed in a box. If and when it decays the decay triggers the release of a poison gas. In the box with the atom and poison is a cat.
Now with decaying particles, we just do not know when any atom will decay – all we know is that on average en masse, half of the atoms will decay during the half-life period.
With a single atom, we simply do not know when it will decay.
Now the Copenhagen Interpretation would put it that if we do not observe the atom in the box, it is in a superposition state where it is both decayed and not decayed and when we open the box to observe, this superposition function will collapse to just one state.
So we do not know whether the cat will be dead after 10 minutes, poisoned by the released gas triggered by the decay of the atom.
But under the Copenhagen interpretation, the atom is both decayed and not decayed, and logically the cat is both dead and alive.
When we open the box the superimposed wave function collapses to either a dead cat or an alive cat.
And that is the best ever demonstration of some of the absurdities of the Copenhagen interpretation.
Similarly when someone insists that an electron is in two places at once they are making the Copenhagen interpretation assertion.
But if an electron is in two places at once, then, if that statement has any meaning at all, the charge of the electron and the mass of the electron is duplicated.
Unfortunately if you make such observations you will be told (as I was) that you are suffering from a lack of imagination and are hidebound by intuition.
Should you find yourself under such attack, simply quote Schrodingers Cat!
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Post by abacus9900 on Oct 30, 2010 9:50:42 GMT 1
Personally, I think it goes a lot deeper than this.
The trouble, I think, with all of these interpretations is that they are considered as something happening 'out there' yet the *observer* is an inseparable part of any observation/measurement. This is why I think (and this is a personal view) that reality is not necessarily already 'set' but is a continual 'dance' between consciousness (us) and whatever it is that is actually 'out there.' You see, through the 'lens' of our perception we human beings are constricted to interpreting whatever sensations we receive in terms of our mental constructions such as mathematics, language, pictures, analogies etc., so that, actually, we are an active agent in the formation of reality (within certain limitations, of course). It is as if we have been programmed to interpret incoming 'data' according to the way our 'programme' dictates, which is a programme laid down by evolutionary processes.
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Post by olmy on Oct 30, 2010 14:31:49 GMT 1
naymissus, You have touched on a real open question here. Unfortunately there is some confusion in your post. Superposition is not part of the Copenhagen Interpretation, neither is the wave-function. They are both part of the mathematical formalism. That the mathematical formalism is a very good match to reality is not in question by anybody serious. It explains, for example, the chemical properties of the elements, spectral lines and is used in engineering in semiconductors and lasers. The interpretations (including Copenhagen) attempt to interpret the formalism (amazingly enough). Now, superposition (which is a mathematical concept that is not even specific the quantum mechanics)..... An example may help so let's take spin - which is a kind of intrinsic angular momentum. Classically, angular momentum is treated as a vector that points along the axis of rotation, the direction indicating clockwise or anticlockwise. The following is part of the mathematical formalism of quantum mechanics and has nothing to do with any interpretation.... For a spin 1/2 particles the magnitude of this spin angular momentum is always 1/2 of the reduced Planck's constant, no matter what axis it is measured along. In general, we describe the spin state in terms of spin 'up' or 'down' along some arbitrary z-axis, so a general state is a superposition of up and down... psi = a|+ z> + b|- z> Where |+ z> is spin up along the z-axis and |- z> is spin down along the z-axis and a and b are complex numbers (may include i, the square root of -1). This is what a superposition is, just a linear combination of different 'basis states'. What this means is that if one measures the spin state along the z-axis, the probability of getting each of the two possible outcomes is the square of the magnitude of the relevant coefficient. Prob 'up' = | a| 2, Prob 'down' = | b| 2. After such a measurement, let's say we got 'up', the state is now.. psi = |+ z>. This is what is referred to as 'the collapse of the wave function'. Further measurements along the z axis will give up with certainty. BUT... |+ z> = (|+ x> - |- x>)/sqrt(2) Where |+ x> and |- x> are the two spin states in the x direction. Another superposition - being a superposition is not an absolute, it depends on what basis you use (which relates to what is being measured). If we measure along the x-axis we are dealing with probabilities again. ...end of mathematical formalism stuff. So, what do we make of this? How does one describe states like a|+ z> + b|- z> ? Is it spin up and spin down or is it neither? Is ' psi' (the 'wave-function') the reality until we make a measurement or does it mean something else and what does a 'measurement' mean anyway? It is tempting to think that a 'real' or definite spin state exists and all this probability lark is due to our ignorance of this 'real' state (as is usually the case with probability). Unfortunately experiments have ruled out such 'hidden variable' schemes unless one is prepared to accept equally bizarre and non-intuitive ideas. This is the stuff of the interpretations - of which there are many..... en.wikipedia.org/wiki/Interpretations_of_quantum_mechanicsI rather like 'objective collapse' interpretations but then I think rain is wet so who am I to say...... |
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Post by marchesarosa on Oct 30, 2010 16:05:11 GMT 1
Fascinating, Olmy!
