Exploring the Paradoxical Einstein-Podolsky-Rosen Experiment

[akhmeteli]

That's very much the issue, and note this is a purely classical issue.

I guess I have no choice but to make the following conclusion from this statement: you were not really talking about any interpretation of quantum mechanics (as more or less everything you said was applicable to classical mechanics). Rather you were talking about interpretation of probabilities in general. As for me, the question that bothers me most is: "Did quantum mechanics radically change the notion of causality?"

So it is with the Moon-- it is pure philosophy if the Moon is there or not. Now I realize that you might think it is more natural to assume the Moon is there, even if you don't know it, but that's not the point I'm making. I'm saying that if you have two things that can happen to the Moon, maybe it is or is not hit by an asteroid, then all science can ever tell you is your estimate of the chances that the Moon is still there. It makes no difference at all if it is or not, scientifically speaking, until it affects you in some way. You can't use it to test your prediction, you can't perceive the result, it can't make you a happy or miserable person, it just doesn't matter. That we think something "really happened", even though we don't know what, is just a handy picture for thinking about all this-- it cannot be tested in any way, so it isn't science. I would say it is scientifically in a "mixed state" and leave it at that, science has no more to say on the matter.

What this means to me is, we will agree to enter into the "interpretation", or "picture", that the computer stores "real" results even if we do not know what they are. That is fine with me-- I use that picture of reality myself, as a matter of fact.

I fully agree: "it is pure philosophy if the Moon is there or not". You may give any answer to this question: "yes", "no", or "I prefer to sit on the fence". However hard I try, I cannot understand what your answer is. My guess is your answer is either "yes" or "I prefer to sit on the fence". However, I believe that if we are not able to agree on this philosophical question, we cannot agree on the "question in question": "Can non-humans make observations?" Because if you answer "yes" to the first question, I think "yes" to the second question is natural and logical. If you don't say "yes" to the first question, then we have philosophical differences, and I readily admit that I have no chance to convince you. And vice versa, you have no chance to convince me. Thus, it looks like the second question is purely philosophical as well.

The registering in an intelligence what happened. Isn't that what you would mean by that phrase too?"

I just did not understand the phrase at all. I suspected it could mean that a human makes a (to some extent arbitrary) decision on what the result is. That is how I understood the word "determine". Maybe this is just my problem with English, which is not my mother tongue.

That was a bad assumption made by the post-Newtonians. In point of fact there was never any way to do that, long before quantum mechanics, for a "suitably shaken die". If the die is not suitably shaken, it is not functioning like a die.

I don't think the assumption is bad. I think we just differ on definitions. I did not discuss a "suitably shaken die", I discussed a die as a well-known material object. Whether it fulfills the function of a die, I did not care. If you believe that it is not possible to predict a result of a throw for a die with accurately defined kinematic parameters (and known material properties of the die and of the surface), please advise.

The point is, even classical systems involve probability concepts in their analysis-- always have and always will (consider the crucial role of "ergodicity" in thermodynamics, for example). Are we in a position to replace thermodynamics?

As I wrote elsewhere in physicsforums, I have no problems with probabilities. I have problems with their status in the Kopenhagen interpretation. If you say that their status in quantum theory is the same as in classical physics (and it seems that you do say that), I have no problems with that. Again, I don't have problems with thermodynamics. What I want to emphasize is thermodynamics fulfills its function splendidly even if it is a superstructure upon classical microscopic dynamics, not quantum microscopic dynamics. While there is no irreversibility in classical mechanics (or quantum mechanics, by the way), there is practical irreversibility in classical statistical physics.

The point is, and perhaps reilly can corroborate, one does not seek an experiment to "falsify" Peierl's postulate, for the postulate is built right into how we do science. How will one set up an experiment to falsify that postulate, when the postulate is central to what we mean by an experiment? It is really an axiom, that is the point-- it is an inseparable part of science itself, and that's what it has to do with science.?

If this is an axiom, I am fully entitled to reject such an axiom. I do not agree, furthermore, I don't know why I should agree that it is an inseparable part of science itself. Indeed, if you think about it, you might agree that this "axiom" states pretty much the same as the statement "non-humans cannot make observations" (and I argued that this is a purely philosophical question). Indeed, if we assume the opposite, i.e. "non-humans can make observations" (like a computer storing results of an experiment), then the collapse of the wavefunction occurs prior to a review of the results by the human, i.e. outside of the human brain. Of course, you have every right to sell your philosophy, but I am under no obligation to buy.

Then I would like to see you, or them, describe a means for doing science that does not include the "mantra": the final stage of all science is classical, it's in the guts of science. Will anyone please cite for me an example of an experimental result whose final stage was not classical? How can anyone claim this is something they "don't need to agree with"?

