What is the current perspective on quantum interpretation?

[Lord Jestocost]

Trying to play philosophical games about reality rewriting itself once you "consciously" are aware of it.. that is sensationalism, not science. Quantum processes occurred in the universe countless times over billions of years before human consciousness existed, and they are occurring and "resolving" in over billions and billions of light years (cubed) of space and in billions and billions of galaxies through out the vast cosmos without a need for any consciousness to collapse anything.

Simple declarations make no sense. One should, as John von Neumann has done, merely rely on the unambiguous mathematics constituting quantum theory. The quantum mechanical time evolution is valid for all "physical systems". That's the reason why all “quantum processes” finally boil down - in mathematical language - to something like a purely quantum-mechanical von Neumann measurement chain when physical systems are interacting which each other.

And what happens at the end of such a purely quantum-mechanical von Neumann measurement chain? In case the “observer” is regarded as a “pure physical system”, mathematics is unambiguous: Nothing happens; the “purely physical observer” is simply part of the purely quantum-mechanical von Neumann measurement chain and entangles with the system the state of which is to be measured! The system is sucked into a vortex of entanglement and no longer has its own quantum state. On top of that, the entangled state fails to indicate any particular measurement outcome.

 

[EPR]

With the risk of being banned, the formalism of QM does not provide an explanation for single outcomes. The ones observed at the classical scales. No matter how you turn it, philosophy must enter to explain this missing bit. You can sideline it as minor detail or try to delve deeper(if such knowledge is even possible or obtainable).

 

[PeterDonis]

the formalism of QM does not provide an explanation for single outcomes

In fact, the formalism does not even require single outcomes, since at least one interpretation, the MWI, does not have single outcomes.

 

[EPR]

Indeed. The MWI is philosophy

 

[PeterDonis]

The MWI is philosophy

To the extent that any interpretation of QM is philosophy, yes.

 

[vanhees71]

What in classical mechanics says that there are "single outcomes"? That's all empty philosophical gibberish (I know I'm provocative here ;-)).

Physics is an empirical science and all our theories provide just descriptions of observed facts, and one observed fact is that we are able to construct measurement devices to measure various observables, which always give a well-defined "reading" for the measured observable.

Classical physics is a very much coarse grained description of the underlying quantum dynamics and there often the randomness of all kinds of fluctuations (particularly quantum fluctuations but also "thermal fluctuations" etc.) are simply neglected, because they are not resolved in the coarse-graining procedure. Before we were able to measure much more accurately we had only such coarse-grained observables and thus came to the wrong conclusion that (a) observables have always determined values and (b) that we can measure these observables without considerable influence on the measured system.

Famously (thermal) fluctuations came into the point of view by Einstein's seminal work on classical statistical physics, where he not only rediscovered much older results by Maxwell, Boltzmann, and Gibbs (many of which he was not aware of, because he didn't bother to read all the literature of a subject he was thinking about for himself) but also considered the said fluctuations, finally leading to convincing evidence for the "reality" of the "atomistic structure" of matter which was not commonly accepted among physicists (while for chemists it was pretty much obvious).

Finally more and more evidence lead to the discovery of quantum theory and thus forced the physicists to accept that the above mentioned conclusions (a) and (b) from "macroscopic" evidence and theorizing, is fundamentally wrong, i.e., that there is inherent randomness in Nature, i.e., that there is no state of any system where, all its observables take determined values, and even the preparation state of the system in a quantum theoretical pure state (which is the most complete possible preparation of the system) does thus not imply the determination of values of all observables. That's all what QT says and that's all that is observed in all measurements done today. There's no need for "philosophy" and esoterics or fancy interpretations of the quantum-theoretical mathematical formalism. All you need is simply to accept that the natural sciences are an endeavor enabling us to learn how Nature really behaves as it can be observed by us, and this can lead to tremendous corrections of older worldviews as is deterministic classical physical theories, which turn out to be approximations of the more detailed description provided by quantum theory.

Maybe one day, we'll find discrepancies between observed objective facts and quantum theory too. Then we'll have to find a new more comprehensive theory to describe it. It's obvious that we need something like this, because we have no satisfactory description of the gravitational interaction, i.e., no quantum formulation of General Relativity yet.

The claimed "interpretational problems" philosophers seem still to have with quantum (field) theory are just philosophical but no physical problem though, at least not given the known empirical objective facts we have today.

 

[PeterDonis]

What in classical mechanics says that there are "single outcomes"?

