I Physicists disagree wildly on what quantum mechanics says about real…

[Ben vdP]

It seems to me that the root of the problem or issue is that it is tried too much to
see quantum particles as semi-classical objects or as particles\waves.
The message would then be to abandon those ideas or see those as approximations or illusions.
It is more modern to view a quantum particle as a field.

Is there an interpretation that is based on quantum particles as being fields?

Assumptions that are made at the measurement level can make perfect sense and be fruitful or even vital for all kinds of calculations. And yet, at the quantum level they can turn out to be false.

For example, if you assume that a quantum particle qp must be at a certain spot or occupies an amount of space with a certain shape and size, then already you have made a false assumption.

There is no necessity for a qp to have a certain size or shape. If you would be able to shrink to the size of a proton then there will be nothing there that you would be able to hold in your hand. There does not exist any tangible substance. A wall looks massive or solid but on a smaller scale it turns out to be an illusion.

What there is, is getting described as a field. A field has no shape and size. A galaxy hasn't either.
In the large it appears to have some disk shape. But when looking closer at it there are no sharp boundaries.
The solar system doesn't either. Here you have a tug of war between the radiation and fields of the sun versus interstellar space. But what defines the shape and size of the solar system, it's fuzzy.

A field inherently has a non-local aspect, so does a force that works at a distance. I think Bohm captured this the most but I do not expect Bohm to be right. If there is an issue with propagation faster then the speed of light, well, energy cannot go faster. But if there is no energy involved like with classical group waves then there might be a door open.

So, are there existing interpretations that does more justice to the field concept?

A bit silly, but try, for a change, to view a qp as a disturbance in space, an excitation, a resonance, an agglomerate of (group) waves, a peace of spacetime that has gotten itself into a knot, a cluster of adjacent virtual particle pairs constantly getting created and destroyed, a node in a large dynamic network showing collective behaviour , a fluidium, the exact nature is tbd.

 

[bhobba]

A field inherently has a non-local aspect, so does a force that works at a distance.

You need to become acquainted with Wigner's No-Interaction Theorem.

It explains both why fields must exist and why they most definitely are local.

The correct setting to discuss all this stuff is QFT, and it is a fruitful area of active research - but difficult and complex with several open questions:

https://arxiv.org/abs/2410.19101

Intuitively, in QFT, when particles are entangled, they become a single 'double knot' in the field. When observed, it is like cutting the knot. Think of a rubber band that is stretched further and further. When cut, it becomes two pieces of rubber. Was locality violated? I don't mean Bell Locality - we know it surely is - but the everyday common sense locality that SR is built on.

IMHO, the root of the endless discussions of Bell and its implications is tied up with not distinguishing Bell locality from our usual conceptions of locality. Bell locality (or IMHO a much better name - factorizability) is the condition that any correlations between distant events be explicable in local terms. Note that it concerns correlations—a statistical concept—not locality in SR.

Thanks
Bill

 

[elias001]

I am a fan of the "shut up and calculate" approach. I mean i expect it of engineers when they have to make use of it.

 

[weirdoguy]

Is there an interpretation that is based on quantum particles as being fields?

That is why I think that all those "foundations of quantum mechanics" and interpretational stuff are total waste of time at the moment. We know that QFT is in a sense more fundamental than non-relativistic QM. And we know it works differently. So even if one finds intepretation that most physicists would be ok with, what is the chance that it would survive going into full relativistic mode?

 

[bob012345]

I’d like to see an AI trained only on the accumulated experimental data and ask it to come up with a logical and consistent theory of nature from scratch.

 

[PeroK]

I’d like to see an AI trained only on the accumulated experimental data and ask it to come up with a logical and consistent theory of nature from scratch.

It will be fascinating to see what AI eventually comes up with. My guess is that we won't understand what it's doing, or how it comprehends the universe. In fact, my guess is it will be free of the philosophical hang-ups that bedevil human thinking.

 

[gentzen]

That is why I think that all those "foundations of quantum mechanics" and interpretational stuff are total waste of time at the moment. We know that QFT is in a sense more fundamental than non-relativistic QM.

So your guess is that there is no interpretation of non-relativistic QM that is comparable to Einstein's solution of the riddles of Maxwell's equations, namely that simultaneity is relative to the state of motion of the observer.

And we know it works differently. So even if one finds intepretation that most physicists would be ok with, what is the chance that it would survive going into full relativistic mode?

On the other hand, you guess that the interpretational riddles do have a "nice solution" for QFT. Who knows, maybe you are right. But Heisenberg&co believed that interpreting QFT (especially nuclear/particle physics) would be even more challenging than interpreting QM. Especially, there won't be a return to classical concepts, only to concepts even less intuitive than those required for understanding QM.

