I What is the current perspective on quantum interpretation?

[Tendex]

No, it won't. As I have already said, the only "result" of the experiment I proposed is which signal arrives first. There is no measurement of speed or indeed any numerical value involved; it's just a simple choice between three discrete possibilities: A arrived before B, B arrived before A, or A and B arrived at the same instant. The time ordering is all along a single timelike worldline. No "interpretation" is required. No assumption about simultaneity or the speed of light or anything else is required.

I'm sure you can make the distinction between "result" (the 3 possibilities) and "conclusions that can be obtained from a certain result depending on the theoretical assumptions applied" just as well as I can. The latter are what give different interpretations of a "result".

No, it doesn't. The three possible results are discrete alternatives--see above. There is of course a finite resolution to our comparison of arrival times of the two signals, but that just means the third discrete alternative, "A and B arrived at the same instant", has a finite "width", so to speak--if the two signals arrive within some small enough time interval of each other, our apparatus will tell us they arrived at the same instant even though that's not literally true. But this is not a matter of statistical error; it's just a matter of finite resolution, which will be true for any detector

We agree here, I just called error what you called resolution.

 

[PeterDonis]

The latter are what give different interpretations of a "result".

And my whole point was that you do not need to do any of this in order to test whether "FTL influences" are present. The results of such a test might have different implications for different interpretations of theories, yes. But that is not what originally started out this subthread. Here is the original statement of yours that I responded to, and my response:

I would ask you how you are determining that light travels at its characteristic speed, using a one-way or a round-trip measure of lightspeed to campare it with the FTL influences

You don't have to know what speed light is traveling to test for FTL influences. You just have to emit a light signal at the same time you emit whatever supposed FTL influence you are testing, and see which one arrives first at the destination.

 

[Tendex]

And my whole point was that you do not need to do any of this in order to test whether "FTL influences" are present. The results of such a test might have different implications for different interpretations of theories, yes. But that is not what originally started out this subthread. Here is the original statement of yours that I responded to, and my response:

Ok, I have no problem with that response. I might have mixed it up with a second instance where you responded talking about your experiment being "one way" but that was when we hadn't cleared up yet about the issue with tachyons. Sorry about my insistence.

 

[Sunil]

In classical theory with just Galilean relativity FTL influences are no big deal and don't affect causality in any way since the speed of light is not a maximum,so they shouldn't require a theory that constructs probabilities in a different way than the classical real probabilities, however quantum theory does require it to obtain better predictions.

There is no reason and no base to construct probabilities in some different way. $\rho(q)=|\psi(q)|^2$ is a quite normal probability, it follows a continuity equation.

There is no such thing as "the sound waves taken alone". The sound waves don't exist without what you are calling the "environment". This makes it fundamentally different from light, which can travel through a vacuum. You can't just handwave away that fundamental physical difference.

We don't know the theory below Planck length, so we don't know if the waves we observe travel through a "vacuum" or some sort of ether which does not have Lorentz invariance on the fundamental level. If there is a fundamental difference between them is your metaphysical hypothesis.

By this criterion, General Relativity is the same theory as Newtonian mechanics, since "in the limit" it makes the same predictions.

No. I have not said that the limit is the same theory. What I claim is that an ether interpretation of field theoretic GR exists. It is the limit of Schmelzer's ether theory.

If your theory has a preferred frame, what's the point of even talking about Lorentz invariance--or any other kind of invariance, for that matter?

It allows to construct for every solution of the equations various Doppler-shifted solutions. So it is a quite useful mathematical tool. Symmetries of the equations are always useful tools, even if they are only approximate symmetries.

 

[Tendex]

There is no reason and no base to construct probabilities in some different way. $\rho(q)=|\psi(q)|^2$ is a quite normal probability, it follows a continuity equation.

That's the quantum one which is different to the classical.

 

[Sunil]

That's the quantum one which is different to the classical.

It follows a slightly different equation, but it is also a standard probability distribution, which is non-negative everywhere and has an integral of 1 over the whole configuration space. Qualitatively the same. It only changes differently. If you simply put $\hbar=0$ you get the classical equation.

