Quantum Interpretation Poll (2011)

[rodsika]

I think, in principle, yes.

How is that possible. Pure state in the cat body simply meant all the particles are entangled. How can you make this create both old and young cat? Hmm.. are you saying that if you can put the old Einstein in pure state, he can become young again... like the fountain youth? What in pure state makes this possible at all? Hope you can explain a bit more so it can be clear to both of us the limitations and possibilities. Thanks.

 

[tom.stoer]

You have to specify what "create a pure state" and "put it in a superposition" means. In QM this means "preparation of the state" and that's what is done in setting up an experiment with well-defined initial conditions (position, momentum, ...).

You can prepare a superposition "alive + dead" simply by following Schrödinger's Gedankenexperiment: take the cat, the box, ... - put the cat into the box - close the box and wait for some time (defined by half-life) - voila

 

[rodsika]

You have to specify what "create a pure state" and "put it in a superposition" means. In QM this means "preparation of the state" and that's what is done in setting up an experiment with well-defined initial conditions (position, momentum, ...).

You can prepare a superposition "alive + dead" simply by following Schrödinger's Gedankenexperiment: take the cat, the box, ... - put the cat into the box - close the box and wait for some time (defined by half-life) - voila

But according to a physicist, Ken, it is not even possible in principle to know the cat pure state before closing the box. So the Schroedinger Cat thought experiment is impossible in principle. Which of the following part don't you agree:

(Ken stated)

"No, that is just exactly what you could never do, not even in principle. Because the only way to know that would be to do measurements on the cat, but that would involve a measuring device, so immediately the cat becomes a subspace of the thing that is a pure state. Unlike measuring the spin of a single particle, where there is no information being ignored, if you measure an "entire cat", there is vast amounts of information you could never get a handle on, like herding cats (literally). There's no measurement like that which even in principle could result in complete information about the cat's wave function that could be treated as a closed system going forward, too much of the data (all the phase coherences) that would need to be tracked is going to be entangled with the instruments doing the measuring, not to mention the brain processing that information.

This is the key point-- the information that goes into determining a wave function is not in the entity being observed, it is in the environment doing the observing and processing that information. Physics is done by physicists, even if we can imagine the action of hypothetical physicists not actually present in the environment. If that environment does include a real brain, it might be able to treat the entity as having a pure-state wavefunction (as for the spin of a particle), but it could never be empowered to treat a cat in a pure-state wavefunction, there would always have to be too much overlooked information (indeed, judicious overlooking of information is more or less the foundational principle of physics). It is only ever the whole system including the observer that could be treated as a pure state, and only if it started out in a pure state, which brings in the issue of history."

 

[tom.stoer]

The key point is that Ken wants to "measure" the cat whereas I want to "prepare" it. That is something different.

When setting up an experiment with monochromatic, coherent light emitted by a LASER the light is by definition monochromatic and coherent w/o measuring it! You check the properties of the light before starting the experiment in order to ensure the correctness of the setup, but during the experiment you do no longer check them; you simply believe that these properties persists w/o measurement. The same applies to the cat.

The problem is different: The cat will never be in a pure state "alive" as the cat itself is always a mixed state b/c of the huge number of d.o.f. Therefore preparing the cat in a state "alive + dead" is possible, but this state is not a pure state (a ray) but a mixed state (a density matrix). This is not due to the superposition of "dead" and "alive" but due to the macroscopic nature of the cat.

But as far as I can see that does not affect the interpretation of the experiment b/c again the problem is "why the (mixed) state of the cat collapses to either dead or alive" where again dead and alive refer to mixed states. I guess decoherence is able to explain why the state of the cat collapses to one one these mixed states, but it does not explain why in a certain experiment it collapses to "dead" and not to "alive".

That means that "collapse of the wave function", "split according to MWI interpretation ..." does apply on the level of density matrices. This is technically more involved but causes the same fundamental problems regarding ontology.

 

[rodsika]

The key point is that Ken wants to "measure" the cat whereas I want to "prepare" it. That is something different.

When setting up an experiment with monochromatic, coherent light emitted by a LASER the light is by definition monochromatic and coherent w/o measuring it! You check the properties of the light before starting the experiment in order to ensure the correctness of the setup, but during the experiment you do no longer check them; you simply believe that these properties persists w/o measurement. The same applies to the cat.

The problem is different: The cat will never be in a pure state "alive" as the cat itself is always a mixed state b/c of the huge number of d.o.f. Therefore preparing the cat in a state "alive + dead" is possible, but this state is not a pure state (a ray) but a mixed state (a density matrix). This is not due to the superposition of "dead" and "alive" but due to the macroscopic nature of the cat.

But as far as I can see that does not affect the interpretation of the experiment b/c again the problem is "why the (mixed) state of the cat collapses to either dead or alive" where again dead and alive refer to mixed states. I guess decoherence is able to explain why the state of the cat collapses to one one these mixed states, but it does not explain why in a certain experiment it collapses to "dead" and not to "alive".

That means that "collapse of the wave function", "split according to MWI interpretation ..." does apply on the level of density matrices. This is technically more involved but causes the same fundamental problems regarding ontology.

But if it's a mixed state (a density matrix) then it's just classical probability of being alive or dead. Not a superposition (which involves pure state or ray). Since pure Quantum Mechanics only deal with pure state evolving unitarily. Then preparing it alive + dead is not quantum mechanics already. Just a classical problem. But I wonder why density matrix must fall under quantum mechanics since there is no longer a ray. Any idea?

 

[tom.stoer]

But if it's a mixed state (a density matrix) then it's just classical probability of being alive or dead. Not a superposition

That's not true. It would hold iff the density matrix could be written in terms of two pure states "alive" and "dead" with classical probabilities, but this is not true. Density matrices can describe both classical probabilities and quantum superposition.

