The electron

The electron is usually described as a fundamental or elementary particle. That doesn’t tell you much, but when you look for more information, it’s rather scant. You soon learn that the electron has a mass of 9.109 x 10-31 kg or 511keV/c². You learn that it has a charge of −1.602 x 10−19 Coulombs or -1e, the e being elementary charge. You also learn that it has spin ½. However you don’t learn much else. Instead you get mixed messages. Take a look at the enigmatic electron…

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How pair production works

Yes, there's a hole in the heart of quantum electrodynamics because it describes the interaction between light and matter, but not the interaction between light and light. That's the interaction that creates matter in gamma-gamma pair production. QED misses the crucial point that waves interact. Even though we've all seen waves interact, down on the beach. Imagine a big wave is coming towards you. You make a little wave with your hand and send it scooting towards the big wave: The little wave rides up and over…

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The hole in the heart of quantum electrodynamics

Pair production is the creation of a particle and its antiparticle. Some say it was first observed in 1929, but it's usually accredited to Carl Anderson in 1932. He used a cloud chamber and an electromagnet to investigate cosmic rays. He effectively split a gamma photon over an atomic nucleus to create an electron and an antielectron. He called the latter the positive electron, which was soon shortened to positron: Image from schoolphysics However whilst he realised that he’d discovered the positron, he didn’t realise that he’d performed pair…

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The photon

The photon has a wave nature, which is why we can refract and diffract light. But what sort of a wave nature? When you try to find a picture, a lot of illustrations depict the photon as some kind of wave train. Even Feynman diagrams do this. Image by bitwise, see Wikipedia commons The photon is shown as a squiggly line, sometimes with an arrowhead, something like this: ⇝. That suggests you could split a photon lengthwise and end up with two photons, each with the…

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What is a photon?

OK, so quantum electrodynamics is said to date from 1929 when it was the same thing as quantum field theory. However it immediately suffered from the “problem of infinities”. So much so that some say most workers in the field doubted its correctness, whilst others say physicists believed a conceptual change was needed. As to what, see the conceptual foundations and the philosophical aspects of renormalization theory by Tian Yu Cao and Silvan Schweber dating from 1993. They say QFT embodies a reductionist view, but “serious doubt has often been cast on the…

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Quantum electrodynamics in the 1930s

Quantum electrodynamics or QED is said to be the quantum field theory or QFT which gives “a complete account of matter and light interaction”. Some say it was developed by Sin-Itiro Tomonaga, Julian Schwinger, and Richard Feynman in the 1940s: Image from Rod Nave’s hyperphysics But some say it started with Pascual Jordan in 1925, some say it started with Dirac in 1927, and some say it started with Heisenberg and Pauli’s “canonical” papers of 1929 and 1930. In the history of QFT Meinard Kuhlmann says…

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Quantum electrodynamics in the 1920s

Quantum electrodynamics is often shortened to QED. As for what it is exactly, I find it difficult to say. Wikipedia says it’s the relativistic quantum field theory of electrodynamics, and gives “a complete account of matter and light interaction”. But that’s not enough. The Encyclopaedia Britannica says it’s a quantum field theory which “describes mathematically not only all interactions of light with matter but also those of charged particles with one another”. That’s not enough either. Particularly since it’s defining QED in terms of other things…

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