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

[Lord Jestocost]

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

Let me answer with a section of the paper “Decoherence, the measurement problem, and Interpretations of quantum mechanics“ by Maximillian Schlosshauer (https://arxiv.org/abs/quant-ph/0312059)

II. THE MEASUREMENT PROBLEM

One of the most revolutionary elements introduced into physical theory by quantum mechanics is the superposition principle, mathematically founded in the linearity of the Hilbert state space. If |1i and |2i are two states, then quantum mechanics tells us that any linear combination α|1i+β|2i also corresponds to a possible state. Whereas such superpositions of states have been experimentally extensively verified for microscopic systems (for instance, through the observation of interference effects), the application of the formalism to macroscopic systems appears to lead immediately to severe clashes with our experience of the everyday world. A book has never been ever observed to be in a state of being both “here” and “there” (i.e., to be in a superposition of macroscopically distinguishable positions), nor does a Schroedinger cat that is a superposition of being alive and dead bear much resemblance to reality as we perceive it. The problem is, then, how to reconcile the vastness of the Hilbert space of possible states with the observation of a comparatively few “classical” macrosopic states, defined by having a small number of determinate and robust properties such as position and momentum. Why does the world appear classical to us, in spite of its supposed underlying quantum nature, which would, in principle, allow for arbitrary superpositions?

And now, with respect to decoherence and the measurement problem:

Joos and Zeh remarked on decoherence as a source of spatial localization: "Of course no unitary treatment of the time dependence can explain why only one of these dynamically independent components is experienced." (E. Joos and H. D. Zeh, Zeitschrift Phys. B 59, 223–243; 1985).

Joos states in another article: “Does decoherence solve the measurement problem? Clearly not. What decoherence tells us is that certain objects appear classical when observed. But what is an observation? At some stage we still have to apply the usual probability rules of quantum theory.” (Joos, E. (1999) ‘Elements of Environmental Decoherence’, in P. Blanchard, D. Giulini, E. Joos, C. Kiefer and I.-O. Stamatescu (eds.), Decoherence: Theoretical, Experimental, and Conceptual Problems (New York: Springer), pp. 1-17.)

Or, as Nikolaus von Stillfried remarks: “In his Essay 'Lifting the fog from the north' (Nature 453, 39; 2008), Maximilian Schlosshauer describes how the process of decoherence can explain the famous double-slit experiment. An electron interacting with innumerable quanta in the photographic plate (and its environment) becomes entangled with all of them — and the resulting collective wavefunction is so narrow that it appears particle-like.

But the question remains as to why the wavefunction narrows in precisely the location where it does, or - as Schlosshauer puts it - "Why is a single spot here and not there?"

The author's somewhat 'foggy' answer is suggestive of a version of Everett's 'many worlds' idea (see Nature 448, 15–17; 2007), in which all possible branches of the wavefunction continue to exist autonomously. But this interpretation merely shifts the question to "Why do I find myself experiencing the branch/world with the spot here and not the branch/world with the spot there?" ("Decoherence does not get rid of the quantum paradox", Nature 453, 978-979 (19 June 2008))

 

[jerromyjon]

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

I think that if you don't abuse the "wave-particle duality" nature of light, that it has attributes of both until measured, then there is no retrocausality. It cannot be some "hidden local variable", that much is certain... but when anything interacts with photons it has a measurable effect. This short video I saw yesterday makes it ever so obvious.
https://www.physicsforums.com/media/bells-theorem-the-quantum-venn-diagram-paradox-youtube.653/

 

[bhobba]

Let me answer with a section of the paper “Decoherence, the measurement problem, and Interpretations of quantum mechanics“ by Maximillian Schlosshauer (https://arxiv.org/abs/quant-ph/0312059)

A much better source is his book Deoherence And The Quantum To Classical Transition.

For a more complete definition see page 49 - Section 2.5 - The Measurement Problem and The Quantum To Classical Transition where a much more careful definition is given. It's in 3 parts, but since this whole thing had been done to death and posted before I will not do it again - besides reading the book and going through what it says is a much better way to understanding than quotes without the rest of the context. Suffice to say the problem has 3 parts:

1. The Problem Of The Preferred Basis - to the OP colloquially it would be why does a position measurement for example give a position measurement.
2. The Problem Of The Non-Observability of Interference Patterns - obviously referring to here in the macro world - and of course under some circumstances is observable - just one example of why context is so important
3. The problem of outcomes. Colloquially why do we get outcomes at all - more technically exactly how is a particular outcome selected - even more technically how does an improper mixed state become a proper one.