 

[StevieTNZ]

The fundamental equation that governs any quantum system is the Schrodinger equation. At least, according to Howard Carmichael.

(http://www.physics.auckland.ac.nz/uoa/home/about/our-staff/professor-howard-carmichael/ )

 

[StevieTNZ]

Are you saying that the moment you can create a pure state cat. You can put it in any superposition you like such as dead/alive, pregnant/not pregnant, cancer/healthy, virgin/used, old/young, etc.? Without any limitations whatsoever? If there is limitation, maybe a pure state cat can only have superposition of positions of being on the left and right side at the same time and not on being dead/alive, pregnant/nonpregnant, etc.?

A macroscopic quantum system has an infinite amount of physical configurations as a basis state.

virgin/used

lol

 

[camboy]

　

I read last week that a science advisor and mathematician extraordinaire Arnold Neumaier already declared Bohmian mechanics null and void so I thought you guys refuted it already. Neumaier said:

<snip>　

So Bohmian Mechanics is still alive.

Look, why - in your case of having zero knowledge of this subject - do you think you have the right to behave in a sarcastic manner to people who try to educate you? Someone else already accused you of being arrogant - I can see why.

Arnold is unfortunately guilty of spreading a great deal of misinformation about de Broglie-Bohm theory in these threads. There's nothing one can do about this - even if we point out correct objections he'll just proclaim his superior intellect at us (and say that he's far too clever to bother publishing an objection in the peer-reviewed literature). Doesn't mean he's right though, as has been pointed out many times - see my https://www.physicsforums.com/showpost.php?p=3269901&postcount=27" to him in another thread.

But isn't it that in orthodox QM, a prisoner has non-zero probability of quantum tunneling outside a cement wall? In Bohmian M, no matter how much energy you give the prisoner, you can't quantum tunnel him outside of the cell without accelerating his body to the cement walls shredding it to pieces. Here QM has more flexibility. Isn't it?

No - look, just read some reference, will you. Start with the http://www.tcm.phy.cam.ac.uk/~mdt26/pilot_waves.html" - if I remember rightly Lecture 3 has something about tunnelling..

 

[rodsika]

That's not true. It would hold iff the density matrix could be written in terms of two pure states "alive" and "dead" with classical probabilities, but this is not true. Density matrices can describe both classical probabilities and quantum superposition.

Uhm, how do you prepare the cat in a state "alive + dead" that is not a pure state but a mixed state? an actual example? I only know about superposition of alive and dead where both exist in pure state. But I'm not familiar with mixed state "alive" and "dead". About the outcome, maybe it's is chosen by whether the radioactive source decays or not?

 

[Rap]

How is that possible. Pure state in the cat body simply meant all the particles are entangled. How can you make this create both old and young cat? Hmm.. are you saying that if you can put the old Einstein in pure state, he can become young again... like the fountain youth? What in pure state makes this possible at all? Hope you can explain a bit more so it can be clear to both of us the limitations and possibilities. Thanks.

tom.stoer #102 said it - if you have a box and you arrange it so that, after a certain amount of time, one outcome happens with 50% probability, another with 50% probability, and you know the pure state going in, then after that time, it will be in a superposition of the two outcomes. If you put a male cat and a female cat in a box with a closed door, knowing the pure state, and after a minute the door has a 50% chance of opening and staying open, 50% chance of never opening, then after a few months, the contents of the box will be in a superposed female cat pregnant/not pregnant state. I guess if you had the cat travel around in circles at near the speed of light with 50% probability, then after a year it would be in a superposition of (a little bit older)/(a year older), but you couldn't make it younger.

This is all too simplistic, but it is the general idea. Once you understand this, you can start to get into the details.

I think Ken G. eventually allowed that you could, in principle, close the box knowing a pure state.

The problem is different: The cat will never be in a pure state "alive" as the cat itself is always a mixed state b/c of the huge number of d.o.f. Therefore preparing the cat in a state "alive + dead" is possible, but this state is not a pure state (a ray) but a mixed state (a density matrix). This is not due to the superposition of "dead" and "alive" but due to the macroscopic nature of the cat.

I think that the fact that the cat is macroscopic does not prohibit you, in principle, from describing it by a pure state. I can describe one particle by a pure state, two with more difficulty, etc. There is no particle number at which it suddenly becomes impossible to describe them as a pure state.

But as far as I can see that does not affect the interpretation of the experiment b/c again the problem is "why the (mixed) state of the cat collapses to either dead or alive" where again dead and alive refer to mixed states. I guess decoherence is able to explain why the state of the cat collapses to one one these mixed states, but it does not explain why in a certain experiment it collapses to "dead" and not to "alive".

Decoherence in a closed system is a mathematical approximation, and does not explain collapse. It says that a superposed state can be approximated by a mixed state.

 

[tom.stoer]

Decoherence in a closed system is a mathematical approximation, and does not explain collapse. It says that a superposed state can be approximated by a mixed state.

Sorry for being sloppy; of course it's not "collapse" but simply the fact that we observe classical pointer states instead of coherent superpositions.

 

[rodsika]

The key point is that Ken wants to "measure" the cat whereas I want to "prepare" it. That is something different.

When setting up an experiment with monochromatic, coherent light emitted by a LASER the light is by definition monochromatic and coherent w/o measuring it! You check the properties of the light before starting the experiment in order to ensure the correctness of the setup, but during the experiment you do no longer check them; you simply believe that these properties persists w/o measurement. The same applies to the cat.

The problem is different: The cat will never be in a pure state "alive" as the cat itself is always a mixed state b/c of the huge number of d.o.f. Therefore preparing the cat in a state "alive + dead" is possible, but this state is not a pure state (a ray) but a mixed state (a density matrix). This is not due to the superposition of "dead" and "alive" but due to the macroscopic nature of the cat.

