Undergrad QM objects do not have properties until measured?

[stevendaryl]

From the discussion so far, with its emphasis on Bell's theorem, I believe we can say this:
In Bell-tests, the correlated particles in a pair may have properties like opposite charge and identical spin, but they do not have an EPR element of physical reality as a property until measured.

I don't think it makes to add the prepositional phrase "until measured". If you believe that measurement is not magic, that it's only a matter of amplifying microscopic state variables so that they become correlated with macroscopic state variables, then I don't see how anything fundamental can happen during measurement. So if objects don't have elements of reality before measurement, then they don't after measurement, either. That's the Many-Worlds way out, to allow for even macroscopic quantities to be indeterminate.

 

[N88]

I don't think it makes to add the prepositional phrase "until measured". If you believe that measurement is not magic, that it's only a matter of amplifying microscopic state variables so that they become correlated with macroscopic state variables, then I don't see how anything fundamental can happen during measurement. So if objects don't have elements of reality before measurement, then they don't after measurement, either. That's the Many-Worlds way out, to allow for even macroscopic quantities to be indeterminate.

In my terms, correcting yours: If EPRB objects don't have EPR elements of reality before measurement, they certainly do after measurement. In EPRB, the EPR elements of physical reality are spin-up or spin-down. Just two possible observables from a probable infinity of inputs. So it is not so much an amplification of microscopic variables: it is more like a modification and extrusion of them to conform to one of the two output channels of the "measuring" device.

 

[stevendaryl]

In my terms, correcting yours: If EPRB objects don't have EPR elements of reality before measurement, they certainly do after measurement.

But how can measurement accomplish this? Measurement is just a physical interaction--what makes it special is that it's an interaction that can end up changing my brain state in a definitive way.

 

[N88]

But how can measurement accomplish this? Measurement is just a physical interaction--what makes it special is that it's an interaction that can end up changing my brain state in a definitive way.

But isn't an EPRB measuring device just a preparation device followed by a detector? If I send you a beam of randomly polarised photons and you put it through a single-channel vertically-oriented polariser, you produce a beam of half the intensity but wholly vertically-polarised. Thus the preparation part of the measuring device can accomplish great change. And this is SPECIAL - a special preparation interaction - whether you add a detector (to register the change, for your brain's sake) or not.

 

[stevendaryl]

But isn't an EPRB measuring device just a preparation device followed by a detector? If I send you a beam of randomly polarised photons and you put it through a single-channel vertically-oriented polariser, you produce a beam of half the intensity but wholly vertically-polarised. Thus the preparation part of the measuring device can accomplish great change. And this is SPECIAL - a special preparation interaction - whether you add a detector (to register the change, for your brain's sake) or not.

You're talking about a specific type of measurement, but QM doesn't make such distinction. Any time you set up a situation in which two (or more) different microscopic states lead to different macroscopically distinguishable results, then you have a measurement, and the quantum (Born) probabilities apply.

 

[stevendaryl]

You're talking about a specific type of measurement, but QM doesn't make such distinction. Any time you set up a situation in which two (or more) different microscopic states lead to different macroscopically distinguishable results, then you have a measurement, and the quantum (Born) probabilities apply.

So if you have a metastable macroscopic system such that an electron with spin-up in the z-direction will perturb it into one macroscopic state (for example, a black dot on one photographic plate), and an electron with spin-down in the z-direction will perturb it into a second, distinguishable macroscopic state (for example, a black dot on a different photographic plate), then you've measured spin in the z-direction.

 

[zonde]

You're talking about a specific type of measurement, but QM doesn't make such distinction. Any time you set up a situation in which two (or more) different microscopic states lead to different macroscopically distinguishable results, then you have a measurement, and the quantum (Born) probabilities apply.

I don't get your point. When detector amplifies microscopic state quantum phase is lost and macroscopic record is produced. Before that quantum phase is there. Say, I can split coherent unpolarized photon beam with PBS then rotate polarization in one beam and perform interference measurement. And interference pattern will be there.

EDIT: It seems I made a mistake. In order to observe interference I would have to use diagonally polarized light source or alternatively I can place diagonal polarizer before detector without rotating light beam in one path.

 

[stevendaryl]

I don't get your point. When detector amplifies microscopic state quantum phase is lost and macroscopic record is produced. Before that quantum phase is there. Say, I can split coherent unpolarized photon beam with PBS then rotate polarization in one beam and perform interference measurement. And interference pattern will be there.

