Interpretations of Quantum Mechanics

[nikman]

Bohr anyone? Also, since we've mentioned positivism, most of that movement was explicitly based on Wittgenstein's thoughts on language, meaning, and verification.

It was based on the Tractatus. The language game stuff came later. Philosophical Remarks was an in-between work.

Bohr was unaware of Wittgenstein all of his life, AFAIK. He had explicit problems with Husserl and the phenomenologists but that's different. Anyway there's an interesting interview that David Peat conducted with Heisenberg where they got into LW. Heisenberg did not like Tractatus (too dryasdust or whatever) but really got behind Philosophical Investigations.

Or maybe he was just trying to be hip.

 

[kote]

It was based on the Tractatus. The language game stuff came later. Philosophical Remarks was an in-between work.

Bohr was unaware of Wittgenstein all of his life, AFAIK. He had explicit problems with Husserl and the phenomenologists but that's different. Anyway there's an interesting interview that David Peat conducted with Heisenberg where they got into LW. Heisenberg did not like Tractatus (too dryasdust or whatever) but really got behind Philosophical Investigations.

Or maybe he was just trying to be hip.

I don't have any knowledge of Bohr being directly influenced by Wittgenstein, but he surely had positivist ties and held similar views to theirs (though he arguably got there different ways). I don't agree with all of Jan Faye's conclusions here, but this paper talks about a lot of the historical links: http://philsci-archive.pitt.edu/archive/00003737/" . If Bohr was holding positivist conferences at his mansion and acknowledged positivist views, he probably knew about Wittgenstein. That's just speculation though.

 

[nikman]

I don't have any knowledge of Bohr being directly influenced by Wittgenstein, but he surely had positivist ties and held similar views to theirs (though he arguably got there different ways). I don't agree with all of Jan Faye's conclusions here, but this paper talks about a lot of the historical links: http://philsci-archive.pitt.edu/archive/00003737/" . If Bohr was holding positivist conferences at his mansion and acknowledged positivist views, he probably knew about Wittgenstein. That's just speculation though.

Neurath might have mentioned Wittgenstein if Bohr had read the Trac, but as you say it's speculation. By 1936 LW was well beyond positivism. According to legend he'd earlier treated the Vienna Circle with a degree of boorishness remarkable even for him. (Turning his back to the assembled savants for at least one entire meeting and staring out the window without speaking. With friends like that.)

Edit: Turning his back, not turing it. Different thread, different forum.

 

[WaveJumper]

Those questions don't make much sense. I can't even make sense of the language in the "where is everything" question.

I think you do. I was asking if you think the characteristics of the world are to a certain extent dependent on us.

Where is the electron in what space?

There must be a correlation between theoretical models and reality.

You need a theory to define the concept of time, and you didn't specify one.

None of our theories gives a good foundation about what time is. I was interested in your personal opinion wrt time in your chosen quantum interpretation.[Edit: you choose to refrain from making guesses, that's ok, it sounds sensible]

What does it mean to be an essential part of reality?

It means that by choosing the measuring equipment we can influence the outomes in experiments(that probably applies to reality too).

What I said in #100 answers your question about electromagnetic fields (if "are real" means the same thing as "exist").

If a theory produces a prediction that matches an experiement that does not point in any way to what exists independently of us. So it doesn't answer my question.

I have no idea what it would mean to see an absolute material background-dependent universe. The word background-dependent is especially confusing in this context.

Any theory of quantum gravity has to be background independent, if we are to preserve GR. If you believe in a fixed, absolute universe, you are believing in a model of a universe where the defining equations of a unified theory would be background-dependent. I am not saying you do, but you didn't give clues as to what a reality independent of us should look like in your opinion.

See post #11. If the word "algorithm" bothers you (apparently it bothered someone), just replace "an algorithm" with "a set of rules". See also #27.

Is that an instrumentalist approach or is it closer to the - "we don't have enough information to draw a conclusion" type of argument? When you said this in post 11:

They are all trying to tell us what QM really describes, but a theory doesn't have to describe anything

What do you mean by "a theory doesn't have to describe anything"? Do you mean anything deeper than what appears to perception? If yes, i think our positions aren't too far apart.

IMO, since we can never differntiate between information about reality and the Reality, it is the "thing" that exists independently of us. A chair, a car, a lover, etc. is all information about these entities, manifested by abstract quantum fields in relative space-time. Everything we perceive is a construct based on information. The images that we form on the basis of this are our constructs. In this sense the information is the basic building block of the world we perceive. Space and time are concepts aimed at giving meaning to our world of appearances. So they are entirely reasonable constructs, as long as they are used for their relational purposes. I guess that puts me closer to the CI, but i don't want to open another can of worms.

Does anyone think a universe can exist that's devoid of information and information transfer? If we were able to strip the universe of all the information, what would remain of it?

 

[RUTA]

In your earlier post you a building a straw man. The device in question is not studying the paths of the particles [edit: or the particles themselves] but the behavior at the center of the collision. Dissassociating the clicks is just disassembling your measuring device. The whole of the tracks once reconstructed using the prior verified theory is the single "click" associated with a particle of a certain mass and momentum (range). Or more specifically a specific configuration of particle paths is the single "click" for a particular resonance at the collision center.