But as far as I can see that does not affect the interpretation of the experiment b/c again the problem is "why the (mixed) state of the cat collapses to either dead or alive" where again dead and alive refer to mixed states. I guess decoherence is able to explain why the state of the cat collapses to one one these mixed states, but it does not explain why in a certain experiment it collapses to "dead" and not to "alive".

That means that "collapse of the wave function", "split according to MWI interpretation ..." does apply on the level of density matrices. This is technically more involved but causes the same fundamental problems regarding ontology.

After hours of reading many threads and articles. I still can't fully understand everything you said above. First I need to know. When you say mixed state, do you mean classical collapsed state or not? If not. Are you saying that if we don't know the pure state of the cat and we totally isolate it in the box. It won't necessarily go into classical state but mixed state, meaning some parts still in superposition, is this what you meant? Also you were asking why the mixed state of the cat collapsed into either dead or alive. So you meant here the cat is still in partial superposition? Do you consider the body of a person like Obama walking on street in mixed state or no state? Or is the word mixed state only referred to isolated object? Pls clarify. Sorry if I am so dumb. Thanks.

 

[rodsika]

I think he means that, if we agree on a wave function for a system, it encapsulates our knowledge of the system (subjective), but the probabilities that we calculate as we propagate the wave function forward in time, (using e.g. the Schroedinger equation) are objective.



The thing I objected to was the assumption that the cat and the device were separate systems. This seems arbitrary. I think, in principle, you can have the device and the cat as one pure state, evolving according to the Schroedinger equation. In the case of Wigner's friend, the same applies.



No. QM is about measurements and the only reality is that which is revealed by those measurements. If I said the buckyball took a classical trajectory, that would mean I could measure its position and momentum to a high degree of accuracy without appreciably disturbing it, all along its trajectory. Superposition would not be an issue, the wave function would collapse at each measurement. If you say that the position and momentum is unmeasured during its travel, then QM and superposition will apply. But then, the question of whether it was following a classical trajectory is untestable, and is therefore not a proper scientific question.



Decoherence in this case is a mathematical approximation, not a physical occurrence. It says that you can approximately replace a pure wave function by a mixed state: an ensemble of macroscopic observations which do not yield as much information as a wavefunction collapse, and whose probabilities are additive. These observations do not collapse the wave function to an eigenstate, but rather selects one macroscopic observation out of the ensemble of observations. This is what happens when you open the box. You don't collapse the wave function, measuring the position and momenta of every particle of the cat (to within Heisenberg), such a measurement would destroy the cat. You make a much less informative measurement, noting only whether the cat is alive or dead.

Rap, what do you think of this comment by eaglelake?

"4. A quantum experiment requires a measurement result. (Bohr) If we assume that the particle exists prior to measurement, as was done in the EPR experiment, then we get erroneous results. Taking the results of quantum experiments at face value, quantum particles do not have trajectories and they exist only at the instant they are detected. For this reason, Wheeler calls particle detection, "an elementary act of creation.""

You believe the wave function is not real but only a tool by the physicist. But in the EPR thing, quantum particle do not have trajectories and they exist only at the instant they are detected. So you mean the Copenhagen thought or idea the wave function is not real yet quantum particles are not classical before measurement is compatible? Or more accurately, wave function being not real and local realism false is compatible? But if it is. The wave function has to exist somewhere or else if can't tract quantum objects which are not in classical world.

 

[tom.stoer]

@rodsika: mixed state is a technical term referring to a density matrix q http://en.wikipedia.org/wiki/Quantum_state#Mixed_states A density matrix can describe both pure and mixed states; the criterion to differentiate them is tr(q²).

 

[Rap]

Rap, what do you think of this comment by eaglelake?

"4. A quantum experiment requires a measurement result. (Bohr) If we assume that the particle exists prior to measurement, as was done in the EPR experiment, then we get erroneous results. Taking the results of quantum experiments at face value, quantum particles do not have trajectories and they exist only at the instant they are detected. For this reason, Wheeler calls particle detection, "an elementary act of creation.""

I am not sure what "if we assume that the the particle exists" means. Can you elaborate on this?

 

[rodsika]

I am not sure what "if we assume that the the particle exists" means. Can you elaborate on this?

In the EPR experiment, if the other photon pair exists on the other side, then you can determine with certainty both position and momentum by measuring both the attributes in either side. Hence EPR refutes local realism, meaning properties like position don't exist before measurements. Therefore you can't say there is still classical trajectory unless you go to the Bohmians. But our concern is pure Copenhagen. You said Copenhagen is pragmatic and doesn't care what is the deeper reality underneath.. But at least we can say that Copenhagen rejects or not compatible with classical trajectories but more of the stuff about properties don't exist before measurement variety. Refute this.

 

[Rap]

In the EPR experiment, if the other photon pair exists on the other side, then you can determine with certainty both position and momentum by measuring both the attributes in either side. Hence EPR refutes local realism, meaning properties like position don't exist before measurements. Therefore you can't say there is still classical trajectory unless you go to the Bohmians. But our concern is pure Copenhagen. You said Copenhagen is pragmatic and doesn't care what is the deeper reality underneath.. But at least we can say that Copenhagen rejects or not compatible with classical trajectories but more of the stuff about properties don't exist before measurement variety. Refute this.

To me, the statement that something does not exist means experimentally "I have searched exhaustively and it is not to be found". If something does not exist in principle, then it means "no matter how much you search, you will not find it". What can you say about something that you do not search for? Nothing.

In hard science, to search is to measure. You cannot determine if a particle exists before a measurement, because it requires measurements to make that determination. To ask if a particle exists before a measurement is an improper question. It is not a testable question. It is not a scientific question. It is an improper question and it has no answer.

