If there's a philosophical/metaphysical aspect to this, it would be how or why something that is continually working should be so fundamentally difficult to describe as to its working — tim wood

I watched a video where quantum physicist admits many quantum physicists (not just students) don't fully grasp quantum physics. (the study of what's known about quantum world)

This video requires some background knowledge, but I think the answer to thread title is in the video @10:30
Which is that there are infinite localized field intensities in quantum world. (hopefully I got that right), instead of single source of wave origin origin which makes it difficult to measure or to research deeper.

Also IIRC the study of quantum physics isn't fully researched and understood.

I've made the comment on several occasions that the Schrödinger equation, in its simplest form, is a concept from elementary calculus: the instantaneous rate of change of something is proportional to the amount of that thing at that instant. In calculus the solution of such an equation involves the exponential function, and in the setting of complex analysis, e^it = cos(t)+isin(t), which is a wave structure. Not a physical wave. Nice video, thanks.

Yes, I watched that yesterday. It is based on the fact that in the double-slit experiment, the wave pattern will gradually emerge even if the particles are fired one at a time. This leads to the (to my mind absurd) expression that the 'particle interferes with itself'. The way I put it:

the interference pattern arises not because the particles are behaving as classical waves, but because the probability wavefunction – designated by the Greek letter ‘psi’, ψ, and often referred to as the Schrödinger equation, in honour of Erwin Schrödinger who devised it — describes where at any given point in time, any individual particle is likely to register. So it is wave-like, but not actually a wave, in that the wave pattern is not due to the proximity of particles to each other or their interaction, as is the case with physical waves. Consequently, the interference pattern emerges over time, irrespective of the rate at which particles are emitted, because it is tied to the wave-like form of the probability distribution, not to a physical wave passing through space. This is the key difference that separates the quantum interference pattern from physical wave phenomenon. This is what I describe as ‘the timeless wave of quantum physics’.

The reason it's metaphysically baffling is because it doesn't answer the question 'does the particle exist?' in an unambiguous, yes-no fashion. It neither exists nor does not exist - there are only degrees of possibility that it exists, right up until it is measured, which is the so-called 'wave function collapse'.
This is why the Copenhagen school says things like 'no phenomenon is a real phenomenon until it is an observed phenomena'.

Sir Roger Penrose cannot accept that - he is absolutely adamant that the wave function, and the wave function collapse, are physically real - otherwise, what kind of objects are we talking about? He and Einstein both reject quantum physics as incomplete because it can't answer that question. And, remember, here we're supposed to be dealing with 'fundamental particles', so this kind of pulls the rug from under physical realism.

The interpretation I favour is QBism. (I've written an essay on the topic.)

describes where at any given point in time, any individual particle is likely to register. So it is wave-like, but not actually a wave, in that the wave pattern is not due to the proximity of particles to each other or their interaction, as is the case with physical waves. Consequently, the interference pattern emerges over time, irrespective of the rate at which particles are emitted, because it is tied to the wave-like form of the probability distribution, not to a physical wave passing through space.

Reading this closely, and I hope not misreading, it would seem to leave as many or more problems as there are to start with. Assuming the particles follow a path of some kind, how is it they manage to favour some paths over others? The math of the ψ-function? Does it carry a pocket watch? The selection of paths followed is clearly not random. Not asking, being pretty sure there is no answer (yet). For whatever the particle is or is not, the account for the diffraction pattern is MIA - and so far a great mystery.

Maybe there is a system of resonances that influence the particles as they pass through the slit to follow one or another of a limited number of discrete paths?

Assuming the particles follow a path of some kind, how is it they manage to favour some paths over others? — tim wood

It's assuming too much. Paths are no more definite or real than particles. The brutal way of putting the Copenhagen attitude, is, in my view, there are no particles:

The wave function itself has no physical reality; it exists in the mysterious, ghost-like realm of the possible. It deals with abstract possibilities, like all the angles by which an electron could be scattered following a collision with an atom. There is a real world of difference between the possible and the probable. Born argued that the square of the wave function, a real rather than a complex number, inhabits the world of the probable. Squaring the wave function, for example, does not give the actual position of an electron, only the probability, the odds that it will found here rather than there. For example, if the value of the wave function of an electron at X is double its value at Y, then the probability of it being found at X is four times greater than the probability of finding it at Y. The electron could be found at X, Y or somewhere else.

