5 ms·

Except neutrons are protons bound to electrons, so that's really just 4 of each, so maybe this is just some exotic Beryllium, or a clump of degenerate neutron g

Except neutrons are protons bound to electrons, so that's really just 4 of each, so maybe this is just some exotic Beryllium, or a clump of degenerate neutron gas as might escape from a dead-ish star.

leni536 11y ago
> neutrons are protons bound to electrons No, they are not.
- logfromblammo 11y ago
  To be more specific, you can turn a proton into a neutron by electron capture or beta+ decay, but that's not what a neutron is. A neutron is 2 down (-1/3 charge) quarks and 1 up (+2/3 charge) quark, whereas a proton is 2 up and 1 down quark. Electron (-1 charge) capture changes an up to a down and emits an electron neutrino (0 charge). Beta decay is when a neutron changes to a proton and emits an electron and an electron antineutrino (beta-), or when a proton changes to a neutron and emits a positron and electron neutrino (beta+). Even if you wanted to be generous, the grandparent post left out the electron antineutrino.
winter_blue 11y ago
A proton is neutron bound by an electron? Where did you get that from? Beta decay goes both ways[1]. In β+ decay, a proton decays into a neutron and positron, and in β− decay, a neutron decays into proton and electron. (I don't know much physics, but I suppose there's a limit to them decaying from one to another, and I suppose each proton/neutron is unique in terms of its mass/energy content.) [1] See https://en.wikipedia.org/wiki/Beta_decay https://en.wikipedia.org/wiki/Beta_decay
- raattgift 11y ago
  Let's add "at rest" to the end of your question: "I suppose each proton/neutron is unique in terms of its mass/energy content" Oh boy, so there's a can of worms. "Unique" would need to be nailed down to test that statement, and runs into some observational problems in that atoms exist and can be found in things like monatomic gasses in enormous enough quantities that you can wash out any contributions from other matter. These gas clouds can be measured and manipulated, and have been. The results limit the variation from proton to proton (and climbing the periodic table of elements, from nucleus to nucleus) to be entirely negligible. Theory depends on where you look. Protons are usually taken to be indistinguishable particles (each proton obeys the same particle statistics at low energy). Additionally, there are good reasons to believe that any distinguishability -- however small -- leads to observables (an example is elucidated and generalized in the "Bosonic Birthday Paradox" http://arxiv.org/abs/1106.0849 http://arxiv.org/abs/1106.0849 ). Those observables are not seen. Proton distinguishability also goes to the question of the mechanisms by which the Pauli Exclusion Principle manifests. It does manifest among protons in atomic nuclei, which is important. Retaining that and introducing actual distinguishability at small scales is a challenge. If protons are (barely) distinguishable to us in experiments, they'll be (barely) distinguishable in decays and in electron interactions too. But if you think of a proton as "a mess"[1] and look at it at, say, the QCD scale, your question might be better put as,"how do confinement (and asymptotic freedom) and colour exchange work?". Peering into the structure of a proton at that scale is certainly interesting, but any information in there can only escape in ways permitted by confinement. [1] http://profmattstrassler.com/articles-and-posts/particle-physics-basics/the-structure-of-matter/protons-and-neutrons/ http://profmattstrassler.com/articles-and-posts/particle-phy...
  - winter_blue 11y ago
    Thanks for this comment.
ars 11y ago
I can see why you would think that. But neutrons really are distinct particles. A neutron has 3 quarks in it, not 3 quarks plus an electron. That down quark that became an up quark: An up quark is not a down quark plus an electron.
- raattgift 11y ago
  It gets a bit more complicated than that. Matt Strassler has a couple relevant articles on his blog site. The first goes deeper than the 3-quark simplification. "What's a proton? First and foremost, it’s a mess. A total mess" http://profmattstrassler.com/articles-and-posts/largehadroncolliderfaq/whats-a-proton-anyway/ http://profmattstrassler.com/articles-and-posts/largehadronc... The second digs into both protons and neutrons "So there are reasons to go further and describe things as I have elsewhere on this website: a proton is made from three quarks (two up quarks and a down quark), lots of gluons, and lots of quark-antiquark pairs (mostly up quarks and down quarks, but also even a few strange quarks); they are all flying around at very high speed (approaching or at the speed of light); and the whole collection is held together by the strong nuclear force" http://profmattstrassler.com/articles-and-posts/particle-physics-basics/the-structure-of-matter/protons-and-neutrons/ http://profmattstrassler.com/articles-and-posts/particle-phy... And the third deals with neutron stability in nuclei, and specifically focuses on the stability of the neutron inside a deuteron. http://profmattstrassler.com/articles-and-posts/particle-physics-basics/mass-energy-matter-etc/the-energy-that-holds-things-together/neutron-stability-in-atomic-nuclei/ http://profmattstrassler.com/articles-and-posts/particle-phy... [forgive me for combining a reply to an earlier comment you made on neutron stars] We don't know the equation of state of a neutron star; most viable models have substantial layering and an impressively busy energy-density flow. Most models predict neutron stars to be very bright in neutrinos, although the brightness is typically greatest at the outer layers rather than from the deeper ones where one would expect a superfluid sea of degenerate neutrons to dominate almost to the exclusion of everything else (e.g. there may be small numbers of superconducting protons floating around in it), and mechanisms which produce the Pauli Exclusion Principle are non-negligible. Possible mechanisms are somewhat constrained. How the density profile goes below the superfluid layer is I think mainly speculation; there are BH-remnant-related reasons to hope for a lattice crystal or some block-like structure of subatomic particles forming an inner core. JM Lattimer has a recent (2013) paper: http://arxiv.org/abs/1305.3510 http://arxiv.org/abs/1305.3510
pif 11y ago
A proton bound to an electron is called hydrogen atom. It's radius is five orders of magnitude larger than the radius of a neutron.
mettamage 11y ago
Interesting about the people here claiming that this isn't the case what blahDeeBlahBlah says. I don't know anything about chemistry other than the high school level, but essentially what blahDeeBlahBlah says is what I also learned in high school. Yet another lie they tell young students. They never told anything about quarks as well.
- swombat 11y ago
  Where did you guys go to school? This seems like active anti-education there...
- raattgift 11y ago
  Pedagogical simplification is a tricky subject. Wikipedia's take on it is here. The last two or three paragraphs before "See also" are provocative. Nuclear physics are enormously complicated and the simplified picture usually presented of the Standard Model (in charts showing 3-quark particles) is a compromise between getting across the idea of a composite particle like a proton and digging into why a proton is an extremely messy thing filled with pions and gluons. The latter is where the symmetry groups of the Standard Model lead you, and down that path lies enormous many-body problems. Those are almost always irrelevant at the scale of chemistry, nuclear engineering, or even most of astrophysics, where the simplification is good enough. Indeed, most of the time quarks and gluons don't even arise in the solutions to problems in those fields. Additionally, at that scale one starts running into some problems in the Standard Model which are essentially irrelevant in useful effective field theories, and which are simply not well enough understood by working scientists in the field to boil down to something useful for teaching except at the graduate level. (Well, as long as you believe in the principle that to explain something to a child, or even an adult non-specialist, you have to understand it extremely well or sacrifice accuracy.) https://en.wikipedia.org/wiki/Lie-to-children https://en.wikipedia.org/wiki/Lie-to-children

