As far as I can recall it is about which are the most popular interpretations of QM, and doesn't even mention the measurement problem. — andrewk

But doesn’t the whole question of ‘which interpretation’ - Copenhagen, MWI, etc - revolve around ‘the measurement problem’? Isn’t the ontological status of the wave-function collapse the basic interpretive issue?

But does it accurately represent how the interference pattern arises and why it disappears when we take measurements next to one of the slits? — andrewk

Is it possible to represent that graphically, or only mathematically?

But doesn’t the whole question of ‘which interpretation’ - Copenhagen, MWI, etc - revolve around ‘the measurement problem’ — Wayfarer

To get into that I think we'd first need to take a step back and try to reach a shared understanding of what 'the measurement problem' is. It is often talked about but rarely defined. It is often presented just in terms of a vague gesture towards quantum weirdness in general.

My closest guess is that, rather than being a problem, it is a question, the following one:

'Does conscious observation change the physical universe?'

One can adopt an interpretation of QM in which the answer is Yes, or another in which it is No. QM itself is silent on the issue. For me the question is moot because I see consciousness as primary and the 'physical' as an artifact of our consciousness.

What do you consider the measurement problem to be?

What do you consider the measurement problem to be? — andrewk

The measurement problem in quantum mechanics is the problem of how (or whether) wave function collapse occurs. The inability to observe this process directly has given rise to different interpretations of quantum mechanics, and poses a key set of questions that each interpretation must answer. The wave function in quantum mechanics evolves deterministically according to the Schrödinger equation as a linear superposition of different states, but actual measurements always find the physical system in a definite state. Any future evolution is based on the state the system was discovered to be in when the measurement was made, meaning that the measurement "did something" to the system that is not obviously a consequence of Schrödinger evolution. — Wikipedia

That 'something' is the 'act of observation' which reduces all the probabilities to one particular one, namely, the observed one. Prior to that observation, there is no objective 'particle' but then after it's been measured, there is. Hence Bohr's famous aphorisms on this problem, such as 'When we measure something we are forcing an undetermined, undefined world to assume an experimental value. We are not measuring the world, we are creating it' and more succinctly 'nothing exists until it is measured'. This was the source of the long debates between he and Einstein, ever the scientific realist. It is why Einstein was obliged to ask the question 'does the moon continue to exist when nobody's looking at it?' This is all covered in Manjit Kumar's book Quantum and David Lindley's Uncertainty. (The first is better.)

Incidentally my view is that the so-called probability wave exists in reality - but purely as literal distributions of possibility, i.e. it’s not a physical wave, but a distribution of likelihoods. That’s why, whether you fire one particle per x second or eighty thousand per x seconds, you get the same pattern - because the rate of emissions doesn't affect the distribution pattern, then whatever determines the distribution is not time-bound. That strikes me as profoundly significant. I asked this question on physics forum and also on Stack Exchange. (Notice the reaction on Physics Forum, post #14, when I suggest that it's not time-bound.)

This also ties in with an interpretation by Ruth Kastner et al, which says that '“This new ontological picture requires that we expand our concept of ‘what is real’ to include an extra-spatiotemporal domain of quantum possibility.' In other words, there are real possibilities. I don't think that modern ontology allows for that, however, as I think that part of what happened in the transition to modernity was the 'flattening' of ontology so that something either exists (1) or doesn't (0). Whereas here we are dealing with 'things' (loosely speaking) that have various 'degrees of reality'; when the particle is observed, it is 'actualised' by the observation. And we don't like that because it undercuts scientific realism - hence, Einstein's question.

With the problem as expressed in your quote, the widely-accepted solution is decoherence, which is mentioned later in that wiki article. There are other suggested solutions, which I am not familiar with, and which I haven't bothered to investigate, because decoherence provides such a satisfying answer to the question of why we observe only one of the outcomes that were regarded as possible before the measurement.

