And when not asympotic states?

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Discussion Overview

The discussion revolves around the mechanisms for calculating the probability of evolution between arbitrary fields over time, particularly in the context of nuclear reactions and Feynman diagrams. It explores the limitations of Feynman diagrams when applied to non-asymptotic states and considers alternative approaches such as lattice gauge theory.

Discussion Character

  • Technical explanation
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • Some participants note that Feynman diagrams are derived from asymptotic states, which approach free particle states that are well understood, while interacting states are less clear.
  • It is suggested that Feynman diagrams are effective for scattering and decay processes but inadequate for bound states.
  • One participant proposes that lattice gauge theory can be used for approximate calculations of arbitrary fields, though it requires significant computational power and has associated error terms.
  • Another participant questions the feasibility of performing lattice calculations on personal computers, suggesting that computing clusters are more suitable for such tasks.
  • Monte Carlo simulations are mentioned as another approach for modeling physics in scenarios where Feynman diagrams are insufficient.
  • A link to a resource on lattice QCD techniques is provided, which may be applicable for personal computers.

Areas of Agreement / Disagreement

Participants express differing views on the effectiveness of Feynman diagrams for non-asymptotic states and the practicality of lattice calculations on personal computers. The discussion remains unresolved regarding the best approach for calculating probabilities in these contexts.

Contextual Notes

There are limitations regarding the understanding of interacting states versus free particle states, as well as the computational requirements for lattice gauge theory and Monte Carlo simulations. The discussion does not resolve these complexities.

StarsRuler
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Feynman diagrams is the standard for calculate the probability of nuclear reactions fo particles, but, when we want calculate the probability of evolution of an arbitratry field to another field a fixed time after, what is the mechanism??
 
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Thanx
 
Thanx for the answers
 
It's hard to get these things over the internet, but it looks like you are angry that no one answered your question. The truth is, it's not very clearly worded and we have to guess what you want. So here is my guess:

The rules for feynman diagrams are derived by considering asymptotic states, because asymptotic states approach free particle states. Free particle states are well understood, whereas interacting states are very poorly understood. We use feynman diagrams, based off of free particles, to try to approximate interacting states. This makes sense for scattering and decays, but for bound states it doesn't work very well. So in feynman diagrams are not powerful enough to consider arbitrary states.

For more arbitrary fields, Lattice gauge theory is used sometimes to make approximate calculations. Essentially, if you approximate space as a lattice rather than a continuum, then calculations require a lot of computational power, but are in principle well understood. Usually there is an error term proportional to the lattice spacing, so these approximations are improved by making the lattice spacing smaller, but at the cost of requiring more computational power. Using this, bound states can be considered.
 
And there is any program for calculate this in a PC?

Thanx
 
StarsRuler said:
And there is any program for calculate this in a PC?

Thanx

I don't know if any personal computers are powerful enough to do reasonable lattice calculations, but computing clusters these days can perform good calculations of this kind. One goal of such calculations is to compute the mass of the proton, which has been done to relatively high precision.

For more information, I would search for "lattice QCD". Other computer approximations are generally called "Monte Carlo simulations", which use all kinds of techniques to try to model physics in situations where feynman diagrams fail. The only technique I have any knowledge of is lattice gauge theory, so if you want to know more, you'll have to ask someone else.

Here is an introduction to lattice QCD techniques, which supposedly can be run on a personal computer. http://arxiv.org/abs/hep-lat/0506036
 

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