General · Language · Problem

A force-less physics?

John Healy

[“Quantum foundations” series]

Quantum swirl

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 [7]. 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. [1]

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 [2]

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.[3] 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.” [6]

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.

Notes

[1] 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.

[2] 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.

[3] 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.

[4] 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.

[5] 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” …

[6] 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.

[7] 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’.

Related posts

• Swaying quantum vacuum energy vs compelling charge

• Virtual attraction

15 thoughts on “A force-less physics?”

  1. 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 imagine that you have two particles coming in. so let’s say you have particle one. it’s coming in. it’s moving in some direction, and you have particle two that’s gonna … they’re gonna collide. okay, now you should imagine that, of course, these particles are little waves, and they have little packets that are more or less localized in space. so that there’s a good approximation in which we can talk about the two particles colliding.

    okay, so we do this all the time when we talk about quantum mechanics. we hop back and forth between the reality that we know is quantum and wave functions and the language that we use which is particles and trajectories and stuff like that. as long as we’re in a regime where that kind of approximation is valid, that’s a perfectly legitimate thing for us to do.

  2. 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.[1]

    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.

    Notes

    [1] 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.

  3. 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:

    (transcript quote) … the Feynman diagram is a story. there is a true story, which is what is the amplitude for a certain reaction to happen, but the intermediate steps are calculational devices. you kind of know that has to be true because the real process that you’re looking at is the sum of all of these different diagrams and all the different diagrams have different sets of virtual particles in them. they’re not exactly the same. so Feynman actually … so anyway but that’s … that is the way of thinking about Feynman diagrams: they’re … they’re calculational devices for doing calculations in quantum field theory.

    I just don’t want you to take all of the steps along the way overly literally. okay, including the virtual particles in between.

    Now, I’ll reveal that Feynman when he was inventing this – he had an aspiration. he was hoping that he was not coming up with a set of calculational tools to do quantum field theory better. he was hoping that he was replacing quantum field theory with a good old fashioned particle theory. the theory of particles that be created or destroyed, following the rules of these Feynman diagrams. turned out not to be right.

    Again, many missteps along the way to any great idea, and it turns out this is a way of thinking about quantum field theory, not a replacement for it. part of his motivation was the cosmological constant problem. remember, we talked last time about the fact that when you have fields pervading the whole universe, these fields have energies and the energies can be added up; and if you just do it naively, the quantum mechanical contribution to the energy of empty space is infinitely big.

    And this is one of those things that physicists have known for a long time; but before around the 1980s, they didn’t worry about it that much. But some people did. so Feynman worried a little bit about it. Philip Andersson worried about it a little bit for different reasons. But they thought that this was a problem with quantum field theory. right, that it gave an infinite energy density to empty space. if you could replace the fields with particles you could get rid of that infinite energy.

    It didn’t work. so we are left with both this wonderfully accurate calculational device of Feynman diagrams and this somewhat unnatural formalism of quantum field theory. we don’t know what to do about that. we didn’t … I’m not gonna reveal what to do about that.

    We still don’t know what to do about the energy density of empty space. But we’re thinking, and it might be that we do in one way or the other have to replace quantum field theory. But in the mean time it is absolutely the best way we have of understanding nature currently available.

  4. I wrote about two-photon physics awhile ago. That photons can interact when confined in special conditions still seems almost magical.

    “Under normal circumstances, photons are oblivious to one another,” said Rechtsman [professor of physics at Penn State]. “You can cross two laser beams and neither will be changed by the other. In our system, we were able to get photons to interact and form solitons because the intensity of the laser altered the properties of the glass. The photons became ‘aware’ of each other through the change in their environment.” [1]

    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 [2] 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.)

    Notes

    [1] Phys.org > “Geometry of intricately fabricated glass makes light trap itself” by Sam Sholtis, Pennsylvania State University (June 1, 2020).

    (animation caption) Animation showing a topological soliton rotating anticlockwise. Laser light traveling through waveguides, intricate “wires for light” carved through glass, interacts with itself to form self-sustaining wave patterns called solitons. The spiral rotation of the solitons is a signature of the specific shape of the waveguides and an indicator that the device is topological. Credit: Rechtsman Laboratory, Penn State.

