B Hawking believes "God confuses us throwing dice....", why?

[Mario Rossi]

Hi, I'm trying to understand the QM, I have no background and I can only do some research sometime because I've no time for this. Yesterday I read the quote above. He's talking about black holes and the horizon of events. I read that the microcosm can make indeterminate the macrocosm, for example in the Shroedinger's cat, were we can't be sure the cat is still alive (macrocosm) because of the nuclear decay's casuality. But in the normal life is the macrocosm casual? I also read about the two slits experiment made with atoms and molecules. Is it possible it works with a basket ball? Is "the moon disappearing when we don't look at it"? I'm very confused, like the other time I asked a question here :). Sorry for my ignorance on this topics, I search a lot but I can't find nothing but books, and unfortunately I've no time to read books... Is it possible for me to understand the QM? Maybe in the old age when I will no job :D

 

[phinds]

Hi, I'm trying to understand the QM, I have no background and I can only do some research sometime because I've no time for this. Yesterday I read the quote above. He's talking about black holes and the horizon of events. I read that the microcosm can make indeterminate the macrocosm, for example in the Shroedinger's cat, were we can't be sure the cat is still alive (macrocosm) because of the nuclear decay's casuality. But in the normal life is the macrocosm casual? I also read about the two slits experiment made with atoms and molecules. Is it possible it works with a basket ball? Is "the moon disappearing when we don't look at it"? I'm very confused, like the other time I asked a question here :). Sorry for my ignorance on this topics, I search a lot but I can't find nothing but books, and unfortunately I've no time to read books... Is it possible for me to understand the QM? Maybe in the old age when I will no job :D

Sir,

You are asking so many different questions that your post became a jumble.

I suggest that you focus on one single issue and give us a specific quote from a reputable source regarding that issue. Let's take it a step at a time. That is more likely to get you useful help.

 

[StevieTNZ]

Perhaps you can inform us, firstly, where you got the quote and other statements from.

 

[Lord Jestocost]

"Is the moon there when nobody looks? Reality and the quantum theory" is the title of a paper by N. D. Mermin ( [PDF]Is the moon there when nobody looks? - Caltech Particle Theory Group ).

 

[PeterDonis]

I'm trying to understand the QM, I have no background and I can only do some research sometime because I've no time for this.

Unfortunately, QM is not a subject that you can get a good understanding of with "some research sometime". And the questions you are asking are advanced questions, for which you would need quite a bit of background knowledge to understand the answers. In short, you have not picked a good topic for a "B" level thread.

In addition, as @phinds has already pointed out, your OP is not one focused question but a jumble of questions, thoughts, and misunderstandings. I'm not sure it's possible to sort them out; you need to pick one simple question and start with that.

I've no time to read books... Is it possible for me to understand the QM?

Unfortunately, the short answer to this is "no". See above.

 

[Mario Rossi]

Ok sorry guys for the jumble. Ok I want to ask just one question to you: the casuality and its relation to the measure paradox: I read that when a quantum system is not observed it is casual and when it is observed it is deterministic.

The 1st quote Hawking

So Einstein was wrong when he said, "God does not play dice." Consideration of black holes suggests, not only that God does play dice, but that he sometimes confuses us by throwing them where they can't be seen.

• During the same 1994 exchange with Penrose as the previous quote, transcribed in The Nature of Space and Time (1996) by Stephen Hawking and Roger Penrose, p. 26 and also in "The Nature of Space and Time" (online text)
• Unsourced variants: Not only does God play dice with the Universe; he sometimes casts them where they can't be seen.
  Not only does God play dice, but... he sometimes throws them where they cannot be seen.

The 2nd quote:

We often discussed his notions on objective reality. I recall that during one walk Einstein suddenly stopped, turned to me and asked whether I really believed that the moon exists only when I look at it.

• As recalled by his biographer Abraham Pais in Reviews of Modern Physics, 51, 863 (1979): 907. Cited in Boojums All The Way Through by N. David Mermin (1990), p. 81

Source: wikiquote

Unfortunately, QM is not a subject that you can get a good understanding of with "some research sometime". And the questions you are asking are advanced questions, for which you would need quite a bit of background knowledge to understand the answers. In short, you have not picked a good topic for a "B" level thread.

