3 thoughts on “Advancing QFT visualization – further demystification?”

1. 

   Well, here we go again … yet another recap … although it’s really about fields (QFT) … but here there be ‘particle’ words … quantum particles, photons – real & virtual … here there be Feynman diagrams … (virtual) mediation of the EM force (somehow in the math). I felt stuck in Quantum Weirdness 1.0.

   Well, at least Siegel put “exchanged photons” in quotes. And he does mention quantum field theory. And he does use Matt Strassler’s term ‘wavicle’ (for which Siegel wrote a book review, eh).

   He starts by clarifying what real photons are … well, sort of, since there’s no mention of wavepackets, just a standard EM wave graphic. Another diagram uses standard plane wave squiggles [1].

   And a “visualization of a quantum field theory” is a standard quantum vacuum fluctuation animation (from Wiki).

   So, no advance in visualization: no mention that Feynman really was a ‘particle’ guy; no mention that the sum-over-all-paths thing really might be about the need to accomodate photons as extended wavepackets; no mention of variations in energy density & interactions of quanta in a fluid-like Grid (Wilczek) and resulting topology of field gradients, … Just more again about doing the math.

   • Big Think > “Ask Ethan: How do photons mediate both attraction and repulsion?” by Ethan Siegel (January 10, 2025) – The electromagnetic force can be attractive, repulsive, or “bendy,” but is always mediated by the photon. How does one particle do it all?

   (excerpts)

   Looking at the picture of Feynman diagrams and putting together what most of us know about electrons and photons (and momentum conservation), it’s easy to see how one would look at this and think that “repulsion” is natural, but “attraction” or “magnetic bending” is difficult to understand. But this fundamentally misunderstands what it is that these Feynman diagrams are actually encoding.

   (image caption) A Feynman diagram representing electron-electron scattering, which requires summing over all the possible histories of the particle-particle interactions. The idea that a positron is an electron moving backward in time grew out of the collaboration between Feynman and Wheeler, but the strength of the scattering interaction is energy-dependent and is governed by the fine structure constant describing the electromagnetic interactions.

   What Feynman diagrams show isn’t, in fact, related to the strength or direction of an interaction in any sense.

   The reality is that these forces, mediated by the bosons in our illustrated Feynman diagrams, can always be of either sign: positive or negative. What determines that? For electrostatic forces, it’s whether the charge “signs” on the particles that are exchanging the photons are like (positive-positive or negative-negative), which leads to repulsion, or opposite (negative-positive or positive-negative), which leads to attraction.

   … because these aren’t real photons that are exchanged, but virtual ones. These photons don’t exist in the conventional sense: if you placed a detector between two electrons that were repelling one another, you wouldn’t detect photons being exchanged between them at all. Unlike real photons, which carry both energy and momentum, virtual photons exist solely as a calculational tool; there is no “exchange” that’s occurring in any measurable way.

   What you have to recognize is that the “internal photons” (or any other “exchanged” particles) are not real particles, and they are not transferring momentum from one particle to another. Those wiggly lines aren’t truly representing particles, but are instead representing what’s known as the propagator: a function that gives the correct probability amplitude for interactions to occur, and which is derivable from Feynman’s other great contribution to theoretical physics, the path-integral.

   Notes

   

   [1] As a wavepacket, the photon emitted (or “absorbed”) in an electron’s state transition is NOT monochromatic (a plane wave).

   Related posts

   • Virtual attraction

2. 

   Well, on my to-do list for commentary, there’re a few more articles by well-known physicists. Here’s a recent one by Brian Cox (below).

   PROLOGUE

   Before my take on Cox’s presentation (below), here’s my take on quantum physics.

   Here’s a quick sketch of my visualization for Quantum Weirdness 2.0. The landscape at the “tiniest scales in the subatomic realm.” Something beyond our ability to conjure up other than with mathematical models.

   Nevertheless, imagine energy packets (bundles) which are complex superpositions of numerous (perhaps unlimited) wave forms in a foundational fluid-like medium (field). Wavepackets extended in spacetime.

   These packets are “particles” only in the sense that they are ‘discrete’ and ‘indivisible’ and ‘localized.’

   These energy packets are defined relationally. In a sense that complex superpositions are tangled components with a dynamic topology (with an uncertainty relationship for position & momentum, eh).

