I'm sure I won't understand the answer
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Darkchilde wrote:The cat will be in a superposition of states until the box is opened. This thought experiment was a way by Schroedinger to show his malcontent with the Copenhagen interpretation of QM. However the thought experiment has remained as a way to explain the Copenhagen interpretation.
Now, the major point of the Copenhagen interpretation is measurement. What measurement is, is not defined in this interpretation, and could be anything from a simple observer (like a photon) to measuring equipment. In another thread, I had posted a concise summary of the Copenhagen interpretation, which I am repeating here:
The Copenhagen interpretation was put forth by people like Niels Bohr, Werner Heisenberg, etc. and it is the mainstream one, if I could call it that. It has been named the Copenhagen interpretation because of the location of its main proponents, like Niels Bohr between 1924 and 1927. In the Copenhagen interpretation, the wavefunction describes the state of a quantum system. The solutions to the Schrodinger equation for a specific quantum system are all wavefunctions, and each describes one of the probable states of the quantum system. Each wavefunction has a probability associated with it; until we measure one of the observables (measurable properties of a quantum system), the system does not have any quantum state associated with it.
Darkchilde wrote:
When we take a measurement, the system “decides” its quantum state, and the solution of the Schrodinger equation collapses to the specific wavefunction associated with the measurement. According to the Copenhagen interpretation, only the measurement of observables has any meaning, and this measurement “decides” the state of the quantum system.
Rilx wrote:"Observation" means that the observer detects the observed by "touching" it with some system which changes its energy state. If the observed itself radiates some detectable energy, you don't need to "touch" it, but the radiation itself changes it's energy state.
Thought experiments have their pitfalls, always.
But that implies theres something special about humans. That we have the power to make it so just by observing.
Rilx wrote:You are right concerning the CI, Darkchilde, but my post was addressed to OP. "Observation" is prone to confuse people to think that it (especially human "seeing") doesn't have any physical effect to the observed.But that implies theres something special about humans. That we have the power to make it so just by observing.
Panderos wrote:Ok so, until I look in the box, the cat might be in the alive state, it might be in the dead state, or it might be in the superposition of dead and alive states.
Then I look and the wavefunction collapses and it will be either dead or alive.
But that implies theres something special about humans. That we have the power to make it so just by observing. But I've also heard, in reference to quantum computing, that 'even a passing electron can 'look' and collapse the wavefunction' of some delicate system. I think I've heard this anyway.
So surely, if electrons can do it, then a passing electron in the cat box will make the wavefunction collapse and I'll have nothing to do with it. So whats the answer?
Darkchilde wrote:Twistor, other than energy/time and position/momentum, are there any other pairs of variables that we cannot measure both accurately, as per the Heisenberg Uncertainty Principle?
Eric8476 wrote:isn't the entire thought experiment flawed? the variable is the decaying matter, it either decays or not then therefore the cat would be dead or alive, not in limbo.
hackenslash wrote:Under the Copenhagen interpretation, the atom exists in both the decayed and un-decayed states simultaneously, and observations collapses the wavefunction, defining the eigenstate of the atom. Thus, in the thought experiment, the cat is both alive and dead at the same time, because the atom is both decayed and un-decayed, and therefore the poison is both released and unreleased at the same time.
hackenslash wrote:It isn't in limbo, it's actually both alive and dead. In any event, I've covered this above. It's a thought experiment, and really only analogises the principle of quantum superposition. The decaying atom most definitely can exist in a state of superposition, and this has been experimentally verified. Indeed, the computer you are posting from employs a variation of superposition, in the form of quantum tunnelling, for its operation.
eric8476 wrote:if the decaying matter can be both decayed and undecayed then schrodinger disproves quantum mechanics.
his linear approach is not consistant with measuring waves, am i right?
isn't it how to measure wavefunction that collapses the wavefunction, not obsevations?
the geiger measuring instrument for detecting decay would detect the matter's decayed position in time if the decaying matter is both decayed and not decayed, that would render that cat dead.
if we can observe without collapsing the wavefunction then we would not have any problems.
we don't have the technology to observe these things. if we do have the technology then the copenhagen interpretation would be obsolite.
hackenslash wrote:Really? You might want to have a word with your computer about that.
hackenslash wrote:No. Indeed the function we use for these waves is the Schrödinger equation, also known as the Schrödinger wave equation.
hackenslash wrote:Huh? That doesn't parse correctly in English. If it's what I think you're trying to say, then no. It's observation that collapses the wavefunction, but you have to be careful how you define 'observe' and 'observer', because those terms don't necessarily mean what you think they mean.
hackenslash wrote:Indeed. That would constitute an observation of the system, thereby collapsing the wavefunction.
hackenslash wrote:Well, observation is collapse of the wavefunction, and we don't actually have a problem.
take the quantum state measuring electrons that are around a nucleus, for instance. with advanced technology, the electrons can be observed in the electron cloud of the atom. thus the wavefunction collapsing or not would be a moot point.hackenslash wrote:No, because this is nothing to do with technology. We can't possess the technology to observe without collapsing the wavefunction, because observation and collapse are one and the same. There exists no such technology.
lucek wrote:OK first I'm going to echo the others. Schrodinger's Cat is actually a straw man that has sense been adopted to describe effects inconceivable to most 100 level physics students. Others like this include the big bang, the lader of evolution etc.