Niels Bohr would soon argue that until an observation or measurement is made, a microphysical object like an electron does not exist anywhere. Between one measurement and the next it has no existence outside the abstract possibilities of the wave function. It is only when an observation or measurement is made that the ‘wave function collapses’ as one of the ‘possible’ states of the electron becomes the ‘actual’ state and the probability of all the other possibilities becomes zero.

For Born, Schrödinger’s equation described a probability wave. There were no real electron waves, only abstract waves of probability. ‘From the point of view of our quantum mechanics there exists no quantity which in an individual case causally determines the effect of a collision’, wrote Born. And he confessed, ‘I myself tend to give up determinism in the atomic world.’ Yet while the ‘motion of particles follows probability rules’, he pointed out, ‘probability itself propagates according to the law of causality’ — Kumar, Manjit. Quantum: Einstein, Bohr and the Great Debate About the Nature of Reality (pp. 219-220)

I recall you writing the other day that 'science gave up talking about causation 100 years ago.' Isn't this one of the main reasons for that? The famous Fifth Solvay Conference, where all of this was first discussed, was in 1927.

Maybe there is a system of resonances that influence the particles as they pass through the slit to follow one or another of a limited number of discrete paths? — tim wood

Sounds like Bohm's hidden variables. See this Space-Time episode.

I don't find 'the Copenhagen interpretation', vague though many say it is, hard to take. It maps against Kant's noumena-phenomena distinction.

Hi. Two separate issues. 1) the likelihood the particle will be here (and presumably not there). And 2) accounting for why in the diffraction pattern the particle is so choosy of landing places.

As to "resonances," the slit has to be narrow for the two-slit experiment to work. I wonder if near mass there is as field of some kind that can influence the very small passing nearby to take this or that path, the number of paths being discrete, and the influence to such paths being unequal, to account for the diffraction pattern and its uneven stripes. - I like the idea myself!

Analogously, a large ship traversing a narrow passage is subject to the influences of resident turbulence combined as well with its own self-caused turbulence; and if the ship not so massive, who knows where it might end up!

What does "real" even mean with respect to a "wave in quantum physics"?

Also, more significantly, what existential or epistemological difference do the ontological interpretations of "quantum physics" make to classical beings classically living in a classical world (re: locality¹)?

https://en.m.wikipedia.org/wiki/Principle_of_locality [1]

How nice of you to ask! Let me put on my fizzicist's hat, made of old pie-tins. I think I'm getting some local waves. They're telling me that "real" by itself doesn't mean anything - or rather, too many things. Instead you have to decide what is real, and then compare the Wave to see if it is real in comparison, and by what criteria. In my new book, Advanced Surfing Without Water, a wave is described as just a momentary surge in the amount of stuff going by, either in terms of density or volume. Seen that way, a quantum "wave" isn't. As description, however, it appears to be very real, a very real description. I hope that makes everything perfectly clear. If not, you can ask the ladies on Aurora Ave.; their answers might be better.

Also, more significantly, what existential or epistemological difference do the ontological interpretations of "quantum physics" make to classical beings classically living in a classical world (re: locality¹)? — 180 Proof

There is a fair bit of mathematical machinery that is used up again and again with these quantum interpretations. They are epistemologically silent, yet ontologically distinct, and sometimes even so obscure or unvisualizable in their presentations that they border on being declared as 'metaphysical nonsense'.

They are pragmatically a beast demanding some sort of Occam's razor to shave all of them away for cleaner but blander observable absolutism.

However, what if the mere mental fascination with any particular interpretation or indulgence in the 'chase' is what actually leads to the pragmatic results one desires?

When the dust settles. . . after all the epistemological external world skepticism. . . and the highest form of scientific under-determination of theories makes its appearance. . . what are you supposed to turn to in informing your 'free choice' or 'decision'? The aesthetically pleasing. . . the simplicity of theories. . . the indulgence in playful fantastical stories. . . and language attempts to put into pleasing speech the patterns we observe.

What difference does fantasy do to the 'free choice' and directing of the will of a Human being?

I'd say. . . a lot. Even if it is nothing but fantasy.

what existential or epistemological difference do the ontological interpretations of "quantum physics" make to classical beings classically living in a classical world — 180 Proof

Three of the better popular science books on the subject:

Uncertainty: Einstein, Heisenberg, Bohr, and the Struggle for the Soul of Science, David Lindley (2007)

Quantum: Einstein, Bohr, and the Great Debate about the Nature of Reality, Manjit Kumar (2011)

What Is Real?: The Unfinished Quest for the Meaning of Quantum Physics, Adam Becker (2018)

So you cannot answer the question?