Decoherence solves the first 2 despite some of your other quotes - the one that's the issue is 3. It requires specific interpretations to resolbe it and they all do it in a different way. In the Ensemble Interpretation taking that into account you get a slight variation called the Ignorance Ensemble where the answer is 'somehow' it becomes a proper mixed state. My view on that somehow is who cares - you can't tell the difference between a proper and improper mixed state so why worry. Ballentine thinks decoherence is of no value and many many other views exist. What would have Einstein thought? Well he thought QM incomplete so he would likely believe the key question is that how - and so it goes.

Decoherence has NOT solved the measurement problem - I will repeat it for emphasis - it has NOT solved it - but it has shifted the issue somewhat. In a previous paper I linked to by Weinberg, while I can't get into his head, where he said both Bohr and Einstein were wrong its likely that's what he meant - they didn't understand the real issue which only emerged after they died. Of the originals Wigner was quickly converted to it - Dirac - well he was always the odd person out concentrating more on the actual math rather than musing about what it means - but its likely, since its based on simply a mathematical analysis of the formalism, he would he been converted to it as well.

Thanks
Bill

 

[Blue Scallop]

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".

If experiments in the future can determine say the trajectories of the bohmian particles or prove there are really different worlds where the branches exist, then it's no longer an interpretation but a theory? It's just weird that all the intepretations were tailored to match the math of QM as if constraining them to certain dynamics. But you are right that to avoid getting sinked in interpretations for a lifetime.. one must focus on the math and instead spend time to understand road to a fuly interacting non-perturbative quantum field theory.

 

[phinds]

If experiments in the future can determine say the trajectories of the bohmian particles or prove there are really different worlds where the branches exist, then it's no longer an interpretation but a theory? It's just weird that all the intepretations were tailored to match the math of QM as if constraining them to certain dynamics. But you are right that to avoid getting sinked in interpretations for a lifetime.. one must focus on the math and instead spend time to understand road to a fuly interacting non-perturbative quantum field theory.

If I understand it correctly, you have this backwards. The interpretations were not tailored to fit the math, they are INTERPRETATIONS of what the math means physically, so of course they all use the same math.

 

[Blue Scallop]

-

If I understand it correctly, you have this backwards. The interpretations were not tailored to fit the math, they are INTERPRETATIONS of what the math means physically, so of course they all use the same math.

Here are the confusing parts.

Map = Model = orthodox shut up and calculate Quantum Theory

Territories = Realities = Bohmian Mechanics, Many Worlds, etc.

So if someday BM trajectories can be observed or branches in MWI can be seen then it becomes or make the quantum theory become a different theory? but I don't understand the shift from map to territories. I mean. Is Map a theory too? Or are both Map and Territories considered as both Theories. Can you give an example where a Map or Model is a theory and example where territories or reality is a theory? This distinction is important to get the gist of it all. Thanks.

 

[bhobba]

If experiments in the future can determine say the trajectories of the bohmian particles or prove there are really different worlds where the branches exist, then it's no longer an interpretation but a theory? It's just weird that all the intepretations were tailored to match the math of QM as if constraining them to certain dynamics. But you are right that to avoid getting sinked in interpretations for a lifetime.. one must focus on the math and instead spend time to understand road to a fuly interacting non-perturbative quantum field theory.

Of course if it somehow is possible to experimentally tell one interpretation from another then we know some interpretations are kaput - that's Feynman's very famous explanation of science:


Just as an aside when faced with any issue, not just in science, but in general life, the first thing I do is watch that video and say - how does it solve the issue. Here is an example - here in Australia we want to spend Billions on education in something called Gonsky without going into it - it's not important to the point I am trying to make. You watch Feynman - well you have this guess - spending money on Gonsky will raise education standards. You now do an experiment - you hunt around for those that have investigated this issue and you find the number one expert here in Aus, possibly the world, Professor Hattie at the University of Melbourne on EVIDENCE based education, has shown what it want's to do is useless, by analysing data from thousands of schools worldwide. Hypothesis failed - Gonsky useless. But just to show how stupid people can be they don't care and want Gonsky anyway. Also as Feynman said - they say we live in a scientific age - well basically it's not what he observes. Read his book about the Challenger disaster. He solved it - scientifically - but his solution was relegated to an appendix. There is something deep in us that, on occasion, grates against the scientific method in general life - it's a very strange phenomena.