As the article explains, decoherence is not tied to a particular interpretation. It can be used in both Copenhagen and many-worlds, and maybe in others too (but not in Bohm, I suspect).

I read your discussion on PF, and I agree with the answers, although I would not have used the word 'gobbledegook' myself.

As to whether wave functions or probability fields are 'real' I prefer to leave those questions to ontologists. They have no meaning to me. For me, what is 'real' is subjective experience, and everything else is speculative theorising.

belief in a real world is dubious because our perception is based on our own created life values. science uses experiment to validate theories about the real world but they only validate it to other beings that share the same values. In that process the idea of the real world sneaks by without resolving the fact that we are basically making up the world to conform to our values. Scientific instruments are not real in the sense that there is no possible way to ascertain the real world from a being that cannot objectively ascertain the real world external to their values. Why do values pose such a problem? well look at how we behave economically and politically. Saying this I do believe that science is our best shot and also that our value created world is still a valid mirror of the external world and not some pure simulation, but it is not special,external or real. But the point I was trying to make was only made if there was naivety that our observations could change the external world. i raised my point because if you forget yourself and philosophically merge your perceptions to the objective world you are trying to accurately mirror, you forget that your creating what you percieve to conform to a value matrix; you believe the mirror of your perception is flawless (for that is one of our values in operation, self aggrandisement). Now one off shoot of believing this is that because the truth is, that your 'making it up', is that you can also effect the real world, you can make up the external world, you can manipulate it by knowing it. We can of course manipulate the external world through our knowledge of it, but not by observation alone, this would definitely be an error. but someone already pointed out that it was detection not observation that interfered with the experiment. That means to me that we are still respecting our perceptual boundaries. well the scientists are, the commentators, not so much.

As to whether wave functions or probability fields are 'real' I prefer to leave those questions to ontologists — andrewk

Well, this being a Philosophy Forum, we would rather hope to find some here, would we not?

Then again, if everything is ‘subjective experience’, maybe it doesn’t matter.

you mean I am not in touch with reality? My name is there, you can say it. So by way of minimal comment and abbreviation you suggest to the other members that you of course are in touch with reality. The internet gives young people a means to express themself and all they do is act like their institutions are all that should matter. Don't think I don't notice your tone is borrowed from the current political climate in the U.S. Look, Philosophy is about escaping from the pressure to always think and do what will be accepted. I know that my every expression is not defined clearly for others and do not think that any failure to express elevates what I say, but if you were a real thinker and not just a child determined to be accepted, you wouldnt mind a little confusion in an expression.and you certainly would not mind a point of view that does not conform correctly, be it by error or otherwise.

I read your discussion on PF, and I agree with the answers, although I would not have used the word 'gobbledegook' myself. — andrewk

Please see Post # 16, which says:

A simple way to see it is that it means that each particle is interfering with itself, not with other particles.

Which you yourself have already dismissed. So, interesting that you agree with an answer there, which you dismissed here.

I think I'm raising a serious and possibly novel argument in that thread, and I don't think the person there I was discussing it with understood it.

belief in a real world is dubious because our perception is based on our own created life values. science uses experiment to validate theories about the real world but they only validate it to other beings that share the same values. In that process the idea of the real world sneaks by without resolving the fact that we are basically making up the world to conform to our values — Martin Krumins

What is being called into question through QM is the independent reality of atoms as material particles. If you believe that the world ultimately comes down to atoms, then it's a challenge for that view, and for scientific realism, generally. That was the main bone of contention between Einstein on the one side, and Bohr and Heisenberg on the other. Einstein was very much a scientific realist, whereas Bohr and Heisenberg had much more philosophically nuanced views.

The whole subject is very controversial for a number of reasons. One the one hand, physics in general and quantum mechanics in particular are the Crown Jewels of science. But on the other they seem to throw common-sense and even scientific realism out the window. Actually not a lot of people know how to deal with that. But from a philosophical point of view, if you're not committed to scientific materialism or scientific realism, then it's not that big a deal.