In addition, as @phinds has already pointed out, your OP is not one focused question but a jumble of questions, thoughts, and misunderstandings. I'm not sure it's possible to sort them out; you need to pick one simple question and start with that.
Unfortunately, the short answer to this is "no". See above.

D: D: it's sad for me. But is it possible nobody in the world invented a way to explain the QM simply? I chose the B grade because the first time I make a post I used the A grade an they told me it was too high, so this time I thought to the minimal grade but you say it is too much... maybe it is time for me to quit the science world ahah!

 

[phinds]

Even though Einstein's math shows the possibility of the existence of black holes, he did not believe that they actually ever physically exist, thus some of the confusion around his statements about black holes.

Yes, it is true that the state of quantum objects is weird except when measured. For example, an electron exists in a "probability cloud" around an atom and actually has a position only when measured. I still have a hard time getting my head around this but I'm just an amateur at this stuff. I always want to think that it HAS a specific position at all times, we just don't know what it is until we measure it, but apparently that's not the case.

As for the moon thing that's all a misrepresentation of the Copenhagen Interpretation of Quantum Mechanics, based on some faulty reasoning in the very early days of QM. Schrodinger pointed out the ridiculousness of that faulty reasoning by coming up w/ the cat example which is intended to show how silly it is if you carry the Copenhagen Interpretation too far. He NEVER intended anyone to believe that a cat was actually alive and dead at the same time, only that we don't know which it is until we measure it.

 

[PeterDonis]

I read that when a quantum system is not observed it is casual and when it is observed it is deterministic.

You are reading pop science sources. That's not a good way to learn actual science. You need to read textbooks or peer-reviewed papers. There is no shortcut.

 

[Mario Rossi]

Ok guys thank you all. @PeterDonis you are right :) I just searched pop knowledge and there is no shortcut. All right, I understand the situation, just a little curiosity before quit this topic: the QM interpretations are just interpretetions? Is the QM fully understood and verified or not? Thank you for the help. I wasn't aware of the "pop" side of the science. The first step is to be aware, right? Goodbye everyone.

 

[PeterDonis]

the QM interpretations are just interpretetions?

The different QM interpretations all make the same experimental predictions, because they all use the same underlying math of QM. That's why they are called "interpretations" instead of "different theories".

Is the QM fully understood and verified or not?

Within its domain of validity, QM is well tested. Ordinary QM is non-relativistic, so it breaks down when relativity becomes important. Quantum field theory is based on special relativity, and works well as long as gravity is not significant and energies are within the range of our current experiments. We can do quantum field theory in curved spacetime, i.e., in the presence of gravity, but it is only approximate; we don't currently have a good comprehensive theory of quantum gravity.

 

[Lord Jestocost]

As for the moon thing that's all a misrepresentation of the Copenhagen Interpretation of Quantum Mechanics, based on some faulty reasoning in the very early days of QM. Schrodinger pointed out the ridiculousness of that faulty reasoning by coming up w/ the cat example which is intended to show how silly it is if you carry the Copenhagen Interpretation too far. He NEVER intended anyone to believe that a cat was actually alive and dead at the same time, only that we don't know which it is until we measure it.

With all due respect, that's a complete misinterpretation of Schroedinger's reasoning:

From: "Do We Really Understand Quantum Mechanics?" by Franck Laloë

 

[phinds]

With all due respect, that's a complete misinterpretation of Schroedinger's reasoning:

So is it your contention that he DID think the cat was both dead and alive at the same time?

 

[bhobba]

So Einstein was wrong when he said, "God does not play dice." Consideration of black holes suggests, not only that God does play dice, but that he sometimes confuses us by throwing them where they can't be seen.

He may or may not be wrong - its an interpretation thing - in some interpretations of QM (eg Bohmian Mechanics and Many Worlds ) he doesn't.

Actually most interpretations are agnostic on if it, at rock bottom, is probabilistic or not. At the B level I can't explain why but we know why the formalism is as it is in QM - I will give the best link I can at your level:
https://www.scottaaronson.com/democritus/lec9.html

Most interpretations, believe it or not, are just arguments about what probability means as explained by John Baez (he is a science adviser here when he gets the time):
http://math.ucr.edu/home/baez/bayes.html

Hawking and Penrose are VERY great physicists, but it's not in QM where they made their fame, and Penrose has some unusual views on such things. A better person to read is the perhaps even greater physicist, Weinberg, who I would say is THE no 1 expert on QM alive today:
http://physicstoday.scitation.org/doi/full/10.1063/1.2155755

Note - and this is important - we now know BOTH Einstein and Bohr were wrong - we know a lot more about QM these days. Also the popular misconception is Einstein did not believe in QM - that's wrong (of the later Einstein - he attacked it and failed for a time - his last failure with Bohr seemed to have cured him of that). He believed it true - but incomplete. He even came up with his own interpretation - the Ensemble interpretation me and other people here hold to:
https://en.wikipedia.org/wiki/Ensemble_interpretation

That's enough for now - its already a lot for a beginner to digest.