Similarly when one is measuring the spin of an electron with an SG magnet or rather its magnetic moment one is using the electron's position and momentum as a classical measuring device. This is inherent in the |up> or |down> kets one writes and in the ignoring of the HUP with regard to localizing the electron's lateral position while assuming zero lateral momentum.

It is important to distinquish a "quantum particle" from "a particle" in the classical sense. The definition of a "quantum particle" is a quantum system with non-trivial irreducible Poincare group representation. It is not an object it is a system of activity, a process.

[EDIT: In fact I think you have pinned down a key point. When you find it necessary to make metaphysical assumptions you must have crossed the system cut from quantum system to measuring device/mechanism! This is exactly the "why" of the CI postulate that we must treat our measuring devices classically.]

This has NOTHING to do with my post. Nothing. You didn't understand one word.

 

[jambaugh]

This has NOTHING to do with my post. Nothing. You didn't understand one word.

You are talking about post #74 in this thread I presume? What were you implying with the question?

What would happen to this enterprise if we rather believed there were no click-causing particles?

As I understood it you were arguing the relevance of metaphysical questions about quantum systems is necessity...

in order to collect "objective data"

I was asserting that the system in question was classical and part of the measuring device at the point where you were invoking these metaphysical questions.

Possibly that was not your point. I still would, for the sake of others who may mistakenly think it was, argue that such metaphysical question about components of the observational devices themselves are within the context of a classical model we use in describing those devices while using them to probe the actual quantum processes. In CI one insists on treating the devices classically because that is a (praxic) fundamental requirement for their use in obtaining the information not an assertion about the devices' (ontic) fundamental nature.

The "metaphysical" questions within a model are not metaphysical issues outside the use of that model except and only when one is making a broader metaphysical postulate that the model is a representation of a physical fundamental reality. They are just artifacts of that model's classical treatment no different from "metaphysical" question about say the existence of a solution to some abstract differential equation even if that equation is being used in some hard scientific application.

BTW I never did answer your question:

Do you think a Hilbert space structure "is all that is necessary" to generate particle physics data?

No it takes a laboratory experment to generate particle physics data. Interpreting that data and setting up the experiment for that matter (what you mean by going from "instrument readings" to "data") requires we invoke the mathematical structure of the theory along with the operational (praxic) interpretation, i.e. which operations and objects in the mathematics correspond to what operations and objects in the laboratory. Note however that the mathematical objects in QM (with CI) do not correspond to the system or system state but to the (classically treated) devices. Hence the necessity of their classical treatment.

Frankly I don't see Hilbert spaces as the primary mathematical objects we should use but rather the operator algebra and its dual of co-operators. But that's a whole other thread. (Though I think some of the biases in interpretation come from focusing too closely on the Hilbert space formulation.)

Again you may say I totally missed your point. If so and you feel generous with your time why don't you break it down in simple terms my sluggish brain can absorb. PM it to me if you like so we won't have to bother everyone with my remediation.

 

[RUTA]

Neo-Copenhagenists like Brukner and Zeilinger are busy trying to marry the above to avant-garde informatics and create a new synthesis based on the principle that in the deepest possible sense you can't separate a thing from what you know about that thing. I for one say more power to them.

In your previous Zeilinger quote he said the premeasurement object has absolutely no properties. Couple that with the claim in this quote and you have to wonder whether the premeasurement object has any ontic status at all.

 

[RUTA]

Again you may say I totally missed your point. If so and you feel generous with your time why don't you break it down in simple terms my sluggish brain can absorb. PM it to me if you like so we won't have to bother everyone with my remediation.

Sorry, jambaugh, I'm not effectively communicating my point so I'm frustrated. We're talking past one another. Let me try again.

My post was in response to an attitude that I see here, at conferences, seminars, etc. -- that physics doesn't need interpretation b/c we're guided by empiricism. My argument is that we interpret theory to create experiments and interpret instrument readings to create data. I used the example of particle physics b/c I'm familiar with it and it strikes me as particularly poignant. Returning to that example, ask yourself whether we would spend billions of dollars building accelerators and detectors if we didn't believe that matter is made of fundamental building blocks (electrons, quarks, muons, neutrinos, etc). That we call detector clicks "hits" and search for "tracks" belies a particular interpretation of quantum field theory (QFT) based on this belief. Suppose that we rather believed there were no "quantum particles" creating those detector clicks -- they are the response of the detector to the accelerator, things which DO exist, nothing more. In this interpretation, greater accelerator energies merely produce more complex patterns in the detector. Would we bother to spend billions of dollars looking for such patterns in these highly contrived situations? Probably not. We would probably spend this money and manpower on problems related to truly fundamental physics, i.e., the "true" decomposition of objects based on some alternate interpretation of QFT.

I'm not trying to establish and debate alternate interpretations of QFT. I'm trying to present an argument against the belief that physics doesn't need "interpretation." That's all.

 

[nikman]

In your previous Zeilinger quote he said the premeasurement object has absolutely no properties. Couple that with the claim in this quote and you have to wonder whether the premeasurement object has any ontic status at all.