I am not sure anybody can cite an example of an experimental result whose final stage is classical, for the simple reason that classical mechanics is wrong and quantum mechanics is right. Nothing can be precisely classical. For example, a voltmeter pointer has only approximate classical position. If you tell me that the position of a voltmeter pointer is not a "final stage", then we just return to the same question: "can non-humans make observations?", and we cannot agree due to philosophical differences. Actually, I do not agree with Bohr and Heisenberg that quantum mechanics requires classical mechanics for its interpretation, and again, this is not brazen irreverence, as I have no choice but to be irreverent either towards Bohr or towards Einstein. I choose to side with Einstein, you have every right to side with Bohr or anybody else.

I'll give it a look, but I expect it to provide complete verification of my position. You see, thermodynamics is the quintessential example of a classical theory of probability, where nothing is ever actualized beyond what the intelligence can discern! All thermodynamic concepts (temperature, pressure, etc.) are based on the idea that states never distinguished by any intelligence are to be treated as if they were indistinguishable elements of reality.
I completely agree with all of that-- the irreversibility comes from our analysis technique. The instant we "average over" what we cannot know, we obtain a probabilistic treatment, and probabilistic treatments are also quintessentially irreversible. None of that refutes the importance of consciousness in deciding "what counts as indistinguishable", i.e., what is the very meaning of "the probability of X".

Again, I have no problems with thermodynamics, probabilities, or Bayesian approach. I just think that they cannot be the last word, and at the most fundamental level nature is strictly causal. I am not trying to impose my beliefs on you, I'm just trying to explain that my point of view may be equally viable.

 

[akhmeteli]

The notion that most of what happens in the brain is the result of pulses traveling through neural networks is a central tenant of the field -- this is elegantly discussed by Sir Francis Crick in his book The Astonishing Hypothesis: the Scientific Search for the Soul.

I am not sure though that this is relevant to collapse of wavefunction. Furthermore, you seem to agree that a human cannot change what is stored by the computer (without reprogramming etc.) That seems to suggest that the collapse occurs without any human brain.

One day it struck me that that there is a physically understandable mechanism behind probability collapse. As in, right now, the best we can say is that one of three candidates will become the next US president, add a dark horse if you want. This knowledge is stored in your memory. Then, once the election is over, and you hear about it, your knowledge changes, and your brain has to do some readjusting. Among the things it will have to change is the probability structure of the election; that structure clearly can be said to collapse to from (p1,p2,p3,p4) to (0,1,0,0). In fact, it's pretty unlikely that you will consciously be aware of such a collapse, but there is no doubt that it happens.

You decide to do an interesting double slit experiment with photons or electrons. Randomly change the width of the slits; randomly change the distance between slits; use polaroid or mylar to slow down the particles, randomly with one or two slits as you wish. Do the experiment for a long time, and do the random thing however you want. You probably won't have a clue about the pattern you'll see on the detector screen. So the probability structure in your brain will very likely be (?). If you do not look at the screen until the experiment is done, and then wait ten minutes, before you open your eyes, you still have that (?) structure, and after you have ("pattern").

If you watched the screen for the entire experiment, your notions of the pattern will clearly converge stochastically to the final pattern. The probability structure -- not a great name here -- changes gradually, but still is consistent with collapse as a change in knowledge. I think that this knowledge approach makes repeated and continuous measurements -- every day vision for example -- easier to handle in QM.

So you can see that noway a human can change what's on a disc without 1. programming and executing some program or routine, or, 2. trashing the disc. Once you read the disc, you know.Once you read a mystery novel you know, at the end for sure, who donnit. When neither of us is participating in the forum, it's still there. The best game in town is to assume there is an objective reality. Seems, generally, to be a good working assumption.

I was delighted to discover Peierls' work on QM interpretation promoting the idea that the wave function and consequent probabilities refer to our knowledge. For me, at least, many issues I had with QM were solved with the knowledge interpretation. And let's be clear:My state and actions have, generally, little effect on the world, so whether my eyes are open or closed makes no difference to anyone or anything but me.

As far as I know, he did not discuss neural networks -- they were yet to become important when he was writing. Also, it's consistent with the standard statistical practice of many years and in many disciplines. There's collapse in any practical probabilistic system; once you know, things change in your head often as a consequence of what's outside your head.

You see, all you're saying can be said about a classical, not quantum system. Does this mean that the status of causality is the same in classical and quantum mechanics? That is, is there a causal structure underlying probabilities? If yes, I have no problem with that. If no, you need some arguments that are not equally applicable to classical mechanics.

 

[Ken G]

I guess I have no choice but to make the following conclusion from this statement: you were not really talking about any interpretation of quantum mechanics (as more or less everything you said was applicable to classical mechanics).