EDIT: It seems I made a mistake. In order to observe interference I would have to use diagonally polarized light source or alternatively I can place diagonal polarizer before detector without rotating light beam in one path.

I'm not sure I understand your point. What I'm saying is that whenever a macroscopic record is produced such that different microscopic states lead to different macroscopic records, then the producing of that record constitutes a measurement of the microscopic state. Of course, you might also consider it to be a "measurement" (although it doesn't really correspond to the usual meaning of measurement) whenever two different microscopic states become correlated with different macroscopic states, regardless of whether those macroscopic states correspond to a persistent record, or not.

But in any case, it doesn't make sense to me to say that something physically meaningful (such as "acquiring an EPR element of reality") should hinge on correlating a microscopic state to a macroscopic state.

 

[zonde]

I'm not sure I understand your point. What I'm saying is that whenever a macroscopic record is produced such that different microscopic states lead to different macroscopic records, then the producing of that record constitutes a measurement of the microscopic state.

But you don't measure polarization of photon with detector. Meaning, detector produces record "click in H channel at ..." or for another detector "click in V channel ...". But detector does not produce record "H click at ..." or "V click at ...". It's PBS that does the trick of separating "H photons" from "V photons" whatever that means.

 

[stevendaryl]

But you don't measure polarization of photon with detector. Meaning, detector produces record "click in H channel at ..." or for another detector "click in V channel ...". But detector does not produce record "H click at ..." or "V click at ...". It's PBS that does the trick of separating "H photons" from "V photons" whatever that means.

I'm not sure what point you're making. I'm saying "Doing X constitutes a measurement of microscopic observable x". You seem to be saying: "I'm not doing X, I'm doing something different." Well, then I'm not talking about that case. I'm talking about the case in which you have a setup in which a microscopic observable x is amplified to make a macroscopic record X.

 

[Jilang]

Would it be correct to say that it is not the act of the measurement that does anything special, but the application of the magnetic field just before it that causes the quantisation of the spin in a given direction in a Stern Gerlach type experiment?

 

[AlexCaledin]

But, if I got it right, according to R. Penrose and H. Stapp, the physicist's decision to apply a certain magnetic field also is an outcome of a measurement - the physicist's consciousness measures his brain's state, thus making the choice of action. So it all seems to work according to Feynman saying about the great "chess game" of Nature - the quantum potentiality is the "chessboard" and measurements are "moves" creating actual properties and forming (reducing) the superposition of potential ones.

 

[bhobba]

But, if I got it right, according to R. Penrose and H. Stapp, the physicist's decision to apply a certain magnetic field also is an outcome of a measurement

Well I won't be nice about it and say be careful with populist stuff or something along those lines - its rubbish. Added later: Rereading it I was not 100% clear about the issue. The decision the experimenter makes is irrelevant to anything and obviously so. It could be made by a computer or simply the result of some normal process like dust particles interacting with stray photons from the CBMR. All are 'measurements', 'observations' etc etc.

You have been posting here long enough to know this consciousnesses stuff is very very fringe and most definitely not mainstream.

I need to be clear though - its a valid view - just one most reject as - well - silly - like most reject solipsism.

Thanks
Bill

 

[bhobba]

Would it be correct to say that it is not the act of the measurement that does anything special, but the application of the magnetic field just before it that causes the quantisation of the spin in a given direction in a Stern Gerlach type experiment?

No.

Whats going on is interpretation dependent.

Specify an interpretation then we can discuss questions like that.

Thanks
Bill

 

[Jilang]

No.

Whats going in is interpretation dependent.

Specify an interpretation then we can discuss questions like that.

Thanks
Bill

Isn't what I posted an interpretation?

 

[secur]

this consciousnesses stuff is very very fringe and most definitely not mainstream.
I need to be clear though - its a valid view - just one most reject as - well - silly

Irrefutable logic: this is how science makes progress! But since I'm not a QM master, it's hard to understand this difficult math. Perhaps if you could help me on one step, I can figure out the rest myself in a week or so. How do I formally write down the covariant derivative of "silly"?

 

[bhobba]

Isn't what I posted an interpretation?

No. An interpretation is something like Bohmian Mechanics, Many Worlds or Ignorance Ensemble.

Specify something like that and we can discuss it.

Thanks
Bill

 

[rootone]

How do I formally write down the covariant derivative of "silly"?

ʎllᴉs

 

[Dale]

Closed pending moderation

Edit: after discussion with the mentors we will leave the thread closed.