If you mean the interview I quoted from, the interviewer asked him this:

"... Ultimately that implies something monstrous: namely that the particle had absolutely no characteristics before it was measured. The great Danish physicist Niels Bohr once said: no one has ever seen a chair. There is no objective reality. Only that which is measured exists. We construct reality, and only in the moment of measurement or observation."

And Zeilinger replied:

"n my view there is something that exists independently of us – in physics we call that the singular event. For example the activity of a particle detector. Or the activity of a certain cell in my eye, which registers a certain number of light particles and then provokes a chemical reaction that is then registered in the brain. The images that we form on the basis of this are our constructs. Bohr's chair or on a much more abstract level, the quantum mechanics equation of states, are our concepts of an object. Of course they are very purpose-oriented, because they've been corroborated with repeated use."

Which doesn't address the issue explicitly raised by the interviewer, that of "what's there" (if anything) prior to observation/measurement. Z may or may not have evaded it deliberately, it's hard to say. (Anyway, is a potentiality ontic?) As one of the co-authors of one of the two Leggett experiment papers (the other paper being by Nicolas Gisin's Geneva group, which ran a separate experiment also violating Leggett's inequality) he's complicit in suggesting that:

"[O]ne could consider the breakdown of other assumptions that are implicit in our reasoning leading to the [testable Leggett] inequality. These include Aristotelian logic, counterfactual definiteness, absence of actions into the past or a world that is not completely deterministic ... We believe that our results lend strong support to the view that any future extension of quantum theory that is in agreement with experiments must abandon certain features of realistic descriptions."

Zeilinger has also talked about "the two freedoms" -- the freedom of the experimenter to set part of the terms for realization by asking the question he or she decides to ask, and the freedom of nature to return serve by giving the answer it damn well pleases. This has a constructivist feel about it, although I don't know that he's ever openly identified with that tendency and he's not a featured player among the Constructivist Foundations crowd.

 

[nikman]

"... absence of actions into the past or a world that is not completely deterministic."

To be understood (I'm almost 100% sure) as "absence of a world that is not completely deterministic," i.e., "presence of a world that's completely deterministic." As an assumption of realism. Sometimes I wish I could edit this stuff for these people.

 

[molinaro]

I vote transactional. It seems the simplest and if it's good enough for Feynman it's good enough for me.

 

[RUTA]

Zeilinger has also talked about "the two freedoms" -- the freedom of the experimenter to set part of the terms for realization by asking the question he or she decides to ask, and the freedom of nature to return serve by giving the answer it damn well pleases. This has a constructivist feel about it, although I don't know that he's ever openly identified with that tendency and he's not a featured player among the Constructivist Foundations crowd.

Thanks for supplying all that text, nikman! It's interesting that Z talks about these two freedoms in light of the delayed choice experiments he has conducted. I saw him present this one: Anton Zeilinger, “Why the quantum? ‘It’ from ‘bit’? A participatory universe? Three far-reaching challenges from John Archibald Wheeler and their relation to experiment,” in Science and Ultimate Reality: Quantum Theory, Cosmology and Complexity, John D. Barrow, Paul C.W. Davies and Charles L. Harper, Jr. (eds.), (Cambridge Univ Press, Cambridge, 2004), pp 201-220. Therein, one photon (call it 1) of an entangled pair goes through a double slit to detector C while its partner (call it 2) goes through a lens to a detector A at the focal length (f) or to a detector B at 2f. If photon 2 is detected at f, photon 1 contributes to an interference pattern. If photon 2 is detected at 2f, photon 1 contributes to a particle pattern. The outcomes are strikingly in agreement, what makes it weird is that photon 1 is detected before photon 2. So, is the experimenter really free "to set part of the terms," i.e., free to choose detector A or B for photon 2, given that photon 1 has already contributed to its related pattern at C? Is Nature really free to give "the answer it damn well pleases" at C, given the freedom of the experimenter to choose A or B?

 

[jambaugh]

We're talking past one another. Let me try again.

I believe I understand. I still see a bias in how you explained it as far as the form that interpertation should take. Yes we must believe we are studing nature and not the behavior of detectors. But I say beliving there is a "real" (ontological) structure of some type and believing there is no "real" (ontological) structure are just two opposite ontological interpertations. There is a third path.

This may have undeservedly flown at you but its, a point I've tried to make to others. One may believe on is studing nature (outside of ourselves or our devices) without imposing specific implicit formats to that nature inherent in a conceptualizable "state of reality". It is hard to step out of this mindset since it is the proper and practical way to study nature on the scale in which we normally live (and have evolved the brain to understand it). One must appreciate the weight of years over which we evolved both mind and language where objective reality works fine for throwing rocks or shooting arrows and firing bullets at prey (and enemies). Suddently in the past century we hit the limit of classical thinking with the study of phenomena at the quantum level.

It is unprecedented and much of the "of course" and "obvious" ways of understanding needs revision. We still have the strong (and normally appropriate) habit of casting phenomena in terms of a continuous sequence of states. Some still try to do this with QM.

