Particles Tell Stories

By JoAnne Hewett | October 19, 2005 3:10 pm

The discovery of new particles helps us to understand how the universe works. It is the dream of every high energy physicist, part of our raison d’être. The Large Hadron Collider (LHC) under construction in Geneva Switzerland should be good at this. The Tevatron, currently in operation in Batavia Illinois, has a shot as well. We have reason to expect that the experiments at the LHC will discover a host of new particles. We’ve given the possibilities seemingly whimsical names: Higgs, squarks, gluinos, Z-primes, Kaluza-Klein gravitons, WIMPS, axi-gluons, etc., but each one serves a purpose in our candidate theories about nature.

However, merely producing new particles and cataloging them gives only part of the understanding. Rather, particles are messengers, telling a profound story about the nature of the universe, or what we like to refer to as the nature of matter, energy, space, and time. Learning about the new particles, studying their properties and how they interact, leads to discoveries of new theories or new symmetries of spacetime. That’s the role of the proposed International Linear Collider.

There’s plenty of historical precedent. When the positron, the brother of the electron, was first detected, the discovery was not just the identification of a particle. The positron revealed a hidden half of the universe: the world of antimatter. The positron showed us how to reconcile the laws of relativity with the laws of quantum mechanics, telling a brand new story about the structure of spacetime.

When physicists first observed the pion in cosmic ray experiments, they were puzzled. Within a few years, particle accelerators had produced a plethora of pion cousins: etas, deltas, omegas, etc. Physicists were running out of Greek letters to name them all, but finally the story became clear. These were not elementary particles after all, buy tiny bags of quarks, held together by a new force so strong that no quark could ever escape it.

We hope to break new ground with discoveries at the LHC and ILC; these accelerators will probe nature at energies where she has never before been tested. Here, we exect other aspects of nature to unveil themselves. One possibility is extra dimensions of space. An electron moving in tiny extra dimensions would generate much heavier partner particles, which are related to its motion in the additional dimensions. Producing these partner particles at an accelerator would be a great discovery; however, an equal challenge would be to pin down their identities as travelers in extra dimensions. How much we learn from these particles depends on how well we determine their properties. For example, by measuring their masses and interactions, physicists could discover the shape, size, and number of extra dimensions.

This is how our science works and is the message of a new report, Discovering the Quantum Universe: the Role of Particle Accelerators, which will roll off the presses this week. I was one of the authors and have liberally borrowed some of its text for this post. You can be sure I’ll be blog more about the contents in the future.

  • Nicholas

    Fun read—Please post a link or place we can get at the report.

    non sequetur: I have always wondered, with all the high tech and fundamental science that goes on, why more particle accelerators are not depicted in movies. Certainly it strikes me that the venue should be able to be presented as exciting, especially with all the enourmously high energies, extra dimensions, and creation of exciting particles, (possible black holes!) etc.

    Really the only exposure I have seen (in science fiction or elsewhere) is in Dan Brown’s Angels and Demons.



  • citrine

    Great post, JoAnne. Most accounts of HE Physics read like a jumble-sale catalog of particles. Your description makes sense, and puts the material in a broader context. Any chance the contents of the report expand into a book?

  • ed hessler

    Thanks for posting this.

    Please tell us the availability of this report. I had reason to re-read the obituary of Robert Wilson yesterday and I was reminded again of his incredible range of talents and glad for them…aesthetics everywhre. I smiled, of course, upon reading again his reason for becoming a physicist: “”We had only electrons and protons, and you could put those together into atoms in various ways and make the whole universe. It was a very simple theory that even a dope could understand. I decided then that I wanted to go into physics.”

    My, what he and others since have made available to us (knowledge and encouragement of wonder and wonderfulness), including one of the best reasons I’ve ever read on why we (well you) do particle physics, a response to a persistent questioner, Senator John Pastore. It is worth reading and be found here ( )

  • JoAnne

    Hi All,

    You can be sure I will post a link to the report, as soon as it’s available. It is supposed to roll off the presses any day now… You can also expect a few more posts from the report!

    Don’t know if we’re up to writing a book yet, though. We’re still recovering just from a 40 page report!

  • janet

    But do they tell tales?

    Seriously, though: very nicely put!