eric8476 wrote:hackenslash wrote:Really? You might want to have a word with your computer about that.
computers use 1 and 0? schrodinger's thought experiment uses the variable of the decaying matter. the cat's status is the result not the variable. copenhagen states that the matter can be decaying and not at the same time then the conclusions of schrodinger is disproving this statement. how is this not debunking?
eric8476 wrote:computers use 1 and 0?
schrodinger's thought experiment uses the variable of the decaying matter. the cat's status is the result not the variable. copenhagen states that the matter can be decaying and not at the same time then the conclusions of schrodinger is disproving this statement. how is this not debunking?
is it the only equation used to measure the wavefunction?
measuring and observing are different things.
we don't have the technology to observe particles in areas as of yet without collapsing the wavefunction
that is a result, observation or not.
check this link here: http://en.wikipedia.org/wiki/Interpretations_of_quantum_mechanics and scroll down the the conclusion area, there is a chart that shows different interpretations and some do not suggest collapsing of the wavefunction?
take the quantum state measuring electrons that are around a nucleus, for instance. with advanced technology, the electrons can be observed in the electron cloud of the atom. thus the wavefunction collapsing or not would be a moot point.
we can possess the advanced technology for observing without collapsing the wavefunction. it is possible. it doesn't exist yet, but it can exist. our grandchildren could be using them and not us but it's possible none the less.
eric8476 wrote:
we can possess the advanced technology for observing without collapsing the wavefunction. it is possible. it doesn't exist yet, but it can exist. our grandchildren could be using them and not us but it's possible none the less.
twistor59 wrote:By "conclusions of schrodinger", you presumably mean Schroedinger's cat experiment, not the conclusions of Schroedinger himself. If so, then I wouldn't say "disproving", but rather "highlighting a problem with":
The atom is in a quantum superposition (decayed+not decayed). There would then be a long causal chain of interactions leading to the eventual state of the cat. The atom in the gamma ray detector would be in a superpostion of detected+not detected. The electric current would be in a superposition of generated+not generated. The motor would be in a superposition of in motion + not in motion etc. All the time along the chain the items are getting bigger -- less microscopic and more macroscopic.
We know that we never see cats in a superposition of states. The question is therefore - "where along the causal chain do the rules of quantum mechanics break down and superposition gets lost" ?. This is the "Measurement Problem".
There have been many proposed answers to this over the years, and if you want an animated physics coffee table discussion, this is one topic guaranteed to bring it about.
hackenslash wrote:Computers, or more specifically the semiconductors in computers, employ devices known as Esaki diodes, which operate on the basis of quantum tunnelling. Of course, I already addressed this in the previous post of mine you quoted.
hackenslash wrote:I see that Twistor has covered this in more depth than I would have done.
hackenslash wrote:It isn't used to measure the wavefunction, but to describe the probability amplitude of one of a pair of conjugate variables.
hackenslash wrote:Care to highlight the distinction, or to point out how one can measure something without observation?
hackenslash wrote:It isn't a matter of technology, and your continued reassertion that it is doesn't actually move us forward. Indeed, there's good reason to think that those conjugate variables don't actually possess any definite values until observed.
hackenslash wrote:What?
hackenslash wrote:I'm aware of them, thanks. There are problems with those that don't include the collapse of the wavefunction. Not insurmountable by any means, but suggestive of problems. For example, the Many-Worlds interpretation is horribly unparsimonious. Not that parsimony is indicative of veracity, but as a heuristic in hypothesis selection, it's proved extremely useful, so not to be dismissed lightly. the de Broglie-Bohm intepretation runs into difficulties with the observation of superposition (indeed, and as Darkchilde pointed out above, it has been observed in macroscopic objects), because superposition removes the need for the 'pilot-wave'.
I tend to favour the path integral formulation, but not with any huge conviction. Since they are pretty much inseperable in terms of prediction of observations, there's no reason to choose between them at this point, but those without wavefunction collapse are the easiest to lay aside until some unique predictions arise from one of them. The Copenhagen interpretation has brought us a very long way, and those hypotheses haven't actually brought us any further (apart from the path integral).
In any event, none of this supports your assertion that measurement and observation are different things.
hackenslash wrote:They can certainly be observed, but they can only be observed with a given position or a given momentum, not both. The very best we can do is a kind of weak measurement that can give a vague average of both, to the tolerance of the wavelength of the photon used for observation, but accuracy is impossible, because the uncertainty principle cannot be violated with pairs of conjugate variables. The more accurately we know one, the less accurately we can know the other.
hackenslash wrote:And the evidence in support of this contention is...?
Since there is good reason to suppose that pairs of conjugate variables don't actually possess values until they are observed, I'd love to see how you're going to manage this.
Darkchilde wrote:There is a problem here. Once the wavefunction is observed, by anything, even by a photon or by an electron, or a device, then the wavefunction collapses to one of the associated probabilities. A device that observes that does not collapse the wavefunction, would be one that does not do any observation. The mere act of the device's observation is the one that will collapse the wavefunction.
zaybu wrote:There's one problem with these explanations: the wave function is NEVER observed. Observables in QM are operators, such as position, momentum, energy, spin. The wavefunction is just a mathematical tool that allows calculation of expectation values of these observables. Any other interpretation of the wavefunction is just pure speculation, unsupported by any evidence.
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