Thanks
Bill

 

[bhobba]

Here are the confusing parts.

Map = Model = orthodox shut up and calculate Quantum Theory

Territories = Realities = Bohmian Mechanics, Many Worlds, etc.

That is so loaded with philosophical 'assumptions' you have almost guaranteed an 'argument'.

Watch Feynman's video - its the answer.

Thanks
Bill

 

[Blue Scallop]

That is so loaded with philosophical 'assumptions' you have almost guaranteed an 'argument'.

Watch Feynman's video - its the answer.

Thanks
Bill

Feynman didn't talk about map and territories.. so if there is something wrong with the arguments (actually they are not arguments.. I was just asking... hope someone can correct it or I will ask it again and again in the future when the simple questions (whose answers are not obvious to us) aren't directly addressed or resolved.

 

[bhobba]

Feynman didn't talk about map and territories.

That's correct.

Its got nothing to do with science. He explains what science is.

Its people that try to 'expand' on it and come up with things like - the map is not the territory, reality is what our theories tell us etc etc. Its not science - its philosophy. I believe in some of the things - in fact both of what I mentioned, but it's philosophy, not science, and that's why you are almost guaranteed an 'argument' because in philosophy you never actually reach a conclusion - you simply dialecticaly deconstruct and discuss things. Its a legit area, but not what we discuss here and engenders long threads going nowhere that the mods correctly shut down.

Thanks
Bill

 

[Blue Scallop]

That's correct.

Its got nothing to do with science. He explains what science is.

Its people that try to 'expand' on it and come up with things like - the map is not the territory, reality is what our theories tell us etc etc. Its not science - its philosophy. I believe in some of the things - in fact both of what I mentioned, but it's philosophy, not science, and that's why you are almost guaranteed an 'argument' because in philosophy you never actually reach a conclusion - you simply dialecticaly deconstruct and discuss things. Its a legit area, but not what we discuss here and engenders long threads going nowhere that the mods correctly shut down.

Thanks
Bill

I'm not arguing it. I hate philosophy too when it gets nowhere. But I just want to know the semantics so I can understand others or convey to others. So is it right that (I need to know so know how to communicate with all kinds of people):

Map = Model = orthodox shut up and calculate Quantum Theory

Territories = Realities = Bohmian Mechanics, Many Worlds, etc.

So if someday BM trajectories can be observed or branches in MWI can be seen then it becomes or make the quantum theory become a different theory? but I don't understand the shift from map to territories. I mean. Is Map a theory too? Or are both Map and Territories considered as both Theories. Can you give an example where a Map or Model is a theory and example where territories or reality is a theory? This distinction is important to get the gist of it all. Please address my questions. Thanks.

 

[bhobba]

Map = Model = orthodox shut up and calculate Quantum Theory
Territories = Realities = Bohmian Mechanics, Many Worlds, etc.

People will ague everyone of those statements.

I do not agree 'Map = Model = orthodox shut up and calculate Quantum Theory' nor 'Territories = Realities = Bohmian Mechanics, Many Worlds, etc.'

But I won't ague it because it philosophy - not physics.

People choose different interpretations for all sorts of reasons, some philosophy, some simply gut reaction, some it's all they have read - its endless the reasons.

I you want to understand interpretations better read books about then and make up your own mind.

Here is one to start with:
http://quantum.phys.cmu.edu/CQT/index.html

Thanks
Bill

 

[Blue Scallop]

People will ague everyone of those statements.

I do not agree 'Map = Model = orthodox shut up and calculate Quantum Theory' nor 'Territories = Realities = Bohmian Mechanics, Many Worlds, etc.'

But I won't ague it because it philosophy - not physics.

People choose different interpretations for all sorts of reasons, some philosophy, some simply gut reaction, some it's all they have read - its endless the reasons.

I you want to understand interpretations better read books about then and make up your own mind.

Here is one to start with:
http://quantum.phys.cmu.edu/CQT/index.html

Thanks
Bill

Hmm.. just this question for you now...

Is our shut up and calculate orthodox quantum theory a theory or interpretation?

 

[bhobba]

Is our shut up and calculate orthodox quantum theory a theory or interpretation?

It's an attitude compatible with any interpretation - you are just not worried by the issue of interpretation.

An interpretation is a specific view of the axioms of QM where certain things not stated (eg what is probability in the Born Rule) is spelled out. For example in MW that probability is simply lack of knowledge in a fully deterministic theory. Others have different views - eg in decoherent histories the emphasis is removed from observations and replaced by a history (defined as a series of projection operators). In that interpretation QM is the stochastic theory of histories. But it doesn't matter which one you hold to if you are a proponent of shut up and calculate you are saying it has no effect on the work I do.

