[“Quantum foundations” series]
Force-less physics? No, I do NOT mean that the language of forces (electromagnetism, strong, weak, gravity) does not apply to our everyday experience or to physical descriptions. But only to a point, yes, as maybe counterproductive to deeper understanding. To getting beyond the Standard Model . To understanding how the wave function is an approximation. And taking quantum field theory (QFT) really seriously.
QFT is hard, a combination of the hardest and most important physics. Lots of infinite quantities. Hilbert spaces. Normalizing. Best way to describe nature at its deepest level. – my note from Sean Carroll’s YouTube video The Biggest Ideas in the Universe | 9. Fields
It’s really all about energy. And how that contoured energy emerges in terms of forces. 
So, if the best analogies (or metaphors) for explaining “forces” are tossing objects back & forth, then something’s still “fishy” about quantum theory.
Subatomic forces at the quantum level are best understood as a cloud of force-carrying particles jumping from one object to another. – Don Lincoln 
In one case, for repulsion, analogies use scenarios of standard objects thrown back & forth between “agents” (people, automata, etc.) on a slippery surface. Thrown = emitted. Caught = absorbed. The actions and reactions cause the agents to move apart. Throwing pushes the thrower away; catching pushes the catcher away. So, the agents move away from each other. [Find a video of an actual demonstration?]
In the other case, for attraction, analogies use scenarios of peculiar objects thrown back & forth. Objects that carry momentum in a contrary direction. Objects like boomerangs. For example, agent #1 throws a boomerang in the opposite direction to agent #2, but it loops back toward and around agent #2, who catches the boomerang as it’s going back toward agent #1. Throwing pushes the thrower toward; catching pushes the catcher toward. So, the agents move toward each other.
Moving up a level of understanding, Feynman’s sum over all (possible) paths of exchanged (virtual) particles results in a net metaphorical hill or valley of action/reaction energy between the agents. Hill = repulsion. Valley = attraction. At least in this case, for the electromagnetic (EM) force, there’s only one type of photon rather than standard and boomerang types. [Find a visualization of that?]
Can we do without swarms of force-carrying particles?
Can’t we at least imagine some visualizations involving fluids and pressure gradient differences?
Sure, there are limits to any analogy. A point where any metaphor becomes a counterproductive rabbit hole. But can’t we do better? There’s just something so lacking in analogies presented by physicists. (Perhaps that’s why quantum theory is incomplete as well?)
I’m surprised that veteran physicists and seasoned science communicators can’t do better. I expected more in the last 50 years. Perhaps there’s just no practical reason to pursue better visualizations. After all, in practice everything works just fine. Calculations to 12 decimal places! Technology advances. Career-wise, not much incentive to speculate, more motivation to compute or advance exotic mathematical frameworks.
But there’re problems. Nags that quantum theory is incomplete. Unsolved problems in physics.
So, in quantum electrodynamics (QED) and quantum chromodynamics (QCD), there’re so-called matter particles and “force carrying” particles (bosons). Feyman diagrams are visual ways of organizing the complex math. Physicists recognize that particle exchange really is about field interactions. But visualization goes no further.
Interaction between vacuum energy (of so-called empty space) and field energy is left as “the dance of quantum activity that includes virtual quarks … in the hubbub of virtual activity that surrounds all particles.” 
Feynman diagrams are shorthand accounting. Virtual “force particle” exchange is just a visual way of accounting for a more complex way in which energy density – field potential, is shaped. And contoured energy density sort of sounds like fluid dynamics, eh.
But when I think of sum over all paths, I think of interactions of expansive, extended vibrations in spacetime, not particle paths. Like waves moving in all directions (vs. moving along paths). As Carroll says in his YouTube video The Biggest Ideas in the Universe | 8. Entanglement: “Some smushy spherical disturbance, going off in all different directions.”
And when I think of (matter) fields, I think of interacting excitations. Extended in space and time. Superimposed excitations. Entangled excitations. And the energy in spacetime contoured by “charge.” Contoured so that net gradients between excitations may be characterized as repulsive or attractive.
 In the sense that we tend to identify forces with the (spatial) derivatives of (field) potential.