You're raising some interesting points, but could I ask, have you done any readings or formal study on the topic? There are many interesting titles on the subject for the non-physics specialist. Some of them are crap, some of them are not, although in this field, it can be quite hard to differentiate them. But one thing is for sure, don't let anyone tell you it isn't mysterious. Richard Feynmann said 'I think it's safe to say that nobody understands quantum mechanics', and he understood it better than almost anyone. Likewise Neils Bohr said 'if quantum mechanics doesn't shock you, then you haven't understood it'.

(By the way your posts really would benefit from some more line-breaks. They're quite intelligible but posting them in large paragraphs make them hard to read.)

What causes the interference pattern to disappear when particles are detected going through one of the slits is the interaction between the detector (including the recording apparatus connected to that) and the particles, not the fact that a conscious entity looks at the results of the interaction. The interference pattern would still disappear if nobody looked at the screen or the detector. — andrewk

Which is why I attempted to draw out his thinking about this link he has made with idealism through the seemingly trivial fact that the equipment in the experiment is man-made. But apparently someone here has already outlined the difficulty he was having and there's no need to worry.

Belief in a real world is dubious... — Martin Krumins

Only madmen and philosophers say such things and expect to be taken seriously. The world is real, I can vouch for it. My life values won't alter the results of the double-slit experiment, nor would they shield me from getting hit by a bus if I were to suddenly walk right out in front of one driving at speed.

There are a number of different double-slit experiments, and all of them (or at least, all the ones I know, including several 'delayed choice' and 'quantum eraser' versions) are completely explained by the mathematical analysis, which does not hold any mysteries, — andrewk

Yes. The paradoxes are the result of refusing to let go of Greek atomism and insisting, against all the evidence, that quanta are both particles and waves. The math, which works perfectly, represents quanta as waves.

I think I'm raising a serious and possibly novel argument in that thread, and I don't think the person there I was discussing it with understood it. — Wayfarer

You raised a question, which was whether the particle rate (BTW more accurately characterised as the field strength) determines the degree of undulation in the bars. The answer to that was No, and that answer is correct. In your later posts you tried to articulate a point about time and space but the point was not expressed clearly enough to understand. I too could not understand what point you were trying to raise. I thought the way people said the point was not understandable was regrettably curt.

I hadn't noticed DrClaude's comment about a particle 'interfering with itself', so I do not include that amongst the statements that I said I agree with. On a literal level the statement is not truth-apt. It just points towards a way one might think about something. I think that way is unhelpful, because it de-emphasises the probability field, which is the key to understanding.

Perhaps you could have another go here, at explaining what the argument was that you were trying to make in the PF thread.

The point I tried to articulate was about whether this means that time (being 'rate') is not a factor; which also that means that space (i.e. proximity of particles) is not a factor (as proximity is an aspect of space-time.) So, what is causing the interference pattern is not a function of space-time. (That was what was described as 'gobbledygook'.)

In the Stackexchange thread I put it like this: if the interference pattern is not rate-dependent, then it means that time is not a factor in the generation of the interference pattern i.e. if the same pattern can be generated in 1 second as in 24 hours, then 'time' is not a variable.

Part of the exchange was as follows:

It's the fact that it is not time-dependent which is of interest. I don't think you could replicate this outcome using a physical medium like water waves in a tank, because in that situation, 'time' would be a boundary condition. That is the sense in which 'waves' and 'interference' might actually be a metaphor for the effect; the effect is not the consequence of actual waves, but of the interaction of probabilities only. The interpretive challenge is then that it appears to demonstrate 'real possibilities' i.e. possibilities that have physical consequences. – Wayfarer Dec 5 '16 at 2:29

It is not time dependent because the boundary conditions, which in the end define the probabilities, are not time dependent is what I am saying. It is the particular use of wave equations. with operators on psi, that makes the difference between material waves or energy waves and probability waves. – anna v Dec 5 '16 at 4:49

So just as electrons are not really particles, the so-called interference patterns are not really ‘waves’ either. Actual waves are carried in a medium and are time-dependent. Here time is not a factor.

