- #1

physwiz222

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- TL;DR Summary
- I am confused about Scattering in QED that no one ever actually solves or describes the actual dynamics of the scattering process using Perturbation Theory of course and why only cross sections and decay rates are computed.

When it comes to scattering in QED it seems only scattering cross sections and decay rates are calculated. Why is that does anyone calculate the actual evolution of the field states or operators themselves like how the particles and fields evolve throughout a scattering process not just asymptotic times.

For example when 2 electrons scatter off each other is it possible to compute the dynamical evolution of the particle states themselves of course using perturbation theory and visualizing it in terms of the expectation value of the charge density.

Also can the scattering amplitudes be used to reconstruct the evolution of the fields themselves if so why isnt it ever mentioned is it because constructing the evolution is a trivial exercise maybe. This bugs me because for a theory that is so praised and can supposedly describe Electromagnetic Fields at the fundamental level it seems awfully limited in what it can do like the fact it doesnt describe the actual dynamics from what I know comes off as hollow and unsatisfying.

For the record I dont know any QFT I simply looked at it a bit out of curiosity of whats the big deal about QFT and found myself kinda puzzled so please forgive me if I made any mistakes I am no expert. I simply want to know if its possible to describe the actual dynamics of scattering processes in QED with Feynman Diagrams for non asymptotic times for momentum eigenstates then use superposition to construct wavepackets like in regular QM or only cross sections can be computed for asymptotic tjmes.

I simply am curious as isnt the actual phenomenon and the dynamics also important as well. I know how well tested QED is as much as the next guy for its experimental confirmation in the 10th digit but shouldnt it also describe the actual dynamics of the phenomena as well.

For example when 2 electrons scatter off each other is it possible to compute the dynamical evolution of the particle states themselves of course using perturbation theory and visualizing it in terms of the expectation value of the charge density.

Also can the scattering amplitudes be used to reconstruct the evolution of the fields themselves if so why isnt it ever mentioned is it because constructing the evolution is a trivial exercise maybe. This bugs me because for a theory that is so praised and can supposedly describe Electromagnetic Fields at the fundamental level it seems awfully limited in what it can do like the fact it doesnt describe the actual dynamics from what I know comes off as hollow and unsatisfying.

For the record I dont know any QFT I simply looked at it a bit out of curiosity of whats the big deal about QFT and found myself kinda puzzled so please forgive me if I made any mistakes I am no expert. I simply want to know if its possible to describe the actual dynamics of scattering processes in QED with Feynman Diagrams for non asymptotic times for momentum eigenstates then use superposition to construct wavepackets like in regular QM or only cross sections can be computed for asymptotic tjmes.

I simply am curious as isnt the actual phenomenon and the dynamics also important as well. I know how well tested QED is as much as the next guy for its experimental confirmation in the 10th digit but shouldnt it also describe the actual dynamics of the phenomena as well.

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