Justification for no properties before measurement

[vanhees71]

I didn't know that Heisenberg was that "philosophical"... Sigh.

 

[A. Neumaier]

I didn't know that Heisenberg was that "philosophical"... Sigh.

You should read his book ''Der Teil und das Ganze''!
https://scholar.google.at/scholar?cluster=9928574072894946072

 

[atyy]

No, how? But it's not a big deal. I just thought you might not know the definition of "simplex", so I pointed it out.

Aren't these the same?

"the state space of quantum mechanics is not a simplex" = "the space of quantum states is not an n-simplex for any n."

I think the most common simplex that is not a simplex is the "simplex algorithm" (or at least I've never known why it's called that).

 

[vanhees71]

You should read his book ''Der Teil und das Ganze''!
https://scholar.google.at/scholar?cluster=9928574072894946072

I remember that I've read this book when I was at high school, but it didn't appeal too much to me at that time. Perhaps, I should indeed read it again.

 

[bhobba]

I didn't know that Heisenberg was that "philosophical"... Sigh.

Unfortunately he was - worse than Bohr even who actually wasn't too bad. The worst was the person you would least expect - Pauli - he was bad - really bad - just behind Wigner and Von-Neumann.

For me the only really sane one was Dirac - but he had other issues of a non-scientific nature.

Thanks
Bill

 

[bhobba]

I remember that I've read this book when I was at high school, but it didn't appeal too much to me at that time. Perhaps, I should indeed read it again.

Interesting to hear your reaction - especially the section with the philosopher Greta Herman (who actually was good enough to pick up the error Von-Neumann made in his no hidden variables proof) and the 'wonderful' discussion about what Kant would have thought of QM . It has a whole chapter, chapter 10 - Quantum Mechanics And Kantian Plilosophy - I am sure you will love it .

Basically most of the founders, could at least in part, be described as a mob of mystics - see attached.

Thanks
Bill

 

[A. Neumaier]

most of the founders, could at least in part, be described as a mob of mystics

The deeper reason for this is that in a situation where the right concepts are lacking and one has to grope in the dark, one needs a strong philosophical bend to make progress. All scientific subjects were rooted in philosophy before they matured to a science, and quantum mechanics is no exception.

The philosophy-free position of @vanhees71 is possible only since the subject has matured such a lot since its inception. Except for the measurement problem, where most of the discussion is still on the level of the dark ages.

 

[microsansfil]

In the quantum theory, however, the situation is completely different. The very fact that the formalism of quantum mechanics cannot be interpreted as visual description of a phenomenon occurring in space and time shows that quantum mechanics is in no way concerned with the objective determination of space-time phenomena." [Bold, LJ]
Werner Heisenberg in “The development of quantum mechanics”

it's surprising from Werner Heisenberg. I didn't know he had a philosophical position based on naïve realism. If you don't give a visual description of a space-time phenomenon (vawe, corpuscle, trajectory, ..., from our first-person experience) this shows that the description is in no way concerned with the "objective" (inter-subjective) determination of space-time phenomena !

Best regards
Patrick

 

[dextercioby]

Perhaps W.Heisenberg was simpy trying to advocate the removal of the observer from the foundations of the theory, much like this is absent from any formulation of classical mechanics, or perhaps this is only what I want W.Heisenberg to mean by his quoted words.

 

[bhobba]

The philosophy-free position of @vanhees71 is possible only since the subject has matured such a lot since its inception.

Yes. When something genuinely mystifying turns up one does find philosophy more prominent. Von-Neumann was no mystic - yet was the promulgator of consciousnesses causes collapse in his famous textbook.

Except for the measurement problem, where most of the discussion is still on the level of the dark ages.

Oh dear - do tell

Of course. What do you say to someone like Penrose - if he gets caught up in it anyone is vulnerable.

Thanks
Bill

 

[vanhees71]

The deeper reason for this is that in a situation where the right concepts are lacking and one has to grope in the dark, one needs a strong philosophical bend to make progress. All scientific subjects were rooted in philosophy before they matured to a science, and quantum mechanics is no exception.

The philosophy-free position of @vanhees71 is possible only since the subject has matured such a lot since its inception. Except for the measurement problem, where most of the discussion is still on the level of the dark ages.

Obviously there is no measurement problem, because theory and experiment agree to high accuracy, which means nothing less than that on the one hand the experimentalists can observe what's predicted by QT, i.e., the theory provides precise enough ideas for how to prepare and observe the phenomena it predicts and on the other hand theorists are able to use the theory to make such predictions and describe (hitherto all!) observations with the theory.

So what's "the measurement problem"?

 

[vanhees71]

Interesting to hear your reaction - especially the section with the philosopher Greta Herman (who actually was good enough to pick up the error Von-Neumann made in his no hidden variables proof) and the 'wonderful' discussion about what Kant would have thought of QM . It has a whole chapter, chapter 10 - Quantum Mechanics And Kantian Plilosophy - I am sure you will love it .