 

[ohwilleke]

You have missed the point. The theory, that is the "shut up and calculate" math theory does NOT cause confusion and in fact is, as the article says, "one of the most successful theories in science". It's how we choose to INTERPRET, in English, the results, that differ.

Shut up and calculate, of course, isn't truly just a math theory. In real life, scientists have to deal with what we called "story problems" in grade school, not bare equations and numbers.

To do quantum physics, one still has to make the part of the math that relates to real world observables correspond to things in the real world, and everyone who uses quantum physics still has to be able to operationally define concepts like what a "measurement" that collapses the wave function is, in a consistent and correct manner. In other words, even the "shut up and calculate" folks still have to interpret the math.

And, while there are lots of safe harbor circumstances in which the way that the math corresponds to real life observables is clear, there are indeed circumstances, like the precise definition of a "measurement", where there are gray area circumstances in which a scientist doing quantum mechanics won't be sure about how to apply the math to real world experiments in advance and the scientists just have to do the experiments to find out. This isn't a huge area of research, but there is definitely a subset of physicists who are working on those questions.

What the various "interpretations of quantum mechanics" are interpreting is not really the results. Instead, it is a non-mathematical description of the mechanism that gives rise to the observable results.

"Shut up and calculate" is a slogan for being deliberately incurious and agnostic about the physical reality of, and mechanism associated with, the part of the math in quantum physics calculations that does not correspond to real life observables.

Part of the reason that we feel that we need such interpretations is that we and all of our ancestors and ancestor species for as far back as animals have had brains (with the exception of small numbers of scientists in the last century and a half), have lived in circumstances where classical physics explains everything that they encounter and have to interact with in their entire lives, and any more complex quantum understanding of the world, even though it was more accurate, would have been selective fitness reducing because it would have taken more brain power without producing any different results.

In other words, we are hard wired to conceptualize the world that we encounter in a classical physics kind of way. But, in circumstances where quantum physics predicts things that are different from what classical physics predicts, our hard wiring gives us strong intuitions that are simply wrong. Learning that this intuition is wrong is rather distressing at first. It is the kind of thing that people earnestly trying to understand the world in the context of a comprehensive world view about the physical world can lose sleep over.

Understanding quantum physics requires us to abandon this hard wired intuition, reinforced by almost all of an entire lifetime of experience, in favor of a different, more accurate understanding of how the world works, arising from formal instruction and from experimental observation of the way that the world works in the highly specialized circumstances in which quantum physics makes different predictions about what we will observe than classical physics does.

This isn't to say that there couldn't be some interpretation that is heuristically more natural feeling than "shut up and calculate", which makes it easier to have the correct intuition about what quantum physics predicts in a particular situation accurately without actually doing all of the calculations. But none of the prevailing "interpretations of quantum physics" do this in a particularly satisfactory way that sets it apart from the alternatives as the clearly superior choice. There are interpretations out there that are clearly wrong or unhelpful, but as the survey at the start of the thread demonstrates, there are several alternatives that aren't manifestly incorrect in the eyes of well-informed scientists. And, there is no decisive consensus favorite.

 

[bob012345]

I think of shut up and calculate as more of an inside joke among physicists rather than some dogmatic statement. It mades a point with humor.

 

[ohwilleke]

I think of shut up and calculate as more of an inside joke among physicists rather than some dogmatic statement. It mades a point with humor.

You aren't wrong. But the point that is being made can be easily misunderstood if you aren't living it on a daily basis.

Since the word "interpretation" is slippery, it is useful to be specific and concrete about what it means in this context by demonstrating that "shut up and calculate" isn't literally true in the way that many people misunderstand it to be. This is useful because this narrows and clarifies what is really at issue when we talk about interpretations of quantum physics. The hope is that this clarity, in turn, will produce more enlightened thinking about the subject.

 

[syed]

Shut up and calculate, of course, isn't truly just a math theory. In real life, scientists have to deal with what we called "story problems" in grade school, not bare equations and numbers.

To do quantum physics, one still has to make the part of the math that relates to real world observables correspond to things in the real world, and everyone who uses quantum physics still has to be able to operationally define concepts like what a "measurement" that collapses the wave function is, in a consistent and correct manner. In other words, even the "shut up and calculate" folks still have to interpret the math.

And, while there are lots of safe harbor circumstances in which the way that the math corresponds to real life observables is clear, there are indeed circumstances, like the precise definition of a "measurement", where there are gray area circumstances in which a scientist doing quantum mechanics won't be sure about how to apply the math to real world experiments in advance and the scientists just have to do the experiments to find out. This isn't a huge area of research, but there is definitely a subset of physicists who are working on those questions.

What the various "interpretations of quantum mechanics" are interpreting is not really the results. Instead, it is a non-mathematical description of the mechanism that gives rise to the observable results.

"Shut up and calculate" is a slogan for being deliberately incurious and agnostic about the physical reality of, and mechanism associated with, the part of the math in quantum physics calculations that does not correspond to real life observables.

