Decoherence relationship to the measurement problem

[subquantumboy]

Everyone does not know that because its simply not true.

Collapse, if it occurs at all, is very interpretation dependent.

Only very backwater interpretations, held by a small minority these days, have anything to do with observers.

The most common interpretations, Copenhagen and Ensemble, have no role for observers - only for observations. Confusing the two is a common semantic fallacy made by beginning students or those influenced by populist accounts.

Thanks
Bill

No. It's true. That's self-evident. Observing depends on observers. So observers are the key. Copenhagen or Ensemble doesn't make sense. I disagree.

 

[bhobba]

Do you professionals, or advanced academics, still view the elementary particle as a "solid" piece of something... anything? Or is it really more about the information?

Its viewed in whatever way that's consistent with experimental evidence and is convenient at the time. In the photoelectric effect its convenient to view a photon as a particle is the commonsense way. In the double slit experiment its viewed as a wave. In QED it's viewed as the excitations of a field. Theory shows, in each of those circumstances it is valid, which is all that really matters.

Most physicists do not really give a hoot about such questions - that's really a philosophers game.

Its perfectly understandable that people just starting out in coming to grips with QM ask questions like that, but after you have been exposed to it for a while you understand its a dead end.

Its similar to applying probability in everyday life. Most people don't give much thought to exactly what underlying process is responsible for a coin landing heads or tales, or the weather that will occur tomorrow etc etc. They simply use it. The twist QM adds, is in those cases if you investigate it carefully enough you can understand the underlying process, but in QM that has turned out to be not possible (at least no one has been able to figure out how to do it) - so you just accept it.

Thanks
Bill.

 

[bhobba]

No. It's true. That's self-evident. Observing depends on observers. So observers are the key. Copenhagen or Ensemble doesn't make sense. I disagree.

Mate - before you can argue QM you must understand QM.

Everything I said is from standard textbooks such as Ballentine - Quantum Mechanics - A Modern Development:
https://www.amazon.com/dp/9810241054/?tag=pfamazon01-20

See Chapter 9 - Measurements And Interpretations Of States.

You may not agree with Copenhagen or Ensemble but saying it doesn't make sense is simply exposing your ignorance. The reason is both are simply the formalism with a slightly different take on the role of the state - Copenhagen is more like the Bayesian view of probability, Ensemble is more like the frequentest view. So if they do not make sense QM doesn't really make sense.

But just in case you have spotted some Earth shattering issue the innumerable people that have been exposed to it haven't, mind explaining exactly in what way they do not make sense?

My suspicion is you have not been exposed to the professional literature like the textbook above where the meaning of observation in the sense its used in QM is explained carefully, even some beginning textbooks don't do that, and certainly populist books do not. Its technical meaning is not the usual everyday meaning, which is often a cause of confusion.

Thanks
Bill

 

[WannabeNewton]

Do you professionals, or advanced academics, still view the elementary particle as a "solid" piece of something... anything?

It depends on the context. Fundamentally no they don't because particles are just quanta of fields i.e. photons-EM field and electrons-Dirac field etc. but for various problems yes without a doubt they do. Simple examples wherein the semi-classical picture is useful are relativistic conservation of 4-momentum problems deriving from scatterings and decays.

 

[Feeble Wonk]

Its viewed in whatever way that's consistent with experimental evidence and is convenient at the time. In the photoelectric effect its convenient to view a photon as a particle is the commonsense way. In the double slit experiment its viewed as a wave. In QED it viewed as the excitations of a field. Theory shows, in each of those circumstances it is valid, which is all that really matters.
Most physicists do not really give a hoot about such questions - that's really a philosophers game.
Thanks

Bill.

Of course this is how you would address the nature of the fundamental particle functionally, as a working physicist... because that allows you to make the calculations, and that perspective has resulted in incredible advancements in scientific understanding. But in your more meditative moments, do you really not ponder about this kind of question?

 

[bhobba]

do you really not ponder about this kind of question?

Sure - that's why you come to realize its a dead end.

I think you can see that is philosophy which is an off topic here, but I ask you to consider exactly what philosophers agree on, to me they just seem to go around in circles with endless word games. All physicists however agree on the formalism of QM.

And when you understand it you realize that at its root it is something conceptually quite simple:
http://www.scottaaronson.com/democritus/lec9.html

But each person must come to grips with that one themselves.

Thanks
Bill

 

[Feeble Wonk]

Sure - that's why you come to realize its a dead end.

Fair enough. According to Feynman, "That way madness lies". I was just curious.

 

[bhobba]

Fair enough. According to Feynman, "That way madness lies". I was just curious.

Madness doesn't really lie that way.

It's simply until you can figure out an answer, and it is experimentally verifiable, and such experiments have been done, its a useless endeavor.

Occasionally, some genius like Bell, figures out exactly how to do that, and a bit more light is shined on the issue.

But the fact it only happens occasionally attests to how hard it really is.

Thanks
Bill

 

[Feeble Wonk]

I'd avoid thinking of them as 'solid' since they frequently pass through each other without interacting. 'Information' seems to imply something abstract and devoid of a physical form.

I understand your hesitation with the "information" description. But in the absence of "solidity" even at the fundamental particle level, what image would you consider less abstract, or possessing a more "real" physical form. Non-solid analogies of liquid, gas or plasma don't work, because they are obviously just different phases of the "solid" particles. What physical form does a field fluctuation have? The field is a mathematical construct. So is the quantum wave form. Yes, the "particle" sometimes behaves in a seemingly solid manner, but that's just a description of it's behavior... not it's substance. Why shouldn't we think of the information content of the "particle", field or wave as being the essence of physical form that is "real". I know that this isn't an overly constructive line of discussion Bill, but I can't help myself.