Thanks
Bill

 

[bhobba]

You are reading pop science sources. That's not a good way to learn actual science. You need to read textbooks or peer-reviewed papers. There is no shortcut.

Sigh. Unfortunately its true. Some pop-sci stuff is - how to put it nicely - half truths at best - downright lies at worst.

The sources I gave are not pop-sci - Wienberg's paper was published in Physical Review but you likely will get something from it, as well as the other sources I gave such as an MIT lecture (except Wikipedia which we sometimes use here even though it not a textbook or peer reviewed source - it validity is variable - any I give are reasonably good)

To understand QM will take a long hard slog.

At the non pop-sci and valid level see:
https://www.amazon.com/dp/0465075681/?tag=pfamazon01-20
https://www.amazon.com/dp/0141976225/?tag=pfamazon01-20

Thanks
Bill

 

[Lord Jestocost]

So is it your contention that he DID think the cat was both dead and alive at the same time?

The “damned” cat! Maybe, only a few ones have read Schroedinger’s original paper.

There is one equation and one quantity which define quantum theory – the time dependent Schroedinger equation and the associated wave function. Consider a superposition and its evolution in course of time according to the Schroedinger equation. There is no physical process - how irreversible it might be - which is capable to “destroy” the superposition, viz. to reduce interference terms exactly to zero.

Schroedinger wanted merely to point out with his cat fable - a little bit ironically: "There is a difference between a shaky or out-of-focus photograph and a snapshot of clouds and fog banks." That means, when the quantum mechanical formalism is consequently applied the quantum ignorance “where the desired information simply doesn’t exist” (snapshot of clouds and fog banks) cannot be replaced by the classical ignorance “where the desired information exists but is hidden” (shaky or out-of-focus photograph). The conceptual transition from quantum to classical ignorance has to be put in “by hand”.

So, regarding your question, I would like to quote Terry Pratchett (in “Lords and Ladies“): “In fact, the mere act of opening the box will determine the state of the cat, although in this case there were three determinate states the cat could be in: these being Alive, Dead, and Bloody Furious.”

 

[Lord Jestocost]

So Einstein was wrong when he said, "God does not play dice." Consideration of black holes suggests, not only that God does play dice, but that he sometimes confuses us by throwing them where they can't be seen.

Hawking’s quote is indeed a reminiscence of Einstein’s assertion “God does not play dice.” In his book “Der Teil und das Ganze: Gespräche I am Umkreis der Atomphysik” Werner Heisenberg mentions Bohr’s reply: “But it cannot be our duty to prescribe to God how to govern the world.”

 

[Mario Rossi]

Thank you all guys. Do you think the youtube channel like The Royal Institution (https://www.youtube.com/channel/UCYeF244yNGuFefuFKqxIAXw) are reliable to understand something? Or Ted talks? I'm asking this because sometime I can look videos but it is difficult for me to read a book.

 

[kingaj12]

Note - and this is important - we now know BOTH Einstein and Bohr were wrong - we know a lot more about QM these days. Also the popular misconception is Einstein did not believe in QM - that's wrong (of the later Einstein - he attacked it and failed for a time - his last failure with Bohr seemed to have cured him of that). He believed it true - but incomplete. He even came up with his own interpretation - the Ensemble interpretation me and other people here hold to:
https://en.wikipedia.org/wiki/Ensemble_interpretation

The wikipedia article is a bit short on the subject of entanglement, and spooky action at a distance. Is there a resource that discusses this in more detail from the point of view of the EI?

 

[phinds]

The wikipedia article is a bit short on the subject of entanglement, and spooky action at a distance. Is there a resource that discusses this in more detail from the point of view of the EI?

There have been hundreds if not thousands of threads here on PF. I suggest a forum search.

