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You have this backward. So imagine you have a simulation, and you get an answer out. Yay. How do you know it is correct? You don't. You must compare agains

You have this backward. So imagine you have a simulation, and you get an answer out. Yay. How do you know it is correct? You don't. You must compare against reality. Reality always wins. This is not a "single atom," you might as well say "a single person." Each one of those protons is composed of two up quarks and one down quark. Each one of the neutrons is composed of two down quarks and one up quark. Each nucleon is therefore three quarks, held together by the exchange of virtual quarks. The nucleons themselves interact via a stepped-down approximation of that called the strong nuclear force. And you're not allowed to forget the electromagnetic force, either. And then there's self-interaction ... There's a lot going inside of a nucleus. Simulations are only useful for testing your models.

cwillu 3y ago
Also, the “composed of two up quarks and one down quark” is a dramatic simplification, kinda sorta like saying that the valence electrons of an atom are the only electrons. https://i0.wp.com/profmattstrassler.com/wp-content/uploads/2013/04/nucleons31.png https://i0.wp.com/profmattstrassler.com/wp-content/uploads/2... “Fig. 3: A more realistic, though still imperfect, image of protons and neutrons as full of quarks, anti-quarks and gluons, moving around at high speed. More precisely, a proton consists of two up quarks and a down quark plus many gluons (g) plus many quark/anti-quark pairs (u, d, s stand for up, down and strange quarks; anti-quarks are marked with a bar.) The edge of a proton or neutron is not sharp. Ignore the color-coding for now; it will become clearer in future articles.” -- https://profmattstrassler.com/articles-and-posts/particle-physics-basics/the-structure-of-matter/protons-and-neutrons/ https://profmattstrassler.com/articles-and-posts/particle-ph...
- at_a_remove 3y ago
  Sorry, I meant to type "virtual gluons" instead of "virtual quarks."
wheelerof4te 3y ago
"Each one of those protons is composed of two up quarks and one down quark. Each one of the neutrons is composed of two down quarks and one up quark." And we know this, how? Using magic? Has anyone ever seen a quark? We could barely detect atoms, now we're detecting something even smaller?
- at_a_remove 3y ago
  ... "we could barely detect atoms." You're a few decades out of date on the science. Almost a century, really. Atom detection has been ... quite a while. The parts of the atom: electron, proton, neutron (all somethings even smaller) started with the electron in 1897. Neutrons lagged until the 1930s. Quarks were hypothesized in 1964. Now, you'll never find free quarks (due to something called color confinement) but we started detecting that the nucleons (protons and neutrons) must have something even smaller inside via scattering experiments around 1968. We were producing charm quarks in 1974. 1977 we observed the bottom quark, and in 1995 we got the heaviest of the bunch, the top quark. The current year is 2023.
- ftxbro 3y ago
  They found them by blasting protons at each other and seeing what happened when they collided like this https://en.wikipedia.org/wiki/Quark#/media/File:Charmed-dia-w.png https://en.wikipedia.org/wiki/Quark#/media/File:Charmed-dia-... and then using detective skills to figure out what could have been inside them to make those spirals
- jacquesm 3y ago
  Quarks are a very useful construct because even if we can't perceive them directly theories based on quarks appear to work. That makes them a useful tool and even if we will never be able to 'observe' (for whatever that means: you can't observe an electron directly either but you can observe electricity) quarks directly we can create theories that hold true if quarks exist and see whether the interaction between particle beams is such that it experimentally confirms those theories. This has been done countless times by now and the various properties of quarks and combinations of quarks have been determined to the point that it would be very surprising if quarks were a completely wrong way of describing the fundamentals of matter. But: it's a theory and it may well be displaced by something else at some point, but that something else would have to be even better at describing reality as observed than quarks are. Maybe a unified field theory will do away with the 'zoo' of subatomic particles but that would in itself be a very surprising result. But it could definitely happen.

cwillu 3y ago

Also, the “composed of two up quarks and one down quark” is a dramatic simplification, kinda sorta like saying that the valence electrons of an atom are the only electrons. https://i0.wp.com/profmattstrassler.com/wp-content/uploads/2013/04/nucleons31.png https://i0.wp.com/profmattstrassler.com/wp-content/uploads/2... “Fig. 3: A more realistic, though still imperfect, image of protons and neutrons as full of quarks, anti-quarks and gluons, moving around at high speed. More precisely, a proton consists of two up quarks and a down quark plus many gluons (g) plus many quark/anti-quark pairs (u, d, s stand for up, down and strange quarks; anti-quarks are marked with a bar.) The edge of a proton or neutron is not sharp. Ignore the color-coding for now; it will become clearer in future articles.” -- https://profmattstrassler.com/articles-and-posts/particle-physics-basics/the-structure-of-matter/protons-and-neutrons/ https://profmattstrassler.com/articles-and-posts/particle-ph...

at_a_remove 3y ago
Sorry, I meant to type "virtual gluons" instead of "virtual quarks."

wheelerof4te 3y ago

"Each one of those protons is composed of two up quarks and one down quark. Each one of the neutrons is composed of two down quarks and one up quark." And we know this, how? Using magic? Has anyone ever seen a quark? We could barely detect atoms, now we're detecting something even smaller?

at_a_remove 3y ago
... "we could barely detect atoms." You're a few decades out of date on the science. Almost a century, really. Atom detection has been ... quite a while. The parts of the atom: electron, proton, neutron (all somethings even smaller) started with the electron in 1897. Neutrons lagged until the 1930s. Quarks were hypothesized in 1964. Now, you'll never find free quarks (due to something called color confinement) but we started detecting that the nucleons (protons and neutrons) must have something even smaller inside via scattering experiments around 1968. We were producing charm quarks in 1974. 1977 we observed the bottom quark, and in 1995 we got the heaviest of the bunch, the top quark. The current year is 2023.
ftxbro 3y ago
They found them by blasting protons at each other and seeing what happened when they collided like this https://en.wikipedia.org/wiki/Quark#/media/File:Charmed-dia-w.png https://en.wikipedia.org/wiki/Quark#/media/File:Charmed-dia-... and then using detective skills to figure out what could have been inside them to make those spirals
jacquesm 3y ago
Quarks are a very useful construct because even if we can't perceive them directly theories based on quarks appear to work. That makes them a useful tool and even if we will never be able to 'observe' (for whatever that means: you can't observe an electron directly either but you can observe electricity) quarks directly we can create theories that hold true if quarks exist and see whether the interaction between particle beams is such that it experimentally confirms those theories. This has been done countless times by now and the various properties of quarks and combinations of quarks have been determined to the point that it would be very surprising if quarks were a completely wrong way of describing the fundamentals of matter. But: it's a theory and it may well be displaced by something else at some point, but that something else would have to be even better at describing reality as observed than quarks are. Maybe a unified field theory will do away with the 'zoo' of subatomic particles but that would in itself be a very surprising result. But it could definitely happen.