If reality were God, Copenhagen is agnostic, not atheistic. An agnostic does not know if God exists, an atheist denies the existence of God. Copenhagen is like the agnostic, it does not deny or reject reality, it simply realizes that we cannot have scientific knowledge about any reality beyond what can be repeatably and quantitatively measured.

 

[rodsika]

Rap. About Wigner friend. Can you give a simpler setup to illustrate how the wave function has more to do with the observer knowledge and measurements? In the Wigner friend and the cat inside a bigger box with another scientist outside. You illustrated how the outside scientist can model Wigner in superposition of opening and not opening the box.. while Wigner would say he didn't experience any superposition, but either opening and not opening the box. Here you claimed that the wave function can't be real or there would be paradox. Is this your own argument or did you hear it elsewhere or the mainstream? But the problem is many state that the cat and Wigner can't even be in pure state in principle so no superposition at all is possible. That is why. Try to find a simpler setup using atoms or particles that can show the Wigner friend paradox. Can you think of one or any there in the literature?

 

[StevieTNZ]

Rap. About Wigner friend. Can you give a simpler setup to illustrate how the wave function has more to do with the observer knowledge and measurements? In the Wigner friend and the cat inside a bigger box with another scientist outside. You illustrated how the outside scientist can model Wigner in superposition of opening and not opening the box.. while Wigner would say he didn't experience any superposition, but either opening and not opening the box. Here you claimed that the wave function can't be real or there would be paradox. Is this your own argument or did you hear it elsewhere or the mainstream? But the problem is many state that the cat and Wigner can't even be in pure state in principle so no superposition at all is possible. That is why. Try to find a simpler setup using atoms or particles that can show the Wigner friend paradox. Can you think of one or any there in the literature?

I refer you to pages 243 and 244 of 'Modern Physics and Ancient Faith' by Stephen M. Barr. Publisher: University of Notre Dame Press

 

[Rap]

Rap. About Wigner friend. Can you give a simpler setup to illustrate how the wave function has more to do with the observer knowledge and measurements? In the Wigner friend and the cat inside a bigger box with another scientist outside. You illustrated how the outside scientist can model Wigner in superposition of opening and not opening the box.. while Wigner would say he didn't experience any superposition, but either opening and not opening the box. Here you claimed that the wave function can't be real or there would be paradox. Is this your own argument or did you hear it elsewhere or the mainstream? But the problem is many state that the cat and Wigner can't even be in pure state in principle so no superposition at all is possible. That is why. Try to find a simpler setup using atoms or particles that can show the Wigner friend paradox. Can you think of one or any there in the literature?

It is the central problem in Everett's thesis (see http://www.pbs.org/wgbh/nova/manyworlds/pdf/dissertation.pdf )

His attempt to solve the paradox resulted in his many-worlds interpretation of QM. I disagree with this interpretation because it is not testable.

 

[rodsika]

If he means there is no pure state for the cat I agree, but my understanding of decoherence is that you could still have a reduced density matrix for the cat subsystem, and that although decoherence would drive this reduced density matrix into something close to a mixed state, the interference terms wouldn't quite go to zero so there is still a superposition of sorts. Ken or some other knowledgeable person can correct me if I've misunderstood this stuff though...

Jesse, Just a quick question, you said the electron passing thru the gas in double slit experience decoherence with no collapse. And collapse only occurs in final measurement. How about when you travel daily to work, you are not measuring anything, can the environment entangling with your body be pure decoherence without collapse. Or does collapse occurs in every interaction with the environment even if you don't do any measurements? Let's just focus on Copenhagen for now. Thanks.

 

[JesseM]

Jesse, Just a quick question, you said the electron passing thru the gas in double slit experience decoherence with no collapse. And collapse only occurs in final measurement. How about when you travel daily to work, you are not measuring anything, can the environment entangling with your body be pure decoherence without collapse. Or does collapse occurs in every interaction with the environment even if you don't do any measurements? Let's just focus on Copenhagen for now. Thanks.

In Copenhagen the "collapse" isn't an objective fact but an aspect of how we choose to represent the situation, you can only include a "collapse" at a particular time if you actually have access to information about the value of some variable at that time, it wouldn't be possible in practice to retrospectively figure out something like your position at a particular time just by measuring the positions of gas molecules. But even in cases where a measurement was made and you have access to its measurement records, it's still a matter of choice whether to include a "collapse" at the time of measurement, you are also free to model the measurement as just being a quantum interaction that causes entanglement between the system being measured and the measurement records, and then later include a "collapse" due to observing those records.

 

[yoda jedi]

Rap. About Wigner friend. Can you give a simpler setup to illustrate how the wave function has more to do with the observer knowledge and measurements? In the Wigner friend and the cat inside a bigger box with another scientist outside. You illustrated how the outside scientist can model Wigner in superposition of opening and not opening the box.. while Wigner would say he didn't experience any superposition, but either opening and not opening the box. Here you claimed that the wave function can't be real or there would be paradox. Is this your own argument or did you hear it elsewhere or the mainstream? But the problem is many state that the cat and Wigner can't even be in pure state in principle so no superposition at all is possible. That is why. Try to find a simpler setup using atoms or particles that can show the Wigner friend paradox. Can you think of one or any there in the literature?

Agnostic ?

“The idea of an objective real world whose smallest parts exist objectively in the same sense as stones or trees exist, independently of whether or not we observe them. . . is impossible.” [Heisenberg, 1958]


.

 

[SpectraCat]

... it's still a matter of choice whether to include a "collapse" at the time of measurement, you are also free to model the measurement as just being a quantum interaction that causes entanglement between the system being measured and the measurement records, and then later include a "collapse" due to observing those records.