Basically most of the founders, could at least in part, be described as a mob of mystics - see attached.

Thanks
Bill

I've to look for the book in some corner of my bookshelf first, but Kant did already invent QT (according to a philsophy professor, whose lectures on Kant I've heard, because I wanted to fulfill the recommendation to listen to at least one philosophy lecture during my studies; fortunately there was no exam on it;-)), as die Lenin (read the appendix of Blokhintzev's QM textbook).

 

[vanhees71]

Perhaps W.Heisenberg was simpy trying to advocate the removal of the observer from the foundations of the theory, much like this is absent from any formulation of classical mechanics, or perhaps this is only what I want W.Heisenberg to mean by his quoted words.

It's not absent from classical theory. Already writing done $m \vec{a}=\vec{F}$ involves an observer, who prepares a reference frame and a clock, defining $\vec{x}(t)$ which is the basis for the whole mathematics of Newtonian mechanics condensed in this formula!

 

[SemM]

Basically most of the founders, could at least in part, be described as a mob of mystics - see attached.

Thanks
Bill

hahah!

 

[vanhees71]

Unfortunately he was - worse than Bohr even who actually wasn't too bad. The worst was the person you would least expect - Pauli - he was bad - really bad - just behind Wigner and Von-Neumann.

For me the only really sane one was Dirac - but he had other issues of a non-scientific nature.

Thanks
Bill

Well, Pauli was a great mystic, but he could keep it out of his scientific writings, which are always very clear and very similar to Sommerfeld's style, whose scientific pupil Pauli was. He was not only a follower of philosophical but, even worse, also psychological mysticism. I like Einstein more, who, after some conversation with Freud said, that he prefers to stay "unanalyzed". Pauli was a great "fan" of C.G. Jung.

Dirac was also very unmystical in his scientific writings. He had a pretty bad childhood due to his tyrranic father (see Farmelo's biography "The Strangest Man").

 

[SemM]

Dirac was also very unmystical in his scientific writings. He had a pretty bad childhood due to his tyrranic father (see Farmelo's biography "The Strangest Man").

Even Bohm had tendencies to Mysticism, but he also kept it out of science, and wrote an excellent book "Quantum Theory"

 

[vanhees71]

True, for me the most important original contribution to QM by Bohm is his work on the Aharonov-Bohm effect...

 

[A. Neumaier]

what's "the measurement problem"?

To define the meaning of ''measurement'' in a clean enough way that Born's rule becomes more than a heuristic principle, and the nearly hundred year old discussion comes to an end.

Kant did already invent QT

I only know that Thomas Aquina first discussed the Pauli exclusion principle.

 

[stevendaryl]

It's not absent from classical theory. Already writing done $m \vec{a}=\vec{F}$ involves an observer, who prepares a reference frame and a clock, defining $\vec{x}(t)$ which is the basis for the whole mathematics of Newtonian mechanics condensed in this formula!

I disagree with that completely. Classical mechanics (and by that, I mean non-quantum---I would include Special and General Relativity) give no special role to observers. Classical mechanics describes how particles and fields behave, given boundary conditions and initial conditions. Yes, you need an observer to know what the initial conditions are, and you need observers to discover what the forces are. But particles and fields don't require people to KNOW how they behave in order to do what they do. In classical mechanics, observers are just complex systems made up of the same particles and fields that everything else is. They play no role in the formulation of the laws of physics.

 

[stevendaryl]

I disagree with that completely. Classical mechanics (and by that, I mean non-quantum---I would include Special and General Relativity) give no special role to observers. Classical mechanics describes how particles and fields behave, given boundary conditions and initial conditions. Yes, you need an observer to know what the initial conditions are, and you need observers to discover what the forces are. But particles and fields don't require people to KNOW how they behave in order to do what they do. In classical mechanics, observers are just complex systems made up of the same particles and fields that everything else is. They play no role in the formulation of the laws of physics.

There is a distinction (in classical mechanics, anyway) between what is true and what we know. Observers and observations and measurements and so forth are certainly needed to know anything. But the universe doesn't care what we know. (Classically, anyway).

 

[Fra]

But particles and fields don't require people to KNOW how they behave in order to do what they do. In classical mechanics, observers are just complex systems made up of the same particles and fields that everything else is. They play no role in the formulation of the laws of physics.

In QM its the classical measurement device that "knows" and this is the key.

What the humans in the lab know doesn't matter. You are trying to bring back mysticism here.

In a very superficial way sure its the physicisy that invent or discover tha laws. But this superficial view holds also in classical mechanics.

/Fredrik

 

[Fra]

To define the meaning of ''measurement'' in a clean enough way that Born's rule becomes more than a heuristic principle, and the nearly hundred year old discussion comes to an end.

I think of the measurement problem as to unify the external an internal observer views of interactions.