(I'm preachin' to the crowd now, sorry.) I think it is very similar to someone trying to pin down exact formal definitions for words we use in common speech. The words have meaning but it is not some fixed objective and definable meaning (except of course when we work in fromal contexts such as law or mathematics.) Words are an interaction between people by which we invoke in others a desired mode of thinking. It is process. It isn't just mundane pragmatism which is why I invoke the term "praxic". It includes the poetry and music and inspirational sermons. And carrying the analogy further it to has inexact outcomes.

So too I see nature as an amalgam of processes, studiable, understandable, but not wholy reducible to objective state any more than is the human experience. We can speak of people as individuals while understanding fully that who a given individual is cannot be separated from the society in which he lives or reducible to a clockwork of reflexive responses to his environment. Likewsie an electron is an individable unit process but not definable apart from from its environment or reducible to a point in a state manifold following a trajectory.

This is not to say we need to ascribe any mystic nonsense to it either (which I see as a way of giving up instead of trying a better paradigm of understanding). It is merely an acknowledgment of the flaw in one specific paradigm.

As I mentioned words meanings can't be pinned down except in a specifically formal context. However that is what we have in science. The fundamental root is the definition of science as an epistemological discipline. Thus when we ask the meaning of the word "electron" it must in the context of science derive from the process by which we know something about the electron, those acts of observation which distinguish it from a plumb pudding or a slap on the face. And when we ask the meaning of the wave function so too we must look at the scientific root. It is not something we observe but one level abstracted. Its meaning is thus this abstraction, our knowledge of the system, and not the system with which we do interact in our observatories and laboratories.

You know the old saw about "Have you stopped beating your wife?" I see much of the debate about interpretations and specifically criticism of CI as ritious indignation that I haven't stopped beating my wife without any attempt to understand that I haven't because I'm not even married. CI is not a metaphysical interpetation it is the rejection of metaphysical interpetation. When asked how I can possibly be so stupid as to believe there is no reality, I am taken aback by the assertion that I have made any such claim about reality. To do so would be just as much a heracy in the CI as to assert the reality of the wave-function.

One can be an agnostic theist or an agnostic atheist. The agnostic part asserts the question of the existence of the deity is not knowable and to believe (either way) is a leap of faith. Thereby the agnostic rejects in particular the deity question as a scientific one.

CI (and positivism in general) is agnosticism about reality. One can still choose a leap of faith or simply walk away leaving the question unanswered. But it is an acknowledgment (or assertion if you will) that the choice to leap is a choice for whatever reason to leave the domain of science. Now I think that question is arguable and its answer is knowable which is what I've been up to on these threads.

And finally (stretching the religion analogy for all its worth) the agnostic is understandibly offended by the implication that he cannot function morally because he has not taken the leap of faith toward deism. Because the deist derives his moral code from his belief blinds him to the possibility that it could come from another source. This is true only within the context of his belief which as an article of faith he cannot question. So too I take exception with those who assert a metaphysical interpretation is necessary for science to function.

Hence RUTA my overly strong reaction to your post. Though you may not have been making such a pronouncment or not for the same reason, it resembled a bit to me a that sort of bias.

Well pardon this old windbag for his soapbox sermons. You all will get a break as I'm off to Vegas tomorrow early to behave unscientfically for a bit.

 

[Dmitry67]

I vote transactional. It seems the simplest and if it's good enough for Feynman it's good enough for me.

TI does not address the issue of "incomplete" transactions. Many photons escape to infinity, they will never find their absorbers, because the Universe is expanding and it becomes more and more transparent.

 

[Fredrik]

My post was in response to an attitude that I see here, at conferences, seminars, etc. -- that physics doesn't need interpretation b/c we're guided by empiricism. My argument is that we interpret theory to create experiments and interpret instrument readings to create data.

I would say (and have said, earlier in this thread and in other threads) that a mathematical model needs an interpretation, but a theory by (my) definition already includes one. For example, Minkowski space is a mathematical model of space and time, but the theory of special relativity is defined by a set of axioms that tells us how to interpret the mathematics as predictions about the results of experiments.

When I say that QM doesn't need an interpretation, I mean the theory of quantum mechanics, not the mathematical model (Hilbert space or something mathematically equivalent), and more specifically, I mean that a theory such as the Copenhagen "interpretation" doesn't need further interpretation. I mean, we obviously need to interpret the mathematics as predictions about the results of experiments, but we don't have to interpret it ontologically as a statement about what "is" and what "really happens".

The first kind of interpretation is sufficient, and the second kind isn't really science. I like to point out that it isn't philosophy either. The philosophy part of this is the thought process you have to go through to realize it isn't science.

There are two major problems with the attempts to find an ontological interpretation of QM. The first is that QM may not have an ontological interpretation that has anything to do with reality, and the second is that even if it does, there's nothing we can do to verify that the correct ontological interpretation is in fact correct.