   Relational also in the sense that their states depend on interference / interaction with other packets (even those in measurement devices). Identical “things” do not have identical, intrinsic properties when measured anywhere – independent of context [1] [2].

   As such, any so-called properties which we might measure are indeterminate (identical conditions do not lead to identical results). While unified, there’s no simple (non-complex) entity to measure. One can expect probabilistic values for any such property. For example, spin.

   Our everyday world emerges from the interplay of superposition and entanglement within a multilayered superconducting Grid (Wilczek).

   MY TAKE ON COX’S PRESENTATION

   Well, the good news is a reconsideration of the way to teach Quantum Physics 101, an introductory course to the topic. The bad news is that Cox still uses the phrase “quantum mechanics” (although the article’s title uses “quantum physics“) and a particle framework, when his point really is to skip over all that historical “mechanical” confusion (baggage).

   I like the way he starts with the notion of “spin.” The tired analogy of a heads-or-tails coin is problematical, but that introduces the notion of superposition, with “any mixture of heads and tails.” (Many eyes glazed over at this point?)

   That “perfectly legitimate description [superposition] of the state of the configuration,” however, is just left dangling for mere mortals, with just a note that electrons (still called particles) have a property called spin which is a mixture of ‘up’ and ‘down’ (yet only measured as up or down, eh).

   He clarifies that this “mixture” is not a probability theory thing (like weather forecasting, due to our incomplete knowlege or understanding), but “fundamental” – intrinsic (yeah, okay).

   Then he gets to the “double-slit experiment” (which Art Hobson also focuses on in his book Tales of the Quantum). And Feynman’s lectures from the 1960’s.

   So, a reasonable place to start the discussion; but, basically, still a recap. Stuck in Quantum Weirdness 1.0. He excludes any middle perspective on so-called particles. Just the typical “bullet” and water wave tropes. Although he does introduce the phrase “a big extended wavy thing” (à la Hobson).

   At least Cox avoids the term wavicle. But there’s no notion of photons or electrons et al. as (quantized) bundles of energy – wavepackets. Quanta as topological superpositions of many wave forms. Energy packets with an inherent uncertainty for their measured properties. Which indeed interfere with other packets (and related fields) in devices (or even with themselves).

   In the end, however, while there’s weirdness, “well, it doesn’t really matter so much practically, right?”

   Then Cox discusses quantum computers, that practical landscape: “You can also then ask the question, well, what happens if I get another one [qubit], two electrons together? These can be in what’s called an “entangled state.” And the haze of references – the standard liturgy – to the “Bell state,” etc. (and the ususal handwaving over the 2^n supremacy of qubits over bits in characterizing the state of a system).

   • Big Think > “Physicist Brian Cox explains quantum physics in 22 minutes” (April 2025) [talking head video] – “Quantum mechanics and quantum entanglement are becoming very real. We’re beginning to be able to access this tremendously complicated configuration space to do useful things.”

   (quotes from transcript)

   One of the big changes, actually that’s happened, in teaching quantum mechanics in universities over the last few decades is that it was always, when I learned it, so it’s about even in the 1990s, it was common to teach it historically. … photoelectric effect … Niels Bohr … Ernest Rutherford … a picture of [the atom] that doesn’t work … then Bohr suggests that electrons can only take certain energies …

   But if you do that, you pick up all the confusion, the confusion, decades and decades of confusion that these great physicists felt in trying to come to terms with this counterintuitive picture of the world.

   So now, I think it’s more common in universities to start with the theory as we understand it today, and just say, well, this is the way the world works.

   And perhaps the best introduction would be to think of a property of particles called “spin.”

   The key difference in quantum theory is that these probabilities are fundamental. They’re fundamental to the description of nature. So it is not the case that if we have an electron in some kind of configuration, then our theory predicts probabilities because we don’t quite know exactly what, how this thing is configured. The probabilities are intrinsic to the theory itself. And pretty much all of the intellectual challenges and the confusion around quantum mechanics comes from that very simple property.

   If you look at pretty much any book on quantum mechanics, there is one experiment which you can describe. It’s a very simple experiment which encapsulates all the, I was gonna say weirdness, but it’s, let’s say all the properties of the quantum world.

   It’s called the “double-slit experiment.” And by the way, I’ll strongly recommend, I think it’s almost universally accepted, the best description of the double-slit experiment is freely available. It’s in the Feynman lectures, volume three, first chapter.