That's basically right-- but note the real implication is that what people call "interpretations of quantum mechanics" are really no such things, they are interpretations of the meaning of probability. To be a true interpretation of quantum mechanics, you must be interpreting the meaning of a pure state, but the way most people use the term, they are interpreting the meaning of a collapsed wave function, i.e., a substate of a pure state that also includes a dramatic and untraceable degree of decoherence. In short, a quasi-classical system!

As for me, the question that bothers me most is: "Did quantum mechanics radically change the notion of causality?"

I agree, this is a key question. I say, it did not, yet many people think that it did. I don't know why, I think it's because they imagine that pre-quantum physics was purely deterministic and did not involve probabilities. It is as though they have forgotten thermodynamics and weather forecasting.

I fully agree: "it is pure philosophy if the Moon is there or not". You may give any answer to this question: "yes", "no", or "I prefer to sit on the fence". However hard I try, I cannot understand what your answer is. My guess is your answer is either "yes" or "I prefer to sit on the fence".

My answer would be "I find it very useful to adopt the picture that at any time the Moon is either there or it isn't, but I recognize that no science requires this-- science only requires I can identify a probability that the Moon is there, a probability that may go completely unactualized until I look."

However, I believe that if we are not able to agree on this philosophical question, we cannot agree on the "question in question": "Can non-humans make observations?"

I think decoherence occurs naturally, but decoherence only yields probabilities, not actualities. So it depends on what you mean by "observation"-- most people mean the demonstration of an actualization, and that does require an intelligence, because that is where the actualization "lives". However, it is an important principle of physics that all the actualizations in these intelligent minds must be consistent. No one has any idea why this is, and there are certainly gray areas, but it does seem to hold well-- and it spawns the concept of "objective reality". But saying that actualizations must be consistent is not saying the actualizations don't require minds, it just says that-- the actualizations must be consistent when intelligence further actualizes the higher-order correlations.

Thus, it looks like the second question is purely philosophical as well.

The problem is with the definitions. We cannot say which statements are right or wrong until we can clearly define the words, and here the tricky words are "exist" (by which I mean "a probability that has been actualized") and "observation" (by which I mean, "the demonstration that actualization has occured", and expressly not "the decohering of a substate wave function to get it to behave classically", though that is certainly a key element of observation). I maintain that taking these definitions, an intelligence is required to have an observation, because there is no way to demonstrate that an "actualization" occured, and no way to distinguish it from a "probability", without one.

In other words, you can program a computer to generate a random number (pseudorandom is good enough for me), and it can send that result to another processor, which sends its result to another, and so forth. I would say the issue of at what point this constitutes an "intelligence" is exactly the point at which one can treat that original random number as "actualized". Prior to that point, you can still treat it as a probability distribution, and just propagate that probability distribution through all the subsequent processing, generating new probability distributions. At the point where you can say "treating this as a probability no longer gives useful predictions", then you have an intelligence. So it's not that "intelligence actualizes observations", it is "the actualization of observation is the definition of intelligence".

Whether that intelligence counts as "human" is an even murkier topic, that will probably have to wait until we have the first clue of how to differentiate "human intelligence" from other forms. I'm not sure we know what should qualify as human intelligence, any definition would seem to either leave out too many humans, or not leave out enough non-humans.

I just did not understand the phrase at all. I suspected it could mean that a human makes a (to some extent arbitrary) decision on what the result is. That is how I understood the word "determine". Maybe this is just my problem with English, which is not my mother tongue.

This certainly underscores the problem of definition. We probably need to do a lot more work around what is meant by these words, or we can have purely semantic differences disguised as real disagreements.

I don't think the assumption is bad. I think we just differ on definitions. I did not discuss a "suitably shaken die", I discussed a die as a well-known material object. Whether it fulfills the function of a die, I did not care. If you believe that it is not possible to predict a result of a throw for a die with accurately defined kinematic parameters (and known material properties of the die and of the surface), please advise.

I certainly believe it is not possible to predict the throw of a die no matter how well you prescribe its initial conditions, if the throw "mixes in" enough of the details of the environment. For example, you could specify the initial velocity and angular momentum of the die, but only to the precision of your instrument, and you have to propagate whatever uncertainty exists initially through a lot of exponentially magnifying factors. You can specify the amount of sound in the room, but that's not good enough-- you need to know the amplitude and phase of every vibration that could affect the die. You need to know not just the windspeed, but every eddy current in the air. You need to know not just the dimensions of the rolling area, and the material properties of the surface, but how it varies with position and whether or not "material properties" are defined suitably precisely in the first place. In short, the prediction is doing physics, whereas the "reality" is only the roll of the die itself. And to do physics, we make idealizations and approximations at every stage. At some point, we just throw up our hands and say "forget tracking these details, we're just going to average over what we don't know and make some kind of ergodicity assumption"-- and poof, we have no more than a probability, even in principle, at that moment. Since this is an inevitable component of Newtonian mechanics sooner or later in any complex system, we could never have said that the universe was deterministic, it would simply not be scientifically demonstrable long before quantum mechanics.