 

[kingaj12]

There have been hundreds if not thousands of threads here on PF. I suggest a forum search.

I did. Don't see anything on this topic in the past year. Maybe my search is wrong .. perhaps you can find one?

 

[Aidyan]

I would rephrase your question by asking: "Can someone suggest some books on quantum physics that answer the following questions"? It makes no sense to ask all this hoping to reach a decent understanding of it on the fly...

 

[phinds]

I did. Don't see anything on this topic in the past year. Maybe my search is wrong .. perhaps you can find one?

"spooky action at a distance" ALONE gave me 7 pages of threads x 30 threads / page ==> in excess of 200 threads.

 

[laymanB]

But is it possible nobody in the world invented a way to explain the QM simply?

Mario, I am no expert on QM (and others on here can correct me if I'm wrong), but if we are talking about if the moon exists when we are not looking at it I believe the answer lies in how small a number that Planck's constant is. By using Heisenberg's uncertainty principle, we cannot say for certain what the position and momentum for a particle are to an infinite precision. This only really becomes an issue with particles with very small mass (think subatomic particles) because momentum is mass X velocity. With objects like a baseball or the moon, the mass (and thus the momentum) is so large that it overwhelms it's side of the formula in the uncertainty principle equality. So, although we cannot technically say that we can know the position and momentum of the moon to an infinite precision, it is still there if you are not observing it because the position and momentum of the moon are so well defined in the probability distribution that we can say that it is statistically impossible that the moon is found outside of that one spike of the distribution.

It is my understanding that QM says nothing about ontology or existence, only that exact precision is impossible. I suppose that an implication of the many worlds interpretation of QM does have something to postulate about the existence of other worlds we cannot observe, but that is a whole different ball of wax.

 

[PeterDonis]

It is my understanding that QM says nothing about ontology or existence, only that exact precision is impossible.

I agree that this is a reasonable statement of a "minimal" interpretation of QM, where we focus just on how it makes practical predictions for what we will observe and measure, and don't talk about whether it has any implications for ontology or existence, or if so, what they are. (Some call this general type of viewpoint the "shut up and calculate" interpretation.)

However, for better or worse, many physicists do not stop there, but go on to talk about possible implications of QM for ontology or existence; and they most often don't take care to draw good boundaries between the practical side--the way QM makes predictions for what we will observe and measure, which is the part of QM that has been thoroughly tested and verified by experiments--and the "philosophical" side, the various interpretations that try to tell a story about what QM says "really exists". So we get people like David Mermin saying that the Moon is not there when nobody looks, without bothering to say that that is not part of the practical side of QM that has been confirmed by experiments, but the philosophical side, which has not been tested by experiments (and can't be, because all of the different QM interpretations, some of which are mutually inconsistent, use the same practical math of QM and so make the same predictions for all experiments).

 

[kingaj12]

"spooky action at a distance" ALONE gave me 7 pages of threads x 30 threads / page ==> in excess of 200 threads.

The point of the post was "Ensemble Interpretation". Did you find any spooky post that references Ensemble Interpretation?

 

[Lord Jestocost]

But is it possible nobody in the world invented a way to explain the QM simply?

I recommend the book "Quantum Enigma: Physics Encounters Consciousness" by Bruce Rosenblum and Fred Kuttner.

The intention of the book is a simple one: The authors bring out the experimental facts that show the "reality" to be drastically different in its nature than many people think (even physicists after they have studied quantum mechanics). And they show that quantum mechanics easily accounts for every single one of these bizarre facts.

This book has nothing to do at all with pseudo-science as some may think when reading the title. Check the author’s biographies on http://quantumenigma.com/about-the-authors/. As Fred Kuttner writes: “A concern of both Bruce and myself is the expropriation of the profound mysteries of quantum mechanics by the purveyors of pseudo-science. We have combated this in publications and by many lectures.“

 

[phinds]

The point of the post was "Ensemble Interpretation". Did you find any spooky post that references Ensemble Interpretation?

? I see nothing in your post that mentions "Ensemble Interpretation"

The wikipedia article is a bit short on the subject of entanglement, and spooky action at a distance. Is there a resource that discusses this in more detail from the point of view of the EI?

EDIT: AH HA ... that's what "EI" is. I overlooked it.

 

[laymanB]

I also read about the two slits experiment made with atoms and molecules. Is it possible it works with a basket ball?