We've been through it all before, always ends in impasse.

I'd like to know what variable makes an electromagnetic wave.

I mean ...

In water waves it's the variable water surface height that makes the wave.
In sound waves it's the variable air pressure that makes the wave.

What varies in an electromagnetic wave?

Is it the magnetic field density that varies at a certain frequency?

Assuming the particles follow a path of some kind, how is it they manage to favour some paths over others? — tim wood

The particles do not exist in the transmission of radiant energy, so there is no path. The energy moves as waves not particles. We all know about electromagnetic waves, light waves, radio waves, etc.. Those are real waves and we can see refraction (rainbows) and a variety of interference patterns associated with these waves.

The problem is that we have not identified the medium (sometimes called ether) within which the waves exist. Therefore the waves cannot be modeled or represented as they actually exist, so they are represented as a wave function. At the base of this problem is the fact that there is no adequate understanding of the photoelectric effect, which is the quantized way that fields of radiation waves interact with what are known as material objects. That is the relationship between the medium (ether) and the supposed material objects.

How does the relationship between energy and matter play a role in the nature of the wave-particle? Einstein showed that matter and energy are the same thing. It seems to me that energy of all forms come in waves. Waves on the ocean are two-dimensional while EM waves propagate across space in 3 dimensions. What if the wave in wave particle duality is propagating across 5 dimensions? If time is the fourth dimension would this play a roll in how we perceive particles making wave patterns over time?

Not a physical wave. — jgill

That doesn't mean it's not real. It's just not physical. Likewise energy is real, even though it's a construct.

The selection of paths followed is clearly not random. Not asking, being pretty sure there is no answer (yet). For whatever the particle is or is not, the account for the diffraction pattern is MIA - and so far a great mystery. — tim wood

There is actually a mathematically rigorous theory called stochastic mechanics which shows that you can produce all quantum behavior from classical particles that undergo a non-dissipative diffusion.

https://en.wikipedia.org/wiki/Stochastic_quantum_mechanics

What is a non-dissipative diffusion? Well a dissipative diffusion is something like a pollen particle being pushed about seemingly randomly by H2O molecules in a glass of water. As the pollen bashes into H2O molecules, they impart a drag or frictional force on the pollen meaning it leaks or dissipates energy into the environment.

In a non-dissipative diffusion, energy does not dissipate in these interactions; any energy lost would be returned on average to the pollen by the H2O molecules. The system is frictionless in some sense.

What is really unique about stochastic mechanics is its the only interpretation / formulation I know of that actually derives quantum theory de novo from other assumptions. It then suggests that it is sufficient for quantum behavior to be executed by regular classical point particles so long as you enforce the absence of dissipation in its behavior so that energy is conserved on average.

But if you want a kind of common-sense realistic ontology, it probably means you want a model similar to the pollen floating in the glass of water. There are experiments which actually produce quantum-like behavior in this kind of way:

https://en.wikipedia.org/wiki/Hydrodynamic_quantum_analogs

What isn't mentioned in the article but you can find in the papers is that the reason the quantum-like behavior occurs is that vibrating the bath reduces viscous dissipation in the bath, 'viscous-ity' being related to friction due to interacting molecules in a fluid. Effectively, vibrating the bath replaces energy that is lost due to friction, and this makes the bouncing droplet (video at top of the page) exhibit behavior that looks quantum-like.

If hypothetically reality were to be like this then it implies particles are floating around in stuff. Very big assumption, but not so big considering the fact we know that space isn't really empty but filled with a vacuum energy and fluctuations. This provides a very plausible home for this mechanism and the fact particles are floating in a kind of fluid of stuff would give a mechanism for what you are talking about in the post, about how they seem to be guided along paths in a double slit experiment that appear as an interference pattern. Closing a slit then affects whats going on in the fluid which would then pass along to the particles move through it. You no longer have to think about a particle "interfering with itself".

So I think there is no reason to give up on a classical, realistic universe just yet. It is absolutely mathematically possible.



You see in the image trajectories from this approach produced by a mathematical simulation (far right image). Bohmian mechanics also uses classical particles but it effectively just takes the quantum wavefunction and puts deterministic trajectories on top - it doesn't explain anything about why quantum behavior occurs. In contrast, stochastic mechanics starts with a classical description of particles being pushed about like the pollen in a glass of water, and shows that under specific conditions related to energy conservation, as I previously described, all quantum behavior occurs for regular classical particles.