As I wrote elsewhere in physicsforums, I have no problems with probabilities. I have problems with their status in the Kopenhagen interpretation. If you say that their status in quantum theory is the same as in classical physics (and it seems that you do say that), I have no problems with that.

That is indeed what I would say-- what do you mean by their "status in the Kopenhagen interpretation?"

What I want to emphasize is thermodynamics fulfills its function splendidly even if it is a superstructure upon classical microscopic dynamics, not quantum microscopic dynamics.

Yes, it is a superstructure, and it is also an integral part of Newtonian physics. That's why the latter was never fully deterministic, it was more like asymptotically deterministic in a way that was purely philosophical. Did anyone think that Newton's laws turned thermodynamics into some kind of placekeeper until fully detailed predictions could be made?

While there is no irreversibility in classical mechanics (or quantum mechanics, by the way), there is practical irreversibility in classical statistical physics.

Excellent point, and crucial to understanding why determinism was always a red herring-- it was contradictory to the notion of irreversibility, which is a hugely important physical concept.

If this is an axiom, I am fully entitled to reject such an axiom.

You can claim to reject it, but if you actually apply it, then the claim is irrelevant. To actually reject the axiom, you have to find a way to do without it-- you have to find a way to do science that does not look like confronting an intelligence with experimental results that actualize the results and compare them to probabilistic predictions over a sequence of trials. I am completely at a loss as to how you imagine you can do science in some other way.

Indeed, if we assume the opposite, i.e. "non-humans can make observations" (like a computer storing results of an experiment), then the collapse of the wavefunction occurs prior to a review of the results by the human, i.e. outside of the human brain. Of course, you have every right to sell your philosophy, but I am under no obligation to buy.

But I'm not selling a philosophy, I'm challenging you to use your computer to do science without an intelligence! Remember, if the computer encounters a probability distribution of outcomes, then it generates a probability distribution of recordings and analysis. There is simply no way you can demonstrate it has done anything different, without invoking an intelligence to actualize the distinction. You can imagine that the result was actualized, and indeed we all do, but science is completely moot on the issue-- it doesn't need to take a stance and therefore should not (why would science take a stance on a matter it is moot about?). But science must take a stance when an intelligence actualizes the result, because that is a truth that must be contended with, indeed it is the very point of doing science to generate that truth. Science is an endeavor of an intelligence, surely that at least is noncontroversial.

I am not sure anybody can cite an example of an experimental result whose final stage is classical, for the simple reason that classical mechanics is wrong and quantum mechanics is right.

That is not what I mean by "classical"-- I simply mean a system we choose classical mechanics to describe (more definitions in need of clarification). It has nothing to do with what is "right" and "wrong", those are unsophisticated notions in human endeavors like physics-- it has to do with what we choose to do to solve a problem.

Nothing can be precisely classical.

Of course not-- what is precisely quantum mechanical? Nothing real is "precisely" anything.

I just think that they cannot be the last word, and at the most fundamental level nature is strictly causal. I am not trying to impose my beliefs on you, I'm just trying to explain that my point of view may be equally viable.

I cannot sway you from your beliefs, and don't want to-- but those exceed what science can tell us, and I am trying to keep careful track of where that line is.

 

[JesseM]

But I'm not selling a philosophy, I'm challenging you to use your computer to do science without an intelligence! Remember, if the computer encounters a probability distribution of outcomes, then it generates a probability distribution of recordings and analysis. There is simply no way you can demonstrate it has done anything different, without invoking an intelligence to actualize the distinction. You can imagine that the result was actualized, and indeed we all do, but science is completely moot on the issue-- it doesn't need to take a stance and therefore should not (why would science take a stance on a matter it is moot about?). But science must take a stance when an intelligence actualizes the result, because that is a truth that must be contended with, indeed it is the very point of doing science to generate that truth. Science is an endeavor of an intelligence, surely that at least is noncontroversial.

But by the same argument, why should you believe that any intelligence other than yourself can "actualize the result" in this way? From your point of view, you have no way to falsify the notion that "if someone other than me encounters a probability of outcomes, then they generate a probability distribution of thoughts and memories and analysis." If we are only concerned with laws of physics as a recipe for making predictions, not as things that can give us a model of how objective reality might look independent of our observations, then it seems to me that this solipsist point of view would be perfectly reasonable, perhaps more reasonable than the view that other intelligences can actualize results but computers can't.

 

[akhmeteli]

That's basically right-- but note the real implication is that what people call "interpretations of quantum mechanics" are really no such things, they are interpretations of the meaning of probability. To be a true interpretation of quantum mechanics, you must be interpreting the meaning of a pure state, but the way most people use the term, they are interpreting the meaning of a collapsed wave function, i.e., a substate of a pure state that also includes a dramatic and untraceable degree of decoherence. In short, a quasi-classical system!