I used the example of particle physics b/c I'm familiar with it and it strikes me as particularly poignant. Returning to that example, ask yourself whether we would spend billions of dollars building accelerators and detectors if we didn't believe that matter is made of fundamental building blocks (electrons, quarks, muons, neutrinos, etc). That we call detector clicks "hits" and search for "tracks" belies a particular interpretation of quantum field theory (QFT) based on this belief. Suppose that we rather believed there were no "quantum particles" creating those detector clicks -- they are the response of the detector to the accelerator, things which DO exist, nothing more. In this interpretation, greater accelerator energies merely produce more complex patterns in the detector. Would we bother to spend billions of dollars looking for such patterns in these highly contrived situations? Probably not. We would probably spend this money and manpower on problems related to truly fundamental physics, i.e., the "true" decomposition of objects based on some alternate interpretation of QFT.

You're describing an extreme viewpoint that I don't think many people have. (Does anyone have it?) I think it would be idiotic to refuse to use words like "particle" just because the standard model isn't verifiable. What i think we should do is to continue to say that particles exist, and try to teach as many people as possible what that statement really means. (See #100).

 

[Fredrik]

CI (and positivism in general) is agnosticism about reality.

You too associate the CI with positivism? I really don't see how the CI can be thought of as an example of positivism. As far as I can tell, positivism, or at least logical positivism (I'm not sure if there's a significant difference), requires theories to be verifiable, but the CI is a fantastic example of a theory that's falsifiable but not verifiable.

I realize that the CI may in part have been inspired by positivistic thinking, since it doesn't include an ontological intepretation, but I see no reason to say that it is positivism.

 

[Demystifier]

I remember there is also partial decoherence.
For me this is a proof that MWI is true.

I would say that there is a soft MWI and a hard MWI. Soft MWI merely claims that the wave function satisfies the Schrodinger equation and that it never collapses. Hard MWI claims that this is enough, i.e., that no further assumptions are needed in order to interpret the wave function correctly.

For me, partial decoherence is a strong evidence for soft MWI, but not for hard MWI.
As you admit, the biggest problem of hard MWI is to explain the Born rule.
With soft MWI it is much easier, because you are allowed to assume or postulate something in addition. An example of soft MWI is the Bohmian interpretation which assumes that waves serve as pilots for pointlike particles, which allows to explain the Born rule from other postulates.

 

[nikman]

Thanks for supplying all that text, nikman! It's interesting that Z talks about these two freedoms in light of the delayed choice experiments he has conducted. I saw him present this one: Anton Zeilinger, “Why the quantum? ‘It’ from ‘bit’? A participatory universe?... Therein, one photon (call it 1) of an entangled pair goes through a double slit to detector C while its partner (call it 2) goes through a lens to a detector A at the focal length (f) or to a detector B at 2f. If photon 2 is detected at f, photon 1 contributes to an interference pattern. If photon 2 is detected at 2f, photon 1 contributes to a particle pattern. The outcomes are strikingly in agreement, what makes it weird is that photon 1 is detected before photon 2. So, is the experimenter really free "to set part of the terms," i.e., free to choose detector A or B for photon 2, given that photon 1 has already contributed to its related pattern at C? Is Nature really free to give "the answer it damn well pleases" at C, given the freedom of the experimenter to choose A or B?

This has resonances of the "before-before" experiments of the Gisin group, which is a demonstration of quantum atemporality and which Antoine Suarez dwells upon at length and considers also to be proof of free will. And I must ponder upon it, unless ...

Z and Brukner discuss a somewhat comparable experimental situation, involving the Heisenberg microscope, in a 2005 paper, "Quantum Physics as a Science of Information" ...

http://www.dancing-peasants.com/sciphil/QPSI(2005).pdf ... big file, slow download ...

and they say this about that:

"These experiments also shed interesting light on the role of the observer with respect to reality. We note that it is the experimentalist who chooses the apparatus. The experimentalist, in our case Birgit, decides whether to put the detector into the focal plane or, say, the image plane. That way, she determines which property of the system, wave or particle, can be reality. We might thus conclude that the experimentalist choosing the apparatus determines which physical quantity, i.e., quality, can be reality. In that sense, the experimentalist's choice is constitutive of the universe. However, the specific outcome here, which of the two slits the particle passes through in our case or where on the observation plane it arrives in the other, cannot be influenced by her. That way, Nature avoids complete controllability by the observer." (page 5, aka 51)

 

[Dmitry67]

Regarding CI, it would make sense if it would not try to "sit on 2 chairs"

CI: wavefunction is NOT real (there are some other flavours of CI where it is real, but "classic" CI it is not real)

So only MACROSCOPIC events are real in CI. Particles, both real or virtual, are just a mathematical technique of calculationg the correlation between the macroscopic events: reading of the devices, clicks and beeps.

In that extreme form it is self-consistent.

But when it tried to talk about the particles as something real, it becomes illogical, saying that "these 4 atoms are the measurement device, and these atoms are not"

 

[RUTA]

I believe I understand. I still see a bias in how you explained it as far as the form that interpertation should take. Yes we must believe we are studing nature and not the behavior of detectors. But I say beliving there is a "real" (ontological) structure of some type and believing there is no "real" (ontological) structure are just two opposite ontological interpertations. There is a third path.

I believe I now understand you. In fact, you correctly discerned a bias and it is precisely the bias to which you take exception, so your responses did reflect an understanding of my posts and it was I who did not understand you! Sorry. Anyway, let the argument begin!