Really? What makes a person more significant to the quantum state than the "measurement device" that "recorded the data"? Isn't a human just another measurement device? What's to say that after viewing the data, you don't become entangled with the initial quantum state and the original measurement device? Actually, isn't that kinda what MWI would look like to an "external observer" (i.e. one who is not riding on any of the effective world-lines)?

My issue (maybe?) is that your response sounds uncomfortably like the pseudo-science "Consciousness causes collapse" arguments. I agree that I cannot say for certain that the collapse is not "delayed" until viewed by a human, but I think I can say for certain that the question is the realm of metaphysics and not physics. Or was that your point all along?

 

[Rap]

Agnostic ?

“The idea of an objective real world whose smallest parts exist objectively in the same sense as stones or trees exist, independently of whether or not we observe them. . . is impossible.” [Heisenberg, 1958]
.

By my understanding of the Copenhagen interpretation, this statement is too strong. It makes an untestable statement. I don't think this statement precisely represents a position of the Copenhagen interpretation.

 

[Rap]

Really? What makes a person more significant to the quantum state than the "measurement device" that "recorded the data"? Isn't a human just another measurement device? What's to say that after viewing the data, you don't become entangled with the initial quantum state and the original measurement device? Actually, isn't that kinda what MWI would look like to an "external observer" (i.e. one who is not riding on any of the effective world-lines)?

My issue (maybe?) is that your response sounds uncomfortably like the pseudo-science "Consciousness causes collapse" arguments. I agree that I cannot say for certain that the collapse is not "delayed" until viewed by a human, but I think I can say for certain that the question is the realm of metaphysics and not physics. Or was that your point all along?

You are assuming that the wave function is a fully objective entity. According to the Copenhagen interpretation, it is not. Consciousness does not cause collapse. A scientist's knowledge of a pure state is encapsulated in the wave function. When that knowledge changes as the result of a measurement, the representation of that knowledge (the wave function) changes as well - it "collapses". A mouse, a child, a classical physicist do not collapse the wave function because there is no wave function. A robot or a quantum physicist making quantum mechanical calculations and measurements will collapse the wave function upon making a measurement.

 

[JesseM]

Really? What makes a person more significant to the quantum state than the "measurement device" that "recorded the data"?

Nothing, but you need to include a collapse somewhere to make any statements about probabilities. You are of course free to have a friend[/url] type situation where you model one person's observation as just creating entanglement, and then only have a "collapse" at some later time when his memories are probed by some other person/machine, but it would of course be very difficult to come up with a model for the wavefunction of a human brain that wasn't grossly oversimplified.

 

[yoda jedi]

By my understanding of the Copenhagen interpretation, this statement is too strong. It makes an untestable statement. I don't think this statement precisely represents a position of the Copenhagen interpretation.

...heinseberg and bohr are the fathers of copenhagen

I understood you, long ago, bias choosing...



.

 

[SpectraCat]

You are assuming that the wave function is a fully objective entity. According to the Copenhagen interpretation, it is not. Consciousness does not cause collapse. A scientist's knowledge of a pure state is encapsulated in the wave function. When that knowledge changes as the result of a measurement, the representation of that knowledge (the wave function) changes as well - it "collapses". A mouse, a child, a classical physicist do not collapse the wave function because there is no wave function. A robot or a quantum physicist making quantum mechanical calculations and measurements will collapse the wave function upon making a measurement.

That appears to me to be purely metaphysical mumbo-jumbo ... given your other posts, perhaps you are just trying to make the point that the question of which Q.M. interpretation is preferred to be one of philosophy? I would tend to agree with that statement ... I think of myself as more of an "Experimentalist", in that I find the greatest value in Q.M.'s ability to make predictions about measurements that can be verified experimentally. I would not go as far as to say that I am of the "Shut up and calculate" school, because I think there is intellectual merit in pondering what might be going on behind the scenes. However, until there is a testable hypothesis that can distinguish between, for example, Bohmian mechanics and the Copenhagen interpretation, I will reserve judgment about which on is "correct" or even "preferred".

 

[rodsika]

Nothing, but you need to include a collapse somewhere to make any statements about probabilities. You are of course free to have a friend[/url] type situation where you model one person's observation as just creating entanglement, and then only have a "collapse" at some later time when his memories are probed by some other person/machine, but it would of course be very difficult to come up with a model for the wavefunction of a human brain that wasn't grossly oversimplified.

　

But can't we just treat the wave function as objective and an actual collapse agent not yet discovered. Most would use Wigner cat as counterargument to the objectivity of the wave function. The argument being that there would be inconsistencies in what Wigner and his friend measure like his friend opening the cat inside and seeing it alive, while Wigner would model everything inside in superposition. However, this Wigner cat thought experiment is not possible at all because one can never even in principle put a cat in pure state because alive and dead are already mixed state due to the extremely complex nature of it (it's not like the spin of a particle where you easily can eliminate all the unknown information). This is detailed in the thread "Does Schrodinger's Cat Paradox Suck?" with detailed arguments by Ken G. Also Wigner never intented his thought experiment to prove that the wave function is not real. According to Wikipedia: "Wigner designed the experiment to illustrate his belief that consciousness is necessary to the quantum mechanical measurement process. If a material device is substituted for the conscious friend, the linearity of the wave function implies that the state of the system is in a linear sum of possible states. It is simply a larger indeterminate system."

Bottom line is that the Wigner friend thought experiment can't be shown or prove that the wave function is not objective. Do you know of other arguments beside Wigner friend that shows how the wave function in Copenhagen can't be real. Others beside your George Washington and Duck thought experiment where the person inside the box is presented either picture of George Washington or the Duck. Here one can similarly argue the setup can never be in pure state and can never work in principle, so it makes invalid the thought experiment. Or one can argue that it's not yet proven consciousness is in the brain so perceiving superposition is not rejected.

