Please explain the 'tubes' that connect the quarks

Discussion in 'Physics & Math' started by iwishyoulovedme, May 27, 2013.

  1. rpenner Fully Wired Valued Senior Member

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    Farsight is using italics in a non-standard way to indicate that he is quoting Wikipedia. Here I have replaced his quotes with standard quoting (sometimes with context restored and Farsight's extract emphasized.
    The "quark model" (predating the Standard Model of Particle Physics by some years) was that "purely mathematical" proposal to explain the large spectrum of hadrons (mesons and baryons) that particle colliders can produce, and played a role like the periodic table did in explaining chemistry before the quantum rules of the electron were understood. If taken literally, the quark model strongly suggested that at high energies an electron beam would be able to bounce of the internals of the proton in a way that revealed that it had structure that the electron did not. In fact, the discovered "partons" looked (to electromagnetic probes) like electrons and positrons with scaled down electric charges and more mass. More data led to the equating of quark model "quarks" with experimentally measured "partons" and since those early days we just talk about quarks -- just as we talk about electrons or atoms without the scare quotes or hesitation that they may turn out not to be real someday.


    Specifically in this section http://en.wikipedia.org/wiki/Deep_inelastic_scattering#History where the train of thought begins several paragraphs back:
    So it is clear that each of the excerpts that Farsight quotes is a direct consequence of the experimental picture. By contrast, Farsight passes judgement on the experimental picture by comparing it to his inadaquate and unevidenced self-published pseudo-physics, thus turning the practice of science on its head to further inflate his ego. This is anti-science -- a lone prophet of ineffable mysteries who declares himself to be an authority even when reality says something different.

    "quantum field structure" conveys no meaning. In quantum field theory, all particles are excitations of a quantum field that is (under the standard model) a single thing with several sectors that we can only approximately refer to as the "electron field", "the photon field", and "the up quark field." What "internal structure" here means is that while low-energy experiments (like those of Rutherford) treat protons as fundamental and point-like, high energy experiment reveal that the proton has electric charge spread out over a non-zero radius and higher energy experiment indicate that protons are not simple clouds but are fundamentally chunky.

    "Tripartite" is not the way to think about baryons. Yes, in the quark model they have a content of 3 "valence quarks" but that is not even approximately the whole story except in regards to electric charge. Models that try to model the masses of the baryons based on linear formulas of quark content fail. The complicated experimental picture is that quarks are always found in the interior of mesons and baryons, but in scattering experiments they don't have the mass associated with if they were tightly tied to the other quarks. At high energies quarks appear to be nearly-free particles with much lower mass than 1/3 proton. A successful model of the quarks (like the standard model) has to explain why they seem free and light at high energy while tightly bound and heavy at low energy in precisely the manner that experiments see.

    As you see, not only does Farsight's contribution lack any precision to compare with reality, it doesn't even generalize his ideas about baryons. If "tripartite" structures allow "bipartite" structures, there is no principle at work. It's only post hoc story-telling and not a physical model. In contrast, the SU(3) sector of the standard model gives quantitative details of the gluon field(s) that operate to give specific masses to the baryons and mesons and explains the relative interactions between the various pions and baryons that were formalized as "isospin" decades before the quark model.

    How vacuous this "wrong" now seems when we learn that Farsight is not relying on knowledge to reject a Wikipedia page description of experimental results, but his own soi-disant authority. Farsight has no actual physics credentials and has never acknowledged that reality matters, so when he says "wrong" he means nothing more than "that's not the way I delude myself about it" when sharing a delusion has no value in physics.

    It is unclear what "it" Farsight is referring to, but the standard model is a quantum field theory of point particles. According to the standard model, the electron, muon, tau, 3 types of neutrinos, 6 types of quark, the Higgs boson and the force-carriers are all fundamental particles -- and a particle is nothing more than a quantized excitation of the related field. Because of interactions, you can't really have one without (ultimately) all the others. But approximately we can speak of electrons while ignoring that they couple to the electomagnetic and weak forces and sweeping under the rug that they get the appearance of mass by coupling to the non-zero expectation value of the Higgs field. And when electrons do interact, they interact locally in a way that is localized in time and space -- this is why the electron is called point-like. In the standard model, an electron has zero width, height or depth. In reality, electrons have never had measurable width, height or depth.