As I’ve written elsewhere:
Metaphorically, consider a stream or pond with an outflow point in the bed or bottom. That point does not (symmetrically) pull or push water. What it does is create localized [pressure] gradients in the flow of water. An object caught in those gradients is moved, as if a force is pulling / pushing it. The outflow point does not have a property of attraction (or repulsion).
Or, as Wilczek wrote: “… charge … creates a disturbance in the Grid” – a space-filling medium aboil with virtual particles – what we normally perceive as empty space.
Ordinary matter is a secondary manifestation of the Grid, tracing its level of excitation.
In Wilczek’s view, mass arises because the Grid is permeated with a not-yet-understood property that “slows down” some of the interactions in the field, just as electrons are slowed down in a superconducting medium. In the medium known as the Grid, we perceive that slowed-down quality as mass.
 Regarding analogies (vs. impenetrable math) on how “force” particles cause attraction and repulsion, this Fermilab video probably has the clearest visualizations you’ll find.
YouTube > Fermilab > Don Lincoln > “Subatomic Stories: Forces the Feynman way” (May 6, 2020).
Subatomic forces at the quantum level are best understood as a cloud of force-carrying particles jumping from one object to another. In Episode 5 of Subatomic Stories, Fermilab’s Dr. Don Lincoln gives a brief explanation of this phenomenon, including two analogies for how this complicated mathematics can be understood.
 Or imagine in electromagnetism (EM) that somehow an opposite charge causes the virtual photon to behave as if it (the exchanged particle) has negative mass.
 So, mass might be considered some type of “charge.” In a metric field. Then EM and gravity are about charge. Or, “charge” is some type of energy; and then EM and gravity are about energy density.
 Also, if an electron and positron share the same (electron) field and are reverse excitations in some sense; and “collisions” typically result in annihilation with emission of photons … it may be simpler to visualize wave forms being flipped / nulled (and kinetic surplus carried off as real photons) than swarms of (virtual) photons disappearing. In any case, an interesting experiment might be to detect any time-lag between proximty and emission of radiation.
And as to why there are only two types of EM charge … symmetry?
But the metric field is really the (spacetime) vacuum and effectively neutral. Paired virtual particles of opposite charge may emerge into fields, but the vacuum itself is not characterized by contrary excitations. So, as to whether spacetime geometry can be “reversed” …
 Quanta Magazine > “What Goes On in a Proton? Quark Math Still Conflicts With Experiments” by Charlie Wood (May 6, 2020).
A humble electron, for instance, can briefly emit and then absorb a photon. During that photon’s short life, it can split into a pair of matter-antimatter particles, each of which can engage in further acrobatics, ad infinitum. As long as each individual event ends quickly, quantum mechanics allows the combined flurry of “virtual” activity to continue indefinitely.
 The “Physics preamble” of this “LHC the Guide: faq” CERN Brochure (January 2008) contains a helpful recap of the Standard Model.
Please note that when speaking about particle collisions in the accelerator, the word ‘interaction’ is a synonym of ‘collision’.
• Swaying quantum vacuum energy vs compelling charge
14 thoughts on “A force-less physics?”
Regarding language and mixing particle and wave / field metaphors in descriptions, Carroll puts it this way in his YouTube video The Biggest Ideas in the Universe | 8. Entanglement:
So, what might it mean to take quantum field theory (QFT) really seriously?
One objective might be to revisit models that associate properties with field vibrations which we’d be typically hard pressed to associate with wave phenomenon.
Candidate properties are charge and mass. (Can charge exist without mass? Can stable mass exist without charge? — for elementary particles.)
And in both cases hopefully eliminate mathematical infinities.
While both are entrenched in our everyday experience, there appears to be more progress with the concept of mass. Mass as emerging from an interaction with the Higgs field. The more interaction, the higher the mass. “We perceive that slowed-down quality as mass.” A measure of flux. Stickiness.
A common metaphor is a dynamic tableau of people moving about a highly attended gala. Complete with fans, hangers-on, and paparazzi. Those with more celebrity experience higher resistance moving through the throng. Inconsequential attendees and incognitos move easily about with less interaction, less hinderance.
But there’s still one or more Higgs “particles.” And there’s still the term mass rather than something more akin to inertia (or flux) of energy/momentum.
 For more on the Higgs field, see my post Not so deific particle – the June 2020 update in particular, for analogies on how a “particle” gets more or less mass depending on how it interacts with a field.