leni536 11y ago

> neutrons are protons bound to electrons No, they are not.

logfromblammo 11y ago
To be more specific, you can turn a proton into a neutron by electron capture or beta+ decay, but that's not what a neutron is. A neutron is 2 down (-1/3 charge) quarks and 1 up (+2/3 charge) quark, whereas a proton is 2 up and 1 down quark. Electron (-1 charge) capture changes an up to a down and emits an electron neutrino (0 charge). Beta decay is when a neutron changes to a proton and emits an electron and an electron antineutrino (beta-), or when a proton changes to a neutron and emits a positron and electron neutrino (beta+). Even if you wanted to be generous, the grandparent post left out the electron antineutrino.

winter_blue 11y ago

A proton is neutron bound by an electron? Where did you get that from? Beta decay goes both ways[1]. In β+ decay, a proton decays into a neutron and positron, and in β− decay, a neutron decays into proton and electron. (I don't know much physics, but I suppose there's a limit to them decaying from one to another, and I suppose each proton/neutron is unique in terms of its mass/energy content.) [1] See https://en.wikipedia.org/wiki/Beta_decay https://en.wikipedia.org/wiki/Beta_decay

raattgift 11y ago
Let's add "at rest" to the end of your question: "I suppose each proton/neutron is unique in terms of its mass/energy content" Oh boy, so there's a can of worms. "Unique" would need to be nailed down to test that statement, and runs into some observational problems in that atoms exist and can be found in things like monatomic gasses in enormous enough quantities that you can wash out any contributions from other matter. These gas clouds can be measured and manipulated, and have been. The results limit the variation from proton to proton (and climbing the periodic table of elements, from nucleus to nucleus) to be entirely negligible. Theory depends on where you look. Protons are usually taken to be indistinguishable particles (each proton obeys the same particle statistics at low energy). Additionally, there are good reasons to believe that any distinguishability -- however small -- leads to observables (an example is elucidated and generalized in the "Bosonic Birthday Paradox" http://arxiv.org/abs/1106.0849 http://arxiv.org/abs/1106.0849 ). Those observables are not seen. Proton distinguishability also goes to the question of the mechanisms by which the Pauli Exclusion Principle manifests. It does manifest among protons in atomic nuclei, which is important. Retaining that and introducing actual distinguishability at small scales is a challenge. If protons are (barely) distinguishable to us in experiments, they'll be (barely) distinguishable in decays and in electron interactions too. But if you think of a proton as "a mess"[1] and look at it at, say, the QCD scale, your question might be better put as,"how do confinement (and asymptotic freedom) and colour exchange work?". Peering into the structure of a proton at that scale is certainly interesting, but any information in there can only escape in ways permitted by confinement. [1] http://profmattstrassler.com/articles-and-posts/particle-physics-basics/the-structure-of-matter/protons-and-neutrons/ http://profmattstrassler.com/articles-and-posts/particle-phy...
- winter_blue 11y ago
  Thanks for this comment.