I am not sure this is true for the Bohmian interpretation; I guess it makes an attempt to describe a pure state. I am not trying to decide here whether this interpretation is good or bad.

I think decoherence occurs naturally, but decoherence only yields probabilities, not actualities. So it depends on what you mean by "observation"-- most people mean the demonstration of an actualization, and that does require an intelligence, because that is where the actualization "lives". However, it is an important principle of physics that all the actualizations in these intelligent minds must be consistent. No one has any idea why this is, and there are certainly gray areas, but it does seem to hold well-- and it spawns the concept of "objective reality". But saying that actualizations must be consistent is not saying the actualizations don't require minds, it just says that-- the actualizations must be consistent when intelligence further actualizes the higher-order correlations.

Again, we either agree that objective reality exists, or we don't. If we don't, then we can only debate philosophical problems. My take is it would be unproductive and inappropriate for this forum.

The problem is with the definitions. We cannot say which statements are right or wrong until we can clearly define the words, and here the tricky words are "exist" (by which I mean "a probability that has been actualized") and "observation" (by which I mean, "the demonstration that actualization has occured", and expressly not "the decohering of a substate wave function to get it to behave classically", though that is certainly a key element of observation). I maintain that taking these definitions, an intelligence is required to have an observation, because there is no way to demonstrate that an "actualization" occured, and no way to distinguish it from a "probability", without one.

In other words, you can program a computer to generate a random number (pseudorandom is good enough for me), and it can send that result to another processor, which sends its result to another, and so forth. I would say the issue of at what point this constitutes an "intelligence" is exactly the point at which one can treat that original random number as "actualized". Prior to that point, you can still treat it as a probability distribution, and just propagate that probability distribution through all the subsequent processing, generating new probability distributions. At the point where you can say "treating this as a probability no longer gives useful predictions", then you have an intelligence. So it's not that "intelligence actualizes observations", it is "the actualization of observation is the definition of intelligence".

Whether that intelligence counts as "human" is an even murkier topic, that will probably have to wait until we have the first clue of how to differentiate "human intelligence" from other forms. I'm not sure we know what should qualify as human intelligence, any definition would seem to either leave out too many humans, or not leave out enough non-humans.

It is not very productive to debate definitions, but it seems to me you offer definitions that are far beyond the usual meaning of everyday English words, such as "exists". If, however, you insist on such definitions, there is little left to discuss, as the questions we consider turn into tautologies.

I certainly believe it is not possible to predict the throw of a die no matter how well you prescribe its initial conditions, if the throw "mixes in" enough of the details of the environment. For example, you could specify the initial velocity and angular momentum of the die, but only to the precision of your instrument, and you have to propagate whatever uncertainty exists initially through a lot of exponentially magnifying factors. You can specify the amount of sound in the room, but that's not good enough-- you need to know the amplitude and phase of every vibration that could affect the die. You need to know not just the windspeed, but every eddy current in the air. You need to know not just the dimensions of the rolling area, and the material properties of the surface, but how it varies with position and whether or not "material properties" are defined suitably precisely in the first place. In short, the prediction is doing physics, whereas the "reality" is only the roll of the die itself. And to do physics, we make idealizations and approximations at every stage. At some point, we just throw up our hands and say "forget tracking these details, we're just going to average over what we don't know and make some kind of ergodicity assumption"-- and poof, we have no more than a probability, even in principle, at that moment. Since this is an inevitable component of Newtonian mechanics sooner or later in any complex system, we could never have said that the universe was deterministic, it would simply not be scientifically demonstrable long before quantum mechanics.

Well, this seems to be a quantitative question. I think you'll agree that for a simpler system than a rotating die and for lesser times it is possible to accurately predict the result, and I'll agree that for more complex systems and larger times it can be impossible to predict the result. As for this specific system, let's agree to disagree.

That is indeed what I would say-- what do you mean by their "status in the Kopenhagen interpretation?"

As far as I understand, the Copenhagen interpretation (although, or maybe because I lived in that city for four years, I cannot write its name correctly:-) ) postulates that we cannot have anything more precise than probabilities. If in classical mechanics two similar experiments produce different results, you can standardize them and reduce the difference, or at least indicate the source of the difference (and this is how I understand determinism, not as a possibility to predict everything). Nothing of the kind in the Copenhagen interpretation.

Excellent point, and crucial to understanding why determinism was always a red herring-- it was contradictory to the notion of irreversibility, which is a hugely important physical concept.

I wrote above how I understand determinism. I agree that there is a contradiction, but I believe determinism is more fundamental than irreversibility, which is only a practical convenience: you cannot circumvent the Poincare recurrence theorem, but the recurrence times are mindbogglingly huge for large systems, let alone the environment effects.