When I had my lecture on quantum theory nearly 50 years ago at the Royal College of Advanced Technology, Salford, the lecturer got over the present or absent, here or there, dead or alive quantum conundrum with the remark that these "states" were merely "probabilities".
If they are only "probabilities" and not actual this seems to get round the problem.
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Post by Progenitor A on Oct 30, 2010 16:55:20 GMT 1
naymissus, You have touched on a real open question here. Unfortunately there is some confusion in your post. Superposition is not part of the Copenhagen Interpretation, neither is the wave-function. Actually I prefer the reference books that I read to your doubtful contributions that have shown themselves unreliable on many an occasion |
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Post by abacus9900 on Oct 30, 2010 18:31:13 GMT 1
Here again, all Olmy is really doing is 'counting beans, and not offering any interpretive philosophical ideas with which to gain some insights into such non-intuitive effects. We can measure and describe mathematically gravity but it if far from understood, so come on Olmy, go for it! Take a chance and say something impulsive and wonderful!!
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Post by abacus9900 on Oct 30, 2010 18:38:15 GMT 1
Fascinating, Olmy! When I had my lecture on quantum theory nearly 50 years ago at the Royal College of Advanced Technology, Salford, the lecturer got over the present or absent, here or there, dead or alive quantum conundrum with the remark that these "states" were merely "probabilities". If they are only "probabilities" and not actual this seems to get round the problem and further, all science can observe at the present time is all there is to reality because we have sussed everything out already! Yes but the question is why are they only probabilities? What is going on behind all this to make them only probabilities. Of course, if your name is STA, you would reply that that is the way it is and we simply have to accept it because we have no more to learn about reality. Us, who have been around for less than a blink of an eye have conquered the cosmos and become all-knowing and infallible - in fact godlike! |
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Post by olmy on Oct 31, 2010 12:27:31 GMT 1
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Post by Progenitor A on Oct 31, 2010 12:53:33 GMT 1
Actually I prefer the reference books that I read to your doubtful contributions that have shown themselves unreliable on many an occasion  You read books!? Frankly I'm losing interest. Anybody of reasonable intelligence can go check for themselves. On the page I already gave, we can see that all the interpretations need to deal in some way with the wave function and its 'collapse' (that is, how a superposition becomes a single observed state).... Frankly you simply regurgiate what you have read. 'Explaining' that a complex number may involve i[! And that superposition is not restricted to QM, and that superposition is not a part of the Copenhagen Interpretation, even though Schrodinger used the Cat supeposition paradox to discredit the Copenhagen Interpretataion! Those are idiotic observations. You have no real aptitude as has been demonstrated in your comments upon Darwin, your fumblings with the concept of gravitational fields and latterly demonstrating a complete inabilty to grasp a basic physics problem on antenna gains/path losses. Your unfortunate combination of arrogance and dimness have exposed you to ridicule This forum is rapidly developing into nothing but a backwater for fruit-loops to speak nonsense to each other..... Here is your misplaced hubris in action once again. Just how many topics have you started? Could it be you that is the reactionary, the closed mind pedant? Stay if you wish but do not expect to treated with respect that you have not earned. radio4scienceboards.proboards.com/index.cgi?action=gotopost&board=hahaha&thread=286&post=3789 |
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Post by speakertoanimals on Nov 1, 2010 17:58:20 GMT 1
As others have already said, superposition isn't just a part of the Copenhagen interpretation.
TO those who don't like the idea of superposition -- how do you explain double slit interference with single photons? Either the photons is in a superposition of states corresponding to going through one slit or the other, or it isn't.
Even worse, WHAT state it 'collapses' into, the definite position states that you get when you place a screen behind the slits in order to gradually build up the interference pattern, or whether you decide to make a different measurement.
The point being, you can decide AFTER the photon has passed the slits, what measurement you are going to make!
But whatever the real issues are, it isn't the simplistic -- superposition obviously rubbish, and Schrodingers cat tells us so...........
What Schrodingers cat (and Wigners friend) is actually talking about is where we go from superposition on the quantum scale, to non-superposition on our scale. Various ideas, including Penrose who proposes that it is gravity that does the trick -- a superposition of states which requires very different mass distributions means that the different gravitational effects have to be considered.