ars 11y ago

I can see why you would think that. But neutrons really are distinct particles. A neutron has 3 quarks in it, not 3 quarks plus an electron. That down quark that became an up quark: An up quark is not a down quark plus an electron.

raattgift 11y ago
It gets a bit more complicated than that. Matt Strassler has a couple relevant articles on his blog site. The first goes deeper than the 3-quark simplification. "What's a proton? First and foremost, it’s a mess. A total mess" http://profmattstrassler.com/articles-and-posts/largehadroncolliderfaq/whats-a-proton-anyway/ http://profmattstrassler.com/articles-and-posts/largehadronc... The second digs into both protons and neutrons "So there are reasons to go further and describe things as I have elsewhere on this website: a proton is made from three quarks (two up quarks and a down quark), lots of gluons, and lots of quark-antiquark pairs (mostly up quarks and down quarks, but also even a few strange quarks); they are all flying around at very high speed (approaching or at the speed of light); and the whole collection is held together by the strong nuclear force" http://profmattstrassler.com/articles-and-posts/particle-physics-basics/the-structure-of-matter/protons-and-neutrons/ http://profmattstrassler.com/articles-and-posts/particle-phy... And the third deals with neutron stability in nuclei, and specifically focuses on the stability of the neutron inside a deuteron. http://profmattstrassler.com/articles-and-posts/particle-physics-basics/mass-energy-matter-etc/the-energy-that-holds-things-together/neutron-stability-in-atomic-nuclei/ http://profmattstrassler.com/articles-and-posts/particle-phy... [forgive me for combining a reply to an earlier comment you made on neutron stars] We don't know the equation of state of a neutron star; most viable models have substantial layering and an impressively busy energy-density flow. Most models predict neutron stars to be very bright in neutrinos, although the brightness is typically greatest at the outer layers rather than from the deeper ones where one would expect a superfluid sea of degenerate neutrons to dominate almost to the exclusion of everything else (e.g. there may be small numbers of superconducting protons floating around in it), and mechanisms which produce the Pauli Exclusion Principle are non-negligible. Possible mechanisms are somewhat constrained. How the density profile goes below the superfluid layer is I think mainly speculation; there are BH-remnant-related reasons to hope for a lattice crystal or some block-like structure of subatomic particles forming an inner core. JM Lattimer has a recent (2013) paper: http://arxiv.org/abs/1305.3510 http://arxiv.org/abs/1305.3510

pif 11y ago

A proton bound to an electron is called hydrogen atom. It's radius is five orders of magnitude larger than the radius of a neutron.

mettamage 11y ago

Interesting about the people here claiming that this isn't the case what blahDeeBlahBlah says. I don't know anything about chemistry other than the high school level, but essentially what blahDeeBlahBlah says is what I also learned in high school. Yet another lie they tell young students. They never told anything about quarks as well.

swombat 11y ago
Where did you guys go to school? This seems like active anti-education there...
raattgift 11y ago
Pedagogical simplification is a tricky subject. Wikipedia's take on it is here. The last two or three paragraphs before "See also" are provocative. Nuclear physics are enormously complicated and the simplified picture usually presented of the Standard Model (in charts showing 3-quark particles) is a compromise between getting across the idea of a composite particle like a proton and digging into why a proton is an extremely messy thing filled with pions and gluons. The latter is where the symmetry groups of the Standard Model lead you, and down that path lies enormous many-body problems. Those are almost always irrelevant at the scale of chemistry, nuclear engineering, or even most of astrophysics, where the simplification is good enough. Indeed, most of the time quarks and gluons don't even arise in the solutions to problems in those fields. Additionally, at that scale one starts running into some problems in the Standard Model which are essentially irrelevant in useful effective field theories, and which are simply not well enough understood by working scientists in the field to boil down to something useful for teaching except at the graduate level. (Well, as long as you believe in the principle that to explain something to a child, or even an adult non-specialist, you have to understand it extremely well or sacrifice accuracy.) https://en.wikipedia.org/wiki/Lie-to-children https://en.wikipedia.org/wiki/Lie-to-children