   So the statement is that the electron explores both routes at the same time at once, let’s say, on its route from the electron gun through the slits to the screen. So that’s a very strange picture of reality. … It tells us that the electron must in some sense explore all routes [Feynman] on the way from the gun to the screen.

   So what you can do is you can, you can assign, calculate what’s called a “complex number” for every route that the particle, the electron, can take from gun, through the slits, to the screen. … So a complex number has a clock hand, there’s a length of the clock hand and there’s the time on the clock face. And you can calculate how those clock faces kind of evolve and change, and spin around from the moment the electrons emitted to the moment it hits the screen.

   But I suppose the problem comes when you say, well, what does it mean? Does it really mean, is it just calculational? Is it just mathematics or does it really mean that the electron explores every possible route? … The problem with quantum mechanics, I suppose, is what when you try to interpret what the calculation means for the nature of reality. … How the world that we see emerges from this rather strange but well-defined behavior that we see in the subatomic world. … Because we are using that behavior now in technologies and so it really does become an important theory to try to understand.

   Notes

   [1] Re the point that “Identical ‘things’ do not have identical, intrinsic properties when measured anywhere – independent of context,” I found this article interesting. It’s, as yet, about a theoretical (mathematical) construct, but explores the question as to the strict definition of indistinguishability in the context of superpositions.

   Terms: Anyons (Wilczek), Rydberg atoms

   • Quanta Magazine > “‘Paraparticles’ Would Be a Third Kingdom of Quantum Particle” by Shalma Wegsman (April 11, 2025) – Rather than all (boson) or none (fermion) packing, is there another class of quanta “able to pack just a few particles into the same state, before getting crowded and forcing others into new states?”

   In their (Wang and Hazzard) model, in addition to the usual properties of a particle like charge and spin, groups of paraparticles share extra hidden properties. As with the minus sign that gets squared away during a measurement, you can’t directly measure these hidden properties, but they change how the particles behave.

   The researchers considered the fact that quantum systems can exist in multiple possible states at once — what’s called a superposition. They imagined switching between the perspectives of observers who exist in these superposed states, each of whom describes their branch of reality slightly differently. If two particles are truly indistinguishable, they figured, then it won’t matter if the particles are swapped in one branch of the superposition and not in the other.

   [2] Re relational quantum physics

   • Wiki > Carlo Rovelli

   In 1994, Rovelli introduced the relational interpretation of quantum mechanics, based on the idea that the quantum state of a system must always be interpreted relative to another physical system (like the “velocity of an object” is always relative to another object, in classical mechanics). The idea has been developed and analyzed in particular by Bas van Fraassen and by Michel Bitbol. Among other important consequences, it provides a solution of the EPR paradox that does not violate locality. Rovelli has expressed the main idea of relational quantum mechanics in the popular book Helgoland.

   • AI Overview [carlo rovelli on reality of the wave function]

   Carlo Rovelli, in his relational interpretation of quantum mechanics, does not view the wave function as a direct representation of reality, but rather as a tool for calculating the probabilities of interactions between systems. He argues that the wave function is a “calculation device” that keeps track of past quantum events, rather than a reflection of a fundamental, underlying reality. This perspective shifts the focus from the wave function itself to the relationships and interactions between systems, where reality is constituted by these interactions.

   Elaboration:

   Rovelli’s relational quantum mechanics proposes that the quantum state of a system is only meaningful relative to another system. This means that the wave function, which describes the quantum state, does not represent an objective, pre-existing property of a system, but rather a description of the system’s relationship to another system.

   Key points of Rovelli’s view:

   Quantum mechanics is a theory of interactions:

   Reality is not composed of standalone objects with pre-defined properties, but rather emerges from the interactions between systems.

   Wave function as a calculation tool:

   The wave function is not a representation of reality, but a mathematical tool used to predict the outcomes of interactions between systems.

   Relative nature of reality:

   The properties of a system are only real in relation to other systems, and different observers can have different, equally valid, descriptions of the same system.

   Challenge to realistic interpretations:

   Rovelli’s interpretation challenges the idea that the wave function represents a fundamental, underlying reality, such as in interpretations like many-worlds interpretation.