This holds for the Schrödinger equation rewritten in "hydrodynamic" variables. With $\hbar=0$ the equations become classical, without the quantum potential.

 

[Tendex]

It follows a slightly different equation, but it is also a standard probability distribution, which is non-negative everywhere and has an integral of 1 over the whole configuration space. Qualitatively the same. It only changes differently. If you simply put $\hbar=0$ you get the classical equation.

This holds for the Schrödinger equation rewritten in "hydrodynamic" variables. With $\hbar=0$ the equations become classical, without the quantum potential.

But $\hbar\neq0$, and I don't want to put $\hbar=0$, also "slightly different" is highly subjective, so I don't see the relevance of your answer besides pushing once more the dBB agenda. My point was that going back to a classical explanation(like using classical trajectories or ether preferred frame) doesn't fit very well with the change in procedure to obtain probabilities from just adding up to 1 absolute values of possible outcomes to adding up squares of numbers. It doesn't matter that we get nice good old probability distributions, it doesn't fit well either that the only answers are these irreversible probabilities unlike in the classical case, so I'd say that besides what Bell's theorem discards, it also hints that interpretations that just take the math of QM and varnish it with classical trajectories go nowhere.

 

[vanhees71]

It's a bit sloppy to say $\hbar=0$. What's really meant is to do an expansion in powers of $\hbar$. Usually it's in the sense of "singular perturbation theory". It leads to the WKB approximation when applying "wave mechanics". Within the path-integral formalism the saddle-point approximation of the path integral for the propagator (or the corresponding generating functional or quantum action) is used to get equivalent results.

 

[Tendex]

It's a bit sloppy to say $\hbar=0$. What's really meant is to do an expansion in powers of $\hbar$. Usually it's in the sense of "singular perturbation theory". It leads to the WKB approximation when applying "wave mechanics". Within the path-integral formalism the saddle-point approximation of the path integral for the propagator (or the corresponding generating functional or quantum action) is used to get equivalent results.

Sure, I didn't mean there is no classical limit(in fact QM has a weird unexplained dependence on it), I was just highlighting the departure of that limit that's characteristic for QM.

 

[Sunil]

It's a bit sloppy to say $\hbar=0$. What's really meant is to do an expansion in powers of $\hbar$. Usually it's in the sense of "singular perturbation theory". It leads to the WKB approximation when applying "wave mechanics". Within the path-integral formalism the saddle-point approximation of the path integral for the propagator (or the corresponding generating functional or quantum action) is used to get equivalent results.

No, I simply meant that if you have written down the equations appropriately (continuity equation for ρ with the velocity defined by the gradient of the phase, and the phase following the quantum variant of the Hamilton-Jakobi equation) you can simply put ℏ=0 and obtain the unchanged continuity equation together with the classical Hamilton-Jacobi equation.

Without doubt, the equations are mathematically even better in the quantum variant, the classical equation usually runs quite fast into caustics. So $\hbar\neq0$ can be seen as a sort of regularization of those caustics. And you can, of course, do your expansion in powers of $\hbar$ if you like. But to get the classical equations in the hydrodynamic variables you can simply put $\hbar=0$.

But $\hbar\neq0$, and I don't want to put $\hbar=0$, also "slightly different" is highly subjective, so I don't see the relevance of your answer besides pushing once more the dBB agenda. My point was that going back to a classical explanation(like using classical trajectories or ether preferred frame) doesn't fit very well with the change in procedure to obtain probabilities from just adding up to 1 absolute values of possible outcomes to adding up squares of numbers. It doesn't matter that we get nice good old probability distributions, it doesn't fit well either that the only answers are these irreversible probabilities unlike in the classical case, so I'd say that besides what Bell's theorem discards, it also hints that interpretations that just take the math of QM and varnish it with classical trajectories go nowhere.

As usual if somebody makes claims about my "agenda", the guess is wrong, I think there are better interpretations than dBB. If you don't see the relevance of my reply, then you may have a point, given that I also have not seen the relevance of your argument.