Or is Wigner Friend and your example only valid attempt to prove the wave function is not real. If so. Since the Wigner Friend is not possible in the first place and yours, then it doesn't disprove that the wave function can't be real. If you are aware of other categorical arguments that the wave function in Copenhagen can't be real. Pls. let me know so we can put a closure on this argument. Thanks.

 

[Rap]

...heinseberg and bohr are the fathers of copenhagen
I understood you, long ago, bias choosing...
.

No, you misunderstand me. I am not a disciple of Bohr and Heisenberg, defending to the death my blind faith in their every utterance. I put things together in my mind the best I can, and I find the CI to be closest to the way I think. If Bohr or Heisenberg say something with which I disagree, I will go to work to understand them, because I think their ability to understand the problem is well beyond mine, but, unlike them, we have the benefit of the work of many great minds that have come after them, and need not follow them blindly, even though we are less talented than they. If Heisenberg believes that statement, then I think that statement is improper. If I wake up tomorrow realizing he was dead on, I will turn on a dime and adopt his view as my own, but I won't parrot it because Heisenberg said it. I don't dispute your point of view by finding an authority who disagrees with you, I dispute it on the basis of logical consistency. I attempt to provide an argument from reason, not from authority. I ask that you do the same. I will not engage in a discussion in which the winner is the one who provides the most references, rather than the most cogent argument. What about my understading of the Copenhagen interpretation do you find unsatisfactory, other than a quote by an authority that disagrees with it?

“Do not believe in anything simply because you have heard it. Do not believe in anything simply because it is spoken and rumored by many. Do not believe in anything simply because it is found written in your religious books. Do not believe in anything merely on the authority of your teachers and elders. Do not believe in traditions because they have been handed down for many generations. But after observation and analysis, when you find that anything agrees with reason and is conducive to the good and benefit of one and all, then accept it and live up to it.”

Yes.

That appears to me to be purely metaphysical mumbo-jumbo ... given your other posts, perhaps you are just trying to make the point that the question of which Q.M. interpretation is preferred to be one of philosophy? I would tend to agree with that statement ... I think of myself as more of an "Experimentalist", in that I find the greatest value in Q.M.'s ability to make predictions about measurements that can be verified experimentally. I would not go as far as to say that I am of the "Shut up and calculate" school, because I think there is intellectual merit in pondering what might be going on behind the scenes. However, until there is a testable hypothesis that can distinguish between, for example, Bohmian mechanics and the Copenhagen interpretation, I will reserve judgment about which on is "correct" or even "preferred".

Excellent! This is exactly the Copenhagen attitude! This is why I think the CI is best - it refuses to draw untestable conclusions.

　
But can't we just treat the wave function as objective and an actual collapse agent not yet discovered. Most would use Wigner cat as counterargument to the objectivity of the wave function. The argument being that there would be inconsistencies in what Wigner and his friend measure like his friend opening the cat inside and seeing it alive, while Wigner would model everything inside in superposition. However, this Wigner cat thought experiment is not possible at all because one can never even in principle put a cat in pure state because alive and dead are already mixed state due to the extremely complex nature of it (it's not like the spin of a particle where you easily can eliminate all the unknown information). This is detailed in the thread "Does Schrodinger's Cat Paradox Suck?" with detailed arguments by Ken G.

I would ask, at what degree of complexity does the difficulty of putting the cat into a pure state change from finite (though large) to infinite? Suppose N is the number of particles at which the difficulty becomes infinite. What causes the infinite amount of change, the discontinuous change, from N-1 to N particles?

I believe that Ken G. later in the thread agreed that there was no such N. But we should get Ken G. to join this thread, rather than speculate on what he meant. He has put considerable thought into the problem, and there were many points that he made that I still do not understand.

Also Wigner never intented his thought experiment to prove that the wave function is not real. According to Wikipedia: "Wigner designed the experiment to illustrate his belief that consciousness is necessary to the quantum mechanical measurement process. If a material device is substituted for the conscious friend, the linearity of the wave function implies that the state of the system is in a linear sum of possible states. It is simply a larger indeterminate system."

What Wigner intended is instructive, since he is a great expert on the subject, but it is not binding. Only the truth and consistency of his arguments are binding, and I will bet he would agree. Let's discuss his work in this light, rather than focusing on his intent at the time.

In specific response, it is simply a larger indeterminate system to whom? To an outside observer, of course. A quantum scientist is a "material device" and if that "material device" is making quantum calculations, then that "material device" will be computationally collapsing the wave functions that represent its knowledge when it makes a measurement. The embodiment of these computations will be part of the system which the outside observer is dealing with and he will represent them as a superposition of possibilities. If you are the "material device", you will not experience superposition, because the superposition is in the computations of the outside observer, not in yours.

Or is Wigner Friend and your example only valid attempt to prove the wave function is not real. If so. Since the Wigner Friend is not possible in the first place and yours, then it doesn't disprove that the wave function can't be real. If you are aware of other categorical arguments that the wave function in Copenhagen can't be real. Pls. let me know so we can put a closure on this argument. Thanks.

I am not aware of any other arguments, but this single argument was sufficient to motivate Everett to develop his many-worlds interpretation. (Oops - I appealed to authority, sorry). At any rate, I disagree that Wigner's friend is not valid, for the reasons quoted above, and I know that one argument is sufficient to disprove a negative.

 

[yoda jedi]

I put things together in my mind the best I can, and I find the CI to be closest to the way I think.

Confirmation bias:
tendency to search for or interpret information in a way that confirms one’s preconceptions and to avoid information and interpretations which contradict prior beliefs.

now, i understand, you make your own pastiche..

 

[Rap]

I will assume you are not insulting me, but rather that you are offering constructive criticism. If I am wrong, please let me know, I'm sure we both have better things to do.

