6 ms·

The proton is a collection of quarks and gluons moving at relativistic speeds around a central point. What? Moving at relativistic speeds? I had never heard th

• daveguy 4y ago
  I think that just means "moving fast enough that relativity is significant and has to be accounted for". It doesn't mean they are right at the speed of light (although they could be, I don't know). You could call a rocket "moving a relativistic speeds" because relativity has to be included in the calculations for accurate missions within the solar system.
  • frutiger 4y ago
    Gluons are massless so they must move at the speed of light. However they are strongly interacting with quarks and themselves so their worldlines will be a crazy mess of intersections.
  • bgirard 4y ago
    I wonder what the cut off speed is for relativistic speeds. If you think about it, it's not only a matter of speed but also how much precision you want in your calculations. Even if something was moving very slowly, you need to account for relatively if you want very accurate calculations.
    • quchen 4y ago
      A rule of thumb in classical mechanics is that 0.1c is when you should start taking (special) relativity into account, I think it’s 0.5% contribution then. For general relativity I don’t know such a cutoff rule of thumb. Astronomy-wise, Mercury is the only planet that is obviously general-relativistic (its orbit is not an ellipse because it’s so close to the sun). On Earth, we don’t have strong/inhomogeneous enough gravity, so unless you’re synchronizing satellites or atomic clocks, GR is not something to worry about.
      • thfuran 4y ago
        Some of the most precise clocks can actually measure precisely enough that a few feet of elevation change makes a measurable difference, which I expect also means that what you've placed under the table it's on also could.
        • deleted 4y ago
          [deleted]
      • vkou 4y ago
        Mercury's orbit is absolutely an ellipse. It is incredibly elliptical, with an apogee of 69.8 million km, and a perigee of 46 million km. The relativistic effects on Mercury concern its precession - the way that elliptical orbit rotates [1] around the sun. And it's not caused by Mercury's speed (Which is only ~59 km/s at its maximum, compared to the Earth's 30 km/s). It's caused by spacetime being curved by the immense gravitational field of the sun. If Mercury had a circular orbit, it would have no precession. [1] Precession is akin to spinning a hula hoop around your body - with the hula hoop representing an orbit. https://en.wikipedia.org/wiki/Apsidal_precession https://en.wikipedia.org/wiki/Apsidal_precession
      • joe__f 4y ago
        I think a good rule of thumb is 'check what accuracy you need your answer to, and then include all effects relevant to that precision'. If you needed an answer accurate to four significant figures, then you'd include relativistic effects for v < 0.1 c
        • bawolff 4y ago
          I don't think that fits the definition of rule of thumb.
          • asah 4y ago
            As a rule of thumb, I like to define my definitions first. /s
    • thfuran 4y ago
      Even if something isn't moving at all (relative to your reference frame of choice), you might still need to care about local gravity's effect on time.
    • shagie 4y ago
      You also get some relativity with some elements. Gold is the one that I recall most readily. Relativistic Effects and the Chemistry of Gold - https://link.springer.com/content/pdf/10.1007/BF03215471.pdf https://link.springer.com/content/pdf/10.1007/BF03215471.pdf > In atoms of high nuclear charge (Z), as a consequence of a relativistic effect, the s electrons of an atom become more bound and their orbitals smaller than if this effect were absent. Simultaneously, the d (and f) electrons are less bound because of this effect, which scales roughly as Z2. Gold exhibits a large relativistic effect. This accounts for gold being more resistant to oxidation than silver. It also accounts for higher oxidation states being more accessible in gold than in silver. These effects are illustrated by some fluorine chemistry of gold and silver. https://en.wikipedia.org/wiki/Relativistic_quantum_chemistry https://en.wikipedia.org/wiki/Relativistic_quantum_chemistry > Relativistic quantum chemistry combines relativistic mechanics with quantum chemistry to calculate elemental properties and structure, especially for the heavier elements of the periodic table. A prominent example is an explanation for the color of gold: due to relativistic effects, it is not silvery like most other metals.
• arethuza 4y ago
  "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?
        • 4y ago
• SideburnsOfDoom 4y ago
  This article was around recently: "Inside the Proton, the ‘Most Complicated Thing You Could Possibly Imagine’" https://www.quantamagazine.org/inside-the-proton-the-most-complicated-thing-imaginable-20221019/ https://www.quantamagazine.org/inside-the-proton-the-most-co... https://news.ycombinator.com/item?id=33262637 https://news.ycombinator.com/item?id=33262637
• archgoon 4y ago
  For a back of the envelope calculation we consider the uncertainty principle Δx*Δp >= ℏ/2 Δp = Δ(mv) >= ℏ/(2Δx) m = 9.1 * 10 ^ -31 kg (mass of electron) x ~= 1 * 10^-15 m (radius of proton) ℏ = 6.6 * 10 ^ -34 kg m^2 / s (plancks) Δv >= 31 524 512 m /s Which is about 1/10 the speed of light. There isn't a true cutoff for "relativistic speeds" but in general, 1/10th counts.
• pharrington 4y ago
  The specific composition of baryons is fairly niche physics. Assuming you're not educated in quantum physics, there's as much reason to expect to know about that as there is to expect a non-programmer to know about the minutia of different manual memory management strategies.
• rolenthedeep 4y ago
  I'm not an expert, but I'll try to give a friendly explanation. Consider a photon. We're all pretty familiar with how these work. Photons are light, and move at c. Photons also crucially don't have any mass, which is why they can move at the speed of light-- nothing with mass can move at c. Photons are energy carriers for the electromagnetic field. They transfer electromagnetic energy from one particle to another. There's several quantum fields permeating the universe, and each has its own energy carrier particle[0]. These are known as bosons, or sometimes force mediators. Atoms can influence each other through the electromagnetic field. An electron in one atom can drop to a lower energy state (or orbital), and releases a photon with all the energy that the electron "lost". That photon can bump into another atom, which causes one of its electrons to jump up by the same amount of energy. Protons are made of quarks, which are held together with the strong nuclear force. The energy carrier for the strong nuclear force is called a gluon. Gluons bounce back and forth between the quarks, transferring energy for the strong nuclear force. This energy is used to pull the quarks together[1]. Again, because the gluons don't have mass, they can (and must) move at light speed. The quarks themselves do have mass, and they vibrate and wiggle around, but only at sub-light speeds. Particle physics is really weird at first glance, but it makes a certain kind of sense once you learn a bit about it. It also makes less sense the more you learn. You've been warned. [0] Except gravity. Maybe. We've theorized, but haven't observed the graviton particle mediating the gravitational force [1] gluons keep quarks a certain distance apart, sort of like a spring