    So Farsight conveys a complete misunderstanding of quantum field theory and how it compares to reality.
    Remember, the pre-Rutherford model of the atom was a cloud of positive charge that was roughly atom-sized with electrons stuck in it for neutrality. The experimental results were very much as surprising as a warship firing at at cloud only to have their shells bounce back.
    This completely misstates the experimental record and is problematic.

    Rutherford's experiments demonstrated elastic collisions between alpha particles and nuclei. Like all elastic collisions, both the alpha particle and the gold nucleus recoil, but because the alpha particle is lighter, its recoil is more dramatic. Compare the experiment with column of elastic balls of different masses. (Like dropping a ping pong ball and a solid superball into a long graduated cylinder.)

    Deep elastic scattering experiments between electrons and protons did not conserve kinetic energy and were called inelastic right there on title of the Wikipedia page. That's because what holds the proton together does not leave the quark completely free to recoil. Some of the momentum gets shuffled around in a messy way and notably the quark never springs free from the proton. If it springs loose at all, it comes with an anti-quark partner to form a meson.

    But what is most problematic about Farsight contrast of "hard" versus "elastic" is that one does not preclude the other. That's why the balls in the Newton's cradle desktop toy are often made of steel.
     
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  3. Guest254 Valued Senior Member

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    That sounds fantastic! If I make a thread titled something along the lines of "An introduction to topological quantum field theory", would you be willing to take the lead? I, for one, would like to know more about this subject.
     
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  5. iwishyoulovedme Registered Member

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    rpenner,

    you mentioned the 'single thing with several sectors' . That was what I tried to express in one of my earlier posts. Can you elaborate on that for the quarks and gluons and how they exchange these gluons to change the color of the quark? If indeed the quarks are pointlike particles which can be described as fields, don't they still need to know the current and present location of the other quarks in three dimensional space in order to exchange these gluons?
     
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  7. rpenner Fully Wired Valued Senior Member

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    Here's an article from 1966 which states that it is a basic phenomenon of electromagnetism -- or that the electron quantum field couples to the photon quantum field, so it's natural that momentum and energy can pass from a photon-photon state to an electron-anti-electron state. While its clear it there is jargon (for example, total cross section is the differential cross section integrated over the angles of the electron directions and not the total contribution of all orders of perturbation theory), there is no gibberish.

    http://www.fcaglp.unlp.edu.ar/astrofrelat/astrofisica/media/Papers/Gould_Schreder_1966.pdf

    Also let \(c\) be the speed of light, \(v\) be the speed of the electron (in the center-of mass frame, not the lab frame), and \(r_0 = \frac{1}{4 \pi \varepsilon _0 } \frac{e^2}{m_e c^2} = \alpha \frac{\hbar}{m_e c} = \alpha^2 \frac{4 \pi \varepsilon _0 \hbar^2}{m_e e^2} \) is a length factor that relates electric charge, the mass of the electron, the speed of light and Planck's constant that comes from quantum electrodynamics (the sector of the standard model that concerns electrons and photons).

    Then we have:
    \(z = \textrm{haversine} \theta = \frac{1}{2} ( 1 - \cos \theta ) = sin^2 \left( \frac{\theta}{2} \right) s_0 = \frac{\epsilon E}{m_e^2 c^4} s = s_0 z = \frac{\epsilon E}{m_e^2 c^4} \textrm{haversine} \theta \beta = \sqrt{1 - \frac{1}{s} } = \sqrt{1 - \frac{m_e^2 c^4}{\epsilon E sin^2 \frac{\theta}{2}} } v = \beta c = c \sqrt{1 - \frac{1}{s} } \sigma = \frac{\pi r_0^2}{2} ( 1 - \beta^2 ) \left[ ( 3 - \beta^4) \ln \frac{1+\beta}{1 - \beta} - 2 \beta ( 2 - \beta^2 ) \right] = \pi r_0^2 \frac{(2s^2 + 2s - 1) \ln \left( 2 s +2 \sqrt{s^2 - s} - 1 \right) - 2 \sqrt{s^2 - s} (s + 1)}{2 s^3}\)
    which is a sensible answer if \(\left| \theta \right| \geq 2 \sin^{\tiny -1} \frac{m_e c^2}{\sqrt{\epsilon E}}\) which is a sensible condition if \(\epsilon E \geq \left(m_e c^2 \right)^2\).