Part of the reason that we feel that we need such interpretations is that we and all of our ancestors and ancestor species for as far back as animals have had brains (with the exception of small numbers of scientists in the last century and a half), have lived in circumstances where classical physics explains everything that they encounter and have to interact with in their entire lives, and any more complex quantum understanding of the world, even though it was more accurate, would have been selective fitness reducing because it would have taken more brain power without producing any different results.

In other words, we are hard wired to conceptualize the world that we encounter in a classical physics kind of way. But, in circumstances where quantum physics predicts things that are different from what classical physics predicts, our hard wiring gives us strong intuitions that are simply wrong. Learning that this intuition is wrong is rather distressing at first. It is the kind of thing that people earnestly trying to understand the world in the context of a comprehensive world view about the physical world can lose sleep over.

Understanding quantum physics requires us to abandon this hard wired intuition, reinforced by almost all of an entire lifetime of experience, in favor of a different, more accurate understanding of how the world works, arising from formal instruction and from experimental observation of the way that the world works in the highly specialized circumstances in which quantum physics makes different predictions about what we will observe than classical physics does.

This isn't to say that there couldn't be some interpretation that is heuristically more natural feeling than "shut up and calculate", which makes it easier to have the correct intuition about what quantum physics predicts in a particular situation accurately without actually doing all of the calculations. But none of the prevailing "interpretations of quantum physics" do this in a particularly satisfactory way that sets it apart from the alternatives as the clearly superior choice. There are interpretations out there that are clearly wrong or unhelpful, but as the survey at the start of the thread demonstrates, there are several alternatives that aren't manifestly incorrect in the eyes of well-informed scientists. And, there is no decisive consensus favorite.

This is not an accurate way of viewing things. It is not that we have a true quantum explanation of the world that is complete and that our intuitions are wrong. It is rather that we simply don't know what is going on. For you to say that our intuitions are wrong implies that there is no clear, coherent picture of reality under the equations in current quantum mechanics. But there is no evidence behind this claim, and that would immediately rule out any interpretation that does claim to say there is more going on under the hood, like the many worlds interpretation or bohmian mechanics or whatever else may arise.

Equations alone never explain everything: they just restate patterns we observe. Schrödinger’s equation, for instance, tells us how the wavefunction evolves, but it does not tell us how and why we get particular measurement outcomes rather than others. This is true across physics: Newton’s laws didn’t explain what gravity “is,” they described the fact that masses influence each other, not how. Many were baffled as to how masses separated far apart from each other could affect each other at a distance. This is a classic case of a conflict with intuition. And their intuitions ended up being right: there was no action at a distance. Relativity and quantum field theory, for all their mathematical power, still need an ontological picture to make sense of what the math is describing: whether it’s curved spacetime, fields, or particles.

Historically, progress has come not just from better equations but from finding concepts that make those equations intelligible. Thermodynamics made sense once we understood molecules; relativity became intuitive once we saw spacetime as a geometric entity. So, to say that our classical intuitions are “wrong” in quantum physics misses the point. Our intuitions reflect the best ontological pictures we’ve had so far, shaped by the classical world. Quantum mechanics hasn’t provided a comparable picture yet. Without that, calling our intuitions wrong is premature.

 

[Herman Trivilino]

Any theory which causes more confusion than clarity after a century of use should probably be junked.

You'd be junking the most successful theory ever constructed. What would you have the tens of thousands of scientists, engineers, and technicians who use it every day to make contributions to society do? And do you propose we junk all the devices whose inventors made use of it? Or keep them but put a stop to the development of any new ones? And have the metrologists discard all the precision it has provided?

 

[ohwilleke]

This is not an accurate way of viewing things. It is not that we have a true quantum explanation of the world that is complete and that our intuitions are wrong.

Our intuitions are absolutely wrong, because our hard wired intuitions are based upon classical physics and classical physics are inconsistent with quantum physics.

It is rather that we simply don't know what is going on. For you to say that our intuitions are wrong implies that there is no clear, coherent picture of reality under the equations in current quantum mechanics.

It doesn't imply that. It implies that the true nature of, for example, electromagnetism is QED and not Maxwell's equations.

The reality of the equations is inconsistent with our classical physics intuition.

But there is no evidence behind this claim, and that would immediately rule out any interpretation that does claim to say there is more going on under the hood, like the many worlds interpretation or bohmian mechanics or whatever else may arise.

You are misstating the claim. There may or may not be a coherent picture of reality "under the hood" so to speak. "Reality" itself is arguably an inherently classical physics concept, although defining it is challenging.

