5 ms·

"Each of these particles, or “nucleons,” is composed of a dense, frothing mess of other particles: quarks, which have mass, and gluons, which do not. Yet the qu

"Each of these particles, or “nucleons,” is composed of a dense, frothing mess of other particles: quarks, which have mass, and gluons, which do not. Yet the quark masses only add up to a mere 1% of a proton or neutron’s mass, with the bulk of the proton mass coming purely from the motion and confinement of quarks and gluons." https://physics.aps.org/articles/v11/118 https://physics.aps.org/articles/v11/118

narag 4y ago
So the interior of baryons is analogous to the interior of atoms, with gluons instead of electrons dancing frantically... weird. Also the part about mass being generated by motion and how it seems to be an established fact.
- nimish 4y ago
  Not really. The "roiling sea of particles" is a metaphor for perturbation series, which very specifically does not work for the strong force at low energies. Take anything involving virtual particles as just that, virtual. They're an aid for computation and cannot be observed directly. They aren't necessary either; lattice gauge theory is always applicable if not practical. The mass(-energy) being from the strong interactions is still true. And the residual bit of the strong force between protons and neutrons works with the virtual particle/perturbation theory approach pretty well, using pions.
  - tines 4y ago
    I'm glad you brought this up, because I've been reading some stuff lately that makes it seem like virtual particles actually have visible effects, like this one: https://www.forbes.com/sites/startswithabang/2019/07/12/yes-virtual-particles-can-have-real-observable-effects/ https://www.forbes.com/sites/startswithabang/2019/07/12/yes-... So is it that these articles are wrong, or that I'm reading them wrong, or that the idea that virtual particles are just for calculations is outdated?
    - tadfisher 4y ago
      We discovered the mesons by photographing their tracks on plates exposed to the sky. They're real, just extremely short-lived.
    - marcosdumay 4y ago
      What a bad piece of journalism, intent on confusing instead of explaining. Virtual particles were invented because they have measurable effects. Physicists don't go around inventing invisible things for no reason. What they are not is "particles". The particle facade is only there because it fits the math. (The article seems to be describing an experiment that measured energy-time uncertainty.)
    - cwillu 4y ago
      Incomplete analogy that's probably a better starting point: if the tone of a bell is a particle, then the other movements of the bell that don't resonate are virtual particles. Now, imagine we called the thermal motions of that bell “virtual tones”, and you have an idea why physicists always sigh and emphasize that virtual. particles. are. not. particles.
      - nine_k 4y ago
        If virtual particles "fit the math" the same as real particles, what makes them not real? What do they not fit?
        evanb 4y ago
        What makes particles travel long distances as lumps is that they are on-shell. Virtual particles are not on shell. https://en.wikipedia.org/wiki/On_shell_and_off_shell https://en.wikipedia.org/wiki/On_shell_and_off_shell
        nimish 4y ago
        You don't _need_ them, and IIRC _can't_ (in general) use them if you deal with non-perturbative effects, unless you do stuff like re-summing infinite series of diagrams and that really makes interpreting the ultimately observable effect in terms of virtual particles interacting difficult.
- marcosdumay 4y ago
  You meant gluons instead of photons? Because the things analogous to electrons and the nucleus are the quarks. Anyway, the similarity is only on the level of "it's a bunch of moving things locked together by a force". Those things are about as similar to themselves as they are to planetary motion.
- squeaky-clean 4y ago
  > Also the part about mass being generated by motion and how it seems to be an established fact. That's what they mean by relativistic speed. When effects from special relativity become large enough that you need to account for them in your math and measurements. There is a difference between invariant mass (aka rest mass) and relativistic mass, which depends on the object's velocity relative to the observer. https://en.m.wikipedia.org/wiki/Relativistic_speed https://en.m.wikipedia.org/wiki/Relativistic_speed
  - tsimionescu 4y ago
    While your description of what relativistic speeds means is accurate, this has nothing to do with the mass. Instead, composite "particles" have mass mostly because of the energy of their components. This is a famous observation (the most famous by far) in general relativity: E=mc². E here can be the kinetic energy of the constituent particles, or some other kind of energy (for example, a polar molecule like water owes some of its mass to the electrical energy of the bond; and its mass will increase or decrease if placed in a strong electric field, depending on the orientation of the field). This has nothing to do with the concept of "relativistic mass", which is anyway not commonly used in modern physics anymore. Mass almost always refers to "rest mass", and observer-dependent "relativistic mass" is accounted for only through differences in observer-dependent time and position measurements. That is, instead of saying "as an objects speed approaches the speed of light, its relativistic mass approaches infinity", the preferred interpretation is "as an object approaches the speed of light, time passes more slowly for it, so it takes longer for it to accelerate even if pushed with a constant force".
- Melatonic 4y ago
  I have no good background in this but could it not be that from an outside observer view the motion appears as mass but when thought of modeled within it is instead energy/motion ?
- tsimionescu 4y ago
  > Also the part about mass being generated by motion and how it seems to be an established fact. It's not motion per se, it's energy of any kind. And it's also probably the most famous equation in all of physics: E=mc² (so, m = E/c²).
ProAm 4y ago
The Strong Force and Strong Nuclear Force are so utterly fascinating to read about. Gluon Flux Tubes! Seems like pure science fiction and imagination.