You can claim to reject it, but if you actually apply it, then the claim is irrelevant. To actually reject the axiom, you have to find a way to do without it-- you have to find a way to do science that does not look like confronting an intelligence with experimental results that actualize the results and compare them to probabilistic predictions over a sequence of trials. I am completely at a loss as to how you imagine you can do science in some other way.

I am afraid you've lost me here. You called the Peierls postulate an axiom, I said I reject such an axiom. This postulate states that the wavefunction collapse occurs in the brain. Why do I need it to do science? The bulk of the science does not even need a notion of wavefunction, never mind the Peierls postulate.

But I'm not selling a philosophy, I'm challenging you to use your computer to do science without an intelligence! Remember, if the computer encounters a probability distribution of outcomes, then it generates a probability distribution of recordings and analysis. There is simply no way you can demonstrate it has done anything different, without invoking an intelligence to actualize the distinction. You can imagine that the result was actualized, and indeed we all do, but science is completely moot on the issue-- it doesn't need to take a stance and therefore should not (why would science take a stance on a matter it is moot about?). But science must take a stance when an intelligence actualizes the result, because that is a truth that must be contended with, indeed it is the very point of doing science to generate that truth. Science is an endeavor of an intelligence, surely that at least is noncontroversial.

I see no reasons to accept your challenge "to use your computer to do science without an intelligence" as I did not claim it is possible. I was saying that "observation" without intelligence may be possible, and therefore wavefunction collapse does not need to occur in a human brain.

That is not what I mean by "classical"-- I simply mean a system we choose classical mechanics to describe (more definitions in need of clarification). It has nothing to do with what is "right" and "wrong", those are unsophisticated notions in human endeavors like physics-- it has to do with what we choose to do to solve a problem..

As for what you choose to describe a system, you may choose classical mechanics, or you can choose quantum mechanics.

Of course not-- what is precisely quantum mechanical? Nothing real is "precisely" anything.

Of course, there are no absolutes, however quantum mechanics is more precise than classical mechanics.

I cannot sway you from your beliefs, and don't want to-- but those exceed what science can tell us, and I am trying to keep careful track of where that line is.

You see, there are a lot of things that exceed what science can tell us. For example, science cannot tell us that the Earth rotates around the Sun. You can use the Earth as the system of reference. The resulting dynamics will be more complex, but it will be still correct. Science cannot tell us that the speed of light is the same in all inertial systems of reference - the results of the special relativity coincide with those that Lorentz obtained using his contraction. The science does not tell us that there is objective reality. I prefer to accept some of these things. If you don't want to accept any such things, its your choice based on philosophy. I am not ready to discuss philosophy.

 

[Ken G]

But by the same argument, why should you believe that any intelligence other than yourself can "actualize the result" in this way? From your point of view, you have no way to falsify the notion that "if someone other than me encounters a probability of outcomes, then they generate a probability distribution of thoughts and memories and analysis."

That's quite correct, when I was talking about "actualizing probabilities by an intelligence", I meant "for that intelligence". There is no requirement that someone else's intelligence actualize my reality, you're right I could never demonstrate that nor would I even care to, my consciousness actualizes my reality. I merely avow based on the symmetry of the situation that if my conscious intelligence can actualize my reality for me, then so can yours for you. The only scientific constraint on it is that when an intelligence actualizes higher-order correlations (we "compare notes" on reality), the actualizations must be consistent, which allows us to imagine an objective picture of reality (to some extent). That's really amazing, but it says no more than it says-- the correlations between actualizations must be total to within our ability to test (with perhaps some transliteration prior to comparison, as with time dilation). Aspects that cannot be tested suffer from no such requirement of objectivity. This is all science needs, the rest is philosophy.

It seems correct that a scientific prediction is a mapping between a probability distribution of inputs onto a probality distribution of outputs. Our intelligence decides what counts as the possible array of inputs, and what counts as an array of outputs, and that determines the probabilities we obtain. We then use our intelligence to test that mapping, and none of this requires actualization. One could imagine a mind capable of saying "the individual trial yielded x heads and 1-x tails", and could average many trials to see if <x>=1/2. Our minds don't happen to interact with reality that way, we say "it's heads" or "tails"-- no one knows why, but science must deal with it, so that is why we have "interpretations of quantum mechanics", but they are really "interpretations of actualizations", and they are entirely classical (in the sense of pertaining solely to classical objects like measuring apparatus).

If we are only concerned with laws of physics as a recipe for making predictions, not as things that can give us a model of how objective reality might look independent of our observations, then it seems to me that this solipsist point of view would be perfectly reasonable, perhaps more reasonable than the view that other intelligences can actualize results but computers can't.

Exactly, and that is why it is indeed the scientific perspective. Adding a bunch of untestable pictures to that may appease our psychology, but it is an extraneous component of science (that we all like to do, certainly).