Classical mechanics doesn't really have a concept of "outcomes" as distinct from the state of the system, the way QM has a distinction between measurement outcomes and the wave function. In classical mechanics, the state of the system just is the "outcomes".

 

[stevendaryl]

What in classical mechanics says that there are "single outcomes"? That's all empty philosophical gibberish (I know I'm provocative here ;-)).

Yes. All philosophical positions other than yours are gibberish. But your position is considered gibberish by others, as well.

 

[gentzen]

Einstein's seminal work on classical statistical physics, where he not only rediscovered much older results by Maxwell, Boltzmann, and Gibbs (many of which he was not aware of, because he didn't bother to read all the literature of a subject he was thinking about for himself)

Do you have evidence for that claim with respect to Boltzmann? And do you have evidence that this was really intentional from his side with respect to Maxwell and Gibbs, and not just explained by language barrier and availability?

 

[Lord Jestocost]

@vanhees71

The fundamental and essential question quantum theory has risen is simple. As Harald Atmanspacher formulates it in “Determinism Is Ontic, Determinability Is Epistemic”:

“Can nature be observed and described as it is in itself independent of those who observe and describe – that is to say, nature as it is ‘when nobody looks’? This question has been debated throughout the history of philosophy with no clearly decided answer one way or the other. Each perspective has strengths and weaknesses, and each epoch has had its critics and proponents with respect to these perspectives.”

I don’t think that such debates were or are merely philosophical gibberish.

 

[ShayanJ]

Finally more and more evidence lead to the discovery of quantum theory and thus forced the physicists to accept that the above mentioned conclusions (a) and (b) from "macroscopic" evidence and theorizing, is fundamentally wrong, i.e., that there is inherent randomness in Nature, i.e., that there is no state of any system where, all its observables take determined values, and even the preparation state of the system in a quantum theoretical pure state (which is the most complete possible preparation of the system) does thus not imply the determination of values of all observables. That's all what QT says and that's all that is observed in all measurements done today. There's no need for "philosophy" and esoterics or fancy interpretations of the quantum-theoretical mathematical formalism. All you need is simply to accept that the natural sciences are an endeavor enabling us to learn how Nature really behaves as it can be observed by us, and this can lead to tremendous corrections of older worldviews as is deterministic classical physical theories, which turn out to be approximations of the more detailed description provided by quantum theory.

You're pretending that anyone who is interested in interpretations of quantum mechanics is someone who was just too comfortable with classical physics and now doesn't want to let go of that comfort. But that's not true! Only hidden variable interpretations are trying to get quantum physics as close to classical physics as they can but other interpretations are driven by different motivations that is answering actual questions.

You're also pretending there is nothing more to understand about quantum mechanics. But I should remind you that its actually these kinds of questions that led to a clear understanding of decoherence which is a very important part of quantum physics. And I think it proves that although you may not see anything "physical" in arguments about interpretations of QM right now, it doesn't mean that they won't lead to a profound discovery in physics.

 

[vanhees71]

Yes. All philosophical positions other than yours are gibberish. But your position is considered gibberish by others, as well.

Fine with me, but it's at least physics not philosophy ;-)).

 

[vanhees71]

You're pretending that anyone who is interested in interpretations of quantum mechanics is someone who was just too comfortable with classical physics and now doesn't want to let go of that comfort. But that's not true! Only hidden variable interpretations are trying to get quantum physics as close to classical physics as they can but other interpretations are driven by different motivations that is answering actual questions.

You're also pretending there is nothing more to understand about quantum mechanics. But I should remind you that its actually these kinds of questions that led to a clear understanding of decoherence which is a very important part of quantum physics. And I think it proves that although you may not see anything "physical" in arguments about interpretations of QM right now, it doesn't mean that they won't lead to a profound discovery in physics.

In my opinion the interpretational problems are solved with Bell's work and the empirical facts from experiments all of which with high precision excludes local deterministic hidden-variable models in the sense defined by bell and confirm the predictions of quantum theory.

It's also true that the physics part of all this work has been very fruitful, including what you say concerning decoherence, the theory of open quantum systems, and finally now developing "quantum engineering", i.e., making use of the results for technical developments like quantum cryptography and quantum computers etc.

All this was possible, because Bell had the ingenious insight how to make the philosophical vagueness of EPR, Bohr, et al a clear scientific question addressable by experiment.

 

[ShayanJ]

In my opinion the interpretational problems are solved with Bell's work and the empirical facts from experiments all of which with high precision excludes local deterministic hidden-variable models in the sense defined by bell and confirm the predictions of quantum theory.