I am claiming that metaphysical interpretation is necessary to do experimental particle physics (given the thread, we should keep the argument to quantum physics). We devise particle physics experiments and gather data from them under a specific metaphysical interpretation, i.e., that particles exist or, if you like, more loosely, that detector clicks always trace out classical trajectories. This is a metaphysical assumption. There are other metaphysical interpretations of quantum field theory (QFT) which would lead to different experiments altogether, e.g., that what we observe in a particle physics experiment is evidence of the relationship between the detector and the accelerator. In this second metaphysical interpretation, contrary to your assertion supra, we ARE studying the detector (in concert with the accelerator). In fact, to study the behavior of detectors (and accelerators) IS a study of nature. Apparently, you believe that if we assumed the second metaphysical interpretation of QFT (no particles), we would still be building huge accelerators and looking for the masses of ... well, you tell me.

(I'm preachin' to the crowd now, sorry.) I think it is very similar to someone trying to pin down exact formal definitions for words we use in common speech. The words have meaning but it is not some fixed objective and definable meaning (except of course when we work in fromal contexts such as law or mathematics.) Words are an interaction between people by which we invoke in others a desired mode of thinking. It is process. It isn't just mundane pragmatism which is why I invoke the term "praxic". It includes the poetry and music and inspirational sermons. And carrying the analogy further it to has inexact outcomes.

This sounds like Finkelstein, D. R. Emptiness and relativity. In B. Alan Wallace, ed., Meeting at the Roots, Berkeley CA: Univ, of California Press (2001). You can read it on his website: http://www.physics.gatech.edu/people/faculty/dfinkelstein.html#publications
You might want to read this paper (if you haven't already), I think you'd be interested in it.

As I mentioned words meanings can't be pinned down except in a specifically formal context. However that is what we have in science. The fundamental root is the definition of science as an epistemological discipline. Thus when we ask the meaning of the word "electron" it must in the context of science derive from the process by which we know something about the electron, those acts of observation which distinguish it from a plumb pudding or a slap on the face. And when we ask the meaning of the wave function so too we must look at the scientific root. It is not something we observe but one level abstracted. Its meaning is thus this abstraction, our knowledge of the system, and not the system with which we do interact in our observatories and laboratories.

The reliance on metaphysical interpretation in particle physics is illustrated nicely by answering the question, what is an "electron?" First, one does preprocessing -- you create individual clicks, i.e., spacetime locations, from voltage/current surges in your detector. Second, you do pattern recognition -- you use the clicks you created from voltage/current surges to create tracks, based on the assumption that there are indeed tracts to be found, which means you throw away clicks that don't fit on your best-fit collection of tracks. Third, you do geometrical fitting -- you do curve fitting on the tracts, based on the assumption that there are dynamical entities tracing out these paths, to obtain the dynamical characteristics of the "click-causing particles." This last step is pure classical physics, by the way. After all this massaging of instrument readings, you may find an "electron," i.e., a trajectory characterized dynamically via a particular mass, spin, charge, etc.

To refute my claim, you must argue that we would invest billions of dollars and huge IQ-human-hrs to build these devices and create this data from the instrument readings, announcing the discovery of various particles, even if we rather believed the detector events were the result of the second metaphysical interpretation above, i.e., there are no "click-causing particles." I eagerly await that argument!

You know the old saw about "Have you stopped beating your wife?" I see much of the debate about interpretations and specifically criticism of CI as ritious indignation that I haven't stopped beating my wife without any attempt to understand that I haven't because I'm not even married. CI is not a metaphysical interpetation it is the rejection of metaphysical interpetation. When asked how I can possibly be so stupid as to believe there is no reality, I am taken aback by the assertion that I have made any such claim about reality. To do so would be just as much a heracy in the CI as to assert the reality of the wave-function.

In my view, CI is not the rejection of metaphysical interpretation but the acceptance of ambiguity in the metaphysical interpretation of QM. In other words, there are different ways to think metaphysically about QM which allow physicists to create experiments and turn instrument readings into data. So, why commit to anyone of them? But, that's not part of this argument.

And finally (stretching the religion analogy for all its worth) the agnostic is understandibly offended by the implication that he cannot function morally because he has not taken the leap of faith toward deism. Because the deist derives his moral code from his belief blinds him to the possibility that it could come from another source. This is true only within the context of his belief which as an article of faith he cannot question. So too I take exception with those who assert a metaphysical interpretation is necessary for science to function.

Hence RUTA my overly strong reaction to your post. Though you may not have been making such a pronouncment or not for the same reason, it resembled a bit to me a that sort of bias.

Your reaction was warranted, we do disagree on this very point (as regards particle physics, anyway).

Well pardon this old windbag for his soapbox sermons. You all will get a break as I'm off to Vegas tomorrow early to behave unscientfically for a bit.

On the contrary, I'm very grateful that you are taking the time to argue this point with someone of "lesser ability." Good luck in Vegas

 

[RUTA]

When I say that QM doesn't need an interpretation, I mean the theory of quantum mechanics, not the mathematical model (Hilbert space or something mathematically equivalent), and more specifically, I mean that a theory such as the Copenhagen "interpretation" doesn't need further interpretation. I mean, we obviously need to interpret the mathematics as predictions about the results of experiments, but we don't have to interpret it ontologically as a statement about what "is" and what "really happens".