   In essence, Rovelli’s relational quantum mechanics provides a different perspective on the wave function, emphasizing its role in describing interactions rather than directly representing a fundamental reality. This interpretation offers a way to address some of the puzzles of quantum mechanics, such as the measurement problem and the nature of quantum entanglement, by focusing on the relational nature of reality.

   Generative AI is experimental

   Also, Rovelli argues in this article that Max Born and his collaborators may help clear “confusion about what quantum phenomena tell us about reality.”

   • New Scientist > “Carlo Rovelli on what we get wrong about the origins of quantum theory” by Carlo Rovelli (15 April 2025) – “Introductory quantum physics classes … I think the emphasis on Schrödinger’s waves is responsible for today’s confusion about what quantum phenomena tell us about reality.” [Paywall]

   • “Matrix mechanics mis-prized: Max Born’s belated nobelization” by John L. Heilbron and Carlo Rovelli (18 October 2023)

   Abstract

   We examine evaluations of the contributions of Matrix Mechanics and Max Born to the formulation of quantum mechanics from Heisenberg’s Helgoland paper of 1925 to Born’s Nobel Prize of 1954. We point out that the process of evaluation is continuing in the light of recent interpretations of the theory that deemphasize the importance of the wave function.

   • AI Overview

   Carlo Rovelli, in his work, emphasizes that Max Born’s contribution was not solely about the probabilistic interpretation of the wave function, but also about recognizing the fundamental role of matrices in quantum mechanics. Rovelli highlights that Born’s work, alongside Werner Heisenberg and Pascual Jordan, established the foundations of matrix mechanics, a formulation of quantum theory that was later overshadowed by Erwin Schrödinger’s wave mechanics. Rovelli suggests that Born’s Nobel Prize, awarded in 1954, was a belated recognition of his earlier, more fundamental contributions, which included understanding the statistical interpretation of the wave function before Schrödinger’s wave mechanics.

   Here’s a more detailed breakdown:

   Rovelli’s Perspective:

   Rovelli argues that Born’s work, particularly his collaboration with Heisenberg and Jordan, was crucial in developing the mathematical framework of quantum mechanics, specifically matrix mechanics. This framework, which predates Schrödinger’s wave mechanics, provided a solid foundation for understanding quantum phenomena.

   The Wave Function:

   While Born’s interpretation of the wave function as describing probabilities is important, Rovelli emphasizes that Born’s contributions extended beyond that, including his work on matrix mechanics.

   The Nobel Prize:

   Rovelli notes that Born’s Nobel Prize was awarded for the probabilistic interpretation of the wave function, but suggests that this was a delayed recognition of his earlier and more fundamental contributions to quantum mechanics.

   The History of Quantum Theory:

   Rovelli and historian of science John Heilbron analyze the historical development of quantum theory, highlighting that the evaluation of scientific contributions evolves as new ideas emerge. In this context, Rovelli suggests that Born’s work on matrix mechanics deserves more recognition for its foundational role in quantum mechanics.

   Generative AI is experimental

   References

   • Phys.org > “Proving quantum computers have the edge” by Whitney Clavin, California Institute of Technology (4-10-2025)

   The most well-known problem in which quantum computers are expected to have the edge, a trait physicists call “quantum advantage,” involves factoring large numbers, a hard math problem that lies at the root of securing digital information.

   … Ultimately, when quantum computers are ready and working – a goal that researchers say may still be a decade or more away – these machines will be able to [in theory] quickly factor large numbers behind cryptography schemes.

   But, besides Shor’s algorithm, researchers have had a hard time coming up with problems where quantum computers will have a proven advantage.

3. 

   Also from my to-do list for commentary … an interview.

   Here’s an article (below) about Gerard ‘t Hooft‘s dissatisfaction with quantum mechanics. (Is this the same as quantum physics?) Not a hint of visualization.

   ‘t Hooft seeks to explain quantum (particle) trajectories in an exact, deterministic way. Without any mysticism – because “the world is very simple and straightforward.”

   (quotes from transcript)

   … I believe that quantum mechanics is not the right way of ultimately saying what basic laws objects obey when they [elementary particles] hit each other.

   I think, in fact, that you can understand and explain quantum mechanics very well if you only assume that the laws are local laws [that is, what happens at other spots in the universe, in principle, should not matter].