One thing non-professionals who post here tend to forget is while they are VERY interested in what QM means etc, all the foundational questions and what not, most physicists don't really care. If you pin them down they will probably say some version of Copenhagen, or if they read Ballentine The Ensemble interpretation, but in their day to day work, say in condensed matter physics, it makes no difference.

Thanks
Bill

 

[Blue Scallop]

It's an attitude compatible with any interpretation - you are just not worried by the issue of interpretation.

An interpretation is a specific view of the axioms of QM where certain things not stated (eg what is probability in the Born Rule) is spelled out. For example in MW that probability is simply lack of knowledge in a fully deterministic theory. Others have different views - eg in decoherent histories the emphasis is removed from observations and replaced by a history (defined as a series of projection operators). In that interpretation QM in the stochastic theory of histories. But it doesn't matter which one you hold to if you are a proponent of shut up and calculate you are saying it has no effect on the work I do.

One thing non-professionals who post here tend to forget is while they are VERY interested in what QM means etc, all the foundational questions and what not, most physicists don't really care. If you pin them down they will probably say some version of Copenhagen, or if they read Ballentine The Ensemble interpretation, but in their day to day work, say in condensed matter physics, it makes no difference.

Thanks
Bill

So if experiments has proven say Bohmian Mechanics.. then what would happen to orthodox QM. This is what I'd like to know. Does it means Bohmian Mechanics will be a theory different from the orthodox QM.. this means we will set Bohmian Mechanics as the theory of QM and orthodox QM an incomplete theory (or somewhat like an effective field theory)? What language must we use? Also if Bohmian Mechanics is correct, then there will never be need for any interpretation because it is the QM. Right?

 

[zonde]

I'm not arguing it. I hate philosophy too when it gets nowhere. But I just want to know the semantics so I can understand others or convey to others. So is it right that (I need to know so know how to communicate with all kinds of people):

Map = Model = orthodox shut up and calculate Quantum Theory

Territories = Realities = Bohmian Mechanics, Many Worlds, etc.

So if someday BM trajectories can be observed or branches in MWI can be seen then it becomes or make the quantum theory become a different theory? but I don't understand the shift from map to territories. I mean. Is Map a theory too? Or are both Map and Territories considered as both Theories. Can you give an example where a Map or Model is a theory and example where territories or reality is a theory? This distinction is important to get the gist of it all. Please address my questions. Thanks.

All our theories, interpretations, speculations, ideas about physical reality are "maps".
"Territory" is physical reality or philosophically speaking it's our idea that there is something independent of "maps" that we can describe with our "maps" and we can benchmark our "maps" for how accurately they describe "territory".

 

[Blue Scallop]

All our theories, interpretations, speculations, ideas about physical reality are "maps".
"Territory" is physical reality or philosophically speaking it's our idea that there is something independent of "maps" that we can describe with our "maps" and we can benchmark our "maps" for how accurately they describe "territory".

Really.. do the rest of thousands of physicists believe this too that quantum intepretations are all maps? I just want to learn how to communicate with physicists in general. In the case of temperature.. is it the map and the moving particles the territory? But prior to Einstein or in the time of Newton. They just know what is the temperature. In this case.. they only know the map and not the territory? Any book or papers about the which theories are maps or territory? I just want to be well converse about the semantics of it just to communicate with others. Thanks.

 

[PeterDonis]

So if experiments has proven say Bohmian Mechanics

How would experiments confirm Bohmian Mechanics? It uses the same math and makes the same predictions as all of the other interpretations of QM. That's why they are called "interpretations" instead of "different theories". And that's why discussions of which interpretation is "right" are not discussions about physics--because such questions can't be answered by doing experiments.

 

[zonde]

Really.. do the rest of thousands of physicists believe this too that quantum intepretations are all maps?

Yes, at least majority.

Well, philosophy of science is still philosophy so it just lies out the options and scientists have to chose. But to have meaningful discussion you have to have some common basis, so they have to chose similar enough philosophies to have meaningful discussions. So currently I would say it's mostly Popper's ideas that are chosen.
From Wikipedia article about Karl Popper":
Popper argued strongly against the latter, holding that scientific theories are abstract in nature, and can be tested only indirectly, by reference to their implications. He also held that scientific theory, and human knowledge generally, is irreducibly conjectural or hypothetical, and is generated by the creative imagination to solve problems that have arisen in specific historico-cultural settings.
Logically, no number of positive outcomes at the level of experimental testing can confirm a scientific theory, but a single counterexample is logically decisive; it shows the theory, from which the implication is derived, to be false.

