Why Is Action Considered a Fundamental Concept in Physics?

  • Thread starter Thread starter robousy
  • Start date Start date
  • Tags Tags
    Physics Power
AI Thread Summary
Action is a fundamental concept in physics because it provides a unifying framework for understanding the dynamics of systems across various fields, including classical mechanics and modern theories like string theory. It is more than just the Lagrangian or Hamiltonian, as it encapsulates the principle of least action, which states that the path taken by a system is the one that minimizes the action. This principle allows physicists to derive equations of motion and analyze complex systems effectively. Understanding action also facilitates the transition between different formulations of mechanics, making it a versatile tool in theoretical physics. Overall, mastering the concept of action enhances the ability to solve and interpret physical problems.
robousy
Messages
332
Reaction score
1
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
 
Physics news on Phys.org
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.
 
Last edited by a moderator:
Thread 'Gauss' law seems to imply instantaneous electric field'

Thread 'Gauss' law seems to imply instantaneous electric field'

Imagine a charged sphere at the origin connected through an open switch to a vertical grounded wire. We wish to find an expression for the horizontal component of the electric field at a distance ##\mathbf{r}## from the sphere as it discharges. By using the Lorenz gauge condition: $$\nabla \cdot \mathbf{A} + \frac{1}{c^2}\frac{\partial \phi}{\partial t}=0\tag{1}$$ we find the following retarded solutions to the Maxwell equations If we assume that...
View full post »

Thread 'Do electron density waves accompany EM waves in coaxial cables?'

Maxwell’s equations imply the following wave equation for the electric field $$\nabla^2\mathbf{E}-\frac{1}{c^2}\frac{\partial^2\mathbf{E}}{\partial t^2} = \frac{1}{\varepsilon_0}\nabla\rho+\mu_0\frac{\partial\mathbf J}{\partial t}.\tag{1}$$ I wonder if eqn.##(1)## can be split into the following transverse part $$\nabla^2\mathbf{E}_T-\frac{1}{c^2}\frac{\partial^2\mathbf{E}_T}{\partial t^2} = \mu_0\frac{\partial\mathbf{J}_T}{\partial t}\tag{2}$$ and longitudinal part...
View full post »

Similar threads

B Lagrangrian and Hamiltonian mechanics: A historical picture
Replies
7
Views
3K
Why is Hamilton's Principle assumed to be valid for non-holonomic systems?
Replies
25
Views
3K
I Lagrangian doesn't change when adding total time derivative
Replies
19
Views
3K
I Classical Field Theory - Something isn't clicking
Replies
12
Views
1K
Does the action have any physical significance?
Replies
16
Views
4K
I End point information in lagrangain variation principle
Replies
3
Views
1K
A Geometry of Classical Physics in terms of Gauge Theory geometry?
Replies
2
Views
1K
I Is Maxwell's electromagnetism an effective (field) theory?
Replies
3
Views
112
Why are the Lagrangian and the Hamiltonian defined as they are?
Replies
15
Views
10K
B Can Time Truly Flow Backwards in Quantum Physics and Cosmology?
2
Replies
51
Views
5K

Hot Threads

Recent Insights

Back
Top