Quantum field theory

Grand Unified Theories

I was talking to a guy the other day about Grand Unified Theories, and I thought I ought to say something about them. The Wikipedia Grand Unified Theory article gives a fair account. It says a GUT is a model where “at high energy, the three gauge interactions of the Standard Model that define the electromagnetic, weak, and strong interactions, or forces, are merged into a single force”. You’ve doubtless seen the picture: Image from the particle adventure That’s from the particle adventure website. They say this: “one of the major goals of particle physics…

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Misconceptions in particle physics

Physics is said to be the king of the sciences, and particle physics is said to be the most important branch of physics. As per the Wikipedia particle physics article, it’s the branch of physics that studies the nature of the particles that constitute matter and radiation. The article tells us that elementary particles are excitations of the quantum fields, and says this: “the currently dominant theory explaining these fundamental particles and fields, along with their dynamics, is called the Standard Model”. Glenn Starkman gives a…

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Quantum physics is cargo cult science

Ethan Siegel wrote a blog post this week called This Is Why Quantum Field Theory Is More Fundamental Than Quantum Mechanics. I read it and sighed, because so much of it is misleading. This sort of thing has been in the air recently, because Lee Smolin gave a lecture on Einstein's unfinished revolution. Smolin said quantum mechanics was incomplete, then doubled down and said it was wrong. I think he's right, only more than he knows. So I thought I'd use Siegel's post to show just…

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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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Quantum electrodynamics

Quantum electrodynamics arguably goes back to Werner Heisenberg and Wolfgang Pauli in 1929, when it was the same thing as quantum field theory. But as pointed out by Robert Oppenheimer in 1930, it suffered from the "divergence issue", also known as the “problem of infinities”. So much so that some historians say most workers in the field doubted its correctness, and some say the accepted wisdom was that it was no good. Others say physicists were overwhelmed by the problems and believed that a conceptual change…

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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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