  • Dissident

    Nicholas, there is an accelerator in “Terminator 3: Rise of the Machines”. The rationale for its presence is unclear, but its role is to temporarily restrain the Evil Terminatrix with its powerful magnets. No particles, black holes or extra dimensions though. But hey, you did get time travel and the Gubernator!

  • CapitalistImperialistPig

    So far, the story they tell reminds me of what the famous biologist (Huxley, Haldane?) said when asked what studying nature had taught him about the ways of the Lord. His reply: “He seems to have an inordinate fondness for beetles.”

    And particles.

  • Elliot

    OK this is going to sound naive but I want to confirm my layman’s working definition of dimension (physical sense) I have always considered physical dimensions as equivalent to degrees of freedom of motion. Am I being overly simplistic here? Please set me straight if I am wrong as I am here to learn as well as hopefully contribute.


  • Aaron

    I’m sort of curious. Who’s the intended audience for this report?

  • Sean

    Okay, JoAnne. Where did you learn to make the circumflex-e in “raison d’être“?

  • Clifford

    Sean, she did it by pointing and clicking, of course…. ;-)


  • JoAnne

    Sean, I cheated! It’s a story of pure-hearted determination rather than knowledge or finesse. But, it’s a secret….you’ll have to ply me with champagne or a very fine red wine to find out!

    However, Clifford guessed – I actually did do it by pointing and clicking! I’ts amazing how far you can go by pointing and clicking. Nonetheless, Sean, you still owe me a very fine wine if you want to learn how to point and click.

  • JoAnne


    You’d be surprised at the wide spectrum of people who should read this post.

    Now, I’m curious – why do you ask???

  • JoAnne


    You are on the right track! In a very practical sense, one can think of spatial dimensions as physical degrees of freedom.

    For instance, imagine throwing a ball, and then trying to describe its position in space. What are the independent directions (i.e., directions that cannot be related to a set of other directions) that are needed to describe its motion? Well, you’ve got how far the ball is in front of you. How far the ball is to your left or right (left vs right is just a minus sign). And, how high the ball is. That’s it. There are 3 *independent* spatial degrees of freedom to describe the motion of the ball. Any other direction is a combination of these three degrees of freedom. Hence, we live in a world, where the motion of things we can perceive are described by *three* dimensions.

    Now, imagine that very tiny objects need another degree of freedom (i.e., dimension) to describe their motion. That’s what we mean by an extra dimension. We can’t perceive it, but very tiny objects may be able to.

    There are many, many fancier and more mathematical descriptions of extra dimensions and the definition of a dimension. I recommend `The Elegant Universe,’ a Nova production based on Brian Greene’s book if you want to learn more.

  • Aaron

    Not the post — the report. I’m curious if it’s written for the general public, for scientists, for policy-types, for lawmakers or some combination therof.

  • JoAnne

    Ah Aaron – sorry. My vision is a bit clouded tonight after the big loss (see my previous post).

    We actually wrote *two* reports! One is more technical and is geared at the EPP2010 panel that I have written about. The second is less technical and is indeed intended for members of our national government, i.e., the ones who hold our purse-strings. I also think that it works well for the general public and that’s why I intend to blog about it. Afterall, the general public provides the purse that the purse-stringers dole out, and they deserve to know.

    And, to be very honest, I think there’s alot of material in the report that many scientists themselves (in all areas of science, including HEP) should be informed about.

  • agm

    The positron showed us how to reconcile the laws of relativity with the laws of quantum mechanics, telling a brand new story about the structure of spacetime.

    As if that was truly a settled matter.

  • Doug

    Elliot wrote:
    OK this is going to sound naive but I want to confirm my layman’s working definition of dimension (physical sense) I have always considered physical dimensions as equivalent to degrees of freedom of motion. Am I being overly simplistic here? Please set me straight if I am wrong as I am here to learn as well as hopefully contribute.

    You will notice that our definition of motion is one-dimensional, as the motion of the ball in JoAnne’s answer to your post reveals. So, the idea of physical dimensions is taken to mean physical dimensions of space; that is, we can describe 1D motion in terms of three independent variables of space and one of time, which is a total of 4 dimensions, forming a background structure in which the Schrödinger equation can be evolved. HE physicists need this background. It is a fixed spacetime container that enables them to tell the particle story. Without it, there is no story.