The inside view is an information update. But consistency requires that in the small subsystem limit an external observer must be able to explain this process as an ordinary expected evolution.

This woulf have to restore the consistent coexistences of the evolving inside view with the timeless deductive causation that we see in the limit of a small subsystem observed by a classical dominant environment and I see two general strategies for this.

/Fredrik

 

[vanhees71]

There is a distinction (in classical mechanics, anyway) between what is true and what we know. Observers and observations and measurements and so forth are certainly needed to know anything. But the universe doesn't care what we know. (Classically, anyway).

The universe doesn't care about what we know also quantum theoretically, and I still think that physics is an empirical science, and to be able to write down mathematical formulae that have a meaning in the sense of physics you need an operational definition of the quantities you describe, and that implicitly uses the idea of observers who measure something, no matter whether you have a classical theory (no matter whether relativistic or non-relativistic) or QT in mind.

 

[vanhees71]

To define the meaning of ''measurement'' in a clean enough way that Born's rule becomes more than a heuristic principle, and the nearly hundred year old discussion comes to an end.

The meaning of measurement is defined what experimentalists do in their labs. Why you call Born's rule "heuristic" is not clear to me either since it clearly gives a probabilistic meaning of the state, and probabilities are measured via observations on ensembles and statistical analysis. Then, if you call Born's rule "heuristic", you'd also call the statistical meaning of probabilities (in this frequentist sense) "heuristic". If so, fine, because obviously the "heuristics" works with an amazing accuracy.

Concerning Thomas Aquina, I'd say he simply takes "angels" as being "usual matter" or "substance", and there it's empirically clear that two bodies cannot occupy the same space. Today we attribute this to the Pauli principle, but how one can conclude Thomas may have used the Pauli principle, is an enigma. He simply used everyday experience about matter.

 

[A. Neumaier]

In QM its the classical measurement device that "knows" and this is the key.

How does in classical mechanics a measurement device made up of many particles subject to the classical laws know the exact position of a particle whose position it is supposed to measure?

In classical mechanics, the measurement process is as ill-defined conceptually as in quantum mechanics. In both cases, an informal working definition exists in the head of experimenters and in calibration procedures, but not in a way that would be amenable to mathematical analysis, and hence to answer without doubt any questions about the meaning of a measurement.

 

[A. Neumaier]

Why you call Born's rule "heuristic" is not clear to me either

Well, this is because I have a philosophical bent and you don't. You sweep under the carpet of ''operational definition'' what for me is something to be clarified theoretically.

Then, if you call Born's rule "heuristic", you'd also call the statistical meaning of probabilities (in this frequentist sense) "heuristic".

I call everything heuristic that contains mathematically undefined terms. Born's rule contains the mathematically undefined term ''measurement'' that plays no role in the quantum formalism, hence is heuristic only, and with it Born's rule.

I have no difficulty with the formal Born rule that calls the modulus squared of a wave function a probability density. This is just mathematics. The heuristic comes in when it relates this probability to ''finding the particle on some region'', which is a theoretically undefined notion.

 

[vanhees71]

How can it be undefined? Experimentalists measure positions of subatomic particles in various ways. In Born's time by using a photoplate or scintillation screen, today some electronic detector. It's defined by the concrete setup in the lab, and that it matches with the mathematical definition of position in the theory is an empirical finding. How else do you want to justify that the theoretical and empirical notion of a quantity matches?

 

[A. Neumaier]

How can it be undefined? Experimentalists measure positions of subatomic particles in various ways. In Born's time by using a photoplate or scintillation screen, today some electronic detector. It's defined by the concrete setup in the lab, and that it matches with the mathematical definition of position in the theory is an empirical finding. How else do you want to justify that the theoretical and empirical notion of a quantity matches?

A very high precision position measurement is based on a lot of theory that goes into the construction of the measurement device and the calibration procedure. The theoretical analysis is the one that tells that the device actually measures the position. Thus everything about experimental measurement is actually encoded into the theoretical physics of the measurement device.

But Born's rule is device independent, relying on an undefined notion of measurement, that always delivers infinitely precise results - which is experimental nonsense.

 

[vanhees71]

I complete agree with your first paragraph, which contradicts the second one. Born's rule predicts probabilities, and you cannot get probabilities by measuring on an esemble but probabilities with some statistical (in practice also systematic) error, but Born's rule relies not on an undefined notion of measurement but on a well-defined notion of measurement as you explain yourself in the 1st paragraph. It's clear that theory and experiment are both needed to define the meaning of the mathematical theory. Pure math has no such meaning but is an invention of pure thought. This is the distinction between pure math and a physical theory which uses math as a language.

 

[SemM]

How does in classical mechanics a measurement device made up of many particles subject to the classical laws know the exact position of a particle whose position it is supposed to measure?

And how does, in quantum physics, a measurement device subject to the observer's choice? Never really. Only in time and place, but the result would still be the same, considering the same experiment.