I had this same misunderstanding when I started to learn about QM. When you look at the experiments of determining the wave/particle nature of light you will see that just watching the light/slit experiment does not effect the light from acting like a wave. If you turn on your laser and set the laser to pass through two slits, you will see light acting like a wave based on what appears on the screen. It will have constructive and destructive interference that gives you the pattern you would expect from waves on the screen. Just by observing the experiment the wave function doesn't collapse into just particle type nature to only give you two marks on the screen consistent with particles. This behavior arises from setting up the experiment differently.

 

[laymanB]

So we get people like David Mermin saying that the Moon is not there when nobody looks, without bothering to say that that is not part of the practical side of QM that has been confirmed by experiments, but the philosophical side, which has not been tested by experiments (and can't be, because all of the different QM interpretations, some of which are mutually inconsistent, use the same practical math of QM and so make the same predictions for all experiments).

It makes you wonder how the universe existed and evolved prior to observers. (Insert sarcasm in a medium in which it is hard to discern)

 

[jerromyjon]

It makes you wonder how the universe existed and evolved prior to observers.

I was tempted to say " Well, people at the beach can watch the tide rolling in while not looking at the Moon." but then you had to take it to universal proportions...

 

[Lord Jestocost]

So we get people like David Mermin saying that the Moon is not there when nobody looks, without bothering to say that that is not part of the practical side of QM that has been confirmed by experiments,

With all due respect, what are you talking about? Do you even know who N. David Mermin is?

Einstein asked the question "Is the moon there when nobody looks?" during a conversation with Abraham Pais. “We often discussed his notions on objective reality. I recall that during one walk Einstein suddenly stopped, turned to me and asked whether I really believed that the moon exists only when I look at it.” Rev. Mod. Phys. 51, 863–914 (1979), p. 907

N. David Mermin has merely used this passage as the title for his paper "Is the moon there when nobody looks? Reality and the quantum theory." Physics Today, April 1985, pp. 38-47.

 

[PeterDonis]

Do you even know who N. David Mermin is?

Sure, he's the physicist who, as I understand it, did not merely title his paper with the question, but argued that the actual observed behavior of quantum systems in experiments means that the answer to the question is "no"--that the Moon is not there when nobody looks. Which, as I said, is not actually what the experiments tell us, since the experiments are consistent with all QM interpretations, including ones in which the Moon is there when nobody looks.

 

[bhobba]

The wikipedia article is a bit short on the subject of entanglement, and spooky action at a distance. Is there a resource that discusses this in more detail from the point of view of the EI?

There sure is - but is at the advanced undergraduate or graduate level and is called - Ballentine- Modern QM - as per my Sig. You probably are not ready for it - you need at least an intermediate course on QM before undertaking it.

But I have written a number of posts on exactly what's going on eg - see post 3 where I also explain entanglement and a small glimpse into what's called decoherence which has had a strong influence on modern interpretations of QM:
https://www.physicsforums.com/threads/entanglement-what-is-it.927145/#post-5853260

Strangely, and he is the odd man out, Ballentine doesn't think so - of course he believes in decoherence but doesn't think it has anything to do with interpretations - interesting isn't it.

Thanks
Bill

 

[Lord Jestocost]

Sure, he's the physicist who, as I understand it, did not merely title his paper with the question, but argued that the actual observed behavior of quantum systems in experiments means that the answer to the question is "no"--that the Moon is not there when nobody looks. Which, as I said, is not actually what the experiments tell us, since the experiments are consistent with all QM interpretations, including ones in which the Moon is there when nobody looks.

Please, use "Google Scholar" and search for N. David Mermin! I think he knows what experiments and quantum physics tell us.

 

[PeterDonis]

I think he knows what experiments and quantum physics tell us.

The specific paper of Mermin's that is being referred to is behind a paywall, so I can't read it, I can only read the abstract, which appears to claim what I said it claimed, but does not give the detailed basis for the claim (since it's just an abstract, I wouldn't expect it to). Without that basis, any claim that Mermin's statements should be accepted simply because he's a well-known knowledgeable physicist is an argument from authority and carries no weight here.