    Now, cosmologists, on the other hand, like Sean, have to use a slightly different version of this 4D spacetime. For them, it’s a container that is not fixed, but varies according to the mass of a particle in such a way that it can precisely eliminate the force of gravity between masses. Since modern physics is fond of describing particles in terms of their interactions these days, eliminating the gravitational interaction like this presents quite a problem, as you can imagine. So, as you try to understand the definition of “dimension” in a physical sense, you’ll find it’s a little like peeling off the layers of an onion. There are layers upon layers of mystery here, but they won’t tell you about it up front, because they don’t have the pat answers that they would like to have. Actually, they don’t really know anymore. It used to be simple, but they are very disconcerted over it these days.

    When you check out the NOVA production JoAnne recommends, be sure and read the interview with David Gross. You will see what I’m talking about. Something is missing, and they know it.


  • Elliot

    Joanne/Doug thanks for your kind responses. It appears this is more subtle than it appears in that the number of dimensions “seems” to be tied to whether or not there is a fixed backgound to spacetime and/or what the structure of that background may or may not be. It also seems to be tied to the ability to describe motion of a particle or other object. (You need as many as you need to describe the motion).

    What if things are completely relational? that is there is no “background” but only objects/particles in motion based on the forces they experience based on other objects particles. Does this imply that the number of dimensions may be tied to the number of interacting objects? That would be seem to be strange.


  • Doug

    Elliot wrote:

    What if things are completely relational? that is there is no “background” but only objects/particles in motion based on the forces they experience based on other objects particles. Does this imply that the number of dimensions may be tied to the number of interacting objects? That would be seem to be strange.
    You see, it gets mysterious really fast, doesn’t it? The relative motion of bodies is all there is. We can’t define one-dimensional motion any other way, can we? But then, if we consider the electrodynamics of moving bodies, we have to abandon the idea of absolute measures of length and time, because of the constant speed of light. But, fortunately, we can think of the fixed stars as providing a relative background. In this way, all motion can be relative, allowing us to make appropriate corrections to lengths and times affected by it at high speeds, but yet we are not forced to interpret Newton’s bucket experiment as evidence that space and time measures are absolute. In this way, acceleration is relative to the fixed stars. Indeed, this is the path Smolin recommends as the paradigm of choice for forming a relational strategy that seeks “to make progress by identifying the background structure in our theories and removing it, replacing it with relations which evolve subject to dynamical law,” and he cites Einstein’s success with GR as vindicating it (see The case for background independence).

    But in all this, it’s a background-free (non-perturbative) string theory that is sought, with its extra dimensions of space. For an interesting look at Lawrence Krauss’s new book on string theory, and a discussion of the cultural fixation on extra dimensions of space, see Not Even Wrong. My question, though, is this, Elliot: Why hasn’t anyone considered multi-dimensional motion? Just as you observed in your first post, it is really the degrees of freedom of motion that gives meaning to physical dimensions. A cursory consideration of mathematics indicates that going beyond three dimensions of magnitude only produces a repetition of what you get with three dimensions anyway (Bott’s periodicity).

    The concept of two and three-dimensional magnitudes of vibrational motion (for instance, an expanding/contracting plane and volume, respectively) has lots of possibilities, but it requires a new definition of motion, which opens up a whole new system of physical theory, one based on the definition of space and time as simply the reciprocal aspects of motion. Such a system goes beyond the Newton program of research that seeks to describe nature in terms of a few kinds of interactions between a few kinds of particles: instead, it seeks to describe nature in terms of space and time. I don’t know what implications that would have for the LHC, and the ILC, though.


  • JoAnne

    Elliot & Doug,

    Nice exchange. I’m going to try to keep things simple here, to ensure that the basics are understood.

    Doug is right – there are different definitions of coordinate systems which may or may not be useful in solving a particular problem. However, let’s be clear on one point. All currently observed physical phenomena in the universe is described by 4 dimensions (3 spatial + 1 time), no more and no less, no matter what coordinate definition is used.

    Elliot is right that one can think of dimensions as the number of *independent* degrees of freedom that are required to describe the position of an object. The word *independent* is key here, and should be written in flashing, neon pink letters.