narag 4y ago

So the interior of baryons is analogous to the interior of atoms, with gluons instead of electrons dancing frantically... weird. Also the part about mass being generated by motion and how it seems to be an established fact.

nimish 4y ago
Not really. The "roiling sea of particles" is a metaphor for perturbation series, which very specifically does not work for the strong force at low energies. Take anything involving virtual particles as just that, virtual. They're an aid for computation and cannot be observed directly. They aren't necessary either; lattice gauge theory is always applicable if not practical. The mass(-energy) being from the strong interactions is still true. And the residual bit of the strong force between protons and neutrons works with the virtual particle/perturbation theory approach pretty well, using pions.
- tines 4y ago
  I'm glad you brought this up, because I've been reading some stuff lately that makes it seem like virtual particles actually have visible effects, like this one: https://www.forbes.com/sites/startswithabang/2019/07/12/yes-virtual-particles-can-have-real-observable-effects/ https://www.forbes.com/sites/startswithabang/2019/07/12/yes-... So is it that these articles are wrong, or that I'm reading them wrong, or that the idea that virtual particles are just for calculations is outdated?
  - tadfisher 4y ago
    We discovered the mesons by photographing their tracks on plates exposed to the sky. They're real, just extremely short-lived.
  - marcosdumay 4y ago
    What a bad piece of journalism, intent on confusing instead of explaining. Virtual particles were invented because they have measurable effects. Physicists don't go around inventing invisible things for no reason. What they are not is "particles". The particle facade is only there because it fits the math. (The article seems to be describing an experiment that measured energy-time uncertainty.)
  - cwillu 4y ago
    Incomplete analogy that's probably a better starting point: if the tone of a bell is a particle, then the other movements of the bell that don't resonate are virtual particles. Now, imagine we called the thermal motions of that bell “virtual tones”, and you have an idea why physicists always sigh and emphasize that virtual. particles. are. not. particles.
    - nine_k 4y ago
      If virtual particles "fit the math" the same as real particles, what makes them not real? What do they not fit?
      - evanb 4y ago
        What makes particles travel long distances as lumps is that they are on-shell. Virtual particles are not on shell. https://en.wikipedia.org/wiki/On_shell_and_off_shell https://en.wikipedia.org/wiki/On_shell_and_off_shell
      - nimish 4y ago
        You don't _need_ them, and IIRC _can't_ (in general) use them if you deal with non-perturbative effects, unless you do stuff like re-summing infinite series of diagrams and that really makes interpreting the ultimately observable effect in terms of virtual particles interacting difficult.
marcosdumay 4y ago
You meant gluons instead of photons? Because the things analogous to electrons and the nucleus are the quarks. Anyway, the similarity is only on the level of "it's a bunch of moving things locked together by a force". Those things are about as similar to themselves as they are to planetary motion.
squeaky-clean 4y ago
> Also the part about mass being generated by motion and how it seems to be an established fact. That's what they mean by relativistic speed. When effects from special relativity become large enough that you need to account for them in your math and measurements. There is a difference between invariant mass (aka rest mass) and relativistic mass, which depends on the object's velocity relative to the observer. https://en.m.wikipedia.org/wiki/Relativistic_speed https://en.m.wikipedia.org/wiki/Relativistic_speed
- tsimionescu 4y ago
  While your description of what relativistic speeds means is accurate, this has nothing to do with the mass. Instead, composite "particles" have mass mostly because of the energy of their components. This is a famous observation (the most famous by far) in general relativity: E=mc². E here can be the kinetic energy of the constituent particles, or some other kind of energy (for example, a polar molecule like water owes some of its mass to the electrical energy of the bond; and its mass will increase or decrease if placed in a strong electric field, depending on the orientation of the field). This has nothing to do with the concept of "relativistic mass", which is anyway not commonly used in modern physics anymore. Mass almost always refers to "rest mass", and observer-dependent "relativistic mass" is accounted for only through differences in observer-dependent time and position measurements. That is, instead of saying "as an objects speed approaches the speed of light, its relativistic mass approaches infinity", the preferred interpretation is "as an object approaches the speed of light, time passes more slowly for it, so it takes longer for it to accelerate even if pushed with a constant force".
Melatonic 4y ago
I have no good background in this but could it not be that from an outside observer view the motion appears as mass but when thought of modeled within it is instead energy/motion ?
tsimionescu 4y ago
> Also the part about mass being generated by motion and how it seems to be an established fact. It's not motion per se, it's energy of any kind. And it's also probably the most famous equation in all of physics: E=mc² (so, m = E/c²).

ProAm 4y ago

The Strong Force and Strong Nuclear Force are so utterly fascinating to read about. Gluon Flux Tubes! Seems like pure science fiction and imagination.