Of course, the complex function $\psi$ does not define a probability, the probability is defined by $|\psi|^2$. So, if you want to get some probability from $\psi$ you have to do something nontrivial. Why this would be relevant or give some hints about whatever I don't understand.

 

[jambaugh]

Orthodox Copenhagen Interpretation
(Consciousness causes collapse because wave functions represent what we know about a quantum system. They are not analogues of the system's physical reality. Wave function collapse = "when we suddenly change what we know, we suddenly change what we know.")

 

[stevendaryl]

Orthodox Copenhagen Interpretation
(Consciousness causes collapse because wave functions represent what we know about a quantum system. They are not analogues of the system's physical reality. Wave function collapse = "when we suddenly change what we know, we suddenly change what we know.")

I don't think that interpreting wave function collapse as simply a change in the knowledge of the observer is actually consistent. To say that only your knowledge changed is (it would seem to me) to say that whatever you learned was true before you learned it to be true. But that is not consistent with Bell's inequality (unless we give up locality, or exploit one of the other loopholes).

 

[jambaugh]

... But that is not consistent with Bell's inequality (unless we give up locality, or exploit one of the other loopholes).

How does Bell's inequality relate in any way to wave-function collapse? If you view wave functions as mathematical objects of the same nature as probability distributions over classical sets of states then note that they both collapse when we update our information due to observation.

The collapse in Copenhagen Int. is due to CI's interpretation of wave functions et al as being descriptions of knowledge, not descriptions of state.

 

[AlexCaledin]

Oh, just assume the whole physical reality to be somehow the outcome of Collapse - and then the Copenhagen FAPP-applicability follows.

 

[Fra]

How does Bell's inequality relate in any way to wave-function collapse?

I am gussing the link stevendaryl has in mind is if you consider the wave function collapse to "only" be a simple information update of the physicists ignorance, then that is exactly the line of thinking underlying Bells hidden variables. Ie. the information is out there, and preset, and its just the experimenet who is not informed.

But violation of Bells inequality suggests the systems interacts even with the measurement device "as if" there is more to this than just ignorance of the experimenter. Ie. it seems like not only the physicists, but the whole environment, including the measurement device, is ignorant about this, and then its something more to this than merely something in the head of the physicists.

/Fredrik

 

[vanhees71]

Well, this confusion just arises from not taking the probabilistic interpretation of the state seriously. Within QT an observer has the most complete knownledge about a system, if he has prepared it in a pure state. You cannot have "more information" about the system. That's quantified by the von Neumann entropy which is 0 for pure states, which means that you have "complete information".

What's different to classical physics is that having "complete information" about the system does not imply to know the outcome of measurements of all observables but only of any complete set of compatible observables for which the prepared pure state is $\hat{\rho}=|\psi \rangle \langle \psi|$ with $|\psi \rangle$ being a common normalized eigenstate of the self-adjoint operators representing these complete compatible set of observables. Note that the preparation of the system making a complete set of compatible observables simultaneously determined uniquely leads to the preparation in the state $\hat{\rho}$.

The difference between classical and quantum physics is the difference in what is considered a state: In classical physics complete knowledge means to know the point in phase space at some time (and thus knowing the point in phase space and thus the values of all observables on the system at any time through the time-evolution of the system). That's "determinism", i.e., complete knowledge about a classical system means to know the values of all possible observables of the system.

In quantum mechanics if you completely know the system at one time, this means it's prepared in a pure state at this time, and then you have complete knowledge about the system at any later time (causality), i.e., through the time evolution of the quantum system it stays in a pure state, but this doesn't imply that you know the values of all possible observables (indeterminism).

 

[Fra]

Within QT an observer has the most complete knownledge about a system, if he has prepared it in a pure state. You cannot have "more information" about the system.

I am sure we agree on all this.