Equations alone never explain everything: they just restate patterns we observe. Schrödinger’s equation, for instance, tells us how the wavefunction evolves, but it does not tell us how and why we get particular measurement outcomes rather than others. This is true across physics: Newton’s laws didn’t explain what gravity “is,” they described the fact that masses influence each other, not how. Many were baffled as to how masses separated far apart from each other could affect each other at a distance. This is a classic case of a conflict with intuition. And their intuitions ended up being right: there was no action at a distance. Relativity and quantum field theory, for all their mathematical power, still need an ontological picture to make sense of what the math is describing: whether it’s curved spacetime, fields, or particles.

Why does there have to be an ontological picture?

You "need" a way to operationalization how to turn equation results into observables. But, an ontological picture is a "want" not a "need". It is an unnecessary luxury that would be nice if we could get it.

Historically, progress has come not just from better equations but from finding concepts that make those equations intelligible.

Maybe we've hit the end of that history.

Thermodynamics made sense once we understood molecules; relativity became intuitive once we saw spacetime as a geometric entity.

Thermodynamics makes sense because deep down, it is just classical physics.

Relativity is, and always will be, contrary to our hard wired physical intuition. Even the leading researchers in the field struggle to really understand it outside some idealized special cases. One can overcome the drag down provided by intuition with grit, experience doing calculations with GR, and by rigorously overcoming one's natural intuitions, but it will always be a second language.

So, to say that our classical intuitions are “wrong” in quantum physics misses the point. Our intuitions reflect the best ontological pictures we’ve had so far, shaped by the classical world. Quantum mechanics hasn’t provided a comparable picture yet. Without that, calling our intuitions wrong is premature.

Our intuitions are wrong, without a doubt. There are half a dozen ways, at least, that quantum mechanics is flabbergastingly defiant of our lived experience and our wiring.

Whether our brains are even capable of intuitively groking quantum mechanics, as opposed to merely knowing how to use the equations that have been worked out, remains to be seen. Maybe we can, maybe we can't.

Nature has no obligation to work in a way that some evolved apes on a planet in an insignificant solar system at the fringe of a pretty ordinary galaxy in a vast universe are capable of understanding.

You can't teach a worm to understand English no matter how hard you (and the worm) try. There are many animals that are fundamentally incapable of understanding what their picture in a mirror is. We will never be able to truly appreciate the colors that butterflies can see, or what it feels like to have the sense of smell that a tracking dog does.

It could be that the ontological picture that is necessary to deeply and truly understand quantum mechanics is more than the 2025 model of Homo sapiens brain can process.

It could be that our brains our running on the metaphorical equivalent of Windows XP with a 256 KB memory card, and the "ontological picture of quantum mechanics" program requires Windows 11 and a 4 MB memory card to run. So, we may never be able to do this unless we can find a way to upgrade our brains, either through genetic engineering, or cyborg style part-machine enhancements. Indeed, we already rely on computers to grasp it and calculate it as it is.

If we're lucky, we can find some clever way to fit that kind of understanding with a very efficient "program" (i.e. interpretation of quantum mechanics) that can be understood by particularly intelligent people with the right mental bent. But, there is no guarantee that this is possible.

 

[bhobba]

So your guess is that there is no interpretation of non-relativistic QM that is comparable to Einstein's solution of the riddles of Maxwell's equations, namely that simultaneity is relative to the state of motion of the observer.

It is simply that we know standard QM is wrong, eg it predicts the hydrogen states are stationary, so can't jump between them. Yet they do. Interpreting it may be fun and help with interpreting the correct theory (which, as far as we can tell these days, is QFT that explains why the hydrogen states are not stationary), but is ultimately a dead end.

The modern situation is referred to as Effective Field Theory. This is based on what Wienberg refers to as a folk theorem. This states that any theory at sufficiently large distances will appear to be a QFT. The idea then is to accept our theories as approximations. One must then ask why try to interpret approximations? We know it is the only approximation from Wienberg's Folk Theorem - so there is no other choice. That there is no other choice is in itself an interpretation.

Also, surprisingly, usual QT is not a limiting case of QFT:
https://arxiv.org/abs/1712.06605

One must then ask, other than as mentioned, as an interesting exercise, the value of ordinary QM interpretations.

Thanks
Bill

 

[syed]

Our intuitions are absolutely wrong, because our hard wired intuitions are based upon classical physics and classical physics are inconsistent with quantum physics.

It doesn't imply that. It implies that the true nature of, for example, electromagnetism is QED and not Maxwell's equations.

The reality of the equations is inconsistent with our classical physics intuition.

You are misstating the claim. There may or may not be a coherent picture of reality "under the hood" so to speak. "Reality" itself is arguably an inherently classical physics concept, although defining it is challenging.

Why does there have to be an ontological picture?

You "need" a way to operationalization how to turn equation results into observables. But, an ontological picture is a "want" not a "need". It is an unnecessary luxury that would be nice if we could get it.

Maybe we've hit the end of that history.

Thermodynamics makes sense because deep down, it is just classical physics.