 

[bhobba]

Why shouldn't we think of the information content of the "particle", field or wave as being the essence of physical form that is "real". I know that this isn't an overly constructive line of discussion Bill, but I can't help myself.

Well it depends on what is thought as real.

The particle state, mathematically, is like probabilities, and most would say probabilities are not 'real'.

Classical fields however are a different matter. You have probably seen definitions of fields like an electric field is defined by the force experienced by a charge. In that sense you may think it too is simply something that's introduced for convenience.

Actually it isn't. Classical fields are necessary so that momentum and energy are conserved - if they were not real in some sense then such conservation laws would not be possible - and there are very deep reasons associated with symmetry (look into Noethers Theorem) why it is believed such are true.

Physicists are not driven to these ideas without reason.

Thanks
Bill

 

[bhobba]

But in the absence of "solidity" even at the fundamental particle level, what image would you consider less abstract,

Oh - another point.

The everyday solidity of objects is actually a quantum effect from Pauli's exclusion principle:
http://cornellmath.wordpress.com/2007/08/08/why-stuff-is-hard/

But exactly how it does that is not particularly simple. Freeman Dyson was the first to figure it out in a famous paper in 1965.

Solidity at the atomic level is much much more nebulous.

Thanks
Bill

 

[craigi]

I understand your hesitation with the "information" description. But in the absence of "solidity" even at the fundamental particle level, what image would you consider less abstract, or possessing a more "real" physical form. Non-solid analogies of liquid, gas or plasma don't work, because they are obviously just different phases of the "solid" particles. What physical form does a field fluctuation have? The field is a mathematical construct. So is the quantum wave form. Yes, the "particle" sometimes behaves in a seemingly solid manner, but that's just a description of it's behavior... not it's substance. Why shouldn't we think of the information content of the "particle", field or wave as being the essence of physical form that is "real". I know that this isn't an overly constructive line of discussion Bill, but I can't help myself.

The problem is that you're asking for a depiction of something that has very peculiar properties in time and space. If you follow through an introductory QM course this will become apparent to you.

To give you an analogy: if I give you a pen and paper, could you draw the complete spectrum of human emotion? How would you go about it? Maybe you'd draw a heart or an angry face. It might be an abstract represention of an aspect of what you're trying to draw, but it's just not possible to depict it in its entirety. You don't have the necessary medium. That's the same problem with depicting quantum mechanical objects. You'd be using the classical world to try to represent something that is non-classical.

 

[atyy]

Thanks atyy. I haven't been able to find Wallace's book yet that you recommended.

Wallace's home page http://users.ox.ac.uk/~mert0130/index.shtml links to a short essay which summarizes his recent views on many-worlds: http://philsci-archive.pitt.edu/8888/1/Wallace_chapter_in_Oxford_Handbook.pdf.

 

[Feeble Wonk]

"My suspicion is you have not been exposed to the professional literature like the textbook above where the meaning of observation in the sense its used in QM is explained carefully, even some beginning textbooks don't do that, and certainly populist books do not. Its technical meaning is not the usual everyday meaning, which is often a cause of confusion."

It's been a long time Bill, but I'm still rolling this thread around in my head trying to come to grips with it. And I think your comment that I pasted above might be at the crux of my confusion.
Would you please try to explain to me what the "formal" definition of observation/measurement is with regard to QM, and how that differs from the customary usage. If I fully understand that, maybe the rest will come into focus better.

 

[Feeble Wonk]

My suspicion is you have not been exposed to the professional literature like the textbook above where the meaning of observation in the sense its used in QM is explained carefully, even some beginning textbooks don't do that, and certainly populist books do not. Its technical meaning is not the usual everyday meaning, which is often a cause of confusion.

Thanks
Bill

 

[bhobba]

"Would you please try to explain to me what the "formal" definition of observation/measurement is with regard to QM, and how that differs from the customary usage. If I fully understand that, maybe the rest will come into focus better.

The formal definition unfortunately requires exposure to technical aspects of QM. Its when decoherence has reduced interference terms way below detectability and you have an improper mixed state.

You need to build up to it.

I suggest starting with Susskind:
https://www.amazon.com/dp/0465036678/?tag=pfamazon01-20

The customary one is some variant of everyday observation where somebody observes something. In QM it requires no conscious observer. Its assumed to exist in a classical common-sense world.

The problem is that you're asking for a depiction of something that has very peculiar properties in time and space. If you follow through an introductory QM course this will become apparent to you.

Now a question for you - what actual professional literature have you consulted to try and sort this out?

Thanks
Bill

 

[Feeble Wonk]

Thanks Bill... I'll check out your Susskind reference. Was the last question for me or Craigi?

 

[bhobba]

Thanks Bill... I'll check out your Susskind reference. Was the last question for me or Craigi?

It was for you.

But its not an issue now because you will be reading Susskind.

The reason I asked it is people here go to a lot of trouble answering questions and recommending things to read. I just like to know those on the other side make use of it.

Thanks
Bill

 

[Feeble Wonk]

I've got Susskind's book ordered. Looking forward to it. I'm almost afraid to ask, but how mathematically challenging is it. My skills in that arena are worse than pitiful.

 

[Feeble Wonk]

...and for whatever it's worth, I recognize and very much appreciate the time and effort you and the other physics forum contributors provide. I think I've told you in the past that I'm not a physicist. Biology is my field. But the concepts I'm struggling with at present require guidance and insight by real physicists. I'm trying very hard not to be dependent on material in various pseudoscience types of publications. So, thank you.

 

[bhobba]

I've got Susskind's book ordered. Looking forward to it. I'm almost afraid to ask, but how mathematically challenging is it. My skills in that arena are worse than pitiful.

It requires a smattering of calculus.

Thanks
Bill