    So because the electron field is coupled to the photon field, these fields are not distinct and if the center-of-momentum energy of a photon-photon collision is high enough, then the energy and momentum of the photon field excitations can transfer to a pair of excitations in the electron field.

    But please feel free to move this to Farsight's TQFT thread.
     
    Last edited: May 30, 2013
  8. rpenner Fully Wired Valued Senior Member

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    Quarks don't need to "know" anything about other quarks, but because they couple to the gluon field(s) they get this information for free since disturbances in the gluon field spread at the speed of light.

    To think about the up quark field, think of 12 complex quantum amplitudes, because there are not just 1 type of up quark.
    There are 3 colors a quark can have, 2 polarizations a quark can have and the same field represents both matter and antimatters, and \(3 \times 2 \times 2 = 12\). There are also 16 gluon fields (8 SU(3) color choices and 2 choices of polarization.) When a quark exchanges energy and momentum with the gluon field, the quark starts in one state and ends up in another. It is no longer the same quark but may have a different color and polarization. Because all the up quark fields have the same mass, we treat it as an identical particle, but that's ignoring color and spin quantum numbers. So at this level of detail quarks and gluons are born and die in every QCD interaction.

    Since anti-up quarks are just another way of exciting the quark field(s), pair-production, annihilation, quark-gluon and anti-quark-gluon interactions are all related to each other in a mathematically precise way.

    This is why one typically studied Quantum Electrodynamics of photons and electrons first -- because the calculations that are easy to do by hand are stepping stones to understanding QCD where everything useful is hard.
     
  9. iwishyoulovedme Registered Member

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    Well, I'm trying my best to understand you guys, but one of the many things that puzzle me is about the gluon field. When quarks change from one type to another then is there not another quark that also changes its' character through these gluon transmissions? So how and why does this gluon field selectively affect only the two of the three quarks in a three quark particle? Why not when one quark changes its' characteristics why are not the other two quarks both affected?
     
  10. rpenner Fully Wired Valued Senior Member

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    Partly because everything is happening all at once, all the time -- but mostly because SU(3) is a gauge symmetry and so there is no net loss of, say, red-ness. (Reddity??)

    King Ptolemy was once famously told that even for kings, "there is no royal road to geometry." Here, I suggest what you are trying to do is to understand physics at a level that your experience and education have not yet prepared you for. Asking questions about how to understand models that are predicated on many mechanisms (quantum theory, relativity, Pauli exclusion, gauge theory, SU(3) and gauge theory) means that most of the time you are asking questions where you are not prepared to get value from a precise answer and not able to apply the lesson of an imprecise analogy.
     
  11. Farsight

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    Don't settle for that, Iwishyoulovedme. Ask rpenner how a "high-dimensional knot of quantum field configurations" can be reconciled with "the standard model is a quantum field theory of point particles". When his response is wanting and he attempts to fob you off with something like "you are not equipped to understand it" along with criticism of my responses, pursue your point.

    Stop right there. I said explain gamma-gamma pair production. All we have are photons. We don't have any electrons. So instead of quoting "Consider the collision between a high-energy photon (energy ) and a low-energy photon", start again. And this time explain it in your own words. Demonstrate that you understand it. For, as Einstein said, "you do not really understand something unless you can explain it to your grandmother". Note that when it comes to "a basic phenomenon of electromagnetism", the field we're dealing with is the electromagnetic field. So have a think about "these fields are not distinct".

    Guest: your evasion is noted.
     
  12. Markus Hanke Registered Senior Member

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    That section of the page talks about interactions between photons and hadrons. It does not imply that photons have internal structure.
     
  13. Guest254 Valued Senior Member

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    That's hardly fair Farsight! You brought up topological quantum field theory -- not me! I've asked if you'd be willing to talk more about the subject. I genuinely find this area both interesting and complicated. If you have found an easy way of understanding it, I'm simply asking if you would share your knowledge and wisdom.

    If you'd also like to talk about photon-photon scattering (at least in the context of QED), then I can certainly try to offer some input. I can just about remember some quantum field theory! Feel free to make a thread and I'll gladly participate (assuming you're willing to take part in the would-be TQFT thread).

    Please Register or Log in to view the hidden image!

