Why Is Action Considered a Fundamental Concept in Physics?

[robousy]

Hi all,

I'm a 2nd year physics grad student and have recently found this great forum.

I've taken a course on classical mechanics but never really appreciated why action is such a useful concept. I've noticed people talking about action a lot in things like string theory and it seems that action is more fundamental (?) or more useful (?) than simply the Lagrangian or the Hamiltonian but I do not see why.

If anyone could say a few words about why it is so useful to know the action ... and what you would then DO with it - then I would be very appreciative. (ie. what you can DO with the Lagrangian is stick it into the euler lagrange eqtns to get the eqtns of motion - what can you 'do' with the action).

Thanks in advance.

robousy

 

[Doc Al]

This site says it better than I could: http://en.wikipedia.org/wiki/Action_(physics)

Admin edit: fixed link. I'm not sure why it was broken in the first place -- I might need to make sure the url parser vB code is working properly.