   (end)

   And I’m with him as far as quanta not being pure points. That there’s some topology. More degrees of freedom.

   And I agree that quanta require no “strange sort of supernatural [unknowable] feature” (or extra dimensionality?). He feels that “quantum mechanics is already too far away from reason.” But I wonder about his desire for some type of clock-like deterministic mechanism

   (quote)

   I don’t believe nonlocality is necessary. We don’t know exactly what to do when two particles collide because we don’t know whether particles look like grand pianos or like pure points. But, then again, they can’t be pure points because pure points can’t do anything. There’s something in there, and we should be able to write down all the laws on what’s in there, in these particles: How can they collide against each other? And why is it that they sometimes go this way and sometimes go that way? How can they exhibit spin?

   (end)

   And indeed quantum physics is predicated on superposition. And that such framing is a mathematical model, an approximation of reality (nature). I like his question: “Can you formulate quantum mechanics without a superposition principle?”

   (quote)

   Quantum mechanics is the possibility that you can consider [mathematical] superpositions of states. That’s really all there is to it. And I’d argue that superpositions of states are not real. If you look very carefully, things [macroscopic things, such as cats] never superimpose [like saying that a dead cat and a live cat superimpose]. … There must be ways to describe all states for alive cats and for dead cats, but these states will mix with states that don’t describe cats at all. … Using superpositions is then just a trick that works at first but doesn’t get at the states we want to understand.

   And I believe, in the microscopic world, it’s [the reality of superimposed systems] clearly nonsense, too, even though it may seem we have nothing besides superpositions to use for understanding atoms.

   What I’m saying is: we must unwind quantum mechanics, so to speak, as to see what happens underneath. … you want to go to more basic degrees of freedom that do not ever carry any error in them because they’re exact – they’re just classical. … And as soon as you make some wrong assumption, then you again get this quantum-mechanical situation in which things get to superimpose each other.

   (end)

   • Scientific American > “Quantum Physics Is on the Wrong Track, Says Breakthrough Prize Winner Gerard ‘t Hooft” by Lee Billings (April 8, 2025) – Dutch theoretical physicist (professor emeritus at Utrecht University in the Netherlands) reflects on a theory which “can only make statistical predictions.” [A quest for quantum determinism?]

   (quotes from transcript)

   … the real reason why there’s nothing new coming is that everybody’s thinking the same way! … There are insights, of course, but not the ones that are needed to make a basic new breakthrough in our field. … And to my mind, people think in ways that are not novel enough. … everything should be much more logical, much more direct, much more “down to Earth.”

   The Standard Model is based on quantum mechanics, and quantum mechanics tells you what happens when particles approach one another and scatter. But they can scatter in many different ways; they have a large number of choices of ways in which they scatter against each other, and the Standard Model doesn’t give any sound prediction there. It only gives you statistics.

   The Standard Model is a fantastic theory that handles the statistics of what things are doing. But the theory never tells you with infinite precision which choice nature makes; it only tells you that these different possibilities are there at a certain probability amplitude. That is the world as we know it. That’s how we know how to phrase the laws of nature. But it’s not the laws of nature themselves.

   What’s missing is our understanding as to what it is that sometimes makes a particle go this way, sometimes that way. Well, you can easily argue particles can hit each other at a tiny distance. They don’t hit each other directly head-on but hit at some angle, and then they scatter away from some angle. That may be true. But what the theory today is not saying is what I should actually be looking at if two particles approach each other to predict how they’ll scatter ahead of time.

   References

   • Phys.org > “Researchers discover a new type of quantum entanglement” by Technion – Israel Institute of Technology (4-11-2025) – A study [published in the journal Nature] unveils a newly discovered form of quantum entanglement in the total angular momentum of photons confined in nanoscale structures [a thousandth the size of a hair], the first discovery of a new quantum entanglement in more than 20 years.

   • Tech Gig > “Quantum Physics Needs a Reset, Says Nobel Prize Winner Physicist” by Abhijeet V Singh (10 Apr 2025) – Hooft [Gerard ‘t Hooft] believes that the core idea behind the concept of quantum mechanics does not match reality.

   • MIT Tech Review > “Inside the hunt for new physics at the world’s largest particle collider” by Dan Garisto (February 20, 2024) – LHC hasn’t seen any new particles since the discovery of the Higgs boson in 2012.

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