I don't have a clear idea of what you mean when you say time is not a factor. When the experiment begins, there is no pattern on the screen, and when it finishes, after some time has elapsed, there is a pattern. So the experiment cannot be done without time. I suppose that goes without saying for any experiment, or indeed any action at all because to 'do' something is to arrange things so that a property of the world that did not hold at time t1, holds at t2.

Similarly space must be a factor because the pattern on the screen can only be understood in terms of spatial measurements. The pattern is a mapping from the spatial coordinates of points on the screen (a pair of real numbers) to a real number that indicates brightness.

I think the problem is that the statement that something is or is not 'a factor' in an event is too vague. I get the sense that you have a strong idea of what you mean by it but unfortunately it is not coming across.

I don't have a clear idea of what you mean when you say time is not a factor. — andrewk

I'm referring to the amount of time taken, the duration of the exposure. So it's not 'vague'. One of the posters who responded to the thread on Physics Forum said it: '24 hours at 1 per second would give the same pattern as 1 second of 86400.'

Consider if you were actually doing the experiment with water and not with photons. Would you produce the same interference pattern regardless of the rate of flow? I would think obviously not. The interference in the case of water is literally a matter of collisions between molecules - actual interference. But here, there's an interference pattern when you're firing the photons one at a time! Hence the expression that 'the photon interferes with itself', which you already said is nonsense (and it seems so to me).

So no matter how long you take, you will get the same pattern (with the caveat that 'only up to the point where the rate is so high that the interaction between different electrons can no longer be neglected'.) Hence: not a matter of time. And as the pattern is not being caused by actual physical collisions, then it's also not a matter of physical proximity, i.e. space. So whatever is showing up, is not 'inside' time and space. That's the claim that was called 'gobbledygook' but I think the correct term is actually 'metaphysics' ;-)

Consider if you were actually doing the experiment with water and not with photons. Would you produce the same interference pattern regardless of the rate of flow? — Wayfarer

If by 'flow' you mean wave height then Yes, subject to irregularities caused by turbulence.

Water does not flow in a linear manner when the water has waves. Each particle executes a roughly circular motion. It is only the wave that flows, not the water. A better sense of this can be gained by considering the wave in a cracked whip. The whip cord doesn't flow from the handle to the tip. Only the wave does.

In the water analogy, the analog of the 'rate' of the electron gun is the height of the wave. The technical term across both cases is the amplitude of the wave. The wave amplitude affects only the brightness, not the shape, of the interference pattern. The shape depends only on the wave frequency and the distance between the sources.

with the caveat that 'only up to the point where the rate is so high that the interaction between different electrons can no longer be neglected'. — Wayfarer

I saw that caveat on the PF discussion, and I suspect it's wrong. But it doesn't affect the discussion here, so we needn't bother investigating whether it is.

whatever is showing up, is not 'inside' time and space — Wayfarer

I reiterate that I think to call this gobbledegook is uncharitable and, I think, bordering on rude. But I have to confess that I cannot imagine what it would mean for something to show up that is not inside time and space.

But I have to confess that I cannot imagine what it would mean for something to show up that is not inside time and space. — andrewk

And I suggest that is because it is a metaphysical issue, not a physics issue.