My point was rather that, at least from my perspective QM suggests to me that there is MORE to this than "only" what information the observer has or can have: When you start thinking about possible causations that can explain Alice/Bob outcomes in entanglement, its not only the original observer (which in QM is not part of dynamical interactions, except in the preparation and final detection) that has constraints on the possible knowledege, it seems to be there are also constrations on relations of the internal parts of the systems (which are NOT observer in the Copenhagen view) - because how else can we understand how "quantum interference", even after the other remote particle is disclosed?

Ie. We do not yet understand the "logic" of the quantum inteactions. All we know is that the classical Bell logic does not work. And entanglement and collapses of alice and bob are somehow key elememets in this. I am sure there is more in this to be understood here.

So I would like to put it so that I am taking the probabilistic interpretation more seriously than copenhagen interpretation, and suggests that its necessarily agent-relative, and that the "information updates" are not "only" revision of the physicists information, I think it is at the core of all physical interactions. Its not conceptually consistent imo to think of it as "only" applicable to the observer on the other side of the Heisenberg cut, exactly because the cut while important, is arbitrary.

/Fredrik

 

[jambaugh]

Jumping back in. We collapse the wave-function or rather "re-set" it with updated knowledge but to say that knowledge is resetting ignorance is presupposing the very hidden variables being denied.

In the specific EPR case. Our original knowledge is, say, that whatever we observe for A will be mirrored for B. At the same time, due to complementarity what will be measured for A (and likewise B) is something we are totally ignorant of and inherently indeterministic.

When we then measure X for component system A, we have effectively also measured system B in spite of never having interacted with it and our knowledge of them is now expressed as a distinct wave-function for each. A classically correlates product wave function for the two systems.

It hurts our ontologically habituated minds but we can see here that the measurement process is not a matter of measuring previously defined subsets of state variables at the same time as necessarily scrambling complementary state variables that were also predefined. Our measurement of A has no causal effect on B but our change in our knowledge of A changes our knowledge of B in how we are able to predict what future observations of B will be, hence both their wave-functions update. This is no different than say measuring a position of a particle after measuring its momentum. The local measurement of A is complementary to the joint measurement of A and B's "entangled" correlation.

What we have here is, according to CI, facts in that we observe specific outcomes and predictions of transition probabilities for future observed outcomes. This description of what happens is scraping the foundation of our fundamental understanding and there is no operationally meaningful way to dig deeper. It is as ill posed a question to speak about what goes on between or beneath this as it is to ask which twin is older in the classic relativistic paradox without defining a frame of reference.

Bell's theorem helps confirm this fact. But, other than this, it does not speak to the nature of the wave function/density matrix/hilbert space vector et al as representations of our knowledge of the systems potential behavior (past or future) relative to a fact of present observation. This is a distinct and intuitively unsatisfying variation from our usual, classical representation of systems as states within an ontological model.

 

[stevendaryl]

How does Bell's inequality relate in any way to wave-function collapse?

It seems that it has everything to do with wave function collapse. Einstein believed that the “collapse” was not physical, that there was some pre-existing fact of the matter about whether a measurement would give this answer or that answer, and measurement just revealed this pre-existing answer. Bell showed that interpretation can’t be correct (except for various loopholes such as superdeterminism, FTL influences, etc.)

 

[Fra]

This description of what happens is scraping the foundation of our fundamental understanding and there is no operationally meaningful way to dig deeper. It is as ill posed a question to speak about what goes on between or beneath this as it is to ask which twin is older in the classic relativistic paradox without defining a frame of reference

I think our main point of disagreement, is wether we think we can make scientitic progress by digging here or not.

We both agree we are on the edge of scientific development, therefore we necessarily stand with one foot in the air. But how else to make progress?

They KEY reason for why i think there is potential here, has do do with how one can understand the emergent behavior(hamiltonian) of a complex system, from simpler systems. This is something that the foundations of QM does not explain at all. It is simply a postulate that "there exists" a hamiltonian for example. The "knowledge" implicit in the hamiltonian, is not treated on the same beautiful footing as the state. This is why QM is not complete. But this incompleness has a totally different meaning that the Einstein meaning.

