"Perhaps the past, if looked upon with care and hindsight, may teach us where we possibly took a wrong turn"

The information paradox

The information paradox was first mooted by Stephen Hawking in 1976. For an introduction to the subject, see Brian Koberlein’s black holes tell no tales or do they? Then see Hawking’s paper on the breakdown of predictability in gravitational collapse. Hawking said information is lost down a black hole because the quantum emission is completely random and uncorrelated. He also said “this means there is no S matrix for the process of black-hole formation and evaporation”. The S-matrix is the scattering matrix which is to do…

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The Hawking papers

You can find a list of Stephen Hawking’s publications on the Hawking.org website. It starts with his 1965 PhD thesis. This is said to have “borrowed from Roger Penrose's theorem which described a 'spacetime singularity' being present in the centre of black holes”. Penrose was one of Hawking’s PhD examiners. Seven out of Hawking’s first ten papers concerned singularities. Singularities and the geometry of spacetime One of Hawking’s early papers was singularities and the geometry of spacetime dating from 1966. At 91 pages it’s curiously long.…

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Hawking radiation

Everybody knows about Hawking radiation. It’s been on TV. See the YouTube clip from the Channel 4 documentary Stephen Hawking: master of the universe. That’s where Kim Weaver of NASA says black holes offer an ultimate test of the physics of the universe. She says they’re cauldrons of heat and light with jets and particles coming out at half the speed of light, and an enormous amount of stuff going on. She finishes up saying and that’s exciting. I absolutely agree. Because yes, I think black…

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Black holes

We can trace black holes all the way back to John Michell in 1783. He's the man who devised the torsion balance used by Henry Cavendish to determine the mass of the Earth. Michell was something of an expert on gravity. He talked about "dark stars"  which were dark "in consequence of the diminution of the velocity of their light". He also said this: "if there should really exist in nature any bodies, whose density is not less than that of the sun, and whose diameters…

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The mystery of the missing antimatter

There’s an awful lot of articles about antimatter and mystery. For example there’s a 2017 Symmetry magazine article matter-antimatter mystery remains unsolved. It’s about the BASE experiment at CERN where they’ve measured the antiproton magnetic moment. Surprise surprise, it’s the exact opposite of the proton magnetic moment. Then there’s the LiveScience article mystery deepens: matter and antimatter are mirror images. Of course they are, the positron has the opposite chirality to the electron. And then there’s the CERN courier article does antimatter fall up? No it…

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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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