Okay. Again, you've got nothing but ...

Bohmian mechanics also uses classical particles but it effectively just takes the quantum wavefunction and puts deterministic trajectories on top - it doesn't explain anything about why quantum behavior occurs. In contrast, stochastic mechanics starts with a classical description of particles being pushed about like the pollen in a glass of water, and shows that under specific conditions related to energy conservation, as I previously described, all quantum behavior occurs for regular classical particles. — Apustimelogist

The stochastic interpretation of QM isn't an interpretation of QM in the sense that Bohmian Mechanics is, i.e. in the sense of being a non-local or anti-realist account of quantum entanglement,, rather the stochastic interpretation amounts to a phenomenological interpretation of quantum statistics that doesn't explain entanglement and the origin of Bells inequalities.

What varies in an electromagnetic wave? — Quk

Good question, to which I don’t know the answer - but the wavefunction doesn’t describe an electromagnetic wave. The wavefunction is a wave-like distribution of possibilities, but it’s not *actually* a wave. That’s something the video linked in the OP explains (he also remarks that it is a source of confusion about the importance of waves in quantum mechanics.)

the stochastic interpretation amounts to a phenomenological interpretation of quantum statistics that doesn't explain entanglement and the origin of Bells inequalities. — sime

Right. The theory accounts for the observed statistical patterns of quantum mechanics (similar to the Born rule), but it does so by modelling outcomes, not necessarily by explaining the underlying quantum structure. So it’s phenomenological in the scientific sense of being descriptive, not necessarily explanatory.

Is that correct?

it’s not *actually* a wave — Wayfarer

Understood. But it must be "something" that changes its property at a certain frequency, so that a frequency can be detected and filtered by the receiver (to distinguish radio stations or colors). Also, as we know, the higher the frequency, the higher the energy (at the same amplitude).

Infrared ... red ... violet ... ultraviolet ... X-ray ... LF ... HF ... UHF ... gamma ...

In a radio receiver antenna, the electromagnetic waves induce alternating electric current. It's the same effect that occurs when you move a magnet near an electric wire quickly back and forth. The magnetic field, flux, or density changes relative to a certain place in 3D space (e.g. where a copper wire is located). However, that field, flux, or density itself is probably indescribable -- like a ghost ...

Understood — Quk

I don't think so. I think you're confusing electromagnetic waves with the wavefunction in quantum physics. This thread is about the latter, not the former.

It is an interpretation in the sense of Bohmian mechanics, in fact their underlying mathematical structure is very similar.

Entanglement and Bell inequalities are direct consequences of the non-dissipative diffusion like all other quantum behavior. The background hypothesis gives a conceivable way in which the non-dissipative diffusion could be physically realized, albeit without specific details. This is an interpretation explicitly intended to give a physical account of quantum theory.

Right. The theory accounts for the observed statistical patterns of quantum mechanics (similar to the Born rule), but it does so by modelling outcomes, not necessarily by explaining the underlying quantum structure. So it’s phenomenological in the scientific sense of being descriptive, not necessarily explanatory. — Wayfarer

As I said in my first post, it derives quantum theory from non-quantum assumptions about classical particles undergoing diffusion. It proves that in principle quantum mechanics can be instantiated in normal classical particles given the correct specifications which basically just amounts to conserving energy on average.

Thanks for the clarification — I take your point that stochastic mechanics aims to be a constructive theory, grounding quantum phenomena in classical-like processes with added stochastic dynamics.

It does seem to follow Bohm’s realist sentiment: to recover quantum statistics from an underlying deterministic mechanism. But it still relies on a hypothetical substrate — diffusing particles and a non-dissipative background — that isn't observable and must be posited as a metaphysical assumption (presumably subject to further investigation.)

By contrast, the Copenhagen interpretation is more circumspect. It doesn’t posit unknowables, but draws a line at what can meaningfully be said — more in the spirit of Wittgenstein: “Whereof one cannot speak, thereof one must be silent.” The Copenhagen attitude is not nearly so 'mystical' as many of its critics contend. It's a philosophical humility, not a metaphysical fog.

What varies in an electromagnetic wave? — Quk

In my understanding, it is the strengths of the interacting electric and magnetic fields that vary. There is no medium beyond that.

I think you're confusing electromagnetic waves with the wavefunction in quantum physics. This thread is about the latter, not the former. — Wayfarer

Are we not talking about the double slit experiment where light is sent through slits and certain interferences are observed?