And in this line of reasoning, the "information update" seems a key concept. I object to saying it is only an information update of the observer. There is likely physics containt here. But it is not obvious until you raise the question about "interacting observers". Communicating wigners friends etc is a sort of pre-version of interaction observers. This is out of scope for current consensus of course. But I do not see how one can dismiss this as meaningless. The hypothesis generation part of the scientific process is possibly ill posed yes, but this is more a philosophical question of science.

/Fredrik

 

[Zaitsev Maxim]

I can propose an experiment. Don't really know if it was already, so you may delete this post as well, if it's nothing new.
The question is: is it only when we, people, look at it, is important, or not. If it does, then it's connected with understanding, not looking.
The experiment is as follows. We have device to fix position of particle. And we're not looking at what it fixes up to the very end. And not looking at what happens there at all. And look only at the end result. BUT we have this thing: device should forget instantly what it fixed (to the very end: we should clear this memory with zero instantly). I.e. we're not adding this result in some array, writing on hard drive or something is left in operative memory (RAM) in any way, so you can never extract it. And then look only at the end result, how this particles behaved themselves. If they change their behaviour like when we're looking, then it's done.
If not, then there's more.
1. We cold add line in code to remember info in array, and clear it comletely with zero just before the end. And then not clear.
2. We should try the same as initial but look at what happens there, not what device fixes. I.e. on picture through video or directly, if possible, through glass, even if we're not seeing this particle. And again not look at the result to the very end. Just look at where this particle goes through. If it doesn't change its behaviour then it's done. If it does you could try place there monkey, cat or even cockroach to check brains needed for it to change (or maybe you even should wait a little for this information to completely disappear from their minds and then look at result). Then try looking only at computer which fixes it, but forgets instantly and never tells you.
3. You could try initial experiment, but draw info on screen and forget instantly. But only in special screen without graphic card. You can even encode this through lamps in bitwise code (but without any memory to forget it instantly). And again not look at it at all, better isolate this place so that there's no light that goes through. And look at result. Then monkey and everyone else. And you may try to encode it so you will never understand, what this light means.
So you can determine if it's understanding or looking. Looking only something alive or even computer. Although it will end immediately, if only when computer looks, it already changes.
You can even never remember this information in operative memory and just fix it with device, which tells no one and never remembers itself, to determine, if it is extraction of information, not looking, which is important.

 

[AlexCaledin]

- but, whatever we do, it consists of elementary observations of choices made by the actual universal avalanche of events - inside and outside one's brain - we are simply learning about Nature's choices, never able to know how exactly they are made... Although, yes, some choices do seem made by ourselves and there is a very strong feeling of responsibility.

 

[Zaitsev Maxim]

But isn't it important which action triggers this change: extraction of information without keeping it at all, keeping this information somewhere for some time or trying to understand this information? You say looking, but maybe not looking.
If we're extracting it, not looking at it at all, not trying to understand, what happens there at all, can you tell me, what will happen? Should it change when we're not looking, but just fixing it without remembering it at all? Maybe it's important that we're trying to fix it, not look, so it should change and have fixed position.

 

[ObjectivelyRational]

There is currently no evidence to suggest that consciousness in the human brain, versus an animal's brain, versus a computer, or a sensor, or any other sufficiently "measurmenty" natural system has any fundamentally different causative effect on the outcome of a complex quantum system or experiment. Specifically, no evidence shows that measurement actually depends on consciousness.

We are grappling with our ignorance, and also the counter intuitive nature of the temporary indeterminacy of certain aspects of physical systems, and we are still trying to understand the mechanisms involved in measurement, but more experimentation is required for the answers, not more (or the same) "groundless maybes" (complete speculation).

According to the evidence there is nothing which "knows" whether a consciousness is watching a quantum experiment, and there is no evidence showing consciousness is in any way involved in the physical process of measurement.

 

[Zaitsev Maxim]

Sorry, if I'm being ignorant. I'm not a physicist. But I read in the book Beyond Weird, that even if we're sure that we're not influencing particle in any way during measurement, it changes its behaviour when we measure it. And it very strongly says that it's looking that's important. But is it really? Maybe it's measurement (extraction of information) in itself that's important, not looking.