As to the standing of Feynman’s clever visual mathematical tools, Sean Carroll says in the wrap-up of his YouTube video “The Biggest Ideas in the Universe | 10. Interactions” (May 26, 2020) that:
I wrote about two-photon physics awhile ago. That photons can interact when confined in special conditions still seems almost magical.
A soliton is one such special case. We’re not talking about just two photons, however; but pulses containing lots of photons. Special glass waveguides confine and channel these pulses much like an optical fiber. But in this case, due to peculiar boundary conditions  in the waveguide, photons in the pulses interact to form self-sustaining wave patterns – much like a classic solitary wave localized in a canal or wave tank.
A soliton propagates as a fundamental waveform without dispersing or decaying. Its shape does not change over time. (And solitons can interact with other solitons.)
 Phys.org > “Geometry of intricately fabricated glass makes light trap itself” by Sam Sholtis, Pennsylvania State University (June 1, 2020).
 Wiki: A topological soliton or “toron” occurs when two adjoining structures or spaces are in some way “out of phase” with each other in ways that make a seamless transition between them impossible. One of the simplest and most commonplace examples of a topological soliton occurs in old-fashioned coiled telephone handset cords, which are usually coiled clockwise. Years of picking up the handset can end up coiling parts of the cord in the opposite counterclockwise direction, and when this happens there will be a distinctive larger loop that separates the two directions of coiling. This odd looking transition loop, which is neither clockwise nor counterclockwise, is an excellent example of a topological soliton. No matter how complex the context, anything that qualifies as a topological soliton must at some level exhibit this same simple issue of reconciliation seen in the twisted phone cord example.
In mathematics and physics, a topological soliton or a topological defect is a solution of a system of partial differential equations or of a quantum field theory homotopically distinct from the vacuum solution.
Topological defects are not only stable against small perturbations, but cannot decay or be undone or be de-tangled, precisely because there is no continuous transformation that will map them (homotopically) to a uniform or “trivial” solution.
A central problem with our understanding of gravity, as depicted by General Relativity, is singularities: above some 10^n (high) energy scale or below some 10^-n (small) length scale, the mathematical formalism for the curvature of spacetime calculates infinities.
Quanta Magazine > “Why Gravity Is Not Like the Other Forces” by Natalie Wolchover (June 15, 2020) – We asked four physicists why gravity stands out among the forces of nature. We got four different answers.
• Claudia de Rham, a theoretical physicist at Imperial College London, has worked on theories of massive gravity, which posit that the quantized units of gravity are massive particles …
• Daniel Harlow, a quantum gravity theorist at the Massachusetts Institute of Technology, is known for applying quantum information theory to the study of gravity and black holes …
• Juan Maldacena, a quantum gravity theorist at the Institute for Advanced Study in Princeton, New Jersey, is best known for discovering a hologram-like relationship between gravity and quantum mechanics …
• Sera Cremonini, a theoretical physicist at Lehigh University, works on string theory, quantum gravity and cosmology …
Degree of freedom
Non-renormalizable (where counterterm infinities fail to cancel pesky infinities)
 The notion of “particles” as defects (or topological defects) is something that I’ve been pondering since reading about solitons, as noted in  for the above comment (June 3, 2020). As sort of “knots” or “twists” in spacetime energy that only can be de-tangled (or created or destroyed) by energetic interactions.
 Re homotopy and the trefoil knot:
• Swaying quantum vacuum energy vs compelling charge > June 30, 2019 comment: Wilczek’s paper “What is space?”
Space is not an empty stage.
While looking for visualizations of coupled oscillators, I found this interesting animation of an interaction between two solitons. (Other demonstrations may be viewed from the main page.)
Penn State U (Dan Russell) > “Interaction Between Two Solitons” (2009) > Collision between two solitons traveling in the same direction – animation showing that solitons do not obey the principle of superposition.
My comment above (June 2, 2020) notes progress with the concept of mass. Regarding progress with the concept of “charge,” my comment (April 19, 2019) on Science Asylum’s video “Where Does Light Come From?” includes this quote about field primacy.
“To be (real) or not to be (real)” – that is the question. Words, formalism. Do the (abstract) entities of successful concepts merit concreteness?