Relativity is, and always will be, contrary to our hard wired physical intuition. Even the leading researchers in the field struggle to really understand it outside some idealized special cases. One can overcome the drag down provided by intuition with grit, experience doing calculations with GR, and by rigorously overcoming one's natural intuitions, but it will always be a second language.

Our intuitions are wrong, without a doubt. There are half a dozen ways, at least, that quantum mechanics is flabbergastingly defiant of our lived experience and our wiring.

Whether our brains are even capable of intuitively groking quantum mechanics, as opposed to merely knowing how to use the equations that have been worked out, remains to be seen. Maybe we can, maybe we can't.

Nature has no obligation to work in a way that some evolved apes on a planet in an insignificant solar system at the fringe of a pretty ordinary galaxy in a vast universe are capable of understanding.

You can't teach a worm to understand English no matter how hard you (and the worm) try. There are many animals that are fundamentally incapable of understanding what their picture in a mirror is. We will never be able to truly appreciate the colors that butterflies can see, or what it feels like to have the sense of smell that a tracking dog does.

Again, this just isn't describing the issue correctly and is a common misunderstanding. You literally cannot even test QM's truth without some sort of intuitions that inevitably relate to classical physics. As just one quick example, when physicists say that they've measured the momentum of a particle, they never measure the momentum of a particle directly. They're basically measuring the time of flight and then use classical mechanics, not quantum mechanics, to calculate a momentum. The amount that people use classical physics unknowingly when trying to explain anything in quantum physics is phenomenal.

To this day, all tests of QM rely upon the concept of a measurement, and those measurement outcomes are locally and classically defined. As John Bell said, "The word ‘measurement’ should be banned altogether in quantum mechanics. It has no place except perhaps in discussions of experimental practice." See this link for a more detailed discussion on this.

In regards to the worm analogy, it is true that they are incapable of understanding certain things that we can, but this is not because their intuitions are different. It is because the very notion of understanding, especially conscious understanding, requires a certain type of brain that only we and possibly very few other animals have. So it is not that the worms have a different understanding. They have little to no conscious understanding of anything at all.

Last but not least, you cannot escape intuitions. You are using intuitions that you think are reasonable to even make your case that QM defies our historical intuitions, which again, given the current state of understanding of QM, is a very premature conclusion

 

[PeroK]

Last but not least, you cannot escape intuitions.

You have to if you study mathematics or modern physics. Although your main target is QM, the general theory of relativity entails curved spacetime. Not just curved space, but curved time. That is not intuitive. It also rests on the Lagrangian principle of maximal proper time, as the equivalent of Newton's second law, in order to describe timelike geodescics as the natural paths through spacetime for massive objects. Meanwhile, light travels along null geodesics, paths of zero spacetime distance. None of this is intuitive.

In fact, one could argue that Newton's law of gravity is unintuitive. This is what Newton had to say about his own theory:

“It is inconceivable, that inanimate brute matter should, without the mediation of something else, which is not material, operate upon and affect other matter without mutual contact…That gravity should be innate, inherent, and essential to matter, so that one body may act upon another at a distance, through a vacuum, without the mediation of anything else, by and through which their action and force may be conveyed from one to another, is to me so great an absurdity, that I believe no man who has in philosophical matters a competent faculty of thinking, can ever fall into it. Gravity must be caused by an agent, acting constantly according to certain laws; but whether this agent be material or immaterial, I have left to the consideration of my readers.”

— Sir Isaac Newton (Third letter to Bentley, 25 Feb 1693. Quoted in The Works of Richard Bentley, D. D. (1838), Vol. 3, 212-3.)

"Intuition", by definition, is a subjective collection of ideas that you have developed from ad hoc experiences as a human, living on planet Earth. That is not something that, in my opinion, can seriously be taken as the basis on which to reject all modern physics.

 

[Fra]

It is simply that we know standard QM is wrong, eg it predicts the hydrogen states are stationary, so can't jump between them. Yet they do. Interpreting it may be fun and help with interpreting the correct theory (which, as far as we can tell these days, is QFT that explains why the hydrogen states are not stationary), but is ultimately a dead end.

The modern situation is referred to as Effective Field Theory. This is based on what Wienberg refers to as a folk theorem. This states that any theory at sufficiently large distances will appear to be a QFT. The idea then is to accept our theories as approximations. One must then ask why try to interpret approximations? We know it is the only approximation from Wienberg's Folk Theorem - so there is no other choice. That there is no other choice is in itself an interpretation.

Also, surprisingly, usual QT is not a limiting case of QFT:
https://arxiv.org/abs/1712.06605

One must then ask, other than as mentioned, as an interesting exercise, the value of ordinary QM interpretations.

Thanks
Bill

I can't speak for others, but when I worry about "foundations of QM" it does not refers to non relativistic models of the atom, it refers to the foundations and constructing principles such as non commutative information and the measurement problem etc. All these issues are still in qft.

