The nuclear force

The nuclear force holds atomic nuclei together. When protons and neutrons are a femtometre apart, the nuclear force between them is powerfully attractive. If you could turn this powerfully attractive force off, an atomic nucleus would explode into a spray of protons and neutrons. That’s because there’s an electromagnetic force between the protons, and it’s powerfully repulsive. In stable nuclei, the forces are in balance. But as Rod Nave says on his most excellent hyperphysics website, when the balance is broken the resultant radioactivity yields particles…

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The neutron

There’s a nice potted history of the discovery of the neutron on the Nobel website. It mentions the great Ernie Rutherford who discovered the proton in 1917. He knew all about Prout's hypothesis wherein the atomic weights of various elements were integer multiples of the atomic weight of hydrogen. However Rutherford also knew that the atomic number, the number of protons, was circa half the atomic weight. So in 1920 he suggested that this disparity was due to neutral particles called neutrons. The evidence of beta…

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The nuclear disaster

The nuclear force is the force that keeps protons and neutrons together in atomic nuclei. It is often said to be due to a pion exchange proposed by Hideki Yukawa in 1935. His Nobel prize lecture Meson theory in its developments gives some background: “As pointed out by Wigner1, specific nuclear forces between two nucleons, each of which can be either in the neutron state or the proton state, must have a very short range of the order of 10-13 cm, in order to account for…

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Electroweak theory

The weak interaction is said to be responsible for beta decay, muon decay, and some other decays. For example it’s said to be responsible for charged pion decay, but not for the more rapid neutral pion decay. That’s said to be caused by electromagnetism. However the electroweak interaction is said to be a unification of the weak interaction with electro-magnetism, and thus is said to cover all pion decays. The beginnings of unification As to when this unification began, it’s hard to say. Some might say…

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A partial history of the weak interaction

The weak interaction is said to be responsible for beta decay, where a neutron decays into a proton, an electron, and an antineutrino. All four of these particles are said to be fermions. Fermions are of course named after Enrico Fermi, who proposed what’s now known as the Fermi interaction. That was in his 1933 paper Attempt at a theory of β rays. It was famously rejected by Nature, then published in both Italian and German in 1934. The Fermi Interaction The Fermi Interaction is “the…

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Electromagnetic gauge theory

The standard model of particle physics is said to be a gauge theory. It’s made up of different sectors, including the electroweak sector which is said to be a Yang-Mills gauge theory. The Encyclopaedia Britannica electroweak theory article says it “arose principally out of attempts to produce a self-consistent gauge theory for the weak force, in analogy with quantum electrodynamics”. Quantum electrodynamics is the theory that says the electron is a point-particle, that electrons and protons interact by throwing photons at one another, and that photons…

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The neutrino

The neutrino was proposed by Wolfgang Pauli in 1930 to account for the conservation of energy and spin angular momentum in beta decay. You can find his original letter to Lise Meitner and others on the Fermilab MicroBooNE database, along with the English translation: Pauli later said “I have done a terrible thing. I have postulated a particle that cannot be detected”. He was wrong about that. He was wrong about some other things too. He talked about a particle that travels slower than light, and…

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The proton

If you look around the internet you can find articles like Matt Strassler’s what's a proton anyway? He says the proton isn’t made up of three quarks joined together by three gluons. He says that’s a lie, a white lie, but a big one. Instead he said there’s “zillions of gluons, antiquarks, and quarks in a proton”, and gives a picture of a whole host of quarks and gluons, all mixed up together like beans in a bag. All “rushing around as fast as possible, at nearly…

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What the proton is not

The proton was discovered by the great Ernie Rutherford in 1917. He used alpha particles to convert nitrogen into oxygen, and in doing so detected hydrogen nuclei. He’d previously done experiments with alpha particles and hydrogen, so he was confident they were hydrogen nuclei. This confirmed William Prout's hypothesis which dated back to 1815. Prout had observed that the atomic weights of other elements were integer multiples of the atomic weight of hydrogen. So he came up with the idea that the hydrogen atom was a…

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The mystery of mass is a myth

When you look around on the internet, you can find a whole host of articles about the mystery of mass. For example there’s a Guardian piece by Ian Sample, who says the origin of mass is “one of the most intriguing mysteries of nature”. Or there’s Concepts of Mass by Max Jammer, who says ”the notion of mass, although fundamental to physics, is still shrouded in mystery”. There’s also the ATLAS article by Michael Chanowitz, who talks about uncovering “the deep mystery of the origin of…

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