• Phys.org > “A question of quantum reality” by Springer (September 24, 2020)
• Springer Link > “Real or not real that is the question…” by Reinhold A. Bertlmann (Sep 14, 2020) [PDF 32 pages]
• “For Schrödinger and Bell the concepts of ‘quantum jumps’ is a relict, a hangover from Bohr’s old quantum theory and should not occur in a complete, consistent theory.”
• “Words to be forbidden… System, apparatus, environment. The concepts system, apparatus, environment imply an artificial division of the world and neglect the interaction across the split. …”
• “John particularly disliked von Neumann’s description of ‘projective measurement’, where the quantum state ‘jumps’ from one state into another. It’s also called ‘collapse of the wave function’. As mathematical operation it functions extremely well, it agrees with the experimental outcomes. But does it correspond to a real physical change of the system?”
• “The concept of virtual [‘not actualized’] particles arises in perturbation theory of quantum field theory, …”
• “In an electron-electron scattering process the whole phenomenon is described perfectly by a well-defined mathematical formalism and the formalism is approximated and visualized by the exchange of one photon, two photons, etc. But the mathematical formalism is not the reality! Or is it? This certainly depends on the definition of reality.” [Virtual particles as a successful concept, being real to physicists “as long as their influence can be seen in experiments.” Cf. Lamb shift, anomalous magnetic moment, Casimir effect, Hawking radiation, Unruh effect.]
• “To `understand’ quantum mechanics on physical grounds is nearly an impossible task, … We rely on the mathematical formalism and that’s safe. Well, may be the mathematical formalism – mathematics in itself, the geometry, topology, symmetries, etc. – is more real than we think? Then we certainly have to expand our vision of reality.“
Another excellent visualization by Veritasium (below). This team production (which included a professor of astrophysics) brings together many threads and pieces from explanations over the decades. Free-falling, rocket ship frames of reference, so-called gravity wells, historical stories, equations.
• YouTube > Veritasium > “Why Gravity is NOT a Force” (Oct 9, 2020) – The General Theory of Relativity tells us gravity is not a force, gravitational fields don’t exist. Objects tend to move on straight paths through curved spacetime.
A comment (core point) on the video from October 10, 2020: “acceleration is a deviation from a geodesic.”
There’s a comment to my post “Sightseeing near the speed of light – realistic simulation” regarding what being stationary entails.
• YouTube > Sabine Hossenfelder > “Do we travel through time at the speed of light?” (Aug 29, 2020) – In this video I explain why it is correct to say that we all travel through time at the speed of light and just what this means.
A new set of graphics summarizing the Standard Model.
• Quanta Magazine > “A New Map of All the Particles and Forces” by Natalie Wolchover + Samuel Velasco, Lucy Reading-Ikkanda (October 22, 2020) – We’ve created a new way to explore the fundamental constituents of the universe.
Re fundamental = no deeper internal structure … LHC … quantum gravity … wave models … confinement … scales … new physics …
• Symmetry Magazine > “How big can a fundamental particle be?” by Sarah Charley (09/29/20) – Extremely massive fundamental particles could exist, but they would seriously mess with our understanding of quantum mechanics.
Recap of quantum gravity theories … condensate cosmology aka “Group Field Theory (GFT) condensate cosmology” … Loop Quantum Gravity … spin-networks and spin foams … vs. string theory … space-time as a thermodynamic system …
• Ars Technica > “Can we craft a theory in which space and time aren’t assumed to exist?” by Conor Purcell (4/20/2020) – In some versions of quantum gravity, time itself condenses into existence.
Regarding use of the term force: at a minimum, I like the way this article uses the term interaction, which better fits my visualization of spacetime topology and dynamics: the interplay between entangled localized excitations & fields and the quantum vacuum. It’s really all about energy. And how that contoured energy interacts (in Wilczek’s Grid, a “medium in many senses”).
• Space.com > “Proof of new physics from the muon’s magnetic moment? Maybe not, according to new theoretical calculation” by Zoltan Fodor, Professor of Physics, Penn State (April 26, 2021)
Here’s a useful summary of space-time phenomena (space-time as a malleable medium) predicted by General Relativity. Getting beyond the everyday notion of gravity as a force. This article includes videos and graphical overview: “12 things to know about Relativity.”
• Space.com > “Einstein’s theory of general relativity” by Nola Taylor Redd, Meghan Bartels (June 4, 2021)
Comments are closed.