Either way, the consciousness does the magic trick stuff so beloved by woo-woo merchants is not the only option, and usually rests on a total misunderstanding of what is meant by observation...........
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Post by Progenitor A on Nov 1, 2010 18:11:50 GMT 1
As others have already said, superposition isn't just a part of the Copenhagen interpretation. No-one has said that it is exclusive to QM. Electrical engineers often use it in solving network equations. TO those who don't like the idea of superposition -- how do you explain double slit interference with single photons? Sum of histories? Even worse, WHAT state it 'collapses' into, the definite position states that you get when you place a screen behind the slits in order to gradually build up the interference pattern, or whether you decide to make a different measurement. Your explanations are not improvwed by that terrible misuse of English that you often apply, as here. QM is difficult enough without mangled English. Slow down! The point being, you can decide AFTER the photon has passed the slits, what measurement you are going to make! Abacus has made this point But whatever the real issues are, it isn't the simplistic -- superposition obviously rubbish, and Schrodingers cat tells us so........... It certainly is not simplistic and Schrodinger did not think so either. He was simply pointing out an absurdity a reductio ad absurdum of the Copenahagen theory Either way, the consciousness does the magic trick stuff so beloved by woo-woo merchants is not the only option, and usually rests on a total misunderstanding of what is meant by observation........... Consciousness evidently plays a part in it! And invoking consciousness is simply an attempt at understanding, trying to find a method of explaining, just as the Copenhagen method does. |
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Post by speakertoanimals on Nov 1, 2010 18:48:17 GMT 1
Not at all evident! Granted, we can only be aware of the result of a measurement when we go read the meter etc, but that doesn't tell us that the act of conscious observation is WHERE the collpase occurs, that everything is in a state of superposition until WE observe it.
SO, more realistic interpretations say that the dividing line (as Penrose suggests) is between the quantum system, and a piece of measuring apparatus that can essentially be treated classically. And things such as quantum decoherence go partway towards explaining this.
Copenhagen didn't actually explain much as regards wavefunction collapse. But nor does consciousness does the trick explanations, rather they try to hide one unknown within another, since we don't yet know what consciousness itself consists of, we don't know why, a priori, consciousness should be such that it collapses anything!
Of course, much of this can be thouight of as our need to have a decent explanation, it doesn't mean that there is one! You can view quantum theory as just a way to predict the frequency of various measurements on a system, it doesn't necessarily have anything to say about the ontological status of the state of a photon in between measurements, or even the ontological status of the wavefunction.
If you can't measure it, it doesn't matter, is one way to think of it................
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Post by Progenitor A on Nov 3, 2010 8:23:58 GMT 1
Of course, much of this can be thouight of as our need to have a decent explanation, it doesn't mean that there is one! Exactly what theists have being saying for millenia! |
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Post by jean on Nov 3, 2010 9:58:58 GMT 1
That's what atheists say, surely?
The theists say that God is the explanation.
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Post by abacus9900 on Nov 3, 2010 10:56:16 GMT 1
That's what atheists say, surely? The theists say that God is the explanation. Perhaps it is because without the participation of consciousness, quantum probabilities would never be realized. The physical world has to have conscious observers to exist otherwise it would just be 'smeared out' and ghostly. The quantum wavefunction has not got the ability to collapse itself and relies on conscious observers like us to decohere and form physical reality. This is the lesson of entanglement; the entangled particles remain 'incognito' until a measurenet is made by someone, which coaxes the potentials inherent in quantum objects (which are just smeared out and only half real) to become fully part of spacetime. One is tempted to conclude from all this that the 'mind of God' forms a backdrop (what we call the quantum wavefunction) in which we, sentient beings, choose to create our own 'Heaven' or 'Hell.' It is undeniable that our actions cause a ripple effect in the quantum 'ocean' of existence so that good deeds will create positive quantum ripples while bad ones will cause negative ones. Even something as simple as a smile generates positive quantum ripples which, in turn, promotes positive echos in the human community at large. Just look at the good will and sense of community Christmas generates - it is because it is a time of giving and concern for one's fellow human beings and so is reflected in the quantum backdrop which in turn creates a sense of hope and goodwill, which in turn, feeds back into the quantum field..... What the physicists have failed to grasp is that it is completely false to assume a dichotomy between 'us' (as in observers) and 'it' (as in the material world and other individuals) because we have a direct feedback effect on everything we touch and therefore play a major role in making the world what it is. Isaac Newton may have been profoundly correct when he asserted that he 'wanted to know the mind of God' through the study of physics, something that today seems to have been lost in the quest for an increasingly utilitarian way of life. |
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You read books!?