I don't if you glanced at the article I mentioned by Ruth Kastner, but it really does seem to address this: related

Werner Heisenberg, the quantum pioneer famous for his uncertainty principle, considered his quantum math to describe potential outcomes of measurements of which one would become the actual result. The quantum concept of a “probability wave,” describing the likelihood of different possible outcomes of a measurement, was a quantitative version of Aristotle’s potential, Heisenberg wrote in his well-known 1958 book Physics and Philosophy. “It introduced something standing in the middle between the idea of an event and the actual event, a strange kind of physical reality just in the middle between possibility and reality.”

look i agree with you but im using the term real as if real is variable and relative to our evolution. I totally believe there is an external world for which sense is in relation, but i dont think its real as in the universal concrete version chosen by abstract thought, which i believe has no special place, like we can ascertain a reality that is totally accurate universally simply because we use a culture of mathematics and experiment. the thing is you don´t either, at present nobody does.

our senses are susceptible to illusion and ignorance, and so is our abstract world. but that is a good thing because the external world is always there, even though its changing, we can change with it and always keep our relation to it as close as possible.

usually when you give the argument people agree with you in essence but they still want to believe in the possible universal validity of their senses or abstract thought. they want this so bad because its a social value to be closest in the relationship to the external world, so the value real means that you are at that pinnacle of accuracy. but this drive to be accurate is always in danger of being mistaken to make the world we experience as the real one. or that science has achieved a universal perception that can clarify the senses and thought for eternity.

but what would happen if believing that we had finished the job has a negative effect on us for we have evolved to perceive a changing world and not a static one. so if science says we know whats going on maybe that degrades our relationship to the external world rather than enhancing it. that is the route and reason for my skepticism, not that i think we live in a dream.

yeah thanks, I'll try to make it less spewy. Its really just laziness, i spend a lot of time crafting writing either for legal work or lyrical prose. Both of those disciplines are time consuming, so I get online and want to chug espresso and spew ideas.

Im approaching the topic by reading a book by Schrodinger called 'what is life' because apart from just observing the world in my way, i have only really read philosophy (mostly nietzsche) some biology and the rest novels and plays etc. so im hoping shrodengers book will be a window into modern physics for me. I like abstraction but just havent any time to develop my math.

If you can recommend other books that do not explain through math, that would be good. but i totally understand if you simply cannot understand modern physics without math.

I had a great Listmania! list on Amazon but Amazon has nixed those lists and it’s disappeared. But titles for non-mathematicians are Quantum by Manjit Kumar (review here); Uncertainty by David Lindley (here); The Quantum Enigma, Bruce Rosenblum.

There’s an [in]famous book called Tao of Physics, by Fritjof Capra. This was published in the early 1970's and is still in print. I think it's well worth reading, even despite its critics (although also good to read the critics of course). That and a book called The Dancing Wu Li Masters by Gary Zukav initiated a minor social movement based on the popularisation of quantum mysticism. You would have to read them to really get the picture, but the basic idea is that the ‘consciousness causes collapse’ theory, which was at one time popular in QM, restores consciousness to the central role that scientific materialism has tried to banish it from. Of course this is wildly controversial and even political. But if you go to Amazon and enter Quantum Consciousness in the search bar you will find hundreds of titles on it and not all of them are rubbish. Oh, and How the Hippies Saved Physics by David Kaiser, which has this great photo of San Francisco's 'Fundamental Fysiks Group':


Left to right: Jack Sarfatti, Saul-Paul Sirag, Nick Herbert; bottom corner: Fred Alan Wolf.

Also have a read of Quantum Mysticism: Gone but not Forgotten.

Bernard D'Espagnat What we call reality is a state of mind

Richard Conn Henry The Mental Universe.

yes it gets very complicated as it pertains to a being in the world. Should we bother to differentiate reactions? I think we should so I see observation as not effecting will (maybe guiding and persuading it but not effecting it), which i percieve as work from more primordial/fundamental reactions.

I do not see sense reactions as structurally as important as digestive reactions, or digestive reactions as important as fertilization and the work that proceeds them. I think a natural hierarchy of reactions is important. therefore i think differentiation is important, so although indeed observation is reaction as is digestion or fertilisation, i do not think it honest to say that we have rearranged their hierarchy in any true sense to call observation action.