    The coordinate system that I described above is known as physical coordinates. A reference frame is defined, and the positions of all objects are computed within the set reference frame. This system is extremely useful for particle physics experiments, where the origin of the reference frame is usually taken to be at the center of a detector. In our use of physical coordinates, we assume that all possible reference frames are equal; i.e., that there is no favored set of coordinates and the physics we measure will not depend on the location or rotation of the chosen reference frame. This is a consequence of special relativity which states that inertial reference frames are equivalent and of our belief that the universe is homogeneous and isotropic. There are ways to test this assumption, i.e., to test whether some preferred reference frame exists in the universe. Sean and I have both written papers on this, and it has been tested by numerous experiments with null results.

    The coordinate system that Doug has described is known as comoving coordinates. This system is extremely useful in cosmology as these coordinates are carried along with the expansion of the universe. A useful analogy is to think of a coordinate grid that expands with time, as the universe expands; galaxies then remain at fixed locations in the comoving coordinate system. This system greatly simplifies many cosmological calculations. I must confess that I have never used this system, outside of my GR class.

  • Elliot


    Interestingly I have thought about multidimensional motion (particularly in 3D) in relation to how we “know” about where something is. I think there is a possible connection here with HUP and why we are constrained on information about position/momentum simultaneously. This is admittedly highly speculative. Anyway lots to think about.

  • Elliot


    Thanks again. One more follow up on the co-moving coordinate system if you will indulge me. Is the net effect of Dark Energy (as we current understand it) to accelerate the expansion the background grid as well as the “contents of the universe” or does is its effect only on the contents?

  • Plato

    Reimann whispers in my ear, “Little photon, you have to follow the course I set.”

    Couldn’t find a spot for it on cosmic variance, so I hope you won’t mind it here JoAnne.

  • bittergradstudent

    Elliot–the background grid is a mathematical abstraction–with a twist of a pen, it can be made to do many things, with many properties. What the Dark energy does is push out the contents of the universe.

    Scientists, wishing to describe the matter in the universe, draw a particularly convenient grid with which to describe the matter content. The point being that the grid doesn’t have any real, physical existence, but is a mathematical abstraction made by someone wishing to have simple equations with which to describe cosmology.

  • Doug

    JoAnne wrote:

    Doug is right – there are different definitions of coordinate systems which may or may not be useful in solving a particular problem. However, let’s be clear on one point. All currently observed physical phenomena in the universe is described by 4 dimensions (3 spatial + 1 time), no more and no less, no matter what coordinate definition is used.

    Yes, that’s true IF we exclude the standard model’s masses and coupling constants from the “observed physical phenomena,” but let’s remember that mass, charge, magnetic fields, etc. are also physical phenomena, and can’t be described by any number of dimensions regardless of the definition of the coordinate system.

  • Elliot


    Just a follow up on multi-dimensional motion. Would this be properly called “Superball” theory?

    Seriously though, what if at the planck level all that occured was expansion and contraction of planck scale spheres and all phenomena were function of this action?

    Be kinda like the Matrix?


  • Doug


    You know, I never saw that movie. One day I’m going to go rent the DVD, but let me give you some food for thought, since you seem to be bright and have a keen interest in these things: The negative numbers took centuries to be accepted (see the “crying jag” story posted by Sean), and the imaginary numbers had to be invented to cope with them. Now, we wonder why Bott’s periodicity seems to pop up everywhere (see John Baez’s “spooky facts” story), but it was Clifford, taking his clue from Hamilton and Grassmann, that was the first to recognize the significance of the fact that two interpretations of number are possible, the “quantitative” and the “operational” (see Hestenes GA).

    It turns out that, if we define number as an operational quantity by the ratio of two natural numbers, we form the rational number system, which in turn forms the integer number system, thus integrating the three number systems, the natural, the rational and the integer, into one number system with “negative” and “positive” quantities that make sense (no “crying jag”), and without the need for an imaginary number, since the square root of n/m = 1 is the same as the square root of m/n = 1. On this basis, the negative sign is only an indication of which of the two inverses we’re dealing with. It’s not mysterious at all.