 

[Blue Scallop]

Yes, at least majority.

Well, philosophy of science is still philosophy so it just lies out the options and scientists have to chose. But to have meaningful discussion you have to have some common basis, so they have to chose similar enough philosophies to have meaningful discussions. So currently I would say it's mostly Popper's ideas that are chosen.
From Wikipedia article about Karl Popper":
Popper argued strongly against the latter, holding that scientific theories are abstract in nature, and can be tested only indirectly, by reference to their implications. He also held that scientific theory, and human knowledge generally, is irreducibly conjectural or hypothetical, and is generated by the creative imagination to solve problems that have arisen in specific historico-cultural settings.
Logically, no number of positive outcomes at the level of experimental testing can confirm a scientific theory, but a single counterexample is logically decisive; it shows the theory, from which the implication is derived, to be false.

In the history of science from Newtonian or even Copernicus, is there any example where the territory is known or are all our physics from the beginning all just maps? If there is a single case where the territory is known.. can you give example what it is?

 

[PeterDonis]

are all our physics from the beginning all just maps?

Yes.

 

[Kuzon]

If experiments in the future can determine say the trajectories of the bohmian particles or prove there are really different worlds where the branches exist, then it's no longer an interpretation but a theory? It's just weird that all the intepretations were tailored to match the math of QM as if constraining them to certain dynamics. But you are right that to avoid getting sinked in interpretations for a lifetime.. one must focus on the math and instead spend time to understand road to a fuly interacting non-perturbative quantum field theory.

i agree with everything you said my friend.

 

[Mario Rossi]

Guys what do you think about this: https://phys.org/news/2015-02-big-quantum-equation-universe.html ? Should I open another thread?

 

[Mario Rossi]

In the history of science from Newtonian or even Copernicus, is there any example where the territory is known or are all our physics from the beginning all just maps? If there is a single case where the territory is known.. can you give example what it is?

Are you referring to the Korzybski's "the map is not the territory"? You need to consider that both two the interpretations (thoughts) and the experiences are maps. Remember the human body is limited and need technology (map) to perceive the world (for example in QM). But the important thing is this: "A map is not the territory it represents, but, if correct, it has a similar structure to the territory, which accounts for its usefulness."

 

[OCR]

...Gonsky without going into it...

Gonski, as in Gonski Report ??... without going into it... .

 

[Blue Scallop]

by the way.. are elementary particles like electrons or quarks also maps or territory?

we used vectors or probabilities or other abstract notions to describe them at the fundamental levels or maps.. so the territory should look something like these.. is it not.. or maybe particles could still be pink elephants or output of a Matrix like programme using Zeeghaahehaaa programming language?

 

[bhobba]

Gonski, as in Gonski Report ??... without going into it... .

Yes - it's Gonski - but its just an example.

Thanks
Bill

 

[bhobba]

So if experiments has proven say Bohmian Mechanics.. then what would happen to orthodox QM.

Well first BM is deliberately cooked up to be the same as ordinary QM. So what you are talking about is a BM like theory that differs in some way from QM. In that case QM is proved wrong.

Its so simple I am having trouble even understanding what you are driving at.

The essence of science is correspondence with experiment - its not hard.

All that I can think of is you are not across that interpretations, with a few exceptions such as Primary State Diffusion, are deliberately cooked up to be indistinguishable from ordinary QM. Much of it is simply being more precise on things like probability ie is a level of confidence inside a theorists head or relative frequencies in a practically infinite sequence of the same observation as in the Ensemble Interpretation.

Thanks
Bill

 

[Blue Scallop]

Well first BM is deliberately cooked up to be the same as ordinary QM. So what you are talking about is a BM like theory that differs in some way from QM. In that case QM is proved wrong.

Its so simple I am having trouble even understanding what you are driving at.

The essence of science is correspondence with experiment - its not hard.

All that I can think of is you are not across that interpretations, with a few exceptions such as Primary State Diffusion, are deliberately cooked up to be indistinguishable from ordinary QM. Much of it is simply being more precise on things like probability ie is a level of confidence inside a theorists head or relative frequencies in a practically infinite sequence of the same observation as in the Ensemble Interpretation.