I agree.

There are two major problems with the attempts to find an ontological interpretation of QM. The first is that QM may not have an ontological interpretation that has anything to do with reality, and the second is that even if it does, there's nothing we can do to verify that the correct ontological interpretation is in fact correct.

I don't know to what extent we ever verify ontological interpretations, given under determination. As a physicist who is often chastised by philosophers for being a verificationist and empiricist, I think the value of creating new interpretations lies in their ability to suggest new theory and/or experiments.

You're describing an extreme viewpoint that I don't think many people have. (Does anyone have it?) I think it would be idiotic to refuse to use words like "particle" just because the standard model isn't verifiable. What i think we should do is to continue to say that particles exist, and try to teach as many people as possible what that statement really means. (See #100).

Here are two interpretations of QM whereby there are no "click-causing particles:"

Genuine Fortuitousness, A. Bohr & O. Ulfbeck, Rev. Mod. Phys. 67, 1-35 (1995); A. Bohr, B. Mottelson & O. Ulfbeck, Found. Phys. 34, #3, 405-417 (2004).

Relational Blockworld, Silberstein, M., Stuckey, W.M., Cifone, M., Studies in History & Philosophy of Modern Physics 39(4), 736-751 (2008); Stuckey, W.M., Silberstein, M., Cifone, M., Foundations of Physics 38(4), 348-383 (2008).

I don't know that GF leads to new experiments/theory. RBW does, but until those consequences are accepted for publication, there's nothing to discuss. [We're just now finishing a paper along those lines.]

But, again, I did not post with the intent of arguing for this particular ontological interpretation of QFT. I was simply trying to point out that we would expect to create very different experiments and look for very different data if we subscribed to a very different ontological interpretation of QFT. This strikes me as trivially true, but I'm almost as philosophically naive as the physicists I'm addressing with this claim

 

[kote]

You too associate the CI with positivism? I really don't see how the CI can be thought of as an example of positivism. As far as I can tell, positivism, or at least logical positivism (I'm not sure if there's a significant difference), requires theories to be verifiable, but the CI is a fantastic example of a theory that's falsifiable but not verifiable.

Fredrik, I think maybe we are talking about different CI's (per Demystifiers other post). Bohr talked extensively about the ontological implications of his view and how we should think of and describe reality. His desire for a verifiable concept of reality is what led to his denial of any separably objective reality at all, which he realized we could never say anything verifiable about.

Popper was a realist and objected to CI. Falsifiability was a move to weaken the criteria needed to be able to discuss a realist objective world. Also, Popper "articulated his own view of science, and his criticisms of the positivists, in his first work, published under the title Logik der Forschung in 1934 (http://plato.stanford.edu/entries/popper/" (from 1967).

Asher Peres has one relatively recent defense of CI from Popper here: http://arxiv.org/abs/quant-ph/9910078. Of course, he puts his own twist on CI as well.

Bohr also held a positivist conference at his mansion and acknowledged that reading his work as agreeing with positivism was correct. In general I would not go as far as to say Bohr was a positivist beyond in his interpretation of QM though.

Positivism = Logical Positivism = Logical Empiricism

 

[molinaro]

TI does not address the issue of "incomplete" transactions. Many photons escape to infinity, they will never find their absorbers, because the Universe is expanding and it becomes more and more transparent.

Isn't that just an assumption, that there are photons that are never absorbed?

According to TI, those that would never be absorbed, are never emitted.

 

[nikman]

... So, is the experimenter really free "to set part of the terms," i.e., free to choose detector A or B for photon 2, given that photon 1 has already contributed to its related pattern at C? Is Nature really free to give "the answer it damn well pleases" at C, given the freedom of the experimenter to choose A or B?

Here, for others who might be interested but aren't familiar with the chapter, is a brief summary by Zeilinger of said chapter (his) in the Barrow et al book you cite (Science and Ultimate Reality: Quantum Theory, Cosmology and Complexity; John D. Barrow, Paul C.W. Davies and Charles L. Harper, Jr., eds.; Cambridge Univ Press, Cambridge, 2004, pp 201-220):

http://www.dancing-peasants.com/sciphil/Why_the_Quantum.pdf

Let me pull out these two paragraphs and call them central:

"A number of experiments will be reviewed underlining these views. This will include an entangled photon delayed choice experiment where the decision whether a photon that has passed a double slit did this as a particle or a wave is delayed not only until a time after its passage through the double slit assembly but even after it has already been registered. Thus, while the observed facts, i.e. the events registered by the detectors, are not changed, our physical picture changes depending on our choice what to measure. ...

"Finally an experiment on the teleportation of an entangled photon demonstrates that the decision whether or not two photons are entangled or not again can be made at a time long after these photons have already been observed. More precisely, the quantum state we assign two photons for a time period before they have been registered depends on our future choice whether or not we then implement the Bell state measurement these two photons are entangled with. This experiment lends support to the idea that the quantum state is just a representation of our knowledge and that this knowledge changes when an observation is made. Thus the reduction of the wave packet is just a reflection of the fact that the representation of our information has to change whenever the information itself changes as a consequence of an observation."