It's also true that the physics part of all this work has been very fruitful, including what you say concerning decoherence, the theory of open quantum systems, and finally now developing "quantum engineering", i.e., making use of the results for technical developments like quantum cryptography and quantum computers etc.

All this was possible, because Bell had the ingenious insight how to make the philosophical vagueness of EPR, Bohr, et al a clear scientific question addressable by experiment.

I agree. Bell's work is one of the monumental milestones in the history of quantum mechanics. EPR just proved that there are still unanswered questions about quantum mechanics. But it was Bell who showed that those questions are actually not just philosophical, but deeply physical.

But I should remind you that EPR published their paper in 1935. Bell published his theorem in 1964. I'm pretty sure that 29 year gap is actually because most people had a mindset similar to yours and didn't think there was anything more to be understood. But in hindsight, we're all grateful that Bell didn't think that way. So let's learn from history and don't rush to conclusions!

 

[stevendaryl]

In my opinion, the goal of science is to understand nature. The goal of making falsifiable predictions is to test our understanding. But to say that the goal of science is to make and test falsifiable predictions is to confuse a test with the subject matter it is testing. It’s sort of like saying that the goal of studying physics is to get good scores on physics exams.

 

[Lord Jestocost]

But I should remind you that EPR published their paper in 1935. Bell published his theorem in 1964. I'm pretty sure that 29 year gap is actually because most people had a mindset similar to yours and didn't think there was anything more to be understood. But in hindsight, we're all grateful that Bell didn't think that way. So let's learn from history and don't rush to conclusions!

One should mention here that it was Bohmian mechanics whose nonlocality inspired John Bell to show that nonlocality must be a feature of any interpretation that “completes” quantum mechanics in the sense of Einstein, Podolsky, and Rosen.

 

[RUTA]

In my opinion, the goal of science is to understand nature. The goal of making falsifiable predictions is to test our understanding. But to say that the goal of science is to make and test falsifiable predictions is to confuse a test with the subject matter it is testing. It’s sort of like saying that the goal of studying physics is to get good scores on physics exams.

Here is post 222 in:
https://www.physicsforums.com/threads/assumptions-of-the-bell-theorem.1002054/page-9#post-6492762

Engineering? I always thought of science as the process of creating the tools, and engineering is about as just using the tools.

I have one funny memory from a class in analytical mechanics, where half of the group was in the science program, and half of the group with engineering students, but we both had the same books and made the same exams, the difference was more in emphasis of learning how to use, or conceptual understanding.

I think on a bad day, the lecturer who was very much a person that encouraged deeper questions, was provoced by one of the engineering students that asked many stupid questions like "I do not understand why I need to learn this, I will not have use for this when i get employed", and the teacher responded in frustration to the engineering student that "You are obviously not here to understand, you are just here to learn".

The science part of the group was amused.

/Fredrik

 

[stevendaryl]

Fine with me, but it's at least physics not philosophy ;-)).

I disagree. I think your position very much is philosophy, not physics.

 

[Zaitsev Maxim]

This Feynman quote is ever so remarkable,

You may argue, “I don't care which atom is up.” Perhaps you don't, but nature knows

Very sorry again, if I'm being ignorant. Does it mean nature knows, that we're looking?
I perfectly understand, that even if we just look at the end result then it may change. But we're looking at different information here. If you're saying, that it's during measurement result changes, then shouldn't we determine during which phase it changes? If you always measure and look at results of your measurement, then you're doing very many steps at once and just call it "looking". If you say in QM we're dealing with information, then shouldn't we think in terms of information?
If you Always look inside and Always try determine particle position for oneself, then you're Always doing many steps and simply call it "looking": extract information (by measuring position), transform, transmit, store and only then actually look. And if your theory about looking is built on this, then you're wrong. If you haven't tried yet to divide between these steps, then you can't say that result changes just because we observe it. But you can say, it changes depending on what we do.
What I say is we do a little different thing. If you say, that by measuring for ourselves result changes (no more you can actually say), then we will Never measure it for ourselves and look what happens (you can't yet claim, it changes just because we truly look). We're looking at different type of information here. Your "looking" is (as I think) Always related with "position of particle". But I Never influence it in this way. I only look at what it does and you can't claim it may change if we look at result because your "looking" related with "measuring".
You've always tried to look inside and did many actions at once, but suddenly create theory and transfer this "looking" word to everything. So, first we should look into what this "looking" action means. If every time we "look", we do some action, then it may be this action, not "looking", that is the cause. And you have no basis for this theory yet.
So, we should truncate this action little by little. Remove actual looking (and saving info for later), then saving, then transfering, then transforming (not possible I think), then extracting and look where result changes. Or better from bottom up and look where appears a change. If what you (physicist) say about not influencing particle is true and if we Never register its position with any device (i.e. not even extract information in any form), then you never influence it at all in any form and measuring action without registering any information shouldn't influence result. (You have no basis yet, to say our looking at result in itself is influencing process, because your word "looking" comes from the very definite set if actions)