    Laser light traveling through ornately microfabricated glass has been shown to interact with itself to form self-sustaining wave patterns called solitons. The intricate design fabricated in the glass is a type of “photonic topological insulator,” a device that could potentially be used to make photonic technologies like lasers and medical imaging more efficient.

    Topological materials, which were awarded the Nobel Prize in 2016, have the ability to “protect” the flow of waves through them against unwanted disorder and defects. Until now, our understanding of topological protection of light has been mostly limited to particles of light acting independently, but in a new paper that appears May 22 in the journal Science, researchers at Penn State report that they have used the glass to mediate interaction between photons, directly observing the fundamental wave patterns of these intricate devices.

    [2] 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.

  5. 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.

    According to Einstein, gravity is a feature of the space-time medium; the other forces of nature play out on that stage.

    Physicists think that in this truer theory, gravity must have a quantum form, like the other forces of nature.

    • 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 …

    Furthermore, from the perspective of particle physics, the vacuum of space [vacuum stuff] is a complex object. We can picture [visualize] many entities called fields superimposed on top of one another and extending throughout space. The value of each field is constantly fluctuating at short distances. Out of these fluctuating fields and their interactions, the vacuum state emerges. Particles are disturbances in this vacuum state. We can picture them as small defects in the structure of the vacuum.

    • Sera Cremonini, a theoretical physicist at Lehigh University, works on string theory, quantum gravity and cosmology …

    Terms

    Singularity
    Black hole
    Locality
    Degree of freedom
    Entanglement
    Vacuum
    Non-renormalizable (where counterterm infinities fail to cancel pesky infinities)

    Notes

    [1] The notion of “particles” as defects (or topological defects) is something that I’ve been pondering since reading about solitons, as noted in [1][2] 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.

    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.

    [2] Re homotopy and the trefoil knot:

    In knot theory, a branch of mathematics, the trefoil knot is the simplest example of a nontrivial knot.

    The trefoil knot is nontrivial, meaning that it is not possible to “untie” a trefoil knot in three dimensions without cutting it. Mathematically, this means that a trefoil knot is not isotopic to the unknot [trivial knot].

    The trefoil knot is chiral, in the sense that a trefoil knot can be distinguished from its own mirror image. The two resulting variants are known as the left-handed trefoil and the right-handed trefoil. It is not possible to deform a left-handed trefoil continuously into a right-handed trefoil, or vice versa.

    Though chiral, the trefoil knot is also invertible, meaning that there is no distinction between a counterclockwise-oriented and a clockwise-oriented trefoil.

    Related posts

    • Swaying quantum vacuum energy vs compelling charge > June 30, 2019 comment: Wilczek’s paper “What is space?”

    Space is not an empty stage.

    When energy is fed into space, virtual particles become real. They are like magma beneath the surface, ready to erupt if allowed an outlet. In this sense, the cosmic effervescence is the primary reality, from which particles are born.

  6. 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.

  7. 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.

    If one field can make the other field, then maybe charges don’t make the fields at all. Maybe they just affect [interact with] them. Maybe they’re a thing all by themselves. I mean, we said light was a disturbance in electric and magnetic fields and light is a thing all by itself.

    In fact, that’s exactly how we imagine fields these days. Notice the arrows in this graphic remain in the same place as the charge moves. They’re attached to the space, not the charge. If there aren’t any charges around, we like to imagine the fields are still there and just have a value of zero. We wouldn’t really get confirmation of this though until the 1860s.

  8. “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)

    Physicist Reinhold Bertlmann of the University of Vienna, Austria has published a review of the work of his late long-term collaborator John Stewart Bell of CERN, Geneva in EPJ H. This review, “Real or Not Real: that is the question,” explores Bell’s inequalities and his concepts of reality and explains their relevance to quantum information and its applications.

    Reference:

    • Springer Link > “Real or not real that is the question…” by Reinhold A. Bertlmann (Sep 14, 2020) [PDF 32 pages]

    I will summarize the Bell-type experiments and what Nature responded, and discuss the implications for the physical quantities considered, the real entities and the nonlocality concept due to Bell’s work. Subsequently, I also explain a quite different view of the meaning of a quantum state, this is the information theoretic approach, focusing on the work of Brukner and Zeilinger. Finally, I would like to broaden and contrast the reality discussion with the concept of “virtuality,” with the meaning of virtual particle occurring in quantum field theory. With some of my own thoughts I will conclude the paper which is composed more as a historical article than as a philosophical one.

