Posted: Sep 16, 2011 12:49 pm
twistor59 wrote:
There is a common misunderstanding of what a Feynman diagram represents. It doesn't represent a process that is literally occurring in spacetime. For example, looking at the diagram for electron scattering:
the only components that are detectable by any experimental means are the in and out states, represented by the electron lines. The virtual photon represented by the internal line is not detectable by experimental means. The diagram just represents one of many contributions to the scattering of the two electrons in perturbation theory.
If QED were an exactly solvable theory, there would be no need to do perturbation theory, draw Feynman diagrams and talk about virtual particles. There would just be an interaction between electrons and the electromagnetic field which we could compute exactly. "Exactly solvable" is a requirement on the mathematical model, not on the physics.
First of all, perturbation theory is something you'll find in a QM textbook.That's not how the Feynman diagrams were worked out. It was Dyson who ingeniously combined the Heisenberg picture and the Schroedinger picture to form what is known as the interaction picture. It is in that picture that the Hamiltonian gives out an integral that can only be solved by a Taylor expansion. Feynman was able to translate that Taylor expansion into a series of his eponymous diagrams. Schwinger was able to do the same but instead of using diagrams, he used correlation functions. As in many instances in physics, you have two methods yielding the same results, tho Schwinger loathed the Feynman diagrams!
If you say that these interaction don't represent an exchange of particles then I can easily say that there are no waves passing through the double-slit experiment. You can't have it both ways. We assume a model, and then check if that model explains the data. Yet you are willing to accept readily the wave model in QM but not the QFT model of exchange particles when interactions take place, you are not being honest in your acceptance. What I'm saying is that the wave model is fine at low energies, at higher energies and smaller distance scales, the particle model is all there is.
EDIT: String theorists will argue that at even smaller distances (Planck distances) you get strings. But their theory has a big insurmountable flaw: it cannot be verified.