Thanks
Bill

If Primary State Diffusion was right.. is it a map or territory?

Are elemental particles like electrons map or territory?

 

[Mario Rossi]

by the way.. are elementary particles like electrons or quarks also maps or territory?

we used vectors or probabilities or other abstract notions to describe them at the fundamental levels or maps.. so the territory should look something like these.. is it not.. or maybe particles could still be pink elephants or output of a Matrix like programme using Zeeghaahehaaa programming language?

There is not a way to know the "territory", every knowledge is a map including electrons. Maybe it is an accurate map, maybe it is not.

 

[Mario Rossi]

@bhobba @PeterDonis @Lord Jestocost @phinds what do you think about this: https://phys.org/news/2015-02-big-quantum-equation-universe.html ?

 

[bhobba]

If Primary State Diffusion was right.. is it a map or territory? Are elemental particles like electrons map or territory?

Well what's a map? - define it exactly. Whats a territory? - define it exactly.

Atoms were once considered just a theory so many would say its just a map. But then the tunneling electron microscope came along so you can literally 'feel' individual atoms. Did that change atoms from a map to a territory - does it depend on technology?

Its a philosophical minefield, and since you claim to be ani-philosophy why does it worry you? Exactly what does such 'semantics' change? Nothing - precisely nothing.

Thanks
Bill

 

[bhobba]

what do you think about this: https://phys.org/news/2015-02-big-quantum-equation-universe.html ?

A new theory of the beginning of the universe - they are a dime a dozen.

We will see exactly what observation says about it over time - just like any other theory.

Thanks
Bill

 

[bhobba]

There is not a way to know the "territory", every knowledge is a map including electrons. Maybe it is an accurate map, maybe it is not.

Its a philosophical minefield. I agree with you - but what a professional philosopher would make of it - beats me - nor is it suitable for discussion here.

Why not avoid such in the first place? Surely its the easiest way of handling it. It my view anyway.

Thanks
Bill

 

[Blue Scallop]

Its a philosophical minefield. I agree with you - but what a professional philosopher would make of it - beats me - nor is it suitable for discussion here.

Why not avoid such in the first place? Surely its the easiest way of handling it. It my view anyway.

Thanks
Bill

Ok. Just want to convince myself everything is map. Electron is map. Electron could be made up of strings. Strings is map. Strings could be made up of other things.. so it's maps all the way. Therefore in physics there is no territory or ultimate ontology where there is nothing beyond it. So even if Weinberg is right the final theory is pure math, then the pure math is the map still.. and no territory.

Just want to be clear of all the arguments so beginning today it's all math I'd focus and would take me years to understand it. Thanks.

 

[stevendaryl]

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.

Right. There is a sense, as you say, that decoherence doesn't change anything, at a fundamental level. But in practice, it changes everything.

1. For practical purposes, we don't want to consider the wave function of the entire universe, but only the state of the system(s) of interest.
2. After decoherence, the system of interest can no longer be described by a pure state (wave function), but can only be described by a mixed state.
3. But a mixed state can be given an "ignorance" interpretation: The system is really in this state or that state, but we just don't know which, and the density matrix can tell us the probabilities.

So in practice, you can pretend that after decoherence happens, the wave function of the system of interest "collapses" nondeterministically into one of a number of possibilities. But there is no physical process for such a collapse--it's just an artifact of our pragmatic decision to focus on a small subsystem, rather than the entire universe.

That doesn't answer any of the fundamental questions about the interpretation of quantum mechanics, but it explains why in practice, we don't need to answer those questions.

 

[stevendaryl]

Ok. Just want to convince myself everything is map. Electron is map. Electron could be made up of strings. Strings is map. Strings could be made up of other things.. so it's maps all the way. Therefore in physics there is no territory or ultimate ontology where there is nothing beyond it. So even if Weinberg is right the final theory is pure math, then the pure math is the map still.. and no territory.

Just want to be clear of all the arguments so beginning today it's all math I'd focus and would take me years to understand it. Thanks.

Well a map is something that corresponds in a mathematically precise way to something else. Or in mathematics, the word "map" refers to the correspondence itself. So the paradigm case is a piece of paper that can be thought of as a portion of a 2-dimensional Euclidean space, and each point on the piece of paper corresponds to a point on the surface of the Earth.

It doesn't actually make sense (to me) to say that something is a map without having a second thing that it's the map of. So an electron can't be a map. If we describe the electron by a wave function, then the wave function can be a map. But not the electron.