That said, I think it's highly unlikely that the claim (that the Moon is not there when nobody looks) is independent of any intepretation of QM, since realist interpretations, which treat it as an obvious fact that the Moon is there when nobody looks, exist. And if the claim is not independent of interpretations, then it can't possibly be verified by experiment, since, as I've said, all QM interpretations make the same predictions for all experiments. This is simple logic, and if it is correct, then any physicist who says that the Moon is not there when nobody looks, stating it as a simple fact verified by experiment instead of a highly interpretation-dependent hypothesis, must be misstating something.

 

[bhobba]

Sure, he's the physicist who, as I understand it, did not merely title his paper with the question, but argued that the actual observed behavior of quantum systems in experiments means that the answer to the question is "no"--that the Moon is not there when nobody looks. Which, as I said, is not actually what the experiments tell us, since the experiments are consistent with all QM interpretations, including ones in which the Moon is there when nobody looks.

He may have believed that. But the interesting thing about Meriman is, everyone attributes, with regard to QM, shut up and calculate to Feynman. It certainly is the kind of thing he would have said. But it seems it was actually Meriman, and he is a bit uneasy these days about it:
http://gnm.cl/emenendez/uploads/Cursos/callate-y-calcula.pdf

If he kept to that philosophy, and he did say that view has somewhat weakened for him, but it still was a there at least a bit its likely he would, like Feynman was in his later years, attracted to the Decoherent Histories view of Gell-Mann. In that interpretation the moon is definitely there - looking or not (it being looked at all the time by its environment eg sunlight, photons from the CBMR, etc etc.

To the OP you can investigate that interpretation further via the following book which the author has kindly made free online:
http://quantum.phys.cmu.edu/CQT/index.html

Thanks
Bill

 

[PeterDonis]

everyone attributes, with regard to QM, shut up and calculate to Feynman. It certainly is the kind of thing he would have said. But it was actually Meriman

He says that "shut up and calculate" sums up what the Copenhagen interpretation says ("says to me" are his exact words); that doesn't necessarily mean it's the interpretation he favors. My impression from what I've read is that he favors non-realist interpretations. But his position could be more nuanced than that.

 

[bhobba]

That said, I think it's highly unlikely that the claim (that the Moon is not there when nobody looks) is independent of any intepretation of QM, since realist interpretations, which treat it as an obvious fact that the Moon is there when nobody looks, exist

Thats true - but these days with our modern knowledge of decoherence it's a lot harder to maintain such a view. When one of the high priests of consciousness causes collapse (Wigner) read some early papers on decoherence by Zeth he realized it was now much harder to maintain such a position and did 180% about face. I think that's when that kind of view really went into decline - its still there - but now very much a minority one.

Thanks
Bill

 

[Lord Jestocost]

The specific paper of Mermin's that is being referred to is behind a paywall...

[PDF]Is the moon there when nobody looks? - Caltech Particle Theory Group

 

[PeterDonis]

these days with our modern knowledge of decoherence it's a lot harder to maintain such a view

The view that the Moon is there when we're not looking? I think decoherence makes it a lot easier to maintain such a view, because it gives an obvious way in which the Moon, or indeed any macroscopic object, can constantly be "looking at itself"--interactions between the different parts of the object are continually decohering it, preventing significant macroscopic superpositions from arising. (This is a heuristic description, hopefully you understand what I mean.) It also allows us to easily dispose of conundrums like the Schrodinger's cat thought experiment: the cat can never be in a superposition of dead and alive because it is continually decohering itself in the dead/alive basis.

 

[bhobba]

He says that "shut up and calculate" sums up what the Copenhagen interpretation says ("says to me" are his exact words); that doesn't necessarily mean it's the interpretation he favors. My impression from what I've read is that he favors non-realist interpretations. But his position could be more nuanced than that.

Yes - I think it is rather more nuanced - he laments the whole thing (from the above):
Among them am I, who hereby put forth the hypothesis that I was the first to use "shut up and calculate" in the context of quantum foundations. I'm not proud of having said it. It's not a beautiful phrase. It's not very clever. It's snide and mindlessly dismissive.

Did that lead him down the same path Feynman took in his later years - who knows.

Thanks
Bill

 

[bhobba]

The view that the Moon is there when we're not looking?

Oh dear - I may have not been as clear as I should have been - I was referring to the idea its harder to maintain the view the moon is not here when not looking - and you correctly detail the reason why that is. And yes I get your drift.