 

[Zaitsev Maxim]

In other words, you say: "we measure it and look at it, so just because we look at it result changes". But you forget, that you Always measure as well. It May be as well just because we measure it. So your inference about looking is not complete and wrong.
In this book Beyond Weird is said this thing: "It’s a little like saying that you begin with a box that you know is red and think weighs one kilogram – but if you want to check that weight exactly, you weaken the link to redness, so that you can’t any longer say for sure that the box you’re weighing is a red one. The weight and the colour become interdependent pieces of information about the box." So it changes, depending on what we inquiry about it. And it may very well be that if you inquiry something about it, it should provide this information, but it can't provide it as it's as of now. So it should change to have it. So just because we inquiry it (not even for ourselves) it should transform to have it.
So if we try do measuring without registering and with it, and result is different, then it should be it.

 

[Zaitsev Maxim]

But even if even without registering it it still changes for some reason, then it's still not the end. Before you say, that it's Only looking that's affecting your results, you should be sure it's not measurement in itself in any form. You've made it so that it doesn't influence it in any form, but maybe you've just forgot to exclude inquiring information in itself as a possibility.
It may change depending on what type and how much of information you ask from it, so that if you ask one information, it loses another. (Or if it has one property, it loses another.) If you try to make very imprecise tool, which can ask its position in such a way that in the process of inquiring this position this thing Never needs to have position with more than some precision (the larger the better), then it may not lose this another property fully. (Again) So far (I think) you've just asked it very very precisely, so it should have it very very precisely, but if you ask it imprecisely, then it may change something. The less information you ask the better, because anyway you will see the end result.

 

[Zaitsev Maxim]

A little more (not very useful, if you understood already). Again from Beyond Weird book.

At the end of the book is written, that we should say:
" Not
‘here it is a particle, there it is a wave’
but
‘if we measure things like this, the quantum object behaves in a manner we associate with particles; but if we measure it like that, it behaves as if it’s a wave’
Not
‘the particle is in two states at once’
but
‘if we measure it, we will detect this state with probability X, and that state with probability Y’ "
That's right thing to say.

And also written:
"knowledge we possesses affects what is knowable"
That's baseless.
If you claim it only depending on one example, "looking at position", then it's really baseless. And you can never truly claim that something other that quantum object may behave like this - you can only create theory without proof and think "It Might be so", until you have another examples or something better.

 

[vanhees71]

I'd not say ‘if we measure things like this, the quantum object behaves in a manner we associate with particles; but if we measure it like that, it behaves as if it’s a wave’. I'd rather say with "new quantum theory" (discovered by Born, Jordan, Heisenberg; Schrödinger; Dirac in 1925/26), overcomes the intrinsically contradictory idea of "wave-particle dualism". There is no such thing. All there is are probabilities for the outcome of measurements given the state of the system.

That's indeed what the book seems to say too:
‘if we measure it, we will detect this state with probability X, and that state with probability Y’
That's right thing to say.

It's indeed nonsense to say that if a system is in the superposition of two (or more) states (correct is that it is in a pure state $|\psi \rangle \langle \psi|$ where $|\psi \rangle=\sum_n \psi_n |u_n \rangle$ with $|u_n \rangle$ a complete orthonormal set), it is in all these states at once. Each ket defines simply a possible pure state of the system, namely $|\psi \rangle \langle \psi|$.

I don't understand what "knowledge we possesses affects what is knowable". What does this refer to?

 

[romsofia]

I like any model that invokes some gravitational interaction i.e GRW, or Penrose's interpretation. It's actually where I got my icon from, a paper of his called "Gravity and state vector reduction" (By Roger Penrose) where Bohr, Wigner, Everett, and Von Neumann are all trying to hold $\psi$ from collapsing.

