Archeology and Evolution of…Paradigms in Physics

Life is evolutionary. Sometimes fundamental changes are needed in order to adequately incorporate changing paradigms in physics, like MOND or gravitation theory, for example. This is an idea that was made apparent when I recently read an interesting and amusing review on high energy physics written by A. De Rujula, Archeology and evolution of QCD, arXiv:1610.07466v.1[hep-ph].

Sketch of Bubble Chamber  Photo of Omega Minus

De Rujula’s talk is relatively informal and discusses some of the theoretical and experimental history of discovery on charmed quarks and of the quark model in general. He intersperses his description of the physics with personal asides that I found interesting and humorous.

To begin with, he tells the story of the origin of the idea of quarks – fractionally charged sub-particles which form the basis of composite particles, such as protons and neutrons. He provides evidence to disparage the official history that they were invented by Gell-Mann and Zweig. In the process he raises some interesting background – such as the initial rejection of Gell-Mann’s paper by scientific journal editors or referees. He also makes humorous reference to competing theories (and theorists) at Harvard and Princeton.

What caught my attention in particular was his discussion on p. 8 (Section 10) of his 1975 paper on the sub-structure of hadrons (composite particles like protons, neutrons and pions). He began with a somewhat sarcastic sounding “once upon a time,” to describe physicists who subscribed to the “bootstrap” concept of hadrons – as in “pulling oneself up by one’s own bootstraps.” In this concept, which was a prevalent notion in the late 60’s-70’s, there are no real sub-particles in hadrons – just different combinations of angular momentum states or other dynamical combinations of equally elementary particles, with the hadrons being the most elementary particles.  These elementary hadrons could have a variety of excited states giving rise to the various observed “particles” or “resonances”.  Another term used for this was “nuclear democracy”.

De Rujula and his colleagues subscribed to the alternative idea that there are distinct sub-particles (quarks, gluons) with a “simple underlying force law” – which came to be called QCD – Quantum Chromodynamics. This was in analogy to the then well established theory of Quantum Electrodynamics (QED).

De Rujula then shows how the experimental evidence supported the quark model and in particular how the quantum of charm came to be found and accepted.

I have to admit I was a supporter of the “bootstrap” concept when I did my Master of Science thesis on particle physics: Dispersion Relations in Quantized Field Theory, Dalhousie University, 1968.

The idea that we might be at the elementary rock bottom of nature when observing hadrons, with different particles being different excitations of this set of particles seemed appealing.  The notion was supported by Geoffrey Chew, a noted physicist at the University of California at Berkeley at the time, e.g.: Chew, Geoffrey; Frautschi,S. (1961). Principle ofEquivalence for all Strongly Interacting Particles within the S-Matrix Framework. Physical Review Letters. 7 (10): 394-397 (Reference found from Wikipedia entry on Geoffrey Chew).

In a sense any particular state of matter was just a varied combination of every other state of mater – matter hoisted itself by it’s own bootstraps…

Since the time that Dr. De Rujula talks about, the evidence has overwhelmingly supported the quark model and as well the notion that “atomic like” configurations of quarks give rise to a detailed structure of particles and resonant states.

This in turn implies that the world of sub-nuclear particles is composed of ever finer structure with more particles to be discovered – like an eternal Russian nesting doll. This in turn suggests an underlying fractal like structure to matter-space-time – another concept which appeals to me.

Conventional wisdom suggests this process stops at the “Planck scale” – the distance or energy that is the simplest combination of Planck’s constant with other fundamental units  of Physics that produce a minimum length or maximum energy. Interestingly, the original bootstrap concept has evolved and been applied to theories of physics at and beyond this scale – evolving into what has become known as string theory. But that could be the subject of at least another blog!

What struck me about De Rujula’s article was his comments to the effect that proponents of the bootstrap clung to the theory even when the evidence was available that supported the quark model.

What this shows is that physicists, like all humans generally, will cling to a conventional paradigm, even as evidence mounts to contradict it.

As I mentioned in an earlier blog (MOND versus Dark Matter), this seems also to be the case for the “search” for dark matter particles, even when there is considerable evidence pointing to a needed change in the established paradigm of gravitation theory. Fundamental changes are needed that can adequately incorporate the predictive success of evolving theories, like MOND.

2 thoughts on “Archeology and Evolution of…Paradigms in Physics

  1. Dr. Benjamin Tippett made a comment on Facebook about the blog on Evolution of Paradigms:

    it’s all about galactic rotation curves and the late 90’s.

    see… galaxies spin because they’re in orbit around themselves.. or rather, the stars orbit all of the mass between them and the center of the galaxy.

    so, one fun thing a person can do is get a profile of the average rotation speed of stars as you get farther out, and you can get a profile of the mass of the galaxy.

    they discovered a problem with this, though: if you count up the stars in a galaxy, and look at their distribution, there are not nearly enough stars to account for the rotation curves.

    two possible consequences: either there is some mass in the mix which isn’t shining like a star (which was then called: dark matter), or the rule that the orbital speed reflects on the matter between the star and the center of the galaxy is wrong (this rule is based on newtonian laws of gravity, thus alternate proposals are called “MOdified Newtonian Dynamics” (MOND) )

    so this was a pretty big mystery. You can tell a lot (assuming newton’s laws are true) by looking at the orbital speeds of lots of other stars, and this data dictates that dark matter must be distributed in spherical shape around the galaxy, extending farther out beyond it; and astronomical surveys suggest that there must be 10X more dark matter (by mass) than luminous matter. The current theory is that dark matter is a type of elementary particle that doesn’t interact with the fields and forces of regular matter (it’s called a Weakly Interacting Massive Particle WIMP, and we’ve never detected one, though we are looking).