Of course, there may be no actual electrons, because our concept of electrons might be just an approximation to what's really going. This might be nitpicky, but I don't consider one theory being an approximation to another theory to be an instance of the map/territory distinction. They are two different relationships. A road map is not an approximation to the surface of the Earth, it's a representation of it.

 

[bhobba]

Ok. Just want to convince myself everything is map. Electron is map.

If you want to look at it that way - go ahead - it's doesn't really matter.

Thanks
Bill

 

[Lord Jestocost]

After decoherence, the system of interest can no longer be described by a pure state (wave function), but can only be described by a mixed state.

That's fundamentally wrong! Please, provide a time dependent Schroedinger equation which comprises a physical process that allows to “cut” the wave function of the considered system into “real” pieces, viz. which leads to an increase in entropy and, consequently, to a physical conversion of a pure state into a mixed state.

You cannot trick quantum theory because of your feeling of what “reality ought to be”!

 

[bhobba]

You cannot trick quantum theory because of your feeling of what “reality ought to be”!

There is no trick.

Consider the entangled state 1/√2 |a>|b> + 1/√2 |b>|a>. The two systems are entangled. But now just observe system 1 - it's not in a pure state but with a little math you will find in many sources, even Susskinds Introduction to QM, shows it is in a mixed state:
https://www.amazon.com/dp/0465062903/?tag=pfamazon01-20

I have posted the slightly tedious math before but its so common there is no need eg see section 1.2.3
http://philsci-archive.pitt.edu/5439/1/Decoherence_Essay_arXiv_version.pdf

Its very very basic.

Thanks
Bill

 

[stevendaryl]

That's fundamentally wrong! Please, provide a time dependent Schroedinger equation which comprises a physical process that allows to “cut” the wave function of the considered system into “real” pieces, viz. which leads to an increase in entropy and, consequently, to a physical conversion of a pure state into a mixed state.

You cannot trick quantum theory because of your feeling of what “reality ought to be”!

I'm sorry. I don't understand what you're saying is wrong. It's just a fact that whatever you consider the system of interest, eventually, that system will interact with the rest of the universe. So you're faced with a choice: Either you have a wave function for the rest of the universe, or you somehow have to switch to a nonpure state for the description of the system of interest.

What are you disagreeing with?

 

[stevendaryl]

I'm sorry. I don't understand what you're saying is wrong. It's just a fact that whatever you consider the system of interest, eventually, that system will interact with the rest of the universe. So you're faced with a choice: Either you have a wave function for the rest of the universe, or you somehow have to switch to a nonpure state for the description of the system of interest.

What are you disagreeing with?

I'm unsure about the level at which you are disagreeing. I was assuming that you understood the mathematics of pure and mixed states. Bill Hobba explains it. If you start with a pure state for a composite system, and you perform a "trace" to eliminate the degrees of system that you are not interested in, then the result is a mixed state. There is no assumption being made that there is any nonunitary collapse going on, it's purely a mathematical transformation that is necessary to keep your focus on the system of interest, as opposed to the entire universe.

 

[stevendaryl]

He didn't talk about it in terms of decoherence, but the mathematics of how mixed states arise from pure states by considering subsystems was described in Everett's original paper on Many Worlds (which is not the name that he used---that was Bryce Dewitt).

Suppose that you have a composite system described by a wave function |\Psi\rangle = \sum_{\alpha, j} C_{\alpha, j} |\alpha\rangle |j\rangle, where |\alpha\rangle is a complete set of states for the first subsystem, and |j\rangle is a complete set of states for the second subsystem. You can think of |\alpha \rangle as describing the system of interest--maybe an electron--while |j\rangle describes everything else in the universe. Now K be some operator that only affects the first component. That means that its affect on the composite state |\alpha\rangle|j\rangle is this:

K |\alpha\rangle |j \rangle = \sum_{\alpha'} K_{\alpha' \alpha} |\alpha\rangle |j\rangle

Since operators correspond to observables, K represents an observable of the first subsystem alone. Now, let's compute the expectation value of K in the composite state |\Psi\rangle:

\langle \Psi|K|\Psi \rangle = \sum_{\alpha, \alpha', j, j'} C^*_{\alpha', j'} C_{\alpha, j} \langle \alpha' | \langle j' | K | j \rangle |\alpha\rangle
= \sum_{\alpha, \alpha', j, j'} C^*_{\alpha', j'} C_{\alpha, j} K_{\alpha' \alpha} \delta_{j j'}
= \sum_{\alpha, \alpha', j} C^*_{\alpha', j} C_{\alpha, j} K_{\alpha' \alpha}

Now, if we define \rho_{\alpha \alpha'} to be: \sum_j C^*_{\alpha', j} C_{\alpha, j}, then we have:

\langle \Psi|K|\Psi\rangle = \sum_{\alpha, \alpha'} \rho_{\alpha \alpha'} K_{\alpha' \alpha} \equiv Tr(\rho K)

So for measurements only involving the first subsystem, the density matrix \rho is all that we need for computing expectation values. It's a mixed state, in general.