 

[Ken G]

I am not sure this is true for the Bohmian interpretation; I guess it makes an attempt to describe a pure state.

Yes, my comments are really focused on "MWI" type thinking.

Again, we either agree that objective reality exists, or we don't. If we don't, then we can only debate philosophical problems. My take is it would be unproductive and inappropriate for this forum.

I have no desire to debate whether or not objective reality "exists", the issue is how the concept is used in science. It is of course just that-- a concept, and one that science uses to great advantage, but the issue is, just what does science actually need, and what are we adding just to make ourselves more comfortable? The latter is what is inappropriate for the forum.

It is not very productive to debate definitions, but it seems to me you offer definitions that are far beyond the usual meaning of everyday English words, such as "exists".

One does not "debate" definitions, but the clarification of them is completely crucial. One can only criticize a scientific definition on the grounds that it does not conform to the axioms of science. I have said what I mean by my words, as relying on vague popular meanings is ineffectual.

If, however, you insist on such definitions, there is little left to discuss, as the questions we consider turn into tautologies.

Again I cannot concur, there is everything to discuss-- there is the discussion of what are the ramifications of these definitions! That is not "tautological". If you are using different definitions, I invite you to supply them, so we can consider the ramifications of your definitions-- I only require that they be expressed in a scientifically demonstrable way, as I believe I have done.

Well, this seems to be a quantitative question. I think you'll agree that for a simpler system than a rotating die and for lesser times it is possible to accurately predict the result, and I'll agree that for more complex systems and larger times it can be impossible to predict the result.

Yes, that suffices-- as long as classical mechanics is incomplete without probability theory, it may not be called a purely deterministic description of reality, which is all I'm saying. Quantum mechanics is not fundamentally new in that regard, contrary to how it gets advertised.

If in classical mechanics two similar experiments produce different results, you can standardize them and reduce the difference, or at least indicate the source of the difference (and this is how I understand determinism, not as a possibility to predict everything). Nothing of the kind in the Copenhagen interpretation.

But isn't that just a question of precision? Even a classical measurement of angular momentum was never know to be capable of being precise at the level of h. It was just a guess that it could, pure imagination-- and that's why I don't think of classical physics as establishing a deterministic reality, it had not been demonstrated to be such, even if we adopt your more careful definition of determinism (which one might call asymptotic determinism if you please it).

I agree that there is a contradiction, but I believe determinism is more fundamental than irreversibility, which is only a practical convenience: you cannot circumvent the Poincare recurrence theorem, but the recurrence times are mindbogglingly huge for large systems, let alone the environment effects.

To me, all of science is "a practical convenience", one cannot say irreversibility is and determinism isn't because one has no scientific prescription for demonstrating a difference between a convenience and a principle. Scientific theory is a bunch of convenient concepts, how could it be anything else?

I am afraid you've lost me here. You called the Peierls postulate an axiom, I said I reject such an axiom. This postulate states that the wavefunction collapse occurs in the brain. Why do I need it to do science? The bulk of the science does not even need a notion of wavefunction, never mind the Peierls postulate.

The axiom I was referring to was that the last step of science is classical because it involves a confrontation with our own brains, and our brains function classically. If we could match a superposition in our brain with the superposition of an electron, we would never need that final classical step, but we can't and we do. It's just how we do science, yourself included, so that's why I claim it is a required axiom-- for any scientist. I interpret Peierl's "collapse of the wavefunction" idea entirely in those terms, in the context of quantum mechanics.

I was saying that "observation" without intelligence may be possible, and therefore wavefunction collapse does not need to occur in a human brain.

Then please provide the scientific meaning you attach to the word "observation". Remember, I've been clear that the destruction of coherences is something I consider to be a natural process, but does not by itself constitute an observation, when the latter is defined as "a means to put a scientific theory to the test".

As for what you choose to describe a system, you may choose classical mechanics, or you can choose quantum mechanics.

Precisely, my point is that many people use those terms as if they were different types of reality, like reality at a different scale-- that's what you were doing when you claimed there was no such thing as a classical system. In fact these are just choices made by an intelligence to describe reality.

Of course, there are no absolutes, however quantum mechanics is more precise than classical mechanics.

Only when applied to simpler systems that can be prepared more precisely, yes. But the increased precision is a reflection of the system, not the theory.

I prefer to accept some of these things. If you don't want to accept any such things, its your choice based on philosophy. I am not ready to discuss philosophy.

Neither am I-- which is why none of my statements have espoused any philosophy. The discussion was never about philosophy, it was always about where science ends and philosophy begins.

 

[akhmeteli]

I have no desire to debate whether or not objective reality "exists", the issue is how the concept is used in science. It is of course just that-- a concept, and one that science uses to great advantage, but the issue is, just what does science actually need, and what are we adding just to make ourselves more comfortable? The latter is what is inappropriate for the forum.