    Interesting points:

    • “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.“

  9. 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.

    “Well, I mean, do you feel weightless? No, so you are not an inertial observer.”

    • 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.

    (from transcript) As the rocket gets closer to the planet, it goes faster and faster, but Rocket Man still feels weightless. For him, nothing has changed. So where on this journey would you say the frame of reference changes from inertial to non inertial?

    An onboard accelerometer would never even register a blip. He has continued on his inertial path through spacetime. So the logical conclusion is his frame of reference is inertial up until the instant he crashes into the planet. Okay, so how do you explain the curved path of his rocket without gravitational forces or gravitational fields? The answer is curved spacetime.

    Here’s another analogy. Imagine you and a friend are standing 1000 kilometers apart on the equator. Now you both set off due North. Over time you will come closer together. Ultimately bumping into each other at the North Pole. It’s as though there was a force pushing you together, but you didn’t feel a force and your friend didn’t feel a force. Gravity is just like that force, it doesn’t actually exist. The real reason for you coming together was that you were both on straight paths, geodesics, on a curved surface.

    It is possible for you to be accelerating, even though your spatial coordinates are not changing.

    I will show you one equation [geodesic equation] from general relativity. This [left side] says that the second derivative of your position with respect to time is equal to [right side] your [classical] acceleration [minus an expression for your spacetime geodesic] …

    And if you were in flat spacetime, well, [ignoring the second expression] this is exactly what you’re saying if you’re accelerating – your spatial coordinates have to change.

    But you’re not in flat spacetime, and this [second expression on the right side] is related to the curvature of spacetime, and this [term] is your velocity through time squared. (You don’t have to worry about the details here, the point is your position can be not changing.)

    This [right side] can be zero, which means your acceleration [first term] must be exactly equal to this curvature term times your velocity through time squared. So in curved spacetime, you need to accelerate just to stand still.

    A lot of this may seem more complicated than Newtonian physics, but one classical mystery looks a whole lot simpler in general relativity, which is why all objects fall at the same rate.

    A comment (core point) on the video from October 10, 2020: “acceleration is a deviation from a geodesic.”

    Notes

    Equivalence principle

    In the theory of general relativity, the equivalence principle is the equivalence of gravitational and inertial mass, and Albert Einstein’s observation that the gravitational “force” as experienced locally while standing on a massive body (such as the Earth) is the same as the pseudo-force experienced by an observer in a non-inertial (accelerated) frame of reference.

    Related posts

    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.

  10. 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.

    Chris Quigg, a particle physicist at the Fermi National Accelerator Laboratory in Illinois, has been thinking about how to visualize the Standard Model for decades, hoping that a more powerful visual representation would help familiarize people with the known particles of nature and prompt them to think about how these particles might fit into a larger, more complete theoretical framework. Quigg’s visual representation shows more of the Standard Model’s underlying order and structure. He calls his scheme the “double simplex” representation, because the left-handed and right-handed particles of nature each form a simplex — a generalization of a triangle. We have adopted Quigg’s scheme and made further modifications.

  11. 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.

    For instance, the difference between the masses of the top quark and the electron is equivalent to the difference between the masses of an adult elephant and a mosquito.

    The known laws of physics allow for fundamental particles with masses approaching the “Planck mass”: a whopping 22 micrograms, or about the mass of a human eyelash. To go back to our comparisons with currently known particles, if the top quark had the same mass as an elephant, then a fundamental particle at the Planck mass would weigh as much as the moon.

    “Particles with a mass below the Planck scale can be elementary,” Grabowska [CERN Theory Fellow] says. “Above that scale, maybe not. But we don’t know.”

    For the kind of research performed at the LHC, fundamental particles are all considered to be the same size – no size at all [point-like].

    Treating fundamental particles as points works well in particle physics because their masses are so small that gravity, which would have an effect on more massive objects, is not really a factor.

