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From the article: “Oxygen-28 might prompt physicists to revamp theories of how atomic nuclei are structured.” If the theories are incomplete or wrong, how coul

From the article: “Oxygen-28 might prompt physicists to revamp theories of how atomic nuclei are structured.” If the theories are incomplete or wrong, how could we accurately simulate things we don’t yet understand? It doesn’t matter how powerful the computer is.

rcme 3y ago
Isn’t that the point of simulation? To gain understanding of something? I think the underlying point is that, if our understanding is so incomplete that we can’t simulate a single atom, how can we trust all of our other physical understanding?
- ars 3y ago
  No, that's not the point of simulation. You gain no understand from simulation because what you put into it is what you get out of it. Simulation can help you verify what you already know, and point to areas to examine, but you can't actually directly learn anything from it. We trust our physical understanding by experimentation, not simulation. You can use simulations in areas that are fully understood to run calculation on new arrangements of those those things, without having to make the physical object. But it only works when you already understand the thing, you can't gain that original understanding from the simulation.
  - nomel 3y ago
    I think there’s an assumption that the “unit” of simulation is much smaller than the oxygen atom, allowing these “emergent” behaviors to arise.
    - Retric 3y ago
      We don’t actually know the laws of physics, we just have some decent approximations. So sure run a simulation at whatever level of granularity you want that doesn’t mean it’s correct.
- ChuckMcM 3y ago
  Yes and no. A simulation can test your model, which you then compare with empirical results to validate both the model and the simulation of it. When those results do not match, you have to figure out if your simulation is wrong or the model is wrong. The model said that O28 would be doubly magic and thus stable, and yet when they managed to make it, it was exceptionally short lived. As a result the model they have is missing something. On the plus side, now that they have an empirical result, they can tweak the model such that it continues to accurately describe what it currently describes, and describes a short lived O28. Once they have those tweaks, they can find another experiment to see if their updated model accurately predicts what the experiment would produce. If it does, they gain more confidence in the model, if it does not, they go back to tweaking the model. This is the essential core of scientific research, for science to be believable it needs to predict things that will happen given conditions, and then experimentalists establish those conditions and look for confirmation of the prediction. It is the only way to know if what we think we know is in fact worth knowing!
- at_a_remove 3y ago
  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?
- jacquesm 3y ago
  Because just like statistics don't say anything about an individual person they are quite useful when applying them to larger populations and we usually deal with larger populations of atoms. Gas simulations work well because the noise more or less cancels out and then your macroscopic gas laws emerge and allow you to say useful things about how a gas will behave. Even if under the hood it is a completely stochastic process that gives rise to these laws. The laws themselves are simply our best description of observed reality, they are not laws that any particular atom needs to obey!
addaon 3y ago
There’s multiple levels of “theory” here. We have reasonable confidence that an ab initio simulation of a O28 nucleus would match experiment, but such a simulation is outrageously hard. We simplify things by creating an abstraction of the strong nuclear force, the residual force of the strong force at the scale of nucleons; there’s plenty of room for improvement here. Then, we have a further abstraction of “magic numbers,” a rule-of-thumb level theory that reduces the calculations of the strong nuclear force to a lookup table. While this last step is a pretty good approximation when applied to the EM force and electron orbitals, it’s no surprise that it’s a mediocre-at-best approximation for nuclear structure. Even so, finding cases where it doesn’t apply is useful for developing a refined version of this third-level rule-of-thumb — and a more accurate, more grounded rule of thumb here would be useful for refining speculations about the possible island of stability, where ab initial simulation is even less practical.
eikenberry 3y ago
All theories are incomplete and wrong, that is a core principle of science. When and how simulations might be useful in testing that theory are context dependent. In other words.. it depends.

rcme 3y ago

Isn’t that the point of simulation? To gain understanding of something? I think the underlying point is that, if our understanding is so incomplete that we can’t simulate a single atom, how can we trust all of our other physical understanding?

ars 3y ago
No, that's not the point of simulation. You gain no understand from simulation because what you put into it is what you get out of it. Simulation can help you verify what you already know, and point to areas to examine, but you can't actually directly learn anything from it. We trust our physical understanding by experimentation, not simulation. You can use simulations in areas that are fully understood to run calculation on new arrangements of those those things, without having to make the physical object. But it only works when you already understand the thing, you can't gain that original understanding from the simulation.
- nomel 3y ago
  I think there’s an assumption that the “unit” of simulation is much smaller than the oxygen atom, allowing these “emergent” behaviors to arise.
  - Retric 3y ago
    We don’t actually know the laws of physics, we just have some decent approximations. So sure run a simulation at whatever level of granularity you want that doesn’t mean it’s correct.
ChuckMcM 3y ago
Yes and no. A simulation can test your model, which you then compare with empirical results to validate both the model and the simulation of it. When those results do not match, you have to figure out if your simulation is wrong or the model is wrong. The model said that O28 would be doubly magic and thus stable, and yet when they managed to make it, it was exceptionally short lived. As a result the model they have is missing something. On the plus side, now that they have an empirical result, they can tweak the model such that it continues to accurately describe what it currently describes, and describes a short lived O28. Once they have those tweaks, they can find another experiment to see if their updated model accurately predicts what the experiment would produce. If it does, they gain more confidence in the model, if it does not, they go back to tweaking the model. This is the essential core of scientific research, for science to be believable it needs to predict things that will happen given conditions, and then experimentalists establish those conditions and look for confirmation of the prediction. It is the only way to know if what we think we know is in fact worth knowing!
at_a_remove 3y ago
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?
jacquesm 3y ago
Because just like statistics don't say anything about an individual person they are quite useful when applying them to larger populations and we usually deal with larger populations of atoms. Gas simulations work well because the noise more or less cancels out and then your macroscopic gas laws emerge and allow you to say useful things about how a gas will behave. Even if under the hood it is a completely stochastic process that gives rise to these laws. The laws themselves are simply our best description of observed reality, they are not laws that any particular atom needs to obey!

addaon 3y ago

There’s multiple levels of “theory” here. We have reasonable confidence that an ab initio simulation of a O28 nucleus would match experiment, but such a simulation is outrageously hard. We simplify things by creating an abstraction of the strong nuclear force, the residual force of the strong force at the scale of nucleons; there’s plenty of room for improvement here. Then, we have a further abstraction of “magic numbers,” a rule-of-thumb level theory that reduces the calculations of the strong nuclear force to a lookup table. While this last step is a pretty good approximation when applied to the EM force and electron orbitals, it’s no surprise that it’s a mediocre-at-best approximation for nuclear structure. Even so, finding cases where it doesn’t apply is useful for developing a refined version of this third-level rule-of-thumb — and a more accurate, more grounded rule of thumb here would be useful for refining speculations about the possible island of stability, where ab initial simulation is even less practical.

eikenberry 3y ago

All theories are incomplete and wrong, that is a core principle of science. When and how simulations might be useful in testing that theory are context dependent. In other words.. it depends.