Comfort is extremely important for physicists. Otherwise, as I said, there is no difference whether the Earth rotates around the Sun or it is the other way round. You praised the Occam's razor - this is also a matter of comfort.

One does not "debate" definitions, but the clarification of them is completely crucial. One can only criticize a scientific definition on the grounds that it does not conform to the axioms of science. I have said what I mean by my words, as relying on vague popular meanings is ineffectual.

We use English for discussion, so when definitions of everyday words defy their standard meaning, it makes life a bit difficult.

Again I cannot concur, there is everything to discuss-- there is the discussion of what are the ramifications of these definitions! That is not "tautological". If you are using different definitions, I invite you to supply them, so we can consider the ramifications of your definitions-- I only require that they be expressed in a scientifically demonstrable way, as I believe I have done.

Let us agree to disagree on this. I am really not ready to define every English word, sorry.

But isn't that just a question of precision? Even a classical measurement of angular momentum was never know to be capable of being precise at the level of h. It was just a guess that it could, pure imagination-- and that's why I don't think of classical physics as establishing a deterministic reality, it had not been demonstrated to be such, even if we adopt your more careful definition of determinism (which one might call asymptotic determinism if you please it).

Seems like we disagree on whether classical physics is deterministic. No hard feelings:-) You see, we are talking about different things. Whether classical mechanics is precise or not, it's a matter for experimental tests. But whether classical mechanics is deterministic or not, it's a matter of its structure. Let me give you an example. Whether a specific quantum field theory is renormalizable or not does not depend on whether it describes experiments well, it can be established without experiments, although the theory can be so complex that it may take years to establish it (and that's what happened with the Standard Model).

To me, all of science is "a practical convenience", one cannot say irreversibility is and determinism isn't because one has no scientific prescription for demonstrating a difference between a convenience and a principle. Scientific theory is a bunch of convenient concepts, how could it be anything else?).

So comfort is inappropriate, but convenience is OK? Sorry, just teasing:-) Again, we just disagree on whether classical mechanics is deterministic.

The axiom I was referring to was that the last step of science is classical because it involves a confrontation with our own brains, and our brains function classically. If we could match a superposition in our brain with the superposition of an electron, we would never need that final classical step, but we can't and we do. It's just how we do science, yourself included, so that's why I claim it is a required axiom-- for any scientist. I interpret Peierl's "collapse of the wavefunction" idea entirely in those terms, in the context of quantum mechanics.

It is not obvious for me that our brains function classically. Even if Bohr said they do, that's not enough for me, I'm awfully sorry. I am not even sure anybody really understands how brains function. Another disagreement, I am afraid, now on the axiom:-)

Then please provide the scientific meaning you attach to the word "observation". Remember, I've been clear that the destruction of coherences is something I consider to be a natural process, but does not by itself constitute an observation, when the latter is defined as "a means to put a scientific theory to the test".

Again, I cannot give you a definition of observation. Not only because I am too lazy (although this is certainly a reason:-) ), but also because we are discussing a primary notion, which is difficult to define by other, "more primary" notions. And again, your definition goes against the usual meaning of this English word. On the other hand, it looks like we agree here on the essence of the matter, which for me is: decoherence takes place outside of human brain. For me this also means that the results of measurements are independent of human brain. You, however, are not disposed to recognize objective reality and, consequently, that results of measurements are independent of human brain. This is a philosophical difference.

Precisely, my point is that many people use those terms as if they were different types of reality, like reality at a different scale-- that's what you were doing when you claimed there was no such thing as a classical system. In fact these are just choices made by an intelligence to describe reality.

I am not sure that was what I was doing as classical or quantum mechainc are not realities, they are descriptions of reality, I agree with your emphasis. But quantum description is more precise, that's why I said that there is no such thing as a classical system.

Only when applied to simpler systems that can be prepared more precisely, yes. But the increased precision is a reflection of the system, not the theory.

Sorry, I have to disagree with the first phrase. Semiconductors, superconductors, metals, black body radiation, you name it, are not "simpler systems", they need little preparation, but their classical description just sucks. As for the second phrase, quantum mechanics is more precise than classical mechanics for any system.

Neither am I-- which is why none of my statements have espoused any philosophy. The discussion was never about philosophy, it was always about where science ends and philosophy begins.

Sorry to disappoint you, but your statements are not free from philosophy (neither are mine). When you praise the Occam's razor - it's philosophy, when you declare that the Peierls postulate is an axiom that science cannot do without, that's philosophy. Actually, I suspect that our disagreements may be much less significant than they look, as it seems to me that a wavefunction for you is just a shorthand for probabilities, and I have nothing against Bayesian approach, where probabilities are pretty much subjective estimates.However, for me a wavefunction is something that obeys the equations of quantum mechanics, so I am not sure it's just a record of probabilities, and again we are just talking about different things.