  12. 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.

    Condensate cosmology requires a great deal of abstract reasoning to even try to understand it.

    While quantum mechanics deals with reality in discrete, granular fashion, relativity tells us that space-time, and therefore gravity, is continuous and non-discrete.

    One way to deal with this is to give one of the theories precedence. Since we know the world is quantum, general relativity must be an approximation of an underlying quantum description of space-time itself. And this suggests that any unification of the theories requires that gravity become discrete.

    … during the 1970s and 1980s when physicists began to learn new things from semi-classical physics …

    … rather than simply quantizing general relativity, a new way to understand the nature of space-time at a microscopic level might be needed.

    These ideas derived from black holes suggested that the gravitational field itself is not really fundamental, regardless of whether it is classical or quantum. Instead, it became apparent that the gravitational field might be a manifestation of something more fundamental, something that does not look like a field at all and so cannot be described in standard spatio-temporal ways.

    In string theory, a space-time is generally assumed—the very assumption that quantum gravity aims to explain. From the LQG perspective, space and time must emerge in a successful theory of quantum gravity, rather than being a starting component.

    … without a space-time framework, it is very hard to say anything about the real world.

    … Group Field Theory (GFT) condensate cosmology … proposes that the Universe as we know it came about through a kind of hydrodynamic [time-free] condensation process [analogous to time-based phase transition from steam to water].

    … the mathematical variables required for a hydrodynamical description of GFT condensate cosmology have statistical and thermodynamical origins. Examples of these include the number density and temperature fields of a fluid. For instance, the fluid may be colder and denser in one part than the other; in order to describe the dynamics of such systems as they evolve, one first has to be able to define these differences. This is where statistical mechanics and thermodynamics come in.

  13. 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)

    Almost everything in the universe – from how atoms are built to how your cellphone works to how galaxies move – can be described by four interactions. You are probably familiar with the first two: gravity and electromagnetism. The third is the weak interaction, which is responsible for radioactive decay. Last is the strong interaction, the force that holds the protons and neutrons in an atom’s nucleus together.

    All interactions of the Standard Model contribute to the muon’s magnetic moment and each do so in multiple different ways.

    Of all of the effects that the strong interaction has on the muon’s magnetic moment, the largest and also hardest to calculate with the necessary precision is called the Leading Order Hadronic Vacuum Polarization.

  14. 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)

  15. Gradient contours

    In this recent article, Don Lincoln provides a historical recap: the “force” term, the “action at a distance” discomfort, the “just do the math” mantra, the “spacetime” geometry recasting, the “quantum gravity” quest, and the “force-carrying particle” redux. He ends with a Zen moment (quoted below).

    While, in his popsci articles, Lincoln’s generally reluctant to use technical language and math, he might have unpacked the notion of force in a framework of field interactions and gradients. And then linked that to spacetime curvature (and time flux).

    Perhaps with some fluid dynamics analogies, such as temperature and pressure differences. Flow / flux. With some visuals.

    Like how air flowing (or blowing) faster over the top of an airplane wing (airfoil) produces lift, even warping the airfoil.

    Like how lower density gas – hot air or helium – in a balloon produces lift – the balloon rises. Or the inverse: a balloon filled with higher density gas sinks.

    Like how heat flows from a warmer surface (or area) to a cooler one – without any obvious “pushing.”

    The point being that where there’s a gradient, there’s a flow – there’s a “force.” The hint that energy-momentum gradients (due to sources and sinks) – as “stressors” – manifest as everyday motion, attraction / repulsion, deformation, etc.

    • Big Think > “Is gravity a force? It’s complicated” by Don Lincoln, Fermilab (October 12, 2023) – Which model – Isaac Newton’s or Albert Einstein’s – is the most accurate at describing reality?

    It is clearly a force in the simplest definition of the word. But we also know that Einstein’s theory positing gravity to result from the distortion of spacetime is an incredibly successful model. So perhaps we have reached a moment of scientific Zen: Gravity just is. Or, to paraphrase Forrest Gump, “Gravity is as gravity does.”

    Related posts

    • A force-less physics? (and ditching the notion of “force-carrying particles”)
    • Equal footing in quantum physics

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