Thanks
Bill

 

[Lord Jestocost]

The view that the Moon is there when we're not looking? I think decoherence makes it a lot easier to maintain such a view, because it gives an obvious way in which the Moon, or indeed any macroscopic object, can constantly be "looking at itself"--interactions between the different parts of the object are continually decohering it, preventing significant macroscopic superpositions from arising. (This is a heuristic description, hopefully you understand what I mean.) It also allows us to easily dispose of conundrums like the Schrodinger's cat thought experiment: the cat can never be in a superposition of dead and alive because it is continually decohering itself in the dead/alive basis.

Regarding decoherence and the related misunderstanding:

Consider a superposition and its evolution in course of time according to the Schroedinger equation. There is no physical process - how irreversible it might be - which is capable to reduce interference terms exactly to zero. You can "decohere" as much as you want, you will never get rid of the superposition. Why don't people get this into their heads? The whole information which the observer had at the beginning of the measuring process remains thus unchanged during the measuring act. Thus, no increase in entropy takes place and, consequently, no conversion of a pure state into a mixed state can takes place. A superposition remains always a superposition as long as mere physical processes are considered. That's physics! There is no way out! The conceptual transition from quantum to classical ignorance has to be put in “by hand” - the role of the observer.

 

[PeterDonis]

Regarding decoherence and the related misunderstanding

Where is this quoted from?

 

[bhobba]

Consider a superposition and its evolution in course of time according to the Schroedinger equation. There is no physical process - how irreversible it might be - which is capable to reduce interference terms exactly to zero.

That's an old argument. We are talking physics here - not pure math. Would you consider 1/googleplex physically important? There are quantities so small in physics that FAPP they are zero.

To be even more precise the decoherence models show it quickly falls way below our ability to measure. What about the future - who knows - we may actually be able to measure it - but its so small I doubt it.

Thanks
Bill

 

[Mario Rossi]

You can "decohere" as much as you want, you will never get rid of the superposition.

So the observer effect does not make a quantum system 100% deterministic, right?

 

[bhobba]

So the observer effect does not make a quantum system 100% deterministic, right?

Its not that.

In decoherene models quantum features, most notably interference effects, quickly decay to nearly, but never exactly zero. Some, and I have discussed the issue with a few of them, believe this means the whole decoherence program is wrong. I know from experience they will not be budged from that position, which of course they can adhere to if they wish. However nearly everyone exposed to it recognizes if it quickly goes way below our ability to measure and is so low its doubtful even future progress in measuring such things will not detect it then you can take it as zero.

Its one of those philosophical points that polaritises some.

Personally I think it grasping at straws and it does explain why we don't generally see quantum effects here in the macro world, but as a judgement thing I can't prove it because its a matter of opinion on what an explanation is. All I can say is that it doesn't solve it is very much a minority view.

Thanks
Bill

 

[Mario Rossi]

All right Bill, thank you. Aren't there ways to prove the ontological side? I suppose not yet. And what do you think about that story on von Neumann's discovery (the hidden variable is the cosciusness ecc.)? Thank you all for the help.

EDIT: Another question: what do you guys think about the delayed choice ereaser experiment that seems to be a "retrocasuality" proof?

 

[Lord Jestocost]

Where is this quoted from?

That's my try to translate a section in the book "Philosophische Probleme der modernen Physik" by Peter Mittelstaedt (published 1976!). But you can also read the paper "Why Decoherence has not Solved the Measurement Problem: A Response to P. W. Anderson" by Stephen L. Adler (https://arxiv.org/abs/quant-ph/0112095). And again, please, use "Google Scholar" and search for Stephen L. Adler.

 

[bhobba]

All right Bill, thank you. Aren't there ways to prove the ontological side? I suppose not yet. And what do you think about that story on von Neumann's discovery (the hidden variable is the cosciusness ecc.)? Thank you all for the help.

Philosophy and science parted ways ages ago - ontological side - what you even mean by that; shrug. I can look it up of course and refresh my memory - I did a course in philosophy once. Let's say my teacher, Petra, consigned me to the merely material. I also started a graduate certificate in philosophy, but it wasnt to my taste being not really concerned with the ideas themselves, but its history - and there were other issues that I won't go into to do with my arthritic condition and getting to the uni library to do research, so I gave it away.

For Von-Neumann's issue - see here:
http://philsci-archive.pitt.edu/12443/1/VNProof.pdf

A sad corner of science.

Thanks
Bill