This makes my tennis-serve analogy overly simplistic (if not arguably simpleminded) but I don't see it conflicting with Z's "two freedoms" dictum. Birgit and her particle still enjoy the same mutually dependent relationship as he expounded upthread, only with more (joak here) bells and whistles. Unless I'm missing something, which as a probability could always be closer to one than zero.

 

[DrChinese]

Isn't that just an assumption, that there are photons that are never absorbed?

According to TI, those that would never be absorbed, are never emitted.

I would certainly think that something would be noticable if there were directions in which there were no absorbers (based on that assumption). I think the conclusion would be that there is no such effect. I.e. if TI requires an absorber, then TI is false.

Now imagine that we are talking about neutrinos rather than photons. The universe is essentially transparent to neutrinos, even if were not quite transparent to photons.

 

[RUTA]

I would certainly think that something would be noticable if there were directions in which there were no absorbers (based on that assumption). I think the conclusion would be that there is no such effect. I.e. if TI requires an absorber, then TI is false.

Now imagine that we are talking about neutrinos rather than photons. The universe is essentially transparent to neutrinos, even if were not quite transparent to photons.

The computation of the transition amplitude via the path integral formalism is based on the fact that “the source will emit and the detector receive” (Feynman, 1965, 167); per Tetrode, “the sun would not radiate if it were alone in space and no other bodies could absorb its radiation” (Tetrode, 1922, 325). The path integral formalism requires both an emission event and a reception event; the formalism was motivated by the idea of treating advanced and retarded potentials equally.

Feynman, R.P. (1965). “The development of the space-time view of quantum electrodynamics” in Physics: Nobel Lectures 1963-1970, edited by G. Ekspong, World Scientific, Singapore, 1988, 155-178.

Tetrode, H. (1922). Zeitschrift für Physik 10, 317-328.

 

[QMister]

I remember there is also partial decoherence.
For me this is a proof that MWI is true.

Would you care to elaborate a little further?
How does "partial decoherence" in ANYWAY give "proof" to MWI over any other interpretation such as Bohm?
Explain exactly what you mean by that if you don't mind...

I would say that there is a soft MWI and a hard MWI. Soft MWI merely claims that the wave function satisfies the Schrodinger equation and that it never collapses. Hard MWI claims that this is enough, i.e., that no further assumptions are needed in order to interpret the wave function correctly.

For me, partial decoherence is a strong evidence for soft MWI, but not for hard MWI.
As you admit, the biggest problem of hard MWI is to explain the Born rule.
With soft MWI it is much easier, because you are allowed to assume or postulate something in addition. An example of soft MWI is the Bohmian interpretation which assumes that waves serve as pilots for pointlike particles, which allows to explain the Born rule from other postulates.

I think calling it "soft MWI" is wrong though as this "soft" version would not contain other worlds, hence MANY and WORLDS are out of the interpretation.
Or are you saying there is many worlds, just in a different way than the most prominent MW interpretation states?

 

[molinaro]

I would certainly think that something would be noticable if there were directions in which there were no absorbers (based on that assumption). I think the conclusion would be that there is no such effect. I.e. if TI requires an absorber, then TI is false.

Now imagine that we are talking about neutrinos rather than photons. The universe is essentially transparent to neutrinos, even if were not quite transparent to photons.

Take a sphere of let's say, radius 10 billion light years, centred on a light bulb. Project from the centre of that sphere out to the surface of the sphere a set of lines where each passes through each atom found within the volume of that sphere.

What kind of variation in density of points on the surface of the sphere would you expect to be traced out?

How small would those variations end up if you considered where that same set of lines intersected a sphere of volume 10 meters?

Do you still think you would notice something?

 

[Dmitry67]

I would certainly think that something would be noticable if there were directions in which there were no absorbers (based on that assumption). I think the conclusion would be that there is no such effect. I.e. if TI requires an absorber, then TI is false.

Now imagine that we are talking about neutrinos rather than photons. The universe is essentially transparent to neutrinos, even if were not quite transparent to photons.

Correct
Unless... unless there will be a BIG RIP
BIG RIP created enourmous quantities of hawking radiation from tidal horizons, effectively absorbing everything.

 

[Dmitry67]

Take a sphere of let's say, radius 10 billion light years, centred on a light bulb. Project from the centre of that sphere out to the surface of the sphere a set of lines where each passes through each atom found within the volume of that sphere.

What kind of variation in density of points on the surface of the sphere would you expect to be traced out?

How small would those variations end up if you considered where that same set of lines intersected a sphere of volume 10 meters?

Do you still think you would notice something?

Sphere of 10 billion years is literally transparent to light. Look at the night sky. It is dark!
In fact, most of the absorption occurs in our galaxy (towards its center there is 100% absorption). If a photon was lucky to escape from our galaxy, it has almost no chance of being absorbed. And the Universe is becoming less and less dense, so if it is not absorbed soon, then there will be almost no chance that it will be ever absorbed. Again, unless there will be a big rip.

Regarding your question about the variation, if varies from near 0% if you point your light towards, say, "Hubble deep field" area to 100% when you point it towards the center of our galaxy.