I rather see QFT (ie poincare invariant theory of measurements) as a special case of the applying some general yet unknown onstructing principles. As I think alot suggests at least to me that spacetime must somehow be emergent, it is a big mistake to think that qft in 4d space is a good startiing point.

I would expect that qft would follow as effective descriptions from a generalized qm principles along with spacetime in certain limits involving relationa betwwen system and context.

Its these deeper principles i seek when talking about qm foundations as they transcend 4d spacetime.

Yes QFT is a better bigger theory than nrqm but it has the same conceptual problems incoporating gravity.

/Fredrik

 

[weirdoguy]

This is not an accurate way of viewing things.

And what is your basis for that claim? Have you studied physics? I mean like 5 years of hard work at Uni, or something equivalent? Or are you just someone who knows some QM and thinks it's enough to tell physicists how they should think? Somehow QM interpretations draw the second type of people in here a lot. And I don't think it's fair to tell me what should I think if one hasn't been through the same hell blessing of studing theoretical physics as I was. Just like you don't go to a doctor and tell them how they should cure their patients.

 

[gentzen]

It is simply that we know standard QM is wrong, eg it predicts the hydrogen states are stationary, so can't jump between them. Yet they do. Interpreting it may be fun and help with interpreting the correct theory (which, as far as we can tell these days, is QFT that explains why the hydrogen states are not stationary), but is ultimately a dead end.

I guess this is mostly a mathematical artifact in this situation, caused by a continuum modeling in time, combined with a "discrete"/finite Hilbert space modelling in space: If couplings like those to the photon-field are neglected, then the state space of a bound electron becomes a finite dimensional Hilbert space.

The issue of this slight modeling mismatch came up recently (17. Juli 2025):

The shift in perspective has a lot to do with the prominent position of time and with physics as a description of "objects." For TomS, it seems a necessary thought that every physical "system" must be in a certain "state" at every point in time. The very concept of "point in time" is questionable in a non-local theory.

Well, a continuum modeling in time actually fits quite well with a continuum modeling in position space. On the other hand, if one believes that one should only work with finite Hilbert spaces, then continuum modeling in time is probably misguided. Therefore, I would be rather cautious about conclusions or paradoxes that follow from this "discrete space" + "continuous time" modeling. So if Sean Carroll were to conclude that the dimension of the Hilbert space is invariant from the beginning of time, assuming it is finite, then he has probably fallen into a trap.
But both quantum computers and consistent histories actually work with discrete time.
And as long as you model spacetime continuously in QFT, you essentially have to model time as continuous as well. If you consider it at all, and not just calculate scattering matrices between asymptotic states.

I later (21. Jul 2025) emphasised that (currently existing) quantum computers work with discrete time:

My main concern is that a quantum computer is discrete in time, even its identity.

in an unrelated question, but for other reasons: I tried to avoid/reduce misconceptions caused by over-idealized models of (currently existing) quantum computers:

The quantum gates are indeed applied sequentially. But a quantum computer usually also has a kind of "operating frequency." So the gates are not only applied sequentially, but their application is also perfectly choreographed.

The final measurement of the "output register" must also be just as perfectly choreographed. If this measurement didn't occur at the only right time, then of course one can still philosophize a lot about what it would have measured had it not been missed. And if one wants, one can simply repeat the experiment and actually measure this time.

 

[syed]

And what is your basis for that claim? Have you studied physics? I mean like 5 years of hard work at Uni, or something equivalent? Or are you just someone who knows some QM and thinks it's enough to tell physicists how they should think? Somehow QM interpretations draw the second type of people in here a lot. And I don't think it's fair to tell me what should I think if one hasn't been through the same hell blessing of studing theoretical physics as I was. Just like you don't go to a doctor and tell them how they should cure their patients.

I have a degree in physics. Secondly, contrary to what you might think, many physicists don't really think about these issues as much since it's just not practical for most day to day things, so being a physicist doesn't necessarily imply that you understand certain interpretations of QM better than others, since quite literally no-one knows what's going on under the hood behind these equations.

Secondly, claiming that someone's intuitions are wrong is also making a claim about physics and in turn reality, yet I don't see you questioning the expertise of the other person I was responding to. Is it only because his views happen to align with yours?

While we're at it, what are your credentials?

 

[syed]

“It is inconceivable, that inanimate brute matter should, without the mediation of something else, which is not material, operate upon and affect other matter without mutual contact…That gravity should be innate, inherent, and essential to matter, so that one body may act upon another at a distance, through a vacuum, without the mediation of anything else, by and through which their action and force may be conveyed from one to another, is to me so great an absurdity, that I believe no man who has in philosophical matters a competent faculty of thinking, can ever fall into it. Gravity must be caused by an agent, acting constantly according to certain laws; but whether this agent be material or immaterial, I have left to the consideration of my readers.”