You say that I interpret information in a way that confirms my preconceptions. I'm a near fanatic about not having preconceptions (e.g. underlying reality), because they can interfere with learning. But you are correct in one sense - one preconception that I seem to cling to is the idea that science is about quantitative, repeatable measurements, and any conclusions that are not supported by such measurements are outside the realm of science. It will be difficult (but not impossible, I suppose) to argue me out of this preconception. This is a "prior belief" and I do not so much avoid information and interpretations which contradict this belief, as to ask why one would think otherwise. Let me ask you - why do you cling to the idea that a "reality" that you cannot in principle ever experience in any way is worth pondering?

When you say I make my own "pastiche" - I looked this up and I assume you mean "hodgepodge" or "incongruous mixture" - meaning that my viewpoint is not logically consistent, consisting of rather disconnected viewpoints which are contradictory. If this is the case, please point out the most glaring inconsistency to begin with. I'm not saying you will not find one, but if you do, I will certainly take it as a learning experience and not avoid or reject it.

I will relax and not be a scientist for a moment: Everyone who has some other interpretation of quantum mechanics seems to be obsessively seeking to impose "reality" on the results of quantum mechanics, rather than trying to understand a much deeper truth that these results are trying to tell us. Deterministic reality is what happens when you take quantum mechanics in the macroscopic limit - its a classical effect. Human brains are designed to intuitively understand deterministic classical physics. If we don't, we don't survive. There has never been an evolutionary need for the human brain to intuitively understand relativity or quantum mechanics, and so it is very difficult for us to do so. Quantum mechanics is trying to tell us something, and we keep ignoring it and demanding that it satisfy our classical physics brains, and that is, well, not the most productive way to think, to my mind.

 

[SpectraCat]

Everyone who has some other interpretation of quantum mechanics seems to be obsessively seeking to impose "reality" on the results of quantum mechanics, rather than trying to understand a much deeper truth that these results are trying to tell us. Deterministic reality is what happens when you take quantum mechanics in the macroscopic limit - its a classical effect. Human brains are designed to intuitively understand deterministic classical physics. If we don't, we don't survive. There has never been an evolutionary need for the human brain to intuitively understand relativity or quantum mechanics, and so it is very difficult for us to do so. Quantum mechanics is trying to tell us something, and we keep ignoring it and demanding that it satisfy our classical physics brains, and that is, well, not the most productive way to think, to my mind.

Very well put, and an interesting take on the subject.

 

[harrylin]

[..] I will relax and not be a scientist for a moment: Everyone who has some other interpretation of quantum mechanics seems to be obsessively seeking to impose "reality" on the results of quantum mechanics, rather than trying to understand a much deeper truth that these results are trying to tell us. Deterministic reality is what happens when you take quantum mechanics in the macroscopic limit - its a classical effect. Human brains are designed to intuitively understand deterministic classical physics. If we don't, we don't survive. There has never been an evolutionary need for the human brain to intuitively understand relativity or quantum mechanics, and so it is very difficult for us to do so. Quantum mechanics is trying to tell us something, and we keep ignoring it and demanding that it satisfy our classical physics brains, and that is, well, not the most productive way to think, to my mind.

As we see, currently (at 85 voters) there are more people here who favour some kind of realist interpretation than who favour the "Copenhagen Interpretation". Now, your argument that our brains are not adapted for understanding quantum processes sounds good to me. Nevertheless, that doesn't imply that an intuitively unlikely explanation must be true - only that we should not discard counter-intuitive ideas upfront (and there are many listed!). Until not long ago physics provided an increasing understanding of how nature works. For me that includes relativity, even if many people are still riddled by it. I expect that one day quantum mechanics will be just as well understood.

 

[AlexSerov]

I have heard the following interpretation: Photon emission at point A and its absorption in point B is one event. Light is neither a wave nor a particle. It simply does not exist in this time-space between A an B. Does it fall into one of 11 interpretations above?

 

[Rap]

As we see, currently (at 85 voters) there are more people here who favour some kind of realist interpretation than who favour the "Copenhagen Interpretation". Now, your argument that our brains are not adapted for understanding quantum processes sounds good to me. Nevertheless, that doesn't imply that an intuitively unlikely explanation must be true - only that we should not discard counter-intuitive ideas upfront (and there are many listed!). Until not long ago physics provided an increasing understanding of how nature works. For me that includes relativity, even if many people are still riddled by it. I expect that one day quantum mechanics will be just as well understood.

I agree completely, it doesn't imply that an intuitively unlikely explanation must be true.

I would contend that relativity, like quantum mechanics, is well understood from the "shut up and calculate" point of view. But it has, like quantum mechanics, interpretational problems. Relativistic physics "exists" in a 4-D spacetime. There is no motion in this spacetime. What we perceive as motion of a particle is an unvarying 1-dimensional curve in spacetime. If you use relativity to predict what you will experience, you pretend that you are moving along your world line at the speed of light. How can we use the concept of motion when it has already been absorbed into the spacetime description? Just like the collapse of the wave function in QM, the very point at which we translate the mathematics into experience, we introduce something weird, outside of the formalism.

 

[yoda jedi]

I have heard the following interpretation: Photon emission at point A and its absorption in point B is one event. Light is neither a wave nor a particle. It simply does not exist in this time-space between A an B. Does it fall into one of 11 interpretations above?

http://quasars.org/photon.txt



:

if wave function is regarded as ontologically real, then, there is not need of observer, if the wave function is epistemic, less yet.

your hedge podge (and ignorance):

If I understand the terms "ontology" and "epistemology",...Copenhagen says they are neither.

ontological real is be independent of observer/measurement, a complete description of reality itself.
epistemic is a representation of an observer’s knowledge of reality rather than reality itself.




heisenberg:

a system is completely described by a wave function ψ, representing an observer's subjective knowledge of the system.