Are we not talking about the double slit experiment where light is sent through slits and certain interferences are observed? — Quk

Yes - but the salient question is, why does the interference pattern occur, when light is emitted at the rate of one particle at a time? How can that result in a wave pattern? That question concerns the wave function ψ, not electromagnetic nature of light. It's easy to confuse the electro-magnetic waves, and the wave-function - this is discussed in the video linked in the OP at around 3:28 ('the Dirac wave for the electron IS NOT the Schrodinger wave'.)

But it still relies on a hypothetical substrate — diffusing particles and a non-dissipative background — that isn't observable and must be posited as a metaphysical assumption (presumably subject to further investigation. — Wayfarer

Sure, but I would say it is arguably still better than many other interpretations given it provides an explanation for quantum behavior, it completely deflates the measurement problem and classical limit, it returns metaphysics to what is intuitive and commonsensical. I would say from a standpoint of rationality this is a preferable theory because arguably we shouldn't update our beliefs about the universe (or anything) any more than required given the evidence. And despite the background assumption I think this theory is clearly the least ontologically radical of any alternatives in the sense of diverging as little as possible from pre-quantum beliefs about how the world is, what everyday experience suggests the world is like, what other sciences suggest the world is like.

It seems almost completely conspiratorial to me that the world would have some bizarre, inscrutable ontology when mathematically there is a theory, maybe even multiple theories, that can produce quantum behavior through the kind of common-sensical, realistic, classical-like manner thag the world otherwise presents itself to us as.

And yes, obviously the background is a big assumption; but we already know - or at least quantum field theory tells us - about a kind of background because the vacuum is not empty: vacuum energy and fluctuations. We just don't know if that kind of background could be part of or indicative of the same kind of background as you would want in stochastic mechanics. But at the very least this isn't such a big leap as something like Many Worlds where you are assuming something else radical (and a bit ridiculous) exists that we can never observe and has no basis anywhere else in science. We know a kind of background exists (or you are at least justified in believing it based on quantum field theory):

https://en.wikipedia.org/wiki/Vacuum_energy

We just don't know if it could be the stochastic mechanical one.

I really think that I do understand your point.

Even when just a single photon is sent at a time, and interference occurs, I think my question is on-topic. For example, the changing property might also lie in the photon's kind of spin etc. rather than in its location or velocity. I don't know. But I'm curious, and I still think it's on-topic.

Sure, but I would say it is arguably still better than many other interpretations given it provides an explanation for quantum behavior, it completely deflates the measurement problem and classical limit, it returns metaphysics to what is intuitive and commonsensical. — Apustimelogist

But notice that embodied unstated realist assumptions about 'what the world is like'. And as Sabine Hossenfelder points out in Lost in Math, there's this tendency in today's physics to rationalise posits on the basis that they supposedly make intuitive sense and then to devise the mathematics to make them stand up. So given your realist predilections, then this approach seems natural to you.

(As I've made clear in the other thread on this topic, I'm highly suspicious of the many-worlds theory.)

I would say from a standpoint of rationality this is a preferable theory because arguably we shouldn't update our beliefs about the universe (or anything) any more than required given the evidence. — Apustimelogist

Right - but this is because of a prior commitment to realism, right? Whereas QBism says that the wavefunction ψ does not describe something that exists objectively “out there” in the world. Instead, it represents the observer’s knowledge of the probabilities of the outcomes of observations. In other words, the wavefunction provides a rule that an agent/observer follows to update their beliefs about the likely outcomes of a quantum experiment. These probabilities, much like betting odds, are not intrinsic features of the world but rather reflect the agent’s expectations based on their unique perspective and prior information.

In QBism, measurement outcomes are seen in terms of experiences of the agent making the observation. Each agent may confer and agree upon the consequences of a measurement, but the outcome is fundamentally the experience that each of them individually has. Accordingly the wavefunction doesn’t describe the system itself but rather the agent’s belief about what might happen when they interact with it. So while quantum theory has extremely high predictive accuracy, no two observations are ever exactly the same, and each observation is unique to a particular observer at that moment. And this is being borne out by experimental validation of 'Wigner's Friend'-type scenarios.

(This doesn't mean that the outcome is entirely subjective, either, as it is constrained by the Born Rule to a range of possibilities. But it's not entirely determined, either.)

I don't know. — Quk

I'm not a physicist, what I know about it is based on readings of science and listening to lectures. But you're grasping for a simple explanation of a phenomenon which defies simple explanations. Have a look at this primer https://brilliant.org/wiki/double-slit-experiment/