— Sir Isaac Newton (Third letter to Bentley, 25 Feb 1693. Quoted in The Works of Richard Bentley, D. D. (1838), Vol. 3, 212-3.)

And that intuition from Newton was correct as I already mentioned. There is no action at a distance.

My point is just that in order to have any view on what you think the correct QM interpretation is, you must have intuitions that you rely on. If you accept a view that originally seemed unintuitive to you, there is something that is causing you to accept it, whether it be certain experimental results, or whatever else. But in order to accept that, the views must cohere with other kinds of intuitions you already accept.

“It is not uncommon for the most rigorous and technical of physicists to be guided by intuition, dreams, and aesthetic judgment.” - Freeman Dyson

 

[PeterDonis]

There is no action at a distance.

More precisely, our best current theories of physics do not contain any action at a distance, at least for one common meaning of that phrase--but there are other meanings of that phrase which aren't so clear cut. (QM has the no signaling theorem, but it also has Bell inequality violations.) So I'm not sure the dogmatic assertion you're making here is justified.

 

[PeroK]

And that intuition from Newton was correct as I already mentioned. There is no action at a distance.

So, physics has never been "intuitive" in the sense you demand.

“It is not uncommon for the most rigorous and technical of physicists to be guided by intuition, dreams, and aesthetic judgment.” - Freeman Dyson

It's different to be guided by these things, than to demand that the eventual theory meets certain intuitive criteria. Also, Bohr and Heisenberg must have been guided by their intuition when they broke from classical thinking; while Schrodinger and Einstein's intuition was that QM must be incomplete.

This is back to the point I've made several times. If, like me, you study mathematics and then physics, then you come to the party with a very different sense of what's intuitive.

It's not clear where you draw the line. Perhaps the plane geometry of Euclid is inituitive? What about Minkowski geometry? Is that acceptable as a physical theory? What about more general curved spacetimes? What about complex numbers? Are we allowed to use those? Or, do we defer to those from the middle ages who decried them as imaginary?

What mathematics is acceptable as a basis for physics? And, just as important, why are you the arbiter of this? Why am I wrong because I can conceive of things you can't? What if you met a layman who dismisses all physics and mathematics? Does it have to satisfy their intuition?

 

[Fra]

I agree there is always something one can call intuition, just like in an inference system there are "implicit prior information" that you can't explain, it's just there, it defines your ground or implicit bias of the rest of the constructions. It's not something we want, but it just seems unavoidable. It is not explicitly encoded in prior distributions; just like intuition is not explicitly a clean cognitive processing but more emotional. But even if emotions are more fuzzy, they serve a purpose.

But such intuition is nor more static, thany any given theoretical model framework as it can evolve. For example I am quite sure that someone that is trained in physics and studied lots of systems and models has evolved a differen intuition that than average 19th century pedestrain. If you spend alot time to understnad the world, in terms of say geometry, any geometric objects or notions perhaps seem intuitive to you. If you spend lots of time to undersstand the world in terms of interacting agents, that can become very intuitive as well.

It is very clear to me just from reading the physicsforums, in all the discussions about interpretations, realism etc, that even among those that at least have actually studied physics, their "intuition" and what they find weird or natural is VERY variable. So this different intuition is perhaps mirroring the divergent interpretations.

When I think back, my intuition about these matters is ALOT different now, than there were when i was a teen. Certain things, education and contemplation, changes how I think about things, and it also change what makes sense intuitively.

/Fredrik

 

[bhobba]

While we're at it, what are your credentials?

With my moderator's hat on, please no 'd**k measuring' contests. Let's discuss the physics. These things can often be found in the person's profile.

Thanks
Bill

 

[bhobba]

Yes QFT is a better bigger theory than nrqm but it has the same conceptual problems incoporating gravity.

Renormalisation was once seen as mathematical trickery, but several physicists, such as Wilson and Weinberg, clarified what was happening in the effective field theory approach. I have posted it before, but that new paradigm has changed how physicists look at combining QM and GR:
https://websites.umass.edu/donoghue/research/quantum-gravity-and-effective-field-theory/

One possible interpretation of QM is, as I have mentioned, that any theory at low enough energy will look like a QFT. QM is as it is because the energy scales we can currently probe all lead to the same type of theory.

https://arxiv.org/abs/quant-ph/0401062

Thanks
Bill

 

[Fra]

Renormalisation was once seen as mathematical trickery, but several physicists, such as Wilson and Weinberg, clarified what was happening in the effective field theory approach. I have posted it before, but that new paradigm has changed how physicists look at combining QM and GR:
https://websites.umass.edu/donoghue/research/quantum-gravity-and-effective-field-theory/

One possible interpretation of QM is, as I have mentioned, that any theory at low enough energy will look like a QFT. QM is as it is because the energy scales we can currently probe all lead to the same type of theory.

https://arxiv.org/abs/quant-ph/0401062

Thanks
Bill

Both these views, wilsonian RG flow between effective theories and the idea that qm structures is distinguished in theory space are good and compliant with how i see it, but it does not solve the fine tuning problem and in order to understand nature and the laws, we need to understand the "off-island" processes that converges to qm in a limit. It is effectively tp think that qft corresponds to some asymptotic theory in a theort space where wilder thinga happen.