"The laws of nature which we formulate mathematically in quantum theory deal no longer with the particles themselves but with our knowledge of the elementary particles. ... The conception of objective reality ... evaporated into the ... mathematics that represents no longer the behavior of elementary particles but rather our knowledge of this behavior."

Heinsenberg, February 2, 1960 ..."The act of recording, on the other hand, which leads to the reduction of the state, is not a physical, but rather, so to say, a mathematical process. With the sudden change of our knowledge also the mathematical presentation of our knowledge undergoes of course a sudden change."...

Jammer, M., 1974,


.

I agree with that, completely. The wave function collapse is a collapse in our uncertainty, not a collapse in something physical.

Deterministic reality

and who is talking about deterministic reality ?


.

 

[Rap]

(various insults and an elaborate proof that I did not have a proper understanding of the word "epistemic")

Thank you, I think I have a better understanding now.

yoda jedi, take a chill. I talk like I know everything, but I don't, I'm still learning. Please help me out and counter my arguments by pointing out fallacies and inconsistencies instead of labelling them hodgepodge and calling me ignorant, ok?

 

[StevieTNZ]

Yeah, some people on here need to stop attacking others. No need to jump at each others throats. In other words, "ease up turbo".

 

[Darken-Sol]

we can guess where something is but until we look we won't know? sounds good to me

 

[Varon]

Quantum object is said to be still there even if it has no definite position. And it's not because you don't know the position, but the position doesn't exist in principle (before measurement). How can an quantum object still be there yet no position in principle? It's like the object doesn't register anymore in the spacetime continnum but still there somewhere perhaps outside spacetime?

 

[A. Neumaier]

Quantum object is said to be still there even if it has no definite position. And it's not because you don't know the position, but the position doesn't exist in principle (before measurement). How can an quantum object still be there yet no position in principle? It's like the object doesn't register anymore in the spacetime continnum but still there somewhere perhaps outside spacetime?

''has no position'' only means ''has no position to infinite precision''.

The position is just a little bit fuzzy rather than determined to infinite precision. This is the content of Heisenberg's uncertainty relation.

 

[harrylin]

I agree completely, it doesn't imply that an intuitively unlikely explanation must be true.

I would contend that relativity, like quantum mechanics, is well understood from the "shut up and calculate" point of view. But it has, like quantum mechanics, interpretational problems. Relativistic physics "exists" in a 4-D spacetime. There is no motion in this spacetime. What we perceive as motion of a particle is an unvarying 1-dimensional curve in spacetime. If you use relativity to predict what you will experience, you pretend that you are moving along your world line at the speed of light. How can we use the concept of motion when it has already been absorbed into the spacetime description? Just like the collapse of the wave function in QM, the very point at which we translate the mathematics into experience, we introduce something weird, outside of the formalism.

I agree that SR becomes a bit weird if we insist on interpreting 4D spacetime as a physical object while we still continue to use the standard concept of motion. However I do not introduce something weird like that and I don't pretend that I am moving at the speed of light: no theorem exists according to which we must interpret SR's equations that way. In contrast, Bell's theorem suggests that only implausible looking interpretations of the world can be compatible with QM.

 

[Darken-Sol]

so i can accurately say its over there but precisely miss it with my finger waving?

 

[harrylin]

See also the thread "what is the Copenhagen interpretation"!
https://www.physicsforums.com/showthread.php?t=494788

Thus it may well be that several people here who voted for "Copenhagen" in fact have opposite ideas... And perhaps that's also the case with one or two other interpretations.
I guess that's the problem with "philosophy".

 

[A. Neumaier]

See also the thread "what is the Copenhagen interpretation"!
https://www.physicsforums.com/showthread.php?t=494788

Thus it may well be that several people here who voted for "Copenhagen" in fact have opposite ideas... And perhaps that's also the case with one or two other interpretations.
I guess that's the problem with "philosophy".

No. This is just a problem with setting up this particular poll. A good poll would define its terms, by giving for each option a 1-paragraph description of the intended meaning. The early discussion in this thread revealed a number of limitations of the present poll - with poorly defined terms, missing important interpretations, etc.. To be really meaningful, the next poll of this kind should be much more carefully designed.

 

[Varon]

''has no position'' only means ''has no position to infinite precision''.

The position is just a little bit fuzzy rather than determined to infinite precision. This is the content of Heisenberg's uncertainty relation.

This is your Copenhagen version. But in original Copenhagen. The position literally doesn't exist before measurement. It's not about the position being fuzzy. It doesn't exist in principle. Hope someone can confirm if this is really the view of the original version because this is what I believed all these years.

 

[A. Neumaier]

This is your Copenhagen version.

Indeed, strictly speaking, Copenhagen is completely _silent_ about the position outside measurement.
But my interpretation makes explicit how the classical quantum interface in the Copenhagen interpretation (assumed there without any discussion) works, and hence is completely consistent with it.

If you believe that Bohr, Heisenberg, and other proponents of the Copenhagen interpretation assumed that particles with which experiments are performed are on the experimenter's desk also before it is measured, this already constitutes an approximate, macroscopic position. Without such an assumption (which belongs to the classical, macroscopic background always postulated in the Copenhagen interpretation), no meaningful experiments would be possible.

Neither would relations such as the Ehrenfest theorem make sense, which makes statements about the dynamics of the mean position.

But in original Copenhagen. The position literally doesn't exist before measurement. It's not about the position being fuzzy. It doesn't exist in principle. Hope someone can confirm if this is really the view of the original version because this is what I believed all these years.

There is no original version. The Copenhagen interpretation is essentially the view of Bohr and Heisenberg, as expressed through their (at times quite cryptic and conflicting) statements.