 

[ObjectivelyRational]

Sorry, if I'm being ignorant. I'm not a physicist. But I read in the book Beyond Weird, that even if we're sure that we're not influencing particle in any way during measurement, it changes its behaviour when we measure it. And it very strongly says that it's looking that's important. But is it really? Maybe it's measurement (some interaction) in itself that's important, not looking.

No need to apologize and you are not being ignorant.

I think you are right. Measurement IS interaction, and interaction and causation, that kind of thing is science!

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.

 

[Zaitsev Maxim]

(by the way I changed "some interaction" in "extraction of information" because we really shouldn't influence particle in any way)

To say it more clearly: we can easily differentiate between 4 possibilities (which I can see):
1. Measurement itself.
2. Keeping information in some way.
3. Looking at information.
4. Understanding this information.

1. If we just measure never keeping result at all and never looking or trying to understand what's going on in there. So we never lift uncertainty for oneselves. If it changes result then it's measurement. If not then we're at least completely sure we're not influencing particle in any way by this measurement.

2. If we remember this result temporary in some way but strictly never looking at it and destroy it completely before we look at result (or right after by timer, never looking). Again never lift uncertainty in any way. If it influences, then it's keeping information (or something related).

3. If we look at encrypted information (without information loss) which we can never understand and again never keep it in any way and it influences result, then it's looking. If we write information somewhere, then it doesn't count because we can understand it later. If we look at encrypted information which will be forever lost and it doesn't influence result, then it's not looking. (We can even try encrypt in sound and listen to it if you wish)

4. If we look at information we can somehow understand (maybe shouldn't write it again), and it influences result, then it's understanding. You can even try to place someone who looks at the same thing alone but doesn't know anything and can't remember or understand it. It will be very fun if result is changing depending on who is watching.

Or maybe it's amount of information that is important. We can also try light up some lamp, every time measuring goes through and look at result. Or maybe it can behave the more freely, the less we know or inquiry about it. We're constantly trying to measure as precise as possible, but what if we do reverse thing and purposely limit ourselves in precision of our measurements, so that even measurement tool can't know more than we want? Will its behaviour change again?

 

[ObjectivelyRational]

(by the way I changed "some interaction" in "extraction of information" because we really shouldn't influence particle in any way)

There must be a causal chain to make any measurement. Some causal chains interact with the subject prior to your participation (sunlight falling on an observable projectile), but some interaction must have occurred for you to measure that light. In this case you are using the light bouncing off the projectile to locate the projectile, but you must keep in mind the fact that the light DID interact and affect the projectile.

Something isolated and kept isolated from all external interaction is by definition unmeasurable while it is being kept isolated.

 

[Zaitsev Maxim]

Something isolated and kept isolated from all external interaction is by definition unmeasurable while it is being kept isolated.

But it's the very thing I'm trying to say. What if the cause of change is not observation of this information but simply inquiring about it? We don't measure it for oneselves, you can guarantee that you're not influencing particle (or else there would not be such absurd conjecture about looking) and we're not influencing it by looking or knowing something. If we do the same thing, but never know results of measurements (and never can extract them, if we extract then we're looking) and only look at the end result and it changes, then it is measurement, not looking, because we never looked or tried to understand what's going on. We're not measuring because we want to know result of our measurements, we measure because we should check influence of the act of measurement itself.
And then again if we limit our tool to ask only very approximate information (for example, with error of 1 centimeter) without looking at it and it changes its behaviour to something new, then it's inquiring of information that is important, not measuring.
And more so if we do the same thing when we measure but never fixing it with any device and then do the same but with fixing and forgetting instantly, and result is different, then it's extraction of information and measurement doesn't influence particle completely. But if it changes even without fixing it with device then it should be problem with measurement or interaction.
So, we can prove that we're not influencing it by measurement mothed if we do the same thing as in measurement but never ever even fix it with device. Because we're not even extracting some information from this and if it changes result then it can't be helped. But if not, then we've proved it.

 

[AlexCaledin]

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

 

[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.