52 questions linked to/from Why the Principle of Least Action?
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### What is the reason behind the stationarity of action? [duplicate]

I am reading Goldstein right now to understand the least action principle. I understood that the action needs to be stationary under small variation and this specifies the equation of motion, but do ...
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### Least action principle universality, why does it work? [duplicate]

For example, hen working with general relativity, one sees that Einstein equations can be derived from an action principle via the Einstein-Hilbert action. This occurs too in classical mechanics, ...
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### The action of a physical system

My knowledge in this topic is as follows, correct me if I'm wrong.: the action $S$ of a physical system is quantity such that the system evolves so that it's extemized, maximized or minimized, usually ...
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### Why does it seem like there is always a Lagrangian? [duplicate]

All the fundamental laws of physics can be written in terms of an action principle. This includes electromagnetism, general relativity, the standard model of particle physics, and attempts to go ...
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### Why does nature favour systems that follow from a variational principle? [closed]

When Newton discovered ‘Newton’s law’ he was probably not aware that it could be viewed as a consequence of minimizing an ‘action integral’ (integral of some Lagrangian density). Since the same is ...
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### Why must the action be minimized? [duplicate]

In mechanics, the only physical route a particle can take is the one where action is minimized. Why is this true? Is there a proof?
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### Is there a "geometrical" reason for the principle of stationary action?

The principle of stationary action states that the trajectory $q(t)$ a physical system traces in configuration space is the one for which the action $$S[q]:=\int_{t_0}^{t_1}L(t,q,\dot q)\mathrm dt$$ ...
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### How is Lagrangian Mechanics useful? [duplicate]

I recently started reading about Lagrangian Mechanics. I observed that it uses some basic expressions that are derived by taking Newton's laws of motion as fundamental such as kinetic energy, ...
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### How is Lagrangian mechanics a generalised version of Newton's laws?

I'm talking about the mechanics which uses the minimisation of integral of $L=T-V$ to deduce motion paths. I've read it is a more generalised version of Newton's formulation because it can be used ...
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### Is there anything natural about the principle of "stationary action"?

In Taylor's classical mechanics, he derived Lagrange equations and showed that they are equivalent to Newton's second law. Then, it was obvious that Lagrange equations are similar to the Euler-...
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### Assumptions reg. Kinetic energy and Potential energy in the Lagrangian formulation

I have recently been introduced to Lagrangian mechanics. My previous exposure to Lagrangian math has been in the form of optimizing constrained functions using Lagrange multipliers. I get the math ...
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### Deeper Meaning to the Nature of Lagrangian

Is there a more fundamental reason for the Classical Lagrangian to be $T-V$ and Electromagnetic Lagrangian to be $T-V+ qA.v$ or is it simply because we can derive Newton's Second Law and Lorentz Force ...