    Now, when we add dimensions to these “signed” integers, we get fields of “signed,” n-dimensional, magnitudes and 0 is eliminated altogether! The best way to see this is with the triangle of the binomial expansion:

    Remember, we are interested in the binomial because we have two “directions” or “polarities” of signed integers, operationally interpreted from the rational numbers, formed from the natural numbers. Now, the rows show the composite set of the transformed numbers as the dimension, n, progresses. The 1st row has 1 type of number in it, the scalars, that some want to identify with the reals. The 2nd row has 2 types of numbers in the set, the reals and the complex type, some say. The 3rd row has 3 types, the third of which is identified with the quaternions, and finally, the 4th row has 4 types, the fourth of which is identified with the octonions.

    Interestingly, Bott’s periodicity seems to be tied with this pattern, because the next row (row five) seems to just be the beginning of a repetition of this pattern, and no matter how far you expand the binomial, the pattern just repeats itself, augmenting the original sequence, like a never-ending spiral. Well, since the pattern is equivalent to a scalar and three vectorial directions, what does this tell you? The unreasonable effectiveness of mathematics in physics strikes again, limiting us to 3 + 1 dimensions!

    However, here’s the really interesting part: the operational interpretation of number sheds a whole new light on this curious expansion of two “directions.” Indeed, it shows that the concept of a counting number, that Euclid so carefully kept separated from magnitudes, can be generalized to a concept of n-dimensional magnitudes with two “directions,” negative and positive, if you will; that is, a scalar magnitude with no “directions;” a 1D magnitude with two “directions;” a 2D magnitude with two “directions;” and a 3D magnitude with two “directions,” geometrically corresponding to a point, a line, a plane and a volume, each with two “directions:” a point with two potential, unrealized, “directions,” a line with two ends, a plane with two sides, and a volume with a center point and a surface.

    With the unreasonable effectiveness of mathematics in physics and the incredible symmetry this expansion exhibits, and the fact that the only known relationship of space and time is the reciprocal relation of motion, s/t, you’d think that we could get the attention of some of these practicing physicists by pointing this out. So far, however, we haven’t found any interest. They cling tenaciously to the 1D definition of motion, the function x(t) in n-dimensions of space, in spite of the fact that they could entirely eliminate space and time as a background structure, if they would pay attention to this slightly different way of understanding the mathematics of reciprocal systems.

    Now, Hestenes is one smart fella. Recognizing that Gibbs had side tracked everyone from the young Clifford’s brilliant discoveries that Hamilton and Grassmann were on to something profound, he put together Geometric Algebra, based on Clifford’s C3 algebra (based on row four above). Trouble is, not being able to escape the definition of motion of Newton’s system, he ends up with a confusion of direction and “direction” and gets stuck with artifacts as a result: the non-commutative vector product! Turns out, it’s not so bad from a practical point of view, because it helps to make sense of imaginary numbers, but had he not taken this misstep, he might have broken everything wide open and then maybe he would have called Weinberg to tell him that he found the way to unstick theoretical physics (Weinberg says their “stuck” for the same reasons we’ve been discussing; that is, the incompatibility of the two definitions of coordinate systems JoAnne refers to).

    Anyway, Elliot, it seems that your original question, about the dimensions of motion, go right to the heart of the huge crisis in theoretical physics. Go figure.


  • Doug


    The image of the binomial triangle showed up just fine in the preview, but doesn’t in the submitted post. You can see it here:

    Binomial Expansion

  • Plato

    I couldn’t help but think of Pascal’s triangle and the ideas behind the marble drop. We understand the relation to Boltzman do we not and probabilistic valuation in areas of quantum numbers?

    That to assign dimensional relevance must have invited views within those compacted dimensions?

    So what would emerge from that flash? Layman here scratches his head.

    There still has to be a better discription in concernt with dimensions as with Clifford if corrected, if you can spell this out better, which numbered/geometric system would you use?

    If we deal with quantum gravity what kind of geometry will emerge? ONE WOULD HAD TO ASSUME THAT SOMETHING ALWAYS EXISTED, BUT WHERE?

    Uncertainty reigns large and like any bubble that emerges, it had to emerge from space, and we accept this space is “not empty”, right?

    If one did not accept “hyperdimenisonal views” then none of this would matter would it?

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