I also like the idea from "Continuous state reduction" put forth by Tony Sudbery, but I haven't really kept up with the emerging ideologies that have been put forth (outside of Bryce DeWitt's work where he LOVES to sprinkle in his admiration for MWI haha)

 

[Sunil]

All this was possible, because Bell had the ingenious insight how to make the philosophical vagueness of EPR, Bohr, et al a clear scientific question addressable by experiment.

And all this was possible only because EPR, Bohr etc. have tried to interpret quantum theory in a way you reject as "philosophical vagueness" and Bohm has developed some interpretation which is, AFAIU your position, not useful at all because it makes no different predictions.

 

[vanhees71]

That's the point. Bohm brought the philosophical vagueness of this paper to a scientific level, i.e., made it testable by measurement. The result is that Nature rather behaves as predicted by quantum theory (with an amazing significance and accuracy) and not like what some philosophically inspired physicists thought it should behave. Case closed. We can move on after 85 years now!

 

[Demystifier]

Bohm brought the philosophical vagueness of this paper to a scientific level, i.e., made it testable by measurement.

You meant Bell. But the point is, if there were no philosophers results before Bell, there would be no Bell's results. So philosophers results are useful for science.

Philosophy is one of inspirations for science. Many of the deepest results in science would probably never happen if there was no philosophical inspiration.

Saying that science does not need philosophy is like saying that future scientists do not need child play or SF literature.

 

[vanhees71]

Of course Bell... I think indeed child play, literature (including but not only SF) is indeed much more impotant as inspiration than philosophy, which rather leads to confusion of the mind ;-)).

 

[Sunil]

Of course Bell... I think indeed child play, literature (including but not only SF) is indeed much more impotant as inspiration than philosophy, which rather leads to confusion of the mind ;-)).

Is this a comment about string theory?

 

[Demystifier]

Of course Bell... I think indeed child play, literature (including but not only SF) is indeed much more impotant as inspiration than philosophy, which rather leads to confusion of the mind ;-)).

Philosophy can indeed be confusing, but so can science. And that's not necessarily bad, confusion can produce inspiration. Anyway, if philosophy confuses you, then why do you spend so much time on this subforum on doing philosophy?

 

[Fra]

Philosophy is one of inspirations for science. Many of the deepest results in science would probably never happen if there was no philosophical inspiration.

I think it also helps to distinguish between formal philosophy in some general sense (which usually does not interest me at least) and the philosophy of science, knowledge and nature. If one claims that is irrelevant to science itself, that must be one of the most mysterious forms of denial.

The historial roots of philosophy and science are the same, some roots of philosophy of knowledge are also common to sine foundations of mathematics such as probability theory, resulting from the philosophical insight that one needs a quantiative measure of degree of belief. So even mathematics and logic rests on philosophical foundations.

/Fredrik

 

[physicsworks]

I also don't think that "my interpretation" of QT is much different from Ballentine's.

I also don't like to say, "quantum theory is nonlocal", because it can be misleading.

I completely agree. An amusing fact about Ballentine's book (at least the lastest edition and printing that I have) is that in its Index the item "Nonlocality" is listed as:

Nonlocality (see Locality)

 

[bhobba]

I completely agree. An amusing fact about Ballentine's book (at least the lastest edition and printing that I have) is that in its Index the item "Nonlocality" is listed as:

An interesting thing about Ballentine is he thinks decoherence has nothing to do with QM interpretation:
https://core.ac.uk/download/pdf/81824935.pdf.

Formally I hold to the ensemble interpretation but include decoherence. I think these days, many do not believe (but not all) decoherence solves the measurement problem except in the sense of FAPP (For All Practical Purposes).

Thanks
Bill

 

[physicsworks]

An interesting thing about Ballentine is he thinks decoherence has nothing to do with QM interpretation:
https://core.ac.uk/download/pdf/81824935.pdf.

Thanks, that's interesting, I haven't read this one yet.

Formally I hold to the ensemble interpretation but include decoherence.

Yes, but also Tom Banks's arguments on locality and the classical limit of QM are very important and are often overlooked.

 

[bhobba]

Yes, but also Tom Banks's arguments on locality and the classical limit of QM are very important and are often overlooked.

My views on quantum locality have recently changed a bit. Before, it concentrated on the cluster decomposition property of QFT. To make sense, it must preclude correlation. Also, normal QM is based on the Galeain Transformation so locality is not an issue - it assumes non-locality. The issue lies with relativistic QM. Now I think it is centred on the fact QM is a generalised probability theory and the difference between Parameter independence and Outcome independence:
https://plato.stanford.edu/entries/qm-action-distance/

See section 3.

Thanks
Bill