I think we need to try to figure these processes out in order to find shortcuts to finetuning to find a unified theory at larger energies.

If not i fear the fate is that of string theory, a huge theoryspace that is too large so our inference may diverge.

Edit: Nature seems to have great flexibllity but does not diverge - so an explanation on things based on fine tuning is deeply unsatisfactory.

/Fredrik

 

[Peter Morgan]

Thanks, your comment made me notice that the wikipedia article "implicitly proposes" a solution to the whole conundrum surrounding the Copenhagen interpretation:

Instead of trying to fit Bohr's ideas into the Copenhagen interpretation, or distinguishing between Heisenberg's and Bohr's variant of the Copenhagen interpretation, simply take the ideas of Heisenberg and his pupils as the Copenhagen interpretation, and let Bohr's ideas find a better home.

The survey didn't do this. If you adhere to the ideas of Niels Bohr or Asher Peres, your only reasonable choices were "Copenhagen Interpretation" or "Other - non-categorized".

Ref 16 on that Wikipedia page, an article by Don Howard from 2004, presents a difference between Heisenberg's and Bohr's views that I have found specially helpful. To summarize, Heisenberg espouses collapse of the quantum state at the time of a measurement, whereas Bohr always rejected collapse.
Instead, Bohr discusses the relationship between different measurements (I have relied on the secondary literature about Bohr: I have never read more than brief quotes of his writing.)
In the light of quantum measurement theory since then, I think we can present Bohr as modifying what subsequent measurements are possible after a given measurement, which in mathematical terms is equivalent to the construction of a Positive Operator-Valued Measure, a POVM, for a joint measurement at time-like separation. I present that mathematical version of Bohr's idea (which I of course hope Bohr would not dismiss out of hand if he were still with us) in an article in JPhysA 2022, "The collapse of a quantum state as a joint measurement construction" (arXiv link, DOI there).

 

[Peter Morgan]

So, are there existing interpretations that does more justice to the field concept?

I like to think that my attempt at such is helpful, albeit still developing. I presented a talk to the Oxford Philosophy of Physics Seminar in October 2024 with the title "A Dataset & Signal Analysis Interpretation of Quantum Field Theory", . You will have to be willing to adopt an almost instrumental starting point, but the ideas develop into a mathematics that can be taken to be quite realist if you prefer that. We can use the mathematics of signal analysis as a starting point that I find significantly more helpful than the mathematics of the classical mechanics of particles or even of fields.

 

[Peter Morgan]

Renormalisation was once seen as mathematical trickery, but several physicists, such as Wilson and Weinberg, clarified what was happening in the effective field theory approach. I have posted it before, but that new paradigm has changed how physicists look at combining QM and GR:
https://websites.umass.edu/donoghue/research/quantum-gravity-and-effective-field-theory/

Renormalization is definitely on a better footing than it was before Wilson and EFTs, however I think it's fair to say that mathematicians still think it's problematic. 75 years of attempts tell us, however, that it's difficult to pinpoint the nature of the problem.
That we multiply operator-valued distributions carelessly when we construct Lagrangian densities has always seemed to me one aspect of the problem, but I never found that aspect mathematically helpful in any direct way. More productively, I suggest in arXiv:2109.04412 that we can rethink renormalization as a way to introduce nonlinearity into the Wightman axioms and I give a proof-outline of how models of the resulting nonlinear Wightman axioms can describe any physics that can be described by Lagrangian methods. The models I suggest work with products of test functions, which are always straightforward, instead of with products of operator-valued distributions, which never are.
The ideas in that paper were deemed by reviewers in 2023 1) obvious and 2) not at a mathematical level suitable for JPhysA. 1) was annoying because I had worked hard to make the ideas obvious; 2) has proved difficult to address, so I have instead been developing the ideas by giving talks. You can see how that currently looks in a Yale Physics Seminar on May 1st, starting at 38:56, . The title for the whole talk was “A Dataset&Signal Analysis Unification of Classical&Quantum Physics”, the first few words of which are intended to suggest an empiricist and mathematical perspective that is compatible with the empiricism of Effective Field Theories. The first part of the talk is grounded in published articles. Neither arXiv:2109.04412 nor the talk is perfect, you will be unsurprised to hear, but there are ideas there that some people find interesting. I will welcome comments.