     
  14. rpenner Fully Wired Valued Senior Member

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    There is nothing to reconcile. A field has a value at every point in space, for a quantum field this encodes the probability of finding the particle at such and such a point or with such-and-such a momentum. So a particle is (as I said above) an excitation of the field (where fields other than the Higgs field have a vacuum expectation value of zero). In the standard model the fields are not independent of each other -- they are coupled. I said that above also. So you literally can't perturb one at a spot without perturbing others at that same spot -- that's where the point-like nature of quantum field theory stands out -- all couplings are local. Thus electrons always have electric charge, because the full definition of an electron includes both its particle-like bump in the "electron field" and its related cusp in the "photon field." A hydrogen-like bound system, by definition, has at least two particle-like bumps and some other field to keep them bound, so turns out to depend on the fields coupling to each other. But the fundamental object isn't the particle, but the configuration of (many) quantum fields, which I gave examples of how the degrees of freedom at every point start piling up. Thus the fundamental picture is of the high-dimensional field configuration, which extends through space -- the range of the electromagnetic field (the photon field cusp) is indistinguishable from infinite.

    It's this methodology of quantum field theory that gives the most precise description of electromagnetic events that we have today. If electrons had any physical extent above about 1/10000 of the width of the proton, the assumption of locality built into quantum field theory would conflict with experimental findings, which it doesn't. Thus electrons, quarks, gluons, photons, etc. are effectively point-like fundamental particles in both the Standard Model and the best and latest empirical observations.
    Gee, it's very majestic of you, King Ptolemy, to order forum members about. It doesn't convince me that you understand either quantum field theory or the Standard Model.

    We never have "just photons, no electrons." -- The fields are coupled. Coupled. There's the photon-electron field interaction term right there in every quantitative introduction to Quantum Electrodynamics. The very same theory that described photons also described electrons. And QED is part of the Standard Model. As electrons are the lightest particles with electric charge (and have the highest charge-to-mass ratio to boot) the electron term dominates pair-production from gamma-gamma interaction.

    This reinforces my belief that you have never once performed a QED calculation (even in perturbation theory at tree level). This makes your spouting off about your "deep understanding" of TQFT to Guest254.
    I demonstrated I could read the material and I converted the CGS electric charge conventions to SI conventions for your benefit. But you are moving the goal posts. Your charge was that my paraphrase of the standard model would be gibberish. However, I both demonstrated that not only I had a coherent mental model of the coupled quantum fields of the standard model, but knew that they answered your question about pair production over 50 years ago. (I refer to the 1961 paper where the cross section was calculated from QED.) Did you even see the fine structure constant show up? You won't find it in the 1966 paper, but it comes straight from the coupling coefficient in QED and is preserved as a multiplicative factor in the cross-section.
    Einstein is dead and never explained relativity or photons to his mother. So when and were did he say it? If you can't answer precisely, I will regard you as a molester of the dead.
    The fields are coupled. But don't take my word for it. Look up any textbook definition of the QED Lagrangian.

    It's the last term of \(\mathcal{L} = i \bar{\psi} \gamma^{\mu} \partial_{\mu} \psi - m \bar{\psi} \psi - \frac{1}{4} F_{\mu\nu} F^{\mu\nu} - e \bar{\psi} \gamma_{\mu} A^{\mu} \psi\) where the electron field (\(\psi\)) couples to the photon field (\(A\)).

    Just one source is equation 6.66 of http://www.damtp.cam.ac.uk/user/tong/qft/six.pdf

    This sounds like the "conduct yourself accordingly" threat at the bottom of letter written by hack lawyers.
     
  15. iwishyoulovedme Registered Member

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    I realize there is no royal road that translates the math to words completely; but perhaps you would be kind enough build a royal bark to sail the river Nile? I don't need to understand every mathematical stone here when I'm just trying to see the a general view of the countryside.

    Could you try to elaborate on why only two quarks interact if this gluon field is simply a disturbance in something? Does it relate to these gluons
    generating their own gluons as described here? youtube.com/watch?v=ZYPem05vpS4&list=PL74025093AD4E64DC
     
  16. iwishyoulovedme Registered Member

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    I find this very helpful but I'm wondering how people's arguments about fields and particles would be affected by this video:

    youtube.com/watch?v=p5QXZ0__8VU&list=PL74025093AD4E64DC
     
  17. Farsight

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    I didn't like it. It showed the messenger particles as multi-coloured billiards balls. That's just so wrong. And the "picture" it gives of virtual particles fountaining out of a proton or electron or a planet is badly misleading. "Snapping back to the parent particle" is nonsense. And it presented the graviton as accepted fact, when it isn't. Virtual particles aren't short-lived real particles that are continually being created and destroyed by some kind of magic, they're field quanta. Like you divide the electromagnetic field up into little squares and treat each square as something like a photon. That doesn't mean it's an actual photon. A photon is an electromagnetic field variation propagating through space at c. That electromagnetic field variation isn't made out of lots of little photons magically popping in and out of existence.