    MOND people were also bolstered by a few mysteries involving gravity which have shown up since then, including “dark energy” which causes the universe to accelerate in its expansion, and a result called the “pioneer anomaly” which suggested that the pioneer space probe was accelerating towards the sun in a way which couldn’t be explained using newtonian gravity.

    okay, so fast forward a decade and a half. the current state of the union is that there are a lot of other bits of evidence which support WIMP dark matter; including numerical best fits to the expansion rate of the universe, we see gravitational lensing by clumps of dark matter, and numerical simulations of galaxy formation require the presence of WIMP particles to get the galaxies in the simulation to form in the same way they have in our universe. Long story short: we still haven’t detected them, but there’s lots of evidence for them.

    MOND, on the other hand, isn’t looking so hot. We can take as general wisdom the idea that newtonian gravity isn’t the be-all-and-end-all of gravity. but it was replaced over 100 years ago by Einstein’s general relativity… so… the idea of embracing MOND theories is only pertinent to the numerical physicists who use newtonian gravity as an approximation to speed up their calculations. This said, there is no simple modification to newtonian gravity which can accommodate all of the crazy different observations which MOND proponents want to explain. Furthermore, that thing about the pioneer spacecraft showing modifications of newtonian physics turned out to be a dud.

    … so that’s the context to my point.

    my point is that your dad said:
    “What this shows is that physicists, like all humans generally, will cling to a conventional paradigm, even as evidence mounts to contradict it.”

    which is 100% true. 100%. all the time. 1000%

    but then he said
    “As I mentioned in an earlier blog (MOND versus Dark Matter), this seems also to be the case for the “search” for dark matter particles, even when there is considerable evidence pointing to a needed change in the established paradigm of gravitation theory”

    which.. you know. he’s an example of the previous case.

    and before i say anything more, you need to know that EVERY PHYSICIST is like this about something. we all have our biases and preferences. it’s the fuel we use to get us through the calculations.

    Benjamin Tippett there’s a famous quote about how every physicist, at the outset, automatically thinks that they are the smartest person to work in their field.

    it’s part of the mindset that gets you to work diligently, have faith in your arguments, balance the information you have with the information you expect, and to be incredulous with new data.

    that said.. this particular mindset has its drawbacks.

    Greg MacNevin
    Thank you for your response. It is always good to be challenged. I do try to keep abreast of the latest theories of Dark Matter and Dark Energy. In fact there are some new ideas for Dark Matter ( besides the more conventional ideas for WIMPs ) in some of the latest articles in ArXiv- hepth, for example. The MOND paradigm however has various theoretical versions including a variety of General Relativistic approaches. These include some from Milgrom, the key originator of MOND and others .( Bekenstein and Moffat, come to mind) Most recently McGaugh did a large survey of galaxies and found that a “universal law” appears to provide support for a MOND type modification. I intend to address and review these ideas in future blogs.

    Benjamin Tippett :good luck. until they detect a WIMP, guessing the winning theory is still a gamble.

    I’m pleased to see that the concept of “paradigm shift” has remained in place with at least some scientists, along with the realization that revolution, rather that continued “conventional” science within the paradigm is a worthwhile objective. For the last few years, I have spent too much time with practitioners of “applied science” which is valuable work but not going to change how we see the world.

    Or in this case, going to change the world of people with enough maths to understand quantum mechanics. It’s a shame that we lost the expectation that any person with a well-rounded education could appreciate at least the basics of physics. Special Relativity will probably be the last such theory, and most people are too frightened of math to go that far.
    Unlike · Reply · 1 · Yesterday at 2:55pm
    Benjamin Tippett
    Benjamin Tippett the use of “revolution” is an interesting one. All of the different possible schools on what the next stage in theoretical physics will be is kind of like that scene in monty python’s “the life of brian” where there are all these different groups:”the judean people’s front” and “the people’s front of judea,” etc.

    but yeah. it’s one of those things where, eventually someone (and 100 grad students, postdocs and colleagues) will get it right, and then we’ll just have to wait the 30 years for all of the other revolutionary groups to dry up and drop off so that the right one can be the established wisdom.

    but that thing you said about no “losing the expectation that any educated person..”


    The Titanium Physicists Podcast | The boundary between the…

    Greg MacNevin:
    Thank you for the reference to your blog. Looks like a lot of interesting topics to explore.

    Greg MacNevin
    Thank you Les Howie for your comments. I do think the resolution of some of the long standing conundrums in Physics ( like Dark Matter) do require a paradigm shift.


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