 

[Mario Rossi]

And so, does God confusing us throwing dices (indeterminism)? Does an electron exists when nobody looks at it? If no, why the wave function collapses (maybe this is too difficult for me like you said, if it is, skip it)?

 

[bhobba]

There is no assumption being made that there is any nonunitary collapse going on, it's purely a mathematical transformation that is necessary to keep your focus on the system of interest, as opposed to the entire universe.

Exactly, and that is why it doesn't solve the measurement problem - it just does FAPP - but that is not the same thing.

Still progress has been made in identifying the exact problem.

Thanks
Bill

 

[PeterDonis]

what do you think about this

It's a speculative proposal in an active, ongoing area of research. Which means discussion of it doesn't belong in this subforum. It might possibly be discussible in a new thread in the Beyond the Standard Model forum, if you're careful to limit discussion to how the proposal might be tested.

 

[PeterDonis]

Just want to convince myself everything is map

Who said that? "Everything" doesn't just include our physical models; it includes the things they are models of. The models are maps. What they are models of is territory.

Part of the problem here is vagueness in ordinary language. Consider the word "electron". Does it refer to a particular theoretical model--a part of the Standard Model of particle physics? Or does it refer to the thing, whatever it is, that the theoretical model is modeling? The word is used both ways, so the question "is an electron a map or territory?" doesn't have an answer until you specify what you are referring to by the word "electron". And, of course, once you've specified that, the answer to the question is obvious.

Physics consists of our models; that's why I said all physics is maps. But those models are models of something--or at least they are intended to be. (The models don't always turn out to be accurate, so it's possible that they don't actually refer to anything--for example, back when people thought combustion was due to phlogiston, "phlogiston" was an object in the models--the map--but there was nothing in the territory corresponding to it.)

The reason the map-territory distinction is made is to make it clear that our physical models are distinct from the things they are trying to model. That let's us take a step back, so to speak, and keep ourselves from making commitments based on our models that might be too broad. For example, quantum physics is a model--a map: it can be used to make very accurate predictions about the results of experiments. But there are multiple, mutually inconsistent interpretations of QM, which amount to multiple, mutually inconsistent claims about exactly what kind of territory the map is modeling. Those claims can't be resolved by experiment (because all of the interpretations make the same predictions for all experimental results), so they are off topic for discussion here, because here we focus on claims that can be resolved by experiment.

 

[Lord Jestocost]

And so, does God confusing us throwing dices (indeterminism)? Does an electron exists when nobody looks at it? If no, why the wave function collapses (maybe this is too difficult for me like you said, if it is, skip it)?

Up to now, no serious physicist can answer these questions. Maybe, you will get various answers, depending on the respective interpretation which the responding one is adhering to (very often some implicit, unprovable assumptions are even not disclosed). Nevertheless, all interpretations of quantum theory are myths, or crutches, which should help us to form ideas and conceptions about what’s occurring at the quantum level and which might, perhaps??, help us to make experimentally provable predictions. Myths which - to my mind - centre at the end around one single question: “Which came first — the observer or the particle?” (Vanna Bonta, in "Flight: A Quantum Fiction Novel").

With respect to this, the instrumentalist’s attitude is the most honest one: The formalism of quantum theory provides nothing but calculational recipes to predict the probabilities of various directly observed macroscopic outcomes; the theory is thus about relations and correlations between – so to speak – observable spatial and temporal patterns of “clicks”; about the linkage of pointer readings with pointer readings.

 

[Mario Rossi]

“Which came first — the observer or the particle?”

Yes, this is the main answer. If we try to make an hypothesis on the "came first the observer", what can we think? The universe is prior to the observers, right? If not, so the Big Bang theory is wrong and we must search not the beginning of the universe but the beginning of the observer.

 

[Mario Rossi]

I found a theory made by Penrose and Hameroff, it's called ORCH-OR, what do you think about it?