Quantum Field Theory makes more intuitive sense

I really like Quantum Field Theory; it elegantly resolves some quantum mechanical puzzles and also fits with my own inner intuition on what's happening down there. If it's not spot-on, it's close. Here is the most succinct summary I've seen, from a Quora answer by Rodney Brooks, Ph.D.

In QFT as I learned it from Julian Schwinger, there are no particles, so there is no duality. There are only fields - and "waves" are just oscillations in those fields. The particle-like behavior happens when a field quantum collapses into an absorbing atom, just as a particle would. Here's what I wrote in my book (see quantum-field-theory.net): "The concept of wave-particle duality was introduced by Einstein in the 1905 paper that earned him the Nobel prize. He argued that since EM radiation is emitted in discrete units by single atoms, as Planck had shown, and since it is absorbed by single atoms in discrete units, as he had shown, then surely each unit must be localized in space - like a particle. How else, he asked, could it be in a position to deposit all its energy into a single atom? On the other hand, there is the wave nature of EM radiation described so well by Maxwell's equations, and Einstein would have been the last to deny their validity. If nothing else, there are the well-known interference effects that can only result from spread-out fields. And so was born the idea of wave-particle duality. The concept was extended to matter in 1920 by Louis de Broglie, who showed that the electron, long thought of as a particle, also exhibits wave character­istics. Einstein became de Broglie's biggest supporter and even predicted, independently of de Broglie, that interference effects would be exhibited by electrons in a two-slit experiment. But while de Broglie believed that an electron is both a wave and a particle, Erwin Schrödinger believed, or at least hoped, that matter consists only of waves – that the electron is pure field. In that sense, Schrödinger anticipated QFT. However Schrödinger was outvoted by everyone else, including Einstein. After all, if the photon's particle-like behavior could not be ignored, the electron's was even less ignorable. And so Schrödinger's famous equation came to be taken not as an equation for field intensity, as Schrödinger would have liked, but as an equation that gives the probability of finding a particle at a particular location. So there it was: wave-particle duality. Resolution. The wave-particle duality paradox is resolved in a very simple way by QFT: There are no particles; there are only fields: "[T]hese two distinct classical concepts [particles and fields] are merged and become transcended in something that has no classical counterpart – the quantized field that is a new conception of its own, a unity that replaces the classical duality." – Julian Schwinger The particle-like behavior of the fields is explained by the fact that each quantum maintains its own identity and acts as a unit, no matter how spread out it may be. If it is absorbed by an atom, all its energy is deposited into that atom, just as if it were a particle."*

This last paragraph introduces a new ponderable, though. How does a wave maintain its own identity no matter how spread out? Also, how does the whole wave get desposited/emitted at particle precision? Maybe the book goes into these things.

[Update, 2023] Reading through this post several years later, I've learned enough to see this quotation from Brooks has more gems than I first realized. Did you catch that? "Schrödinger's famous equation came to be taken not as an equation for field intensity, as Schrödinger would have liked, but as an equation that gives the probability of finding a particle at a particular location." Since I first wrote this blog post, I've fallen in love with Schrödinger's way of thinking, and this confirms what I have since realized: Schrödinger's intuition was extraordinary. For this reason, his approach is to be believed above most of his peers, as far as I can tell.

Footnote:

* [emphasis in this quotation is in the original]

Add a comment

HTML code is displayed as text and web addresses are automatically converted.

Page top