    Edit:

    Make your mind up, rpenner. Is it a bump or a spike? Now come on, explain how gamma-gamma pair production works. "The fields are coupled" just doesn't cut it.

    Iwishyoulovedme: rpenner is fighting shy of this because he knows that the QED given explanation exposes an issue. See two-photon physics on Wikipedia. That's not to say that QED is "wrong". It isn't. But the description of what's actually happening is wrong. Catastrophically, obviously wrong. See if you can spot it. Once you see it it's obvious.
     
  18. Markus Hanke Registered Senior Member

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    The Feynman diagrams all check out just fine; there is nothing wrong in the article.
     
  19. iwishyoulovedme Registered Member

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    if you watch the whole video series you'll see they acknowledge the graviton is still theoretical. However, I disagree with you - the series does say that these virtual particles are temporarily existing and that's how these attractions exist due to exchanges of these virtual force carrying particles between real particles. I'm not sure why you don't trust these videos as they appear to be products of CERN.
     
  20. Farsight

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    It's not a matter of not trusting them, it's a matter of knowing that they're misleading. I'm afraid the video I saw is essentially cartoon physics for kids. Again, see Matt Strassler's virtual particles article and read this:

    "The problem here is that the intuition that arises from the word “exchange” simply has too many flaws. To really understand this you need a small amount of math, but zero math is unfortunately not enough. It is better, I think, for the layperson to understand that the electromagnetic field is disturbed in some way, ignore the term 'virtual photons' which actually is more confusing than enlightening, and trust that a calculation has to be done to figure out how the disturbance produced by the two electrons leads to their being repelled from one another, while the disturbance between an electron and a positron is different enough to cause attraction."

    Look around elsewhere, and you can find for example this where you can read this:

    "For all these reasons the concept of a virtual particle on its own does not have any operational meaning. Therefore this facon de parler provokes conceptual confusion as soon as one insinuates that virtual particles are physical..."

    You can find similar things on the internet such as this where you can read this:

    "Virtual particles are an artefact of perturbation theory that give an intuitive (but if taken too far, misleading) interpretation for Feynman diagrams. More precisely, a virtual photon, say, is an internal photon line in one of the Feynman diagrams. But there is nothing real associated with it. Detectable photons are never virtual, but always real, 'dressed' photons. Virtual particles, and the Feynman diagrams they appear in, are just a visual tool of keeping track of the different terms in a formal expansion of scattering amplitudes into multi-dimensional integrals involving multiple propagators - the momenta of the virtual particles represent the integration variables. They have no meaning at all outside these integrals."

    Virtual particles are essentially the "accounting units" of QFT. If you think about your pay check going into your bank account, your accounting units are pennies. But there isn't actually some storm of "virtual pennies" literally flying into your bank account. In similar vein virtual photons don't literally fly back and forth between the electron and the proton. They're virtual, not real, and they aren't "short-lived real particles" either. Like I said, hydrogen atoms don't twinkle.
     
  21. rpenner Fully Wired Valued Senior Member

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    This is not what your sources are saying. They are saying that virtual particles are more like the carry digits of a long calculation in perturbation methods -- not Quantum Field Theory. Other methods like generalized unitarity and lattice methods avoid the issue of promoting virtual particles to first class elements.
    Virtual particles still make sense in the field view if you use wavelet methods to decompose how the fields convey momentum.
    You are not an authority so what you consider to be a pithy soundbite may be unconnected to physics, and you ignore the quantization of action, the Unruh effect and how your hydrogen atoms transition to lower energy states.
     
  22. eram Sciengineer Valued Senior Member

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    John, I'd actually be willing to read through your book if you provide a pdf link or something.
     
    Last edited by a moderator: Jun 1, 2013
  23. iwishyoulovedme Registered Member

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    I am troubled that the videos and other things that I read say that the simply have temporary mass which vanishes and appears.....out of what? Energy? Isn't energy simply matter? So, what then? The fabric of space? The Higgs bosons?
     

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